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14:011 <br />OflNI <br />Water Boards <br />g, EDMUND C. BROWN JR <br />t: GOVERNOR <br />MATTHEW RODRIQUEZ <br />SECRETARY FOR <br />ENVIRONMENTAL PROTECTION <br />Central Valley Regional Water Quality Control Board <br />5 July 2018 RECEIVED <br />JUL i9 <br />IS 'IS <br />4t,L., 1U <br />Mr. Steve Azevedo <br />West Clay Properties/Knife River Corporation <br />P. 0. Box 6099 <br />Stockton, CA 95206 <br />i•;NVIRONMENTAL IlEALTH <br />DEPARTMENT <br />West Clay Property, 639 West Clay Street, Stockton, San Joaquin County <br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br />reviewed the Site Assessment Report (Assessment Report) dated 27 September 2017, and the <br />Groundwater Monitoring Report— First Quarter 2018 (1Q2018 Report) dated 19 June 2018, <br />both submitted on your behalf by Advanced GeoEnvironmental, Inc. (AGE). The West Clay <br />Property is located at 639 West Clay Street in Stockton (Site). <br />In August 2017, AGE advanced and collected depth discrete grab groundwater samples from <br />borings B19 to B21. Borings B19 and B20 were advanced to 90 feet below ground surface (ft <br />bgs) and grab groundwater samples were collected from 56 to 61 ft bgs and 85 to 90 ft bgs in <br />B19, and from 60 to 65 ft bgs and 85 to 90 ft bgs in B20. Boring B21 was advanced to 95 feet <br />bgs, and grab groundwater samples were collected from 60 to 65 ft bgs and 90 to 95 ft bgs. <br />AGE detected up to 57 micrograms per liter (ug/L) total petroleum hydrocarbons as gasoline <br />(TPH-G), 1,300 ug/L TPH as diesel (TPH-D), 0.74 ug/L benzene, 2.5 ug/L TBA, and 0.68 ug/L <br />1,2-dichloroethane (1,2-DCA) in grab groundwater samples collected between 56 and 65 ft bgs. <br />In grab groundwater samples collected between 85 and 95 ft bgs, AGE detected up to 140 ug/L <br />TPH-G, 2,900 ug/L TPH-D, 6.7 ug/L benzene, 0.73 ug/L methyl tert butyl ether (MTBE), 5.1 ug/L <br />TBA, and 2.6 ug/L 1,2-DCA. AGE recommended advancement of additional borings to define <br />the extent of groundwater <br />During the first quarter 2018, AGE detected up to 16,000 ug/L TPH-G, 1,600 ug/L TPH-D, <br />1,500 ug/L benzene, 18 ug/L MTBE, 96 ug/L naphthalene, and 3 ug/L 1,2-DCA. <br />Please continue groundwater monitoring on a semi-annual frequency. The Third Quarter 2018 <br />Semi-Annual Groundwater Monitoring Report is due 15 November 2018. <br />Central Valley Water Board staff agrees that additional assessment is needed to define the <br />extent of petroleum impact to groundwater, but request that you install groundwater monitoring <br />wells to confirm grab groundwater results and to provide repeatable data points. Please submit <br />KARL E. LONGLEY ScD, P.E., CHAIR I PATRICK PULUPA, ESO., EXECUTIVE OFFICER <br />11020 Sun Center Drive 4200. Rancho Cordova CA 95670 I www.waterboards.ca .govicentralvalley <br />0 RECYCLED PAPER