ARCHIVED REPORTS_XR0002055 - Laserfiche WebLink

Home Browse Search

Beacon Station No 641 September 28, 1998 Stockton,California __ Remedial Testinp- Report �) In July 1996, the first phase of field work was conducted in the area east of the replacement USTs, prior to the installation of a new canopy A Horizon geologist observed the drilling and installation of one groundwater monitoring well (MW-1) and four vapor extraction wells (VW-1 through VW-4) After completion of station remodeling and obtaining an offsite access agreement, the second phase of field work was conducted in September 1997 At that time, a Horizon geologist observed the drilling and installation of four groundwater monitoring wells (MW-2 through MW-5), four nested vapor extraction wells (VE-5 / VE-6 and VE-7 / VE-8), and one sparge well (SW-1) as reported in the Additional Subsurface Investigation Report (Horizon, December 8, 1997) During drilling of the monitoring wells, groundwater was found to be present between the depths of approximately 55 to 65 feet below ground surface (bgs) The water-bearing zone encountered beneath the site consisted of interbedded layers of fine-grained sands, silts and clays Previously collected groundwater data in October 1997 had shown a groundwater flow direction toward the east-northeast beneath the site (Horizon, December 8, 1997), while quarterly groundwater monitoring data collected in March and June 1998 had shown a groundwater flow direction toward the northwest (Horizon, June 23 and July 27, 1998) Soil Vapor Extraction Test �i Prior to initiating the Soil Vapor Extraction Test (VET), written notification was provided to the San Joaquin Valley Unified Air Pollution Control District (SJUAPCD) and approval received to perform the VET Equipment utilized for the VET included a 100 cubic feet per minute (cfm) blower and two 200-pound vapor-phase carbon canisters connected in series to be used for abatement of hydrocarbon vapors This equipment, along with the data collection devices, were connected directly to the top of well VW-2 which is screened from 20 to 35 feet below surface grade (bsg) Horizon's Field Methods and Procedures are included in Attachment A On May 27, 1998, the VET was started at approximately 10 45 AM and ran for a total of approximately 9 3/4 hours During the final 6 hours, the VET was operated in conjunction with an air-sparging test As previously mentioned, the VET was performed utilizing well VW-2 as the vapor extraction source with monitoring being conducted on wells VW-3, VW- 4, VW-5, VW-6 and VW-8 During the VET, the following information was obtained: soil vapor-extraction flow rates, discharge flow rates, influent and effluent vapor hydrocarbon levels utilizing a Horiba® Hydrocarbon Analyzer, influence at other subsurface points in the area, and hydrocarbon abatement efficiency During the VET, one air sample from the influent and effluent vapor streams was collected for laboratory analyses to verify field reading of the hydrocarbon concentrations These air samples were collected from the influent and effluent vapor streams after approximately one hour into the VET Laboratory results for Total Petroleum Hydrocarbons as gasoline (TPHg) indicated that the TPHg concentration in the influent vapor stream was 38,000 parts 1641-21 rpt 2 HORIZON ENVIRONMENTAL INC.