Local Limits Study
City of Patterson
Water Quality Control Facility
Prepared For:
Prepared By:
July 26, 2022
Department of Public Works
City Hall
1 Plaza
Patterson, CA 95363
1550 Parkside Drive, Suite 320
Walnut Creek, CA 94596
Local Limits Study
July 2022
Page i
TABLE OF CONTENTS
SECTION 1: INTRODUCTION .................................................................................................... 1 SECTION 2: ESTABLISHED LOCAL LIMITS........................................................................... 2 SECTION 3: CURRENT INDUSTRIAL/COMMERCIAL DISCHARGERS.............................. 3 SECTION 4: IMPACTS OF SALINITY AND CONSTITUENTS ON WQCF............................ 4 SECTION 5: BIOSOLIDS REMOVAL FROM WQCF................................................................ 7 SECTION 6: IMPACTS TO LOCAL LIMITS FOR INDUSTRIAL DISCHARGERS................ 8 List of Figures
Figure 3.1 Water Cycle Surrounding WQCF ................................................................................. 3 List of Tables
Table 2.1 Established Local Limits ................................................................................................ 2 Table 4.1 Recommended Local Limits........................................................................................... 5 Table 4.2 Comparison of Average WDR Limits, Local Limits and WQCF Effluent Data............ 6 Table 5.1 Concentrations of Influent Constituents Removed by Biosolids in 2020 & 2021.......... 7 Local Limits Study
July 2022
Page ii
Abbreviations
AIPS Advanced Integrated Pond System
Ammonia-N Ammonia as N
BOD5 5-day Biochemical Oxygen Demand
City City of Patterson
EC Electrical Conductivity
IPS Influent Pump Station
MGD Million Gallons Per Day
NASTS North Activated Sludge Treatment System
Nitrate-N Nitrate as Nitrogen
pH Potential Hydrogen
POC Pollutants of Concern
SASTS South Activated Sludge Treatment System
TDS Total Dissolved Solids
TSS Total Suspended Solids
Total P Total Phosphorous
TKN Total Kjeldahl Nitrogen
TSS Total Suspended Solids
WDR Waste Discharge Requirements
WQCF Water Quality Control Facility
Local Limits Study
July 2022
Section 1: Introduction
The Water Quality Control Facility (WQCF) in the City of Patterson (City) receives wastewater flows from residential, industrial, and commercial dischargers. The City’s current estimated population is 22,730 with 5,959 residential connections and 261 commercial/industrial connections.
The WQCF is surrounded primarily by agricultural farmland and is adjacent to the floodplain of the San Joaquin River. The City relies solely on the groundwater from the Delta-Mendota Subbasin (located in the San Joaquin Valley Basin) for its water supply. Groundwater beneath the City is present in two aquifers, a lower confined zone and an upper unconfined zone which are separated by a semi-impermeable clay layer.
In order to maintain the ground water quality, it is important to keep salinity, nitrogen, and heavy metal concentrations low in the WQCF effluent which is sent to the percolation ponds. The percolation ponds eventually discharge into the groundwater. To keep the salinity, nitrogen, and heavy metal concentrations low in the WQCF effluent, it is important that these parameters are kept within reasonable limits in the WQCF influent which comprises of residential, industrial/commercial discharges. Also, there are operational, compliance and monetary impacts of these discharges to WQCF and it is reasonable and fair that the industrial/commercial dischargers either treat their wastewaters to established local limits or pay fees in proportion to the pollutant load that they are sending to the WQCF. The City understands the importance of having thriving industries contributing to the local economy and hence so far has taken a stance of being understanding and accommodating of dischargers and not strictly enforcing the local limits, as long as the WQCF effluent discharge limits are being met.
Data has been gathered from some of the industrial dischargers to present the effects that elevated constituents have on the treatment efforts of WQCF. Data was compared to the City’s local limits as well as taking into consideration the parameters set forth in WDR R5-2018-0070.
A high level discussion will be presented on additional flows and loads that the WQCF can potentially take on from residential and industrial and commercial dischargers. The goal of this study is to provide an opinion on the need to make any adjustments to the local limits for all commercial and industrial dischargers going to the WQCF.
Local Limits Study
July 2022
Section 2: Established Local Limits
The City has established local limits as shown in Table 2.1.
Table 2.1 Established Local Limits
Parameter Concentration Unit
BOD5 240 mg/L
TSS 220 mg/L
EC 2,940 umhos/cm
TDS 3,200 mg/L
TKN 40 mg/L
Sodium 510 mg/L
Chloride 460 mg/L
Arsenic 1.00 mg/L
Selenium 2.00 mg/L
pH 6.5 – 8.5 -
Cadmium 0.70 mg/L
Chromium 1.00 mg/L
Copper 2.70 mg/L
Cyanide 1.00 mg/L
Lead 0.40 mg/L
Mercury 0.01 mg/L
Zinc 2.60 mg/L
Nickel 2.60 mg/L
Silver 0.70 mg/L
Temperature at interceptor 100 ° F
The established local limits are set forth by the City, and all dischargers, residential or industrial, are required to meet them. Exceeding these limitations can negatively impact the collection system infrastructure, WQCF operations, WQCF’s ability to meet the effluent limitations and quality of the groundwaters in the Central Valley. Continuous exceedances can negatively impact the beneficial use of groundwaters including potable water sources and agricultural production.
Local Limits Study
July 2022
Section 3: Current Industrial/Commercial Dischargers
There are many industrial and commercial dischargers such as restaurants, car washes, laundromats, and grocery stores contributing to the WQCF. Samples have been taken on the effluent streams of the dischargers which can be seen in Figure 3.1.
Figure 3.1 Water Cycle Surrounding WQCF
Figure 3.1 demonstrates the Water Cycle surrounding the City’s Waste Quality Control Facility, starting from the source water from the ground water wells to the WQCF effluent discharging into the ground waters. The orange circles show where the samples are taken. Sampling data from this report comes from two example commercial/industrial dischargers, the WQCF influent and effluent, and biosolids from drying beds which are all highlighted on this diagram.
Additionally, the City collects ground water quality data from multiple ground water monitoring wells near the effluent discharge percolation ponds.
The source water is a combination of both organic and inorganic pollutants from residential and commercial/industrial uses. Inflow and infiltration enter the collection system through damaged pipes and stormwater cross connections. In addition to this, there is an impact from rainfall, evaporation, and leaching from farming practices on the open areas of the WQCF infrastructure.
A majority of the organic pollutants are removed by the WQCF, while the inorganic pollutants remain in the WQCF effluent and eventually make their way into the groundwater.
Local Limits Study
July 2022
Section 4: Impacts of Salinity and Constituents on WQCF Wastewater generated in the City is primarily from residential sources. Industrial uses within the City are “light industrial”. The existing wastewater collection system serves the current population and consists of three lift stations and terminates at the Wastewater Quality Control Facility (WQCF), where it is treated and disposed of into the ground via 11 different percolations ponds. Streams from the local industrial and residential dischargers combine and enter the headworks and distribution facilities at WQCF where the wastewater is screened to remove coarse material from the raw wastewater. Following screening, wastewater then flows to the Influent Pump Station (IPS) and is pumped to one of the process areas (NASTS, AIPS, or SASTS). Aerators are used for anoxic and aerobic treatment to remove BOD5, solids, and other nutrients. The waste activated sludge that is produced from the NASTS and SASTS is sent to be aerobically digested and dewatered by centrifuge. Sludge is typically stored onsite until needed for planting and land application. Some portion of pollutants of concern (POC) are removed in the biosolids.
Since a high amount of farming takes place in this region, salinity needs to be carefully monitored as it can affect crop production and drinking water sources. The City has been mindful of their TDS, BOD5, TSS and TN effluent discharge as they have the potential to affect the groundwater negatively long term if unmonitored. The TDS is composed of the total dissolved solids and organic volatile solids. A higher BOD5 contributes to more TDS and measures taken to decrease the BOD5 will also decrease the TDS. Higher BOD5 loads from industrial dischargers will put more strain on the treatment efforts of WQCF, requiring more electricity usage from the aerators, and can directly result in higher groundwater salinity and POCs.
The WQCF effluent meets the WDR limits. The combined effluent annual average for TDS in 2021 was 1,167 mg/L which is under the limit of 1,250 mg/L as seen in Table 4.1. The TDS from industrial dischargers have consistently been higher than the TDS in the WQCF plant effluent and higher than the TDS in the groundwater. In 2021 there were some exceedances on the TDS in the groundwater in Monitoring Wells 6 and 12. This was analyzed more closely and it was determined that these wells are two of the furthest wells from the plant property, and these exceedances were likely attributed to nearby agricultural activity which surround the wells’ location. The influent flows to the WQCF have been increasing and will continue to increase over the next several years which will cause more strain on the treatment efforts and could put the plant at risk for meeting the TDS treating requirements. Since there are already groundwater exceedances occurring due to external factors, and with increasing demand on improving groundwater salinity, the City desires to minimize additional exceedances and protect the WQCF infrastructure from the expected elevated loads in the future.
If the Commercial/Industrial dischargers continue to send effluent with concentrations of constituents higher than the local limits or even higher than the WDR limits, the WQCF is likely to face operational and compliance issues as the area continues to experience population growth Local Limits Study
July 2022
and more discharge connections are made to the sewer system. The local limit of 3,200 mg/L for TDS is too high for all Commercial/Industrial Dischargers. The TDS local limit should be brought down to the WDR limit of 1,250 mg/L.
One of the two example discharger has sent up to 14.7% of the WQCF BOD5 load. City recognizes that this example discharger is a major contributor of the pollutant load on the WQCF. The City is working with the example discharger to reduce their pollutant load, including the TDS numbers as this discharger has struggled to stay within the established local limits. The other example discharger has met their local limits consistently, except for one occasion.
Another aspect to take into consideration for the local limits is Total Nitrogen (TN). Currently, the local limit parameter for tracing Nitrogen is TKN. The WDR measures Nitrogen as TN. To be consistent with the WDR, the TKN local limit should be replaced with the TN local limit with a concentration of 40 mg/L.
Table 4.1 Recommended Local Limits
Parameter Concentration Unit
BOD5 240 mg/L
TSS 220 mg/L
EC 2,940 umhos/cm
TDS 1,250 mg/L
TN 40 mg/L
Sodium 510 mg/L
Chloride 460 mg/L
Arsenic 1.00 mg/L
Selenium 2.00 mg/L
pH 6.5 – 8.5 -
Cadmium 0.70 mg/L
Chromium 1.00 mg/L
Copper 2.70 mg/L
Cyanide 1.00 mg/L
Lead 0.40 mg/L
Mercury 0.01 mg/L
Zinc 2.60 mg/L
Nickel 2.60 mg/L
Silver 0.70 mg/L
Temperature at interceptor 100 ° F
Table 4.2 shows the WDR limits, local limits and how WQCF performed within the WDR limits.
The red text shows where exceedances happened and the green text shows where the plant was in compliance with the WDR limits. Despite receiving flow from local discharges that was outside of the local limits, the WQCF mitigated those exceedances and was able to stay withing the local limits and WDR limits, except for the low end of the pH range on two occasions which could be due to an instrument error.
Local Limits Study
July 2022
Table 4.2 Comparison of Average WDR Limits, Local Limits and WQCF Effluent Data Parameter
WDR
2018
Limits
Local
Limits Units
Average
WQCF
Effluent
Data
(2017)
Average
WQCF
Effluent
Data
(2018)
Average
WQCF
Effluent
Data
(2019)
Average
WQCF
Effluent
Data
(2020)
Average
WQCF
Effluent
Data
(2021)
BOD5 23 240 mg/L 7 7.2 12.7 20.9 23.3
TSS 23 220 mg/L 5.2 4.5 8.6 19 22.3
EC -- 2,940 umhos/cm 1,835 1,823.6 1,760 1,825.4 1,874.4 TDS 1,250 3,200 mg/L 1,166.7 1,181.8 1,125 1,173.1 1,216.7 TKN -- 40 mg/L 5 3.2 5.2 7.3 7.7
Total
Nitrogen
(as N)
12 -- mg/L 5.4 3.7 5.2 8.3 10
Sodium -- 510 mg/L 210.3 219.1 223.6 231.7 298.9
Chloride -- 460 mg/L 300.8 306 295.5 296.9 325.6
pH range -- 6.5 – 8.5 - 5.8-7.7 7.6-8.0 7.5-8.0 7.4-8.4 5.1-8.4 Temperature
at interceptor -- 100 ° F -- -- -- -- --
Note: Green = in compliance, Red = exceedance
Local Limits Study
July 2022
Section 5: Biosolids Removal from WQCF
Table 5.1 highlights the concentration of specific types of constituents that are removed by biosolids in the years 2020 and 2021. There is no data present on these constituents in the influent for these years so no analysis on percent removal can be calculated. This table demonstrates that a portion of the heavy metals and nitrogen-based compounds are removed with the plant solids and are sent to decompose organically and not to the percolation ponds.
Table 5.1 Concentrations of Influent Constituents Removed by Biosolids in 2020 & 2021 Constituent 2021 (mg/L) 2020 (mg/L)
Arsenic 0.002 0.0045
Cadmium 0.0002 0.0003
Chromium 0.015 0.0253
Gold 0.043 0.0716
Lead 0.0019 0.0032
Mercury 0.00011 0.0003
Molybdenum 0.0012 0.0016
Nickle 0.0029 0.0062
Selenium 0.0019 0.0039
Zinc 0.13 0.213
TKN 13.69 19.65
Ammonia-N 5.64 6.34
Nitrate-N 0.00033 0.0047
Total
Phosphorus 2.50 8.69
Potassium 0.88 1.70
Boron 0.015 0.0184
pH 5.8 7.6
Organic-N 8.04 13.31
Local Limits Study
July 2022
Section 6: Impacts to Local Limits for Industrial Dischargers The City is pro-actively planning to add Phase III A expansion which will require significant capital and additional operational needs. Part of the capital and operating costs for the expansion can be offset by asking the high load dischargers to contribute in proportion to their discharges or perhaps even more than their proportional contributions because their higher loads is stressing the WQCFs ability to effectively treat the wastewaters, thus accelerating the needs for plant expansion.
One of the example dischargers, who is the major contributor of BOD5 and TDS load to the WQCF, will be asked to meet the new local limits. The implications for this discharger could be addition of a new equalization tank at a minimum and perhaps addition of a pre-treatment system or pay fees in proportion of their pollution impact to the WQCF.
The WQCF is currently meeting the WDR discharge requirements for BOD5, TSS, TN and TDS.
The WQCF is about to add 0.2 MGD of additional capacity through NASTS upgrades. The facility, in theory, will be capable of treating 2.45 MGD with 2022 flows predicted at 1.8 MGD.
However, the flows to the WQCF have been trending upwards for the last five years and a growth spurt may put the WQCF under stress to the extent that existing infrastructure may struggle in meeting the discharge limitations. Due to the age, some of the existing infrastructure is requiring more operational and maintenance oversight. There is a chance, if the existing infrastructure is pushed to treat the 2.45 MGD rated capacity, the WQCF may consistently not meet the WDR limits.
Therefore, to proactively get ahead of this cause, the industrial TDS limit of 3,200 mg/L will be brought down to match the WQCF discharge limit of 1,250 mg/L. The TKN limit of 40 mg/L will be replaced with TN limit of 40 mg/L.