Manteca City Council
March 5, 2024

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9.3.3 Maximum Day Demand plus Fire Flow (MDD+FF)
MDD+FF deficiencies occur when a hydrant is unable to meet the fire flow requirements presented in Table 9-2 while maintaining hydrant residual pressure above the minimum criteria of 20 psi and/or system pipeline velocity below the maximum criteria of 15 ft/s (see Table 9-1).

Each hydrant deficiency was grouped into the following categories:

Within 5%: If a hydrant flow causes residual pressure to drop below minimum criteria or a pipeline to exceed the maximum velocity criteria, the hydraulic model presents the amount of available fire flow at the criteria limits. If the available fire flow is within 5% of the needed fire flow, this was assumed to be within the acceptable margin of error, and these hydrants were not considered to cause a deficiency for this analysis.

Multiple Hydrants: In many cases – particularly surrounding larger commercial or industrial properties which also require higher fire flow – there are two or more hydrants available to meet the required fire flow. These hydrants were not considered to cause a deficiency.

System Dead-End: Deficiencies were triggered in cul-de-sacs or other areas where system dead-ends occur. These are often limited by velocity constraints in the pipelines leading to the dead-end. It is noted the maximum flow rate through a 6-in pipeline at 15 ft/s is 1,320 gpm; thus any greater flow through a 6-in pipeline will cause velocities to exceed the maximum criteria, which is common in multi-family residential cul-de-sacs where fire flow demand is 2,500 gpm. The maximum flowrate through an 8-in pipeline at 15 ft/s is 2,350 gpm, which is 6% less than the required fire flow for multi-family homes (2,500 gpm).

This is not to say that fire flow is not available, but instead that velocities would be outside of the preferred criteria, which may lead to excessive wear and tear. It is also noted that actual flows at hydrants can vary based on pipe roughness and hydrant nozzles/features. While upsizing the pipelines will resolve the fire flow deficiencies, it can promote water quality issues caused by stagnant water, particularly in non-residential areas where water use may decrease on the weekends when businesses are closed.

Some of these deficiencies were in areas of newer development and pipeline installation and it is feasible that these customers are equipped with fire sprinklers, reducing the required fire flow in accordance with the 2022 California Fire Code: Title 24, Part 9, Appendix B – FireFlow Requirements for Building. It is recommended that the City confirm fire flow requirements for these customers prior to implementing improvements.

Hydrant Relocation: Several hydrants that caused deficiencies are located on small diameter pipes (6-in and 8-in) that are near/adjacent to larger diameter pipelines with a greater capacity.

If the hydrant services were reconnected to the larger diameter pipes, these deficiencies would be resolved.

Insufficient Pressure/Flow: The remaining deficiencies that were not addressed by any of the above categories were evaluated and projects were developed to address each of these deficiencies. The major cause for deficiencies is small diameter pipes (4-, 6-, and 8-in).

Each of these categories are identified for the MDD+FF condition on Figure 9-8, Figure 9-9, and Figure 9-10 under Existing, 2030, and 2045 demand scenarios, respectively. A table of the MDD+FF hydrant model outputs for all scenarios is included in Appendix I.

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FIGURE 9-8

CITY OF MANTECA

WATER MASTER PLAN
RESULTS - EXISTING MDD+FF
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FIGURE 9-9

CITY OF MANTECA

WATER MASTER PLAN
RESULTS - 2030 MDD+FF
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FIGURE 9-10

CITY OF MANTECA

WATER MASTER PLAN
RESULTS - 2045 MDD+FF
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ATTACHMENT 2
City of Manteca
Water Master Plan – FINAL
February 2024

www.hydroscience.com

9.3.4 Peak Hour Demand plus Fire Flow (PHD+FF)
As an additional check, fire flow was also analyzed under PHD conditions (PHD+FF) in the 2045 scenario. Deficiencies triggered in the PHD+FF scenario are very similar to those identified in the MDD+FF scenario. Because fire flow is the major trigger of the deficiencies, the increase in demand at each hydrant caused by the peaking of MDD to PHD is largely negligible in comparison to the fire flow demand.

In the 2045 scenario, there are 34 hydrants that meet all criteria for sufficient fire flow under MDD+FF conditions but have insufficient fire flow under PHD+FF conditions. These additional deficiencies are detailed as follows:

Nineteen of these hydrants fall into the “Within 5%” category described above and are thus not classified as deficiencies for this analysis.

One hydrant is 6% deficient and falls into the “Multiple Hydrants” category described above and thus is not classified as deficient for this analysis.

Three are located in the parking lot of the shopping center just south of Big League Dreams.

These are addressed by recommended CIP Project #41.

Four are located in the industrial area in the northwestern corner of the existing City limits, bordered by Airport Way to the east, E Roth Rd to the north, and Intermodal Way to the west.

Multiple hydrants on this loop were also deficient in the MDD+FF scenario and were categorized at system dead-ends due to the nature of this loop. It is recommended that this loop be analyzed wholistically as the area is developed to determine if upgrades are necessary. There may be fire flow exceptions for buildings in this area if they are equipped with fire sprinklers. Also, it is important to balance the need for sufficient fire flow and sufficient turnover to prevent water quality issues; this loop services mostly industrial land uses which typically do not use water consistently every day of the week.

The remaining seven are located within the new skeletonized infrastructure in the expansion area north of the existing City limits. These do not have an effect on the existing infrastructure and it is assumed that the expanded infrastructure will be designed to adequately handle demands in these areas during development and expansion of the distribution system network.

Figure 9-11 presents the PHD+FF results for the 2045 scenario. To underscore the difference between MDD+FF and PHD+FF results, this figure only displays the additional deficiencies triggered by PHD+FF. A table of the PHD+FF hydrant model outputs for 2045 is included in Appendix I.

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FIGURE 9-11

CITY OF MANTECA

WATER MASTER PLAN
RESULTS - 2045 PHD+FF
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ATTACHMENT 2
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Water Master Plan – FINAL
February 2024

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ATTACHMENT 2
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Water Master Plan – FINAL
February 2024

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SECTION 10 – CAPITAL IMPROVEMENT PLAN (CIP)
As detailed in Section 9.3, all scenarios were evaluated for deficiencies based on the performance criteria presented in Section 9.1; most deficiencies are triggered during the MDD+FF scenarios and thus this is the focus of the CIP project development. When evaluating these deficiencies, the approach is to review both the existing and future scenarios in parallel to identify improvements needed to meet long-term needs while also considering the timing and urgency of those improvements if the deficiency is triggered by a change in the way water is used.

Each deficiency was evaluated and recommended improvements were developed to address each one.

This section presents the projects proposed to continue to ensure the reliable and safe delivery of water to the City’s customers and the estimated costs and schedule for implementation of the CIP. Projects are designed to improve water quality, provide redundancy where there is none, and/or meet the performance criteria. In general, the purpose of a water system CIP is to:

Maintain and enhance water infrastructure to continue to maintain a high level of service to the community;
Prioritize and address preventive maintenance, infrastructure replacement at the end of useful life or at risk of failure, regulatory requirements, and safety; and, Develop and implement projects to ensure continued and reliable delivery of safe and highquality drinking water to all customers.

Provided in the following sections is a brief description of the recommended CIP projects and their associated planning-level cost estimates. Detailed cost estimates for each recommended project are included in Appendix J.

10.1 Cost Basis
The purpose of approximating the cost of construction is to appropriate a conservative level of funding for each project. This section describes the basis for development of the unit costs and other associated costs and presents a summary of the total costs for each project.

10.1.1 Pipeline Construction Unit Costs
Unit costs for pipelines, mechanical equipment, and appurtenances were estimated based on recent project bid tabulation for similar Capital Improvement Projects and experience estimating the cost of similar local projects. Pipeline installation projects are estimated using a loaded construction cost estimate per foot of pipeline installed.

Table 10-1 provides a summary of the parameters used for estimating construction costs for conceptual planning and cost comparisons of pipeline projects.

ATTACHMENT 2
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Table 10-1: Construction Unit Cost Estimating Parameters Cost Parameter Unit Cost Applied to:

Mobilization/Demobilization 7% Construction Subtotal
8-in PVC Pipe Replacement $270 per foot Pipeline Length 10-in PVC Pipe Replacement $305 per foot Pipeline Length 12-in PVC Pipe Replacement $340 per foot Pipeline Length 8-in PVC New Pipe $250 per foot Pipeline Length
10-in PVC New Pipe $285 per foot Pipeline Length
12-in PVC New Pipe $320 per foot Pipeline Length
8-in Gate Valve1 $5,000 ea Each
10-in Gate Valve1 $6,500 ea Each
12-in Gate Valve1 $8,000 ea Each
Bore and Jack Trenchless (12-inch pipe+carrier) $1,000 per foot Pipeline Length Excavation Pits $60,000 ea Each
Move Services $9,000 per service Each
New Hydrant/Hydrant Service Relocation $17,000 per hydrant Each Abandon Pipe2 $8 per foot Pipeline Length
Reconnect Services and Abandon Pipe $32 per foot Pipeline Length Service Connections & Meter Box $24 per service Each
Water Main Tie-In $10,000 per tie-in Each
Piping Appurtenances 10% Pipeline Cost
Street Overlay3 $15 per sf Pipeline Length
Traffic Control During Construction4 2% - 8% Cost of Construction Subtotal
Notes:

1. Assumed one valve per 500 ft of pipeline.

2. For planning level cost estimating purposes, it is assumed that abandoned pipes are abandoned in place. During preliminary design, it should be determined whether pipelines will be abandoned in place or removed and disposed.

3. Street overlay assumes a 3 ft trench width and 9-in depth.

4. Traffic control is generally higher for projects on major streets and increases by length of project.

10.1.2 Pipeline Construction Soft Costs
Soft costs are additional project costs that are not considered to be contractor construction costs.

These costs include engineering design, permitting, construction administration, and construction management. Typical soft costs include:

Engineering Design and Permitting: These costs are expected to also address California Environmental Quality Act (CEQA) requirements to identify significant environmental impacts including handling of ACP, if any;
Administrative and Construction Management: These costs are associated with the administration of the contract, Engineering Services during Construction (ESDC), and management and inspection for project construction; and, ATTACHMENT 2
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Water Master Plan – FINAL
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Contingency: The construction and market contingency provides an allotment of funds designated for unexpected issues, including site specific and economic issues, that can change the scope of the project.

Table 10-2 provides a summary of the soft costs which were globally applied to all pipeline projects.

Table 10-2: Soft Cost Estimating Parameters
Cost Parameter Cost Applied to:

Engineering Design, Consulting, and Environmental Permitting Services

17.5% Construction Subtotal
Engineering Services during Construction (ESDC), Construction Management, and Inspection Services
20% Construction Subtotal
Construction Cost and Market Contingency 30% Construction Subtotal

10.1.3 Groundwater Well Construction Costs
Costs for drilling and equipping of a new groundwater well, including basic arsenic removal, as well as the design and construction of wellhead TCP treatment are provided based on the recent construction of Well 29. For planning level cost estimating purposes, it is assumed that all new wells in the City will require some level of wellhead treatment based on the history of water quality issues in the City’s groundwater.

Table 10-3 provides a summary of the estimated costs for the design and construction of a new groundwater well and associated wellhead treatment. These costs include all associated soft costs and contingencies and are based on the assumption that future wells will have a similar capacity to the City’s existing wells (i.e., up to 2,000 gpm). The cost basis details are provided in Appendix J.

Table 10-3: Groundwater Well Construction Cost Estimating Parameters Cost Parameter Cost
Well Drilling, Equipping, and Wellhead Arsenic Treatment $6.7M Wellhead TCP Treatment $5.3M

10.2 CIP Project Development Considerations and Methodology Pipeline Projects: Using the hydraulic model, pipeline improvements projects were developed to address each of the hydraulic deficiencies identified in Section 9.3. Projects were then grouped based on proximity, severity, and project type; pipelines requiring improvements in the same area or on the same street were grouped for efficiency of design and construction. Once hydraulic deficiencies were addressed, pipelines prioritized for replacement based on condition (see Figure 7-1) in the vicinity of hydraulic deficiency projects were also incorporated to take advantage of economies of scale to address both issues together.

For velocity deficiencies, pipelines are recommended for upsize to accommodate the required fire flow. Per industry standards for a distribution system of this size, a minimum diameter of 8-in is ATTACHMENT 2
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Water Master Plan – FINAL
February 2024

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recommended, and where necessary to meet higher fire flow demands, larger diameters are recommended as dictated by the hydraulic model and estimated flow requirements.

When the City was first incorporated, many small diameter water distribution pipelines were installed in alleyways and residential back yards with limited access for maintenance. As improvements have been made to the system, there has been little urgency to transfer the services from these older and smaller pipelines to the new pipelines. Maintaining operation of these smaller pipelines was initially not a significant expense; however, as the pipes approach the end of their useful life, the repair costs will exceed the expense of a systematic planned maintenance approach to replace the pipes. Figure 10-1 presents a map of all the pipelines in the City that are not located within the City right-of-way (ROW).

Where there were deficiencies, pipelines outside the City ROW were not recommended for improvement; these were generally recommended for abandonment. In some cases, abandonment can be achieved by reconnecting all the relevant services to existing adjacent City pipelines; in other cases, construction of a new pipeline is required within the City ROW adjacent to these pipelines to be able to reconnect the services and abandon these pipelines, wherever possible.

Where these pipelines outside the ROW were not triggering any hydraulic deficiencies and the pipes did not have high priority ratings, no projects are recommended at this time. However, as funding is available, it is recommended that the City continue to install pipelines within the ROW in order to abandon these pipelines over time.

Groundwater Well Projects: For planning level cost estimating purposes, Alternative 1 (see Section 5.1.1) of the Storage/Groundwater Supply Analysis is assumed, i.e. peak hour demands will be met with turnout capacity and groundwater pumping capacity without the use of any additional storage. The timing of City development and expansion will dictate the need for construction of new groundwater wells; the budgeting of well construction herein is based on the timing of the growth projections presented in Table 4-12. Well 30 is not included in the CIP cost estimates because the construction of this well is already in progress and it is assumed that the budget is already accounted for.

Surface Water Projects: In addition to new groundwater wells, the City will also need to make infrastructure updates to expand the system’s capacity to accept water from the existing SSJID turnouts. As Phase II of the SCWSP is implemented, it will also likely be necessary for the City to construct at least one new turnout with associated appurtenances and pipeline requirements.

Alternatively, the installation of a storage tank at the M1 turnout would increase the City’s capacity to receive surface water by mitigating pressure concerns within the SSJID pipeline.

For budgeting purposes, $5M is allocated in the recommended CIP for expansion of existing turnout capacity, construction of a new SSJID turnout, and/or construction of a new City storage tank at the existing M1 turnout. Timing of implementation is such that the City will be able to take their current and future allotment as necessary to meet anticipated demand.

Other Projects: In addition to the projects developed solely for the potable water distribution system, $10M is budgeted for the Water Fund for its share of the new Utilities Building to be built at the WQCF.

ATTACHMENT 2
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FIGURE

CITY OF MANTECA

WATER MASTER PLAN

PIPES OUTSIDE CITY RIGHT-OF-WAY
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Water Master Plan – FINAL
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10.3 Proposed CIP Pipeline Projects
This section presents the water distribution system CIP projects proposed to address the City’s infrastructure improvement needs within the next 20-year period. The proposed CIP includes all projects developed to address the identified deficiencies in the system along with projects to improve system reliability.

Each project includes some or all of the following components:

Pipe replacement;
Pipe replacement with upsize;
New pipe construction;
Pipe abandonment and reconnection of all accompanying services; and Hydrant relocation.

Once the projects were developed, they were placed in order of relative priority. Each was identified as addressing:

1. Hydraulic deficiencies (see Section 9.3); and/or

2. High priority pipe replacement based on overall prioritization scores (see Section 7.2).

The project schedule was determined by the severity of the hydraulic deficiencies within each project where % deficiency (i.e. available fire flow ÷ required fire flow) was prioritized followed by the pipeline replacement priority (Figure 7-1). Once placed in order of relative priority, the projects were further divided into phases for budgeting purposes. This section presents the four phases of recommended CIP pipeline projects. Phases 1 and 2 are focused in the downtown area, in the oldest part of the City, while Phases 3 and 4 extend beyond the downtown core.

It is noted that all of the projects in Phases 1 and 2 are high priority and should be addressed in any order where the City can complete the projects effectively, i.e., if there are other surface or subsurface improvement projects slated for construction in the area of any of the projects presented herein, of any phase, it is recommended that they be combined to take advantage of economies of scale.

Detailed cost estimates and figures for each project are provided in Appendix J.

ATTACHMENT 2
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10.3.1 Phase 1
The following projects are budgeted for implementation in the next five years. A summary of the costs for each phase is provided in Table 10-4 and detailed cost estimates and figures for each project are provided in Appendix J.

Table 10-4: CIP Phase 1 Estimate of Costs (2025-2029)
Project # Action Diameter (in) Quantity Unit Total Cost 1 Pipe Replacement w/ Upsize 8 2,292 ft
$2,432,000
New Pipe Construction 8 1,150 ft
Reconnect Services & Abandon - 1,920 ft
Hydrant Relocation - 2 ea
New Hydrant - 1 ea
2 Pipe Replacement w/ Upsize 8 546 ft
$1,611,000
Pipe Replacement w/ Upsize 10 1,120 ft
New Pipe Construction 8 388 ft
Reconnect Services & Abandon - 1,545 ft
Hydrant Relocation - 1 ea
New Hydrant - 2 ea
3 Pipe Replacement w/ Upsize 8 1,866 ft
$1,597,000
Pipe Replacement w/ Upsize 12 8 ft
New Pipe Construction 8 388 ft
Reconnect Services & Abandon - 973 ft
Hydrant Relocation - 1 ea
New Hydrant - 1 ea
4 Pipe Replacement 8 25 ft
$1,820,000
Pipe Replacement w/ Upsize 8 2,064 ft
New Pipe Construction 8 513 ft
Reconnect Services & Abandon - 1,588 ft
New Hydrant - 1 ea
5 Pipe Replacement w/ Upsize 8 4,011 ft $3,282,000 Pipe Replacement w/ Upsize 12 832 ft 6 Pipe Replacement w/ Upsize 8 605 ft
$1,004,000
New Pipe Construction 8 561 ft
Reconnect Services & Abandon - 2,877 ft
Abandon - 688 ft
Hydrant Relocation - 1 ea
7 Pipe Replacement w/ Upsize 8 614 ft
New Pipe Construction 8 452 ft $712,000
Reconnect Services & Abandon - 491 ft
8 Pipe Replacement w/ Upsize 8 1,839 ft $1,200,000
9 Pipe Replacement w/ Upsize 8 2,033 ft $1,323,000
Total $14,981,000
ATTACHMENT 2
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10.3.2 Phase 2
These improvements are budgeted for implementation in the 6- to 10-year timeframe. A summary of the costs for this phase of the CIP is provided in Table 10-5 and detailed cost estimates and figures for each project are provided in Appendix J.

Table 10-5: CIP Phase 2 Estimate of Costs (2030-2034)
Project # Action Diameter (in) Quantity Unit Total Cost 10 New Pipe Construction 8 1,975 ft
$3,100,000
New Pipe Construction 12 1,571 ft
Reconnect Services & Abandon - 5,199 ft
Hydrant Relocation - 6 ea
New Hydrant - 4 ea
11 Pipe Replacement w/ Upsize 8 268 ft
$1,558,000
Pipe Replacement w/ Upsize 12 1,145 ft
New Pipe Construction 8 61 ft
Reconnect Services & Abandon - 1,151 ft
Hydrant Relocation - 11 ea
12 Pipe Replacement w/ Upsize 12 1,485 ft
$3,966,000
New Pipe Construction 12 2,630 ft
Abandon - 568 ft
Bore and Jack Trenchless - 250 ft
Excavation Pits - 2 ea
Hydrant Relocation - 3 ea
13 Pipe Replacement w/ Upsize 8 184 ft
$1,899,000
Pipe Replacement w/ Upsize 12 1,771 ft
New Pipe Construction 8 160 ft
Reconnect Services & Abandon - 2,944 ft
Hydrant Relocation - 1 ea
14 Pipe Replacement w/ Upsize 8 2,614 ft $1,791,000 New Hydrant - 3 ea 15 Pipe Replacement w/ Upsize 8 495 ft $1,098,000 New Pipe Construction 8 1,260 ft 16 Pipe Replacement w/ Upsize 8 1,179 ft
$937,000 Pipe Replacement w/ Upsize 10 104 ft
Reconnect Services & Abandon - 506 ft
Hydrant Relocation - 2 ea
17 Pipe Replacement 8 54 ft
$897,000
Pipe Replacement w/ Upsize 8 962 ft
Pipe Replacement w/ Upsize 10 24 ft
New Pipe Construction 8 301 ft
New Hydrant - 1 ea
18 Pipe Replacement w/ Upsize 8 1,843 ft
$4,957,000 New Pipe Construction 8 4,780 ft
Reconnect Services & Abandon - 8,249 ft
Hydrant Relocation - 7 ea
Total $20,203,000
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10.3.3 Phase 3
These improvements are budgeted for implementation in the 11- to 15-year timeframe. A summary of the costs for this phase of the CIP is provided in Table 10-6 and detailed cost estimates and figures for each project are provided in Appendix J.

Table 10-6: CIP Phase 3 Estimate of Costs (2035-2039)
Project # Action Diameter (in) Quantity Unit Total Cost 19 Pipe Replacement w/ Upsize 8 1,799 ft
$1,854,000 New Pipe Construction 8 691 ft
Reconnect Services & Abandon - 2,671 ft
New Hydrant - 2 ea
20 Pipe Replacement w/ Upsize 8 1,412 ft $1,195,000 Pipe Replacement w/ Upsize 10 373 ft 21 Pipe Replacement w/ Upsize 8 248 ft
New Pipe Construction 8 420 ft $442,000
Reconnect Services & Abandon - 346 ft
22 Pipe Replacement w/ Upsize 8 3,405 ft $2,220,000
23 New Pipe Construction 8 2,665 ft
Reconnect Services & Abandon - 4,211 ft $2,067,000
Hydrant Relocation - 4 ea
24 Pipe Replacement w/ Upsize 8 4,979 ft $3,361,000 New Hydrant - 4 ea 25 Pipe Replacement w/ Upsize 8 668 ft
$504,000 New Pipe Construction 8 10 ft
Reconnect Services & Abandon - 467 ft
Hydrant Relocation - 1 ea
26 Pipe Replacement w/ Upsize 8 1,444 ft $1,193,000 Pipe Replacement w/ Upsize 10 341 ft 27 Pipe Replacement w/ Upsize 10 795 ft $645,000 Reconnect Services & Abandon - 818 ft 28 Pipe Replacement w/ Upsize 8 1,254 ft $821,000
29 Pipe Replacement w/ Upsize 8 1,220 ft
New Pipe Construction 8 252 ft $970,000
Reconnect Services & Abandon - 268 ft
30 Pipe Replacement w/ Upsize 8 1,780 ft $1,195,000 Hydrant Relocation - 1 ea Total $16,467,000
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10.3.4 Phase 4
These improvements are budgeted for implementation in the 15- to 20-year timeframe. A summary of the costs for this phase of the CIP is provided in Table 10-7 and detailed cost estimates and figures for each project are provided in Appendix J.

Table 10-7: CIP Phase 4 Estimate of Costs (2040-2044)
Project # Action Diameter (in) Quantity Unit Total Cost 31 Pipe Replacement w/ Upsize 8 3,318 ft $2,188,000 Pipe Replacement w/ Upsize 10 35 ft 32 Pipe Replacement w/ Upsize 8 3,570 ft $2,358,000 Reconnect Services & Abandon - 484 ft 33 Pipe Replacement w/ Upsize 8 1,019 ft
$1,117,000
Pipe Replacement w/ Upsize 12 328 ft
New Pipe Construction 12 192 ft
Reconnect Services & Abandon - 189 ft
New Hydrant - 1 ea
34 Pipe Replacement w/ Upsize 8 1,021 ft $664,000
35 Pipe Replacement w/ Upsize 8 216 ft $137,000
36 Pipe Replacement w/ Upsize 8 2,002 ft $1,312,000 Pipe Replacement w/ Upsize 12 10 ea 37 Pipe Replacement w/ Upsize 8 1,195 ft
New Pipe Construction 8 198 ft $916,000
Abandon - 467 ft
38 Pipe Replacement w/ Upsize 12 3,986 ft $3,191,000
39 Pipe Replacement w/ Upsize 8 809 ft $530,000
40 Pipe Replacement w/ Upsize 8 342 ft $227,000
41 Pipe Replacement w/ Upsize 12 427 ft $345,000
42 Pipe Replacement w/ Upsize 8 1,339 ft
$2,915,000 New Pipe Construction 8 2,077 ft
Reconnect Services & Abandon - 5,402 ea
New Hydrant - 12 ea
43 Hydrant Relocation - 5 ea $157,000
Total $16,057,000

10.3.5 New Development Transmission Mains 2030 and 2045 As new developments are implemented throughout the City and beyond the current City boundaries, transmission mains will be extended to serve those new developments. The City requested inclusion of a skeletonized transmission network to extend potable water service to potential new developments throughout the buildout of the General Plan. The proposed pipelines are shown in Figure 10-2 and summarized in Table 10-8. Figure 10-2 distinguishes between the planned transmission mains to serve “near-term” development through 2030 (as defined in Section 4.2.1) and separately that skeletonized network of transmission mains that were modeled to serve potential development beyond 2030 through 2045. Over 12 miles of transmission main is planned for construction through 2030 and over 30 miles of the skeletonized network is included to accommodate supply to potential future development through 2045.

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FIGURE 10-2

CITY OF MANTECA

WATER MASTER PLAN

NEW DEVELOPMENT TRANSMISSION MAIN
LEGEND

EXISTING WATER MAIN
2030 TRANSMISSION MAIN
2045 TRANSMISSION MAIN

CITY LIMITS
N
_
0 2,600 5,200
FT
1 IN = 5,200 FT
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Table 10-8: Transmission Main Estimate of Costs through 2045 Project # Action Diameter (in) Quantity Unit Total Cost 2030 New Pipe Construction 12 63,072 ft $52,987,000 New Pipe Construction 16 1,190 ft 20451
New Pipe Construction 8 14,132 ft
New Pipe Construction 12 143,520 ft $131,159,000
New Pipe Construction 16 3,849 ft
Notes:

1. Timing and related costs for future transmission main beyond 2030 will depend upon timing of planned development.

The skeletonized network is sized to accommodate fire flow according to the proposed land uses for undeveloped land. The timing and sequence of these developments have yet to be determined. Pipeline sizes and locations would be confirmed when designing the planned expansion. The actual cost and phasing of these transmission mains are outside of the control of the City. For the purposes of this analysis, estimated costs for each project have been included in the CIP. These could be funded by developers, the City, or others. The detailed cost estimates are provided in Appendix J.

10.4 Proposed CIP Summary and Schedule
Table 10-9 presents a summary of the proposed improvement projects in five-year increments, and Figure 10-3 displays each of the phases of pipeline projects spatially throughout the City.

Table 10-9: Summary of CIP Schedule
Category Phase 1
2025-2029
Phase 2
2030-2034
Phase 3
2035-2039
Phase 4
2040-2044
Estimated Pipeline
Cost
$14,981,000 $20,203,000 $16,467,000 $16,057,000
Estimated
Groundwater Well
Cost1
$6,700,000 $13,400,000 $6,700,000 $6,700,000
Budgeted SSJID
Capacity Expansion/
Storage Cost
$5,000,000 -- -- --
New Utilities
Building at WQCF
$10,000,000 -- -- --
Total CIP $36,681,000 $33,603,000 $23,167,000 $22,757,000 New Development
Transmission Main2
$52,987,000 $131,159,000
Notes:

1. The cost for groundwater well construction is highly dependent on water quality. Cost provided is assuming treatment for arsenic. Additional cost for TCP treatment based on recent implementation is estimated to be $5.3M (see Table 10-3).

2. Timing and related costs for future transmission main beyond 2030 will depend upon timing of planned development.

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10.5 Other Recommendations
Provided below are other recommendations for implementation by the City:

Significant updates and detail were incorporated into the hydraulic model making it a valuable tool for the City’s ongoing use. The model should be updated periodically as new infrastructure is built to ensure the accuracy of the model and to aid in future pipeline, well, and general system design. In addition, it is recommended that the following information is collected and incorporated into the hydraulic model to continue to improve its accuracy:

Pump performance curves and pump speed data;
Pump efficiency data;
Target and on/off set points for each supply source and related operating conditions (i.e. seasonal operation);
Operating parameters for valves throughout the system; and HGL information and pump operation information at SSJID turnouts.

During MDD+FF conditions, the distribution system exhibited some deficiencies in cul-de-sacs where system dead-ends occur (see Figure 9-8, Figure 9-9, and Figure 9-10). These deficiencies are typically the result of velocity constraints in the pipelines leading to the deadend. While upsizing the pipelines will resolve the fire flow deficiency, it can result in water quality issues. These areas should be reviewed for availability of fire sprinklers and possible exceptions to fire flow requirements on a case-by-case basis.

Perform a condition assessment of the water distribution system facilities, including turnouts, wells, pump stations, tanks, and treatment facilities.

Prepare an update to the Water Master Plan in ten years in order to capture the significant amount of planned growth and development that is expected to occur in the near term.

The following recommendations are based on observations made by City Staff in the ongoing operation of the existing potable water distribution system:

Move the SCADA server from Well 19 to a more secure location.

Evaluate conversion of the SCWSP to an uninterruptible water supply as the City’s reliance on surface water increases with population growth.

Convert all existing well site RTU communication systems to communicate via a fiber system to increase reliability.

Install backup generators at LAPS and CATF to maintain their operation in the event of a power outage. Currently, LAPS would not be able to operate the booster pumps during a power outage, leaving only pressure head differential to drive water from M1 turnout; Wells 13,19, and 21 have backup power but CATF does not, deeming them unusable during a power outage.

Construct a new bulk sodium hypochlorite storage facility with a 5,000-gal capacity and the option to expand up to 7,500 gal for easy access for bulk delivery tankers. Include built-in containment, indoor storage for two City delivery trucks, and a truck wash out area.

Perform an in-depth analysis/study to consider additional storage and pumping to manage peak demands and operational needs as desired, including the following:

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Consider an elevated storage tank to assist system pressures during peak demands.

Consider a storage tank located in the northeast area of the City.

Water quality in the southwest part of the City is poor; consider a tank in this area to manage demands in this rapidly growing area.

Determine the size of any storage facilit(y/ies) during the planning and design of the facility based on the City’s desire to cover operational, peaking, emergency, etc. storage.

Consider a storage tank at the M1 turnout as the existing SSJID pipeline direct tap does not conform to SCWSP contract. A storage tank would mitigate pressure issues on the SCWSP pipeline.

Consider construction of a new booster pump station and additional storage at the WTP to improve SCWSP transmission pipeline pressure.

There are pipe friction limits on the surface water line from M2 turnout that blends with Wells 27, 12, 15, and 22 (see Figure 3-1). Currently, Wells 15 and 22 operate at lower production rates than they are able to due to pipe friction in the blending line. Each of these wells has the capacity to produce an additional 1,500 gpm if the friction in the blending line were mitigated. Consider adding wellhead treatment at Well 22 for arsenic removal rather than relying on blending to ensure high water quality. Well 15 could continue current operation with surface water blending, and with construction of wellhead treatment at Well 22, the existing surface water blending line connecting Well 22 to Well 15 could be used to carry water from Well 15 to Well 22 for wellhead treatment during an emergency such as surface water curtailment, surface water pipeline break, etc.

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FIGURE 10-

CITY OF MANTECA

WATER MASTER PLAN

CIP PROJECT PHASES
LEGEND
CIP PHASE 1
CIP PHASE 2
CIP PHASE 3
CIP PHASE 4

WATER MAIN

CITY LIMITS
0 1,000 2,000
FT
1 IN = 2,000 FT
N
_
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10.6 Funding for CIP Projects
The City uses enterprise funds to account for City operations that are financed and operated like private business enterprises. The City’s enterprise utility funds are fully funded by the rates charged to customers. Use of this type of fund permits user charges to finance or recover the cost of providing the City’s services to customers on a continuing basis.

The water funds account for activities associated with providing water services including construction and maintenance of the water distribution systems.

The Water Maintenance and Operations fund accounts for the day-to-day operations, including water pumping and deliveries, billing, collections and system maintenance. These activities are funded through the monthly service fees collected from water service customers.

The Water Fee Improvement and Public Facilities Implementation Plan funds account for the capital improvements necessary to maintain and expand the system, including water main construction and rehabilitation and well construction and rehabilitation. These activities are funded through fees imposed on new development.

Other funding sources may include grant and loan programs for both water system reliability and improvements, as well as reclaimed water projects. Funding may be in the form of grants or loans. Notable programs that the City may qualify for include:

California Department of Housing and Community Development (HCD) Community Development Block Grant (CDBG): Eligible applicants include non-entitled cities or counties that do not receive funding from the U.S. Department of Housing and Urban Development’s (HUD’s) CDBG entitlement program. Water projects must principally benefit low/moderate income persons/households. Eligible projects may include feasibility studies, final plans and specs, site acquisition and construction, grant administration costs, repair or new construction of town’s water tank, assessment fees for low-income families, installation of private laterals and hook-up fees for low-income families under housing rehabilitation activity. For 2022 and 2023, HCD will not be accepting new construction applications. Available funding will be used to fund the waiting list from the 19/20 Notice of Funding Availability.

California Infrastructure and Economic Development Bank Public Agency Revenue Bonds: Bond financings for various state and local government agencies for various public or economic development projects.

Infrastructure State Revolving Loan Fund (ISRF): The ISRF Program provides low-cost, direct loans to local governments for a wide variety of public infrastructure and economic expansion projects that improve and sustain communities. ISRF financing is available in amounts ranging from $1 million to $65 million with loan terms for the useful life of the project up to a maximum of 30 years. Eligible ISRF applicants include any subdivision of a local government, including cities, counties, special districts, assessment districts, joint powers authorities, and eligible nonprofit corporations.

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California Governor’s Office of Emergency Services (Cal OES) Building Resilient Infrastructure and Communities (BRICs): BRIC implements a sustained pre-disaster natural hazard mitigation program to reduce overall risk to the population and structures from future hazard events, while also reducing reliance on federal funding in future disasters. Eligible subapplicants with projects that mitigate risk to public infrastructure, include innovative partnerships, mitigate risk to one or more lifelines, incorporate nature-based solutions, or incentivize adoption and enforcement of modern building codes are especially encouraged to apply. The funding cycle for BRIC begins with the Federal Emergency Management Acts’s (FEMA) release of the notice of funding opportunity (NOFO), typically mid-to-late summer, and sub-applications are due to Cal OES in November.

State Water Resources Control Board (SWRCB)
Drinking Water State Revolving Fund: This program provides low-interest loans and grants for planning and construction projects that support public water systems in meeting compliance with drinking water standards. Eligible projects include planning/design and construction of drinking water infrastructure projects including: consolidation; water meters; water storage; treatment systems; replacement of aged water transmission or distribution mains, groundwater wells, or other infrastructure; private services; interconnections; pipeline extensions.

Groundwater Site Cleanup Subaccount Program (SCAP): SCAP issues grants for projects that remediate the harm or threat of harm to human health, safety, or the environment caused by existing or threatened surface water or groundwater contamination. Eligible projects include remediating the harm or threat of harm to human health, safety, and the environment from surface water or groundwater contamination; human-made contaminates (i.e., tetrachloroethylene, trichloroethylene, perchlorate, and hexavalent chromium); a regulatory agency that issues a directive (unless this is infeasible); a responsible party that lacks financial resources. Projects may include site characterization, source identification, or implementation of cleanup.

Water Recycling Funding Program: This program promotes use of treated municipal wastewater to augment or offset State/local fresh water supplies. Eligible projects include reclaimed water treatment; reclaimed water storage, distribution, and pumping; groundwater recharge; indirect potable reuse; and surface water augmentation.

Federal Bipartisan Infrastructure Law: The legislation’s $55 billion investment represents the largest investment in drinking water, wastewater, water reuse, conveyance and water storage infrastructure in American history, including dedicated funding to replace lead service lines and address the dangerous chemical PFAS. This funding falls into seven major programs covered under this section – (1) the Drinking Water and Clean Water State Revolving Funds ($23.43 billion), (2) Lead Service Lines ($15 billion), (3) PFAS and Emerging Contaminants ($10 billion), (4) Indian Water Rights ($2.5 billion), (5) Indian Health Service Sanitation Facilities Construction ($3.5 billion), (6) Water and Sewer Tax ($1.25 billion), (7) Western Water including Rural Water ($8.3 billion). The majority of the water funding will move through the State Revolving Fund programs.

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United States Bureau of Reclamation (USBR)
Sustain and Manage America's Resources for Tomorrow (WaterSMART): The USBR sponsors a number of funding opportunities through the WaterSMART program including projects that address water and energy efficiency, drought response, water recycling (Title XVI), water marketing, water conservation, desalination, and water resources. Projects are selected through a competitive process and the focus is on projects that can be completed within two or three years. Funding opportunities and cycles can be found on the USBR WaterSMART website at https://www.usbr.gov/watersmart/.

The scope of the project will dictate funding qualification. As projects are defined, an inquiry can be submitted to the California Financing Coordinating Committee (CFCC) to determine program qualification. Appendix K includes a copy of the CFCC Common Funding Inquiry Form.

Additionally, the California State Library has created the California Grants Portal, a website (www.grants.ca.gov/) that provides a centralized location to find State grant opportunities. Grant seekers are now able to see all current grant and loan opportunities that are offered on a competitive or first-come basis and can search and filter their results.

Additionally, the City is performing a Water Rate Study based on this Master Plan.

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SECTION 11 – WATER GROUP STAFFING PLAN
As part of this Master Plan Study, a Staffing Plan was compiled to aid the City in determining the appropriate current and future staffing levels for the Water Group to meet existing operational needs, future demand as detailed in SECTION 4, projected regulatory requirements as described in SECTION 6, and implementation of the CIP projects presented in SECTION 10.

The objective of the Water Group Staffing Plan is to:

Determine the appropriate level of current and future staffing needs; Ensure service levels will be met in consideration of a more stringent regulatory environment, aging infrastructure, and customer base growth;
Support succession planning efforts and prepare for the retirement of key personnel; and Adequately staff the City to allow for planning functions while meeting day-to-day responsibilities.

Overall, the intent of this Staffing Plan is to ensure the Water Group is adequately staffed for both current and future needs, to cost-effectively provide the services required to support water system operations utilizing existing highly skilled staff and continue to meet emerging regulatory drinking water and reclaimed water service objectives.

Recommendations presented herein are based on the findings from City-specific considerations and strategic objectives. Performance indicators from the 2022 AWWA Utility Benchmarking:

Performance Management for Water and Wastewater (AWWA Utility Benchmarking) were used as the basis of comparison herein.

11.1 Existing City Organization and Staffing
This section presents an overview of the current organization, training, and certification of staff in the Water Group. Information about existing City staffing levels were provided by the City and obtained from the FY 2022-2023 Adopted Budget (FY 22-23 Adopted Budget).

11.1.1 City Organization
The City is governed by a five-member City Council consisting of the Mayor, Vice-Mayor, and three council members. The Executive Team of 12 includes the City Manager who is appointed as chief administrative officer. Under the City’s Council-Manager form of government, the City Manager, along with the executive leadership team and staff, implement City Council’s policies and pursue its objectives. The City Manager’s Office provides information and recommendations to the City Council, implements City Council policy direction, directs the delivery of municipal services, and oversees accomplishment of City objectives and capital projects specializing in economic development, media relations, community relations, and special projects. The City currently has a total of 467 full-time employee/equivalent (FTE) positions, based on the operating budget published in the FY 22-23 Adopted Budget, page FS-29.

Water Group: For the purposes of this Staffing Plan, the collection of relevant City staff positions considered will be referred to as the Water Group; FTE numbers are for the Water Group only.

This collection of positions includes the water treatment, water distribution, water facilities ATTACHMENT 2
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maintenance, water meter services, and water regulatory compliance branches of the Water Division in the Department of Public Works and the Water Infrastructure Division of the Department of Engineering.

Department of Public Works: The Department of Public Works is comprised of nine divisions:

Water, Sewer, Transit, Administration, Parks, Fleet, Building Maintenance, Streets, and Solid Waste.

The Water Division is responsible for emergency water line repairs; distribution system maintenance; monitoring and maintenance of water wells; testing and disinfection of the municipal water supply; marking water line locations for construction; installation, repair, and maintenance of water meters; and monthly water meter reading.

Department of Engineering: The Department of Engineering – comprised of the Infrastructure and Development Divisions – oversees planning, design, and construction for new water treatment and distribution, wastewater collection and treatment, drainage and stormwater control, traffic and transportation, and other infrastructure projects. It administers the subdivision review process, participates in site plan review, and manages the City’s CIP. Figure 11-1 shows the portions of the Public Works and Engineering Departments that comprises the Water Group, including the FY 2022-2023 City staffing numbers.

Staff Responsibilities: Responsibilities of staff in the specific job functions are described below.

There are different levels within the job functions based on years of experience and certification.

Water Meter Services: upload, download and troubleshoot meter data; water meter installation, inspection and maintenance; respond to citizens’ complaints and answer questions from the public; and ensure accurate billing to accounts.

Water System Maintenance Worker: assist in the installation, maintenance and repair of water meters and related service lines; inspect meters and service lines for leaks and malfunctions; install and repair meter boxes, fire hydrants and sidewalks; service equipment with oil and grease or replacing filters; perform traffic control; identify water line locations for underground excavations and assist with trenching and refilling of trenches; and investigate and respond to public service complaints and emergencies.

Water Distribution Operator: inspect meters and service lines for leaks, malfunctions, and high usage; initiating and discontinuing service monitoring meter readings; monitor of chemical dosages and adjusting water quality parameters; and investigate and respond to public service complaints and emergencies.

Water Treatment Operator: operate water wells, water connections, water treatment facilities, pumping equipment, piping systems and related components within the City's potable water system; monitor and adjust chemical dosages/blend ratios.

Well Mechanic/ Operator: operate and maintain water wells, pumping equipment, piping systems and related components within the City's potable water system; monitor chemical dosages to assure adequate and safe drinking water; operate, service, and repair the standby generators at the well sites.

ATTACHMENT 2
Deputy Director
(Infrastructure)
Senior Engineer
(Water)
Associate
Engineer
Assistant
Engineer
Administrative
Assistant
Management
Analyst
Engineering
Director
Water Regulatory
Coordinator
Water Distribution
Operator I/II/III
Water Distribution
Supervisor
Water Treatment
Operations Supervisor
Well Mechanic /
Operator I/II
Water Treatment
Operator I/II
Water Resources
Coordinator
SCADA
Engineer
Water
Admin 3
FIGURE 11-
_

CITY OF MANTECA

WATER MASTER PLAN
Meter Reader
I/II
PW Deputy Director
Water Resources
Public Works
Director
Maintenance
Worker I/II/III
Water Regulatory
Compliance Specialist
Water Meter
Services Supervisor

DEPARTMENT OF PUBLIC WORKS
CURRENT NUMBER OF FULL-TIME EMPLOYEESSPLIT ROLE (LESS THAN 100% TIME SPENT FOR THE WATER DIVISION) Note: Org chart and sta ng numbers provided by the
City
LEGEND

ENGINEERING DEPARTMENT
1 WATER GROUP STAFFING AS OF DECEMBER 2023
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Water Regulatory Compliance Specialist: respond to customer service requests; ensure water conservation and backflow prevention compliance; ensure the City's programs and operations comply with state and federal regulations; and prepare a variety of technical reports for submission to regulatory agencies.

Water Resources Coordinator: coordinate, implement, and promote water conservation; assist in activities required to ensure regulatory compliance for water resources; conduct research and prepare written reports, correspondence and promotional materials; serve as water resources liaison; coordinate and implement public outreach and education efforts; perform grant writing; and coordinate with enforcement efforts.

Water Regulatory Coordinator: monitor water regulatory compliance and related programs and priorities; ensure compliance; direct the review and analysis of new and changing regulations; interpret Federal and State regulations related to drinking water quality and environmental aspects of water operations to ensure compliance; and develop and update City ordinances.

SCADA Engineer: ensure proper operation of the water system through observing control data; and designing, installing, programming, and monitoring of control systems at the wells and distribution system.

Assistant/Associate/Senior Engineer: plan, organize and manage assigned capital improvement projects for the Engineering department; and perform technical engineering duties and coordination for the planning, design, construction, budgeting, bidding and analysis of capital improvement projects.

Management: manage staff; ensure adequate staffing; implement procedures for reliable operations of the water system; and recommends new capital improvements projects.

11.1.2 Water Distribution and Treatment Certification and Training The SWRCB’s DDW District Offices and Local Primacy Agencies classify water treatment facilities and distribution systems statewide in accordance with CCR, Title 22, Sections 64413.1 and 64413.3, respectively. The SWRCB uses a five-level classification system, established in regulations for water distribution systems, water treatment facilities, and certified operators.

Water distribution systems are classified into classes D1 through D5, according to population served and the complexity of the distribution system. Water treatment facilities are classified into classes T1 through T5, using a point system based upon source water characteristics, maximum capacity, and treatment techniques utilized.

The City’s water system is classified as a T3 treatment and a D5 distribution system. As such, the Chief Treatment Operator must possess a T3 certification, and the Chief Distribution Operator must possess a D5 certification at minimum. All other operating personnel making process control/ system integrity decisions about water quality or quantity that affect public health must have some level of certification as well depending upon the type of work being performed.

Certification is obtained from SWRCB by passing an exam and having a minimum level of experience per level of certification. Certification renewal is required every three years. Renewal requires a minimum amount of training/contact hours approved by SWRCB. The amount of training needed depends on the level of certification being renewed.

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11.1.3 Staffing Levels
A summary of FTE positions is provided in Table 11-1. This table presents the Water Group positions displayed in Figure 11-1 which are grouped into job categories aligning with the AWWA Utility Benchmarking for analysis herein. This information represents staffing count as of December 2023 as provided by the City.

In some cases, employees may have responsibilities across multiple branches and split their time between roles; a decimal representation of FTEs is provided for estimation if an employee’s time is split between the water, wastewater, and/or stormwater branches.

Table 11-1: Water Group FTE Positions
Category FTEs in 2023
Department of Public Works – Water Division1 28.9
Water System Maintenance Worker 6
Water Treatment Operator/ Well Mechanic 5
Water Distribution Operator 8
Water Meter Services 3
Management, SCADA, Water Regulatory Compliance, Water Resources Coordination 4.9 Department of Engineering – Infrastructure Division1 3.6 Engineering 3.6
Notes:

1. Source: Provided by City Staff.

11.1.4 Vacancies
The City as well as other water agencies have had challenges in recruiting operators and maintenance workers due to the lack of available certified operators and civil engineers. In addition, demand for certified operators have increased as water quality regulations become more stringent and additional water treatment is needed. Water reuse has also increased the need for certified water treatment operators and as development continues to grow so does water distribution systems and the need for additional maintenance workers. Some agencies have turned to vendors or contract operators and/or staff augmentation using consultants or contract employees till vacancies can be filled.

For example, the City and County of San Diego has a rotating consultant list to provide environmental services, staff augmentation, construction management, in addition to specific design projects. For the construction of the Echo Water Project for SacSewer, formerly Regional Sanitation, project management and construction management services were provided by different design engineers. Operations partners such as Veolia Water and Fluid Resources Management provide staff for operations, mechanical repair, controls, and regulatory compliance.

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11.1.5 Overtime and Temporary Staffing
The City’s stance on overtime is that it should be used only when necessary and when other alternatives are not feasible or cost effective. Currently, most positions within the Water Group are working overtime. The City can also use temporary staffing or contractors to meet peak workload requirements in the short-term. The City Manager and Department Managers encourage the use of temporary rather than regular employees to meet peak workload requirements, fill interim vacancies, and accomplish tasks where less than full-time, year-round staffing is required. Contract employees are generally used for medium-term projects, programs, or activities requiring specialized or augmented levels of staffing for a specific period, generally between six months and two years. Temporary staff and contractors are not included in the FTE count in this analysis.

11.1.6 Succession Planning
The City is currently taking several actions for implementation of a succession plan for all management positions to ensure that employees are sufficiently trained or cross-trained in multiple positions with the goal to fill critical vacant positions with qualified personnel. For the Water Group, implementation of the succession planning program continues to be an objective for FY 2023-2024.

In addition, the City currently has a Flexible Staffing Policy, where any water group employee in the maintenance worker or operator series can be promoted with the correct certification and years of service to a higher position in either of these series.

Succession planning is a process for identifying and developing staff with the potential to fill critical roles. Succession planning includes all of these key steps: identification of critical positions; defining competencies required to undertake these roles; assessing people for such competencies; identifying talented people who can perform highly in these key roles; and developing employees to be ready for advancement in these key roles. Key skills include technical knowledge, procedural best practices, and leadership skills. Some municipalities have also developed other strategies to aid in succession planning. The Metropolitan Water District of Southern California has developed a two-prong approach that focuses on workforce development and on the on-boarding process. Workforce development included a focus on clarifying department goals, assessing gaps in skill sets, providing cross-training, providing mentoring and leadership development, and organizing a monthly brown bag to discuss initiatives or key issues.

Energy Services in southern Florida has developed a program to reward employees who give more than normal notice about their retirement plans. Fairfax County in the DC Metro area in Virginia has developed a Deferred Retirement Option Program where the retiree can work for up to an additional three years with the intent to retire and invest additional funds for their pension.

During that time, a replacement overlaps with the retiree to learn key skills for the position.

11.2 Considerations for Staffing Levels
Recommended staffing levels are based on changes in regulatory requirements, CIP needs, growth in the system, and the performance indicators identified in the 2022 AWWA Utility Benchmarking, detailed in this section.

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11.2.1 Changing Near-Term Regulatory Monitoring
In the near-term, legislation is requiring changes to monitoring and reporting which may require additional staffing or contract resources. Legislation packages will require water utilities to track and report annual water use & water loss and cross connection control.

Urban Water Use Objective Calculation
Water use and loss reporting is anticipated with the passage of 2018 Legislation Senate Bill 606.

Assembly Bill 1414 requires analysis of the FY 2022-2023 annual water use with a report due by January 1, 2024. The system specific water loss audit would include development and operations to perform leak detection. Reports would be sent annually to the Department of Water Resources to compile a record of annual system water losses. The regulation would also require the City to establish a volumetric water loss standard (such as five gallons per connection) and maintain this water loss standard by 2028. The water loss staff’s time would involve setting this standard, tracking water losses, and reporting annually. If the volumetric water losses are too high, the staff would also need to alarm the distribution operators. A timeline of implementation is as follows:

Submit questionnaires and data about metering and meter testing practices by January 1, 2023;
Submit feasibility of pressure by July 1, 2023 and update July 1, 2026; Submit feasibility of asset management by July 1, 2024 and update July 1, 2027 Calculation and compliance with leakage reduction with individual volumetric standards by January 1, 2028.

Cross Connection Control Program Revision
The Cross Connection Control program requirements were revised on December 19, 2023 to include four additional components in addition to six existing components. The added components include:

Use of certified backflow prevention assembly testers and cross control specialists; Backflow incident response, reporting, and notification; Public outreach and education; and
Local entity coordination.

These added components would increase the tasks currently undertaken by the cross-connection control specialists and additional staffing is needed to ensure compliance and coordinate within the City. While certified backflow prevention assembly testers can be contracted through agencies within California, an operator or compliance specialist would still need to manage the reporting and verify certification. Additionally, the specialist is required to be contacted within an hour to respond to cross-connection incidents or hazard analysis under the Cross-Connection Control Program.

For water meter staff, at least one staff is recommended to receive certification for performing water loss audits and for cross-connection control, each. As more meters become automated, ATTACHMENT 2
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response to water leaks and cross-connections and reporting will be tasks that water meter staff would need to handle.

11.2.2 Changing Regulatory Compliance
There are two consequences impacting staffing based on future water related threats to the City as discussed in in Section 6.3 that may impact staffing requirements.

Imported water restrictions and curtailments depending on time of the year resulting in increasing need for groundwater during peak times; and
Declining groundwater quality requiring more wellhead treatment.

Currently, City operators are required to have T3 treatment operator certification or D5 distribution operator certification. The D5 distribution system is the highest within the classification. An increase of population or distribution pipeline length would not impact the certification needed.

The treatment certification system also ranges from 1-5 and is based on regulatory limits.

The City’s treatment certification level can go higher if there is an increase in the point system on the following factors related to groundwater treatment as described in CCR, Title 22, Section 64413.1:

Average turbidity,
Average levels of perchlorate, nitrate, and nitrite that exceed the MCLs, If the levels for each of the inorganic contaminants, organic contaminants, and radionuclides based on monitoring are below the MCL, are greater than the MCL, or exceed five times greater than the MCL.

Additional wells and additional population are not expected to push the City to higher certification requirements as currently treatment is provided for nitrate, arsenic, manganese, and TCP (as summarized in Table 2-2). If new MCLs are established for PFOA, PFOS, and NDMA, and if exceedances are considered in future water treatment certification, then this may increase the certification level requirement for the current City staff.

11.2.3 Modifications based on CIP Projects
As the City embarks on implementing the Capital Improvements Program, increased staffing will be needed in the Engineering Department to account for the administration of capital improvements projects as well as to account for asset management of existing assets as they age. The CIP Program is anticipated to administer 10-14 projects within a 4-year window from planning, design, bid, and construction, while coordinating within internal departments and external regulatory agencies. It is recommended for three engineers to be added and then an additional engineer by 2030.

If the City chooses to handle design services or construction management in-house rather than contracting with consulting firms, it is recommended that the City hire additional staff more than is presented in Table 11-2.

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Table 11-2: Recommended Additional Engineering Staff for CIP Administration Parameter Phase 1
2025-2029
Phase 2
2030-2034
Phase 3
2035-2039
Phase 4
2040-2044
Number of Pipeline Projects 9 9 12 13
Estimated Pipeline Construction Cost $14,981,000 $20,203,000 $16,467,000 $16,057,000 Estimated Groundwater Well Cost $6,700,000 $13,400,000 $6,700,000 $6,700,000 Total Miles of Transmission Main in
the City1
317.1 344.9
Number of New Wells 1 2 1 1
Total Number of Wells 17 19 20 21
Recommended Number of
Engineering Staff for the CIP2
3444
Notes:

1. Timing of transmission main construction beyond 2030 is dependent upon timing of development and City annexation of parcels outside of the current City limits.

2. One Engineering Staff FTE is added between 2030 and 2045 to account for the transmission main expansion assuming the pace of development is relatively consistent over that time frame.

11.2.4 Modifications based on Long-term Asset Planning
Long-term asset planning through preventative maintenance and asset management will need to be prioritized in the Water Group as pipelines and facilities continue to age. Roughly one quarter of the existing pipelines are past a 40-year life expectancy based on Table 3-7 and 33% of wells are past a life expectancy of 35 years based on Table 3-2. This job duty is recommended to be separated out within the infrastructure division of the engineering department so that there is a capital improvements branch and operations and maintenance branch. Within the operations and maintenance branch, a GIS technician is also recommended to track existing facilities, work orders, and preventative maintenance.

11.2.5 Increasing Water Production
Additional staffing is required as the City increases annual water production. Estimates for the quantity of staffing are based on the AWWA Utility Benchmarking Program. AWWA began development of a utility benchmarking program in 1995 with the goal of providing water, wastewater, and combined utilities with performance measurements for internal tracking and external comparisons. The basis for performance benchmarking is a system of well-defined and time-tested performance indicators specific to the water sector. These indicators were designed to help utilities improve their operational efficiency and managerial effectiveness. For the 2022 publication, 168 municipalities from the USA and Canada contributed to benchmark data from 2021. Municipalities are identified as providing services for:

Water utilities;
Wastewater utilities; or
Combined utilities offering both water and wastewater services.

Performance indicators reported in the AWWA Utility Benchmarking report include:

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Staffing levels
Total FTEs
FTEs by job category
Water produced per employee (MGD per employee)
The AWWA Utility Benchmarking survey collected responses from utilities to the following question: “Record the number of FTEs working on water services at your utility during the reporting period.” Based on the survey responses, quartile values were recorded. The following analysis utilizes the median or 50th percentile of the survey respondents.

11.3 Recommended Staffing Projections
Staffing projections follow the water demand projections (Section 4.2.4) and proposed CIP Projects (SECTION 10) developed as part of this Master Plan Study through 2045.

11.3.1 Recommended City Water Group Staffing for 2025
The AWWA Utility Benchmarking provides indicators for the entire sample set as well as subsets of utilities broken down based on similar characteristics (i.e., types of services offered, population served, region, etc.). Further, the number of FTEs is calculated using varying metrics (i.e., number of accounts per employee, quantity of water produced per employee, etc.). For this analysis, a range of staffing levels recommended for the City’s Water Group was calculated based on water produced per employee as described in SECTION 4 for the entire sample set and subset if information was provided. An outline of relevant metrics with units and subsets is below:

Water produced per employee (MGD water supplied/ FTE)
Entire sample set: combined utility (water operations and water only utility). This is inclusive of all utilities offering water services whether or not they offer another service such as wastewater.

Subset by combined utility – water operations. The sample size is 97 utilities.

Subset by region. The sample size is 35 utilities.

The AWWA Utility Benchmark includes multiple job categories; some that do not apply to the Water Group as these job functions are performed outside of the Water Group, but within the larger City workforce, such as human resources, information technology, finance, and service calls. An estimated 71% of the job categories included in the AWWA Utility Benchmark are included in the City of Manteca Water Group. As such, the AWWA comparison factors or performance indicators were multiplied by 0.71 to account for the job categories included in the Water Group only.

A range of recommended staffing numbers for the City based on these performance indicators are presented in Table 11-3. The recommended total number of City FTEs is calculated by:
( ) 0.71 = 2025 Recommended No. of City FTEs
/
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Using the water demands and the AWWA indicator value for combined utilities-water and combined utilities in Region V which includes California, the recommended number of total City Staff in FY 2025 based on water production projections is 47 FTEs.

Table 11-3: Range of Total Staffing Using AWWA Indicators AWWA Metric AWWA
Benchmark
Reference1
AWWA Median
Value of Water
Produced / FTE
2025
Water
Produced
2025
Recommended
No. of FTEs2
Water Produced Per Employee
Combined Utilities - Water
Operations
Table 4-2 0.23 MGD/FTE 15.2 MGD 47
Subset: Region V Appendix C, p. 219 0.23 MGD/FTE 15.2 MGD 47 Recommended 47
Notes:

1. The AWWA Benchmark Reference locates the table number or page number within the AWWA Utility Benchmarking publication.

2. A ratio of 0.71 is used to compare job categories included in the City Water Group compared to all of the job categories listed in the AWWA Utility Benchmarking publication.

Table 11-4 presents a comparison of the City’s current staffing levels in each of the City’s job categories compared to the recommended number of FTEs calculated, 47 FTEs, plus the 3 engineers for CIP Project administration as discussed in Section 11.2.3. The resulting organization chart is shown on Figure 11-2 for the Water Group.

The City’s Water Group currently employs 32.5 FTEs which is considerably less than the recommended 50 FTEs.

Table 11-4: City Actual Staffing Compared to Recommended Staffing for 2025 Job Category City Actual Staff in FTEs
(FY 2022-2023)
AWWA Recommended
Staff FTEs (FY 2024-2025)
Water System Maintenance Worker 6 6
Water Treatment Operator/Well Mechanic 5 10
Water Distribution Operator 10 16
Water Meter Services 3 4
Other/Management 5 6
Engineering 3.6 5
Engineering - CIP 0 3
Total 32.5 50
ATTACHMENT 2
FIGURE 11-_

CITY OF MANTECA

WATER MASTER PLAN
2025

NUMBER OF FULL-TIME EMPLOYEES
SPLIT ROLE (LESS THAN 100% TIME SPENT

FOR THE WATER DIVISION)
LEGEND
Water Regulatory
Supervisor
Water Resources
Coordinator
SCADA
Engineer
Water
Admin 3
PW Deputy Director
Water Division
Public Works
Director
Water Regulatory
Coordinator
Water Regulatory
Compliance Specialist
Water Division
Manager
Water Meter
Services Supervisor
Meter Reader
I/II
Maintenance
Worker I/II/III
Water Service
Technician I/II
Water Treatment
Operations Supervisor
Well Mechanic /
Operator I/II
Water Treatment
Operator I/II
Lead Distribution
Operator
Water Distribution
Supervisor
Water Distribution
Operator I/II/III

DEPARTMENT OF PUBLIC WORKS
Engineering
Director
Associate
Engineer
Deputy Director
(Infrastructure)
Senior Engineer
(Water)
Assistant
Engineer
Senior Civil Engineer
(Water O&M)
Associate Engineer (Water O&M -
Wells/Treatment Improvement)
Associate Engineer (Water O&M -
Pipelines Improvement)
GIS
Technician
Administrative
Assistant
Management
Analyst

ENGINEERING DIVISION
2 RECOMMENDED WATER GROUP STAFFING FOR
(Water CIP)
Assoc. Eng.
(Water CIP)
Assist. Eng.
(Water CIP)
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11.3.2 Recommended City Water Group Staffing for 2045
Using the same procedure described in Section 11.3.1, the number of future total FTEs was estimated based on the projected average annual demand as listed in Table 4-12. The number of Water Group FTEs was then calculated using the 0.71 ratio of Water Group staff to total staff as detailed in Section 11.3.1.

Table 11-5 presents the projected City staff FTE recommendations based on this procedure. In 2045, it is recommended that the City employ a Water Group staff comprised of 83 FTEs by 2045.

The resulting organization chart is shown on Figure 11-3 for the Recommended Water Group in 2045.

Table 11-5: Projected FTEs based on Water Demand and Percentage in Job Category Parameter Existing Recommended
2023 2025 2030 2035 2040 2045
ADD (MGD)1 13.2 15.2 17.9 20.2 22.8 25.7
ADD (AFY)1 14,830 16,982 20,117 22,677 25,562 28,814
Population1 87,218 97,404 111,826 128,383 147,392 169,215 Recommended Water Group FTEs2 32.5 50 59 66 74 83
Job Category
Water System Maintenance Worker 6 6 6 7 8 9
Water Treatment Operator/Well
Mechanic
5 10 12 13 15 17
Water Distribution Operator 10 16 20 22 25 28
Water Meter Services 3 4 5 6 7 8
Other/Management 4.9 6 7 8 8 9
Engineering 3.6 5 5 6 7 8
Additional Engineering Staff for CIP3 -- 3 4 4 4 4
Notes:

1. Duplicated from Table 4-12 for reference.

2. Calculated as ADD (MGD) divided by the recommended ratio of 0.23 MGD/FTE as detailed in Section 11.3.1, using a 0.71 ratio of Water Group also detailed in Section 11.3.1, and adding additional engineering staff recommended for CIP administration .

3. Additional engineering staff recommended for CIP administration as described in Table 11-2.

ATTACHMENT 2
FIGURE 11-_

CITY OF MANTECA

WATER MASTER PLAN
2045

NUMBER OF FULL-TIME EMPLOYEES
SPLIT ROLE (LESS THAN 100% TIME SPENT

FOR THE WATER DIVISION)
LEGEND
Water Regulatory
Supervisor
Water Resources
Coordinator
SCADA
Engineer
Water
Admin 3
PW Deputy Director
Water Division
Public Works
Director
Water Regulatory
Coordinator
Water Regulatory
Compliance Specialist
Water Meter
Services Supervisor
Maintenance
Worker I/II/III
Meter Reader
I/II
Water Service
Technician I/II
Lead Distribution
Operator
Water Distribution
Supervisor
Water Distribution
Operator I/II/III
Water Treatment
Operations Supervisor
Well Mechanic /
Operator I/II
Water Treatment
Operator I/II
Water Division
Manager

DEPARTMENT OF PUBLIC WORKS
Assistant
Engineer
Associate Engineer (Water O&M -
Pipelines Improvement)
Associate Engineer (Water O&M -
Wells/Treatment Improvement)
Associate
Engineer
Senior Engineer
(Water)
Senior Civil Engineer
(Water O&M)
Engineering
Director
Administrative
Assistant
Management
Analyst

ENGINEERING DEPARTMENT
GIS
Technician
Deputy Director
(Infrastructure)
3 RECOMMENDED WATER GROUP STAFFING FOR
(Water CIP)
Assoc. Eng.
(Water CIP)
Assist. Eng.
(Water CIP)
ATTACHMENT 2
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11.3.3 Future Staffing Needs Considerations
The Water Group staff of 83 FTEs is recommended for 2045.

Factors that would increase the need for additional staff include:

The City performing engineering services during construction or construction management; MCLs adopted for contaminants that would require the City to increase water treatment operator certification; and
Increased reliance on both groundwater and imported water as a supply source due to availability limitations requiring development of infrastructure for both supply sources.

Mitigation measures include:

Cross-training and cross-certification of City staff to fill vacant and promotional opportunities or providing training as a group for certification;
Using continuing education and training requirements to encourage cross-certification; Reliance on alternative water sources to offset peaks and reduce the rate of requiring new infrastructure as described in Section 6.4; and
Contracting for operators to supplement City staff.

Splitting recommended positions such as GIS technician and water regulatory compliance specialist with other underground utilities such as stormwater, recycled water, and wastewater divisions in the engineering department.

Alternatively, the GIS technician could be cross-trained to also use maintenance planning software to track assets and maintenance work orders.

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SECTION 12 – REFERENCES
Provided are a list of sources used in the development of the Master Plan. These documents are incorporated herein by reference.
2019 SGMA Basin Prioritization, Appendix 1 published by DWR American Water Works Association, Manual of Water Supply Practices M31: Distribution System Requirements for Fire Protection
American Water Works Association, Manual of Water Supply Practices M32: Computer Modeling of Water Distribution Systems
American Water Works Association, Utility Benchmarking: Performance Management for Water and Wastewater 2022
California Regional Water Quality Control Board – Central Valley Region, National Pollutant Discharge Elimination System (NPDES) CA0081558 Order R5-2021-0003, February 18, 2021 California Code of Regulations Titles 22 and 24
City of Manteca, Water Loss Audit Reports, 2016-2020
ESJ Integrated Regional Water Management Plan 2014 Update ESJ Subbasin GSP November 2019, revised June 2022
City of Manteca, 2005 Water Master Plan
City of Manteca, 2013 Storm Drain Master Plan (SDMP)
City of Manteca, 2015 Urban Water Management Plan, September 2016 City of Manteca, Adopted Budget, Fiscal Year 2022-2023
City of Manteca, General Plan Amendment (GPA) published in January 2024 City of Manteca, Reclaimed Water Facilities Master Plan (RWFMP) Department of Water Resources, California’s Critically Overdrafted Groundwater Basins, January 2020
Manteca Municipal Services Review (MSR) published in July 2022 South San Joaquin Irrigation District, 2020 Agricultural Water Management Plan, Adopted March 23, 2021
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ATTACHMENT 2
www.hydroscience.com

APPENDIX A
City of Manteca
Water Master Plan
TM #1 Water Modeling Software Evaluation
ATTACHMENT 2
Technical Memorandum
Sacramento • Berkeley • San Jose
www.hydroscience.com
To: Elba Mijango, Project Manager, City of Manteca
From: Rachel Yenney, EIT
Jonathan Machorro, PE
Reviewed By: Angela Singer, PE
Subject: TM #1 – Water Modeling Software Evaluation
City of Manteca – Water Master Plan
Date: September 23, 2021
The City of Manteca (City) has retained HydroScience Engineers (HydroScience) to prepare a Water Distribution System Master Plan (WMP), which includes the building of a hydraulic model.

This technical memorandum (TM) presents an evaluation of the software programs available for hydraulic modeling of water distribution systems from the two industry-leading vendors: Innovyze (https://www.innovyze.com/en-us) and Bentley (https://www.bentley.com/en).

The City does not have an existing water distribution system model nor does the City own any modeling software licenses and historically has not conducted any hydraulic modeling in-house.

Although the City GIS system is regularly updated and maintained, there are no immediate plans to conduct hydraulic modeling in-house.

This TM will serve as the basis for recommending a hydraulic modeling software. Software programs were evaluated based on consideration for this WMP study as well as future model updates and continued use.

Modeling Software Options
This section discusses and compares Innovyze’s InfoWater®, Innovyze’s InfoWorks®WS Pro (InfoWorks), and Bentley’s WaterGEMS® (WaterGEMS). HydroScience currently owns licenses for both InfoWater and WaterGEMS. These programs are analyzed herein based on the following criteria (and more):

Purchase and subscription pricing;
Available features and applications;
Software stability;
Software accuracy;
Platform compatibility needs/interface (i.e. ArcGIS, AutoCAD, SCADA); Ease of use;
Technical support; and
Vendor reputation.

ATTACHMENT 2
City of Manteca
TM #1 – Water Modeling Software Evaluation
September 23, 2021

www.hydroscience.com
InfoWater®
InfoWater is an Innovyze software that uses an ArcGIS platform and is a successor of H2ONet.

InfoWater includes hydraulic and dynamic water quality modeling, energy management, real-time simulation and control, fire flow analysis, and automated on-line SCADA interface capabilities.

InfoWater uses a relational database and geodatabase to store model data and can automatically assign GIS attributes to be used in the model without manually mapping data from GIS to model data fields. For land use-based analyses, the software allows for import of land use categories from parcel GIS shapefiles, however, limits the number of land use categories to ten.

InfoWater operates using the EPANET engine and utilizes the Colebrook White (CW), Darcy Weisbach (DW), or Hazen Williams (HW) set of friction equations; the user can choose which set of friction formulas will be applied to a simulation run, but these methods cannot coexist within a single simulation. The operating speed of InfoWater’s simulations is restricted by the EPANET engine which is optimized for small to medium networks and performs slower for larger networks and longer simulations.

The InfoWater fire flow module is designed to evaluate the system given fire flow and velocity and residual pressure constraints, identifying critical infrastructure that are either exceeding velocity constraints or below minimum residual pressure. The module also will report the amount of available fire flow at a hydrant.

InfoWater has a rich scenario manager that provides the user the ability to build a single model with an array of modeling scenarios and alternatives for development of various physical and hydrologic conditions. Every change made to a parent scenario is propagated throughout all scenarios.

InfoWater also has InfoWater MSX (Multi-Species eXtension), which adds capabilities to accurately model multiple interacting constituents, sediment deposition and re-suspension in drinking water distribution systems, and water temperature.

Because this software does use an integrated ArcGIS platform, its ease of use is increased with a strong base understanding of GIS. There is a separate software called InfoWater SA (standalone) that is essentially the same software without the GIS platform.

The InfoWater product brochure, along with the overview and specifications from Innovyze’s website (https://store.innovyze.com/WaterDistribution/InfoWater?cclcl=en_US), can be found in Attachment A.

InfoWorks®WS Pro
InfoWorks is an Innovyze product that uses a standalone platform and is a successor of InfoWorks®WS. InfoWorks includes water quality modeling, demand management – including pressure-related demand – for cost-benefit analyses, leak detection, fire flow analysis, criticality assessments for both pipes and valves, and real-time comparisons of actual values against modeling results with linkage to SCADA and telemetry data. The current water quality analysis capabilities include single species chemical transport, water age, source tracing, and turbidity analysis; multiple solute interaction analysis capabilities are also under development and will be ATTACHMENT 2
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available with future software program updates. For land-use based analysis, there is no limit to the number of unique demand types and patterns.

InfoWorks utilizes a workgroup model management system to allow for simultaneous updates by multiple team members; all model data is maintained in a single, centralized, multi-user master database with a conflict management system used to resolve changes made to objects by different users.

InfoWorks does not utilize the EPANET engine, though Innovyze does support a separate version which does: InfoWorks WS Pro EPEng. Similar to InfoWater, the CW, DW, and HW set of friction equations are all available within InfoWorks, and they can coexist within the same simulation.

The operating speed of InfoWorks is much better, compared to InfoWater, for larger networks; simulations are run much faster due to the modified engine and database structure. InfoWorks is most commonly utilized in Europe where a single water system will typically serve large portions of an entire country.

Similar to InfoWater, the fire flow analysis module in InfoWorks will evaluate the system given fire flow requirements and velocity and residual pressure constraints, and infrastructure outside of the stated criteria will be identified.

InfoWorks does not currently support a parent/child scenario management system, though this is in development and will be released as part of a future software program update. Currently, users can have multiple copies of a network within a single master database, but the networks are not related to each other – changes do not propagate throughout. InfoWorks does, however, include a data flagging system which allows each user to track the source of each of their changes.

InfoWorks also offers InfoWorks TS, a module which adds the capability to perform transient analyses to accurately predict water hammer within a system and assess various protection measures.

Results from an InfoWorks model simulation as well as the network itself can be exported directly to GIS for viewing. Innovyze also offers InfoWorks Viewer, which is a limited license option that allows a user to utilize the complete analytical functionality of InfoWorks without the ability to edit/modify the model.

Innovyze does not currently have a product data sheet for InfoWorks. Included in Attachment B is the overview and specifications from Innovyze’s website (https://store.innovyze.com/WaterDistribution/InfoWoWSP?cclcl=en_US).

WaterGEMS®
WaterGEMS is a successor of Bentley’s original water hydraulic analysis software WaterCAD.

WaterGEMS includes fire flow analysis, water quality simulations, and criticality and energy cost analyses. WaterGEMS uses a multi-platform environment, meaning that the same model file can be opened in ArcGIS, AutoCAD, MicroStation, or a standalone WaterGEMS platform without having to import or export any data. In addition, a WaterGEMS model can be opened and reviewed in WaterCAD. WaterCAD is a less expensive water hydraulic analysis software that can be operated with AutoCAD or as a standalone platform. For land use-based analyses, the ATTACHMENT 2
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September 23, 2021

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software allows for import of land use categories from parcel GIS shapefiles with no limit to the number of land use categories.

WaterGEMS utilizes a modified hybrid hydraulic engine. It allows the user to choose between the Manning, HW, or DW set of friction equations, though they cannot coexist in the same simulation run.

The WaterGEMS fire flow module identifies any infrastructure that are exceeding velocity constraints or unable to meet residual pressure constraints. Given these constraints, the fire flow module will also report the amount of available fire flow at each hydrant.

Similar to InfoWater, WaterGEMS contains a rich scenario management system that allows the user to create child scenarios that inherit all data from the parent. If any changes are later made to the parent, those changes will trickle down through all children scenarios. Conversely, the user can override values if the changes are made directly in the child scenario. This allows for the development of multiple alternatives for analysis to evaluate an unlimited number of “what if?” situations. Then, when a model batch run is set up, multiple scenarios can be submitted for calculation at the same time.

Bentley has a format called iModel which has a corresponding free viewer. WaterGEMS can publish iModels which give access to graphically viewable files on PCs and tablets that have individual asset inputs and results available for viewing.

InfoWater and InfoWorks files can be converted to WaterGEMS by exporting/importing using a common platform, such as EPANet. Because the modeling files are compatible with multiple platforms, the user has the option to work in the platform that suits the user’s capabilities or needs.

The WaterGEMS product data sheet, along with an overview of the software from Bentley’s website can be found in Attachment C: (https://www.bentley.com/en/products/productline/hydraulics-and-hydrology-software/watergems).

Summary
InfoWater, InfoWorks, and WaterGEMS are comparable with regards to software capability. All three offer robust tools for system analyzing, such as fire flow, with some tools being easier to run in one software over the others. All three software programs are known to be stable and highly accurate, offering a wide range of features, options, and scenarios for representing and analyzing water system operation.

Both Innovyze and Bentley are known for having timely and quality customer support. In Northern California, Innovyze software programs are more common than Bentley, but their reputations are comparable. Innovyze support will often be a dedicated individual that can be contacted via phone or email. Bentley uses a ticketing system to provide tech support. Innovyze is a more personalized support system, though both are effective. Both offer web-based, live, and on-site training options.

The following table summarizes some of the basic criteria for each software.

ATTACHMENT 2
City of Manteca
TM #1 – Water Modeling Software Evaluation
September 23, 2021

www.hydroscience.com
Table 1: Brief Software Comparison for 5,000 Links
Criteria InfoWater® InfoWorks®WS Pro WaterGEMS®
Company Innovyze Innovyze Bentley
Software Requirements ArcGIS None None1
Initial Purchase Price $11,150 $25,570 $20,968
Annual Subscription
Price
$2,230 $5,114 $5,033
Other Costs $3,500 (GIS seat)2
$500 (annual)
None None
ArcGIS Platform XX
AutoCAD Platform X
Standalone InfoWater SA X X
SCADA Integration XXX
GUI Least intuitive interface Less intuitive interface More intuitive interface Analyzing Tools Comparable Comparable Comparable
Tech Support Dedicated individual –
more personalized
experience
Dedicated individual –
more personalized
experience
Ticketing system – less
personal and contacts
may vary
Notes:

1. Can operate as a standalone software; however, requires licensing for ArcGIS, AutoCAD, or Microstation for operating the respective platform, if desired.

2. Requires ArcMap Basic license. Price listed assumes that the City currently has an ArcMap Basic license that is completely occupied. Price is for an additional concurrent use license.

As mentioned previously, InfoWorks is typically used for very large distribution systems, and is more commonly used in Europe. The City’s water distribution system is considered small-tomedium size, containing approximately 5,000 links. For a system of this size, the speed and robustness of InfoWorks does not provide an advantage over InfoWater and/or WaterGEMS.

Additionally, InfoWorks does not offer parent/child scenario management which is a key component for analyzing different scenarios for this study. InfoWorks is also significantly more expensive. Thus, InfoWorks has been omitted from further consideration. Going forward, a comparison is presented between InfoWater and WaterGEMS. A full detailed comparison of features for InfoWater and WaterGEMS is included in Attachment D.

Model Maintenance Options
For regular hydraulic model maintenance, the City has two options: (1) purchase the software license and maintain the hydraulic model in-house or (2) work with a third-party consulting firm to maintain and operate the hydraulic model for new development and redevelopment analyses on an as-needed basis. This section will present a brief comparison of some of the advantages and disadvantages of each scenario.

ATTACHMENT 2
City of Manteca
TM #1 – Water Modeling Software Evaluation
September 23, 2021

www.hydroscience.com
City-Maintained Model
The two major factors to consider for in-house model maintenance are cost and technical experience. The software costs associated with in-house modeling include the purchase price and the ongoing software subscription costs. Continuing subscription is highly recommended to receive ongoing technical support. In addition, modeling software is typically updated at least annually as the vendor addresses instabilities and makes improvements to the software.

Maintaining a subscription ensures that the City has access to the most current and stable version.

The second factor is technical experience and confidence in the operation and results. To achieve an acceptable level of accuracy and confidence in the model results, staff should be trained and experienced in the use of the software. In addition, hydraulic modeling can be a time-consuming operation; if the staff does not use the program on a regular basis, operational efficiency may decrease as it can be easy to forget how to operate and navigate the tools.

The primary advantage of having in-house modeling capabilities is the immediate access to the software and models for analysis of various scenarios beyond just new and redevelopment. The City can use the model to analyze planned maintenance outages, changes in sources of supply, and/or other operational situations that may occur.

If the City purchases the software program and opts to maintain the hydraulic model in-house, we recommend assigning dedicated staff to this task, preferably staff with robust GIS experience, as well as software training. There is typically a steep learning curve to become familiar with how to navigate, update, and operate a hydraulic model. Prices for training can range depending on whether it is web-based, in-person, or on-site. Course levels also range from introductory to advanced and start around $1,700 and can be up to several thousand dollars and multiple days.

Third-Party Maintained Model
The alternative to in-house modeling and maintenance is contracting with a third-party consultant to evaluate any new development projects, update the model as construction projects are completed, and provide as-needed modeling support. Third-party consultants are typically wellversed in various modeling platforms and have dedicated modeling staff that stay familiar with model software operation. Consultants also own the modeling software and pay for ongoing subscription maintenance, absorbing the purchase and annual costs on behalf of their clients.

Consultants typically have access to various modeling software and platforms to address the range of needs for their clients.

As an example, HydroScience currently has ongoing contracts with other municipalities to maintain their water distribution and sewer collection system hydraulic models. When there is a new development, HydroScience will evaluate the impacts of those new developments, assess the capacity of the system, and identify deficiencies and the necessary requirements for the new development. In the case of the City of Sunnyvale, HydroScience provided training for eight internal staff. However, since the City did not have enough hydraulic modeling work to justify even a dedicated part-time position, other work priorities took precedence. As such, the City opted for an annual purchase order with HydroScience to provide as-needed modeling services based on time and material. There have been some years where there have been no modeling services needed and others in which the City has needed to increase the contract amount.

ATTACHMENT 2
City of Manteca
TM #1 – Water Modeling Software Evaluation
September 23, 2021

www.hydroscience.com
HydroScience has provided ongoing model maintenance support, development impact analyses, fire flow analyses, and litigation support for a variety of municipal clients.

The obvious advantages of having a third-party consultant conduct the analyses are costs as well as experience. The additional advantage is that a third-party analysis limits the potential for conflict-of-interest allegations from developers. For development-related modeling services, it is typical for most public agencies to charge developers a fee to recoup the cost of modeling services and since the charges are from a third-party provider, it is rarely disputed by the developer.

Conclusion
Taking into consideration all the discussed comparisons, HydroScience recommends that the City use InfoWater for the building of the water distribution system hydraulic model for the purpose of this WMP effort.

InfoWater and WaterGEMS both have the capability to easily and accurately model the City’s system. The primary differences in these two programs are front-end graphical user interface (GUI) platform compatibility and cost. WaterGEMS’s GUI is a more intuitive interface and is easier to pick up on a basic level. WaterGEMS also has the added benefit of running in AutoCAD, ArcGIS, and/or standalone, which does not require and additional software license for ArcGIS or AutoCAD integration. However, the City predominately uses ArcGIS, so the AutoCAD capabilities of WaterGEMS are not relevant. There are no other notable advantages between the modeling programs.

Purchase price and other additional costs are not a significant consideration unless the City elects to purchase the software to conduct in-house modeling; HydroScience already carries the required licensing for both InfoWater and WaterGEMS. However, if the City does elect to purchase the software and bring those capabilities in-house, cost does become a consideration.

For this reason, HydroScience recommends that the City uses InfoWater for this WMP study.

City Decision
Given the above considerations as well as conversation between HydroScience and City Staff, the City has elected to use WaterGEMS for the building of the water distribution system hydraulic model for the purpose of this WMP effort. The following criteria motivated this decision:

Compatibility with AutoCAD & GIS,
Viewing capabilities without the need to buy a software license, No limit on land use types,
Intuitive GUI,
Appropriate for a City this size (i.e. 5,000 links),
Short term quarterly licenses available, if needed, and Cost is in the middle (not lowest or highest).

ATTACHMENT 2
City of Manteca
TM #1 – Water Modeling Software Evaluation
September 23, 2021

www.hydroscience.com
Next Steps
The following tasks will be completed next as part of the water master planning efforts:

Continue data collection,
Existing staffing plan evaluation,
Interim water rate study,
Calibration plan and hydrant testing, and
Baseline unit demand analysis.

ATTACHMENT 2
www.hydroscience.com

ATTACHMENT A
City of Manteca
TM #1 – Water Modeling Software Evaluation
InfoWater Product Information
ATTACHMENT 2
Water Supply
InfoWater is a fully ArcGIS integrated water distribution network modeling and management software application. It seamlessly integrates advanced water network simulation and optimization functionality with the latest generation of ArcGIS. InfoWater capitalizes on the intelligence and versatility of the geodatabase architecture to deliver unparalleled levels of geospatial analysis, infrastructure management and business planning.

APPLICATIONS
• Network model build/run in ArcGIS
• Valve criticality analysis
• Pump and valve optimization
•
• Water security planning
• Water quality (multi-species) assessment
• Energy and capital cost management
• Regulatory (IDSE) compliance
• Pipe break analysis

ARCGIS INTEGRATED WATER DISTRIBUTION MODELING AND

MANAGEMENT
• Temperature modeling
• Sediment transport and deposition
• Turbidity modeling
• Leak detection and reduction
• Sensor location optimization
• Carbon cost calculation
• Pressure zone management
•
• Vulnerability/risk assessment
ATTACHMENT 2

COMPLETE MODEL BUILD ENVIRONMENT
InfoWater allows the quick and convenient building of water distribution models as an ArcGIS extension. Models can be created, edited, updated and stored within a geodatabase utilizing data taken directly and inferred from the corporate geodatabase and a variety of other data sources. Multiple scenarios can be created and fully automated updates
maintained using the GIS Data Exchange Tool. InfoWater
contains a powerful set of quality assurance and control features to ensure that models are of the highest standard, including network trace, connectivity, link and node tools; ability to pinpoint disconnected areas.

EXTENSIVE SIMULATION OPTIONS
ensure excellent simulation speed, stability and accuracy.

Comprehensive network modeling capabilities are available, either within the standard InfoWater package or as part simulation, valve criticality, water demand and pressure zone energy use and cost calculations, automatic calibration and design of networks, and carbon footprint analysis.

RICH PRESENTATION OF RESULTS
Using powerful ArcGIS thematic mapping functionality,
InfoWater makes it easy to turn dry database information into stunningly colorful, fully dimensional visualizations.

It is possible to generate beautiful, accurate and smooth contours for any variable — even overlay multiple contours on a single drawing. Users can draw on a range of other coded mapping, dynamic annotation and labeling, graphing, animation to produce truly compelling results.

INFOSURGE TRANSIENT ANALYSIS
InfoSurge provides the most advanced and comprehensive
platform available for analyzing complex hydraulic transients with incredible power, speed and ease of use. Cavitation or excessive pressure surging during transient operation can lead to pipeline or component failure, and surge control devices are often required to prevent the development of such conditions. The proper selection and evaluation of analysis is vital in the design of water supply and distribution systems to ensure their safety and reliability under emergency conditions.

ADDITIONAL INFORMATION
www.innovyze.com/products/infowater

NEWS & CASE STUDIES
www.innovyze.com/news/?infowater

LATEST PRODUCT UPDATES
www.innovyze.com/updates

ADVANCED PIPE BREAK ANALYSIS
InfoWater can explicitly model water main breaks and
leaks, enabling users to develop effective leakage reduction and control and demand and maintenance management
water, minimize economic losses, ensure hydraulic and
water integrity, improve the quality of service, and conserve in the network along with their location, size, and time of occurrence. They can also be automatically distributed at the two end nodes of a pipe. InfoWater will compute and report the total water volume lost to breaks as well as their concentrations) integrity of the water distribution system.

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ATTACHMENT B
City of Manteca
TM #1 – Water Modeling Software Evaluation
InfoWorks WS Pro Product Information
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ATTACHMENT C
City of Manteca
TM #1 – Water Modeling Software Evaluation
WaterGEMS Product Information
ATTACHMENT 2
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www.hydroscience.com

ATTACHMENT D
City of Manteca
TM #1 – Water Modeling Software Evaluation
Software Feature Comparison Table
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APPENDIX B
City of Manteca
Water Master Plan
TM #2 Model Calibration Plan
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FIGURE 1

CITY OF MANTECA

WATER MASTER PLAN

HYDRANT FLOW TESTING LOCATIONS
LEGEND
¡ FLUSHING HYDRANT
¡ ALTERNATE HYDRANT

C-FACTOR TESTING

PIPE DIAMETER (IN)
4 6
8 10
12 14
>16
N
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0 2,000 4,000
1 IN = 4,000 FT
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MELISSA WAY

NL TREBO R NEHPETS

YAWTREBLA

EVA EI RAMANNAI G

MELISSA PL
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SHOPS LN

GROVE AVE
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LOCUST AVE

EL CAPITAN AVE

EVATUNLAW

NL DROFI LLI W
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NL TE I NARG

EVA OS LLECNOCSAV
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EVA ORAJ AP

RETAWEDI T HTAP

LP YERETNOM
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NL KOORBNEVAR

YA WESAHC ELPAM
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EVA NYR NAV
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EVA MLE

NL FAEL N LLE AF

NL AI LEMAC

EVAEDI SKRAP
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YA WTROPRI A

LN HTERDN LA

NL HSENI D

NL NNAMRAHCS

EVA O DASAP

YAWI TNAVA
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www.hydroscience.com

APPENDIX C
City of Manteca
Water Master Plan
TM #4 Water Sustainability Study
ATTACHMENT 2
2023
Water Sustainability
Study

CITY OF MANTECA
THE SHIBATANI GROUP, INC. IN COLLABORATION WITH

HYDROSCIENCE ENGINEERS, INC,
ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page i

TABLE OF CONTENTS
Executive Summary ....................................................................................................................... ES-1 ES.1 Background .................................................................................................................................. ES-1 ES.2 Hydrologic Sustainability and Climate Change ............................................................................ ES-2 ES.3 City of Manteca Hydrogeologic Context and Water Supplies ...................................................... ES-2 ES.4 City Water Supply and Demand Balance ..................................................................................... ES-5 ES.5 Future Water-Related Threats to the City ................................................................................... ES-7 ES.6 Recommendations ..................................................................................................................... ES-11 1 Introduction ................................................................................................................................ 1 2 Background ................................................................................................................................. 2 3 Hydrological Sustainability And Climate Change ........................................................................... 4

3.1 Climate Change Water Implications to the City ................................................................................ 5

3.2 Climate Analysis – Modeling ............................................................................................................. 7

3.2.1 Climate Modeling for Water Purveyors .................................................................................. 7 4 City of Manteca Hydrogeologic Context and Water SupplY AVAILABILITY .................................... 13

4.1 Local Hydrology ............................................................................................................................... 15

4.2 South San Joaquin Irrigation District (SSJID) ................................................................................... 20

4.3 Groundwater ................................................................................................................................... 25

4.3.1 Chronic Basin Groundwater Depletion ................................................................................. 27

4.3.2 Groundwater Sustainability Plan (under SGMA) ................................................................... 28

4.3.3 Groundwater Balance and Modeling Simulations ................................................................ 31

4.4 Alternative Water Supply: Stormwater and/or Floodwater ........................................................... 36

4.4.1 Stormwater Capture .............................................................................................................. 37

4.4.2 Dry Wells ............................................................................................................................... 38

4.4.3 Wetland Parks ....................................................................................................................... 39

4.4.4 Stormwater as a Water Source 2013 Study .......................................................................... 40

4.4.5 City Stormwater .................................................................................................................... 41 5 City Water Supply and Demand Balance ..................................................................................... 44

5.1 2020 Water Use .............................................................................................................................. 44

5.2 Water Demand Projections ............................................................................................................. 44

5.3 Water Supply Projections................................................................................................................ 45

5.4 Supply vs. Demand for Normal Water Year .................................................................................... 47

5.5 Supply vs. Demand Under Drought Conditions .............................................................................. 48 6 Future Water-Related Threats to the City ................................................................................... 50

6.1 Hydroclimate Change and Uncertainty ........................................................................................... 50

6.1.1 Climate Change ..................................................................................................................... 50

6.1.2 Hydroclimatic Uncertainties .................................................................................................. 53

6.1.3 Bias in Precipitation Forecasting ........................................................................................... 56

6.2 Surface Water Storage Dilemma ..................................................................................................... 58

6.2.1 Reservoir Management ......................................................................................................... 61 ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page ii

6.2.2 Hydroclimate and Storage..................................................................................................... 62

6.3 Regulatory Impositions – Surface Water Operations ..................................................................... 63

6.3.1 Releases pertaining to Biological and Environmental Objectives ......................................... 63

6.3.2 New Melones Reservoir Operations and related Surface Water Transfers .......................... 67

6.4 Groundwater Challenges for the City ............................................................................................. 68

6.5 Additional Considerations ............................................................................................................... 71

6.5.1 Water Quality ........................................................................................................................ 72

6.5.2 Land Subsidence .................................................................................................................... 72

6.6 Realities of Future Droughts ........................................................................................................... 74 7 Recommendations for the City ................................................................................................... 79

LIST OF TABLES
Table ES-1: Historical Basis of WY Type ................................................................................................... ES-6 Table 4-1: City of Manteca Climate Characteristics .................................................................................... 14 Table 4-2: SCWSP Phase I and II Allotments by City ................................................................................... 22 Table 4-3: SSJID Historic Treated Water Deliveries to City ......................................................................... 22 Table 4-4: Historical Groundwater Pumped within City ............................................................................. 25 Table 4-5: Comparison of WY 2020 and WY 2021 Water Budget (in AF) ................................................... 32 Table 4-6: Average Annual Water Budget – Groundwater System (AFY) ................................................... 33 Table 4-7: Operational Water Budget by Select GSA and for the ESJ Subbasin ......................................... 36 Table 5-1: City Water Supplies 2020 ........................................................................................................... 44 Table 5-2: Potable Water Demand Projections .......................................................................................... 44 Table 5-3: Projected Un-Curtailed Total Available City Water Supplies (AFY) ............................................ 45 Table 5-4: Normal Year Supply versus Demand Comparison ..................................................................... 47 Table 5-5: Historical Basis of WY Type ........................................................................................................ 47 Table 5-6: Single-Dry Year Supply versus Demand Comparison ................................................................. 48 Table 6-1: Historical (1920–1999) and Future Simulated (2020–2099) Precipitation at Seasonal and Total WY ........................................................................................................................................... 52 Table 6-2: Term 91 Curtailment Notices in the Delta Watershed .............................................................. 77 Table 6-3: CVP Contractor Water Allocations by WY, 2012-2022 (Percentage of Maximum Contract Allocation Made Available) ..................................................................................................... 78

ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page iii

LIST OF FIGURES
Figure ES-1: Historical City Groundwater Pumping and City Area ........................................................... ES-3 Figure ES-2: Schematic of Folsom Reservoir showing Operating Rule Curve and Seasonal Spill/Fill Thresholds ............................................................................................................................ ES-8 Figure 3-1: Typical “Forced” Hydrographs from Watersheds of Snow, Rain on Snow, and Rain ................. 4 Figure 3-2: Generic Representation of a Global Climate Model showing 3D Coverage of Atmosphere and Land Surface Area ...................................................................................................................... 8 Figure 3-3: Step Process from Global Climate Modeling through Regional Downscaling to Impact Assessment through to Hydrological Modeling ........................................................................ 9 Figure 3-4: Watersheds Modeled in the Mountain Hydrologic Water Model by BCM Model ................... 10 Figure 3-5: Anticipated Future Warming under Various Assumed GHG Loading Scenarios ...................... 11 Figure 4-1: City of Manteca Average Monthly Climatic Conditions ............................................................ 14 Figure 4-2: Major Hydrologic Features of the Eastern San Joaquin Groundwater Subbasin ..................... 15 Figure 4-3: Eastern San Joaquin Groundwater Subbasin Watersheds ....................................................... 16 Figure 4-4: Soil Depositional Areas and Major Alluvial River Fans ............................................................. 17 Figure 4-5: Existing Areas of Groundwater Recharge ................................................................................. 19 Figure 4-6: Existing Areas of Groundwater Recharge ................................................................................. 20 Figure 4-7: Nick C DeGroot WTP ................................................................................................................. 21 Figure 4-8: SSJID and OID Relied Upon Reservoirs – Tri-Dam Project, New Melones, Goodwin and Woodward Reservoirs ............................................................................................................. 24 Figure 4-9: Historical City Groundwater Pumping and City Area................................................................ 26 Figure 4-10: Groundwater Storage Trends in North America from April 2002 to June 2017 ..................... 27 Figure 4-11: Eastern San Joaquin Subbasin GSAs ....................................................................................... 29 Figure 4-12: Groundwater Level Representative Monitoring Well Locations ............................................ 31 Figure 4-13: Modeled Change in Annual Storage with Water Use and Year Type ..................................... 34 Figure 4-14: Modeled Change in Annual Storage with Groundwater Pumping and Year Type ................. 35 Figure 4-15: National Park Service – Large Cisterns under the National Mall ............................................ 38 Figure 4-16: Curbside Dry Well Installation with Vegetation in Los Angeles .............................................. 39 Figure 4-17: Illustration of Key Flood Infrastructure .................................................................................. 42 Figure 5-1: City Limits Expansion for 2030 and 2045 Projection Horizons ................................................. 46 Figure 6-1: Simulated Future San Joaquin Watersheds – Runoff Exceedance Probabilities for the October-March and April-July Periods .................................................................................... 52 Figure 6-2: San Joaquin Precipitation: 5-Station Index for February 6, 2023 ............................................. 55 Figure 6-3: 50-Year Historical Precipitation and Cumulative Departure from Mean Precipitation for the San Joaquin Valley ................................................................................................................... 58 ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page iv
Figure 6-4: Schematic of Folsom Reservoir showing Operating Rule Curve and Seasonal Spill/Fill Thresholds ............................................................................................................................... 60 Figure 6-5: Stanislaus River Flows WY 2016 Natural Flow and Prescribed Releases ............................... 61 Figure 6-6: Estimated Yearly Natural Production of Adult Fall-Run Chinook Salmon in the Stanislaus River ................................................................................................................................................. 64 Figure 6-7: Key Dams Along the Stanislaus River ........................................................................................ 65 Figure 6-8: Endangered Fish Species Scientific Evaluation Process Chain for the Stanislaus River ............ 66 Figure 6-9: Hydrograph for Representative Monitoring Well – Manteca 18.............................................. 70

ABBREVIATIONS AND ACRONYMS
AFY Acre Feet per Year
AFRP Anadromous Fish Restoration Program
AGU American Geophysical Union
AR Atmospheric River, a long, narrow, and transient corridor of strong horizontal water vapor transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone. Up to 50% of California’s annual precipitation can come from ARs and they are known to bring enough water to a region to effectively end a prolonged drought.

BCM Basin Characteristics Model
cfs cubic feet per second
CMIP5 Coupled Model Intercomparison Project Phase 5
COA Coordinated Operations Agreement
CVP Central Valley Project
CVPIA Central Valley Project Improvement Act
D-1422 SWRCB Decision No. 1422, New Melones Project Water Rights Decision D-1641 SWRCB Decision No. 1641, San Francisco Bay/Sacramento-San Joaquin Delta Estuary, Central Valley Project and the State Water Project in the Southern Delta Water Rights Decision
DO Dissolved Oxygen
DWR Department of Water Resources
ENSO El Niño and the Southern Oscillation
ESA Endangered Species Act
ESJWRM Eastern San Joaquin Water Resources Model
ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page i
ET Evapotranspiration
GCM Global Climate Model
GHG Greenhouse Gas
GHM Global hydrological models
gpm gallons per minute
GSA Groundwater Sustainability Agencies
GSP Groundwater Sustainability Plan
InSAR Interferometric Synthetic Aperture Radar satellites for monitoring geodetic data IPO Interim Plan of Operations for the New Melones Reservoir LAO Legislative Analyst’s Office, The California Legislature’s Nonpartisan Fiscal and Policy Advisor
LSM Land surface models
M&I Municipal & Industrial
MAF Million Acre Feet
MAR Managed Aquifer Recharge
MGD million gallons per day
MHWM Mountain Hydrologic Watershed Model
NASA LIS National Aeronautics and Space Administration Land Information System NAO North Atlantic Oscillation, an irregular fluctuation of atmospheric pressure over the North Atlantic Ocean
NEPA National Environmental Policy Act
NMRPO New Melones Revised Plan of Operation
NRCS Natural Resource Conservation Service
OCAP CVP Operations Criteria and Plan
OID Oakdale Irrigation District
PDO Pacific Decadal Oscillation, a long-lived El Niño-like pattern of Pacific climate variability PMM Pacific Meridional Mode, Climate mode in the North Pacific RCM Regional Climate Model
RCP Representative Concentration Pathway (4.5 lower emission scenario, 8.5 high emission scenario)
ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page ii
RWH Rainwater Harvesting
SCWSP South County Water Supply Project
SDMP Storm Drain Master Plan
SDWA Safe Drinking Water Act
SEP Scientific Evaluation Process
SGMA Sustainable Groundwater Management Act
SRP Stanislaus Stepped Release Plan
SSJID South San Joaquin Irrigation District
SSP585 SSP5-8.5 represents the high end of the range of future emission pathways, corresponding to RCP8.5 and refers to an additional radiative forcing of 8.5W/m2 by the year 2100
SST Sea-Surface Temperature
SWE Snow Water Equivalent
SWP State Water Project
SWT Stanislaus Watershed Team
SWRCB State Water Resources Control Board
TM Technical Memorandum
USBR U.S. Bureau of Reclamation
UWMP Urban Water Management Plan
WES Wind-Evaporation-Sea
WIF Winter Instability Flow
WRF-Hydro an open-source community model used for a range of projects, including flash flood prediction, regional hydroclimate impacts assessment, seasonal forecasting of water resources, and land-atmosphere coupling studies
WY Water Year
ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page ES-1

EXECUTIVE SUMMARY
The purpose of this Technical Memorandum (TM) No. 4 (“Water Sustainability Study”) is to examine the long-term reliability of the City of Manteca’s (City’s) water supply sources and delivery allocations and develop a water supply strategy
reliability. Its companion TM No. 5 addresses various existing and potential regulatory constraints associated with the City water supply.

Water reliability generally speaks to the delivery capability of a water supply and is sometimes referred to as a measured firmness of supply. Alternatively, water sustainability has to do with the guaranteed protection of the resource so that it is not irreparably damaged or irretrievably depleted, such as groundwater safe yield.

ES.1 Background
This section acknowledges and introduces the many different forms of drought that may affect the City and its water operations. These drought types include:

Meteorological drought
Hydrological drought
Infrastructural drought
Operational drought
Regulatory drought
Institutional or administrative drought
This Water Sustainability Study is intended to identify the risks, such as drought, to the City’s water resources so that proper strategies can be put in place to protect these resources. If there is a shortage between water supply and demand and the City is challenged to meet near- or intermediate-term water delivery obligations or, if the projected supplies are considered too uncertain, either further demand reduction or alternative water supply sources must be sought.

The first step in any future water resource or supply planning effort is to establish the baseline yield. In order to do that, it is important to properly identify the causes of any shortfalls that may inhibit supply; recognizing that not all water shortages are due to a lack of rainfall.

While baseline yield had always been established through a relatively straightforward process, rapidly changing hydroclimatic conditions make it necessary to now account for climatic changes. The water industry now accepts that natural hydrology is non-stationary. For water supply planning, this is a major shift.

ATTACHMENT 2
The SHIBATANI GROUP, Inc. City of Manteca December 2022 Water Sustainability Study
Page ES-2
ES.2 Hydrologic Sustainability and Climate Change
This section provides a discussion of climate change and specifically, climate change hydrology. It reviews contemporary climate change modeling, global climate models (GCMs), regional climate models (RCMs), as well as the various methodological and analytical processes required to make use of modeling data output. Climate modeling features such as bias correction, dynamical and statistical downscaling, spatial downscaling, and representative concentration pathways are briefly discussed.

Climate change water-related implications potentially affecting the City are presented. A brief description of the various City water supply facets that could be affected by rapidly changing hydroclimatic conditions include the following:

Water supply delivery stipulations based on quantity agreement(s) between any and all wholesale/retail suppliers and the City for water supplies drawn from California rivers, streams, reservoirs, lakes, or managed embayments;
Water supply delivery stipulations based on quantity agreement(s) between wholesale/retail suppliers relied upon by the City and federal/State water regulatory agencies for water supplies drawn from California rivers, streams, reservoirs, lakes, or managed embayments; Water supply delivery stipulations based on (timing) agreements(s) among and within these same parties; and
Assumed safe yield (aka sustainable yield) volumes based on calculated and negotiated recharge of the Eastern San Joaquin Groundwater Basin through the ongoing Sustainable Groundwater Management Act (SGMA) process, the Groundwater Sustainability Plan (GSP), and ultimately the established pumping allowances afforded the City.

Assessment of the sustainability of the City’s primary surface water supply, pre-1914 water rights water purchased under agreement with the South San Joaquin Irrigation District (SSJID), should take into account the effects of climate change.

The section concludes with a discussion of the established findings of how a continually shifting hydroclimatic environment is affecting California and, more specifically, the Sierra Nevada and southern Central Valley. In particular, changes are occurring through often diminishing snowpack, earlier springmelt, a corresponding temporal shift in the rainfall/runoff relationships, increasingly frequent extreme events (i.e. drought and flood), and potentially hotter temperatures. While the accumulating climate change data is vast, the results can be as diverse as there remains considerable uncertainties in the specifics of the various modeling platforms. Each study is site, time, and method specific.

ES.3 City of Manteca Hydrogeologic Context and Water Supplies This section provides the hydrologic and hydrogeologic background setting of the City and surrounding regional water characteristics. The City’s climate, underlying basin aquifer, regional areas of groundwater recharge, subbasin watersheds, surface drainage ways, and soil cover are described. Specifically, much of the City’s corporate boundary lies within the Eastern San Joaquin Groundwater Subbasin’s furthest southwest watershed, the Lone Tree Creek/San Joaquin River watershed, and a small western portion of the Lone Tree Creek watershed.

ATTACHMENT 2
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A discussion is included in this TM of SSJID’s water supplies including its Nick C. DeGroot Water Treatment Plant, the South County Water Supply Project (SCWSP), and the City’s Phases I and II allocations of 11,500 and 18,500 Acre-feet per year (AFY), respectively, under the Project Participant’s Agreement. Treated water deliveries from SSJID to the City have increased from 6,107 AFY in 2016 to 9,416 AFY by 2020.

SSJID’s notable 600,000 AFY pre-1914 water rights are discussed in this TM along with those of the Oakdale Irrigation District (OID) in the Stanislaus River basin and diverted at Goodwin Dam which are coordinated through a 1988 Stipulation and Agreement with the U.S. Bureau of Reclamation (USBR) for operations. The USBR’s Tri-Dams and New Melones Reservoir system includes its downstream reservoir cascading reservoir system through Goodwin, Tulloch, and Woodward reservoirs.

Groundwater. Chronic groundwater depletion over the decades has made the Eastern San Joaquin Groundwater Subbasin one of the most stressed aquifer systems relied upon by multiple users across the U.S. Comprising some 707,000 Acres (1,105 square miles), it includes the major tributaries: San Joaquin River, Stanislaus River, Calaveras Rover, Mokelumne River, Mormon Slough, and Little Johns Creek.

The City owns and operates 15 active and two standby potable water wells along with 31 irrigation wells.

Between 1990 and 2020, the City’s groundwater use diminished from a high of 14,900 AFY in 2004 to 8,022 AFY in 2020. On an annual AFY per Acre (AFY/Ac) basis, the City pumped a high of about 1.4 AFY/Ac in 2004, but this has since decreased to about 0.5 AFY/Ac between 2014 and 2019. Figure ES-1 presents a visual representation of the City’s total water supplies and City area between 1990 and 2020 to display the fluctuations in groundwater pumping quantities relative to the City area.

Figure ES-1: Historical City Groundwater Pumping and City Area Source: Water supply data provided by the City.
0 5,000
10,000
15,000
20,000
0 5,000
10,000
15,000
20,000
1990 1995 2000 2005 2010 2015 2020
Total Groundwater Surface Water City Area
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This section also describes the City’s participation in the various requirements set forth under the 2014 SGMA including the various objectives of required GSPs. The City has one Listed SGMA Project. Project #3 is the City’s Advanced Metering Infrastructure water conservation project. The City has also identified Project #19, its “Recycled Water Transfer to Agriculture” project. The City’s anticipated annual water savings from Project #3 is 272 AFY and for Project #19 it is 5,193 AFY.

The City’s net effect on the regional groundwater aquifer based on the latest groundwater modeling is calculated at 20,310 AFY of depletion by 2040. This can be compared to the net groundwater balances of SSJID and OID which show a net gain of 57,800 AFY and 1,000 AFY, respectively, while the overall net groundwater balance for the entire Eastern San Joaquin Groundwater Subbasin shows a deficit of 363,480 AFY by 2040. While the City’s net effect is offset by SSJID and OID net gains, regionally there is still a significant deficit.

Alternative Water Supply. There are potential water supply shortfalls for the City at some point in the future. Precisely when this would occur is uncertain but represents a focal point of this analysis. This section identifies the advantages of stormwater over all other supply sources and notes the following regarding stormwater:

It is uncontrolled by the State or federal regulators;
It has no effect on State water quality or endangered species; It has no effect on any other water purveyor’s claimed water entitlements (there can be no injury claims made against it);
It cannot be curtailed, even under the worst drought conditions; It is virtually guaranteed every year;
It is a relatively clean water source;
It requires no treatment for agricultural use;
It directly helps City, County, and regional flood control efforts; Existing infrastructure required for conveyance/collection already exists to some degree; and It is a free resource.

Pursuing water resources that a water purveyor can maximize influence or control over is ideal to minimize risk. For water entities seeking to fill projected supply gaps, storm- or floodwater capture is a recommended resource to explore. For water purveyors facing a potential supply shortfall, identifying additional water resources and reducing demands even further from any already committed objective, or demand management have to be examined.

An effective, cheaper, and more ubiquitous new water supply alternative for the San Joaquin Valley is stormwater or floodwater. Stormwater capture, storage, and utilization is the most overlooked water supply asset in California water resources management today. From the perspective of year-to-year reliability, spatial representation, water quality, cost to capture, unentangled legal rights, and volume, there is no greater supplemental water supply source than this. The amount of time, resources, and personnel the State dedicates to flood management and damage control is testimony as to how widespread stormwater is across the State.

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The integration of a traditional flood issue with a water supply interest is not a foreign concept. The State has long acknowledged the importance of linking flood risk strategies, with ecosystem health and water supply reliability to achieve short-term success as well as long-term sustainability. Average annual precipitation within the Eastern San Joaquin Groundwater Subbasin ranges from about 11 inches in the southeast to about 25 inches in the northeast. There is of course significant interannual variability as shifting hydroclimatic trends continue to force water managers to recalibrate assumptions on water yield based on these emerging and intensifying climatic patterns.

A 2014 Public Policy Institute of California study estimated that the State could generate an additional supply in excess of 600,000 AFY from stormwater in the Bay Area and southern California alone, a boost of 10% to their annualized water supplies. A 10% supply enhancement, if similarly applicable to the City would help, particularly in dry years and early years of any protracted drought.

While the City’s 2015 UWMP acknowledges utilization of stormwater (floodwater) as a water supply source, it has not yet been studied in detail. According to the UWMP, however, the City owns existing infrastructure to store and treat stormwater runoff. Existing stormwater runoff is transmitted through the City’s current system, into SSJID drains and laterals, and ultimately discharges into the San Joaquin River. This drainage infrastructure could serve as the vital backbone of any new stormwater retention or enhanced water supply program that the City might decide to pursue.

One of the biggest hurdles will be in restructuring the existing City/SSJID Master Drainage Agreement, or drafting a completely new agreement, that would address the many complexities involved in fully implementing a stormwater collection, storage, treatment, and distribution program. It is likely that existing capacity in any element of SSJID’s stormwater drainage infrastructure do not currently accommodate the volumes of additional water necessary to meet the City’s requirements should they decide to proceed with a significant stormwater collection and storage program.

Accordingly, under such a program, the City would have to build its own storage/retention basins, some options of which are illustrated in this Study. The extent to which additional conveyance facilities and necessary appurtenances would be required to integrate these new retention basins with SSJID’s existing infrastructure would depend on the ultimate design plans for this new program.

ES.4 City Water Supply and Demand Balance
This section provides the water supply and demand comparisons typical in most water master planning exercises. Water supply and demand balance computations are based on a series of factors, including:
raw data (measured and estimated), hydrologic assumptions, engineering system assumptions, use (consumption) and loss assumptions, as well as anticipated growth.

In 2020, total City water supplies, including distribution system water losses, were 17,266 AF. This was comprised of 9,244 AF of imported surface water from SSJID, 6,038 AF of potable groundwater, and 1,984 AF of groundwater for other non-potable uses. These quantities in 2020 were below the total right and safe yield quantities available to the City: 11,500 AFY of surface water contractually available from SSJID through the SCWSP and 13,737 AFY of groundwater (both potable and non-potable) available within the safe yield based on the City’s area (13,737 Acres) and a sustainable pumping rate of 1 AFY/Ac.1 Note that
1 City of Manteca “2015 Urban Water Management Plan,” September 2016, Kennedy/Jenks Consultants, page 6-2.

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there are other known entities within the City pumping groundwater (Manteca Unified School District [MUSD] and Eckerts Cold Storage) whose groundwater pumping also factors into the City’s safe yield.

The State-mandated Urban Water Management Plan (UWMP) guides suppliers through a Water Supply Reliability Assessment under normal years, single dry years, and multiple dry year sequences. Projected available water supplies are calculated and compared against anticipated future demands with differences (e.g., supply surpluses or shortfalls) identified.

During dry years, each of the City’s supplies are assumed to be curtailed based on historical dry year curtailment records assuming that SSJID surface water is curtailed by 25% and groundwater is un-curtailed consistent with UWMP methodologies. Table ES-1 presents the percentages of normal supply available during dry years for surface water and groundwater and the historical base hydrologic years – the same years and associated percentages used in SSJID’s 2020 UWMP – used to develop these percentages using the prescribed DWR UWMP methodology.

Year Type Base Year1 % of Normal Supply Available
Surface Water1
% of Normal Supply Available
Groundwater
Average Year 2010 100 100
Single-Dry Year 1977 75 100
Five Consecutive Dry Years 1st Year 2012 100 100
Five Consecutive Dry Years 2nd Year 2013 95.6 100
Five Consecutive Dry Years 3rd Year 2014 75 100
Five Consecutive Dry Years 4th Year 2015 75 100
Five Consecutive Dry Years 5th Year 2016 100 100
Notes:

1. Base years listed and percentages of average surface water supply available are based on SSJID 2020 UWMP.

Table ES-1: Historical Basis of WY Type
There are many assumptions in dry year analysis that may not account for potential supply limitations over sustained dry year conditions. The 2012-2016 drought period proved that as surface water supplies became increasingly strained, groundwater reliance increased to about 80% of the supply in the San Joaquin Valley. At that usage rate, it is conceivable that after successive years, for groundwater reserves to be impacted and potentially deplete. Therefore, it is prudent to assume a reduction in the current safe yield pumping rate of 1 AFY/Ac during a period of sequential drought years for two reasons: 1) to prepare for the possibility of a curtailment and 2) to plan for the management of the Subbasin’s sustainable yield under drought conditions.

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ES.5 Future Water-Related Threats to the City
This section addresses the future threats to the City’s water supply that have the potential to induce a supply shortfall. Future potential threats to the City’s water supplies can be grouped into the following categories: 1) Hydroclimatological Uncertainty, 2) Existing Surface Water Storage Capacity Limitations, 3) Regulatory Impositions, and 4) Declining Groundwater.

Hydroclimatological Uncertainty. Hydroclimatology is primarily intended to address the uncertainties associated with our rapidly shifting climates due to climate change. A thorough review of the most current scholarly research on California water resources affected by climate change and, specifically, for those regions that the City relies on for its water supplies from SSJID entitlements, namely, the central Sierra Nevada is provided. Overall trends for the San Joaquin Valley and the Stanislaus River watershed indicate an anticipated future increase in October-March runoff, mainly as a result of increasingly less snowfall and a more direct rainfall-runoff response. The high spring flows (runoff period April–July) that have become such a characteristic part of the Sierra Nevada hydrology are expected to continue to steadily decline with the onset occurring earlier and earlier.

Hydroclimatic uncertainties include those associated with variations between individual GCMs and RCMs.

A common theme among these various studies/models is the extent of uncertainties associated with the various assumptions for climate change models used in the analyses. Such uncertainty can impart considerable influence on simulated changes in WY classification and hydrological droughts. The interannual range of expected precipitation in any given year in the San Joaquin Valley is large; it has ranged between 15 inches (1976-77) and 77 inches (1982-83) with an annual average of 40 inches. WY 2021-22 saw a total of 25.3 inches, significantly below average.

Existing Surface Water Storage Capacity Limitations. The ongoing surface water storage issue relates to the limitation in available reservoir storage capacity across the system relied upon by SSJID and the City.

Since all reservoirs have a maximum storage capacity less than the unimpaired yield of the draining watersheds above it, careful management of storage volumes/water levels is necessary to ensure that all primary functions of the facility are adequately accommodated. These include flood control, water supply, hydropower generation, instream flow releases, and recreational flows. This operational balancing act is further challenged by the fact that these reservoirs are operating in a Mediterranean, semi-arid climate where the annual rainy season is limited to four or five winter and spring months. New Melones Reservoir operates under a rule curve, similar to that of Folsom Reservoir, shown in Figure ES-2.

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Figure ES-2: Schematic of Folsom Reservoir showing Operating Rule Curve and Seasonal Spill/Fill Thresholds
Source: U.S. Army Corps of Engineers
This illustrates the top of the variable seasonal rule curve and its periods of “spill” and “fill.” It is designed specifically for its storage volume, upper catchment unimpaired runoff (e.g., basin yield), and planned reservoir operations. Terminal or “rim” reservoirs in the Sierra Nevada need to delicately balance anticipated annual/seasonal hydrology since the rainy/snowmelt season only lasts for a few months.

Municipal and industrial (M&I) water diversions should be fairly consistent throughout the year, particularly for indoor water use. Diversions from reservoir carryover rely on full reservoirs or, at the very least, reservoirs that can provide a consistent allocation across all months of the year.

The hydrologic records and characterization of the Stanislaus River basin that were once known and from which the design of all current reservoirs were based must now be operated under a rapidly changing hydroclimate. All of the existing facilities, particularly, dams/reservoirs were designed based on assumptions that are now growing increasingly outdated.

The precarious nature of reservoir storage operations, including those of New Melones Reservoir, drive the need for two continual improvements: improved hydroclimatic forecasting (meaning more advanced hydrometric instrumentation) and additional reservoir storage (whether at existing reservoirs or new site locations).

Regulatory Impositions. Regulations, particularly as they relate to surface water operations of the primary water regulators in the State are of notable interest to the City. The City’s surface water supplies are generated in the headwaters of the Stanislaus River in the central Sierra Nevada. Operationally, that ATTACHMENT 2
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runoff is controlled by the USBR’s Central Valley Project (CVP) through the Tri-Dams Project, New Melones Reservoir, and downstream at Tulloch, Goodwin, and Woodward reservoirs. Operations of the CVP must adhere to various regulatory requirements including the federal Endangered Species Act (ESA), the Central Valley Project Improvement Act (CVPIA), the Anadromous Fish Restoration Program (AFRP), Long-Term Operations of the CVP and SWP, CVP Operations Criteria and Plan (OCAP), and the Coordinated Operations Agreement (COA), to name a few.

Operations specific to the Stanislaus River must adhere to the New Melones Revised Plan of Operation (NMRPO), Stanislaus Stepped Release Plan (SRP) – WY 2022, and Operations Plan (January 2022 Flows) as well as the various SWRCB decisions pertaining to Bay-Delta water quality objectives, 1995 Bay-Delta Plan, Vernalis salinity objectives, and related water right permits/licenses, incidental take permits, etc.

The City’s contracted surface water allotment with SSJID both now and in the future is dependent on the hydrology of the Stanislaus River system meeting the instream flow requirements of the river and, more importantly, meeting all of the flow, water quality/salinity, and flow/habitat requirements of the BayDelta. The federal agencies through the USBR, NOAA Fisheries, U.S. Fish & Wildlife Service, U.S. EPA can and do impose restrictions on diversions from the Stanislaus River system. State agencies, primarily the SWRCB, California Department of Water Resources (DWR), California Department of Fish & Wildlife (CDFW) can also impose restrictions on any water diversions hydrologically connected to the Bay-Delta; this includes the entire Stanislaus River watershed from which SSJID holds pre-1914 water rights.

Declining Groundwater. The groundwater challenges for the City are consistent with what the United States Geological Survey (USGS), the primary federal regulatory and management agency for groundwater, has identified and which form a foundational basis for many SGMA objectives. These groundwater challenges include:

Recharge, discharge, and change in storage response to climate variability on interannual to multidecadal timescales and climate change from human activities in the principal aquifers of the United States.

Identifying how much hydrologic response is caused by natural variability and how much is caused by human activities with respect to future climate change.

Identifying potential need for time-varying groundwater management strategies, such as artificial storage and recovery efforts due to climate variability.

Identifying whether certain principal aquifers are more or less susceptible to changes in storage caused by climate variability and change.

Identifying whether trends in groundwater quality can be linked to climate variability and change.

Identifying what strategic role groundwater storage will play in adapting to climate change.

According to the American Geophysical Union (AGU), California has a less than 1 in 5 chance of achieving groundwater overdraft recovery over the 20-year period following a drought based on the expectations of a drier climate in the immediate future. Given that drought frequencies in California are easily within 20-year timeframes, full groundwater recovery is unlikely.

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Other Considerations. There are many factors that can affect the availability and reliability of water supply including:

Water Quality: Water quality can affect the availability of a water supply where treatment is required or where treatment is cost prohibitive. The City’s tap water is generally considered safe to drink as there are no active health-based violations of the Safe Drinking Water Act (SDWA).

Land Subsidence: Reduced surface-water availability during 1976-77, 1986-92, 2007-09, and 2012- 2015 caused groundwater pumping to increase across the San Joaquin Valley, thus exacerbating declines in groundwater-levels to near or beyond historic lows, resulting in renewed aquifer compaction. Intensified statewide subsidence monitoring efforts showed that land subsidence continues and that the San Joaquin Valley experienced the most subsidence in WY 2021, with a maximum of 1.1 feet of subsidence observed in the region.

Realities of Future Droughts. Water scarcity is a growing problem in California and water leaders are working to develop long lasting effective solutions. Key amongst these solutions is the identification and development of diversified, interconnected, flexible, and resilient water supply portfolios. Examples of actions water purveyors can take to address potential water supply shortfalls include various capital investment plan improvements (e.g., improving infrastructure sizing and efficiencies), water transfers, and a reverse cyclic program (e.g., allowing agencies to purchase State Water Project allotments, for banked security in future years).

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ES.6 Recommendations
This final section identifies seven recommendations for the City to embrace, incorporate, or otherwise implement as a result of the observations stemming from this Water Sustainability Study. These include:
1 Use industry acknowledged shortage provisions
When forecasting future water supply versus demand projections, assume a worst-case delivery scenario for available water supplies.
2 Use climate-sensitized future hydrology projections
An uncertain future hydroclimate is and will continue to impart ambiguity and insecurity on both surface and groundwater supplies relied upon by the City. Its effects are broad ranging, from reduced surface water yield in the upper Stanislaus River basin to increased depletions from the Eastern San Joaquin Groundwater Subbasin groundwater reserves.
3 For planning purposes, assume maximum regulatory curtailments to SSJID’s Pre-1914 Water Rights Last year’s Term 91 imposition is one of many already existing regulatory impositions used by regulators (in this case, the State) to curtail surface water diversions from Delta watershed water right entitlement holders. The degree to which these types of restrictions are amplified or made more frequent in the future is uncertain, but it is guaranteed that it won’t become laxer. 4 Assume SWRCB will impose maximum curtailments in the interests of Delta assets during droughts The SWRCB can claim severe/critical drought conditions and their authority over water use can be extensive. This possibility encourages development of an independent water supply. 5 Explore whether there are supply enhancement opportunities with SSJID, OID, or others Identify if the City can renegotiate its existing SSJID Water Supply Agreement in terms of the Phase II allocations from the SCWSP and secure additional supply commitments. 6 Develop storm- and/or floodwater capture and retention program Initiate an extensive storm- and/or floodwater capture and retention exploratory development plan.

Make stormwater the third water supply source of the City. The City should explore developing its own supply source(s); one that is unencumbered by outside control – and stormwater represents just such a supply.
7 Develop an integrated MAR, recycled water, and stormwater program Using recycled water, storm- and/or floodwater as a primary supply source for future City MAR programs.

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1 INTRODUCTION
The purpose of this Technical Memorandum (TM) is to examine the long-term reliability of the City of Manteca’s (City’s) various water supply sources and delivery allocations and provide recommendations to supply portfolio so that
long-term water resource sustainability can be secured.

Under a separate TM No. 5, the various existing, ongoing, and anticipated future regulatory constraints and risks associated with maintaining current and projected future City water supplies are identified and discussed.

The duty to serve for today’s water purveyors is based on the requisite need to meet both reliability and sustainability principles. And while it is often common for the water industry to use reliability and sustainability interchangeably, there are notable differences.

Water reliability generally speaks to the delivery capability of a water supply and thus, the trust or expectation with which one can assume or associate with that delivered allocation. It is sometimes referred to as a measured firmness of supply. Water sustainability, on the other hand has to do with the guaranteed protection of the resource so that it is not irreparably damaged or irretrievably depleted. In this context, groundwater safe yield immediately comes to mind. These are not hard and fast definitions but ones that can be used as general guidance by water purveyors.

The duty to serve based on both reliability and sustainability is set against an established demand threshold, usually cast into the distant future and often corresponding to General Plan buildout or ultimate buildout estimates. Here, the water purveyor has an identified target threshold from which to set all water delivery obligations. The manner with which target thresholds are achieved are set out in thoughtfully conceived water implementation strategies, such as Urban Water Management Plans (UWMPs).

An appropriate water supply “strategy” must take into account the various water constraints possible as well as an array of prioritized potential mitigative tactics designed to address these shortcomings. Any strategy must be flexible enough to withstand the uncertainties associated with varied water supply availability. Water supply variability results from traditional threats such as meteorological and hydrological drought, but also a number of other factors including water shortages imposed by various institutional, operational, infrastructural, and regulatory constraints (see Section 2 Background, below).

Throughout this TM references are made to the City’s various water supplies; infrastructure; and past, present, and future agreements, etc. These agreements are incorporated herein by reference with brief introductory remarks and explanations.

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2 BACKGROUND
Water reliability is contingent on the identification of the potential future water supply shortfalls.

Traditional significant threats facing water purveyors today include those constraints affecting the ability to meet existing and planned delivery obligations. Constraints include both resource restrictions (water supply), population growth, and climate change. Today, it is recognized that there are many different forms of drought, including:

Meteorological drought
Hydrological drought
Infrastructural drought
Operational drought
Regulatory drought
Institutional or administrative drought
The most common is Meteorological drought. This is what is typically reported in the media and reflects climatological (or meteorological) conditions. When people talk of the megadrought, 2 this is typically
what they are referring to.

Hydrological drought is the next step in the hydrological sequence. Hydrological drought depends on how much incident precipitation (e.g., rain, sleet, or snow) ended up as accessible reservoir carryover storage, river flows, or groundwater. Much depends on the antecedent moisture conditions of the watershed(s) relied upon by the water purveyor, for not all precipitation ends up as accessible water; the vast majority is lost to evaporation, transpiration, deep groundwater seepage, and out-of-basin losses.

Infrastructural drought refers to conditions where the water infrastructure needed to capture, store, convey, treat, and/or distribute water is limited by capacity and thus made unavailable to the purveyor.

This could result from a lack of existing facilities; for example, lack of stormwater or rainwater collection facilities. The classic example occurs when there is ample rainfall, but a water purveyor simply does not have the collection and storage facilities to retain the necessary quantities of wet-season rainfall for later use.

Operational drought commonly refers to situations where the function of the infrastructure relied upon by a water purveyor is not dedicated solely for that purveyor’s use. For example, if a portion of the water infrastructure of the State Water Project (SWP) or wholesale supplier to the purveyor is restricted in any way due to operational reasons (e.g., need to maintain empty space for flood storage). It can also occur where a component of a system must be placed off-line for any lengthy period of time due to planned or unplanned maintenance, disaster repairs, or retrofitting.

Regulatory drought is a challenge as interests of consumptive users such as municipal and industrial (M&I) and agricultural (Ag) conflict with potential environmental interests such as water quality, fisheries, and/or wildlife. Many of the provisions of the Bay-Delta Water Quality Control Plan, other stipulations of 2 The searing “megadrought” that has gripped the southwest U.S. for more than two decades is the driest 22-year period in at least 1,200 years. The region hasn’t seen a more severe drought since the start of the scientific record around the year 800.

Williams, A.P., Cook, B.I. & Smerdon, J.E., (2022) “Rapid intensification of the emerging southwestern North American megadrought in 2020–2021”, Nat. Clim. Chang. Vol.12, pp.232–234. https://doi.org/10.1038/s41558-022-01290-z ATTACHMENT 2
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the Water Code, or any of the federal Biological Opinions under the federal Endangered Species legislation are cases where resulting curtailments in water allocations become examples of regulatory drought.

Institutional or administrative drought is the last category and can be described as situations where thirdparty agreements can affect the ability of the water utility to fully meet its delivery obligations during any specific water year (WY) due to contractual arrangements made with other parties for any portion of the water entitlement or infrastructural capacity.

Just as there exist many different types of drought, there are also many different indices water managers use and continue to rely on to gauge drought effects. These indices include the Palmer Drought Severity Index, the Standard Precipitation Index, the Aggregate Drought Index, the Standardized Runoff Index, the Standardized Precipitation-Evapotranspiration Index, the Multivariate Standardized Drought Index, and the Groundwater Drought Index.

This “Water Sustainability Study” is intended to identify the risks to the City’s water resources so that proper strategies can ultimately be put in place to ensure that these resources are not irreparably damaged or irretrievably depleted. In order to do that, it is important to properly identify the causes of potential shortfalls; recognizing that not all water shortages are due to a lack of rainfall.

The first step in any future water resource or supply planning effort is to establish the correct baseline yield or the projected future water yield. For years, identifying this quantity involved a relatively straightforward process since the water industry always assumed hydrologic stationarity – meaning it always assumed that long-term hydrologic availability (e.g., projected rain and snowfall) would not change outside of its variable historic range. Future hydrologic baselines simply took the historic hydrograph(s) and projected them into the future, making necessary adjustments for anticipated demand depletions and changing regulatory allocations. No significant adjustments were made to the projected hydroclimatology to account for future variability. This is how virtually all water-related federal environmental assessments traditionally conducted their NEPA and Endangered Species Act-related future water availability analyses.

A changing hydroclimate and how it pertains to water resources has been known for a couple of decades but the Milly3 paper in 2008 really established climate change as a vital new element in contemporary water resources planning. As a result, today, climate change is widely accepted as a requisite feature of water supply planning.

City water master planning or water sustainability effort should be undertaken with a thorough examination of anticipated future changes in water yield brought about by a rapidly shifting climate. 3 P.C.D. Milly, Betancourt, J., Falkenmark, M., Hirsch, R.M., Kundzewicz, Z., Lettenmaier, D.P., and R.J. Stouffer, (2008) “Stationarity Is Dead: Whither Water Management?”, SCIENCE, Vol.319, pp.573-574.

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3 HYDROLOGICAL SUSTAINABILITY AND CLIMATE CHANGE
Everything a water purveyor/utility typically does, whether it’s supply/demand planning, meeting current and future delivery obligations, operating multi-faceted systems, maintaining and ensuring infrastructure stability, safeguarding ongoing regulatory compliance, etc., is contingent on the future projected yield and knowing what that is. For California, climate change indicates a shift in projected water yield to water purveyors.

Ideally, the estimated projected future yield will incorporate changes in its spatial and temporal projected yield. In so doing, the fundamental future baseline will be generated from which all water management priorities can be derived. Specifically, projected water yield must be adjusted based on assumed climatic changes. The resulting hydrograph that is generated then represents the assumed new hydrologic response of the area in question. The manner with which to accomplish this is through climatic modeling4 (see Section 3.2 Climate Analysis – Modeling).

The forcing shift is simplistically illustrated in Figure 3-1, a hypothetical depiction of an annual streamflow hydrograph. The x-axis represents month of the WY starting on October 1 (10th month) with the y-axis indicative of hypothetical streamflow or river runoff (in this case, illustrated as dimensionless). The three curves represent three different types of streamflow response based on changing precipitation patterns.

Figure 3-1: Typical “Forced” Hydrographs from Watersheds of Snow, Rain on Snow, and Rain Source: D.P. Lettenmaier, J.C. Adam, and T.P. Barnett (2006) “Sensitivity of Snow-Dominated Hydrologic Regimes to Global Warming,” European Geosciences Union, April, 6, 2006, Vienna, Austria. 4 https://www.climate.gov/search?query=&section=maps&datasetgallery=1&sorting=relevance; https://climate.mit.edu/explainers/climate-models; https://ncar.ucar.edu/where-we-focus/climate.

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The red curve represents a typical snowmelt response that peaks in June (6th month). This is the traditional delayed spring runoff characteristic of many snow-dominated regions like those found in the Sierra Nevada mountains of California. Under a “forced” climatic shift where winter precipitation increasingly falls as rain instead of snow, the river runoff response is more immediate as shown by the blue curve. Here, river runoff more closely matches the period when rainfall occurs – in this case, the winter wet season; note the disappearance of the springmelt peak. The black curve represents a hybrid or intermediary river runoff response under a combination of both rain and snow.

This pertains to the seasonal availability of runoff. Two salient conclusions arise relative to current or historic conditions:

Peak runoff magnitude is significantly reduced under warmer conditions (reduced snowmelt), and A marked shift occurs in the hydrograph response to earlier in the season making less water available in the warmer summer months.

The projected future effects of a warming climate on regions such as California and, in particular, the Sierra Nevada and Central Valley regions has been established for years and is well supported in the scientific literature.5
Many have simplified the likely result of a forced hydroclimate on Mediterranean climates such as those for California as merely, “…more rain, less often….” While there is some truth to this adage, it is a little more complicated.

3.1 Climate Change Water Implications to the City
Given these rapidly shifting hydroclimatic and hydrologic conditions, the hydrology that the City’s existing agreements are based on must now be revisited. Any contractual agreement for which the City is currently party, should now be reviewed in light of the uncertain nature of the future water yield upon which it relies and the changing understanding of the basic hydrological facts that served as the basis for the various stipulations of the agreement(s) in the first place. The hydrology that is changing includes, but is not limited to, river flows, reservoir carryover storages, groundwater levels, raw water deliveries to water treatment plants (WTPs), natural groundwater recharge, etc., that the City assumed would exist at specific levels.

All agreements, whether made by the federal or State governments, local third-party purveyors, or other stakeholders, are contingent upon the projected yield assumed in the development of the agreements.

Specifically, the agreements are contingent upon the assumptions that the hydrology remain both 5 Miller, N.L., Bashford, K.E., and E. Strem (2007), “Potential Impacts of Climate Change on California Hydrology”, Journal of the American Water Resources Association, https://doi.org/10.1111/j.1752-1688.2003.tb04404.x; Dracup, J.A. and S. Vicuna (2005) “An Overview of Hydrology and Water Resources Studies on Climate Change: The California Experience”, World Water and Environmental Resources Congress; Maurer, E.P. (2007) “Uncertainty in hydrologic impacts of climate change in the Sierra Nevada, California, under two emissions scenarios”, Climatic Change 82, 309–325 (2007). https://doi.org/10.1007/s10584-006-9180-9; Maurer, E.P. and P.B. Duffy (2005) “Uncertainty in projections of streamflow changes due to climate change in California”, Geophysical Research Letters, https://doi.org/10.1029/2004GL021462; Dettinger, M.D., Cayan, D.R., Meyer, M.K. et al. (2004) “Simulated Hydrologic Responses to Climate Variations and Change in the Merced, Carson, and American River Basins, Sierra Nevada, California, 1900–2099”, Climatic Change 62, 283–317. https://doi.org/10.1023/B:CLIM.0000013683.13346.4f.

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unchanged and known to the parties. Under a rapidly changing hydroclimate, such conditions unfortunately, are no longer the case.

Therefore, it is highly recommended that all applicable agreements should ideally be reviewed by City legal counsel together with its climate change engineering/hydrology team. A brief list of where changing hydroclimatic conditions could affect the City’s existing water operations include the following:

Water supply delivery stipulations based on quantity agreement(s) between any and all wholesale/retail suppliers and the City for water supplies drawn from California rivers, streams, reservoirs, lakes, or managed embayments;
Water supply delivery stipulations based on quantity agreement(s) between wholesale/retail suppliers relied upon by the City and federal/State water regulatory agencies for water supplies drawn from California rivers, streams, reservoirs, lakes, or managed embayments; Water supply delivery stipulations based on (timing6) agreements(s) among and within these same parties; and
Assumed safe yield (aka sustainable yield) volumes based on calculated and negotiated recharge of the Eastern San Joaquin Groundwater Subbasin as established through the ongoing Sustainable Groundwater Management Act7 (SGMA) process.

In any assessment of the effects of climate change on the operations of a water purveyor, it is important to appreciate the interrelated nature of these changing climatic conditions on all water resources that are relied upon. It is essential to understand the hydrologic trail: where the supplier’s water comes from and how these supplies are constrained or otherwise restricted by a changing climate.

While the City may not directly divert water from the upper reaches of the Sierra Nevada Mountains, their suppliers might. Should those water supplies be constrained or otherwise affected either naturally (e.g., by a shifting or changing hydroclimate, see Figure 3-1) or by man (e.g., through imposed regulation), such restrictions on water availability would have bearing on the City.

The constraints need not necessarily be obvious. For example, water purveyors in the Central Valley are regulated by water quality conditions and related standards associated with the Sacramento-San Joaquin River Delta (Delta). Should Delta water quality degrade into non-compliant conditions due to a lack of adequate freshwater flows discharging from headwater basins thus allowing upstream migration of the leading saline wedge into inner Delta environs, State regulations allow for mandated cessation of withdrawals (diversions) from the Delta and upstream systems. This includes the San Joaquin River and its tributaries (this is discussed more thoroughly in the companion TM No. 5, “Regulations Impacting City Water Operations”).
6 “Timing” agreement(s) pertain to the period or season of delivery. All water agreements have an authorized period of delivery; under climate change, such delivery periods can become increasingly tenuous, particularly in snow-dominated regions such as California where water yield is dependent on snowmelt timing. As annual hydrographs for California’s Sierra Nevada rivers continue to shift temporally, the ability to meet the scheduled delivery obligations set out in the original agreements may become increasingly difficult.
7 The Sustainable Groundwater Management Act (SGMA) is a three-bill package that passed the California state legislature and was signed into California state law by Governor Jerry Brown in September 2014. Its purpose is to ensure better local and regional management of groundwater use and it seeks to have a sustainable groundwater management in California by 2042. It emphasizes local management and formed groundwater sustainability agencies (GSAs) from local and regional authorities.

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3.2 Climate Analysis – Modeling
Climate models are numerical representations of the climate system that furnish valuable tools for understanding climate and for anticipating future behavior changes. Numerical methods may vary from model to model depending on whether the emphasis is on the accuracy of the calculations or on their efficiency. Parameterizations are used to represent the transfers of water, energy and momentum, and other significant parameters and are often universal for a specific model.8 The complexity of a model is typically defined by the number of climate processes that are considered.

The first climate models developed in the 1970s represented only the atmospheric component. The models evolved rapidly and were able to include additional components by the late 1990s. There are very simplified, one-dimensional models based on the terrestrial radiative balance, which simulate only the global average temperature, not regional disparities. On the other hand, the most complex models represent the entire carbon cycle, and allow the estimation of carbon exchanges between the different components. Between these various types, there exists a whole range of models of increasing complexity developed for specific applications.9

With increasing complexity, one also introduces more degrees of freedom into the system. This complicates their calibration and validation, sometimes at the expense of the robustness of the model. It is therefore important to determine whether added complexity provides a commensurate amount of added value to the model and its results.10

3.2.1 Climate Modeling for Water Purveyors
Climate change modeling for water purveyors follow traditional methods and procedures developed for climate change analysis. It starts with a projected simulation of forced global hydroclimatic changes identified through global climate models (GCMs). Such models are highly complex mathematical representations of the major climate system components (i.e., atmosphere, land surface, ocean, and sea ice) and their interactions with each other.

At their most basic level, climate change models use equations to represent the processes and interactions that drive Earth’s climate. These cover the atmosphere, oceans, land, and ice-covered regions of the planet. The models are based on the same laws and equations that underpin scientists’ understanding of the physical, chemical, and biological mechanisms going on in the Earth system. The model simulates all the dynamic processes in 3-dimensions many kilometers into the atmosphere (see Figure 3-2).

From Figure 3-2, the complexities of global climate modeling are evident. The ultimate objective(s) of the modeling exercise can focus on a wide range of specific issues and thus, can take many different forms.

For future projected water yield, the fundamental analysis involves modeling or simulating the projected forcing mechanisms (e.g., temperature, precipitation) that affect the projected yield of those waterbodies relied upon by the water purveyor.
8 Magazù, S. and Caccamo, M.T., (2022) “Climate Change Dynamics and Modeling: Future Perspectives”, Climate, 10(5) 65, https://doi.org/10.3390/cli10050065.
9 Caccamo, M.T.; Magazù, S. (2019) “A physical-mathematical approach to climate change effects through stochastic resonance” Climate, 7, 21, https://doi.org/10.3390/cli7020021. 10 Lea, D.J.; Allen, M.R.; Haine, T.W.N. (2000) “Sensitivity analysis of the climate of a chaotic system” Tellus A Dyn. Meteor.

Ocean. 52, 523–532, https://doi.org/10.3402/tellusa.v52i5.12283.

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Figure 3-2: Generic Representation of a Global Climate Model showing 3D Coverage of Atmosphere and Land Surface Area
Source: Compiled from numerous sources.

Climate change modeling has significantly evolved over the decades as practitioners and hydrological experts refined their various analytical understandings and techniques. One of the first challenges followed the realization that global climate modeling could not provide the regional or local acuity necessary to effectively implement local area water resource prescriptions. Globally derived climate forecasts were simply too coarse (i.e., broad scale) to be directly applicable and thus needed to be reduced or “downscaled” to a more usable spatial orientation. Hence, the issue of “downscaling” emerged.

Downscaling brings the hydroclimatic forcing process down to a more manageable scale. It generates output data that can then be input into various hydrologic models depending on what output information is desired by a water purveyor. Figure 3-3 illustrates the general downscaling process.

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Figure 3-3: Step Process from Global Climate Modeling through Regional Downscaling to Impact Assessment through to Hydrological Modeling
Source: Adapted from Willems, P., 2011. Systems approach in water engineering, 2nd year Master of Water Resources Engineering, Course text, K.U. Leuven, Leuven, Belgium.

Currently, most GCM simulations are still performed at relatively coarse horizontal resolutions (~1°) due to the tremendous computational cost required for finer resolution simulations. Accordingly, modeling hydroclimatological characteristics, especially in mountain regions, at these coarser GCM resolutions is problematic as orographic features are heavily smoothed and inaccurately represented. The complex geographic characteristics of California, including the Central Valley and Sierra Nevada regions, necessitate finer-resolution climate simulations that can resolve important details in topography and land use coverage.11
As illustrated in Figure 3-4, the relationship between a GCM grid to areas of regional hydrologic models in California and to the Central Valley is depicted. Also shown are the various watersheds modeled in the regional model (in this case, the Mountain Hydrologic Watershed Model [MHWM] using the Basin Characteristics Model [BCM]) and the active model grid for the valley-wide Central Valley hydrologic model (CVHM) along with various diversion locations, selected precipitation and streamflow-gaging stations, and wells.
11 Chin, H.-N. S., (2008) “Dynamical downscaling of GCM simulations: Toward the improvement of forecast bias over California,” Lawrence Livermore National Laboratory Tech. Rep. LLNLTR-407576, 16 pp., https://e-reports-ext.llnl.gov/pdf/365755.pdf.

Pierce, D. W., Cayan, D.R., Das, T., Maurer, E.P., Miller, N.L., Bao, Y., Kanamitsu, M., Yoshimura, K., Snyder, M.A., Sloan, L.C., Franco, G. and M. Tyree (2013) “The key role of heavy precipitation events in climate model disagreements of future annual precipitation changes in California”, Journal of Climate, 26, 5879–5896, https://doi.org/10.1175/JCLI-D-12-00766.1.

Huang, X., A. M. Rhoades, P. A. Ullrich, and C. M. Zarzycki (2016), “An evaluation of the variable resolution-CESM for modeling California’s climate”, Journal of Advanced Modeling of Earth Systems, 8, 345–369, https://doi.org/10.1002/2015MS000559.

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Figure 3-4: Watersheds Modeled in the Mountain Hydrologic Water Model by BCM Model Source: USGS California Water Science Center, California's Central Valley, Conjunctive Use in Response to Potential Climate Changes in the Central Valley, California, Importance of Climate Change on Water Supply.

As with any modeling effort, it must be fully understood and appreciated that climate change modeling remains a highly assumptions-loaded process. It is not necessarily a “black box” exercise since we define the modeling structure and develop required coding, but no matter how sophisticated, it is a simple representation of reality. There is an anticipated amount of uncertainty associated with the future projection as there are limits to long term climate change projections.

Figure 3-5 below shows this future projection uncertainty dilemma graphically. It shows the projected increase in global temperature under a range of assumed future atmospheric greenhouse gas (GHG) loading scenarios. The x-axis is time from the year 1900 forward and the y-axis represents the relative change in temperature from the 1850-1900 baseline average (dimensionless axis).

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Figure 3-5: Anticipated Future Warming under Various Assumed GHG Loading Scenarios Source: IPCC AR5
The graphical relationship illustrated in Figure 3-5 can be transposed into virtually any hydrologic characteristic or metric. In other words, the depiction shown may equally apply to streamflow in any of the many rivers and streams tributary to the Californian Sierra Nevada. The salient point is that beyond present day, the future uncertainty range of how the hydroclimatic environment will respond expands as shown in the right-hand side of Figure 3-5. The breadth of that expansion is based solely on our assumptions of the future.12 The RCP notations indicate the “Representative Concentration Pathway;” they depict the various ranges of GHG emissions that are assumed to affect, in this case, global temperature rise (e.g., the higher the assumed GHG emissions, the higher the resulting projection of air temperature increase).

Fortunately, technological advances are continuing, and California’s water purveyors have an increasingly broader reference base from which to access every year. For example, the NASA Land Information System (LIS)/WRF-Hydro system is a coupled modeling framework that combines the modeling and data assimilation capabilities of the NASA LIS with the multi-scale surface hydrological modeling capabilities of the WRF-Hydro model, both of which are widely used in both operations and research. This new system has recently been used to demonstrate the impact of assimilating snow water equivalent, measured from an aircraft, on both the land surface and streamflow from the model in the Tuolumne River basin in Central California. Results show that assimilation of snow water equivalent into the coupled model corrects snow errors and improves the streamflow in both wet and dry years.13 12 In this figure, the assumption is our estimate of future GHG loadings or concentration trajectory as depicted by the term RCP (Representative Concentration Pathway). The numerical identifiers (8.5, 6.0. 4.5 ad 2.6) are labelled as a possible range of radiative forcing values in the year 2100 representing assumed energy fluxes in W/m2. 13 Lahmers, T.M., Kumar, S.V., Rosen, D., Dugger, A., Gochis, D.J., Santanello, J.A., Gangodagamage, C. and R. Dunlap (2022), “Assimilation of NASA’s Airborne Snow Observatory snow measurements for improved hydrological modeling: A case study enabled by the coupled LIS/WRF-Hydro system” Water Resources Research, 58(3), https://doi.org/10.1029/2021WR029867.

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The second most significant processing issue in climate modeling has to do with bias correction. Climate modeling possesses inherent systemic errors (biases) in its generated outputs. These errors result from a number of factors including limited spatial resolution (e.g., large grid scale), simplified coding of complex thermodynamic processes in the atmosphere (e.g., effect of El Niño and the Southern Oscillation, also known as ENSO or North Atlantic Oscillation, also known as NAO), or omitted climatic processes (e.g., aerosol feedbacks). To overcome large biases in climate models, a number of bias correction methods have been developed and applied over the years. Despite many decades of improvements, GCMs continue to show negative bias, or underestimation.14
It is important to note that, at present, there is no “official” future GCM platform that is universally accepted by all governing authorities. For its part, California, through various jurisdictional agencies including the Department of Water Resources (DWR) maintains an expansive and constantly growing informational database including modeling results, supporting documentation, and program updates.

These include many continually evolving State and federal agency programs.15 The inflection point begins at present day. Future uncertainty of whatever hydroclimatic variable we are considering (e.g., air temperature, rainfall, reservoir storage, spring river flows, etc.) will depend on our GCM, our downscaling and bias correction procedures, and our selected RCP. The spread of our projection, the farther into the future we look, only gets larger. This reemphasizes the importance of knowing precisely what processes are being used in the model, the rationale used to defend the selected process(es), and the validity of the assumptions relied upon. 14 Frei, A., Mukundan, R., Chen, J., Gelda, R.K., Owens, E.M., Gass, J. and A. Ravindranath (2022) “A Cascading Bias Correction Method for Global Climate Model Simulated Multiyear Precipitation Variability” Journal of Hydrometeorology, https://doi.org/10.1175/JHM-D-21-0148.1
15 https://water.ca.gov/programs/all-programs/climate-change-program; https://www.waterboards.ca.gov/climate/; https://wildlife.ca.gov/Science-Institute/Climate-Change; https://www.usbr.gov/climate/.

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4 CITY OF MANTECA HYDROGEOLOGIC CONTEXT AND WATER SUPPLY AVAILABILITY The City lies along the northern portion of the San Joaquin River valley floor and is located south of Stockton and east of Lathrop along Highway 99. The modern-day physiographic features are a direct result of the geologic history of the region. It is characterized by broad river flood plains, channels, and overflow lands; low alluvial plains and fluvial fans; and dissected uplands. The dissected uplands lie along the flanks of the valley between the Sierra Nevada to the east and the alluvial plains and fluvial fans to the west. Overflow lands of the valley trough tributary to the San Joaquin River define the area inundated by rivers when floods are highest under natural conditions.

The City’s climate is warm and dry ranging from an average high in July of 91°F to an average low of approximately 57°F. Winters are cool and mild, with an average high of 59°F and a low of 38°F in January.

The average temperatures range from December lows of 37.2°F to July highs of 91°F (see Table 4-1 and Figure 4-1). The City’s annual average precipitation of 12.2 inches is typical of the San Joaquin Valley floor.

Precipitation occurs as rain most of which falls between the months of November through April, peaking in January. This will have particular relevance to the City’s potential new future water supplies (see Section 4.4).

The City relies on two main water sources: surface water from the Stanislaus River supplied via an agreement with South San Joaquin Irrigation District (SSJID) and groundwater pumped by some 15 cityowned potable water wells (plus two standby) and 31 non-potable irrigation wells from the critically overdrafted Eastern San Joaquin Groundwater Subbasin,16 a subbasin of the San Joaquin Valley Groundwater Basin. In 2021, the City had 25,872 unique water meters, with an average potable demand of just under 13 MGD.17 Annually, the City distributes between 4.5 and 5.0 billion gallons of potable water; the majority of this water is surface water, supplemented with groundwater from the City’s wells. The City has a 4.0 MG round level storage tank (Atherton Tank) with a booster pump station capable of pumping 12,000 gallons per minute (gpm).18 As noted in its 2015 UWMP it is the City’s stated goal to achieve a 53% to 47% annual balance of surface water to groundwater, respectively. To meet this proposed allocation target, a variety of differing water sources must be relied upon each with their own limitations, long-term challenges, and costs.

The City holds no surface water entitlements. The surface water furnished by SSJID as a wholesale seller is made through the South County Water Supply Project (SCWSP). To the extent the City is reliant on SSJID for its surface water supply, the water rights, storage, conveyance, and delivery infrastructure of SSJID and its partnering purveyors become an important consideration for the City’s long-term water security.

The City began receiving treated surface water from the SCWSP in 2005 to augment groundwater supplies and will ultimately be allocated up to 18,500 Acre-feet per year (AFY) in Phase II of the Project. The City has historically used approximately 1,000 AFY of reclaimed wastewater as applied water to fodder crops on City-owned and leased lands though this use is expected to be eliminated by 2040 as the lands are developed.19
16 DWR’s Bulletin 118 – 80, Ground Water Basins in California classified the Eastern San Joaquin Groundwater Subbasin as a basin in a critical condition of overdraft.
17 Water supply data provided by the City.
18 City of Manteca "2015 Urban Water Management Plan," September 2016, Kennedy/Jenks Consultants. 19 City of Manteca “2015 Urban Water Management Plan,” September 2016, Kennedy/Jenks Consultants, page 6-11.

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Table 4-1: City of Manteca Climate Characteristics
Source: California Irrigation Management Information System for Station 70-Manteca (January 1988 – December 2020).

Figure 4-1: City of Manteca Average Monthly Climatic Conditions Source: California Irrigation Management Information System for Station 70-Manteca (January 1988 – December 2020).

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4.1 Local Hydrology
As discussed in the following subsection, waterways and storage reservoirs relied upon by SSJID (e.g., New Melones Reservoir, Goodwin Reservoir, Tri-Dams Project, and the lower Stanislaus River) have a direct effect on surface water availability to SSJID, and thus ultimately to the City. SSJID delivered an average of 8,484 acre-feet per year (AFY) to the City between 2016 and 2020. Figure 4-2 shows the major hydrologic features of the Eastern San Joaquin Groundwater Subbasin.

Figure 4-2: Major Hydrologic Features of the Eastern San Joaquin Groundwater Subbasin Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” Figure 2-7, November 2019, page 2-11.

The two major westerly flowing tributaries to the San Joaquin River within the southern portion of the Eastern San Joaquin Groundwater Subbasin relevant to the City are the Stanislaus River and to a lesser extent, Lone Tree Creek. The flow in the Stanislaus River varies seasonally from less than 134 AF per day (AF/day) during the dry season in early fall to over 16,400 AF/day during the wet season in winter. These flows correlate to discharges that have varied from 68 to over 8,270 cubic feet per second (cfs) recorded ATTACHMENT 2
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at the Orange Blossom Bridge gauging station approximately one mile east of Oakdale and eight miles west of the Subbasin boundary along the river.20
Much of the City’s corporate boundary lies within the Eastern San Joaquin Groundwater Subbasin’s furthest southwest watershed, the Lone Tree Creek/San Joaquin River watershed, and a small western portion of the Lone Tree Creek watershed (see Figure 4-3).

Figure 4-3: Eastern San Joaquin Groundwater Subbasin Watersheds Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” Figure 2-8, November 2019, page 2-14.

Soils in the Eastern San Joaquin Groundwater Subbasin are one of the primary controlling factors on surface water percolation rates through the vadose zone, a key variable in the recharge process of the local groundwater table. Soils in the region can be grouped into five main categories:

Alluvial fan and flood plain soils
Organic basin soils
20 Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” November 2019, page 2-12.

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Basin soils
Lower terrace soils
Higher terrace and upland soils
Alluvial fan and floodplain deposits are present in three areas of the Eastern San Joaquin Groundwater Subbasin bounding major east-west rivers: Mokelumne, Calaveras, and Stanislaus Rivers (see Figure 4-4).

These are diagnostic pedologic characteristics of major river valley bottoms that have undergone longterm outwashing and sedimentation after orogenic development.

Figure 4-4: Soil Depositional Areas and Major Alluvial River Fans Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” Figure 2-9, November 2019, page 2-15.

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These Alluvial River Fan areas have the best infiltration rates, exclusive of the peat locales in the Delta (northwest portion adjacent to the Mokelumne River). Soils of the Stanislaus Alluvial River fans have young soil profiles of sandy loam to loam. Infiltration rates of the soils are predominantly between 0.6 and 2 inches per hour(in/hr). Areas of silt loam are also common especially in the floodplain and have a lower infiltration rate of less than 0.6 in/hr. Soils in the alluvial fans tend to coarsen toward the apex of the fan.

The Natural Resource Conservation Service (NRCS) categorizes soils by hydrologic soil groups. The hydrologic soil group is an estimation of the infiltration rate of the first five feet of soil based on depositional characteristics (mostly grain size and sorting) and secondary characteristics (compaction, lithification, and weathering).

Hydrologic soil groups for the Eastern San Joaquin Groundwater Subbasin and their relative infiltration rates are indicated by subjective descriptors shown in Figure 4-5: A (high), B (medium), C (slow) and D (very slow). The City, situated in the southwestern corner of the Eastern San Joaquin Groundwater Subbasin lies within the hydrologic soils group categorized as having a “high” infiltration rate.

Groundwater recharge and discharge is driven by both natural and anthropogenic (human-influenced) factors, and a high infiltration rate increases the rate of aquifer recharge. Areas of potential groundwater recharge and discharge within the Eastern San Joaquin Groundwater Subbasin are described in greater detail in the Groundwater Sustainability Plan (GSP) (see, for example, GSP Section 2.3. 2.1.4.5.1 Description of Recharge Areas).21
The recharge potential of soils and formations encountered in the Eastern San Joaquin Groundwater Subbasin varies considerably and is dependent on primary and secondary geologic effects (see Figure 4-6 below). In line with NRCS characterization, primary geologic patterns that influence permeability relate to grain size and sorting as a result of depositional characteristics. Secondary geologic effects that influence soil recharge characteristics are associated with post-depositional events such as consolidation, lithification, and weathering, including the development of hardpan soils. Additional information on geologic formations is provided in Section 2.1.5 of the GSP.22 21 Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” Section 2.3. 2.1.4.5.1 Description of Recharge Areas, November 2019. 22 Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” November 2019.

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Figure 4-5: Existing Areas of Groundwater Recharge
Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan”, Figure 2-13, page 2-22, November 2019.

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Figure 4-6: Existing Areas of Groundwater Recharge
Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan”, Figure 2-13, page 2-22, November 2019.

4.2 South San Joaquin Irrigation District (SSJID)
The SSJID formed in 1909 under the predecessor to the Irrigation District Act and was established to provide a reliable and economical source of irrigation water for the agricultural areas surrounding the cities of Escalon, Ripon, and Manteca. Since then, SSJID has expanded providing domestic water service to several additional cities in South San Joaquin County. Water sales represent an important part of the SSJID revenue stream and provide them with the income necessary to pay for required O&M on their water delivery system and help keep water rates stabilized.

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Figure 4-7: Nick C DeGroot WTP
Source: SSJID Strategic Plan 2017-2021, page 5.

A primary feature of SSJID’s role as a domestic water service provider is the joint SCWSP; a regional effort between SSJID and the cities of Manteca, Escalon, Lathrop, and Tracy to furnish high quality drinking water for urban use. The SCWSP consists of an intake facility at Woodward Reservoir, a state-of-the-art membrane filtration water-treatment plant (WTP), and about 35 miles of pipe ending in the City of Tracy.

The key infrastructure of the SCWSP is the Nick C DeGroot WTP (Figure 4-7) built in 2005 and water conveyance pipeline system jointly funded by the SCWSP participating agencies.

The WTP currently has a maximum sustained capacity of approximately 40 million gallons per day (MGD).

The WTP includes pre-chlorination, coagulation, dissolved air flotation pretreatment for removal of solids and dissolved material, chemical stabilization to minimize internal pipe corrosion, membrane filtration, and chlorination for disinfection.23
23 Information regarding City water supplies, demands, infrastructure, and supply availabilities have been described in prior TMs and UWMPs and are not detailed here:

City of Manteca "2015 Urban Water Management Plan," September 2016, Kennedy/Jenks Consultants.

City of Manteca, “2005 Urban Water Management Plan,” 2005.

City of Manteca, 2005 Water Master Plan, July, 2005, Kennedy/Jenks Consultants. 2020 Urban Water Management Plan for South San Joaquin Irrigation District, June 2021, EKI Environment & Water.

City of Manteca, General Plan 2023, Policy Document, October 6, 2003.

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When constructing the WTP and conveyances, the goals of SSJID and the SCWSP agencies were to protect and enhance the economic health of the region by providing reliable and safe supplemental water to cities; use conserved surface water from SSJID; maximize deliveries to current agricultural customers to the extent possible; meet local needs by keeping adequate water in the region; and reduce the area’s long-term reliance on groundwater.

Each city has an agreement with SSJID to receive treated water through December 2049. If SSJID and the cities do not agree to extend the contract past 2049, then SSJID, by agreement, agrees to transfer the project to a Joint Powers Authority composed of the four cities, which would run it at their cost.

The water supply from the SCWSP comes from SSJID’s senior pre-1914 appropriative water rights to the Stanislaus River. As noted, treated water deliveries began in July 2005. SSJID is able to make this water available to the cities as a result of its existing firm water rights, numerous agricultural water conservation measures, and through the loss of irrigated agriculture to urban development.

Under the Initial Project Participant’s Agreement24 with SSJID, the City is currently allotted 11,500 AFY under Phase I and will be allotted a total of 18,500 AFY under Phase II (see Table 4-2).

Phase City Total
Escalon Lathrop Manteca Tracy
Phase I Allotment (AFY) 2,015 6,887 11,500 11,120 31,522 Phase II Allotment (AFY) 2,799 10,671 18,500 11,120 43,090 Table 4-2: SCWSP Phase I and II Allotments by City
Source: Reproduced from Table 5-6, South San Joaquin Irrigation District, “2020 AGRICULTURAL WATER MANAGEMENT PLAN,” Final Draft Adopted March 23, 2021, page 5-22.

SSJID delivered an average of 8,484 AFY to the City between 2016 and 2020,25 well below the allotted Phase I allocation. Table 4-3 documents the historic treated water deliveries (drinking water quality) from SSJID to the City from 2016 through 2020. Note that these data, from SSJID, are slightly higher than the data records of the City which could be attributed to water losses in the SSJID trunk mains or meter read errors on either SSJID’s or the City’s end.
2016 2017 2018 2019 2020
Historic SSJID Drinking Water Delivery
to City of Manteca (AFY) 6,107 8,249 9,537 9,120 9,416
Table 4-3: SSJID Historic Treated Water Deliveries to City Source: Reproduced from Table 4-1 “Demands for Potable and Non-Potable Water, Actual (DWR Table 4-1),” 2020 Urban Water Management Plan for South San Joaquin Irrigation District, June 2021, EKI Environment & Water, page 28.

SSJID derives its water supply from three sources; these include surface water diverted from the Stanislaus River at Goodwin Dam, groundwater it pumps along with private landowners, and irrigation return flows.

The main source of water is the Stanislaus River.
24 The Water Supply Development and Operating Agreement (Water Supply Agreement) was updated on December 18, 2020, between the City and SSJID. This most current agreement extends the initial agreement made between the City and SSJUD on October 1, 1995. The term of this current Water Supply Agreement extension runs to 2049. An additional Project Participant, the City of Ripon, was added in this most recent Water Supply Agreement. 25 Ibid, 16
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A vital fact to the City is that SSJID has surface water rights to approximately 600,000 AFY jointly held with Oakdale Irrigation District (OID), and that the full allocation to SSJID and OID is subject to seasonal runoff availability from the Stanislaus River and other constraints per the 1988 Stipulation and Agreement with the U.S. Bureau of Reclamation (USBR). The USBR, who constructed and operates not only the expansive New Melones Reservoir (2.42 million AF [MAF] capacity) on the Stanislaus River, but also the Tri-Dams Project (230,400 AF capacity) and Goodwin Reservoir (68,400 AF capacity) has complete control over operations from and to these facilities.

The average annual unimpaired runoff in the Stanislaus River watershed is about 1.2 MAF.26 The median historical unimpaired runoff is 1.1 MAF per year, with a range of between 0.2 and 3 MAF.27 Snowmelt contributes the largest portion of the flows in the Stanislaus River, with the highest runoff occurring in April, May, and June. For a watershed of this importance, the unimpaired runoff is not large, just 1.1 MAF; by comparison, the American River watershed has an average annual unimpaired runoff of

2.4 MAF, more than twice the Stanislaus River watershed. This limited yield of the Stanislaus River watershed has ramifications for the City as will be discussed later.

As noted previously, water for the SCWSP comes from SSJID’s appropriative water rights on the Stanislaus River, specifically from the lower portion originating from releases made from New Melones Reservoir, a federal Central Valley Project (CVP) facility in the Sierra Nevada that is integrated with, though not part of, the Tri-Dams Project. New Melones Reservoir, Goodwin Reservoir, and the Tri-Dams Project (with Donnells,28 Beardsley, and Tulloch reservoirs) are all operated by the USBR as part of their East Side Streams Division of the CVP (see Figure 4-8).

As shown in Figure 4-8, releases from Donnells and Beardsley dams affect inflows into New Melones Reservoir. Under contractual agreements between the USBR, OID, and SSJID, Tulloch Reservoir provides afterbay storage to re-regulate power releases from the New Melones Powerplant. The main water diversion point on the Stanislaus River is Goodwin Dam, approximately 1.9 miles downstream of Tulloch Dam.

Goodwin Dam, constructed by OID and SSJID in 1912, creates a re-regulating reservoir for releases from the Tulloch Powerplant and provides for diversions to canals north and south of the Stanislaus River for delivery to OID and SSJID and their applicable retail customers. Water impounded behind Goodwin Dam may also be pumped into the Goodwin Tunnel for deliveries to the Central San Joaquin Water Conservation District and the Stockton East Water District.29 26 U.S. Bureau of Reclamation (2008) “Biological Assessment on the Continued Long-term Operations of the Central Valley Project and State Water Project”, U.S. Bureau of Reclamation, Mid-Pacific Region, Sacramento, California. August 2008. 27 U.S. Fish and Wildlife Service (1995) “Working Paper on Restoration Needs: Habitat Restoration Actions to Double Natural Production of Anadromous Fish in the Central Valley of California”, Volumes 1 to 3. Prepared for the U.S. Fish and Wildlife Services under the direction of the Anadromous Fish Restoration Program Core Group, Stockton, California. 28 Donnells and Beardsley reservoirs providing 134,000 AF of storage and Tulloch Reservoir providing an additional 58,803 AF. 29 U.S. Department of the Interior (2004) “Long-Term Central Valley Project Operations and Criteria and Plan CVP-OCAP”, page 3-37, Bureau of Reclamation, Mid-Pacific Region, Sacramento, California, June 30, 2004.

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Figure 4-8: SSJID and OID Relied Upon Reservoirs – Tri-Dam Project, New Melones, Goodwin and Woodward Reservoirs
Source: South San Joaquin Irrigation District and Oakdale Irrigation District https://www.savethestan.org/about-sts/
The requirements for New Melones Reservoir operations involve many factors. The operating criteria for New Melones Reservoir are affected by water rights, instream fish and wildlife flow requirements (including the U.S. Department of the Interior’s Central Valley Project Improvement Act [CVPIA] 3406 (b)(2) fishery management objectives), D-1641 Vernalis flow and water quality requirements, dissolved oxygen (DO) requirements, and CVP water service contract and flood control considerations. Water released from New Melones Dam and Powerplant is re-regulated at Tulloch Reservoir and is either diverted at Goodwin Dam or released from Goodwin Dam to the lower Stanislaus River.30 Flows in the lower Stanislaus River serve multiple purposes concurrently. The purposes include water supply for riparian water rights, fishery management objectives, and DO requirements per the State Water Resources Control Board (SWRCB) D-1422. Additionally, water from the Stanislaus River enters the San Joaquin River where it contributes to baseflow and helps improve water quality conditions at the one of the key State water monitoring stations on the San Joaquin River near the City of Vernalis.

D-1422, issued in 1973, provides the primary operational criteria for New Melones Reservoir and was the vehicle that helped the USBR ultimately utilize water from the Stanislaus River for irrigation and M&I purposes. D-1422 requires that the operation of New Melones Reservoir incorporate releases for existing 30 U.S. Department of the Interior (2004) “Long-Term Central Valley Project Operations and Criteria and Plan CVP-OCAP”, page 3-38, Bureau of Reclamation, Mid-Pacific Region, Sacramento, California, June 30, 2004.

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water rights, fish and wildlife enhancement, and the maintenance of water quality standards on both the Stanislaus and San Joaquin rivers.

For its share, according to the 1988 Agreement, SSJID is entitled to 300,000 AFY from the Stanislaus River during “normal”31 WYs; however, drought conditions and seasonal variations have the potential to reduce the SSJID allocation and those of the contracted cities it delivers water to, including the City.

In efforts to extend the use of SSJID’s Phase I system, an investigation into modifying the existing infrastructure to increase the plant’s current capacity is underway according to the SSJID 2020 Urban Water Management Plan (UWMP). Phase II includes a future plant expansion to increase the design capacity to approximately 60 MGD.

4.3 Groundwater
As noted previously, the City pumps groundwater from the Eastern San Joaquin Groundwater Subbasin.

DWR’s Bulletin 118 – 80, Ground Water Basins in California has long acknowledged the Eastern San Joaquin Groundwater Subbasin as a basin in a critical condition of overdraft. Therefore, the Eastern San Joaquin Groundwater Subbasin has been the focus of considerable interest and work towards achieving long-term sustainability.

As mentioned earlier, the City owns and operates 15 active potable water wells, two standby wells and 31 irrigation wells. While the trend has been to always assume that groundwater pumping by San Joaquin water purveyors/utilities has steadily and uniformly increased over time, not all trend lines are uniformly linear.

Between 1990 and 2020, the City’s groundwater use diminished from a high of 14,900 AFY in 2004 to 8,022 AFY in 2020. On an annual AF/Ac basis, the City pumped a high of about 1.4 AFY per acre (AFY/Ac) in 2004, but this has since decreased to about 0.5 AFY/Ac between 2014 and 2019.

Details of groundwater use in the City are not readily apparent by Table 4-4 alone since certain information are embedded in the date. With the new WTP commissioned in 2005, the City’s reliance on groundwater began to decline concomitant with delivery of surface water. Figure 4-9 presents a visual representation of the City’s total water supplies and City area between 1990 and 2020 to display the fluctuations in groundwater pumping quantities relative to the City area. 1990 2000 2010 2015 2020
Groundwater Pumped (AFY) 9,873 12,608 8,463 7,249 8,022 City Area (Ac) 5,543 10,204 11,399 13,189 13,737
AFY/Ac 1.8 1.2 0.7 0.6 0.6
Notes:

1. Includes both potable and non-potable groundwater pumped.

Table 4-4: Historical Groundwater Pumped within City
Source: Water supply data provided by the City.
31 “Water Year” (WY) has many different definitions. The WY runs from October 1st to the following September 30th. Five types of WYs are based on the relative amount of precipitation received: very dry (or critically dry), dry, average (or normal), wet and very wet. “Wet” and “very wet” are commonly interchanged with “above normal” and “wet”, respectively.

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Figure 4-9: Historical City Groundwater Pumping and City Area Source: Water supply data provided by the City.

Additionally, as noted in the City’s 2015 UWMP, while all of its municipal wells were then metered, not all of the irrigation wells were metered until 2015. This led to large uncertainties in pumping estimates in all years prior to 2015.32 Since that time, the City has been logging meter reads monthly. Meter reads are logged by hand, which may be prone to error.33
There are some undocumented wells and groundwater extractions occurring within the City’s corporate boundaries for which there is little detail. Wells currently in operation not owned by the City include private domestic wells, agricultural wells, wells for school irrigation owned by the Manteca Unified School District (MUSD), and irrigation wells owned by SSJID, among others.34 Well completion reports obtained from DWR suggest that approximately 1,000 water wells have been constructed within the General Plan area since record keeping began in the 1960s; however, many may not have been registered as abandoned when they were discontinued. It is anticipated that many domestic wells are no longer in use, though further investigation is needed to corroborate the exact extent. Because there are potentially numerous wells not owned by the City that are drawing from the Eastern San Joaquin Groundwater Subbasin, this could affect the amount of groundwater available to the City within the groundwater basin safe yield – as detailed in the City’s 2015 UWMP, the Eastern San Joaquin Groundwater Subbasin’s safe yield is 1 AFY/Ac. Quantifying this effect, however, is impossible without a concerted effort to examine all wells and related records. 32 Existing sources of uncertainty in historical irrigation pumping estimates include: six (6) wells with non-verifiable data and another four (4) without meter readings (pumping volumes are estimated). 33 City of Manteca “2015 Urban Water Management Plan,” September 2016, Kennedy/Jenks Consultants, page 6-3. 34 City of Manteca "2015 Urban Water Management Plan," September 2016, Kennedy/Jenks Consultants, page 6-3. 0 5000
10000
15000
20000
0 5000
10000
15000
20000
1990 1995 2000 2005 2010 2015 2020
Total Groundwater Surface Water City Area
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4.3.1 Chronic Basin Groundwater Depletion
Chronic groundwater depletion over the decades has made the Eastern San Joaquin Groundwater Subbasin one of the most stressed aquifer systems relied upon by multiple users across the U.S.

Comprising some 707,000 acres (1,105 square miles), it includes the major tributaries: San Joaquin River, Stanislaus River, Calaveras River, Mokelumne River, Mormon Slough, and Little Johns Creek.

Figure 4-10 shows, at a continental scale, the three primary aquifer-regions in the conterminous U.S. that experienced the highest groundwater storage losses over a recent 15-year period. Units are headloss in mm/yr for the April 2002 to June 2017 period. Dark blue to black coloration denote annual headloss values between 20-30 mm. Clearly shown are the cones of depression for the Ogallala Aquifer in northern Texas and northwestern Oklahoma, eastern Arizona along the Gila River, and in the San Joaquin River Valley Aquifer. The City is located very near the centroid of the Central Valley aquifer (e.g., Eastern San Joaquin Groundwater Subbasin) (red arrow).

Figure 4-10: Groundwater Storage Trends in North America from April 2002 to June 2017 Source: Wang, H., Xiang, L., Steffen, H., Wu, P., Jiang, L., Shen, Q., Li, Z. and M. Hayashi (2022) “GRACE-based estimates of groundwater variations over North America from 2002 to 2017” Geodesy and Geodynamics, 13(1), pp. 11-23 https://doi.org/10.1016/j.geog.2021.10.003.

Water bearing strata of the Mehrten and Laguna Formations, along with flood plain deposits, and alluvium and Modesto/Riverbank formations of the Eastern San Joaquin Groundwater Subbasin have been well described in other documents.35 The Mehrten Formation is considered the oldest freshwater bearing formation on the eastside of the basin, even though the older underlying Valley Springs Formation also produces minor quantities of groundwater. The groundwater aquifers underlying the City extend to depths greater than 600 feet and include four geologic formations. In increasing depth from the surface downwards, the identified aquifers are the Victor Formation, Laguna Formation, Mehrten Formation, and 35 Eastern San Joaquin Groundwater Authority, Draft ESJWRM Version 2.0 Update, January 2022, Woodard & Curran, Inc., page

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Valley Springs Formation. The City’s wells primarily withdraw water from the Laguna and Victor Formations.36
Based on current estimates, the Eastern San Joaquin Groundwater Subbasin storage decreased by 157,000 AF for WY 2021. This volume represents about 0.3% of the total fresh groundwater in storage, which was estimated to be more than 50 MAF in 2015. This loss, while notable, is less than the WY 2020 change in storage (-213,000 AF). This “reduced” annual loss has been attributed to statewide water use restrictions put in place in response to dry hydrologic conditions.37 Storage losses of this magnitude are likely unsustainable in the long-term.

None of the subbasin’s current and existing three groundwater recharge projects (e.g., Tracy Lake Groundwater Recharge Project, CalFED/Costa Recharge Project, or the Farmington Groundwater Recharge Project) are within the City’s corporate boundary, or hydraulically upgradient.

4.3.2 Groundwater Sustainability Plan (under SGMA)
A major effort of the City together with San Joaquin Valley water users is the ultimate stabilization and long-term security of the groundwater aquifer which has been declining for decades. California has long recognized this need and passed the landmark SGMA in 2014. SGMA is well known and has been thoroughly defined in several readily accessible documents38 and will not be discussed at length here, other than to highlight potential implications to the City insofar as the ability of SGMA to help the City meet its long-term water supply requirements. In short, implementing SGMA requires:

Local agencies and stakeholders to develop institutions, plans, and implementation strategies to manage their groundwater resources sustainably for the long run,39 If local agencies fail to act, SGMA directs the state to intervene. The law defines sustainable management as the avoidance of six “significant and unreasonable” effects:

1. Drawing down water levels too far,

2. Depleting storage in the aquifer,

3. Degrading water quality,

4. Allowing seawater intrusion,

5. Causing land to subside, or

6. Using groundwater in ways that reduce other people’s surface water or harm ecosystems.

Local stakeholders are in charge of carrying out the key provisions of SGMA. New or existing agencies overlying important groundwater basins—those designated by the Department of Water Resources (DWR) as medium- and high-priority, and critically overdrafted—have established groundwater sustainability agencies (GSAs), which are tasked with formulating sustainability plans. Any local water 36 City of Manteca "2015 Urban Water Management Plan," September 2016, Kennedy/Jenks Consultants, page 6-4. 37 Eastern San Joaquin Groundwater Subbasin Groundwater Sustainability Plan Water Year 2021 Annual Report, March 2022, page ES-3.
38 San Joaquin County (2021), “Eastern San Joaquin Integrated Regional Water Management Plan 2020 Addendum” Greater San Joaquin County Regional Water Coordinating Committee, GEI Consultants and Woodard Curran, Inc., January 21, 2021. 39 Kiparsky, M. (2016) “Unanswered questions for implementation of the Sustainable Groundwater Management Act,” California Agriculture, 70(4), pp.165-168. https://doi.org/10.3733/ca2016a0020.

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or land use agency in a basin can form a GSA, and there may be multiple GSAs in a basin, but they may not have overlapping boundaries. GSAs must engage local stakeholders and coordinate their planning to ensure that the entire basin is sustainably managed.

GSAs in critically overdrafted basins were required to develop plans by January 2020; those in other medium- and high-priority basins had two additional years to do so. With plans in place, GSAs have a 20-year horizon to manage their basins to achieve or maintain sustainability. Although the plans themselves are exempt from review under the California Environmental Quality Act (CEQA), projects that GSAs carry out to attain sustainability will generally require CEQA review.

GSAs must annually provide DWR with data and a description of their progress toward plan implementation. They must evaluate whether their plans are meeting sustainability goals for the basin at least every five years. This provides an opportunity to adapt goals and plans to new information and changing conditions.

The City (circle in red) as shown on Figure 4-11 is located in the lower southwestern portion of the Eastern San Joaquin (ESJ) Groundwater Subbasin surrounded by SSJID to the north, south, and east; the City of Lathrop to the west; and South Delta Water Agency to the south.

Figure 4-11: Eastern San Joaquin Subbasin GSAs
Source: Eastern San Joaquin County Groundwater Basin Annual Report 2021, Figure 1.

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The State did not approve the initial Eastern San Joaquin (ESJ) Groundwater Subbasin proposed GSPs.

However, as of March 2023, the ESJ GSP submitted in July 2022 was approved by DWR.

There are some 23 final possible SGMA Projects in the Eastern San Joaquin Groundwater Subbasin GSP ranging from direct and in-lieu recharge, intra-basin water transfers, demand conservation, water recycling, and stormwater reuse.

The City has one listed SGMA Project. Project #3 is the City’s Advanced Metering Infrastructure water conservation project. It was originally identified in the GSP as being implemented between 2019-2021 at a cost of $650,000, with an estimated annual O&M of $300,000 and an anticipated annual water savings of 272 AFY.

The City’s project is one of eight Planned Projects of the GSP. These are considered immediate projects and are planned to be completed and be online prior to 2040. The projected supply, therefore, is considered as offsetting the projected 2040 supply imbalance.

There are several larger, Planned Projects with considerably higher anticipated groundwater reduction targets such as the South San Joaquin GSA’s Stockton East Water District (SEWD) and Central San Joaquin Water Conservation District (CSJWCD) Long-Term Water Transfer Project. This is an in-lieu recharge effort targeting to save about 45,000 AFY.

Of the longer-term or Conceptual Projects, these are projects that could conceptually provide a benefit to the Eastern San Joaquin Groundwater Subbasin at some point in the future but are not on the immediate planning horizon. Accordingly, they would require further development. The City has identified Project #19, “Recycled Water Transfer to Agriculture” under this category. This project is currently in the planning phase with preliminary evaluation completed as part of the “Draft Reclaimed Water Facilities Master Plan.” Anticipated groundwater offset savings from Project #19 is 5,193 AFY. The project still requires NPDES Permit amendment, completed CEQA review, and SWRCB approval.

Figure 4-12 shows the location of the representative wells identified in the GSP monitoring network for the chronic lowering of groundwater levels. The City’s Well 18 (Manteca 18) (red arrow) can be seen in the lower southwest portion of the Subbasin, in the northeast corner of the City.

On November 18, 2021, as a part of the review process DWR notified the GSAs in the Eastern San Joaquin Groundwater Subbasin that the GSP needed to address certain deficiencies in order to be approved. As of March 2023, the ESJ GSP submitted in July 2022 was approved by DWR.

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Figure 4-12: Groundwater Level Representative Monitoring Well Locations Source: Eastern San Joaquin County Groundwater Subbasin, Water Year 2021 Annual Report, Fig 2, page 3-2, March 2022.

4.3.3 Groundwater Balance and Modeling Simulations
Since the ESJ Subbasin GSP was finalized in November 2019, the Eastern San Joaquin Water Resources Model (ESJWRM) has undergone three notable updates:

Extension of Data from WY 2016 through WY 2019
Extension of Data through WY 2020
Full Model Update and Recalibration (resulting in ESJWRM Version 2.0) ESJWRM original development is fully documented in a report, “Eastern San Joaquin Water Resources Model (ESJWRM) Final Report,” published in August 2018 and available in Appendix 2-A to the GSP.

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Various updates to the ESJWRM have been ongoing, the latest occurring in 2021 and resulting in the ESJWRM Version 2.0 Update. The major component updates are described in the WY 2021 Annual Report and are summarized as including: surface water diversion deliveries, groundwater pumping, population, land use, precipitation, streamflow, and boundary conditions.40 A comparison of water budgets between WY 2020 and 2021 is illustrated in Table 4-5.

Table 4-5: Comparison of WY 2020 and WY 2021 Water Budget (in AF) Source: Eastern San Joaquin County Groundwater Subbasin, Water Year 2021 Annual Report, March 2022, page 3-23.

Evaluation of WY 2021 in Table 4-5 shows that the Eastern San Joaquin Groundwater Subbasin experienced, on an average and net basis, 652,000 AF of inflows and 809,000 AF of outflow, leading to an annual decrease of groundwater in storage of 157,000 AF. Deep percolation from the root zone is the largest contributor of groundwater inflow (251,000 AFY), followed by recharge from managed aquifer projects, unlined canals or reservoirs, and ungauged watersheds (154,000 AFY); boundary flows from surrounding groundwater subbasins (122,000 AFY); and recharge from streams (125,000 AFY).

Groundwater production (809,000 AFY) accounts for the greatest outflow from the Eastern San Joaquin Groundwater Subbasin.

The SGMA regulations require that the annual water budget quantify three different temporal conditions:

Historical,
Current, and
Projected.41
The hydrologic elements under these conditions are listed in Table 4-6, below. 40 Eastern San Joaquin County Groundwater Subbasin, Water Year 2021 Annual Report, March 2022, page 3-22. 41 As per the GSP, “current conditions” represent those of the most recent 50-years of hydrology, water supply, water demand and land use information. “Projected conditions” are those used to estimate baseline conditions of supply, demand and aquifer response to GSP implementation. The projected conditions, again consistent with the GSP, is to evaluate those conditions assuming a 2040 level of development but using the hydrology from WYs 1969-2018.

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Table 4-6: Average Annual Water Budget – Groundwater System (AFY) Source: Eastern San Joaquin Groundwater Authority, Eastern San Joaquin Groundwater Subbasin, “Groundwater Sustainability Plan,” Table 2-15, November 2019, page 2-129.

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Notes:

1. WY Types based on San Joaquin Valley WY Index. WY 2021 classification is Critical (C) based on the hydrologic conditions for that year.

Figure 4-13: Modeled Change in Annual Storage with Water Use and Year Type Source: Eastern San Joaquin County Groundwater Basin, Water Year 2021 Annual Report, March 2022, page 3-6.

Shown graphically, Figure 4-13 shows the annual and cumulative change in storage from WY 1996 to 2021 for the Eastern San Joaquin Groundwater Subbasin.

In WY 2021 (October 1, 2020 to September 30, 2021), the Eastern San Joaquin Groundwater Subbasin experienced a decrease of groundwater in storage of approximately 157,000 AF (see Table 4-5), reflecting the dry conditions of the year. Figure 4-13 shows the declining “Cumulative Change in Storage,” meaning that inflows consisting of deep percolation, recharge, flow from streams, and boundary inflows were less than outflows from 2019 onwards.

The cumulative change in storage is easy to track particularly when one follows the WY type classifications starting in 2012, the mid-decade 5-year drought sequence (e.g., megadrought). This decline in groundwater storage corresponds with an increase in groundwater pumping during this same period (see Figure 4-14).

The groundwater budgets generated by the modeling simulations represent a balance of the groundwater system based on all components of the land and water supply system that affect the hydrology and physical conditions of the groundwater system. The groundwater budgets shown above (Figure 4-13) are hydrologic groundwater budgets for the Eastern San Joaquin Groundwater Subbasin incorporating the historical calibration as well as current and projected future conditions baseline.

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Figure 4-14: Modeled Change in Annual Storage with Groundwater Pumping and Year Type Source: Eastern San Joaquin County Groundwater Basin, Water Year 2021 Annual Report, Figure 7, March 2022, page 3-8.

Operational water budget components include deep percolation from rainfall and applied water, recharge from conveyance and carriage losses, and any recharge as a result of managed aquifer recharge projects or storage reservoirs that are operated by an entity within the water budget region. These operational water budgets were calculated using annual averages of GSA hydrologic groundwater budget results; full details of the various modeling assumptions and variables are described in other documents incorporated herein by reference.

Insofar as the projections for the City are concerned, Table 4-7 shows the projected annual groundwater budgets of the City, relative to the overall Eastern San Joaquin Groundwater Subbasin.

Two adjacent purveyors to the City, SSJID and OID, have also been added for comparative context. The table represents a simplified mass balance depiction of how the aquifer beneath the City would react to projected accretions (additions of water) and depletions (withdrawals or losses of water). For the City, the total annual projected accretions (through precipitation and applied water) are minimal (e.g., 290 AFY). Total depletions, however, are significantly higher (e.g., 20,600 AFY), resulting in a total groundwater storage deficit of 20,310 AFY. Overall, the Eastern San Joaquin Groundwater Subbasin projected an annual deficit of some 363,480 AF is assumed and calculated mass balancing of the contributing water purveyors. Projected annual losses or deficits are shown as red numbers in parentheses. By comparison, both SSJID and OID, with significantly higher anticipated accretions (92,700 AFY and 32,100 AFY, respectively), provide a net gain to the aquifer water balance (shown as black numbers).

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Water Balance Element City of
Manteca
SSJID OID Eastern San Joaquin
Groundwater Subbasin
Deep Percolation1 290 51,300 14,600 282,020
Precipitation 90 8,500 1,900 70,060
Applied Water 200 42,800 12,700 211,960
Other Recharge2 0 41,400 17,500 105,700
Carriage/Canal Recharge and
Managed Aquifer Recharge3
0 25,400 17,500 89,700
Local Reservoir Seepage 0 16,000 0 16,000
Total Accretions (Water Added) 290 92,700 32,100 387,720 Groundwater Pumping 20,600 34,900 31,100 751,200
Total Depletions (Water Depleted) 20,600 34,900 31,100 751,200 Net Effect on Groundwater System
(Aquifer Balance)
(20,310) 57,800 1,000 (363,480)
Notes:

1. Deep Percolation – includes percolation due to both precipitation and applied water (both surface and groundwater).

2. Other Recharge – includes canal seepage, reservoir seepage, aquifer recharge projects, and drainage from ungauged watersheds.

3. Carriage/Canal Recharge and Managed Aquifer Recharge – includes canal seepage and MAR projects attributed to each GSA. Also includes calculated 5% of total Camanche Reservoir releases for NSJWCD assumed to be Mokelumne River stream seepage.

4. Units in AFY.

Table 4-7: Operational Water Budget by Select GSA and for the ESJ Subbasin Source: Adapted from Table 11, Eastern San Joaquin Groundwater Authority, Draft ESJWRM Version 2.0 Update, January 2022, Woodard & Curran, Inc., page 48.

4.4 Alternative Water Supply: Stormwater and/or Floodwater In our multifaceted water industry, it is best to invest and pursue water resources that a water purveyor can maximize influence or control over. For water entities seeking to fill projected supply gaps, storm- or floodwater capture is a recommended resource to explore.

The salient and uncontested advantages of stormwater over all other supply sources include the following:

It is uncontrolled by State or federal regulators;
It has no effect on State water quality or endangered species; It has no effect on any other water purveyor’s claimed water entitlements (there can be no injury claims made against it);
It cannot be curtailed, even under the worst drought conditions; It is virtually guaranteed every year;
It is a relatively clean water source;
It requires no treatment for agricultural use;
Controlling it directly helps City, County, and regional flood control efforts; Existing infrastructure required for conveyance/collection already exists to some degree; and It is a free resource.

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4.4.1 Stormwater Capture
An effective, cheaper, and more ubiquitous new water supply alternative for California and the San Joaquin Valley is stormwater or floodwater. Stormwater capture, storage, and utilization is the most overlooked water supply asset in California water resources management today. From the perspective of year-to-year reliability, spatial representation, water quality, cost to capture, unentangled legal rights, and volume, there is no greater supplemental water supply source than this. The amount of time, resources, and personnel the State dedicates to flood management and damage control is testimony as to how widespread stormwater is across the State.

The integration of a traditional flood issue with a water supply interest is not a foreign concept. The State has long acknowledged the importance of linking flood risk strategies, with ecosystem health and water supply reliability to achieve short-term success as well as long-term sustainability.42 Average annual precipitation within the Eastern San Joaquin Groundwater Subbasin ranges from about 11 inches in the southeast to about 25 inches in the northeast. There is of course significant interannual variability as shifting hydroclimatic trends continue to force water managers to recalibrate assumptions on water yield based on these emerging and intensifying climatic patterns. But examples of storm- and floodwater capture and use are widespread across America and the globe.

Figure 4-15 shows the large cisterns to capture stormwater under the National Mall in Washington D.C.

Stormwater is processed through microscreens and ultraviolet light disinfection (right photo). On-site stormwater use is attractive where rainfall is more uniform throughout the year.

Similarly, stormwater harvesting in Royal Park, Melbourne, Australia employs a cistern. The runoff passes through a sediment trap, wetlands, and open-water storage, followed by UV disinfection and holding in a

1.3 MG (5000 m3
) underground tank prior to use for irrigation. The water is applied through spray irrigation at night to minimize human health risks.43
42 DWR and USACE (2013) “California’s Flood Future: Recommendations for Managing the State’s Flood Risk”, Final, November 2013, FloodSAFE California.
43 City of Melbourne (2013) “Royal Park Stormwater Harvesting Project”, March 2013.

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Figure 4-15: National Park Service – Large Cisterns under the National Mall Source: Luthy, R.G., Sharvelle, S. and P. Dillon (2019) “Urban Stormwater to Enhance Water Supply”, Environ. Sci.

Technol. 53(10), pp.5534-5542 https://doi.org/10.1021/acs.est.8b05913

4.4.2 Dry Wells
Dry wells, also called vadose zone wells or leaky wells, are vertical pipe-like devices with coarse media and an open bottom and holes in the walls that percolate water to the surrounding soil. The only treatment may be a sediment trap to remove debris or a geotextile fabric to prevent clogging.44 In California, dry wells are used with caution due to the concern that they provide a conduit for contaminants to enter the groundwater.45 Dry wells in New Jersey are prohibited in industrial or other areas where toxic chemicals might be used, whereas in Pennsylvania dry wells are permitted in industrial areas with restrictions, but not along roadways. Some newer designs consist of three parts: a vegetated pretreatment feature, a structural pretreatment sedimentation well, and the dry well itself, which contains layers of sand or gravel. The goal of this design is to maximize the removal of particle-associated pollutants, reduce clogging of the dry well, and promote efficient infiltration. 44 Hunters Council. Vegetated Drainage Devices, Practice Note #5; Environment Division, Hunters Councils Inc.: New South Wales, Australia, 2013.
45 California Office of Environmental Health Hazard Assessment Dry Wells: Uses, Regulations, and Guidelines in California and Elsewhere [Fact Sheet]; September 25, 2014.

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These types of designs are implemented in Los Angeles in the San Fernando Valley, as shown in Figure 4-16 below.46 However, data on actual water volume infiltrated and water quality in such dry wells are lacking. The system comprises three chambers—one for particle settling with the second and third chambers allowing percolation from the base into crushed rock or by an overflow pipe in the third chamber set into crushed rock.

Figure 4-16: Curbside Dry Well Installation with Vegetation in Los Angeles Source: Luthy, R.G., Sharvelle, S. and P. Dillon (2019) “Urban Stormwater to Enhance Water Supply”, Environ. Sci.

Technol. 53(10), pp.5534-5542 https://doi.org/10.1021/acs.est.8b05913

4.4.3 Wetland Parks
Some claim that in arid regions with Mediterranean climates, cisterns may be impractical owing to the asynchronous nature of rainfall and water demand, which requires storing large amounts of water for six to eight months until the dry season. In such situations, urban aquifers may be better suited to store stormwater by infiltration. In Los Angeles, for example, the Rory M. Shaw Wetlands Park in the Sun Valley neighborhood is being built to capture up to 900 AFY of urban runoff.47 The collected stormwater is pumped to an adjacent infiltration system that takes advantage of the permeable media in this area. This neighborhood-scale project contributes to water supply while converting a blighted landscape into 46 acres of green space and recreation.
46 Los Angeles Department of Water and Power Branford Street Dry Well Details, Sun Valley EDA Public Improvements Project; Los Angeles, CA, 2015.
47 Hagekhalil, A.; Kharaghani, S.; Tam, W.; Haimann, R.; Susilo, K. Becoming the Green-Blue City. Civil Engineering Magazine Archive 2014, 84 (11), 68– 91, DOI: 10.1061/ciegag.0000516.

Los Angeles County Flood Control District. Sun Valley Watershed, Strathern Wetlands Park Project (Fact Sheet), Los Angeles, CA, 2012.

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4.4.4 Stormwater as a Water Source 2013 Study
Storm- or floodwater has been considered as a potential additional water supply source for many years.

A 23 city, seven region examination of rainwater harvesting potential across the U.S. was undertaken in 2013 where water-saving efficiency benefits were determined using a water-balance approach applied at a daily time step for a range of rainwater cistern sizes.48 The analysis was conducted for a standard residential parcel size and rooftop size using daily precipitation records and a daily water demand pattern developed for each city. Stormwater management benefits were quantified using USEPA SWMM to simulate the performance of an 11-hectare, 100-parcel residential neighborhood for precipitation patterns representing the seven regions.

Their results revealed a high potential for rainwater harvesting (RWH) to provide supplemental water supply and stormwater benefits across a diverse continental landscape. Water-saving efficiency benefits for regions with precipitation above 30 in were over 90% for modified (non-potable) indoor water use, such as the Southeast, East Coast, Midwest, and Pacific Northwest. For regions with less precipitation, the potential water-saving efficiency ranged from 20 to 50% for 80% rooftop water yield.

The ability of RWH to supply water is dependent on several factors including cistern size, water use pattern, and precipitation. The cistern size required to capture 80% or more of the average annual runoff from the residential rooftop ranged in size from 190 to 1,800 gal. Of interest was the potential for high rooftop yield capture from RWH in the semiarid cities, while accomplishing lower water-saving efficiency benefits in these regions.49 They concluded that RWH has the potential for water supply benefits and stormwater management and that the actual potential is dependent on several factors including precipitation, cistern size, and water usage patterns. Regions with higher precipitation have a higher water-saving efficiency, with a lower stormwater management potential. Semiarid regions have modest stormwater management potential at the neighborhood scale.

A 2014 report by the Pacific Institute and NRDC titled “The Untapped Potential of California’s Water Supply: Efficiency, Reuse, and Stormwater,” spoke about the need to capitalize on the State’s surplus seasonal hydrology, a fact that will get more extreme with each passing year. In 2014, they were estimating that the State could generate an additional supply in excess of 600,000 AFY from stormwater in the Bay Area and southern California alone, a boost of 10% to their annualized water supplies.

This 10% supply enhancement could easily cover the water supply/demand gap currently projected for many water purveyors, including the City, should the City decide to pursue its own storm- and/or floodwater capture, storage, and use program.
48 Steffen, J., Jensen, M., Pomeroy, C.A., and S.J. Burian (2013) “Water Supply and Stormwater Management Benefits of Residential Rainwater Harvesting in U.S. Cities”, Journal of the American Water Resources Association (JAWRA) 49(4): 810-824.

DOI: 10.1111/jawr.12038.
49 Ibid, 105
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4.4.5 City Stormwater
In the City’s 2015 UWMP, it acknowledges that utilization of stormwater (floodwater) as a water supply source had not yet been studied in detail. According to the UWMP, however, the City owns existing infrastructure to store and treat stormwater runoff.50 Existing stormwater runoff is transmitted through the City’s current system, into SSJID drains and laterals, and ultimately discharges into the San Joaquin River.

The City’s current Storm Drain Master Plan (SDMP) dated March 2013 does not discuss the use of stormor floodwater as a potential alternative water supply source. The SDMP aptly focused instead on the essential service of storm drainage control, disposal, and relevant regulatory compliance, discussing the need to assess the condition of existing drainage facilities and by identifying additional facilities needed to accommodate runoff from future development; all of which is made consistent with the requirements of the State of California and the U.S. EPA.51
SSJID owns a complex network of irrigation laterals and drains that run throughout the City’s limits. These facilities deliver irrigation water to various farming operations and play an important role in conveying excess irrigation water and field runoff to downstream receiving waters, specifically the San Joaquin River.

The City relies on these SSJID facilities to convey its stormwater runoff to the San Joaquin River, and fully intend to continue to do so.52 This drainage infrastructure could serve as the vital backbone of any new stormwater retention or enhanced water supply program that the City might decide to pursue.

One of the biggest hurdles will be in restructuring the existing City/SSJID Master Drainage Agreement, or drafting a completely new agreement, that would address the many complexities involved in fully implementing a stormwater collection, storage, treatment, and distribution program. It is likely that existing capacity in any element of SSJID’s stormwater drainage infrastructure do not currently accommodate the volumes of additional water necessary to meet the City’s requirements should they decide to proceed with a significant stormwater collection and storage program.

Under such a program, the City would have to build its own storage/retention basins. The extent to which additional conveyance facilities and necessary appurtenances would be required to integrate these new retention basins with SSJID’s existing infrastructure would depend on the ultimate design plans for this new program. The SDMP, however, already identifies several types of detention facilities intended to capture peak stormwater runoff: permanent detention basins, interim percolation basins, and permanent sole use percolation basins.

Detailed analysis would be necessary to determine the extent to which any existing detention basins could be used or otherwise be converted for use as water supply storage basins. Careful planning would be required to synchronize flood and water supply development since, although these two water uses may share the same facilities and infrastructure, their fundamental operational objectives are diametrically opposed.

As managed aquifer recharge gains increasing popularity, various water supply sources capable of providing the input necessary to initiate and perpetuate this process are being sought such as stormwater or excess floodwater. Factors affecting quantity and quality of recharge influence and are influenced by 50 The City's Storm Drain System consists of approximately 170 miles of pipeline, 36 pump stations, and 35 detention basins. 51 City of Manteca, Storm Drain Master Plan, March 2013. 52 Ibid, 5
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state/local land development policy, state/local groundwater policy, regulation and codes and climate change effects, as well as pretreatment requirements.

Site selection for possible managed aquifer recharge (MAR) projects will include hydrogeologic considerations, onsite footprint and construction factors as well as the need to match technology with hydrogeologic setting, state/local policy regarding the avoidance of hydraulic and pollutant effects, consideration during high water levels (flooding), representative groundwater monitoring, as well as lifecycle costing including vulnerable geology.53 Figure 4-17 shows a schematic of potential key flood infrastructure components as noted by the California Legislative Analyst’s Office (LAO). Interestingly, the LAO recognize the use of detention basins, acknowledging that not all flood prone areas drain to controlled reservoir impoundments. This would apply to lands downstream from terminal or “rim” reservoirs, such as the entire City lands. Ultimately, if stormwater capture, storage, treatment and distribution emerges as an option the City intends to pursue, new institutional agreements will be necessary.

Figure 4-17: Illustration of Key Flood Infrastructure
Source: Adapted from Figure 5, LAO, “Managing Floods in California”, page 13. 53 Job, C. (2022) “A Review of Low-Impact Development Factors Affecting Managed Aquifer Recharge: Groundwater, https://doi.org/10.1111/gwat.13207.

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One of the benefits of using stormwater for managed aquifer recharge is that it shifts water quantity and quality effects away from entitled surface waters. This can be a good or bad thing depending on which source supply is considered more fragile or “at-risk.” It can be considered a good thing if traditional surface water supplies are constrained and there is little surplus to store. Using excess stormwater at no cost instead of contracted surface water could be viewed as a good thing. It might be viewed negatively, however, if the existing aquifer or immediate regions of the aquifer boundaries were pristine and injecting or percolating poorer quality stormwater would reduce the overall groundwater quality.

A changing hydroclimate primarily affects groundwater reservoirs through its influence on annual recharge. Here, timing is not so much an issue as is quantity. For, unlike surface water storage reservoirs, groundwater storage is dictated by the hydraulic conductivity of its overlying and surrounding matrix, none of which is homogeneous or easy to model.

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5 CITY WATER SUPPLY AND DEMAND BALANCE
It is important to note that water supply and demand balance computations are based on a series of factors including: raw data (measured and estimated), hydrologic assumptions, engineering system assumptions, use (consumption) and loss assumptions, as well as anticipated growth. While these factors and assumptions may not be consistent among prior documents, it is important to acknowledge that the City is currently working on both the Water Master Plan and final 2020 UWMP to assure that consistency is maximized and that development does not outpace water resource supplies, infrastructure, and operations.

5.1 2020 Water Use
Table 5-1 presents the actual water use for 2020 alongside the total right or safe yield for each supply source utilized by the City. Note that the City also produces recycled water which is currently used to irrigate fodder crops near the wastewater treatment plant (WWTP), distributed at fill stations for dust control on construction sites, and used for irrigation at the Great Wolf Lodge.

Supply Source Water Quality Total Right or Safe Yield
(AFY)
Quantity Supplied
(AFY)
SSJID Surface Water Potable 11,500 9,244
Groundwater
Potable
13,737 1 6,038
Non-Potable 1,984
Total 25,237 17,266
Notes:

1. Based on the City’s 2020 area (13,737 Acres) and a sustainable pumping rate of 1 AFY/Ac.54 Note that there are other known entities within the City pumping groundwater (such as Manteca Unified School District [MUSD], and Eckerts Cold Storage) whose groundwater pumping also factors into the City’s safe yield but are not considered herein.

Table 5-1: City Water Supplies 2020
Source: Water supply data provided by the City

5.2 Water Demand Projections
Table 5-2 presents the potable water demand projections, including water losses, through 2045 developed as part of the City’s Water Master Plan (WMP).

Units 2025 2030 2035 2040 2045
MGD 15.2 18.1 20.3 22.9 25.8
AFY 17,029 20,242 22,786 25,649 28,872
Notes:

1. Note that these numbers do not include non-potable groundwater pumping for irrigation purposes as the WMP is specifically concerned with the potable water entering the City’s distribution system; this is why the projected demand for 2025 listed in Table 5-2 is less than the total supply for 2020 listed in Table 5-1.

Table 5-2: Potable Water Demand Projections
Source: “TM #3 – City Growth & Development Study,” April 2023, HydroScience Engineers, Inc., page 26. 54 City of Manteca “2015 Urban Water Management Plan,” September 2016, Kennedy/Jenks Consultants, page 6-2.

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5.3 Water Supply Projections
Table 5-3 below presents the projected total right or safe yield of City groundwater and surface water supplies during a historically normal year without any curtailments. As part of the City’s 2015 UWMP future water supply reliability analysis, there was no anticipated change in the City’s future available groundwater supply projections. For this analysis, however, it is assumed that the available groundwater supply within the safe yield will increase as lands are annexed into the City and the City limits are expanded. These City limits expansions were also developed as part of the City’s ongoing WMP and are shown in Figure 5-1. 55
Supply Source 2025 2030 2035 2040 2045
SSJID Surface Water 11,500 11,500 11,500 18,500 18,500
Groundwater1 14,074 14,411 16,057 17,704 19,350
Total 27,599 27,941 29,592 38,244 39,895
Notes:

1. Includes both potable and raw water groundwater pumping.

Table 5-3: Projected Un-Curtailed Total Available City Water Supplies (AFY) As in Table 5-1, groundwater supply availability is based on City area and a sustainable pumping rate of 1 AFY/Ac, as presented in the City’s 2015 UWMP. Additionally, there are other known entities within the City (such as Manteca Unified School District [MUSD] and Eckerts Cold Storage) whose groundwater pumping may impact the City’s pumping rates relative to the safe yield but are not considered herein.

The projection horizons developed for the WMP are 2030 and 2045. While it is difficult to predict how the City will expand between those years, for planning purposes the groundwater safe yield quantities are linearly interpolated for the interim years (2025, 2035, and 2040).

According to SSJID’s 2020 UWMP, it is assumed that Phase II of the SCWSP will be completed and online by 2040, an update from the 2015 UWMP which assumed 2025. Phase II will increase the City’s uncurtailed allotment to 18,500 AFY.

One of DWR’s noted UWMP requirements is the single- and multi-year drought analysis that compels water purveyors to evaluate a potentially depleting base supply (over several years) against future demand projections to determine whether adequate water supplies would exist under such conditions.

The last single- and multi-year supply and demand analysis was undertaken as part of the 2015 UWMP effort; herein, an updated supply and demand analysis is presented using the UWMP-prescribed methodology and the updated projections presented in Table 5-2 and Table 5-3. 55 “TM #3 – City Growth & Development Study,” December 2022, HydroScience Engineers, Inc., page 20.

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Figure 5-1: City Limits Expansion for 2030 and 2045 Projection Horizons Source: Reproduced and altered from “TM #3 City Growth & Development,” April 2023, HydroScience Engineers Inc., page 20.

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5.4 Supply vs. Demand for Normal Water Year
The water supply estimate presented above is based on a current normal water year. This section will evaluate current normal year water supply versus demand as well as additional scenarios that consider potential reduction of supply in the event of drought and curtailment.

Table 5-4 presents a comparison of supply versus demand for a normal year given the supply and demand projections presented above and assuming no curtailments to the City’s available surface water supply or available groundwater within the Easter San Joaquin Groundwater Subbasin safe yield. Though some additional irrigation wells may be built by the City, these projections assume that non-potable groundwater pumping for irrigation will stay relatively constant into the foreseeable future. Future parks are included in the potable water demand projections presented in Table 5-2. For the purposes of this analysis, we assume a constant non-potable groundwater pumping rate of 2,000 AFY. It is noted, again, that there are other known entities within the City, such as Manteca Unified School District [MUSD] and Eckerts Cold Storage, whose groundwater pumping may impact the City’s pumping rates relative to the safe yield but are not considered herein.

Projected (AFY) 2025 2030 2035 2040 2045
Total Projected Supply (AFY) 27,599 27,941 29,592 38,244 39,895 Total Projected Demand (AFY) 19,029 22,242 24,786 27,649 30,872 Difference (AFY) 8,570 5,699 4,806 10,595 9,023
Table 5-4: Normal Year Supply versus Demand Comparison
Water purveyors completing UWMPs must identify their base “hydrologic” years that they intend to use for the dry-year evaluations. Because the City receives water from SSJID, it has in the past for the 2015 UWMP, used the same base years as SSJID for this analysis.

Table 5-5 presents the percentages of normal supply available during dry years for surface water and groundwater and the historical base hydrologic years – the same years and associated percentages used in SSJID’s 2020 UWMP – used to develop these percentages using the prescribed DWR UWMP methodology.

Year Type Base Year1 % of Normal Supply Available
Surface Water1
% of Normal Supply Available
Groundwater
Average Year 2010 100 100
Single-Dry Year 1977 75 100
Five Consecutive Dry Years 1st Year 2012 100 100
Five Consecutive Dry Years 2nd Year 2013 95.6 100
Five Consecutive Dry Years 3rd Year 2014 75 100
Five Consecutive Dry Years 4th Year 2015 75 100
Five Consecutive Dry Years 5th Year 2016 100 100
Notes:

1. Base years listed and percentages of average surface water supply available are based on SSJID 2020 UWMP.

Table 5-5: Historical Basis of WY Type
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5.5 Supply vs. Demand Under Drought Conditions
In Table 5-5, the average supply assumptions under imposed curtailment percentages are not as conservative as the most recent restrictions seen in 2022. Whether such curtailments are hydroclimatologic (e.g., precipitation-based), runoff-based (e.g., precipitation, facility, or regulatorybased), or purely institutional, the percent reductions are less than would be expected, particularly, in the 5th consecutive year of a protracted drought. While this may have been the case in the 2012-2016 drought, it is overly optimistic to assume that a 5th consecutive year drought would not restrict or otherwise curtail the City’s water supply. Selecting 1977 as the single-dry year is appropriate, however, limiting imported water shortages to only 75% is likely not conservative enough.

Original maximum CVP M&I contract shortage were 75% of normal and over the past several decades have been increased to 50% in extreme circumstances. Granted, SSJID is not a CVP or SWP contractor subject to the deep shortage provisions imposed by federal and State water contracting stipulations, however, 2022 has demonstrated how even standard curtailments have now been exceeded.

Additionally, only surface water deliveries from SSJID are curtailed and groundwater pumping is left completely unconstrained – an unlikely long-term outcome given the status of the Eastern San Joaquin Groundwater Subbasin. The 2012-2016 drought period proved that as surface water supplies became increasingly strained, groundwater reliance increased to about 80% of the supply in the San Joaquin Valley.56 At that usage rate, it is conceivable that after successive years, for groundwater reserves to be impacted and potentially deplete. Therefore, it is prudent to assume a reduction in the current safe yield pumping rate of 1 AFY/Ac during a period of sequential drought years for two reasons: 1) to prepare for the possibility of a curtailment and 2) to plan for the management of the Subbasin’s sustainable yield under drought conditions.

Based on the established water supply and demand projections, various assumptions, and base hydrologic years, Table 5-6 presents the supply versus demand comparison for a single dry year with SSJID surface water curtailed by 75% and groundwater un-curtailed. It is noted that in reality, during drought years, the City will typically implement the necessary stage of its Water Shortage Contingency Plan (WSCP) which lays out actions the City plans to take to encourage City residents to conserve water. To be conservative and for consistency with UWMP methodology, demands are assumed to stay the same as presented in Table 5-2 for the analysis presented herein.
2025 2030 2035 2040 2045
Total Projected Supply (AFY) 22,699 23,036 24,682 31,579 33,225 Total Projected Demand (AFY) 19,029 22,242 24,786 27,649 30,872 Difference (AFY) 3,670 794 -104 3,930 2,353
Table 5-6: Single-Dry Year Supply versus Demand Comparison Based on this analysis, there are shortages by 2035. Note, though, that if there is unaccounted for groundwater pumping by others, it could push shortages further in 2035 and as early as 2030. 56 California’s Fourth Climate Change Assessment, 2018, San Joaquin Valley Region Report, p. 17.

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Given that the multiple-dry year analysis curtailments do not provide additional limitations as compared to the single-dry year analysis, Table 5-6 presents the most extreme case for both the single- and multipledry year analyses. It is noted, however, that during a multi-year drought, there will likely be carryover storage shortages due to the occurrence of multiple consecutive dry years. Consistent with UWMP methodology, year-to-year storage effects are not considered here but would likely only exacerbate any deficits.

As shown in Table 5-6, the shortage between supply and demand is less than 1 percent by the year 2035.

This shortage can be managed with the implementation of the City’s WSCP. However, under prolonged drought conditions, the projected supply could be much lower than what is presented under single-dry year conditions if curtailments increase. With such a tight margin , a prolonged drought would likely cause a deeper deficit.

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6 FUTURE WATER-RELATED THREATS TO THE CITY
The future threats to deliverable water supplies in the City for the foreseeable future (e.g., General Plan buildout) can be categorized into the following:

Hydroclimatological Uncertainty. Uncertainties associated with a rapidly shifting climate due to forced anthropogenic global warming (e.g., climate change) Existing Surface Water Storage Capacity Limitations. Limitation in reservoir storage capacity across the system relied upon by SSJID and the City
Regulatory Impositions. Regulatory impositions as they relate to surface water operations of the primary water regulators in the State.

Declining Groundwater. Long-term aquifer declines have been chronic among water purveyors.

For a City totally reliant on another party for its surface water supply, future hydroclimatology is an important consideration. The megadrought, for example, received considerable attention in recent years and water providers have struggled to put this hydroclimatic anomaly into proper perspective. This has been made all the more challenging since no historic benchmark exists from which to draw comparisons or contrast similarities and dissimilarities.

6.1 Hydroclimate Change and Uncertainty
Climate change modeling is far from an exact science. New developments and various nuances emerge continuously as researchers contend with an extremely dynamic and volatile new discipline. However, it is clear that our climate is changing and affecting precipitation.

6.1.1 Climate Change
Global warming is changing the intensity distribution of daily precipitation, with an increased frequency of heavy precipitation and reduced frequency of light/moderate precipitation as expressed in GCM/RCM projections. While an increase in extreme hydrology, particularly, rainfall-runoff is now fully accepted as a result of warming global air temperatures and the manifestation of this effect during the winter months, the exact regional nuances are still largely undefined.57 Projected future Coupled Model Intercomparison Phase 5 (CMIP5)58 GCM changes in regional daily precipitation distribution can be described by a combination of two idealized modes: a frequency decrease mode, representing a reduction in the frequency of precipitation at all rain rates, and a frequency shift mode, where the distribution shifts toward heavier rain rates. A decrease in daily precipitation frequency and an increase in intensity are projected in most regions, but the magnitude of change shows large regional variations.59
57 Williams, A.I.L. and P.A. O’Gorman (2022) “Summer-Winter Contrast in the Response of Precipitation Extremes to Climate Change over Northern Hemisphere Land”, Geophysical Research Letters, https://doi.org/10.1029/2021GL096531. 58 Lawrence Livermore National Laboratory, https://pcmdi.llnl.gov/mips/cmip5/ 59 Chadwick, R., Pendergrass, A.G., Muniz Alves, L., and L., A. Moise (2022) in Journal of Climate, “How Do Regional Distributions of Daily Precipitation Change under Warming?”, pp. 3243-3260, https://doi.org/10.1175/JCLI-D-20-0864.1.

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In a recent DWR study, four important watersheds in the San Joaquin River region (Stanislaus River at New Melones, Tuolumne River at Don Pedro, Merced River at Lake McClure, and San Joaquin River at Millerton Lake) were selected for future hydrologic analysis. The sum of runoff from these four watersheds was used to represent the overall wetness of the region in practice.

The mean elevation of the four San Joaquin River watersheds is 2,345 meters with an average total annual runoff of 5.75 MAF. Runoff from the San Joaquin River watersheds is dominated by snowmelt, due to the relatively high watershed elevations (in comparison to their Sacramento River watershed counterparts further north). Snowmelt runoff, which is typically represented by runoff during the snowmelt season from April to July, accounts for two-thirds of the annual total runoff for San Joaquin Valley’s four rivers.

California’s Fourth Climate Change Assessment selected four GCMs for use in this analysis. These included a “cool/wet” model CNRM-CM5; an “average” model CanESM2; a “warm/dry” model HadGEM2-ES; and a “complement” model MIROC5 that “is most unlike the first three models for the best coverage of different possibilities.” These were selected after a prioritization process that originally identified 32 GCMs that participated in the CMIP5 under two emission scenarios: Representative Concentration Pathways (RCP) 4.5 (lower emission scenario) and RCP 8.5 (high emission scenario). Details on the applied bias correction methods, study variables, and index metrics are not replicated here and can be found in the DWR study.60
From Figure 6-1, it is evident that total annual runoff is projected to increase across nearly all of the exceedance probabilities via the “cool/wet” model (CNRM-CM5) and the “average” model (CanESM2) (Figure 6-1a). The increases are generally larger for higher flows with lower exceedance probabilities.

The “complement” model (MIROC5) and “warm/dry” model (HadGEM2-ES) projected similar annual runoff to the historical baseline.

The San Joaquin River region is expected to experience larger volumes of October-March runoff than the baseline in all of the projections (Figure 6-1b). The increases are larger for runoff volumes with lower exceedance probability, however, not all four models project decreases in the April-July runoff (Figure 6-1c). The “cool/wet” model projects increases under both of the emission scenarios for the San Joaquin River region. Finally, under the higher emission scenario, the “cool/wet” model projects higher OctoberMarch runoff and lower April-July runoff, while the “average” model predicts higher runoff across all three timescales.
60 He, M., Anderson, J., Lynn, E. and W. Arnold (2021) in Climate, “Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century,” 9(2), 26 https://doi.org/10.3390/cli9020026.

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Figure 6-1: Simulated Future San Joaquin Watersheds – Runoff Exceedance Probabilities for the October-March and April-July Periods
Source: Figure 3 from He, M., Anderson, J., Lynn, E. and W. Arnold (2021) in Climate, “Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century,” 9(2), 26, https://doi.org/10.3390/cli9020026.

As shown in Table 6-1, October-March precipitation is projected to increase in most models, with greater increases expected under the higher (versus lower) emission scenario. The compound effect of atmospheric warming, together with increases in precipitation, is to increase runoff during the OctoberMarch period, particularly under the higher emission scenario.

Model/Scenario Representative
Concentration
Pathways (RCP)
October-March
(mm)
April-July
(mm)
Total WY
(mm)
GCMs Historical 869 166 1,060
MIROC5
(compliment)
RCP 4.5 838 130 998
RCP 8.5 839 126 990
CNRM-CM5
(cool/wet)
RCP 4.5 1,127 151 1,317
RCP 8.5 1,138 149 1,325
CanESM2 (average) RCP 4.5 1,016 145 1,211
RCP 8.5 1,157 142 1,364
HadGEM2-ES
(warm/dry)
RCP 4.5 876 137 1,048
RCP 8.5 879 142 1,054
Table 6-1: Historical (1920–1999) and Future Simulated (2020–2099) Precipitation at Seasonal and Total WY
Source: Recreated from Table 2. The mean of historical (1920–1999) and projected (2020–2099) precipitation and temperature data at annual and seasonal scales from He, M., Anderson, J., Lynn, E. and W. Arnold (2021) in Climate, “Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century,” 9(2), 26 https://doi.org/10.3390/cli9020026.

April-July runoff largely comes from snowmelt, as April 1st is typically deemed as the date when the snowpack is at its maximum. The projected warming in the wet season will likely lead to earlier snowpack maximums and melting, resulting in a smaller-than-usual snowpack on April 1st and, thus, less April-July runoff. This is particularly the case under the higher (versus lower) emission scenario where higher a b c
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warming is assumed. The April-July precipitation also contributes to runoff during this period. On average, all four GCMs project non-stationary decreases in the April-July precipitation under both emission scenarios.

From a practical standpoint, the findings of this study can inform decision-makers in long-term water resources planning strategies, some of which may not have previously received much attention. For example, study results indicate that wet season runoff is projected to increase in the San Joaquin River region in each of the four representative models used, but that this runoff would skew to the OctoberMarch period. This indicates greater (than the historical) flooding risk during a period where flood control is already an operational priority throughout the San Joaquin River valley and source area catchments in the Sierra Nevada. In light of this increased flooding risk, it appears imperative that water managers increase the resilience of the current water system to large, rapidly developing floods, in some cases, larger and more quickly forming than ever before to deal with this potential excess surge in floodwater.

An option to mitigate this increase in flood water is to divert it for recharge to groundwater. The potential benefits of groundwater recharge have already been discussed and include flood risk reduction, land subsidence mitigation, ecosystem enhancement, and drought preparedness, among others. Another option, one that has received little interest despite its hydrologic advantages, is to divert excess flood water to retention basins as managed storm- and floodwater storage for later consumptive use. This is detailed in Section 4.4.

A recent study of San Joaquin River valley watersheds demonstrated that the flow regimes downstream of hydropower facilities were likely to be increasingly altered by reservoir operations rather than by climate change. The observation of stepped and wider flow duration curves indicated an intermittent flow variation more conducive to managed reservoir operations.61 In the complex hydro-water supply operations that define Tri-Dams, New Melones, Goodwin and Stanislaus River operations, such future alterations in baseline hydrology have particular relevance to SSJID and each of its retail customers like the City.

A common theme among these various studies is the extent of uncertainties associated with the various assumptions for climate change models used in the analyses. Such uncertainty can impart considerable influence on simulated changes in WY classification and hydrological droughts.

6.1.2 Hydroclimatic Uncertainties
Reviewing a range of hydroclimatic models with varying conditions and assumptions helps in understanding the possible effects of climate change on our water supply. The importance of selecting the appropriate climate models that represent state-of-the-art climate science in this type of analysis cannot be overstated. Models are continually being improved; the DWR study discussed in the previous section utilized four priority climate models that were recommended in California’s Fourth Climate Change Assessment, which was based on CMIP562 projections. While next generation CMIP663 projections are now available at increasingly improved spatial scales, their use is largely limited to the research 61 Maskey, M.L., Facincani Dourado, G., Rallings, A.M., Rheinheimer, D.E., Medellin-Azuara, J. and J.H. Viers (2022) in Front.

Environ. Sci., “Assessing Hydrological Alteration Caused by Climate Change and Reservoir Operations in the San Joaquin River Basin, California” https://doi.org/10.3389/fenvs.2022.765426. 62 Lawrence Livermore National Laboratory, Coupled Model Intercomparison Project Phase 5, https://pcmdi.llnl.gov/mips/cmip5/. 63 Lawrence Livermore National Laboratory, Coupled Model Intercomparison Project Phase 6, https://pcmdi.llnl.gov/CMIP6/.

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community. California’s next (fifth) climate change assessment is in its scoping phase and is expected to downscale and tailor CMIP6 projections for planning and management practices across the State.

Precipitation. While air temperature and other climatic variables at many scales drive the generation of precipitation and are important considerations in overall climate change investigation, for practical water resource management planners and water purveyors, precipitation is the key metric of concern.

One of the most challenging aspects of precipitation is accurately defining its inherent variability. This challenge makes it extremely difficult for water planners to discern what observable changes in trends are the result of climatic volatility brought about by contemporary climate change or are embedded as part of natural variability. The current efforts at attribution science, for example, where actuaries attempt to assign a numerical percentage to specific causation often result in highly questionable results.

A recent study incorporated the role of sea level pressure in critical oceanic regions on California winter precipitation in observations and CMIP6 simulations. It showed projected wetter end-of-century northern and central-southern California regions (mean precipitation increased by 20% and 25%, respectively) with much lower uncertainty ranges. Results confirmed increased precipitation at the end of 21st century compared to precipitation observations of recent decades. This study estimated precipitation could increase by as much as 1.5 to 6.8 inches over central-southern California by the end of the century compared with present-day. They go on to state that up to 71% of their modeling projection uncertainties were reduced mainly due to the strong and consistent causal relationship between North American west coast sea level pressure and California precipitation in both observations and CMIP6 models.64 While such CMIP6-based investigations were presenting these rather precise and large estimates, the San Joaquin Region Report of California’s Fourth Climate Change Assessment, 2018, showed a maximum change in average annual future precipitation of less than 0.5 inches for either Stanislaus or San Joaquin counties from now until the end of the century.65 Accepting the significantly drier climate of San Joaquin County compared to many parts of southern California, this discussion is meant to show the high degree of uncertainty and variability that exists in hydroclimatic projections.

In another recent study in the southwestern U.S. using moisture budget analysis, results projected a decrease in spring precipitation but an increase in summer precipitation under a warming climate. The investigators noted that the spring dry period is caused by enhanced zonal drying advection and that, in contrast to the spring, the moisture gradient change and the wind convergence change both act to actually increase precipitation in summer.66
These types of variations and differences in study results are not uncommon. This reflects the complexity of modeling methodologies and reinforces the importance and influence of choosing between a wide range of simulation assumptions.
64 Li, F., Zhu, Q., Riley, W.J., Yuan, K. Wu, H. and Z. Gui (2022) “Wetter California projected by CMIP6 models with observational constraints under a high GHG emission scenario”, Earth’s Future, https://doi.org/10.1029/2022EF002694. 65 San Joaquin Region Report, California’s Fourth Climate Change Assessment, Table 5, page 23, 2018. 66 See W. Liang and M. Zhang (2022) “Increasing future precipitation in the southwestern US in the summer and its contrasting mechanism with decreasing precipitation in the spring” Geophysical Research Letters, https://doi.org/10.1029/2021GL096283.

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