WORK PLANS - Laserfiche WebLink

Home Browse Search

V + y 16- .� 8.2 Contaminant Mass Removed Known contaminant mass that has been removed from the Site was estimated using data V%lk collected during the 1997 UST closure activity. The northwest portion of the UST basin �1 r exhibited elevated adsorbed-phase hydrocarbon concentrations, namely TPHd (22,000u mg/Kg) in sample S-17-T1n. 'A soil volume dimension of approximately 13 feet wide by 18r feet long by 7 feet in thickness was excavated from this area (Figure 3, Grayland Environmental, March 1998). This area is also depicted j n Figure 20, prepared by ATC. '-• Three post excavation confirmation samples (S-19-E1 n, S-17-E1w,-and S-24-E1b) were collected from the northwest portion of the UST basin. The hydrocarbon concentration used to estimate the mass of hydrocarbons remaining in-place was derived by averaging the analyticalresultsresults from the three post excavation samples, previously noted, and the UST closure sample, S-17-T1 n. Refer to Appendix B for a detailed summary of the mass calculations. V Soil: Removed Analyte Mass lbs BTEX 0.118 TPHg 3.56 TPHd 938.85 MTBE 0.00 +r TBA 0.00 1,2-DCA 0.00 �v 9.0 SOIL VAPOR SURVEY 9.1 Soil Vapor Probe Installation �- Four soil vapor probes (VP1, VP2, VP3, and VP4) will be completed a Site (Figure 21). The soil vapor probes will be manually advanced to approximately ur,feet bgs using a 2.5- inch diameter hand auger. A discrete soil sample will then be colle ed at the base of each boring using a mechanical compression device fitted with a 6-inch long by 2-inch diameter brass sleeve. Each soil sample will be analyzed for Site-specific contaminants. Using similar sampling techniques, an additional soil sample from one boring will be collected for physical soil characteristics. Upon completion of each boring, a temporary vapor probe 16- assembly will then be installed. Each vapor probe will be constructed using 0.25-inch outer diameter (OD) Teflon tubing fitted with an ESP-brand stainless steel wire screen tip implant at the base of the vapor probe. The aboveground Teflon vapor probe tip will be fitted with a swaglok valve for future purging and vapor sample collection. The screen tip and subsurface assembly will be backfilled with four inches of 2/12 Monterey sand and overlain with hydrated granular bentonite to seal the annular space above the sampling interval to prevent ambient air intrusion within the boring annulus. Each aboveground vapor probe assembly will be secured in concrete directly below the ground surface and fitted with a 5-inch diameter traffic rated surface cover (man-way). ATC will return to the Site to collect vapor samples no sooner than 48 hours from installation. i Workplan to Conduct Subsurface Soil Vapor Intrusion Study \\�/// ATC Project 54.26874.0001 v Page 6