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Mr. Mike Lescisin - 2 - �./ 29 July 2003 other metal precipitates. DWG proposes using a dual cartridge filter. DWG must demonstrate that the dual cartridge filter is capable of removing the particulate load. 3. The Conceptual Plan states, "The purpose of this system will be to produce a dilute ferrous hydroxide solution from extracted groundwater, and infiltrate the solution as closely as possible through the migration pathways that originally contaminated the groundwater. The ferrous hydroxide solution is intended to reduce the Cr VI in the subsurface to Cr III, and stabilize Cr III." DWG must demonstrate that ferrous hydroxide as the reducing agent will remain in solution to effectively treat the subsurface pollutant mass and will not precipitate out and plug the infiltration gallery. The groundwater extraction and treatment must continue even if the infiltration gallery is plugged. Thus, if this occurs, an alternative discharge method will be necessary. DWG should contact the local sewer authority to discuss the possibility of discharging the treated water into the sanitary sewer. 4. Reinjection of treated water or injection of a reductant into the subsurface requires Waste Discharge Requirements (WDRs) and discharge of treated groundwater to surface water at Mormon Slough would require a National Pollutant Discharge Elimination System (NPDES)permit. The process to obtain either WDRs or an NPDES permit begins with submitting a Report of Waste Discharge,which requires complete waste characterization information. This information is typically gathered in a treatability study. DWG must work closely with Board staff to accomplish this element of the cleanup. Thus,before moving forward with the development of this treatment strategy DWG must complete a bench scale treatability study. The treatability study must consider site specific conditions, such as using contaminated soil and groundwater from MW-3. Control tests should use unaffected soil and groundwater from the site. Pre and post treatment sampling should include the analyses necessary to completely characterize the groundwater before treatment and the discharge after treatment. DWG should also consider other reductants such as calcium polysulfide. DWG must also develop a strategy to model the infiltration gallery. By 15 September 2003,please submita workplan far a berrclrscale treatability studyfor the cleanup of the hexavalent chromium pollution in soil and groundwater. If you have any questions, you may contact me at (916)255-3082. 'e" MAR"ERPA Private Sites Cleanup Unit cc: Ms.Margaret Lagorio, San Joaquin County Environmental Health Department, Stockton Ms. Jeanne Homsey, ATC Associates, Modesto