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,16 Report on Additional Site Assessment and Soil Vapor Extraction Testing
<br /> 7-Eleven Store No 20632 4627 Da Vinci Drive Stockton CA August 14,2002
<br /> 10 INTRODUCTION
<br /> This report is submitted by Shaw Environmental & Infrastructure, Inc (Shaw E&I) to summarize the
<br /> results of well installation and soil vapor extraction (SVE) testing at the 7-Eleven, Inc Store No 20632,
<br /> located at 4627 Da Vinci Drive in Stockton, California (Figures 1 and 2) The scope of work Included
<br /> drilling and soil sampling of one boring and installing three groundwater monitoring wells and two nested
<br /> SVElair-sparge (AS) wells SVE testing was also conducted The work was designed to fulfill the
<br /> requirements of the San Joaquin County Public Health Services (SJCPHS)
<br /> 20 BACKGROUND
<br /> On February 21, 1997, Fluor Daniel GTI supervised the advancement of six angled and four vertical
<br /> geoprobe borings (GP-1 through GP-10) at the site Sall samples were collected from the borings at
<br /> vertical depths of 5 to 15 feet below grade (bg) The six angled borings (GP-1 through GP-7) were drilled
<br /> beneath the three 10,000-gallon underground storage tanks (USTs) at the site as required by SJCPHS
<br /> prior to tank lining permit approval In addition, groundwater grab samples were collected from borings
<br /> GP-1, GP-5, and GP-7 through GP-10 The soil and groundwater samples were submitted for laboratory
<br /> analysis of benzene, toluene, ethyibenzene, and total xylenes (BTEX), methyl tert butyl ether(MTBE),
<br /> and total petroleum hydrocarbons as gasoline (TPH-G) using EPA Method 8015/8020 Samples were
<br /> additionally analyzed for tert-butanol (TBA), MTBE, di-isopropyl ether(DIPS), ethyl-tert-butyl ether
<br /> (ETBE), and tert-amylmethyl ether(TAME) by EPA Method 8260 The highest benzene, MTBE, and
<br /> TPH-G concentrations in the sail samples collected from the borings were reported in sample GP-3-6, at
<br /> 0 44 milligrams per kilogram (mg/kg), 12 mg/kg, and 150 mg/kg, respectively The highest benzene,
<br /> MTBE, and TPH-G concentrations In groundwater samples were reported in sample GP-1 at 390
<br /> a micrograms per liter (ug/L), 16,000 µg/L, and 16,000 µg/L, respectively MTBE was reported in sample
<br /> GP-8 at a concentration of 870 µg/L using EPA Method 8260
<br /> On September 21 and 22, 1997, Fluor Daniel GTI supervised the drilling of four groundwater monitoring
<br /> wells (MW-1 through MW-4) to depths ranging from 16 5 to 21 5 feet bg (Figure 2) Soil samples were
<br /> collected from each borehole at 5-foot intervals beginning at approximately 5 feet bg
<br /> On October 21, 1998, three 10,000-gallon USTs and associated product piping were removed from the
<br /> Qsite Eight soil samples collected from the sidewalls of the UST excavation, six sod samples collected
<br /> beneath the former product piping and fuel dispensers, and two sod samples collected beneath the former
<br /> vent piping were analyzed for BTEX, TPH-G, and oxygenates Approximately 967 tons (approximately
<br /> 1,130 cubic yards) of soil were generated during the UST removal and over-excavation of the tank pit to
<br /> accommodate new USTs Due to shallow groundwater at the site, approximately 92,000 gallons of water
<br /> were generated during tank pit dewatering to allow for installation of the USTs Ail soil and groundwater
<br /> generated during the UST replacement were transported from the site for proper treatment and disposal
<br /> Groundwater monitoring well MW-4 was destroyed during excavation Monitoring well MW-5 was
<br /> installed In December 31, 1998, to provide a monitoring point near the dispenser island
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