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Mr. Soon Kim Page 10 August 11, 1995, 102429.AS.T8 Remediation Progress The remediation system consists of two well pairs, a sparging blower, a vapor extraction blower, and an engine for destroying extracted gasoline vapor. Each well pair consists of a sparging well and a soil vapor extraction well. Sparging wells consist of a 2-foot well screen at a depth of 90 feet bgs. Vapor extraction wells have a 10-foot well screen interval at a depth of 60 to 70 feet bgs. Piezometers were installed to assess the influence of the AS/SVE system on groundwater and soil vapor at various depths as described in Section 2 of the PAR/FRP. Piezometers are in two nested clusters as shown in Figure 1: NP-1 and NP-2. NP-1 piezometers are screened at 90, 80,and 70 feet below grade surface to monitor groundwater character at various depths. NP-2 piezometers are screened at 45 and 65 feet below grade surface to monitor vacuum influence and soil vapor character at two depths. The remediation system is described in more detail in the PAR/FRP. Construction of the f remediation system began in August 1994 and was completed in February 1995. The system has been operating continuously since late February 1995. The following discussion summarizes remediation progress by'evaluation of radius of influence, mass removal by SVE, biological respiration in soil and groundwater, and BTEX concentrations in groundwater. Radius of Influence Measurement of radius for the AS/SVE system involves the evaluation of differential soil gas pressure measurements and dissolved oxygen in the groundwater. Dashed circles are shown in Figure 1' to represent the approximate radius of vacuum influence created by the SVE system which is 25 feet. Based on differential pressure measurements made on 5125195 for example, we know that the vacuum created at NP-2 by the applied vacuum on AS/SVE wells is 3 times greater at the 65 foot depth(3.2 inches of water)than at the 45 foot depth(1.2 inches of water) with an applied vacuum at the SVE wells of 20 inches of water. Based on the known distance of the piezometer well screens from the SVE well screens in the subsurface, the horizontal and vertical vacuum pressure gradient can be calculated. By applying the viscosity of air and the known soil porosity, we can theoretically calculate the rate of pore volume exchanges at any depth or horizontal distance from the SVE well pair. ,The applied vacuum at the SVE wells has been highly variable as shown in Table 3,-and the three dimensional aspect of applied i