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1150 <br /> Messers Trommer and Larson Page 2 of 2 <br /> Re:Preliminary Five-Year Review Site Number 2612 09 April 2008 <br /> 110 Filbert Street N,Stockton,CA <br /> • The core area wells (MW-DIS=1, NP1-90, NPl-80 and NPI-70) are still intensely <br /> impacted, with as much as 33,000 micrograms per liter (Ng/1) total petroleum <br /> hydrocarbons quantified as gasoline (TPH-g), 65 pg/1 1,2-dichloroethane, 26 Ng/ <br /> ethylene dibromide, and 1,100 Ng/ benzene detected in the wells during a recent <br /> monitoring event, despite wells NPl-90 and NPI-80 being utilized as air sparge wells, <br /> • For a complex site like this, there is a relative paucity of soil analytical data, especially <br /> recent data, from which to estimate the original and current sorbed contaminant <br /> masses, <br /> • The most impacted soil, encountered in boring SB-DIS-3 from 60 to 76 feet below <br /> surface grade (bsg), is unlikely to have ever been directly addressed by either soil vapor <br /> extraction (SVE) system, and <br /> • A site conceptual model showing the extent and distribution of impacted soil and <br /> groundwater, how each is addressed through the SVE/IAS system and is monitored, <br /> has not been prepared — the EHD believes this is important to demonstrate that the <br /> contaminants have been adequately addressed and that the apparent interpretation of <br /> the contaminant concentration trends is likely to be correct. <br /> The EHD is encouraged by the observed reduction of dissolved contaminants and extracted soil <br /> gas contaminants, and believes that much has been accomplished on this case, but with the <br /> lack of information noted above and the resulting potential to miss significant contamination or <br /> misinterpret contaminant concentration trends, the EHD does not believe it can issue a sound <br /> professional opinion that the site is ready for immediate closure consideration. The EHD <br /> believes that the work needed to address the issues noted above is not likely to require an <br /> excessive commitment of time and money, but should be addressed to have sufficient <br /> information to fully evaluate and concur with a site closure request. At this time, the EHD does <br /> not believe a recommendation for closure consideration from your office will be beneficial for <br /> completing the work and demonstrating that the site is ready for closure in an expeditious <br /> manner. <br /> If you need more information regarding this site, contact either Nuel Henderson, Engineering <br /> Geologist, at (209) 468-3436, or Michael Infurna, Senior Register Environmental Health <br /> Specialist at (209)468-3454, or by mail (address on the letterhead)- <br /> NuNu/ enderso> , PG Margam RENS <br /> Engineering Geologist Program Coordinator <br /> Site 51 Preliminary Five-Year Review Comment Letter 0408.doc <br />