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ED-G. 8"0w*,J. 's oovcw,or oLlroertA WaterBoards INVIPIO."NrAL Fr10T6Cnt Central Valley Regional Water Quality Control Board 7 February 2017 City of Lathrop Greg Gibson, Senior Civil Engineer 390 Towne Centre Drive Lathrop, CA 95330 EVALUATION OF PROPOSED SOLIDS DRYING BEDS, LOUSE AVENUE WATER TREATMENT FACILITY, SAN JOAQUIN COUNTY On 29 December 2016, a conference call was held between the Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff and Mr. Scott of H2O Urban Solutions, the consultant for the Louise Avenue Water Treatment Facility (WTF) (the"Discharger"). The Discharger is proposing to convert their existing solids handling process from a settling basin and filter press to a concrete-lined drying bed to reduce operation and maintenance costs. The treatment plant does not have Waste Discharge Requirements (WDRs) because there are no waste discharges to land or water. The facility's water treatment process currently consists of adding chemicals for coagulating arsenic into an insoluble form, then subsequently removing arsenic using rapid sand filters. Removal of arsenic generates a waste product, or"solids", consisting of removed arsenic, coagulating chemicals, and other miscellaneous inorganic solids. A filter press is used to dewater and concentrate the solids, which are then transported to an off-site landfill for disposal. Operation of the filter press is a labor-intense activity, requiring significant labor hours and associated costs. The filter press has a limited lifespan of 10 to 15 years. Within the next five years, the filter press will need to be replaced, at a cost of approximately $75,000. In an effort to reduce Operation and Maintenance costs, the city has identified a more cost effective solids disposal procedure. Review of Proposed Solids Drying Bed As detailed in a letter to the Central Valley Water Board dated 4 August 2016 and discussed during the conference call, the Discharger plans to construct a solids drying bed to replace the filter press system. The drying bed will consist of a sand layer placed over gravel in a concrete lined basin. Waste sludge solids will then be spread out on the drying bed and allowed to dry. After drying, the solids will be removed by a small loader and transported off site to a disposal facility. The WTF has adequate space for the drying bed. Since solids drying is not effective during cooler months (i.e., November through March),_no solids drying is proposed during this period. Production of solids from November through March is significantly ower unng the winter months due to less demand for potable water. Existing processes (i.e., backwash tanks and solids tank) are expected to have adequate storage capacity until the fluid in storage can be transferred into the drying bed during the warmer months when evaporation is more efficient. KARt.E. LONaLEY ScD.P.E.,rMuuR I Pa eLA C CREEDON P.E.,SCEE,EXECUTIVE OFFICER 11020 Sun Center Orlve 9200.Rancho Cordova.CA 05870 1 www.wstwboarde.ea.gov/centrolvalloy "Cv...o Peri"