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csj ii a1 • 24 July 2000 AGE-NC Project No 99-0654 Page 3 of 6 25 REGIONAL GROUND WATER DEPTH AND FLOW DIRECTION The estimated depth to ground water at the property is approximately 30 to 40 feet below surface grade (bsg), based on the map titled Lanes of Equal Depth to Groundwater Fall 1998 published by the San Joaquin County Flood Control District and Water Conservation District (FCD&WCD) It is inferred from the map titled Lanes of Equal Elevation of Groundwater Fall 1998, also published by the FCD&WCD, that ground water flows toward the northeast in the general area of the site, but this may be modified by changing recharge and discharge patterns Ground water is considered to be of beneficial use and is used for domestic, industrial and commercial purposes The closest surface water feature to the site is San Joaquin River and Walker Slough located approximately 4,500 feet southwest of the site Water from the site drains into the San Joaquin River Deep Water Channel and is primarily used for commercial and recreational boating Based upon well information obtained from nearby saes, ground water flow direction is northeasterly and is currently estimated to occur at a depth of approximately 30 to 40 feet below surface grade (bsg) • 3.0. PROCEDURES An Interim Remediation Work Plan, dated 22 March 2000, for the excavation and disposal of hydrocarbon-impacted soil, was prepared by AGE and approved by PHS-EHD The objective of the interim remediation was to remove hydrocarbon-impacted soil from the floor and sidewalls of the former underground storage tank (UST) excavation prior to installation of new USTs 3 1 EXCAVATION OF HYDROCARBON-IMPACTED SOIL On 20 Apnl 2000, approximately 175 cubic yards of petroleum hydrocarbon-impacted soil were excavated from the former UST area Excavation was performed by Stockton Service Station Equipment Company using a Holt excavator Excavated soil was screened for the presence of organic vapor using a using an organic vapor meter (OVM) equipped with a photo-ionization detector (PID Thermo Environmental 580A, 10 0 eV, calibrated to isobutylene) Based on OVM readings and field observations, excavated soil was segregated into clean soil and impacted soil, only soil exhibiting hydrocarbon odor or measurable OVM readings were stockpile for transportation and final disposal 3 2 EXCAVATION SOIL SAMPLE COLLECTION AND ANALYSIS • Soil samples were collected from the floor and sidewalls of the excavation and stockpiled soil by