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California Regional Water Quality.(;ontrol Board
<br /> Central Valley Region
<br /> Winston H.Hickox Sacramento Main Office
<br /> Secretary for Internet Address: httpa/wwwswreb.ca.govhGray Davisrwgcb5 Governor
<br /> Environmental 3443 Routier Road,Suite A,Sacramento,California 95827-3003 I
<br /> Protection Phone(916)255-3000•FAX(916)255-3015 k '
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<br /> TO: Gordon U Bo gs ,,r, FROM: Marty Hartzell
<br /> Underground Tank Program Manager'', Associate Engineering Geologist" ,
<br /> DATE: 25 Janu ry 2001 t ." SIGNATURE:
<br /> NONCONCURRENCE WITH SAN JOA QUIN COUNTY'S NO FURTHER ACTION REQUIRED
<br /> DETERMINATION, RUIZ GROCERY, 4491 WEST DURHAM FERRYROAD, TRACY
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<br /> I reviewed the 27 December 2000 Case Closure Summary for Ruiz Grocery submitted by Safi Joaquin County
<br /> Environmental Health Division (County),the 27 March 2000 Confirmation Soil Sampling, Groundwater
<br /> Monitoring—First Quarter 2000, and Closure Request, and the 3 August 2000 Groundwater Monitoring Report
<br /> — Third Quarter 2000; both prepared.by Clearwater Group, Incorporated(Clearwater).
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<br /> The Ruiz Grocery site is a small convenience grocery store attached to the Ruiz residence in a rural area southof"
<br /> Tracy. Fruit and nut orchards border the site to the south, and multiple residences are within 1,000 feet of the site
<br /> to the south and west. An irrigation ditch is parallel to the northeast edge of the property. Two 1,000-gallon
<br /> gasoline USTs were removed from the site in February 1989. Multiple borings were completed, and several
<br /> wells were installed: one recovery, seven monitoring, four soil vapor extraction (SVE), and two air sparge (AS).
<br /> Soil consists of silt and sand with minor'clay, and the current depth to water is 16 feet bgs. The attached Figure 1'
<br /> shows a site plan for the Ruiz Grocery. t `' 4.4
<br /> Clearwater operated a combined SVE and AS remediation system at the site from September 1998 to` E
<br /> September 1999, and removed an estimated 7,377 pounds (1,209 gallons)'of TPHg from soil and groundwater'.
<br /> Groundwater monitoring has been"completed quarterly since 1991, and decreasing trends are documented in the
<br /> quarterly monitoring reports. The maximum groundwater monitoring results in micrograms per liter(pgll) for,
<br /> samples collected for the Third Quarter 2000 monitoring event on 24 July 2000, show TPHg at 220,benzene at
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<br /> =4.55,- ethyl-benzene-at 3.0,-Iota-l_zyle- -at-20,=.and-MtBE'at,150:�Toluene,ethylene.dibromide 1 2-D_ CA and 1
<br /> other oxygenates were non-detect at acceptable detection limits.
<br /> MtBE was first identified in monitoring well MW-2 in October 1995 at 1,200 �tg/l. As shown in attached '
<br /> Figure 2, concentrations of TPHg and MtBE in MW-2 show a decreasing trend when the SVE system was
<br /> operating,then an unstable trend since the SVE system was turned off. The groundwater sample collected and
<br /> analyzed from MW-2 in July 2000 show MtBE at 150 pg/I,which is more than ten times the Primary Maximum 41
<br /> ,Contaminant Level (MCL) for MtBE of 13 qg/l. Additional groundwater monitoring is required to identify the
<br /> trend of MtBE in the area near MW-2, and future corrective action may be required to reduce the concentration.
<br /> of MtBE at this site.
<br /> Sparge wells SW-1 and-2 are screened from 23 to 25 feet, and provide depth discrete water sample points below
<br /> first water. These wells have been sampled twice since the SVE/AS system was turned off in September 1999.
<br /> SW-1 is non-detect for all constituents; however, MtBE was identified in SW-2 at 5.8 �tg/l by EPA Method
<br /> 8260B in July 2000. This MtBE concentration is very close to the laboratory detection limit of 5,µg11, and
<br /> California Environmental Protection Agency
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