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• 0 •, Mr. Robert Meleg - 2 - 22 July 2003 Public Works Director capacity4o accommodate the flow limits set forth in the WDRs. The additional disposal ponds will provide additional disposal capacity but not treatment capacity. The RWD proposes to expand the WWTF to accommodate future wastewater flows and increase the disposal capacity by constructing two additional disposal ponds with a combined percolation area of 18 acres on a 40-acre site just east of the existing WWTF. This will increase the WWTF's total disposal capacity to 5.3 mgd. The Discharger also proposes to increase treatment performance by dredging the sludge from the treatment ponds, adding additional aerators if needed, and constructing a wetland for effluent polishing. The 1 May 2003 Regional Board letter specifically requested the City submit a supplemental RWD with information regarding (1) surrounding land uses, (2) a technical evaluation of the existing WWTF, (3) a proposed sampling plan to better characterize the quality of effluent, (4) a summary of the recent groundwater monitoring data, (5) a technical evaluation of the permeability of the existing aerated ponds, (6) additional industrial user data and (7) a technical discussion of the best practicable treatment and control (BPTC) measures the City has implemented or intends to implement. The RWD contains sufficient information for staff to prepare tentative waste discharge requirements; therefore it appears complete. However, we would like to clarify some of the issues noted in the RWD. Summaries of portions of the RWD are in italics with Regional Board staffs comments below. The RWD indicates that groundwater mounding is occurring beneath the evaporationlpercolation ponds[disposal ponds], and so all monitoring wells appear to be located downgradient of the WWTF and are likely all influenced by the WWTF. It is also likely that some wells are subject to additional impacts outside of the WWTF(MW-3 and MW-6). Groundwater data indicates that the existing monitoring wells do not provide "upgradient" groundwater quality. The RWD indicates that, due to site constraints, the City will be unable to provide an upgradient well. Although MW-6 appears to be impacted by sources other than the WWTF(onsite septic tank disposal systems approved and monitored by San Joaquin County), existing monitoring wells (MW-5) directly downgradient of the City's WWTF disposal ponds indicate that the discharge is causing exceedances of water quality limits in groundwater. Additionally, revised WDRs will likely contain a provision requiring the City to characterize background water quality. The City should contact San Joaquin County to inquire about using lands and easements owned by the County for placement of upgradient well(s) to monitor shallow groundwater uninfluenced by the wastewater discharge or by other concentrated sources of waste constituents. The RWD indicates groundwater in the vicinity of the WWTF is not degraded and meets the primary and secondary requirements for drinking water within the upper layer of the aquifer. The above statement is incorrect. The Water Quality Control Plan for the Sacramento River Basin and the San Joaquin River Basin,Fifth Edition, (hereafter Basin Plan) designates beneficial uses, establishes water quality objectives, and contains implementation plans and policies for all waters of the Basin. The