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STA i E OF CALIFORNIA -Environmental Protectio**W—gency %Noe PETE WILSON Governor
<br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD —
<br /> CENTRAL VALLEY REGION �, ,. • `
<br /> 3443 Routier Road, Suite A ��'� IRO"'i.,,-i;___NTAL HEALTH — �
<br /> Sacramento, CA 95827-3098 P€tj; ;T C, V I G E �}
<br /> PHONE: (916) 255-3000
<br /> FAX: (916) 255-3015 93 OCT — t PN
<br /> 2: 12
<br /> 27 September 1993
<br /> Kenneth R. Earnest
<br /> Ultramar, Inc.
<br /> 525 West Third 4
<br /> Hanford, CA 93232-0466
<br /> CONCURRENCE WITH CLOSURE OF BEACON STATION #492, 470 NORTH MAIN STREET,
<br /> MANTECA, SAN JOAQUIN COUNTY
<br /> i
<br /> On 16 September 1993, Donna Heran of the San Joaquin County Public Health Services,
<br /> Environmental Health Department wrote to the Regional Board requesting concurrence with closure
<br /> for this site. Staff review of the file finds that three 10,000-gallon underground storage tanks are
<br /> located on the site, and one of the tanks, which contained diesel fuel, failed a pressure precision test
<br /> for the third time on 12 September 1986. The diesel was subsequently removed from this tank, and
<br /> on 2 and 3 December 1986, three soil borings were drilled and converted into monitoring wells.
<br /> The soil was found to be mainly silty sand, with ground water at a depth of about 15 feet below
<br /> ground surface (BGS). Soil contamination was found to the lowest sampling point of 25 feet BGS,
<br /> where 4.3 parts per million (ppm) total volatile hydrocarbons (TVH) were found. The maximum
<br /> soil contamination found was at 20 feet BGS, with 167.9 ppm TVH. Maximum ground water
<br /> contamination was found in monitoring well 1, with 7.297 ppm TVH and 77 parts per billion (ppb)
<br /> benzene.
<br /> In May 1987 the underground tanks were uncovered and lined with fiberglass. Also at this time,
<br /> four vapor extraction wells were installed between the tanks. In October and November of 1989, a
<br /> vapor extraction system was used to remove 1,950 pounds of hydrocarbon vapor. Another vapor
<br /> extraction system was used between June and September 1992, which removed an additional 338
<br /> pounds of hydrocarbon vapor. Three confirmation soil borings were drilled on 7 October 1992, one
<br /> immediately east of the tanks, one immediately north of the tanks, and one slant boring under two of
<br /> the tanks. All soil samples showed no detectable contamination
<br /> Monitoring wells one, two, and three have been non-detect for gas, diesel, benzene, toluene,
<br /> ethylbenzene, and xylene on the last four sampling dates of 13 December 1991, 26 February 1992,
<br /> 13 July 1992, and 6 April 1993. Monitoring well 4 was installed on 14 February 1992 as a
<br /> downgradient well (northeast of the tanks) and was subsequently sampled on 26 February 1992, 13
<br /> July 1992, and 6 April 1993. No contamination has ever been found in this well.
<br /> Based on the information provided, Board staff has determined that appropriate response actions
<br /> have been completed, that acceptable remedial practices were implemented and at this time, no
<br /> further investigation, remedial or removal action or monitoring is required at Beacon Station #492,
<br /> 470 North Main Street, Manteca, San Joaquin County.
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