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x yd DU P0111 NO SN'NtC IIIlS Page 11 -- August 10, 1989 Job No. 211-71-6 by other consultants. A Well Location Map is presented on Figure 5 and Table B presents a Regional Well Inventory. The closest known potable domestic well to the site is located 2,700 feet to the sc ath(located dawn-gradient). The closest irrigation welt to the site is located 2,000 feet to the southwest. FIELD EXPLORATION The Douglas Gas Station ground-water monitoring system war-installed and completed as proposed in the Workplans prepared by Alpha Consultants,Inc.dated November 9, 1987;January 21, 1988 and August 11, 1988 (Alpha Consultants, Inc is now associated with Du Pont Biosystems). Well locations for the ground-water mari_oring system were based on providing additional information for determination of the"effective zero-line"level of contamination. The screened intervals(if the wells were situated to accommodate expected scasor-al variations in ground-water elevation. A total of eleven functional monitm:. 7 wells were installed as part of this study in the immediate cite as shown on the Site Plan, Figure 2. Soil samples were vicinity of the Douglas Gas Station, collected from all of the monitoring well boreholes as requested by the RWQCB. One of the monitoring wells, designated M1,11-17, was installed near the fuel tanks and piping. The other monitoring wells (MW-15, MW-16; and MW-18 through MW-2`i) were located farther from the tanks and were designed for delineation of the lateral limits for both soil and ground water contamination. Exploratory borings B-I through B-9 were drilled to provide additional information on stratigraphy, aquifer thickness,and the possible presence of hydrocarbon contamination in the destroyed and grouted as soils underlying the site. In addition, monitoring well MW-14 was recommended by GMS Associates (letter dated October 13, 1987). Borahnle Advancement and Soil Samnlin The exploratory borings and ground-water monitoring wells were drilled during three separate phases of.our subsurface exploration of the site. Expled loratory barings B-1 ween December 2nd rough B and 15th51987 monitoring wells MW-15 through MW-20 were using a Mobile B-61 truck-mounted drill rig which is owned and operated by Exceltech (Fremont). Review of the chemical analytical results from the soil and water samples collected during this first k T phase of drilling necessitated the installation of three additional monitoring wells and three clearly delineate the lateral limits of contamination for both exploratory borings in order to more soil and ground water. Exploratory borings B-6,B-7 and B-8 a;,d monitaringwells MW-21, MW- 22,and MW-23 were drilled between March 30 and April 4,1988 using Exceltech's Mobile B-61 and _,_._—_.__..____._____— ._.___._ .____._._._.All Terrain's CME e 550 truck-mounted-drill rigs...Becausthe_limits of ground-water contamination were not fully defined after the second phase of subsurface exploration,two additional ritoniforutig wells(MW-24 and MW-25)were installed between November 4th and 7th, 1988 using Spectrum's J. CME 75 truck-mounted drill rig. Exploratory boring B-9 was also drilled during the third phase of T field work for additional soil contamination data. s .