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ENVIRONMENTAL HEALTH DEPARTMENT
<br /> SAN JOAQUIN COUNTY
<br /> Donna K. Heran, R.E.H.S. Unit Supervisors
<br /> Director 304 East Weber Avenue,Third Floor Carl Borgman,R.E.H.S.
<br /> .l Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I.
<br /> �;. Program Manager Douglas W.Wilson, R.E.H.S.
<br /> Telephone: (209)468-3420 Margaret Lagorio,R.E.H.S.
<br /> Fax: (209) 464-0138 Robert McClellon, R.E.H.S.
<br /> Website:www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S.
<br /> ARTHUR L WYATT JR APR 10 2006
<br /> 6265 CROOKED STICK
<br /> STOCKTON CA 95219
<br /> RE: FORMER ARCO AM/PM SITE CODE: 1216
<br /> 4511 PACIFIC AVENUE
<br /> STOCKTON CA
<br /> The San Joaquin County Environmental Health Department(EHD) has reviewed Remediation Update
<br /> Report—Second, Third, FourthQuar-ters 2005 dated January 4,2006(the report)prepared by your
<br /> consultant,Advanced GeoEnvironmental Inc. (AGE) for the above-referenced site. The
<br /> remediation system at the site is comprised of a soil vapor extraction (SVE) system and a
<br /> groundwater extraction (GWE) system. Groundwater extraction well EW-1 was installed in October,
<br /> 2001, and EW-2 was installed in March,2004. Analytical results of the influent GWE samples of
<br /> EW-1 and EW-2 during 2005 ranged from non-detect (ND) to 1,700 micrograms per liter (ug/1) for
<br /> total petroleum hydrocarbons as gasoline(TPH-g), 130 ug/1 to ND for methyl tert-butyl ether
<br /> (MTBE),and 44 ug/1 to ND for Benzene during 2005- Analytical results of all monitoring event
<br /> groundwater samples were ND for TPH-g,benzene,and MTBE with the exception of vapor well
<br /> VW-1 (5,800 ug/l of TPH-g, 50 ug/1 of benzene, and 18 ug/1 of MTBE),MW-11A (16 ug/1 of
<br /> MTBE),and the furthest groundwater flow down-gradient well MW-18 (8.2 ug/1 of MTBE). AGE
<br /> estimated that the GWE system has extracted a total of 3,750,281 gallons of groundwater to date,
<br /> and recovered approximately 11 pounds of dissolved MTBE and 73.12 pounds of TPH-g since
<br /> October,2001. Between March and December of 2005, the masses extracted by GWE were 0.46
<br /> pounds of MTBE,0.13 pounds of benzene,and 6.25 pounds of TPH-g. AGE requested
<br /> discontinuation of the GWE system operation due to high cost of operation (at$1,400 for discharge
<br /> to city sewer) and reduced efficiency of the system.
<br /> Although dissolved contaminants have been periodically detected in influent GWE samples during
<br /> 2005,EHD agrees with AGE that the low rate of recovery and high cost of operation no longer
<br /> justify operation of the GWE system. MTBE continues to be detected in the off-site wells MW-11A
<br /> and MW-18, but has been ND in other sentinel wells (MW-12 to MW-17) during 2005. Between the
<br /> low concentrations of MTBE detected in the monitoring wells,and limited extent of the MTBE
<br /> plume which is still being monitored by the system of monitoring wells,the need for continued
<br /> hydraulic control via the GWE system has been obviated. EHD approves AGE's request to
<br /> terminate the GWE component of the remediation system,but operation of the SVE system should
<br /> continue.
<br /> Donna Heran,RE HS,Director
<br /> Environmental Health Department
<br /> Jeffrey Wong,Senior REHS iNucl;C. Hctndson,Jr.,PG
<br /> LOP/Site LOP/Site Mitigation Unit
<br /> Cc: CRWQCB, Central Valley Region—James L. L. Barton,PG
<br /> Cc: Advanced GeoEnvironmental,Inc. —Bill Little
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