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i <br />' Southland Stockton 3 <br /> . March 1991 <br />' SITE BACKGROUND <br />' SITE ASSESSMENT AND REMEDIATION ACTIVITIES SUMMARY <br />' A total of seventeen monitoring wells have been installed at the site since work was initiated in <br /> 1986, to acquire data relevant to the lateral and vertical extent of soil and groundwater contamination <br />' (See Figure 2, Site Plan, for well locations) Monitoring of the Initial wells revealed the presence of <br /> separate-phase hydrocarbons (gasoline) on the groundwater surface in monitoring well <br /> MW-5 with a thicknesses of 0 08-feet Gasoline was later detected in monitoring wells MW-1, MW-3 and <br /> MW-4 with increasing thicknesses until product extraction was undertaken by continuous product <br /> pumping on monitoring well MW-4, beginning in May of 1986 The greatest gasoline thicknesses were <br />' found in August 1986 with up to 4 55-feet being detected in MW-4 Due to the presence of free floating <br /> gasoline and dissolved petroleum hydrocarbons, pumping wells PW-1, PW-2 and PW-3 were installed by <br />' December 1986 to further assist in product removal and control of the dissolved plume Additionally, <br /> bottled water was provided for the adjacent residents and sampling of adjacent domestic wells was <br />' initiated (See Figure 3, Domestic Well Location Map, for well locations) A fourth pumping well (RW-1) <br /> was installed in 1988 in the vicinity of the underground tank pit to improve the product recovery and <br />' hydraulic control program (See Figure 2 for pumping well locations) A total of approximately 760 <br /> gallons of gasoline was removed by the free product recovery system, and a total of approximately 16 <br /> million gallons of groundwater have been pumped and treated by the water treatment system <br /> I <br /> Soil contamination by petroleum hydrocarbons had occurred on site in the vicinity of the tank <br />' pit In situ soil venting was initiated by Groundwater Technology in February 1987, using four vapor <br /> extraction points The sod vent system later incorporated monitoring wells 1, 3, 4 and Recovery well <br /> RW-1 as additional subsurface vapor extraction points Since January 1990, sod vent operations have <br /> been overseen by Vapor Extraction Technology (VET) System operation was terminated by VET in <br /> January 1991 based on reductions in the vapor-stream hydrocarbon concentrations A Total of about <br /> 576 gallons of gasoline was removed by the insitu soil vent system <br /> t� <br /> C GROUNDWATER <br /> TECHNOLOGY. INC <br />