Laserfiche WebLink
George W. Lockwood,PE Page 2 of 4 <br /> Re: Russell Chapin 2009 Petition 07 May 2009 <br /> 1766 Monte Diablo Avenue,Stockton,California <br /> • A demonstration that natural attenuation processes are affecting the <br /> contaminants; and <br /> • An understanding of the hydrogeology of the site (an explanation why the <br /> dissolved contaminant mass migrates westward while the groundwater gradient <br /> is eastward). <br /> In the 2009 Petition, Mr. Chapin states that there has been a contaminant mass <br /> reduction of 95% and that the continuing effort is to address the residual 5% of the <br /> original mass. The EHD believes that the sorbed contaminant mass has always been <br /> greatly underestimated and that nowhere near 95% of the original mass has been <br /> removed. In 2004 ATC Associates estimated that 5,733 pounds of contaminants <br /> remained in the subsurface in 2004, an estimate the EHD considered to be too low as <br /> data just previously acquired from soil samples collected under the building on the site <br /> had not been utilized in the estimate; however, assuming the estimate was <br /> approximately correct for 1997, rather than 2004, and that AGE's estimate that 957 <br /> pounds of contaminants were removed by GWE through fourth quarter 2008 is correct <br /> and that approximately 2,645 pounds (407 gallons) had been removed by SVE, a total of <br /> 3,602 pounds of contaminants have been removed though engineering technology. With <br /> these assumptions, it appears that approximately 62% of the original mass has been <br /> removed, but probably not 95 %. While this may be a significant mass reduction, it <br /> should be noted that the dissolved contaminant concentrations typically rebound sharply <br /> during periods lacking active remediation as shown in the following graphs of TPI-Ig and <br /> benzene concentrations in monitoring wells MW-1 and MW-4: <br /> TPHg and Benzene in MW-1 Chapin Bros. <br /> 100000 <br /> 4/30/1997 SVE on <br /> 10000 <br /> t MW-1 TPHg <br /> --a—MW-1 Benzene <br /> CL <br /> °' 1000 f <br /> N <br /> '�O 1/2612002 <br /> c <br /> GWE on 8/9 0 7 GWE on <br /> m <br /> 100 <br /> U <br /> 1(1 5/10/2005 <br /> 6/29/1999 SVE off GWE off 1 <br /> 9h 90 0� 90 9J' 00 O^ Off' O� Oa O� OHO O� O� <br /> Sampling Event Dates <br /> 2009 Appeal Response 0509 <br />