Laserfiche WebLink
Chapin Brothers, Inc. - 2 - 5 January 2011, <br /> 1766 Monte Diablo Ave., _.;kton <br /> San Joaquin County <br /> for treatment. The soil stockpile was first tested and shown to contain low levels of petroleum <br /> hydrocarbons, then spread out and aerated on an access road on the property until <br /> November 1993, when composite soil sampling and analyses showed all constituents were <br /> non-detect. <br /> Between December 1993 and December 2003, grab groundwater (CHP1 through CHP9, WP1 <br /> through WP8) was sampled, multiple soil borings (131 through B13, CB1 through C131 0) were <br /> advanced, and monitoring (MW-2 through MW-7) and remediation (VE-1 through VE-3, VW-1 <br /> through VW-7, EW-1 through EW-5) wells were installed at the Site (Figure 2). The MW-1 <br /> 1990 soil concentrations, 1993 USTs removal soil maximum confirmation samples, and 1995 <br /> and 2003 investigations maximum soil results are listed in Table 2. <br /> Table 2 Maximum Soil Concentrations' <br /> Date Depth2 DepthTPHg benzene toluene eth (benzene xylenes <br /> 12/5/1990 9.5' 34 0.13 0.035 0.63 1.4 <br /> 12/28/1993 21' 380 4.8 6.2 7.6 38 <br /> 1/4/1995 10' 5,900 33 120 58 18 <br /> 12/10/2003 17'-20'j 550 0.95 1.6 11 11 <br /> 1 =soil concentrations reported in milligrams per kilogram(mg/kg) 2=depth in feet below ground surface('bgs) 3=angle borings beneath <br /> auto repair shop <br /> In August 1993, nearly three and a half feet of free product was measured in MW-1. Free <br /> product was also reported in MW-4 after well installation in January 1994. Hand bailing of the <br /> wells continued until January 1995, when free product was no longer reported as present.. <br /> A May 1994 groundwater pumping test of MW-1 recommended groundwater pump and <br /> treatment (GWP&T) as feasible for remediation. In January 1995, soil vapor extraction (SVE) <br /> and air sparging (AS) system were pilot tested, and SVE/AS was selected as the preferred <br /> remedial alternative to GWP&T. The SVE/AS system operated from May 1997 until <br /> June 1999, when rising groundwater levels submerged the SVE wells. The GWP&T system <br /> was installed and operated from March 2002 to May 2005, from December 2007 until <br /> October 2009, and from January 2010 to February 2010. <br /> Since 1990, groundwater concentrations have been reduced by one to four orders of <br /> magnitude. Groundwater monitoring shows the plume is stable and concentrations are <br /> decreasing. A history of groundwater sampling results can be seen on Table 1 attached. <br /> There are no plans to use the groundwater within the next 100 years. Additional soil or <br /> groundwater remediation is not cost effective or necessary, as the residual groundwater plume <br /> will continue to decline without impacting adjacent properties, no supply or domestic wells are <br /> threatened, and site use (auto repair shop) is not proposed to change in the foreseeable <br /> future. Soil vapor testing has shown no risk from vapor intrusion. <br /> Risk Assessment <br /> A soil vapor investigation, conducted in May 2010, passed the San Francisco Bay Region 2 <br /> Environmental Screening Levels (ESLs) for commercial use by onsite workers. Soil <br /> concentrations failed the ESLs for gross contamination and direct exposure. The consultant <br /> states that the most contaminated soil is between 10' and 21', which is deeper than normal <br /> construction worker exposure depths, and that residual petroleum hydrocarbons in site soils <br /> and groundwater did not pose a threat to human health or the environment from vapor <br />