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r <br /> Advanced --I-- <br /> GeoEnvironmental , Inc . <br /> 15 May 2009 <br /> AGE-NC Project No. 95-0103 <br /> Mr. Nuel Henderson <br /> San Joaquin County-Environmental Health Department(EHD) <br /> 600 East Main Street <br /> Stockton, CA 95201 <br /> Subject: Response to Comments-letter 07 May 2009 <br /> CHAPIN BROTHERS INVESTMENTS,INC. <br /> 1766 Monte Diablo Avenue, Stockton,California <br /> Dear Mr. Henderson: <br /> Advanced GeoEnvironmental, Inc. (AGE) has provided the following response to comments from <br /> the EHD letter presented to Mr. George Lockwood of the State Water Resources Control Board <br /> dated 07 May 2009(letter)to respond the Chapin 2009 Petition for Case Closure.The last paragraph <br /> of the first page outlines the required elements for closure concurrence: <br /> • The letter states "A demonstration of the plume stability and degradation". A multiple <br /> decade set of ground water data is available for the site. Ground water samples were first <br /> collected on the site in 1990. Over the remediation cycles (in-situ air sparging and ground <br /> water extraction regimes)the concentrations of dissolved hydrocarbons have been degraded. <br /> The free-phase petroleum product detected on the site in 1990 was abated and no longer <br /> exiting on the site. While the plume stability has been demonstrated by well MW-7 to east, <br /> well MW-2 to the north,well MW-6 to northwest,well MW-3 has declined in concentration <br /> over every remediation cycle and well MW-5 to the west. Additionally, grab ground water <br /> samples collected at borings B 13,B 12,CHP8,CHP9,B8,CHP3,B7,CHP-2,B 11 and CHP7 <br /> were not impacted and defined the fringe areas of the dissolved plume. Impacted soil has <br /> degraded over time as a direct result of in-situ air sparging and ground water extraction <br /> regimes. The shallow adsorbed plume is limited to the site area. <br /> • The letter states"A reasonable estimate of the time required for the impacted ground water <br /> to return to background conditions". The background conditions of shallow ground water <br /> beneath the site are poor and the site has significant concentrations of petroleum <br /> hydrocarbons as aliphatic or`old gasoline' dissolved(greater than the 5 microgram per liter <br /> water quality goal. The ground water below the site and the adjacent streets(MtDiablo and <br /> Buena Vista Avenues) will likely not return to a conditions which meets a standard of the <br /> background water condition. However, off-site monitoring wells MW-5 has achieved a <br /> background conditions. Therefore, the off-site ground water has achieved that goal. <br /> 817 Shaw Road.Stockton.Caliloinia 9�21> <br /> I e1cI,honc (209)407-1000 F'a\ (209)467-11 IS <br />