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EUMUNpRNGR G.BNUWN JH. < ' GOVE b O C AwnRN I♦ M AT'r E w 111 D R I O U E Z WaterBoards ENVIRONMENTAL PROTECTION Central Valley Regional Water Quality Control Board TO: Duncan A. Austin, P.E. Site Cleanup Program Manager FROM: Nathan Casebeer, P.G. Steven Meeks, P.E. DATE: January 5, 2015 SUBJECT: RATIONALE FOR CONSIDERING NO FURTHER ACTION ON THE LANDING SHOPPING CENTER, 3422 WEST HAMMER LANE, STOCKTON, SAN JOAQUIN COUNTY Rationale: Soil vapor and groundwater investigations conducted in 2000 indicate low concentrations or tetrachloroethene (PCE) that do not appear to present a threat to water quality or human health. Issues: A passive soil vapor survey identified a release of PCE behind a former dry cleaner possibly associated with a sewer line. Subsequent sampling of shallow groundwater in this location confirmed low concentrations of PCE in groundwater that were below the Maximum Contaminant Level for drinking water. Setting: A former dry cleaning business that operated at the site between 1989 and 1994. Source: Leaks and/or spills of the dry cleaning solvent PCE. Actions: Investigations were conducted at the site during 2000 beginning with a passive soil gas survey using Gore Sorber® modules followed by drilling, installing and sampling monitoring wells. Maps showing the sampling locations are attached. Gore Sorber® modules were installed and left to collect soil gas at 13 locations at the site between April 24 and May 9, 2000. Laboratory results indicated PCE in 10 of the 13 locations. The location that contained the highest mass of PCE, which was behind the business, also contained detections of trichlorethene, cis-1,2-dichloroethene and trans-1,2- dichloroethene indicating breakdown of PCE at that location. A total of six monitoring wells were drilled at the site on July 13 and August 1, 2000. Each monitoring well was installed to a depth of approximately 15 feet. Groundwater was encountered at approximately 9 feet below ground surface at the site with static depth to water measurements at approximately 8 feet below ground surface. The monitoring wells were developed and subsequently sampled on August 3, 2000. PCE was detected in MW-1 at 2.9 micrograms per liter (pg/L), MW-3 at 3.5 pg/L, and MW-5 at 1.4 pg/L. MW-2, MW-4, and MW-6 did not contain PCE. No other constituents tested were detected in any of the KARL E. LONGLEY SCD, P.E.,CHAIR I PAMELA C. CREEDON P.E., 6CEE, EXECUTIVE orrICER 11020 Sun Center Drive#200,Rancho Cordova,CA 95670 1 www.waterboarde.ca.gov/centralvalley IJ RECYCLED PARER