ARCHIVED REPORTS XR0001362 - Laserfiche WebLink

Home Browse Search

Quarterly Status Report-I"Quarter 1998 2 1 exaco Seryice Station 440 West Charter Way Stockton CA October 2 1998 An SVE test was conducted in.lune 1992 using the four existing nested SVE wells The radius of influence was approximately 25 feet at a flow rate of approximately 25 cubic feet per minute (cfm) The vapor concentrations of TPHg ranged from 3,300 to 30,000 milligrams per cubic meter In September 1993, five soil borings were drilled off site, and monitoring wells were installed in these borings (MW-13 through MW-17), to further define the extent of subsurface petroleum hydrocarbons No TPHg was detected to soil samples from borings MW-13, MW-16, and MW- 17 TPHg was detected in selected samples from MW-14 and MW-15 At this time it was estimated that there were approximately 5,600 pounds (896 gallons) of TPHg in the subsurface Separate phase hydrocarbons (SPH) were historically detected in MW-1, but no measurable SPH has been observed in MW-1 since March 1993 Between May 1989 and December 1989, approximately 45 gallons of SPH was recovered from MW-1 by hand bailing Startup of a SVE system utilizing a thermal oxidizer to extract soil vapor from the four nested SVE wells was conducted at the site on August 28, 1995 The initial TPHg recovery rate was 85 pounds per day (lbs/day) Between January 1996 and March 9, 1998, the SVE system removed the equivalent of approximately 6,256 pounds of TPHg The SVE system was shut down on March 9, 1998 due to low influent concentrations and high water levels Lithology ` Soils encountered during drilling consisted of interbedded clay, silt, and sand A bluish gray clay was found at depths between 39 and 42 feet bgs During drilling in 1993, groundwater was initially encountered in borings in semi-confined, clayey silty sand horizons below the bluish gray clay Hydrogeol9g Groundwater monitoring wells MW-1 through MW-5 have been monitored from May 1989 to the present, MW-6 through MW-11 from May 1990 to the present, and MW-13 through MW-17 from September 1993 to the present Up until 1994, depth to water at the site typically ranged from 39 to 42 feet bgs Depth to water has decreased since 1994, and in November 1997 was approximately 25 feet bgs Since November 1997 the groundwater has risen to 19 feet bgs Groundwater flow is generally to the east or northeast with a gradient of approximately 0 01 ft/ft �� 1 ilc rexaco\Davis\Report\D-CovcrM&S-3rdQ98 LTR wpd