Laserfiche WebLink
S.-'w %we <br /> HORIZON ENVIRONMENTAL INC. <br /> Specialists in Site Assessment,Remedial Testing,Design and Operatlon <br /> October 30, 2009 <br /> Mr. Michael Infurna Jr., Senior R.E.H.S. <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202-3029 <br /> N <br /> Subject: Soil Gas Investigation Work Plan <br /> Beacon Station No. 3641 <br /> 12I0 East Hammer lane, Stockton, California <br /> Mr. Inftuna: <br /> At the request of Ultramar Inc. (Ultramar), Horizon Environmental Inc. (Horizon) has <br /> prepared this work plan for a soil gas investigation (SGI) at the Beacon Station No. 3641 <br /> (site) located in San Joaquin County, California as shown on the enclosed Figure 1. The <br /> purpose of the soil gas investigation is to evaluate the potential for soil gas intrusion into the <br /> on-site buildings and the associated inhalation-exposure pathway human health risk. <br /> Site Description And Background <br /> The site is an operating service station located on the southwest corner of the intersection of <br /> East Hammer Lane and Kathleen Drive in Stockton, California as shown on the enclosed <br /> Figure 2. Site facilities include a service station/convenience store, two canopy-covered <br /> dispenser islands situated in the central portion of the property and three double-walled <br /> underground storage tanks (USTs) located in the western portion of the property. There are <br /> thirteen groundwater monitoring wells (MW-1 through MW-7 and MW-9 through MW-14), <br /> eight vapor wells (VW-1 through VW-8) and one sparge well (SW-1) associated with the <br /> site. The off-site monitoring well MW-8 was destroyed in April 2003. <br /> Quarterly groundwater monitoring has been performed at the site from third quarter 1996 to <br /> third quarter 2009. Monitoring data have indicated variable groundwater flow directions <br /> from quarter to quarter and from location to location on site. The predominant flow <br /> direction in the immediate UST basin area has been predominantly southward under <br /> gradients of less than 0.01. The source of hydrocarbon impacts to soil is limited to the UST <br /> basin area. Soil and groundwater impacts are currently delineated laterally and vertically. <br /> In the second quarter 2008 groundwater monitoring report, Horizon recommended: that the <br /> vapor extraction system be turned off; continuation of monitoring analytical trends and; if <br /> monitoring indicated continued decreases in hydrocarbon concentrations in groundwater, the <br /> site should be considered for low-risk closure. The San Joaquin County Environmental <br /> Health Department (EHD) recommended submittal of an SGI work plan as part of the site <br /> closure evaluation process in their review letter dated August 21,2008 (enclosed). <br /> 4970 Windpluy Drive,#C5 -FI Dorado Hills.CA 95762 - (916)939-2170 - FAX(916)939-2172 <br /> P.O.Box 5283 - Bakersfield,CA 93388 - (661)589-8389 - FAX(661)589-1456 <br />