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INFORMATION SHEET ORDER NO.R5-2004-0028 2 INFORMATION SHEET ORDER NO.R5-2004-0028 ATTACHMENT A CITY OF MANTECA,CITY OF LATHROP AND DUTRA FARMS CITY OF MANTECA,CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY SAN JOAQUIN COUNTY 1 Introduction 2.1 Available Receiving Water Flow Data The City of Manteca and City of Lathrop are currently governed by Order No.5-01-007,NPDES No. DWR collects daily average flow data for the San Joaquin River near Vernalis at station RSAN112. The Cit of adopted n January atter The City n Manteca has submitted a Report of Waste Evaluation of this data for the period 1980 to 2002 provided a 1Q10 value of 567 cfs,a 7Q10 value of 620 cfs,and a 30Q10 value of 680 cfs. This period was selected because all current flow control Discharge for renewal of this Order and for expansion of the wastewater quality control facility (WQCF). structures on the San Joaquin River and its tributaries were in place by 1980. However,the data set may not accurately represent historical critical low flow periods.Table 2 summarizes the flow data and The City of Manteca owns and operates the WQCF that receives wastewater flows from the City of calculations. Stage data collected at the Vernalis station does not indicate any tidal flows this far Manteca and some areas of the City of Lathrop. The City of Manteca is responsible for the operation upstream. Downstream,DWR collects stage data near Mossdale at station RSAN087,near the and discharge from the treatment plant,while the City of Lathrop is only responsible for its portion of Manteca outfall. Stage data fluctuated about 0.5 feet daily implying that the tidal flow is present. the wastewater collection system. The City of Manteca leases 150 acres of land from Dutra Farms for Under critical low flow conditions,upstream flows occur on the flood tide,no flow during the slack application of treated wastewater,therefore Dutra Farms is named in this permit and is responsible for tide,and downstream flows during the ebb tide. Multiple dosing of the receiving water with effluent the proper application and management of the wastewater on its land. The City of Manteca,City of may occur as the tide moves the water column upstream and downstream past the outfall. The Lathrop,and Dutra Farms are hereafter Discharger. complex dynamics of the stream flow,the tidal flows,and the intermittent side bank discharges from The City's treatment process consists of raw influent bar screening,flow metering,and grit removal, the City of Manteca and the Brown Sand impoundment must be considered in an evaluation of the followed by primary sedimentation,biofiltration,conventional activated sludge and secondary available dilution in the immediate area of these side-bank outfalls. sedimentation. Secondary effluent is spread over agricultural fields and the excess flows are 2.2 Available Hydrodynamic/Water Quality Models chlorinated,dechlorinated and discharged to the San Joaquin River. Hydrodynamic and water quality models were utilized for the analysis of the water quality impacts of The City of Manteca currently discharges an average of 2.0 mgd of treated domestic and industrial wastewater at agronomic rates to 210 acres of farmland owned by the City adjacent to the treatment the proposed expansion of the City Resource Management Associates(RMA)performed the modeling that was published in the Analysis of Manteca wastewater discharge to the San Joaquin River. plant,and 150 additional acres leased by the city with the excess flows discharged to the San Joaquin River. The flows to agricultural land are required to be maximized to limit the discharges to surface of the Fate and Water Quality Impacts of the City Manteca Discharge,Resource Management Associates,October 10,2000. Larry Walker Associates utilized the modeling data developed by RMA waters. Surface water discharges average 4.89 mgd. to generate the Water Quality Analysis of Surface Water Discharge,Larry Walker Associates,October The treatment system capacity will be expanded through the addition of primary and secondary 2000. Both of these documents are included in the appendices of the Draft Environmental Impact Report for the Manteca WQCF Phase RVIV Expansion Project,October 2000. treatment units that will be similar to and parallel to the existing units. In addition,nitrification, denitrification,tertiary filtration,and UV disinfection will be added to improve the effluent quality. The near-field analysis was performed using the RMA-10 model which performed the hydrodynamic Only the wastewater that will be discharged to the San Joaquin River will receive tertiary filtration and simulation and the temperature and ammonia evaluations. The near-field analysis was based on the UV disinfection. The expansion will also include additional sludge digestion and dewatering units,as assumptions that: well as improvements to buildings,pump stations,ponds,and chemical handling. Food processing 1. Minimum daily flows in the San Joaquin River at Vernalis since 1983 were used. waste will also be delivered,treated,and land applied separately from the municipal waste collection 2. Discharge to the river would be only during the out-going tide. and treatment system. 3. Ambient water conditions for temperature and ammonia were based on the DWR-D-1485 site 2 Dilution at Mossdale. The City of Manteca utilizes a side-bank outfall on the eastern bank of the San Joaquin River. The The far-field water quality analysis was performed using a link-node hydrodynamic model of the San Joaquin River and Delta. The link-node tidally averaged water quality model simulates the long-term flow in the San Joaquin River can be estimated from the Vernalis gaging station which is fate and transport of a discharge to the Delta. A total of three Delta configurations were considered for approximately 15 miles upstream of the Manteca outfall. There are agricultural diversions and returns the parameters of dissolved oxygen,total organic carbon,and total dissolved solids. A tracer between the Vernalis station and the outfall,which will affect flow and water quality. Additionally, simulation was utilized to determine the potential influence of the treated effluent on downstream Brown Sand discharges approximately 10 cfs of wastewater made up of primarily groundwater intakes. The model predicts very small changes to downstream locations as a result of the discharge. infiltrate from the Oakwood Lake impoundment just 50 feet downstream via a side-bank outfall on the same side of the San Joaquin River as that of Manteca's outfall.