SITE INFORMATION AND CORRESPONDENCE_1985-2004

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• REVISED WASTE DISCHARGE REQUIREMENTS ORDER NO. 97-115 6 CITY OF MANTECA AND CITY OF LATHROP WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY 34. The permitted discharge is consistent with the antidegradation provisions of 40 CFR 131.12 and State Water Resources Control Board Resolution 68-16. This Revised Order provides for an increase in the volume and mass of pollutants discharged. This permit will allow ammonia concentrations to be significantly increased in the discharge, an increase above the concentrations necessary to meet the toxicity limits of Order No. 97-115. However, because of the small size of the chronic mixing zone (51 feet long), the increase will not cause significant impacts on aquatic life,which is the beneficial use most likely affected by the pollutant(ammonia) discharged. This Order specifically allows toxicity within the mixing zone and the initial zone of dilution. The increase may also cause a violation of water quality objectives and the narrative toxicity objective for ammonia within the mixing zone. The mixing zone modeling results submitted by the Discharger describes the acute and chronic toxicity portion of the plume, in general, as described in Finding 20 above. The mixing zone modeling study was a conservative model based on effluent discharged through a diffuser, and restricted to times when the river flow is greater than 0.56 mg N/1 June to September and 0.69 mg N/1 October to May. The increase in discharged pollutants will not cause a violation of water quality objectives beyond 51 feet from the discharge, of either the chronic or acute toxicity objective. To the extent an increase in discharged pollutants results from this order(by an increase up to the permitted flow volume and effluent concentration limitations) the impact on water quality will either be localized or insignificant. Allowing no change to Order no 97-117 would require the discharger to implement the only alternative to control the ammonia problem by re-designing the entire treatment plant to provide full nitrification at a capital improvement cost of approximately 10 million dollars (based on discharger cost analysis). Resolution 68-16 requires that any activity which increases a volume of a waste must meet waste discharge requirements which will result in the best practicable treatment or control of a discharge to assure that pollution will not occur and the highest water quality consistent with maximum benefit to the people of the state will be maintained. To the extent that any increase is regarded as occurring as a result of this order, it will allow wastewater utility service necessary to accommodate housing and economic expansion in the Manteca area, and is considered to be a benefit to the people of the State. 35. The SWRCB, on 16 May 1974, adopted Resolution No. 74-43 titled "Water Quality Control Policy for Bays and Estuaries of California". This Policy is applicable to this discharge to the San Joaquin River, an estuarine water of the state. 36. Effluent limitations, and toxic and pretreatment effluent standards established pursuant to Sections 208(b), 301, 302, 304, and 307 of the Clean Water Act (CWA) and amendments thereto are applicable to the discharge. 37. The discharge is presently governed by Waste Discharge Requirements Order No. 97-115 adopted by the Board on 20 June 1997. 38. The Discharger is required to establish a Pretreatment Program to enforce the requirements promulgated under Sections 307(b), (c), (d), and 402 (b) of the Clean Water Act. The discharger does not have an approved and implemented Pretreatment Program yet. The City submitted the Pretreatment Program to this office,but as of yet has not been approved. This permit contains a time schedule for implementation of a Pretreatment Program.