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Mr. Robert Meleg -4 - 22 July 2003 Public Works Director In light of the additional groundwater data submitted in the RWD, the initial 20 mg/L BODS and TSS limitations specified in the 1 May 2003 Regional Board letter responding to the initial RWD may not be sufficiently protective of groundwater quality. The RWD proposes implementation of various measures to improve effluent quality over the next four-seven years. These include (1) implementing a pretreatment program; (2) conducting additional monitoring and evaluation of the underlying groundwater; (3) lining of the treatment ponds if deemed necessary; and(4) improving effluent water quality by removing sludge from the WWTF's ponds, reconfiguring the treatment ponds, adding additional aerators, and constructing a treatment wetland. The RWD indicates that these improvements will still not likely meet the limits specified in the 1 May 2003 Regional Board letter. With the above-proposed improvements, the RWD characterizes the BODS effluent quality as ranging from 40 to 70 mg/L. It also indicates that the TCO limitation is not warranted because the positive TCO results are infrequent. Although these improvements are acceptable as short-term solutions to reduce the impact of the discharge on groundwater, their implementation will likely still result in exceedances of water quality limits. The City needs-taimplement BPTC measures to minimize the discharge's impact to groundwater and to ensure, at a minimum, that the discharge does not cause exceedances of water quality limits in groundwater. Additional improvements, such as disinfection, are warranted, as `occasional" TCO hits indicate there is inadequate vertical separation distance between the bottom of the disposal ponds and groundwater. Based on recent observation of the bottom of one of the treatment ponds, the RWD acknowledges that the treatment ponds are probably not lined. The RWD indicates that with the increased monitoring of treatment performance and groundwater to determine the actual influence of the lack of a liner may become more evident in the future. The RWD proposes to collect additional data (1 to 3 years) to determine if a liner is needed. If one is needed, the RWD proposes investigating the feasibility of installing a clay liner by introducing benonite to the ponds in a partially-drained condition. Existing concentrations of waste constituents in groundwater already show exceedances of water quality limits. The proposed liner is not reflective of BPTC. Based on best professional judgment, the maximum seepage rate from municipal wastewater ponds reflective of BPTC for most discharge situations is 550 gallons per acre per day. However, this seepage rate may be too rapid for high groundwater table situations like Riverbank's. The RWD proposes to construct a 5.2-acre wetland for use for final polishing (i.e., reduction of TSS and total nitrogen) before disposal. Because concentrations of waste constituents in groundwater exceeds water quality limits and, due to the shallow occurrence of groundwater, the construction of wetlands under these site specific circumstances is not appropriate and will likely not be protective of groundwater quality. Constructed wetlands in the San Joaquin Valley to treat municipal wastewater have not been consistently able meet the requirements specified in the WDRs (e.g., Gustine WWTF). The RWD also does not include plans to line the