CITY OF SANTA MARIA
Santa Maria WWTP Program Management Services
TECHNICAL MEMORANDUM
Time Schedule Compliance Plan
DRAFT / May 2024
ATTACHMENT "A"
CITY OF SANTA MARIA
Santa Maria WWTP Program Management Services
TECHNICAL MEMORANDUM
Time Schedule Compliance Plan
DRAFT / May 2024
This document is released for the purpose of information exchange review and planning only under the authority of Lydia A. Holmes, May 23, 2024, California C-56616, and Graham J. G. Juby, May 23, 2024, California C-67217.
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pw://Carollo/CA/Santa Maria/202301-000000/03 Reports and Studies/02 Deliverables/Time Schedule Compliance Plan/TimeScheduleCompliancePlan.docx Contents
SECTION 1 INTRODUCTION 1
1.1 Background 1
1.1.1 Purpose of This Report 1
SECTION 2 COMPARISON OF EFFLUENT QUALITY TO EFFLUENT AND GROUNDWATER LIMITS 2
2.1 Effluent Quality 2
2.1.1 Carbonaceous Biochemical Oxygen Demand and 5-Day Biochemical Oxygen Demand Test 2
2.1.2 Total Suspended Solids 3
2.1.3 Settleable Solids 4
2.1.4 Total Nitrogen 4
2.1.5 Total Dissolved Solids, Sodium, Chloride, Sulfate, and Boron 5
2.2 Groundwater Quality 7
SECTION 3 IDENTIFICATION OF CHOICE OF COMPLIANCE LOCATION 11 SECTION 4 DESCRIPTION AND CHRONOLOGY OF EFFORTS SINCE NOTICE OF APPLICABILITY 12
4.1 Summary of Investigations 12
4.1.1 Sampling Plan and Data Collection 12
4.1.2 Process Modeling and Optimization Identification 13
4.1.3 Source Control Evaluation 14
4.1.4 Percolation Pond Investigations and Improvements 14
4.2 Further Investigation 15
SECTION 5 JUSTIFICATION OF NEED FOR ADDITIONAL TIME AND DETAILED SCHEDULE OF ACTIONS 15
5.1 Proposed Actions 15
5.2 Justification for Schedule 16
5.3 Detailed Time Schedule of Specific Actions 18
SECTION 6 DEMONSTRATION THAT TIME SCHEDULE IS AS SHORT AS POSSIBLE 18
SECTION 7 PROPOSED INTERIM LIMITS, ACTIONS, AND MEASURABLE MILESTONES 19
7.1 Proposed Interim Limits 19
7.2 Actions and Measurable Milestones 19
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Tables
Table 1 Comparison of Permit Limits and Current Effluent Concentrations 2 Table 2 Groundwater Quality Data (Average From 2018 to 2023) 8 Table 3 City of Santa Maria Proposed Interim WWTP Effluent Limits 19 Table 4 Proposed Time Schedule Tasks and Milestones 20
Figures
Figure 1 Comparison of Effluent CBOD and BOD₅ to NOA Limits 3 Figure 2 Comparison of Effluent TSS to NOA Limits 4
Figure 3 Comparison of Effluent Total Nitrogen to NOA Limit for Total Nitrogen 5 Figure 4 Comparison of Effluent TDS to NOA Limits 6
Figure 5 Comparison of Effluent Sodium, Chloride, and Sulfate to NOA Limits 6 Figure 6 Comparison of Effluent Boron to NOA Limits 7
Figure 7 TDS Values in the Groundwater Compared to NOA Limit 8 Figure 8 Sodium Values in the Groundwater Compared to NOA Limit 9 Figure 9 Chloride Values in the Groundwater Compared to NOA Limit 9 Figure 10 Sulfate Values in the Groundwater Compared to NOA Limit 10 Figure 11 Boron Values in the Groundwater Compared to NOA Limit 10 Figure 12 Total Nitrogen Values in the Groundwater Compared to NOA Limit 11 Figure 13 Timeline for Determining Approach for Interim and Final Limit Compliance 18 Figure 14 Timeline for Implementation of Project for Final Compliance 18
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Abbreviations
BOD₅ 5-day biochemical oxygen demand test
Carollo Carollo Engineers, Inc.
CBOD carbonaceous biochemical oxygen demand
CEPT chemically enhanced primary treatment
CEQA California Environmental Quality Act
City City of Santa Maria
COD chemical oxygen demand
mg/L milligrams per liter
mgd million gallons per day
mL/L milliliters per liter
NOA Notice of Applicability
PTF primary trickling filter
RWQCB Regional Water Quality Control Board
STF secondary trickling filter
TBD to be determined
TDS total dissolved solids
TKN total Kjeldahl nitrogen
TN total nitrogen
TSCP Time Schedule Compliance Plan
TSS total suspended solids
VSS volatile suspended solids
WWTP wastewater treatment plant
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SECTION 1 INTRODUCTION
1.1 Background
The City of Santa Maria (City), California treats domestic, commercial, and industrial wastewater from its service area which serves a population of more than 107,000. The treatment process includes primary clarifiers, trickling filters, secondary clarifiers, and then discharge of the treated wastewater to land via percolation ponds. This discharge is permitted by the Central Coast Regional Water Quality Control Board (RWQCB). In September 2020, the RWQCB adopted a General Waste Discharge Requirements Order (No. R3-2020-0020). The City enrolled in this General Order through submitting a notice of intent on August 5, 2022. The RWQCB issued a Notice of Applicability (NOA) to the City on June 16, 2023, which lays out specific requirements, effluent limitations, and the Monitoring and Reporting Program requirements. As part of the NOA, the City is required to develop a Time Schedule Compliance Plan (TSCP) if additional time is needed to comply with the new effluent limits. Per the NOA, the TSCP must address the following:
1. Comparison of the current effluent quality to the effluent and groundwater limitations in General Permit Tables 3 to 6.
2. Identification of the City’s choice for compliance for each constituent pursuant to General Permit Section V.A.2 Option 1 or Option 2 (complying with an effluent limit or demonstrating compliance through a groundwater monitoring program).
3. A detailed description and chronology of efforts, since issuance of the NOA, to reduce wastes.
4. Justification of the need for additional time to achieve the effluent limitations in General Permit Tables 3 to 6.
5. A detailed time schedule of specific actions the City will take to achieve the effluent limitations.
6. A demonstration that the time schedule requested is as short as possible, considering the technological, operation, and economic factors that affect the design, development, and implementation of the measures that are necessary to comply with the effluent limitation(s).
7. If the requested time schedule exceeds one year, the proposed schedule shall include interim requirements and the date(s) for their achievement. The interim requirements shall include both of the following:
a. Effluent limitation(s) for the pollutant(s) of concern. b. Actions, measurable milestones, and tangible products leading to compliance with the effluent limitation(s).
1.1.1 Purpose of This Report
The City will not be able to implement new treatment processes in time to comply with the final effluent limits by June 2025. Therefore, the purpose of this report is to address each of the items set out above.
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SECTION 2 COMPARISON OF EFFLUENT QUALITY TO
EFFLUENT AND GROUNDWATER LIMITS
This section lays out in more detail how the City’s effluent quality compares to the requirements of the NOA effluent and groundwater limits for each of the major constituents.
2.1 Effluent Quality
A summary of the current permit limits compared to the City’s effluent is shown in Table 1. As indicated in Table 1, the City will have issues complying with the 5-day biochemical oxygen demand test (BOD₅), total suspended solids (TSS), and total nitrogen (TN). Additionally, total dissolved solids (TDS) concentrations have been increasing. Each of these constituents are discussed in more detail below.
Table 1 Comparison of Permit Limits and Current Effluent Concentrations Constituent Units Interim Limits Through
June 16, 2025 Based on
General Order
No. R3-2010-0001
Final Limits as of
June 16, 2025 Based on
New General Order
No. R3-2020-0020
Average Effluent
2018 to 2023(1)
BOD₅(1) mg/L 60 30 44.4 CBOD(2,3)
70.1 BOD₅(2,3)
TSS(1) mg/L 60 30 38.6
Settleable Solids(1) mL/L 0.1 0.3 <0.1
TN(4) mg/L – 10 42
TDS(4) mg/L 1,000 1,000 884
Sodium(4) mg/L 180 230 140
Chloride(4) mg/L 180 165 150
Sulfate(4) mg/L – 500 227
Boron(4) mg/L – 0.5 0.37
Notes:
CBOD - carbonaceous biochemical oxygen demand; mg/L - milligrams per liter; mL/L - milliliters per liter (1) Based on a 30-day average.
(2) Values shown in red indicate which constituents cannot comply with either the interim or final effluent limit. (3) City historically measured CBOD rather than BOD₅ for compliance. CBOD value shown is an average of 2018 to 2023.
BOD₅ value is an average of 24 samples collected in fall of 2023 and early 2024. (4) Based on 25-month rolling median.
2.1.1 Carbonaceous Biochemical Oxygen Demand and 5-Day Biochemical Oxygen Demand Test
The City historically measured effluent using CBOD, as opposed to BOD₅. The NOA requires use of BOD₅.
Figure 1 shows the historical CBOD effluent values collected since 2018 compared to the interim and final NOA effluent limits. Recent data using BOD₅ is also shown for samples collected in fall 2023. Based on sampling conducted at the City’s wastewater treatment plant (WWTP), CBOD values are typically
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45 percent of BOD₅ values. For this reason, as seen in Figure 1 that while the historical CBOD values are typically less than 60 mg/L, use of the BOD₅ method means that the effluent discharge cannot comply with the interim limit of 60 mg/L as a 30-day average, nor the final limit of 30 mg/L as a 30-day average.
Reduction of BOD₅ to reliably meet the lower final effluent limits will likely require additional treatment and/or transitioning away from trickling filters to activated sludge.
Figure 1 Comparison of Effluent CBOD and BOD₅ to NOA Limits
2.1.2 Total Suspended Solids
TSS has an interim limit of 60 mg/L and a final limit of 30 mg/L measured as a 30-day average. As shown in Figure 2, the WWTP effluent is normally under 60 mg/L but is not always able to comply with the 30 mg/L limit. The City is evaluating ways to improve TSS removal, but transitioning away from trickling filters to activated sludge would lead to a more stable secondary effluent discharge.
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Figure 2 Comparison of Effluent TSS to NOA Limits
2.1.3 Settleable Solids
The City’s effluent achieves both the interim and final limit of settleable solids of 0.1 mL/L.
2.1.4 Total Nitrogen
The NOA establishes that the effluent shall not exceed a TN limit of 10 mg/L as a 25-month rolling median. As shown in Figure 3, the sum of the nitrogen species (ammonia, nitrate, and nitrite) far exceeds the total limit of 10 mg/L. Reduction of TN will require new treatment processes as the existing facility was not designed for nutrient removal and is not easily modified to meet these nitrogen limits.
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Figure 3 Comparison of Effluent Total Nitrogen to NOA Limit for Total Nitrogen
2.1.5 Total Dissolved Solids, Sodium, Chloride, Sulfate, and Boron For the protection of the Upper Guadalupe Groundwater Basin, the NOA establishes effluent limits for a number of compounds that are not typically removed by primary and secondary treatment, such as TDS, sodium, chloride, sulfate, and boron. All of these compounds are largely influenced by the source water quality used for the potable water supply. In the case of the City, water supply is a combination of local groundwater sources and imported State Water Project water (surface water from the delta). The compliance for these effluent limits are based on a 25-month rolling median. Because the treatment plant’s influent flow is more than 90 percent domestic in origin, and industrial discharges only account for about 4.2 percent of the influent salinity, the ability to comply with any of these constituents will largely depend on the quality of the drinking water supplies.
The final effluent limit for TDS is 1,000 mg/L, as shown in Figure 4 (solid blue line). Figure 4 also shows the 25-month rolling median of the historical effluent TDS values (dotted blue line) that comply most of the time with the new limit, with a few exceedances in 2022.
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Figure 4 Comparison of Effluent TDS to NOA Limits
Figure 5 shows the historical effluent values for sodium, chloride, and sulfate, whose final effluent limits are 230 mg/L, 165 mg/L, and 500 mg/L, respectively, shown in solid colored lines. Again, compliance is based on a 25-month rolling median shown as dotted colored lines in Figure 5. As shown in Figure 5, effluent sodium is below the 230 mg/L limit and effluent sulfate is below the 500 mg/L limit, but chloride has had individual values in the past that exceeded the 165 mg/L limit. However, the 25-month rolling median for chloride values since mid-2019 meets the 165 mg/L limit.
Figure 5 Comparison of Effluent Sodium, Chloride, and Sulfate to NOA Limits
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The effluent limit for boron is 0.5 mg/L, shown as the solid purple line. As shown in Figure 6, the 25-month rolling median (shown as a dotted purple line) of historical effluent boron levels is below
0.5 mg/L.
Figure 6 Comparison of Effluent Boron to NOA Limits
2.2 Groundwater Quality
In addition to specifying effluent limits, the NOA also establishes groundwater quality limits that are based on a 25-month rolling median. These limits are based on the Basin Plan water quality objectives for the Upper Guadalupe Groundwater Basin. The City can choose to either comply with limits for TDS, sodium, chloride, sulfate, boron, and TN in the effluent (limits discussed in the previous section) or in the groundwater. If the City chooses to comply with limits in the groundwater, the City would need to develop a detailed groundwater monitoring plan and program.
Table 2 summarizes the limits for groundwater quality as well as the City’s historical groundwater data from 2018 to 2023. As shown in the table, most of the constituents are currently meeting the groundwater quality requirements, with the notable exception of TN. The existing wastewater processes were not designed for nitrogen removal nor are they capable of removing nitrogen. As shown in Table 2, TN is the only constituent in the groundwater where the average of historical data exceeds the groundwater limit.
However, it is important to note that the well that is upgradient of the City’s percolation ponds has significantly higher TN levels than the downgradient wells, likely due to the extensive agricultural use of lands surrounding the wastewater treatment and disposal facilities.
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Table 2 Groundwater Quality Data (Average From 2018 to 2023) Constituent Limits Based on
General Order
No. R3-2020-0020(1)
Well 5H
(Upgradient)
UMW-1
(Downgradient)
DMW-1
(Downgradient)
DMW-2
(Downgradient)
TDS, mg/L 1,000 1,047 1,025 978 972
Sodium, mg/L 230 67 154 144 145
Chloride, mg/L 165 54 158 151 152
Sulfate, mg/L 500 386 214 215 235
Boron, mg/L 0.5 0.2 0.4 0.4 0.4
TN, mg/L 1.4 16.1(2) 7.0(2) 12.7(2) 17(2)
Notes:
(1) NOA groundwater limits based on 25-month rolling median. (2) Values shown in red indicate which constituents cannot comply with either the interim or final effluent limit.
Figures 7 to 12 show the groundwater sampling results from 2018 to 2023. While there are a few instances of individual sampling events higher than the limits, when using the 25-month rolling median the City is mostly in compliance with all groundwater limits except for TDS and TN.
Figure 7 TDS Values in the Groundwater Compared to NOA Limit
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Figure 8 Sodium Values in the Groundwater Compared to NOA Limit
Figure 9 Chloride Values in the Groundwater Compared to NOA Limit
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Figure 10 Sulfate Values in the Groundwater Compared to NOA Limit
Figure 11 Boron Values in the Groundwater Compared to NOA Limit
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Figure 12 Total Nitrogen Values in the Groundwater Compared to NOA Limit SECTION 3 IDENTIFICATION OF CHOICE OF
COMPLIANCE LOCATION
While the City is able to comply for most constituents with either the effluent or groundwater limitations, the requirements for groundwater compliance are extensive. The Monitoring and Reporting Program established in the NOA states that the City’s current groundwater monitoring network is inadequate and requires that if the City chooses compliance in the groundwater they must comply with the following:
Submit a groundwater monitoring work plan by October 16, 2024. Submit a preliminary hydrogeologic groundwater model by October 16, 2024. Propose installation of a minimum of three shallow groundwater monitoring wells and that these wells must be installed within 90 days of RWQCB approval.
Given this relatively short timeline to develop a groundwater monitoring plan and construct the monitoring wells, the City does not believe it can comply within the required timeline. Therefore, the City has elected to move forward with compliance in the effluent (Option 1) for all constituents.
Option 1 can be implemented right away as compared to Option 2 (groundwater compliance) which would require new infrastructure to be constructed, taking more time to implement. As the City continues to develop a plan and implementation process to meet the requirements of the General Order, it would like to reserve the right to utilize groundwater limitations (Option 2) in the future.
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SECTION 4 DESCRIPTION AND CHRONOLOGY OF
EFFORTS SINCE NOTICE OF APPLICABILITY
Following the issuance of the NOA in June 2023, the City has invested significant time and effort to improve its treatment performance and comply with the interim effluent limits. As part of this effort, Carollo Engineers, Inc. (Carollo) was engaged to develop a WWTP Master Plan to determine how best to achieve the interim and future limits, to estimate what new facilities will cost, and to lay out how long it will take for implementation. In addition, Carollo has analyzed the existing wastewater treatment performance to evaluate several alternatives for implementation to meet the interim effluent limits.
Detailed descriptions of efforts to comply with the new interim effluent limits are discussed in more detail in the following section. Efforts include the following:
Sampling plan and data collection.
Process evaluations and optimization identification.
Source control evaluation.
Percolation pond investigations.
4.1 Summary of Investigations
4.1.1 Sampling Plan and Data Collection
Historically, the City has regularly monitored the influent and effluent streams for CBOD, TSS, total Kjeldahl nitrogen (TKN), and ammonia-nitrogen. In addition to the two liquid streams, the City also monitors solids streams including raw sludge, digested sludge, and solids hauled from the drying beds.
However, to evaluate the treatment capabilities of each unit process, additional data was required. A comprehensive sampling plan for a period of seven consecutive days was recommended by Carollo to collect additional process data. In December 2023, the City executed the sampling plan and collected daily composite data for 17 different constituents (chemical oxygen demand [COD], BOD₅, CBOD, TSS, volatile suspended solids [VSS], TKN, etc.) at 20 different process locations. The data collected during the sampling event allowed for detailed evaluation of the processes. The following bullets summarize the key findings from the evaluation:
The average influent COD to BOD₅ ratio and COD to VSS ratio is higher than the typical range for municipal wastewater. The higher ratio suggests an impact from industrial waste streams or other non-municipal components in the influent.
The primary clarifiers and primary trickling filters (PTFs) seem to be performing well and within the typical performance range. However, the secondary trickling filter (STF) performance was below the typical range, suggesting there may be ways to improve performance. Effluent BOD₅ data collected during the sampling event averaged around 66 mg/L. The City has also started sampling BOD₅ regularly since October 2023 and averages around 71 mg/L. Therefore, the
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City will not be able to comply with the interim discharge limit of 60 mg/L and final discharge limit of 30 mg/L without improving the current performance and/or implementing new technologies. Historically, the City has collected time-based composite samples for regular monitoring. However, flow-based composite samples are considered more representative and were, therefore, collected during the sampling event. These flow-based composite samples had lower BOD₅ results than the time-based composite sampling, indicating that the historical sampling method may be overestimating BOD₅. To get more representative data, the City is making an effort to implement flow-based sampling for regular monitoring.
4.1.2 Process Modeling and Optimization Identification
A steady state plant-wide process model was developed using BioWin version 6.2 (Envirosim) to help evaluate the current performance and develop near-term recommendations for process improvements and to establish unit process capacity. The model was utilized to evaluate recommendations for process improvements. Understanding that the TN limit cannot be met with the current treatment plant technologies, the focus has been on working towards achieving the interim limit for BOD₅ and TSS. The following are some of the potential opportunities recommended by Carollo based on the performance evaluation:
Although the primary clarifiers’ performance is adequate and well within the typical performance, further improving performance could help reduce organic loading on trickling filters and improve effluent discharge. The process modeling analysis showed that with the improvement of primary clarifier performance, BOD₅ concentration in the final effluent will improve. Jar testing has been conducted to evaluate the impact of addition of ferric chloride at the primary clarifiers. Secondary clarifier performance is also adequate and well within typical performance. However, adding polymer or coagulant at the secondary clarifiers will help reduce TSS and BOD₅ in the final effluent. The process modeling analysis showed that with the improvement of secondary clarifier performance, BOD₅ concentration in the final effluent will also improve. Jar testing has been conducted for evaluating the addition of various coagulants at the secondary clarifiers. Distributor speed for PTFs and STFs: Spulkraft values were calculated for both PTFs and STFs which indicated that the distributors on trickling filters are rotating much faster than typical recommended rates. The trickling filter performance can be optimized by reducing the rotation speed of distributor arms. The rotational speed can be reduced by adding braking nozzles on the hydraulic drives or replacing the hydraulic drives with motorized units. The City is currently making progress on this alternative. Additionally, the City is also working on replacing distributor arms for one of the PTFs which has reached the end of its useful life.
Tertiary filters: The addition of tertiary filtration would remove suspended solids from secondary effluent resulting in reducing both TSS and BOD₅ in the final effluent. Particle removal is achieved by passing wastewater through a filtering media. While the City does not currently have tertiary filtration, they are investigating the costs and feasibility of bringing in temporary filtration to help improve the final effluent quality.
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4.1.3 Source Control Evaluation
Due to the City’s inability to comply with the interim and final limits for BOD₅, TSS, and TN, as well as uncertainty about consistently meeting TDS requirements, a review of the City’s pretreatment program records was conducted to evaluate if industrial or septage discharges are contributing to elevated influent concentrations. Findings included the following:
On average, septage discharges account for 2.3 percent of BOD₅ loading to the WWTP influent.
However, considering that septage deliveries are only accepted during business hours, the septage BOD₅ loading ranges from 2 to 9 percent of the influent loading during those hours. Even at these higher percentages during business hours, the septage loads were not considered a significant contribution to the overall BOD₅ concentration in the treated effluent from the WWTP. Industrial discharges monitored as part of the City’s pretreatment program are 3.7 percent of the BOD₅ and 1.5 percent of the TSS loading to the WWTP influent. TN discharges from the industries are not currently tracked by the City. Due to the agricultural activity in Santa Maria, the industrial users discharge more in the summer and can reach discharges of 7 percent of BOD₅ and 2.6 percent of TSS loading to the WWTP influent. But, even at these levels, industrial discharges were not considered a significant contribution to the overall loading to the WWTP influent. From 2019 to 2023, average TDS concentrations from individual significant industrial users remained well below their 1,800 mg/L local limit. Monthly effluent concentrations range from 700 to 1,600 mg/L of TDS. When compared with the effluent limits, this results in a combined contribution of 4.2 percent of the influent load from all the industrial dischargers. Therefore, industrial discharges are not considered a significant contribution to the overall loading of TDS to the WWTP.
4.1.4 Percolation Pond Investigations and Improvements
The NOA limits the disposal of effluent to the percolation ponds at 8 million gallons per day (mgd) based on information the City provided to the RWQCB regarding pond capacity. The City is currently investigating the pond capacity further and looking for ways to improve performance, including developing a water balance, performing geological and hydrogeological sampling and testing, and developing recommendations for improved percolation. The City submitted a letter request to the RWQCB on April 10, 2024, proposing to re-establish pond capacity on the southeast portion of the WWTP to accommodate retention and percolation of additional effluent from the infiltration/inflow generated from the recent back-to-back wet winters on the Central Coast, to provide some redundancy in similar weather conditions in the future, and to complement with additional storage the WWTP’s pond maintenance and performance evaluation currently being performed by the City’s consultant team. The request included details on approximate sizing and location of the three re-established percolation ponds.
The Master Plan (under development) will also identify improvements needed for disposal in the future including pond maintenance/rehabilitation and potentially new percolation pond development to meet the growth demands of the City.
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4.2 Further Investigation
Based on the discussion above, the following are the potential alternatives and considerations for interim compliance that need further investigation by temporary trials before finalizing the alternatives for full-scale implementation:
Tertiary filter piloting.
Coagulant addition at secondary clarifiers.
Ferric chloride addition at primary clarifiers.
TDS source water study.
Percolation pond capacity and improvements.
Each of these additional investigations are discussed in greater detail in the next section.
SECTION 5 JUSTIFICATION OF NEED FOR ADDITIONAL
TIME AND DETAILED SCHEDULE OF ACTIONS
The approach for both interim and final compliance has many steps and therefore will take time. The City has already hired a consultant (Carollo) recognizing help is needed to investigate alternatives for compliance and that a comprehensive plan needs to be developed.
5.1 Proposed Actions
Based on the discussion above, the following are the proposed actions that need further investigation before finalizing an alternative for full-scale implementation:
Tertiary filters: The City is evaluating whether temporary tertiary filters could help meet compliance in the near term. Investigations have shown that filtration of the secondary effluent may reduce the BOD₅ to below the interim limits. The City is evaluating logistics and seeking pricing to rent a 1-mgd pilot tertiary filter system that can be installed at the WWTP to confirm the viability of this approach.
The concept will be to operate the pilot for approximately four to five months to establish/determine the following:
» Filter performance criteria and the filterability of the secondary effluent. » The need for chemicals to assist with filtration.
» BOD₅ and TSS removal efficiency.
» Filter backwash frequency and flow.
» Impacts of backwash water on the existing solids handling facilities.
If the testing is successful, then the next step would be to determine the scalability, pricing, and approach for a more permanent facility that would treat all or part of the secondary effluent to meet the interim limits for BOD₅ and TSS.
Coagulant addition at secondary clarifiers: Several rounds of jar testing have been conducted by Carollo to determine the type and optimum dosage for coagulant addition upstream of the secondary clarifiers. Based on the jar testing results there may be potential for water quality improvement. If the
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tertiary filtration work, described above, is not successful, the City may conduct a trial test by adding coagulant to one of the clarifiers to assess its effectiveness. The addition of coagulant at secondary clarifiers is complicated for the City’s plant as there are significant return flows back into the plant.
This may have potential detrimental impacts to the trickling filter performance and other processes or require additional modifications to the treatment regime. It is anticipated that it will take approximately six months to set up and conduct such tests to determine if it is feasible to implement coagulant addition full scale at the secondary clarifiers. Ferric chloride addition at primary clarifiers: Several rounds of jar testing have also been conducted by Carollo to determine the optimum dosage for the addition of ferric chloride upstream of primary clarifiers. Jar testing using three different coagulants was performed and ferric chloride performed best. The process model that Carollo developed for the existing plant was used to simulate the impact of implementing chemically enhanced primary treatment (CEPT). The model results show there is potential to reduce the BOD₅ concentration in the effluent stream to below the interim limits.
However, there are uncertainties about the impacts of ferric chloride addition on the other treatment processes. In addition, this approach is expected to have the highest costs for chemicals. Accordingly, since the primary clarifiers are already performing within expected values, the City is focusing on other improvement options described above. However, if the tertiary filtration and coagulant addition at the secondary clarifiers are not successful, a pilot test of CEPT could be developed to add coagulant to the primary clarifiers. It would take at least four to six months to implement such a pilot test. TDS source water study: With the historical TDS data showing an increasing trend in concentrations and the 25-month rolling historical median showing a few values exceeding the new limit, the City will do an evaluation of the TDS in its source water to determine if the cause of the increases is due to conservation, contributions through use (wastewater), and/or use of water softeners. The City will also explore options for blending of supplies or implementing a self-regenerating softener ban to determine if any of these actions would help reduce TDS in the effluent. The study will identify the increase in TDS from source water to wastewater influent (human additions) and identify if an “intake credit” is an applicable regulatory approach. It is anticipated that this study would take one year to complete.
Percolation pond capacity and improvements: As part of planning for future expansion and growth within the City, an important aspect is understanding the capacity of the existing percolation ponds.
The ongoing study and water balance calculations (part of the Master Plan) will identify capacity and near-term improvements needed to sustain and/or improve performance. It will also help identify the long-term disposal needs for the Master Plan.
Master Plan: The City has already committed to completing a Master Plan to lay out the needed improvements for long-term wastewater treatment to meet the final effluent limits. This Master Plan development effort is already underway and includes data collection and review, flow and load projections, condition assessment, regulatory assessment, treatment process performance and capacity assessment, evaluation of liquid and solids alternatives (including reuse and energy management), capital improvement plan development, and financial planning.
5.2 Justification for Schedule
The first step is the evaluation of interim compliance options and the investigations into these options as discussed above. These investigations and pilots will be carried out in a stepwise process so that the
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improvements from each specific action can be assessed before trying another improvement option. The stepwise process also reduces the risk that multiple, significant changes in the wastewater treatment process may have unintended, negative consequence on effluent discharge.
Task 1 includes ongoing optimization of the existing plant performance and all the investigations and piloting for meeting the BOD₅ and TSS interim limit of 60 mg/L. This task includes the current ongoing effort on optimizing plant performance through rehabilitation and reducing the speed of distributor arms for both PTFs and STFs (shown as Task 1a in Figure 13). Following completion of the existing plant optimization, piloting tertiary filtration will be the next step (shown as Task 1b in Figure 13). The tertiary pilot will take time to get into place and needs to run for several months. If successful, a larger scale filter system could be implemented. If tertiary filtration pilot testing is unsuccessful, then the other approaches will be tested for implementation (Tasks 1c and 1d for coagulant addition to the secondary and primary clarifiers) in a sequential order to determine if the new process is working prior to proceeding with the next step. Since the City’s peak flows and loads are during the summer months due to food processing, it is important for any pilot testing to include the summer months. The need for summer testing of any option, paired with the need for several months of operations and the need to only change one parameter at a time to determine impact of the change, means that Task 1 will take approximately a year and a half. Following completion of each of these Task 1 studies, the City will meet with the RWQCB to discuss an appropriate approach for interim compliance, including potential capital improvements and permit modifications, if needed.
In Task 2, the City will also begin a study on TDS in the source water to investigate the increasing concentrations of TDS in the influent. As discussed above, it is expected that this study would take approximately one year to complete. The study would be started after RWQCB approval of this TSCP. It is anticipated that this study will require discussions with the RWQCB regarding implications of findings on the permit and if regulatory solutions are viable.
Task 3 includes the ongoing percolation pond water balance and hydrogeologic/geologic study that will continue to develop near-term improvement recommendations. This work is being conducted as part of the ongoing Master Plan and is expected to be completed by the end of 2024.
In parallel to the additional investigations and pilot studies, the Master Plan is being developed to identify improvements for long-term wastewater treatment to meet the final effluent limits (Task 4). Because the Master Plan effort is a large, comprehensive evaluation of the wastewater system, it is not expected to be completed until the end of 2025. When the Master Plan is near completion, a Program Strategy and Execution Plan for project implementation delivery will be developed (Task 5) which will include a more detailed implementation schedule. Task 5 will also be completed at the end of 2025.
Once the Master Plan and Program Strategy and Execution Plan are completed, the City will begin design on the required wastewater improvement projects to meet the final effluent limits. It is anticipated that a large capital project to improve effluent BOD₅, TSS, and TN will take approximately two and a half years to design and up to four years to construct. Therefore, the final effluent compliance project will not be online and operating until the end of 2033.
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5.3 Detailed Time Schedule of Specific Actions
Figure 13 shows the time schedule of the specific actions that have been described in the section above.
These tasks are expected to be completed by the end of 2025.
Figure 13 Timeline for Determining Approach for Interim and Final Limit Compliance Figure 14 shows the overall timeline for implementing a WWTP improvement project to meet final effluent limits.
Figure 14 Timeline for Implementation of Project for Final Compliance SECTION 6 DEMONSTRATION THAT TIME SCHEDULE IS
AS SHORT AS POSSIBLE
The schedule presented in Figure 14 is the shortest timeline possible given the need to plan, design, and construct major improvements to meet the final effluent limits, which will require the City to move away
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from a trickling filter only secondary treatment technology and instead move to a treatment process that can both reduce effluent BOD₅/TSS and nitrify/denitrify to meet TN requirements. Likely processes include moving to an activated sludge process or adding additional nitrification/denitrification processes following the existing treatment facilities. The Master Plan will evaluate treatment options, including costs and time to implement, and will develop recommendations for implementation to meet the final effluent limits. This Master Plan and the resulting WWTP improvement project will require a significant investment of City staff time and budget. Therefore, it is prudent to develop a thorough plan before starting an implementation project, hence the two years of master planning shown in Figures 13 and 14. The improvement project costs are likely to be in the hundreds of millions for a facility of this size. Therefore, the design and construction will be lengthy. The timelines shown in Figure 14 are based on designs and construction timelines of similar facilities.
SECTION 7 PROPOSED INTERIM LIMITS, ACTIONS, AND
MEASURABLE MILESTONES
As demonstrated in the discussion above, planning, designing, and constructing a wastewater treatment facility that can meet the final effluent limits will require time. The City will continue its efforts to improve effluent quality with the goal of meeting interim limits. However, because the TN limits cannot be met without major modifications and upgrades to the WWTP, the City requests that the interim limits laid out in the NOA be extended until the end of 2033 when the WWTP improvement project will come online.
7.1 Proposed Interim Limits
The interim limits proposed are shown in Table 3 for the constituents that are likely to need interim limits longer than through June 16, 2025, as provided in the NOA.
Table 3 City of Santa Maria Proposed Interim WWTP Effluent Limits Constituent Units Proposed Interim Interim Dates
BOD₅ mg/L 100 (daily maximum)
60 (30-day average)
Until June 2033
TSS mg/L 100 (daily maximum)
60 (30-day average)
Until June 2033
TN mg/L Not applicable Until June 2033
7.2 Actions and Measurable Milestones
As presented earlier, the City is proposing a phased approach that includes investigations and determination of the most suitable option for compliance. This measured response recognizes the high costs of implementing treatment options and a commitment to identifying a program that best serves the ratepayers’ needs while achieving the intent of the General Permit.
Table 4 lays out the series of tasks and milestones that the City is proposing to bring the WWTP into compliance with the new permit requirements.
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After completion of Tasks 1, 2, 3, 4, and 5, it is recommended that the City meet with the Central Coast RWQCB to discuss the next steps and the refinement of the implementation timeline. Meetings with the RWQCB will also be held at several points during Task 1 to discuss results.
Table 4 Proposed Time Schedule Tasks and Milestones
Task/Milestone Dates Description/Purpose
Central Coast RWQCB accepts
TSCP
TBD Establish interim and final limits, and lay out a plan and timeline for compliance.
Task 1 - Studies for Interim
Compliance for BOD₅ and TSS
5/2024 - 10/2025 The City will study potential solutions for interim limit compliance including modification of trickling filters, addition of temporary tertiary filtration, and coagulant addition to secondary and/or primary clarifiers.
Milestone 1 12/2024 Meet with RWQCB to discuss Tertiary Pilot results.
Milestone 2 8/2025 Meet with RWQCB, if needed, to discuss Secondary Clarifier Coagulation Pilot results.
Milestone 3 12/2025 Meet with RWQCB to discuss summary of Task 1 investigations, results of changes, and plan of action, if needed.
Task 2 - TDS Source Water Study 9/2024 - 9/2025 The City will conduct a study to investigate source water TDS including evaluating different sources, if increases in TDS are due to conservation or water softeners, and if blending supplies can meet objectives. The study will also consider if softener bans (addressing human added TDS) can be used
to meet the effluent limits.
Milestone 4 9/2025 Submit TDS source water study to RWQCB.
Task 3 - Percolation Pond
Investigation
1/2024 - 12/2024 The City will conduct a study to investigate percolation pond water balance, geology/hydrogeology, and capacity.
Recommendations for improvements will be developed.
Milestone 5 12/2024 Submit percolation pond study to RWQCB.
Task 4 - Master Planning for
Long-Term Improvements
1/2024 - 12/2025 Develop Master Plan to identify needed WWTP improvements to comply with NOA final effluent limits.
Milestone 6 12/2025 Notify RWQCB of completion of Master Plan and meet to discuss recommendations.
Task 5 - Program Strategy and
Execution Plan
6/2025 - 12/2025 Develop strategy and execution plan for implementing the recommended project from the Master Plan. Will include
delivery method and revised implementation timeline.
Milestone 7 12/2025 Submit new implementation schedule to RWQCB.
Task 6 - Procure Team, Design and
CEQA of WWTP Improvement
Project
1/2026 - 1/2029 The City will begin design and CEQA environmental review of recommended improvements following completion of Tasks 4 and 5.
Milestone 8 1/2029 Notify RWQCB of design completion and intent to construct.
Task 7 - Bid and Construct WWTP
Improvement Project
2/2029 - 8/2033 Bid and construct WWTP improvement project. Commission and operate upgraded WWTP to meet new effluent limits.
Milestone 9 9/2033 Notify RWQCB of completion of construction and compliance with final effluent limits.
Notes:
CEQA - California Environmental Quality Act; TBD - to be determined