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Ms.Vicki McCartney,SJCEHD August 29,2008 Work Plan for Bench-Scale Test and Injection Well Installation Project No.2046-3250-01 Parkinson's I-5 ARCO Service Station,Stockton,California Page 2 situated in the southeastern portion of the property. The area immediately surrounding the site is commercial, with residential neighborhoods situated about 500 feet east, south and west of the property. The general configuration of the facility is shown on Figure 2. According to information available on the State Water Resources Control Board's (SWRCB) GeoTracker website, an active environmental case under SJCEHD regulatory jurisdiction is located immediately east of the site (across a small access easement road). This property is currently in use as a ConocoPhillips/76-branded service station dispensing gasoline and diesel fuels (BP No. 11193, 3202 W. Hammer Lane, Global I.D. No. T06077000612). The location of this property is shown on the site vicinity map included as Figure 3. PREVIOUS SITE ASSESSMENT AND FEASIBILITY TESTING According to historical documents contained in SJCEHD's files, subsurface petroleum hydrocarbon impact at the property was discovered in January 2000, during product piping and fuel dispenser construction upgrade activities. Gasoline range organics (GRO) and benzene, toluene, ethylbenzene, and total xylenes (BTEX) were identified in compliance soil samples collected at a depth of about 3.0 feet below ground surface (bgs) from beneath the former piping and dispenser locations. Maximum concentrations of GRO (4,450 milligrams per kilogram [mg/Kg]) and benzene (0.134 mg/Kg) were reported in samples D-1 at 3 feet bgs and D-8 at 3 feet bgs,respectively. r- Prior to installing the new product lines and fuel dispensers, a limited over-excavation was completed at the dispenser islands in an attempt to remove a portion of the adsorbed hydrocarbon mass from shallow subsurface soils. The excavation extended to a maximum depth of 10 feet bgs. The excavation depth was limited by the presence of groundwater and was laterally constrained by f the presence of the concrete canopy footings. Approximately 262 tons of soil was removed from the site at this time. Maximum concentrations of GRO (4,110 mg/Kg) and benzene (8.47 mg/Kg) were reported in a sample (D-1-C at 10 feet bgs) collected beneath the�vestern fuel dispenser. In August 2000, IT Corporation (IT) oversaw the advancement of five direct-push soil borings (GP-1 through GP-5). Each boring was advanced to groundwater and discrete grab water"samples were collected. In September 2000, based on analytical results of samples collected from the direct-push borings, IT installed three on-site groundwater monitoring wells (MW-1 through MW-3) screened across first-encountered groundwater from approximately 10 to 25-feet bgs 11 quarterly groundwater monitoring and sampling program was initiated during thefi t quarters and has continued to date. Well construction details for all borings/wells dril ed at the site are included as Table 1. Historical soil analytical results, grab water sample analytical results, and historical groundwater elevation and analytical data are summarized on Tables 2, 3, 4, and 5. Iri May 2002, IT installed two off-site groundwater monitoring wells (MW-4 and MW-5) also screened across first-encountered groundwater from approximately 10 to 25 feet bgs. In addition, K:\Parkinsons Hammer 1-5 Arco\Work Plans\Work Plan for Ozone Bench Scale Test.doc