ARCHIVED REPORTS XR0002745 - Laserfiche WebLink

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v ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors , 1 a,?i Donna K Heran,R E H 5 304 East Weber Avenue,Third Floor Carl Borgman,R E H S H' ADrrector Mike Huggins,R E H S,R D I • Al Olsen,R.E H s Stockton, California 95202-2708 Douglas W Wilson,R E H S e P` Program Manager Telephone (209) 468-3420 Margaret Lagono,R E H S 4�rFoa` Laurie A Cotulla,R E H S Fax (209) 464-0138 Robert McCiellon,R E H S Program Manager Mark Barcellos,R E H S PAUL SUPPLE NOV 0 7 2002 ATLANTIC RICHFIELD COMPANY PO BOX 6549 MORAGA CA 95470 RE ARCO Station 4932 SITE CODE 11136 16 E Harding Way Stockton CA 95204 San Joaquin County Environmental Health Department (SJCIEHD) has reviewed the "Site Assessment and Aquifer Testing Results" dated June 7, 2002 and the "Problem Assessment Report" (PAR) dated August 29, 2002 that were prepared on your behalf by SECOR International Incorporated (SECOR) and has the following comments • The June 7, 2002 report documents the installation of one deeper screened monitoring well (DMW-1) and one groundwater extraction well (EW-1) in March 2002, and the performance of a step-drawdown and constant rate pumping test in April 2002 DMW-1 was installed to monitor for possible vertical migration of the onsite groundwater contamination documented to extent to at least 50 feet below surface grade in soil boring SBA, and to be present in onsite shallow groundwater monitoring wells MWA thru MW-4 EW-1 was installed to perform the aquifer testing Analytical results from the soil sample collected at 80 feet below surface grade (bsg) from boring DMW-1 confirmed the non-detect results at depth from deep soil borings SB- 1 and SB-2 that were advanced on-site in July 2001 Analytical results from the initial groundwater samples collected from DMW-1 were 9 6 parts per billion (ppb) benzene and 140 ppb methyl tertiary butyl ether (MtBE) The step-drawdown test was performed to determine the appropriate pumping rate to use for the constant-rate pumping test This rate was determined to be 6 gallons per minute, and the constant rate pumping test was initiated at this rate However, as the test progressed it became necessary to decrease the pumping rate to prevent dewatering of the well The rate was decreased to 5 5 gallons per minute, and then to 4 5 and finally 4 0 gallons per minute The remainder of the test was performed at this rate Based on the drawdown measured in the selected observation wells, SECOR calculated a capture zone radius of 31 feet and 48 feet in the down-gradient and cross- gradient directions, respectively With the installation of additional extraction points, SECOR recommends groundwater extraction as an effective remedial alternative for mitigation of the petroleum hydrocarbon impact at this site MCF&R-w MI Nov 1 1 2002 BY.-------------------.