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_ GROUNDWATER ASSESSMENT WORK PLAN 521 NORTH CHEROKEE LANE LODI, CALIFORNIA SITE CODE. 1324 (lb wp, 13 March 1994) BACKGROUND: The following background summary and the proposed scope of work is based on a review of the Preliminary Report Evaluation of Soil and Ground-Waxer Contamination (Applied GeoSystems [AGS], September 21, 1988), the Preliminary Investiganon and Evaluanon Report (Geological Audit Services, Inc [GAS], 10 August 1991), and the Groundwater Sampling Report (Dana Booth, 4 March 1994) The site is located at 521 North Cherokee Lane in Lodi, California (Plate 1) GAS reported that Ramcon removed five underground gasoline storage tanks (UST's) from the site by on 5 February 1988. Soil samples collected from beneath the largest tank (10,000 gallons) contained total petroleum hydrocarbons as gasoline (TPHg). Based on these results, Ramcon retained AGS to further delineate the extent of soil contamination and the potential that groundwater had been impacted In August 1988, Applied GeoSystems drilled four borings (B-1 to B-4, Plate 2). After drilling, Applied GeoSystems converted B-4 into a 2-inch diameter shallow-groundwater monitor well (MW-1) Soil samples were collected at five foot intervals from each of the borings and qualitatively field screened for volatile organics using a photoionization detector (PID) Relatively low but positive PID readings were recorded by AGS on the Log of Boring for B-3 throughout most of the drilled hole. The highest PID reading from B-3 was recorded at a depth of 20 feet below ground surface (bgs) Although the upper hole (0 to approximately 25 feet bgs) of B-4 recorded background type PID readings, the highest recorded PID reading was recorded in boring B-4 at approximately the groundwater surface(40 feet bgs) None of the soil samples were submitted for quantitative analysis Boring B-4 was advanced to approximately 60 feet bgs and completed as MW-1 Prior to development, AGS observed a sheen on water removed from MW-1. The sheen was again observed prior to presampling purging Upon attempting to sample MW-1, AGS measured an immiscible product layer of 0.5 inches. The sample was not analyzed In April 1991, Mr. Ganzer (Ganzer and Williams) retained Falcon Energy and GAS to further define the extent of groundwater impact by TPHg at the site In May 1991, GAS supervised the installation of two additional 4-inch diameter monitor wells (MW-2 and MW-3, GAS reported installing 2-inch wells). Soil samples were collected at five foot intervals from each of the monitor well borings from 10 to 45 feet bgs Field observations during the drilling of MW-2 indicated the potential presence of petroleum hydrocarbons from approximately 45 feet 1