ARCHIVED REPORTS_XR0012273 - Laserfiche WebLink

Home Browse Search

4< Ms Margaret Lagorio S E C ® R August 1, 2005 Page 3 � encountered between 55 and fit feet bgs The vapor extraction wells were constructed of 4-inch PVC casing with a 25-foot screened interval and set between 49 and 50 feet bgs Groundwater was not encountered during the installation of these wells Laboratory 9 analysis of collected sod samples detected the presence of TPHg and BTEX compounds (RESNA, 1992) Additionally, in March 1992, RESNA performed a vapor extraction test (VET) The highest observed vacuum was 0 60 inches of water in VW-4 while VW-2 was undergoing an air flow rate of 81 cubic feet per minute (cfm) and a vacuum of more than 50 inches of water RESNA concluded that soil vapor extraction was a viable means to remediate petroleum hydrocarbon contamination in the vadose zone Two additional vapor extraction wells were installed (VW-5 and VW-6) (RESNA, 1992) In August 1992, RESNA installed five additional offsite monitoring wells (MW-9 through MW-13) and one onsite groundwater extraction well (PTW-1) The offsite wells were constructed of 2-inch PVC casing with a 20-foot screened interval and set at depths ranging from 70 to 72 feet bgs PTW-1 was constructed of 6-inch PVC casing with a 20-foot screened interval and set at 72 5 feet bgs Laboratory analysis of the soil samples did not detect petroleum hydrocarbons (RESNA, 1991) Additionally in August 1992, RESNA performed an aquifer test utilizing PTW-1 as the ' extraction well The results identified a water bearing zone between 55 and 75 feet that is heterogeneous, anisotropic, and unconfined The parameters of the aquifer were calculated to be 0 4 to 0 8 square feet per minute (Wlmin) for the transmissivity and a 5 to • 10 percent specific yield (RESNA, 1992) A vapor extraction system (VES) utilizing a catalytic oxidizer unit was in operation at the site from September 1994 through the second quarter of 2001 By the end of the second quarter of 2001, approximately 14,794 pounds of TPHg and 183 pounds of benzene were extracted and treated The remediation method was revised in late 2001, from full-time VES using the catalytic oxidizer unit to ozone sparging ' In February 1996, wells MW-3, MW-10, MW-12, and MW-13 were abandoned at the request of the City of Stockton This work was performed to facilitate reconstruction of the intersection and widening of Pacific Avenue In August 1999, Gettler Ryan (GR) installed three groundwater monitoring wells (MW-14 through MW-16), one groundwater sparging well (VW-7) and advanced one soil boring (VW-9) These groundwater monitoring wells replaced the wells that were abandoned in February 1996 In April 2000, the service station building and all related facilities were removed from the site, including two 12,000-gallon double-wall steel gasoline USTs Soil samples were collected from beneath the USTs, product lines, and dispenser islands Soil thought to be potentially impacted was over-excavated A total of approximately 200 cubic yards of soil was excavated from beneath the northwest and southeast dispenser islands and product lines immediately north of the west UST In addition, the UST pit was excavated to a depth of 21 feet bgs Soil samples were collected, analyzed, and reported as non-detect for • petroleum constituents except for 2 73 parts per million (ppm) of TPHg beneath the northeast dispenser island at 4 75 feet bgs, and 38 3 ppm of TPHg and 0 125 ppm of r 8981 2Q2005 QSSR doc SECOR International Incorporated 3' r i