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<br /> Former Chevron Service Station 9-0557 Page 6
<br /> 139 South Center Street May 6, 2010
<br /> Stockton, California
<br /> Monitored Natural Attenuation
<br /> MNA was not directly tested; in fact, HFA recommended collecting data related to MNA
<br /> evaluation and monitoring during the next groundwater monitoring event. - The action of
<br /> natural attenuationwas inferred from the decline of contaminant concentrations.in.. several
<br /> outboard monitoring wells. Contaminants in monitoring wells MW-1, MW-2, MW-5, MW-6 and
<br /> MW-8 `cleaned up' between February 1996 and May 2000, and contaminant concentrations in
<br /> MW-7 have been declining; however, the trend, in monitoring wells MW-15, MW-15D and
<br /> MW-18D2 is not clear.
<br /> The EHD approves collection of the pertinent data, but doesn't have sufficient data at this time
<br /> to approve MNA as the cost-effective remedial technology for this site. The lack of estimates
<br /> of sorbed and dissolved contaminant masses and rate of degradation, in addition to what the
<br /> EHD currently perceives as incomplete pilot testing and interpretation of GWE, TPE, and
<br /> ozone injection prevents the ,EHD from adequately evaluating the cost effectiveness of each
<br /> method. To assist the EHD to complete the evaluation of the FS, please provide the
<br /> information needed as described above.
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<br /> If you have any questions or concerns regarding this letter, please contact Vicki McCartney at
<br /> (209) 468-9852, or by email at vmccartney@sjcehd.com.
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<br /> Sincerely,
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<br /> Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG
<br /> r Senior Registered Environmental Health Specialist Engineering Geologist
<br /> c: Mr. Elias W. Scott, Holguin,Fahan &Associates, Inc., 5627 Stoneridge Drive, Suite 320,
<br /> Pleasanton, California 94588
<br /> Mr. James.L.L. Barton, PG, California Regional Water Quality Control Board Central
<br /> Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670
<br /> Ms. Ava Langston-Kenney, Program Manager, City of Stockton, Revitalization
<br /> Department Redevelopment Division, Real Property Section, 425 North El Dorado
<br /> Street, Third Floor, Stockton, California, 95202-1997
<br /> Greyhound Bus Lines, Post Office Box 660362, Dallas, Texas 75266-0362
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