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H2O 4159 Anatolia Drive urban solutions Rancho Cordova, CA 95742 (916) 869-4957 Date: August 4, 2016 To: Tim McCoy, Public Work Director Greg Gibson, Senior Civil Engineer Milton Daley, Utility Superintendent From: Scott A. Myers, P.E. Cort Abney, P.E., M.S. Subject: Louise Avenue Water Treatment Facility Recommendations to Reduce Solids Processing Costs Introduction The City of Lathrop ("City") Louise Avenue Water Treatment Facility("LAWTF") began operations in 2012 for the purpose of removing arsenic from the City drinking water supply. The facility's water treatment process consists of adding chemicals for coagulating arsenic into an insoluble form, then subsequently removing the arsenic using rapid sand filters. Removal of arsenic generates a waste product, or "solids", consisting of the removed arsenic, coagulating chemicals, and other miscellaneous inorganic solids that are inadvertently removed with the treatment process. Currently, the solids are processed on site (dewatered and concentrated) using settling basins and a filter press. After a sufficient volume of solids are processed, the solids are transported to a landfill for disposal. Operation of the filter press is a labor-intense activity, requiring significant man-hours and associated cost. In addition, the filter press has a limited lifespan, and must be reconditioned or replaced every 10 to 15 years. Other options for solids processing may be less expensive and require fewer man-hours. Specifically, drying beds are a commonly used solids dewatering process, whereby concentrated solids are spread onto a sand bed and allowed to dry using solar radiation (evaporation). This process is much less labor-intense, and requires no electrical power or operator oversight during the drying process. After the solids are dried, they can be removed using a small loader (i.e. Bobcat Skidsteer) and transported to a disposal facility. Impediments to drying beds include adequate space or area for spreading the materials sufficiently for proper solar exposure, and periods of low or no rainfall to allow uninterrupted drying. Neither of these would obstruct use of drying beds at LAWTF. The facility has adequate space for drying beds, and the long, hot summers in the Central Valley are ideal for this process. Due to the ongoing costs and operator time currently incurred by the City, the use of drying beds for dewatering were investigated, as discussed herein.