ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

INFORMATION SHEET ORDER NO.R5-2004-0028 5 INFORMATION SHEET ORDER NO.R5-2004-0028 6 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 2.5 Evaluation of Available Dilution for Chronic Criteria 2.7 Evaluation of Available Dilution for Priority Pollutant Human Carcinogen Criteria The TSD states that: The human health-based criteria for carcinogens,other than arsenic,are based on safe levels for "Concentrations above the chronic criteria are likely to prevent sensitive taxa from taking up long- lifetime exposure and utilize the harmonic mean flow to represent the receiving water flow. The term residence in the mixing zone. In this regard,benthic organisms and territorial organisms are harmonic mean flow at Vernalis is 1976 cfs. The current annual average discharge rate is 5.72 mgd likely to be ofgreatest concern. The higher the concentration occurring within the isopleth,the more (8.9 cfs). A steady state analysis utilizing the harmonic mean flow provides a dilution of 222:1. The taxa are likely to be excluded,thereby affecting the structure and function of the ecological Regional Board is not required to grant a mixing zone or allocate the full assimilative capacity of the community. It is thus important to minimize the overall size of the mixing zone and the size of elevated receiving water. For limitations based on human health criteria,dilution is limited to that required to concentration isopleths within the mixing zone." maintain compliance. Where the ambient background concentrations are lower than the applicable human health criterion,the dilution credits determined in Table 12 of the Information Sheet apply for The temperature model,while subject to the limitations discussed in section 2.2,provides information the determination of effluent limitations for carcinogens. used as a basis to establish available dilution for compliance with chronic criteria to protect aquatic life. The model concludes that,for the timed discharge,the four degree F differential would reach a 3 Biosofids Management maximum area of 0.3 acre and would be contained in a shallow(less than one foot in depth)plume that hugs the east river bank until dissipating 450 feet downstream. The model also shows that significant The City of Manteca currently discharges biosolids that has been dewatered in drying beds to vertical mixing does not occur until about 500 feet downstream at which point there will be contact City-owned farmland adjacent to the treatment plant at agronomic rates,as described in the Order. with the benthic community. This is illustrated in Figure 8 of the Resource Management Associates, New limitations on metal concentrations in sludge/soil mixtures and new conditions for sludge use as a 2000,analysis. Using the conclusions of the temperature model,a 4 degree temperature differential soil amendment have been established. This new permit requires the City to reevaluate the sludge and downstream where the effluent and receiving water have a 15°F initial difference indicates that mixing effluent application rates to land and submit a land application plan. in the near field is small and does not reach 4:1 until nearly 450 feet downstream and 15:1 at 1300 feet downstream. Complete mixing,which is defined in the SIP as not more than a 5 percent difference in 4 Pretreatment Program the concentration of a pollutant across a transect of the water body,would not occur until over 1000 feet downstream. The SIP requires that a mixing zone not dominate or compromise the integrity of the The Discharger submitted a draft pretreatment program to the Regional Board for approval. The entire water body and shall be as small as practicable. The thermal modeling presented a spatial Regional Board,in an October 2001 Pretreatment Audit,identified areas of the program that were definition to the changes in temperature that occur in the receiving water as discussed in the previous deficient or not implemented. The Regional Board staff,on 22 January 2003,provided comments to paragraph. Tbis allowed a mixing zone to be defined and dilution to be determined at the edge of this mixing zone. The mixing zone will be restricted to the surface layer of the water column in a plume the Discharger identifying provisions of the City's Waste Ordinance and the Interjurisdictional hugging the eastern shore of the river and extending to 450 feet downstream of the outfall. Agreement between the City of Manteca and the Lathrop County Water District that are deficient. Temperature differences at the edge of this mixing zone indicate that a 4:1 dilution exists at the edge of This Order provides a compliance schedule for the Discharger to submit a pretreatment program that this mixing zone. For constituents subject to chronic aquatic criteria,a 4:1 dilution will be applied. corrects the deficiencies noted in the October 2001 Pretreatment Compliance Audit and in the 22 This mixing zone will provide protection to the benthic community and minimize the impacts of the January 2003 letter. The Regional Board will reopen this Order to approve the pretreatment program discharge to the river. upon submittal of a program that corrects the deficiencies. This Order requires full compliance with all pretreatment program requirements by 1 October 2004. 2.6 Evaluation of Available Dilution for Specific Constituents 5 Ground Water The overlap of the plumes from the City of Manteca and the Brown Sand impoundment will limit the extent of a mixing zone for arsenic,a constituent of mutual concern between these discharges. Domestic wastewater contains constituents such as total dissolved solids(TDS),specific conductivity, Additionally,the receiving water monitoring shows an average arsenic concentration of 3.0 ug/l, pathogens,nitrates,organics,and metals. The Discharger's use of unlined ponds and the application of exceeding the USEPA recommended water quality criterion for protection of human health at the 1-in- wastewater to land may result in an increase in the concentration of these constituents in groundwater. a-million risk level. Therefore,the receiving water lacks assimilative capacity for arsenic,and there is The increase in the concentration of these constituents in groundwater must be consistent with no dilution available. Resolution 68-16. Any increase in pollutant concentrations in groundwater must be shown to be necessary to allow wastewater service necessary to accommodate housing and economic expansion in The assimilative capacity of the river is dependent on the background concentration of the receiving the area and must be consistent with maximum benefit to the people of the State of California. Some water. Data collected in 2002 indicates that the receiving water has no assimilative capacity,and degradation of groundwater by the Discharger is consistent with Resolution 68-16 provided that: therefore no dilution can be granted for aluminum,electrical conductivity,iron,manganese,and mercury. a. The degradation is confined to a specified area;