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Staff Report <br /> City of Manteca and City of Lathrop <br /> Wastewater Quality Control Facility <br /> it potentially impacts both water column and benthic organisms. Construction of the <br /> proposed$575,000 project will eliminate the large zone of ammonia across the river that <br /> occurs at stagnant flow conditions and will minimize the cross-section of the river in which <br /> elevated concentrations of ammonia occur. By allowing Manteca to continue to discharge <br /> the higher concentrations of ammonia,the City will not have to construct nitrification <br /> facilities, which would cost the City an estimated $10 million and increase sewer rates by <br /> $3.00 per month. <br /> • Endangered Species. The San Joaquin River is a migration route for salmon, and is also <br /> habitat for Delta Smelt. The presence of rare and endangered species certainly deserves <br /> special consideration when determining whether a mixing zone should be granted. <br /> However, if the mixing zone prevents lethality within the zone, and fully protects beneficial <br /> uses outside of the mixing zone, there should be no impact on rare and endangered species, <br /> or any other aquatic species. <br /> • Impaired Water Bodies. The Delta in the vicinity of Manteca is on the 303(d) list of water <br /> quality impairments for: mercury, electrical conductivity, diazinon and chlorpyrifos, Group <br /> A Pesticides (DDT, Lindane, etc.), and unknown toxicity. The proposed mixing zone will <br /> have no impact on electrical conductivity of the river. The 303(d) listings for mercury, <br /> diazinon and chlorpyrifos, Group A Pesticides, and unknown toxicity indicate that there is, <br /> at least at times, a background level of toxicity in the San Joaquin River. Ammonia and the <br /> organophosphate pesticides (diazinon and chlorpyrifos)would not have the same <br /> biochemical mechanisms, so the chronic impacts from these pesticides and from ammonia <br /> may not be additive. A similar statement can not be made for the"unknown toxicity" since <br /> we don't know what chemical or chemicals are causing the toxicity. Acute chemical <br /> toxicity, from any source is generally considered additive, that is, exposure to sub-acute <br /> concentrations of several chemicals may collectively kill the organism. Given that there is a <br /> background level of toxicity,there is a policy issue of whether a mixing zone should be <br /> granted for any constituent at toxic concentrations. <br /> The San Joaquin River 12 miles downstream of Manteca near Stockton is on the 303(d) list <br /> for low dissolved oxygen. Under low-river flow conditions, pumping for the State Water <br /> Project and Delta-Mendota Canals near Tracy overwhelms the natural flow of the Delta, so <br /> Manteca's effluent will predominantly flow westward. Modeling performed by Manteca in <br /> the EIR for the proposed expansion of the treatment plant to 8.11 mgd concluded that the <br /> Manteca discharge will have an insignificant impact on the dissolved oxygen concentration <br /> in the Delta. <br /> • Bay Protection Hot Spot Policy/TMDL. Because of the 303(d) listing for low dissolved <br /> oxygen in the Delta, a TMDL has been initiated to determine the sources of oxygen <br /> demanding substances and to allocate loads to various point and non-point sources to <br /> achieve compliance with the receiving water dissolved oxygen standards. The TMDL <br /> process, and the resultant loading allowed for Manteca,will not be completed for a number <br /> of years. Until the TMDL is completed,the Board provided direction on handling permit <br />