ARCHIVED REPORTS_XR0004494 - Laserfiche WebLink

Home Browse Search

Di Salvo-Lathrop MWJ Report lune 28. 1995 Page-2. 2.2 Over-excavation On May 6, 1994, Condor observed the over-excavation of soil at the east end of the former location of TK4. Michael Collins of SJCPHS,EHD was on site to identify soil sample locations and select laboratory analyses. The east sidewall was extended toward the east approximately 4 feet and the depth of the excavation was increased to approximately 15.5 feet bgs. Very moist soil was encountered at approximately 15.5 feet bgs. The over-excavation did not continue below 15.5 feet because of the potential for known soil contamination coining into contact with, and leaching into, potentially uncontaminated groundwater. The excavated soil was screened in the field using an OVA (organic vapor analyzer) and field observations were made. No petroleum staining, odors or OVA readings were noted during the over-excavation. A total of; soil samples were collected from the over-excavation. One soil sample was collected from the Boor at a depth of approximately 15.5 feet bgs and two soil samples were collected from the east sidewall at approximately 15 feet bgs. Laboratory analyses of the floor sample detected 6.2 µglkg toluene and 14 pg/kg xylene. No other evidence of hydrocarbon contamination was detected at or above the reported laboratory detection limits in the soil samples collect from the over-excavation. Historical analytical results are presented in Table 1, Appendix B. Based on the results of field observations and laboratory analyses, Condor concluded that the lateral extent of soil contamination at the site had been evaluated. 3.0 SCOPE OF WORK The Tri-Regional Guidelines generally require the installation of one monitor well within ten feet and in the verified down gradient direction of a detected contamination source at sites with seasonal high _ groundwater less than fifty feet bgs. To evaluate the groundwater gradient direction at the site. Condor consulted SJCPHS,EHD regarding the sites near to the Di Salvo - Lathrop site. SJCPHS,EHD indicated the groundwater gradient at the Sharpe Army Depot, located immediately north of the Di Salvo site, has consistently been toward the northwest. Based on the information provided by the SJCPHS,EHD, Condor installed one two-inch diameter monitor well within the former tank excavation approximately 10 feet northwest of the east end of TK4. The monitor well location is shown on Figure 2, Appendix A. On behalf of Spectrum Exploration, (C57 license 512268), Condor obtained from SJCPHS,EHD a permit to install one 2-inch diameter monitor well at the site. Prior to commencement of field work, a tailgate safety meeting was held and a site-specific health and safety plan was discussed with, and signed by all crew members. �� CONDOR