Manteca City Council
July 19, 2022

California Department of Water Resources
Sustainable Groundwater Management Office Page 2 of 2
determination. A determination of incomplete would allow the GSAs to formally address identified deficiencies and submit a revised GSP to the Department for further review and evaluation. Department staff will contact you before making the final determination to discuss the potential deficiencies and the amount of time needed by the GSAs to address the potential corrective actions detailed in the enclosed document.

Materials submitted to the Department to address deficiencies must be part of the GSP.

The GSAs must justify that any materials submitted are part of the revised GSP; this justification is also part of the submittal. To facilitate the Department’s review of the revised GSP, the GSAs should also provide a companion document with tracked changes of modifications made to address deficiencies. The GSAs must submit the revised GSP through the DWR SGMA Portal where, as is currently available, interested parties may provide comments on submitted materials to the Department.

Department staff will work expeditiously to review materials submitted to address deficiencies and to evaluate compliance of the revised GSP. The Department will keep a GSP status designated as incomplete during its review of the submitted materials. The Department could subsequently approve an incomplete GSP if the GSAs have taken corrective actions to address deficiencies identified by the Department within a period not to exceed 180 days from the determination. The Department could also issue a determination of inadequate for an incomplete GSP if the Department, after consultation with the State Water Resources Control Board, determines the GSAs have not taken sufficient actions to correct the deficiencies identified by the Department.

If you have any questions, please do not hesitate to contact the Sustainable Groundwater Management Office staff by emailing [email protected].

Thank you,
Paul Gosselin
Deputy Director for Sustainable Groundwater Management
Enclosure:

1. Potential Deficiencies and Corrective Actions
DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B 2020 Groundwater Sustainability Plan
Eastern San Joaquin Subbasin (Basin No. 5-022.01)
California Department of Water Resources
Sustainable Groundwater Management Office Page 1 of 10
Potential Deficiencies and Corrective Actions
Department of Water Resources (Department) staff have identified deficiencies regarding the Eastern San Joaquin Subbasin (Subbasin) Groundwater Sustainability Plan (GSP) that may preclude the Department’s approval. Therefore, consistent with the GSP Regulations, Department staff are considering corrective actions the Subbasin’s groundwater sustainability agencies (GSAs) should review to determine whether and how the deficiencies can be addressed. The deficiencies and potential corrective actions are explained below, including the general regulatory background, the specific deficiencies identified in the GSP, and specific actions to address the deficiencies. The specific actions identified are potential corrective actions until the Department makes a final determination.

General Background
Potential deficiencies identified in the Eastern San Joaquin Subbasin GSP relate to the development and documentation of sustainable management criteria, including undesirable results and minimum thresholds that define when undesirable results may occur.

The Department's GSP Regulations describe several required elements of a GSP under the heading of “Sustainable Management Criteria”6, including undesirable results, minimum thresholds, and measurable objectives. These components of sustainable management criteria must be quantified so that GSAs, the Department, and other interested parties can monitor progress towards sustainability in a basin consistently and objectively.

A GSA relies on local experience, public outreach and involvement, and information about the basin it has described in the GSP basin setting (i.e., the hydrogeologic conceptual model, the description of current and historical groundwater conditions, and the water budget), among other factors, to develop criteria for defining undesirable results and setting minimum thresholds and measurable objectives.7
The Sustainable Groundwater Management Act (SGMA) defines sustainable groundwater management as the management and use of groundwater in a manner that can be maintained during the planning and implementation horizon without causing undesirable results.8 Avoidance of undesirable results is thus explicitly part of sustainable groundwater management as established by SGMA and critical to the success of a GSP.

The definition of undesirable results is critical to establishing an objective method to define and measure sustainability for a basin. As an initial matter, SGMA provides a 6 23 CCR § Article 5, Subarticle 3. 7 23 CCR §§ 354.8, 354.10, 354.12 et seq. 8 Water Code § 10721(v).

DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B Attachment 1
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Sustainable Groundwater Management Office Page 2 of 10
qualitative definition of undesirable results as “one or more” of six specific “effects caused by groundwater conditions occurring throughout the basin.”9 GSAs define, in their GSPs, the specific significant and unreasonable effects that would constitute undesirable results and the groundwater conditions that would produce those results in their basins.10 The GSAs’ definition must include a description of the processes and criteria relied upon to define undesirable results and describe the effect of undesirable results on the beneficial uses and users of groundwater, surface land uses (for subsidence), and surface water (for interconnected surface water).11 SGMA leaves the task of establishing undesirable results and setting thresholds largely to the discretion of the GSAs, subject to review by the Department. In its review, the Department requires a thorough and reasonable analysis of the groundwater conditions and the associated effects the GSAs must manage the groundwater basin to avoid, and the GSAs’ stated rationale for setting objective and quantitative sustainable management criteria to prevent those undesirable conditions from occurring.12 If a GSP does not meet this requirement, the Department cannot evaluate the GSAs’ likelihood of achieving their sustainability goal. That does not necessarily mean that the GSP or its objectives are inherently unreasonable; rather, the Department cannot evaluate whether the GSP's implementation would successfully achieve sustainable management if it is unclear what undesirable conditions the GSAs seek to avoid.

Potential Deficiency 1. The GSP lacks sufficient justification for identifying that undesirable results for chronic lowering of groundwater levels, subsidence, and depletion of interconnected surface waters can only occur in consecutive non-dry water year types. The GSP also lacks sufficient explanation for its chronic lowering of groundwater levels minimum thresholds and undesirable results.

The first potential deficiency relates to the GSP’s requirement of two consecutive non-dry (i.e., below normal, above normal, or wet) water-year types and the exclusion of dry and critically dry water-year types in the identification of undesirable results for chronic lowering of groundwater levels, and, by proxy, land subsidence and depletions of interconnected surface water.

Background
Related to this potential deficiency, SGMA defines the term “Undesirable Result,” in part, as one or more of the following effects caused by groundwater conditions occurring throughout the basin:13
9 Water Code § 10721(x). 10 California Department of Water Resources, Best Management Practices for the Sustainable Management of Groundwater: Sustainable Management Criteria (Draft), November 2017. 11 23 CCR §§ 354.26(b), 354.28(c)(5), 354.28(c)(6).
12 23 CCR § 355.4(b)(1).
13 Water Code § 10721(x).

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• Chronic lowering of groundwater levels indicating a significant and unreasonable depletion of supply if continued over the planning and implementation horizon.

Overdraft during a period of drought is not sufficient to establish a chronic lowering of groundwater levels if extractions and groundwater recharge are managed as necessary to ensure that reductions in groundwater levels or storage during a period of drought are offset by increases in groundwater levels or storage during other periods.
• Significant and unreasonable land subsidence that substantially interferes with surface land uses.
• Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.

Potential Deficiency Details
Department staff identified two areas of concern, described below, which, if not addressed, may preclude approval of the GSP. Regarding the first area of concern, the GSP identifies that an undesirable result occurs “when at least 25 percent of representative monitoring wells used to monitor groundwater levels (5 of 20 wells in the Subbasin) fall below their minimum level thresholds for two consecutive years that are categorized as non-dry years (below-normal, above-normal, or wet), according to the San Joaquin Valley Water Year Hydrologic Classification.” The GSP further states that “the lowering of groundwater levels during consecutive dry or critically-dry years is not considered to be unreasonable, and would therefore not be considered an undesirable result, unless the levels do not rebound to above the thresholds following those consecutive non-dry years.”14
Department staff find that the water-year type requirement in the definition of the undesirable result for chronic lowering of groundwater levels (i.e., two consecutive nondry years) is not consistent with the intent of SGMA. The water-year type requirement could potentially allow for unmanaged and continued lowering of groundwater levels under certain hydrologic or climatic conditions that have occurred historically. A review of historical San Joaquin Valley water-year type classifications15 indicates the potential for dry periods without the occurrence of a second consecutive non-dry year to persist for greater than ten years (see, e.g., the 11 years from water years 1985 through 1995).

Department staff also note that concurrent below normal, above normal, or wet years occurred in only five of the last twenty water years from 2001 through 2020. Because of this definition, GSAs in the Subbasin could disregard potential impacts of groundwater level declines below the minimum thresholds during extended periods of dry years, even if interrupted by normal or wet years.
14 ESJ GSP, p. 253. 15 Chronological Reconstructed Sacramento and San Joaquin Valley Water Year Hydrologic Classification Indices, Water Year 1901 through 2020. California Department of Water Resources, https://cdec.water.ca.gov/reportapp/javareports?name=WSIHIST.

DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B

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Department staff also find this methodology inconsistent with other portions of the GSP.

For example, while describing measurable objectives for groundwater levels, the GSP states, “the margin of operational flexibility is intended to accommodate droughts, climate change, conjunctive use operations, or other groundwater management activities. The margin of operational flexibility is defined as the difference between the minimum threshold and the measurable objective.”16 Based on these statements, it appears the minimum thresholds already accommodate drought conditions, so it is unclear why the GSP's definition of undesirable results further excludes minimum threshold exceedances during dry water years. (See Potential Corrective Action 1a.) SGMA states that “overdraft during a period of drought is not sufficient to establish a chronic lowering of groundwater levels if extractions and groundwater recharge are managed as necessary to ensure that reductions in groundwater levels or storage during a period of drought are offset by increases in groundwater levels or storage during other periods.”17 If the GSAs intended to incorporate this concept into their definition of the undesirable result for chronic lowering of groundwater levels, the GSP fails to identify specific extraction and groundwater recharge management actions the GSAs would implement18 or otherwise describe how the Subbasin would be managed to offset, by increases in groundwater levels or storage during other periods, dry year reductions of groundwater storage. The GSP identifies many projects that, once implemented, may lead to the elimination of long-term overdraft conditions in the Subbasin. However, the GSP does not sufficiently detail how projects and management actions, in conjunction with the proposed chronic lowering of groundwater levels sustainable management criteria, will offset drought-related groundwater reductions and avoid significant and unreasonable impacts when groundwater level minimum thresholds are potentially exceeded for an extended period in the absence of two consecutive non-dry years. (See Potential Corrective Action 1b.)
As noted above, the GSP states that minimum thresholds developed for chronic lowering of groundwater levels serve as proxies for subsidence19 and depletion of interconnected surface waters.
20 Therefore, Department staff assume the GSAs intend to apply the same water-year type criteria to undesirable results for those sustainability indicators (i.e., land subsidence or depletion of interconnected surface water undesirable results do not occur until groundwater levels exceed the thresholds for two consecutive non-dry water years).

However, where SGMA acknowledges that groundwater level declines during drought periods are not sufficient to cause an undesirable result for chronic lowering of groundwater levels, the statute does not similarly provide an exception for subsidence or stream depletion during periods of drought. (See Potential Corrective Action 1c.) 16 ESJ GSP, p. 259. 17 Water Code § 10721(x)(1). 18 23 CCR § 354.44(b)(9). 19 ESJ GSP, p. 270. 20 ESJ GSP, p. 271.

DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B

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1.4 Attachment 1
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Sustainable Groundwater Management Office Page 5 of 10
Department staff's second area of concern is the GSP's evaluation of the effects of the proposed minimum thresholds and undesirable results on beneficial uses and users of groundwater. The GSP identifies that the chronic lowering of groundwater levels could cause undesirable results from wells going dry, reductions in pumping capacities, increased pumping costs, the need for deeper well installations or lowering of pumps, and adverse impacts to environmental uses and users.21 The GSP builds an analysis of domestic wells going dry into its minimum thresholds, thereby considering the factors of wells going dry and the need for deeper well installations. However, it does not address how the management criteria address the other factors identified by the GSAs as potential undesirable results, including reductions in pumping capacity or increased pumping costs for shallow groundwater users, or adverse impacts to environmental uses and users.

The GSAs set minimum thresholds in the Subbasin at the shallower of the 10th percentile domestic [or municipal] well depth or the historical low groundwater levels with a subtracted buffer value, which the GSP states allows for operational flexibility. 22 These
minimum threshold values generally allow groundwater levels to decline below historic lows; minimum thresholds defined using the buffer value approach allow twice the historical drawdown from the shallowest recorded groundwater levels. 23 Aside from the
GSP's domestic well analysis, the only description of how minimum thresholds were evaluated to avoid undesirable results appears to be the statements that “for the majority of the Subbasin, GSA representatives identified no undesirable results, even if groundwater were to reach historical low groundwater levels” and that no GSA indicated undesirable results would occur “if the minimum threshold was set deeper than the [historic low] based on their understanding.”24 The GSP provides no further explanation or description of how the individual GSAs concluded that there would be no undesirable results based on the minimum thresholds.

The GSP only considers an undesirable result to occur for groundwater levels in the Subbasin when at least 25 percent of representative monitoring wells (5 of 20 wells) fall below their minimum threshold value for two consecutive non-dry water years.25 The GSP does not justify or discuss how the GSAs developed the 25 percent threshold, nor does it explain or disclose the potential impacts anticipated during extended drier climate conditions using this threshold. In other words, the proposed management program may lead to potential effects on domestic wells or other beneficial uses and users during prolonged dry- or below-normal periods, and that information should, at a minimum, be disclosed and considered in the GSP. (See Potential Corrective Action 1d.) If, after considering this potential deficiency, the GSAs retain minimum thresholds that allow for continued lowering of groundwater levels, it is reasonable to assume that some 21 ESJ GSP, p. 253. 22 ESJ GSP, p. 254.
23 ESJ GSP, p. 258.
24 ESJ GSP, p. 255. 25 ESJ GSP, p. 253.

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groundwater well impacts (e.g., loss of production capacity) will occur during the implementation of the GSP. SGMA requires GSAs to consider the interests of all groundwater uses and users and to implement their GSPs to mitigate overdraft conditions.
26 Implementing specific projects and management actions prevents undesirable results and achieves the sustainable yield of the basin. The GSAs should describe how projects and management actions would address drinking water impacts due to continued overdraft between the start of GSP implementation and the achievement of the sustainability goal. If the GSP does not include projects or management actions to address drinking water impacts, the GSP should contain a thorough discussion, with supporting facts and rationale, explaining how and why GSAs determined not to include actions to address those impacts from continued groundwater lowering below pre-SGMA levels. (See Potential Corrective Action 1e.)
Additionally, related to the groundwater level declines allowed for by the GSA’s minimum thresholds, the GSAs have not explained how those groundwater level declines relate to the degradation of groundwater quality sustainability indicator. GSAs must describe, among other items, the relationship between minimum thresholds for a given sustainability indicator (in this case, chronic lowering of groundwater levels) and the other sustainability indicators.27 The GSAs generally commit to monitoring a wide range of water quality constituents but they have only developed sustainable management criteria for total dissolved solids because they state they have not observed a causal nexus between groundwater management and degradation associated with the other constituents. While Department staff are not aware of evidence sufficient to conclude that the GSAs acted unreasonably by focusing on total dissolved solids, it is clear that the GSAs did not consider, or at least did not document, the potential for degradation to occur due to further lowering of groundwater levels beyond the historic lows. (See Potential Corrective Action 1f.)
Potential Corrective Action 1
a) Department staff believe the management approach described in the GSP, which couples minimum thresholds and measurable objectives that account for operational flexibility during dry periods with a definition of undesirable results that disregards minimum threshold exceedances in all years except consecutive below normal, above normal, or wet years, to be inconsistent with the objectives of SGMA. Therefore, the GSAs should remove the water-year type requirement from the GSP’s undesirable result definition.
b) The GSP should be revised to include specific projects and management actions the GSAs would implement to offset drought-year groundwater level declines. c) The GSAs should thoroughly explain how their approach avoids undesirable results for subsidence and depletion of interconnected surface waters, as SGMA does not 26 23 CCR § 355.4(b)(4), 355.4(b)(6).
27 23 CCR § 354.28(b)(2).

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include an allowance or exemption for those conditions to continue in periods of drought.
d) Removing the water-year type requirement from the definition of an undesirable result (item a, above) would result in a GSP with groundwater level minimum thresholds designed to be generally protective of 90 percent of domestic wells regardless of regional hydrologic conditions. In that scenario, the GSAs should explain the rationale for determining that groundwater levels can exceed those thresholds at 25 percent of monitoring sites for two consecutive years before the effects would be considered significant and unreasonable. The GSAs should also explain how other factors they identified as "potential undesirable results" (e.g., adverse impacts to environmental uses and users) factored into selecting minimum thresholds and describe anticipated effects of the thresholds on beneficial uses and users of groundwater. Furthermore, the GSAs should explain whether other drinking water users that may rely on shallow wells, such as public water systems and state small water systems, were considered in the GSAs’ site-specific thresholds. If not, the GSAs should conduct outreach with those users and incorporate their shallow wells, as applicable, into the site-specific minimum thresholds and measurable objectives.
e) The GSAs should revise the GSP to describe how they would address drinking water impacts caused by continued overdraft during the period between the start of GSP implementation and achieving the sustainability goal. If the GSP does not include projects or management actions to address those impacts, the GSP should contain a thorough discussion, with supporting facts and rationale, explaining how and why the GSAs determined not to include specific actions to address drinking water impacts from continued groundwater lowering below pre-SGMA levels. f) The GSP should be revised to explain how the GSAs will assess groundwater quality degradation in areas where further groundwater level decline, below historic lows, is allowed via the minimum thresholds. The GSAs should further describe how they will coordinate with the appropriate groundwater users, including drinking water, environmental, and irrigation users as identified in the GSP. The GSAs should also discuss efforts to coordinate with water quality regulatory agencies and programs in the Subbasin to understand and develop a process for determining if continued lowering of groundwater levels is resulting in degraded water quality in the Subbasin during GSP implementation.

DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B Attachment 1
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California Department of Water Resources
Sustainable Groundwater Management Office Page 8 of 10
Potential Deficiency 2. The GSP does not provide enough information to support the use of the chronic lowering of groundwater level sustainable management criteria and representative monitoring network as a proxy for land subsidence.

Background
The GSP Regulations state that minimum thresholds for land subsidence should identify the rate and extent of subsidence that substantially interferes with surface land uses and may lead to undesirable results. These quantitative values should be supported by: 28 • The identification of land uses or property interests potentially affected by land subsidence;
• An explanation of how impacts to those land uses or property interests were considered when establishing minimum thresholds;
• Maps or graphs showing the rates and extents of land subsidence defined by the minimum thresholds.

The GSP Regulations allow the use of groundwater elevations as a proxy for land subsidence. However, GSAs must demonstrate a significant correlation between groundwater levels and land subsidence and must demonstrate that groundwater level minimum thresholds represent a reasonable proxy for avoiding land subsidence undesirable results. Additionally, the GSAs must demonstrate how the monitoring network is adequate to identify undesirable results for both metrics.

Potential Deficiency Details
Department staff find that the GSP does not adequately identify or define minimum thresholds and undesirable results for land subsidence. The GSP also does not provide adequate justification and explanation for using the groundwater level minimum thresholds and representative monitoring network as a proxy for land subsidence.

Generally, the GSP identifies that irrecoverable loss of groundwater storage and damage to infrastructure, including water conveyance facilities and flood control facilities, are potential impacts of land subsidence.
29 However, the GSP does not identify specific
infrastructure locations, particularly those associated with public safety, in the Subbasin and the rate and extent of subsidence that would substantially interfere with those land surface uses and may lead to undesirable results. Additionally, without identifying infrastructure considered at risk for interference from land subsidence, Department staff cannot evaluate whether the groundwater level representative monitoring network is adequate to detect potential subsidence-related impacts.

Department staff find the GSP does not provide adequate evidence to demonstrate a significant correlation between groundwater levels and land subsidence in the Subbasin. 28 23 CCR § 354.28(c)(5). 29 ESJ GSP, p. 269.

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Without explaining this correlation, the Department cannot evaluate whether the groundwater level minimum thresholds and associated conditions required for identifying an undesirable result would protect against significant and unreasonable impacts related to land subsidence. The GSP states a significant correlation exists between groundwater levels and land subsidence, with lowering groundwater levels driving further land subsidence.30 Department staff agree with this general statement. However, the GSP fails to provide adequate evidence to evaluate further this correlation, specifically concerning potential subsidence caused by groundwater levels falling below historic lows, as would be allowed by the groundwater level minimum thresholds set in the GSP.

The GSP's justification for using the proposed groundwater level minimum thresholds as a proxy for land subsidence appears to rely mainly on an incomplete analysis and a data set with significant data gaps. The GSP states there are no historical records of significant and unreasonable land subsidence in the Subbasin.
31 The GSP also states that there is
a lack of direct land subsidence monitoring in the Subbasin.32 The GSP uses this absence of historical records to assert that historically dewatered geologic units are not compressible and, therefore, not at risk for land subsidence. Although groundwater level minimum thresholds are below historic lows, the GSP states that the GSAs do not expect further declines in groundwater levels to dewater materials deeper than 205 feet below ground surface (the deepest groundwater level minimum threshold value in the Subbasin).
33 The GSP states that subsurface materials encountered up to this depth are the same [non-compressible] geologic units that have been historically dewatered.

Department staff find multiple aspects of this justification speculative and not supported by the best available science. First, the GSP presents no analysis of historic groundwater levels or historically dewatered subsurface materials to support the conclusion that the geologic units are not compressible. Second, the GSP does not provide an evaluation showing how additional declines in groundwater levels would only affect subsurface materials similar to those which have been historically dewatered. Third, the GSP is unclear on whether the conditions required to identify an undesirable result for chronic lowering of groundwater levels in the Subbasin are also required to identify an undesirable result for land subsidence. Management proposed in the GSP could allow groundwater level minimum thresholds to be exceeded in periods where two consecutive non-dry years do not occur, which does not support the claim that only materials up to the deepest groundwater level minimum threshold (205 feet below ground surface) will be dewatered.

Department staff note that the legislature intended that implementation of SGMA would avoid or minimize subsidence34 once GSAs achieve the sustainability goal for a basin.

Without analysis examining how allowable groundwater levels below those historically 30 ESJ GSP, p. 270. 31 ESJ GSP, p. 269. 32 ESJ GSP, p. 270. 33 ESJ GSP, p. 270. 34 Water Code § 10720.1(e).

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Potential Corrective Action 2
The GSAs must provide detailed information to demonstrate how the use of the chronic lowering of groundwater level minimum thresholds are sufficient as a proxy to detect and avoid significant and unreasonable land subsidence that substantially interferes with surface land uses. Alternatively, the GSAs could commit to utilizing direct monitoring for subsidence, e.g., with remotely sensed subsidence data provided by the Department. In that case, the GSAs should develop sustainable management criteria based on rates and extents of subsidence. Department staff suggest the GSAs consider and address the following issues:

1. The GSAs should revise the GSP to identify the total subsidence that critical infrastructure in the Subbasin can tolerate during GSP implementation. Support this identification with information on the effects of subsidence on land surface beneficial uses and users and the amount of subsidence that would substantially interfere with those uses and users.

2. The GSAs should revise the GSP to document a significant correlation between groundwater levels and specific amounts or rates of land subsidence. The analysis should account for potential subsidence related to groundwater level declines below historical lows and further declines that are allowed to exceed minimum thresholds (i.e., during non-consecutive non-dry years, if applicable based on the resolution to Potential Deficiency 1, above). This analysis should demonstrate that groundwater level declines allowed during GSP implementation are preventative of the rates and magnitudes of land subsidence considered significant and unreasonable based on the identified infrastructure of concern. If there is not sufficient data to establish a correlation, the GSAs should consider other options such as direct monitoring of land subsidence (e.g., remotely sensed data provided by the Department, extensometers, or GPS stations) until such time that the GSAs can establish a correlation.

3. The GSAs should explain how the groundwater level representative monitoring network is sufficient to detect significant and unreasonable subsidence that may substantially interfere with land uses, specifically any identified infrastructure of concern. If the groundwater level monitoring network alone is not adequate, based on specific infrastructure locations, Department staff suggest incorporating continued analysis of available InSAR data to cover areas with data gaps.

DocuSign Envelope ID: 90098AF4-85B5-4D3D-9995-AF15E867F30B Eastern San Joaquin Groundwater Authority 1 Woodard & Curran, Inc.

TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 TECHNICAL MEMORANDUM NO. 3 - Groundwater Quality
Degradation in Areas where further Groundwater Level Decline is Allowed
TO: Paul Gosselin, California Department of Water Resources Deputy Director CC: Kris Balaji, on behalf of the Eastern San Joaquin Groundwater Authority PREPARED BY: Matt Zidar, San Joaquin County Public Works, Water Resources Division Leslie Dumas and Natalie Cochran/Woodard & Curran
DATE: June 24, 2022
RE: Eastern San Joaquin Groundwater Authority Response to DWR’s November 18, 2021 Consultation Initiation Letter - Response to DWR Deficiency 1(f) and Corrective Actions

The Eastern San Joaquin Groundwater Authority (ESJGWA) received a Consultation Initiation Letter (Letter) on November 18, 2021 (Attachment 1), from the California Department of Water Resources (DWR). The Letter identified two potential deficiencies with the Eastern San Joaquin Groundwater Subbasin (Subbasin) Groundwater Sustainability Plan (GSP) which may preclude DWR’s approval, as well as potential corrective actions to address each potential deficiency. The Letter thus initiated consultation between DWR, the Plan Manager, and the Subbasin’s groundwater sustainability agencies (GSAs) regarding the amount of time needed to address the potential deficiencies and corrective actions. A subsequent meeting with DWR was held on April 4, 2022 to discuss the Subbasin’s proposed approach to addressing the identified deficiencies.

The analysis presented in this memorandum was completed in response to the Letter, based on direction provided by the ESJGWA, the Subbasin GSAs and DWR. It is intended to supplement the Eastern San Joaquin GSP that was submitted in January 2020 and fill potential gaps identified in the Letter provided by DWR.

Deficiency 1, as described in the DWR November 18, 2021 letter, is summarized as follows:

Potential Deficiency 1: The GSP lacks sufficient justification for determining that undesirable results for chronic lowering of groundwater levels, subsidence, and depletion of interconnected surface waters can only occur in consecutive non-dry water year types. The GSP also lacks sufficient explanation for its minimum thresholds and undesirable results for chronic lowering of groundwater levels.

The letter then went on to identify six potential corrective actions that could address this deficiency. This Technical Memorandum (TM) was prepared to address the deficiency as described in Potential Correction Actions 1(f), which states the following:
“1(f) The GSP should be revised to explain how the GSAs will assess groundwater quality degradation in areas where further groundwater level decline, below historic lows, is allowed via the minimum thresholds. The GSAs should further describe how they will coordinate with the appropriate groundwater users, including drinking water, environmental, and irrigation users as identified in the GSP. The GSAs should also discuss efforts to coordinate with water quality regulatory agencies and Eastern San Joaquin Groundwater Authority 2 Woodard & Curran, Inc.

TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 programs in the Subbasin to understand and develop a process for determining if continued lowering of groundwater levels is resulting in degraded water quality in the Subbasin during GSP implementation.”
The following subsections provide a response to each of the Potential Corrective Action 1(f) subparts listed above, and include a discussion with supplemental information, analysis, justification, and data needed to support the GSP and to address each issue identified.

Potential Corrective Action 1(f)-1: Explain how the GSAs will assess groundwater quality degradation in areas where further groundwater level decline, below historic lows, is allowed via the minimum thresholds.

Initial Review Provided by DWR
The Letter states the GSAs “…have not explained how those groundwater level declines [allowed for by the GSP’s minimum thresholds] relate to the degradation of groundwater quality sustainability indicator. GSAs must describe, among other items, the relationship between minimum thresholds for a given sustainability indicator (in this case, chronic lowering of groundwater levels) and the other sustainability indicators.”
As a Potential Corrective Action, the following is suggested: “Explain how the GSAs will assess groundwater quality degradation in areas where further groundwater level decline, below historic lows, is allowed via the minimum thresholds.”
Proposed Supplemental Information in Response to DWR Letter Explanation of Groundwater Level Declines and Degradation of Water Quality The only clear correlation between groundwater levels and water quality impairment from constituents of concern are related to the regional migration of poor-quality water from under the Delta to the groundwater pumping trough that is east of the City of Stockton. A gradient from the Delta toward the east causes the migration of poor-quality water into the Subbasin’s principal aquifers which can be exacerbated by increased pumping east of the Delta. U.S. Geologic Survey (USGS) data and prior studies suggest that high chloride groundwater is the result of the eastern movement of brackish San Joaquin Delta water and the upward movement of saline water associated with older marine deposits underlying freshwater aquifer units (Izbicki, 2006). Chloride and total dissolved solids (TDS) have been the indicator constituents for this potential degradation mechanism.

Other than for the movement of poor-quality saline groundwater from the Delta eastward as a result changes in groundwater gradients (whether occurring naturally, induced by groundwater pumping, and/or as a result of some other hydrologically-related parameter), there is no simple correlation between groundwater levels and groundwater quality (as characterized by a large number of naturally-occurring constituents such as manganese, arsenic, boron, and manmade constituents such as 1,2,3-TCP and PFOS.

Numerical modeling is one method of evaluating the hydraulic conditions which could cause migration and mixing of poor-quality water and the resultant degradation in groundwater quality; however, with the exception of simulating project-specific impacts, simulating long-term basin management would be difficult Eastern San Joaquin Groundwater Authority 3 Woodard & Curran, Inc.

TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 and speculative given the large number of potential constituents of concern and possible sources of those constituents.

This potential for regional migration of saline waters was one of the reasons for developing prior groundwater management plans and the Integrated Conjunctive Use Program, and for implementing related Project Management Actions (PMAs) over the past 20 years. Projects implemented to date include projects to reduce groundwater pumping by providing treated surface water in-lieu of groundwater use, such as the City of Stockton’s Delta Diversion Project, which diverts Delta water for treatment and distribution in lieu of groundwater supplies. The Stockton East Water District (SEWD) Dr. Joe Waidhofer Water Treatment Plant also treats and purveys surface water to urban contractors, including the County of San Joaquin, City of Stockton, and California Water Service. These two in-lieu projects have helped decrease groundwater pumping and have allowed for recovery of groundwater levels on the order of 14 to 20 feet.

This has reduced, but not eliminated, the eastern migration of poor-quality water from the Delta into the Subbasin by reducing the groundwater hydraulic gradient eastward from the Delta.

Implementation of the other PMAs included in the Eastern San Joaquin (ESJ) Groundwater Sustainability Plan (GSP) is intended to raise groundwater levels or, at minimum, keep levels in the operating zone defined as the elevations between the Measurable Objective (MO) and the Minimum Threshold (MT) established to avoid undesirable results. These sustainable management criteria were set specifically to help prevent the further migration of saline water. The relationship between the MOs and MTs for groundwater levels considered water quality and the afore-described saline water migration because there was a known potential and causality, even if no clear correlations.

There are dedicated monitoring wells that have been constructed in the past 20 years and a production well network which together serve as sentinels to track chloride and TDS as indicators of the saline water and potential migration (please see ESJ GSP Figure 2-58, pg. 2-84) and to monitor the sustainability indicators for this management problem. These wells are also part of the ESJ GSP representative monitoring well network.

California Code of Regulations (CCR) Title 22 establishes water quality standards for drinking water contaminants. A secondary MCL (SMCL) is defined for a variety of parameters, including chloride and TDS.

Secondary MCLs are based on user acceptability of the quality of drinking water, as opposed to being established to protect human health. For the purposes of this GSP, comparing chloride and TDS concentrations to their respective SMCLs is the basis for monitoring the above-described groundwater quality concerns in the Eastern San Joaquin Subbasin. [should reference data for the water in or under the Delta that is of concern – do levels of chloride and/or TDS in these waters exceed SMCLs? i.e. do they pose a risk of causing exceedances in adjacent groundwater?] Nexus Between GWL and WQ
Except for the potential for regional migration of saline water, there is no evidence or historical data to indicate that there is relationship between lowering of groundwater levels and groundwater quality degradation. We have not observed, nor can we anticipate, any causal connection between groundwater management actions that can be undertaken by GSAs, and lowering groundwater levels that would result in degradation associated with other constituents of concern.

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TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 There are, however, potential mechanisms for lowering groundwater levels to influence water quality. These include:
 Falling groundwater levels which may cause migration of already-contaminated groundwater from natural sources, nonpoint sources (salt, nitrate), or a plume from a point source where a potential responsible party is known.
 Rising groundwater levels creating changes in oxidation potential and mobilization of arsenic.  Rising groundwater levels from recharge operations or reduce pumping that could mobilize nitrates or salts in the vadose zone.

The GSP reviews water quality issues regarding nitrates, arsenic, and salts, referencing Regional Water Quality Control Board (RWQCB) programs under the Central Valley Water Quality Control Plan, and those of the State Water Resources Control Board, including the Irrigated Lands Regulatory Program and the CVSALTS initiative, generally describing these programs and relationship to these efforts. The intent is to acknowledge those jurisdictions and authorities, create awareness of the areas of responsibility for management and regulation, and identify where there are known water quality issues and impairments to beneficial use being addressed through those authorities. The GSP acknowledges the Central Valley Regional Water Quality Control Board (RWQCB)/State Water Resources Control Board (SWRCB) responsibilities, including those of the Division of Drinking Water, and documents these programs and how they influence the GSAs PMAs and groundwater management in the region to be consistent and respectful of the authorities and programs of these related agencies. This includes local Environmental Health Department authorities to protect drinking water quality, health, and safety.

There may be a relationship between PMAs to be implemented by GSAs that merit review at the time such projects are proposed and subject to California Environmental Quality Act (CEQA), and if potential impacts are identified during scoping and the input of the responsible or trustee agencies. Any PMA that could result in violation of MCLs as a threshold of significance would require mitigation and monitoring to ensure there are no negative effects. For example, groundwater recharge has been observed to result in short term increases in nitrogen concentration in groundwater due to the flushing of nitrate from the soil and/or vadose zone to the water table. This known potential negative effect would require evaluation during project development and ongoing monitoring and mitigation during operation. The rising water table associated with a recharge project could also intersect with nitrogen entrained in the pore space in the vadose zone and mobilizing this constituent. Both effects have been observed to be short term in nature as more clean water is recharged over time and typically improves ambient water quality. Regardless, impacts would be evaluated and mitigated as required under CEQA.

Varying groundwater levels may also change geochemical conditions and result in oxidation and mobilization of some elements. This is one mechanism for mobilizing arsenic; however, there is not enough data to evaluate causal relationship or correlations with groundwater levels at this time. The GSP notes the monitoring well and drinking water well monitoring and reporting of arsenic levels.

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TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 Potential Corrective Action 1(f)-2: Describe how they will coordinate with the appropriate groundwater users, including drinking water, environmental, and irrigation users as identified in the GSP
Initial Review Provided by DWR
The Letter states “The GSAs generally commit to monitoring a wide range of water quality constituents, but they have only developed sustainable management criteria for total dissolved solids because they state they have not observed a causal nexus between groundwater management and degradation associated with the other constituents. While Department staff are not aware of evidence sufficient to conclude that the GSAs acted unreasonably by focusing on total dissolved solids, it is clear that the GSAs did not consider, or at least did not document, the potential for degradation to occur due to further lowering of groundwater levels beyond the historic low.”
As a Potential Corrective Action, the following is suggested: “The GSAs should further describe how they will coordinate with the appropriate groundwater users, including drinking water, environmental, and irrigation users as identified in the GSP.”
Supplemental Information in Response to DWR Letter
GSAs Assessment of Groundwater Quality Degradation
The ESJ GSP and PMAs are designed to prevent further groundwater level declines below the historic level and MTs established. The representative water quality monitoring well network in the area where lowering of groundwater levels may lead to degradation of water quality, along with tracking of other regional monitoring by the RWQCB, SWRCB and local water purveyors, will allow the GSAs to observe water quality conditions and identify when groundwater level MTs are exceeded to determine if water quality exceeds the SMCLs at the MT for the constituents of concern referenced in the GSP. If groundwater level MTs and groundwater quality SMCLs as MTs are exceeded, the GWA will convene a working group consisting of GSAs, regulators and local water purveyors to conduct and publish an assessment of the effect of groundwater management activities on the documented exceedance and propose timely corrective actions to manage groundwater differently, if needed, to avoid exacerbating the exceedance and to address the resultant undesirable results.

Through the ESJGWA, the GSAs will collaborate and share data with other programs monitoring water quality data to observe both ambient and regulated conditions.

Coordination with Groundwater Users
GSP implementation by the ESJGWA includes stakeholder coordination, outreach and engagement of groundwater users, and seeks to involve representatives of the different beneficial uses and users, including non-governmental organizations. The ESJGWA maintains a web site, is working to implement a data management system to provide transparent access to available groundwater level and quality data, and produces and distributes the required Annual Report which is a primary tool for communicating basin conditions and progress in achieving sustainability. The Annual Report includes documentation of efforts to coordinate with the other monitoring and regulatory programs to bring data and information into the Eastern San Joaquin Groundwater Authority 6 Woodard & Curran, Inc.

TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 ESJGWA discussions and build awareness of how groundwater levels and quality may be managed together to achieve sustainability.

The Subbasin’s Technical Advisory Committee will be used to review monitoring data from the GSP programs, and to integrate information from other monitoring programs into the Annual Report to identify where constituents of concern are degrading water quality and will seek to define if there is a relationship between groundwater levels and impacts to beneficial use.

Potential Corrective Action 1(f)-3: Discuss efforts to coordinate with water quality regulatory agencies and programs in the Subbasin to understand and develop a process for determining if continued lowering of groundwater levels is resulting in degraded water quality in the Subbasin during GSP implementation Initial Review Provided by DWR
The Letter states “While Department staff are not aware of evidence sufficient to conclude that the GSAs acted unreasonably by focusing on total dissolved solids, it is clear that the GSAs did not consider, or at least did not document, the potential for degradation to occur due to further lowering of groundwater levels beyond the historic lows.”
As a Potential Corrective Action, the following is suggested: “The GSAs should also discuss efforts to coordinate with water quality regulatory agencies and programs in the Subbasin to understand and develop a process for determining if continued lowering of groundwater levels is resulting in degraded water quality in the Subbasin during GSP implementation.” Supplemental Information in Response to DWR Letter
Coordination with Water Quality Regulatory Agencies and Programs The primary state authority for protecting water quality under the Porter Cologne Water Act is the SWRCB and RWQCB via the Water Quality Control Plans (also known as Basin Plans) which define the beneficial uses of water (including groundwater), set water quality numeric and narrative objectives, establish priorities, and implement programs to manage both point and non- point sources of contamination. The Water Boards coordinate with the other state programs including, the Department of Pesticide Regulation.

Section 3.2.3.1.1 of the GSP discusses the Irrigated Lands Regulatory Program (ILRP) and Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS), two existing regulatory programs for the monitoring and regulation of nitrate and salts in the Central Valley. Under the ILRP, the San Joaquin County & Delta Water Quality Coalition (Coalition) is required to test and potentially mitigate for nitrate in domestic wells. The Coalition has 40 trend monitoring wells throughout San Joaquin County that are sampled yearly to determine the nitrate levels in the groundwater. They also hold grower meetings and conduct outreach to growers on best management practices that are protective of water quality for both surface water and groundwater. The Coalition completed its Groundwater Assessment Report in 2015 that identified areas that were highly susceptible to nitrate from agriculture leaching into groundwater (High Vulnerability Areas). The Coalition also analyzes monitoring data and grower-prepared nitrate Eastern San Joaquin Groundwater Authority 7 Woodard & Curran, Inc.

TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022 management plan information to determine if the growers follow the requirements of the Irrigated Lands Regulatory Program. The Coalition then reports this analysis with required information to the Central Valley Regional Water Quality Board on an annual basis.

Additionally, the 2017 Salt and Nitrate Control Program, developed by CV-SALTS, identifies long-term nitrate management requirements (CVRWQCB, 2016). The Eastern San Joaquin Basin is Priority 2 Basin under the nitrate control program. The CV-SALTS Prioritization and Optimization (P&O) Study is a longterm effort to develop, plan and implement solutions for managing and controlling salt accumulation in the Valley.

In May 2018, because of CV-SALTS program efforts, a new Salt and Nitrate Management Plan (SNMP) was approved by the Central Valley Regional Water Quality Control Board as Amendments to the Basin Plans for the Sacramento River, San Joaquin River Basin and the Tulare Lake Basin. The State Water Resources Control Board then directed targeted revisions to the Amendments adopted by the Central Valley Water Board. The following Proposed Revisions were approved with an effective date of November 10, 2021.  Salt and Nitrate Control Program Basin Plan Amendments – Proposed Revisions (2021)  Salt and Nitrate Control Program – Basin Plan Amendment (2019) The State Water Resources Control Board Division of Drinking Water and local health agencies monitor drinking water quality to protect public health and safety. Their programs and the proposed ESJ monitoring should share data to better diagnose and treat potential or known water quality impairments.

ESJGWA and GSA Project Management Actions
The ESJ GSP also proposes the following program management actions for the Subbasin GSAs to be coordinated through the ESJGWA. These include:

1. Regular Process for coordination
a. The ESJGWA will hold an annual “groundwater water quality state of the basin” meeting or workshop in January and invite the members of the Coalitions to present the results of the monitoring program.
b. The ESJ Technical Advisory Committee (TAC) will invite participation and ex officio representation from the RWQCB staff to receive regular information regarding ILRP, CV-SALTS and any planned updates or amendments to the San Joaquin Water Quality Control Plan.

2. Monitoring
a. The ESJGWA will seek to develop monitoring and data sharing agreements with the Coalition. b. ESJGWA staff will work with the local Environmental Health Division and SWRCB Division of Drinking to identify drinking water wells which are nearing or have exceeded MCLs or SMCLs, noting the location, number of wells and the constituents of concern.

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TM3 - ESJ GSP Deficiency 1(f) Response_24Jun22 June 2022

3. Data Management. Where possible, the ESJGWA will include the water quality data collected via other monitoring networks in their annual assessments, and will use this information to further evaluate trends and any correlations between groundwater levels, the groundwater level MTs, and observed water quality conditions.

4. Annual Report. Beyond the reporting of data from the GSP groundwater level and water quality monitoring network, the ESJ Annual Report will include expanded groundwater quality discussion to document:
a. The annual results of the Coalitions monitoring program b. Known impairments identified by the RWQCB pursuant to the Water Quality Control Plans c. Wells and locations where MCLs have been exceeded as identified by the SWRCB Division of Drinking Water, consumer confidence reports, or the local Environmental Health Department

REFERENCES
Central Valley Regional Water Quality Control Board. 2022. Irrigated Lands Regulatory Program, Program Brochure. As viewed at
https://www.waterboards.ca.gov/centralvalley/water_issues/irrigated_lands/outreach_brochure.pdf.

Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS). 2016. Central Valley Region Salt and Nitrate Management Plan, Final Document for Central Valley Water Board Consideration.

December. As viewed at https://www.cvsalinity.org/resources/basin-planning/ CV-SALTS. 2022. New Salt Control Program for the Central Valley. January. As viewed at https://cvsalinitymy.sharepoint.com/personal/cvsalts_cvsalinity_org/_layouts/15/onedrive.aspx?id=%2Fpersonal%2Fcv%2Dsalts%5Fcvsalinity%5Forg%2FD ocuments%2FWebsite%5FResources%2FGeneral%20Information%20Materials%2FSalt%20Control%20Fact %20Sheet%201%2D13%2D21%2Epdf&parent=%2Fpersonal%2Fcv%2Dsalts%5Fcvsalinity%5Forg%2FDocu ments%2FWebsite%5FResources%2FGeneral%20Information%20Materials&ga=1.

CV-SALTS. 2022. Salt Control Program and P&O Study Update. February. As viewed at https://cvsalinitymy.sharepoint.com/personal/cvsalts_cvsalinity_org/Documents/Website_Resources/General%20Information%20Materials/Salt%20Control %20Program%20Brief%20final%203-15-22.pdf?ga=1.

Izbicki, John A., Loren F. Metzger, Kelly R. McPherson, Rhett R. Everett, and George L. Bennett V. 2006.

Sources of High-Chloride Water to Wells, Eastern San Joaquin Ground-Water Subbasin, California. U.S.

Geological Survey Open File Report 2006-1309. As viewed at https://pubs.usgs.gov/of/2006/1309/pdf/ofr2006-1309.pdf Eastern San Joaquin Groundwater Authority 1 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 TECHNICAL MEMORANDUM NO. 4 – LAND SUBSIDENCE
TO: Paul Gosselin, California Department of Water Resources Deputy Director PREPARED BY: Kris Balaji, on behalf of the Eastern San Joaquin Groundwater Authority DATE: June 24, 2022
RE: Eastern San Joaquin Groundwater Authority Response to DWR’s November 18, 2021 Consultation Initiation Letter – Response to Potential Deficiency No. 2 and Corrective Actions

1. Introduction
The Eastern San Joaquin Groundwater Authority (ESJGWA) received a Consultation Initiation Letter (Letter) on November 18, 2021 (Attachment 1), from the California Department of Water Resources (DWR). The Letter identified two potential deficiencies with the Eastern San Joaquin Groundwater Subbasin (Subbasin) Groundwater Sustainability Plan (GSP) which may preclude DWR’s approval, as well as potential corrective actions to address each potential deficiency. The Letter thus initiated consultation between DWR, the Plan Manager, and the Subbasin’s groundwater sustainability agencies (GSAs) regarding the amount of time needed to address the potential deficiencies and corrective actions. A subsequent meeting with DWR was held on April 4, 2022 to discuss the Subbasin’s proposed approach to addressing the identified deficiencies. The analysis presented in this memorandum was completed in response to the Letter, based on direction provided by the ESJGWA, the Subbasin GSAs and DWR. It is intended to supplement the Eastern San Joaquin GSP that was submitted in January 2020 and fill potential gaps identified in the Letter provided by DWR.

The following sections provide a response to the Potential Corrective Actions identified under Potential Deficiency 2.

2. Potential Deficiency 2
Potential Deficiency 2. The GSP does not provide enough information to support the use of the chronic lowering of groundwater levels sustainable management criteria and representative monitoring network as a proxy for land subsidence
Under Potential Deficiency 2, DWR identified deficiencies related to the use of the chronic lowering of groundwater levels sustainable management criteria and representative monitoring network as a proxy for land subsidence.

Specifically, DWR requests additional information demonstrating significant correlation between groundwater levels and land subsidence to demonstrate that groundwater level minimum thresholds represent a reasonable proxy for avoiding land subsidence undesirable results. The GSAs must additionally demonstrate how the monitoring network is adequate to identify undesirable results for land subsidence.

To address findings identified under Potential Deficiency 2, DWR has put forward Potential Corrective Action 2 for GSA consideration. Potential Corrective Action 2 contains three subparts, which are summarized below. • Potential Corrective Action 2-1: Identify the total extent and rates of subsidence that critical infrastructure in the Subbasin can tolerate during GSP implementation. • Potential Corrective Action 2-2: Document a significant correlation between groundwater levels and specific amounts or rates of land subsidence. Account for potential subsidence related to groundwater level declines below historic lows and further declines that would exceed minimum threshold levels. Demonstrate that Eastern San Joaquin Groundwater Authority 2 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 groundwater level declines allowed during GSP implementation are preventative of the rates and extent of land subsidence.
• Potential Corrective Action 2-3: Explain how the groundwater level representative monitoring network is sufficient to detect significant and unreasonable rates or extents of land subsidence that may substantially interfere with land uses.

The following subsections provide a response to each of the Potential Corrective Action subparts listed above, and include a discussion with supplemental information, analysis, justification, and data needed to support the GSP and address each issue identified.

Potential Corrective Action 2-1: Identify the total extent and rates of subsidence that critical infrastructure in the Subbasin can tolerate during GSP implementation Initial Review Provided by DWR
The Letter states the GSP “does not adequately identify or define minimum thresholds and undesirable results for land subsidence… [and] does not identify specific infrastructure locations, particularly those associated with public safety, in the subbasin and the rate and extent of subsidence that would substantially interfere with those land surface uses and may lead to undesirable results”. The Letter further clarifies that, “without identifying infrastructure considered at risk for interference from land subsidence, Department staff cannot evaluate whether the groundwater level representative monitoring network is adequate to detect potential subsidence-related impacts.” As a Potential Corrective Action, the following is suggested: “The GSA should revise the GSP to identify the total subsidence that critical infrastructure in the Subbasin can tolerate during GSP implementation. Support this identification with information on the effects of subsidence on land surface beneficial uses and users and the amount of subsidence that would substantially interfere with those uses and users.” Supplemental Information in Response to DWR Letter
Identification of Critical Infrastructure
The GSP describes an undesirable result for land subsidence in the Eastern San Joaquin Subbasin as occurring if land subsidence substantially interferes with beneficial uses of groundwater and infrastructure within the Subbasin over the planning and implementation horizon of the GSP. In coordination with the San Joaquin County Department of Public Works and the San Joaquin County Office of Emergency Services, the following infrastructure types have been identified as those potentially at risk for interference from land subsidence, if it were to occur in the Subbasin. Please note that, as discussed with DWR during the April 4th meeting, due to the sensitive nature of the critical infrastructure, specific infrastructure are not named and, rather, only the principal categories of these types of infrastructure are discussed below.

Critical infrastructure at risk for subsidence impacts:
• Major highways, roadways, and bridges
• Canals, pipelines, and levees
• Electrical transmission lines
• Schools
• Fire stations
• Hospitals and other medical facilities
• Law enforcement facilities (police stations, jails, correctional facilities) • Water and wastewater treatment, distribution, and storage facilities • Communication facilities
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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 The Subbasin is served by an extensive road network, including major interstate highways. The San Joaquin County Department of Public Works maintains the County’s 120-mile network of underground facilities, over 1,600 miles of roadway, 265 bridges, and 364 minor structures. In addition, San Joaquin County supports air service, a deep water port, transcontinental rail, and commuter trains. Major roadways located within the Subbasin boundary include Interstate 5 (I-5) and multiple State Routes (4, 12, 26, 88, 99, 120). Major bridges in the Subbasin serve both automobile and railroad transport. Major bridges in the subbasin include the San Joaquin River Bridge, Littlejohns Creek Bridge, Mormon Slough Bridge, and the Union Pacific Mossdale Bridge East.

Service buildings within the Subbasin include fire stations, hospitals, jails and correction facilities, police stations, and wastewater plants. The County also maintains 30 water systems with 52 wells, 3 sewage treatment plants, 9 sewage pumping stations, 68 storm drain pumping stations, and over 300 miles of levees and flood channels. In general, major pipelines that run through the County are in areas south of Lodi and southwest of Tracy along the foothills (outside of the Subbasin boundary).

In addition to identifying critical infrastructure at risk for subsidence impacts, the ESJGWA has worked with OES to identify the total subsidence load that critical infrastructure in the Subbasin can tolerate during GSP implementation, and what would be considered an undesirable result. Through input from OES, the critical infrastructure in the Subbasin can generally tolerate a significant amount of uniform settlement due to subsidence across the Subbasin, though the total amount of settlement that can be tolerated is dependent on the design of the specific infrastructure. Differential settlement across facilities in a locale, on the other hand, will result in more damage. However, it is worth noting that it is less common for subsidence to cause significant local differential sediment. In addition, the San Joaquin County 2017 Local Hazard Mitigation Plan identifies land subsidence as a potential cause for levee breakage; however, the hazard of subsidence is ranked “not likely” to occur.

Potential Corrective Action 2-2: Document a significant correlation between groundwater levels and specific amounts or rates of land subsidence. Account for potential subsidence related to groundwater level declines below historic lows and further declines that would exceed minimum threshold levels. Demonstrate that groundwater level declines allowed during GSP implementation are preventative of the rates and extent of land subsidence.

Initial Review Provided by DWR
The second part of this Potential Corrective Action seeks additional information to document a significant correlation between groundwater levels and land subsidence. The Letter states the GSP “fails to provide adequate evidence to evaluate further [the correlation between groundwater levels and land subsidence], specifically concerning potential subsidence caused by groundwater levels falling below historic lows, as would be allowed by the groundwater level minimum threshold set in the GSP. The Letter further states that the GSP “presents no analysis of historic groundwater levels or historically dewatered subsurface materials to support the conclusion that the geologic units are not compressible”, “does not provide an evaluation showing how additional declines in groundwater levels would only affect subsurface materials similar to those which have been historically dewatered”, and “is unclear on whether the conditions required to identify an undesirable result for chronic lowering of groundwater levels in the subbasin are also required to identify an undesirable result for land subsidence.” As a Potential Corrective Action, the following is suggested: “The GSAs should revise the GSP to document a significant correlation between groundwater levels and specific amounts or rates of land subsidence. The analysis should account for potential subsidence related to groundwater level declines below historical lows and further declines that are allowed to exceed minimum thresholds (i.e., during non-consecutive non-dry years, if applicable based on the resolution to Potential Deficiency 1, above). This analysis should demonstrate that groundwater level declines allowed during GSP implementation are preventative of the rates and magnitudes of land subsidence considered significant and unreasonable based on the identified infrastructure of concern. If there is not sufficient data to establish a correlation, the GSAs should consider other options such as direct monitoring of land subsidence (e.g., remotely Eastern San Joaquin Groundwater Authority 4 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 sensed data provided by the Department, extensometers, or GPS stations) until such time that the GSAs can establish a correlation.”
Supplemental Information in Response to DWR Letter
Areas Potentially At-Risk for Subsidence
As discussed in the GSP, despite long-term declining groundwater levels in the Subbasin, there are no historical records of impacts from land subsidence in the Eastern San Joaquin Subbasin. Figure 1 shows regional subsidence produced from TRE Altamira Interferometric Synthetic Aperture Radar (InSAR) data, provided by DWR for SGMA application. This figure illustrates that subsidence has historically been minimal in the Subbasin and surrounding areas (ranging from -0.1 to 0.1 feet of vertical displacement annually). This corresponds with what San Joaquin County Public Works and San Joaquin County Office of Emergency Services staff have observed anecdotally, that the Subbasin has not historically experienced issues with land subsidence.

In the Subbasin, there are two potential mechanisms that could potentially contribute to inelastic land subsidence: 1) groundwater extraction resulting in dewatering and collapse of compressible clays in the subsurface, 2) and the oxidation of peaty soils.

Mechanism 1: Subsidence Caused by Dewatering and Collapse of Compressible Clays The first mechanism for inelastic land subsidence involves the presence of compressible clays and strata in the subsurface, which are not known to be common in the Eastern San Joaquin Subbasin. The Corcoran Clay is one type of subsurface material that is potentially predisposed to compression, especially in the San Joaquin Valley. While dominant in basins to the south, the extent of Corcoran Clay within the Eastern San Joaquin Subbasin is limited to the extreme southwest corner of the Subbasin, near the City of Manteca. Figure 2 shows the extent of Corcoran Clay within the Subbasin. This figure also includes hydrographs for two monitoring wells located in this area, one in the Representative monitoring network for chronic lowering of groundwater levels, and one in the Broad monitoring network for chronic lowering of groundwater levels. In addition, there are two other Broad groundwater level monitoring network wells that fall within the Corcoran Clay boundary but are outside of the boundary of the available Corcoran Clay depth raster dataset. As shown in the hydrographs provided, historical water levels have remained relatively constant in this area and are well above the Corcoran Clay elevation.

Well 02S07E31N001M (shown as well “A” in Figure 1) is in the Representative monitoring network for chronic lowering of groundwater levels. This well is located in the South Delta Water Agency (SDWA) GSA and has a minimum threshold set at 1.5 feet mean sea level (ft MSL), which while below the historical average, is still well above the Corcoran Clay elevation at that location (-176 ft MSL). The ESJGWA has identified a numeric trigger for groundwater levels at which subsidence would become a concern as -150 ft MSL in the portion of the Subbasin were Corcoran Clay is present.

This numeric trigger was selected based on available Corcoran Clay elevation data and is intended to capture the shallowest Corcoran Clay in the Subbasin.

The Corcoran Clay layer in the Subbasin is not anticipated to become dewatered if groundwater levels do not drop below the elevation at which Corcoran Clay is present. Because the minimum thresholds for groundwater levels in the portion of the Subbasin where Corcoran Clay is present are higher in the aquifer than the elevation of the Corcoran Clay, groundwater levels are not anticipated to drop below the elevation at which Corcoran Clay is present. Therefore, if groundwater levels are maintained above their minimum thresholds, the Corcoran Clay layer, which is lower in elevation, would not become dewatered and therefore would not become compressed. Thus, the chronic lowering of groundwater levels minimum threshold is protective against dewatering of Corcoran Clay in the Subbasin.

Figure 3 (GSP Hydrogeologic Cross-Section E-E’) shows the extent of Corcoran Clay in cross-section. As shown, the Corcoran Clay becomes interbedded with the sands and silt of the upper Turlock Lake Formation. Here, the clay is typically 20 to over 100 feet thick and is locally eroded and interfingered with coarser materials at its margin. It is not found in the central and northern portions of the Subbasin.

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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Mechanism 2: Subsidence Caused by the Oxidation of Peaty Soils The second mechanism for inelastic land subsidence in the Subbasin area, the oxidation of peaty soils, does not appear to be directly related to groundwater pumping in the Subbasin (the management mechanism for Subbasin sustainability). As shown in Figure 4, the organic basin soils are restricted to the lower Sacramento-San Joaquin River Delta (Delta) portion of the Subbasin. Peat, muck, and clay loam are terms commonly applied to soils in this group.

Figure 5 shows the distribution of present-day modeled subsidence rates due to the oxidation of peaty soils in the Delta region, which ranges from 0 to 1.84 centimeters per year.

There are numerous factors that contribute to peat oxidation-related subsidence. Generally, these include (1) shrinkage due to dewatering, (2) consolidation due to loss of buoyant force and loading, (3) wind and water erosion, (4) oxidation of soil organic matter, and (5) burning. According to findings presented in Present-day oxidative subsidence of organic soils and mitigation in the Sacramento-San Joaquin Delta, California, USA (Deverel et al., 2016), subsidence rates in the Sacramento-San Joaquin Delta are primarily related to soil organic matter content, and secondarily to water- and land-management practices that determine depth to groundwater. This paper identifies rice cultivation and permanently flooded wetlands as the primary mitigation tools. As noted by Deverel et. al., depth to groundwater on Delta subsided islands is controlled primarily by networks of drainage ditches that feed to island drainage pumping stations that, in turn, continuously discharge drainage water to Delta channels. Drainage ditches collect water that seeps from adjacent channels and deep percolation of applied irrigation water. There are few depth-to-groundwater measurements in Delta organic soils and, in general, groundwater levels have been maintained at about 0.8–1.2 meters below land surface as the result of drainage system operation. Deverel also notes that based on his experience in working in the organic soils throughout the Delta since the early 1980s, depth to groundwater has not changed substantially over time in most places and prior research indicates a lack of change in Delta groundwater levels since the late 1980s (Deverel et al. 2016).

Figure 6 shows annual groundwater pumping in the Subbasin for Water Year 2021 and indicates that minimal groundwater extraction occurs in this area of the Subbasin.

Supplemental Land Subsidence Monitoring
To further supplement the land subsidence data collection efforts put forward in the GSP, continuous global positioning system (CGPS) data, InSAR data, and other subsidence data have been, and will continue to be, evaluated annually by the ESJGWA in coordination with the planned use of chronic lowering of groundwater level minimum thresholds as a proxy for land subsidence. The GSAs will monitor these data sets to better understand and report actual subsidence that occurs (if any) as groundwater levels decline. These data will be compiled and evaluated each year as part of the data assessment and production of the Annual Report, submitted to DWR each April 1. In addition, the ESJGWA will revisit the Hydrogeologic Conceptual Model (HCM) presented in the Subbasin’s GSP after DWR’s Airborne Electromagnetic (AEM) data become available.
1 At that time, the ESJGWA will adjust the representative monitoring network and methods as needed based on improved basin understanding to refine their methods for monitoring for inelastic land subsidence. This analysis and any subsequent revisions will be incorporated in the GSP five-year update.

In time, the ESJGWA will endeavor to identify a correlation between groundwater levels and subsidence, as suggested by DWR. Below is a description of land subsidence datasets currently available for ESJGWA use and analysis.

UNAVCO’s Plate Boundary Observatory Program – Reporting since 2004, the UNAVCO (formerly University Navigation Satellite Timing and Ranging or NAVSTAR Consortium) Plate Boundary Observatory network consists of a

1 DWR is conducting AEM surveys in California’s high- and medium-priority groundwater basins, where data collection is feasible, to assist local water managers as they implement the Sustainable Groundwater Management Act (SGMA) to manage groundwater for long term sustainability. AEM surveys began in the summer of 2021 and will continue over the next several years. Eastern San Joaquin Subbasin is included in DWR's Survey Area 6, which is expected to be surveyed April 3-23, 2022, per the Tentative AEM Survey Schedule released by DWR. By this schedule, AEM data for the Subbasin is tentatively expected to be available in the first quarter of 2023.

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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 network of about 1,100 CGPS and meteorology stations in the western United States to measure deformation resulting from the constant motion of the Pacific and North American tectonic plates in the western United States. Stations located within the Subbasin contain data from at least 2006 to current and include Station P309, located east of Linden, and Station P273, located west of Lodi. Other stations are also available in nearby Subbasins.

United States Geological Survey – The USGS report Land Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, California, 2003-10 (Sneed et al., 2013) presents land subsidence data in the southwestern portion of the Eastern San Joaquin Subbasin from 2007 to 2010. Data for about 100 square miles of the Subbasin were recorded using InSAR processing, a satellite-based remote sensing technique that can detect groundsurface deformation. Two InSAR techniques were used: conventional InSAR and persistent scatter (PS) InSAR. Both sources of data were collected from the Japanese Aerospace Exploration Agency’s Advanced Land Observing Satellite.

Other -– DWR has made two InSAR datasets available for SGMA application: TRE Altamira InSAR point and raster data and NASA JPL raster data. Vertical displacement approximations in both datasets are collected by the European Space Agency’s Sentinel-1A satellite. The two different datasets represent two different processing results, one by TRE Altamira Inc. and one by NASA JPL. The TRE Altamira data have coverage between January 2015 and October 2020. Both annual and total raster datasets from TRE Altamira are available and represent interpolations of the vertical displacement point features. The NASA JPL processed dataset spans Spring of 2015 to Summer of 2017.

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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Note: This dataset represents measurements of vertical ground surface displacement in between spring 2015 and summer 2017 (TRE Altamira, 2019).

Figure 1. Subsidence (Annual Rate of Vertical Displacement) Eastern San Joaquin Groundwater Authority 8 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Figure 2. Extent of Corcoran Clay in the Eastern San Joaquin Subbasin with Select Representative Well Hydrographs
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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Figure 3. Hydrogeologic Cross-Section E-E’
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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Figure 4. Soil Depositional Areas
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TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Source: Present-day oxidative subsidence of organic soils and mitigation in the Sacramento-San Joaquin Delta, California, USA (Deverel et. al, 2016) Figure 5. Oxidative Subsidence Rates in the SacramentoSan Joaquin Delta Eastern San Joaquin Groundwater Authority 12 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Figure 6. Average Annual Groundwater Pumping (Water Year 2021) Eastern San Joaquin Groundwater Authority 13 Woodard & Curran, Inc.

TM 4 - ESJ GSP Deficiency 2 Response_24Jun2022 June 2022 Potential Corrective Action 2-3: Explain how the groundwater level representative monitoring network is sufficient to detect significant and unreasonable rates or extents of land subsidence that may substantially interfere with land uses.

Initial Review Provided by DWR
The third part of the Potential Corrective Action under Deficiency 2 seeks additional information on how the chronic lowering of groundwater levels representative monitoring network is sufficient to detect significant and unreasonable subsidence that may substantially interfere with land uses, specifically any identified infrastructure of concern. The Letter states the GSP “is unclear on whether the conditions required to identify an undesirable result for chronic lowering of groundwater levels in the Subbasin are also required to identify an undesirable result for land subsidence.” In addition, the Letter states, “While SGMA does not require prevention of all land subsidence, the GSP does not provide sufficient evidence to conclude that the proposed chronic lowering of groundwater level minimum thresholds are adequate to detect and avoid land subsidence undesirable results.” As a Potential Corrective Action, the following is suggested: “The GSAs should explain how the groundwater level representative monitoring network is sufficient to detect significant and unreasonable subsidence that may substantially interfere with land uses, specifically any identified infrastructure of concern. If the groundwater level monitoring network alone is not adequate, based on specific infrastructure locations, Department staff suggest incorporating continued analysis of available InSAR data to cover areas with data gaps.” Supplemental Information in Response to DWR Letter
The decision to use the groundwater levels representative monitoring network as a proxy for land subsidence was based on the information discussed in the prior section of this document. The GSAs recognize that additional land subsidence data collection and monitoring in the Subbasin over the first few years of GSP implementation will be an important indicator in assessing if the groundwater levels representative monitoring network alone will be sufficient to evaluate potential movement towards significant and unreasonable impacts to infrastructure due to inelastic land subsidence, particularly given that the Subbasin has not historically experienced issues related to land subsidence.

For this reason, and in response to DWR’s suggestion to incorporate continued analysis of available InSAR data to cover areas with data gaps, the GSAs have committed to annual collection and evaluation of land subsidence data from publicly available sources, including CGPS, InSAR, and other data sources, for assessment with data collected from its representative monitoring network. Data will be evaluated annually, and if subsidence is apparent, projects and management actions in that area will be triggered. The ESJGWA will establish a trigger value of 0.25 feet (annual rate of vertical displacement) at which point an analysis will occur to determine if the subsidence is directly related to groundwater management, and if deemed so, additional projects and management actions are triggered.

The ESJGWA has also determined that, following receipt of the DWR’s AEM data, the GSAs will re-evaluate and update the representative monitoring network for land subsidence as part of GSP five-year update and in coordination with improvements and refinements to the GSP HCM through the use of the AEM survey data and new boring log data that becomes available.

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REFERENCES
Deverel, Steven J., Timothy Ingrum, and David Leighton (2016), Present-day oxidative subsidence of organic soils and mitigation in the Sacramento-San Joaquin Delta, California, USA. Hydrogeology Journal (2016) 24:569-586.

Sneed, Michelle, Justin T. Brandt, and Mike Solt (2013), Land Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, California, 2003-10. U.S. Geological Survey Scientific Investigations Report 2013-5142. As viewed at https://pubs.er.usgs.gov/publication/sir20135142.

ATTACHMENT 1 – DWR Consultation Initiation Letter