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0 0 <br /> City of Lathrop - 2 - 23 October 2015 <br /> San Joaquin County <br /> Well Installation Reports. Please note that once monitoring wells KMW-10 and KMW-11 are <br /> installed, they shall be monitored in accordance with Monitoring and Reporting Program <br /> 5-01-25. <br /> Groundwater Salinity Mitigation Plan: <br /> The Groundwater Salinity Mitigation Plan identifies four primary sources of salt that have <br /> contributed to the elevated salinity concentrations observed in groundwater beneath Land <br /> Application Area LAS-2. The sources include (1) land application of effluent from the W WTF, <br /> (2) regional agricultural irrigation, (3) historical discharges of wastewater from the Occidental <br /> Chemical Company unlined wastewater ponds located north-east of the of the land application <br /> areas, and (4) historical discharges of wastewaterfrom the Libby Owens Ford Company unlined <br /> wastewater ponds located at the current Consolidated Wastewater Treatment Facility property. <br /> The City proposes to cease land application of effluent to Land Application Area LAS-2 and <br /> cover the land application area under a parking lot and/or buildings which will prevent further <br /> infiltration and mobilization of constituents associated with the City's W WTF. Finally, the City <br /> proposes to monitor groundwater for natural attenuation of salinity constituents (total dissolved <br /> solids)as a remedial action. <br /> Staff Comments: <br /> Staff agrees with the proposal to cease the discharge and cap the land application areas to <br /> prevent future percolation and mobilization of salts. However, the Groundwater Salinity <br /> Mitigation Plan failed to delineate the extent of groundwater impacts of total dissolved solids or <br /> provide an estimated time frame for groundwater to return to pre-discharge conditions, as <br /> required by the Order. <br /> Additionally, soil sample data presented in the Groundwater Salinity Mitigation Plan from Land <br /> Application Areas LAS-1 and LAS-2, taken from 1-5 feet below ground surface, indicates <br /> increasing concentrations of salts occur with depth beneath LAS-2. Measured electrical <br /> conductivity values (ECe) for LAS-2 were two to seven times greater than ECe values <br /> measured in LAS-1. However, no data is presented for Land Application Area LAS-3 and the <br /> potential for the continued use of LAS-3 to affect water quality. <br /> The Groundwater Salinity Mitigation Plan identifies the use of former unlined wastewater ponds <br /> associated with the Libby Owens Ford Company as contributing salinity to groundwater beneath <br /> the land application areas. Since these former ponds are a potential source of salt, they must <br /> be clean closed to comply with State Board Resolution 92-49, which requires the Discharger to <br /> remove all probable sources of contamination. However, no discussion is provided regarding <br /> the current condition of the ponds or the soil chemistry beneath the ponds and their potential to <br /> impact water quality. <br /> By 1 February 2016, the Discharger shall submit an Engineering Feasibility Study that contains <br /> the following: <br /> 1. A proposal for delineation of the total dissolved solids groundwater plume migrating <br /> away from Land Application Area LAS-2. <br /> 2. An estimated time line for salinity constituents (total dissolved solids)concentrations <br /> beneath Land Application Area LAS-2 to return to background concentrations (pre- <br />