ARCHIVED REPORTS_XR0008796 - Laserfiche WebLink

Home Browse Search

Former Beacon Station No 12419 March 18, 2002 Stockton California Problem Assessment Re ort/Corrective Action Plan The vertical extent of gasoline constituents in the groundwater plume is not clearly delineated by the monitoring data The deepest groundwater samples collected at the site are from air sparge well AS-2 screened from 123 to 128 feet bsg The concentrations of reported gasoline constituents have decreased steadily by an order of magnitude since the well was installed in October 2000 (Table 1) The reported concentrations may be the result of installation of the well through impacted soil in the central portion of the groundwater plume, and may continue to decrease to provide vertical delineation 8.0 MASS OF PETROLEUM HYDROCARBONS IN SOIL AND GROUNDWATER The distribution of TPHg and benzene-impacted soil suggests that the source of petroleum hydrocarbons in soil and groundwater is the vicinity of the north end of the USTs as shown on Figures 3, 4 and 6 The distribution of TPHg and benzene-impacted groundwater was evaluated from the latest (fourth quarter 2001) groundwater monitoring data and are shown on Figures 7 and 8 8.1 Mass of TPHg and Benzene in Soil The estimated soil volumes impacted by TPHg and benzene were evaluated on the basis of soil concentration data from soil borings and distribution assumptions For the purposes of evaluating the masses of TPHg and benzene present in soil, the surface area of the lateral extent of TPHg and benzene is assumed to a 30-feet diameter circle or approximately 707 square feet (ftz) as shown on Figure 6 The vertical distance of the assumed volume of impacted soil is from 15 feet bsg (based on field screening and analytical data from soil boring S13-6) to the groundwater level when initial soil impacts occurred as previously discussed in section 6 1 or approximately 90 feet Therefore, the assumed volume of impacted soil is the surface area times the depth, or 314 ft2 x 75 feet = 53,014 cubic feet (ft) 419PARCAP3-02 doc 14 Project No 1419 23 HORIZON ENVIRONMENTAL INC.