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., NVES N ;390 EASTvEAArMR MEET GE-C.-ET'-LT rE \EEERS j�700DL.4ND, C-4,95776-16003 CA-LIF. CONTRACTOR 4!513857 (530) 668-5300 . IREGISTF-RED GEOLOGIS'T'S F-4X (530)662-0273 �r e,e�cal.�et May 23, 2005 Mr. Richard Stiffler Environmental Control Section, Department of Municipal Utilities City of Stockton 2500 Navy Drive Stockton, CA 95206-1191 (209) 937-8740 Fax (209) 937-8708 RE: Request for modification to treatment system for Discharge of treated groundwater to City of Stockton at Sanchez Property, 1876 Country Club BIvd, Stockton, California. Dear Mr. Stiffler: As per our phone conversation on Friday, May 20, 2005, the following discusses the changes to the treatment system to alleviate TBA (tert Butyl Alcohol) from being discharged to the sanitary sewer. Revision to treatment system. A revised schematic reatment system is shown on Figures I and 2. The treatment system is designed toe remove contaminants of concern (COC) from groundwater extracted from excavation well MWIO. Maximum pump rates from MW10 are not to exceed 10 gallons per minute. We wish to modify the treatment system by adding a fifth water carbon unit in series to the pre-existing four and placing an aeration tank between carbon units 42 and #3. The existing treatment system was able to remove all of the COCs with the exception of tert Butanol (TBA). The aeration tank will allow for the further oxidation of TBA followed by three water carbon units, prior to discharge. The majority of petroleum hydrocarbons are removed in the initial water carbon unit with further removal occurring in the second water carbon unit. Placing the aeration tank after the second carbon unit will aIIow the oxidation to be concentrated on MtBE and TBA. Summary of operation and maintenance (O&M) practices for the treatment system. Operation: Groundwater is extracted from well MWIO by electrical submersible pump_ This pump is capable of pumping 12 gallons per minute. A valve at the influent of the 41 water carbo in used to adjust the flow rate to the permit condition of 10 gpm or less. The pumped water travels to the two in series water carbon units 41 and #2, prior to be sprayed into the newly added aeration tank (poly tank). A centrifugal pump (capable of Pumping the treated water at 20 gpm) attached to the bottom bung of the aeration tank, Pumps the water from the tank to a manifold that will allow IO gallons per minute 1 WATER TREATMENT modification May 2005