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California conal Water Quality Cont Board <br /> `\- Central Valley Region t <br /> vKarl E. Longley,ScD,P.E.,Chair <br /> Linda S.Adams Arnold <br /> Secrerarpfor Sacramento Main Office Schwarzenegger <br /> Environmental 11020 Sun Center Drive#200,Rancho Cordova.California 956706114 Governor <br /> Protection Phone(916)464-3291 •FAX(916)464-4645 _ <br /> http://www.waterboards.ca.gov/centralvalley G�j <br /> 24 April 2007 <br /> APr? 2 <br /> Mr. Dale Gillespie ENVIR0iVf,%-.IV1tf iEALIH <br /> Geweke Land Development and Marketing PERM! /;ERVICES <br /> PO Box 1210 <br /> Lodi, CA 95241 <br /> REPORT REVIEW, CLEANUP AND ABATEMENT ORDER (CAO) NO. 93-701, <br /> GEWEKE PROPERTY, 16 SOUTH CHEROKEE LANE, LODI, SAN JOAQUIN COUNTY <br /> I reviewed the 20 April 2007 Quarterly Report— First Quarter 2007 (Report), submitted on your behalf <br /> by Advanced GeoEnvironmental, Inc. (AGE). The Report (see enclosed Figures 2 through 5) provides <br /> the graphical interpretations and analytical results from the groundwater monitoring event conducted <br /> 21 February 2007 at your site. Depth to water varied from 54 to 56 feet below ground surface. The <br /> downgradient groundwater direction was towards the south at a varying gradient of 0.001 Wit (onsite) <br /> to 0.003 ft/ft (off-site). Maximum groundwater concentrations in micrograms per liter (ug/L) were: <br /> Analyte TPHg' benzene' ethylbenzene3 toluene' Xylenes' 1,2-DCA' <br /> Concentration 2,000 ug/L 6.3 ug/L 7.9 ug/L 2.5 ug/L 41 ug/L 90 ug/L <br /> 1 —TPHg:Total Petroleum Hydrocarbons as gasoline; MW-8 2—MW-14 3—MW-8 4—MW-14 <br /> 5—MW-14 6-1,2-DCA: 1,2-dichloroethane;MW-14 <br /> The Report states the corrective action utilizing an ozone injection system, which was suspended <br /> temporarily in January 2007 to conduct a rebound test, was effective in reducing concentrations for <br /> constituents of concern (CDCs) while in operation. The Report shows that groundwater concentrations <br /> have rebounded to the highest levels in three years. The Report included a Fate and Transport model: <br /> to evaluate mobility of the groundwater plume over a 100-year period for two monitoring wells (MW-12 <br /> and MW-20), located 60 and 200 feet downgradient; and to assess human health risks to indoor air <br /> from the groundwater plume. The modeling showed minimal plume impacts to MW-12 (126 ug/L) and <br /> MW-20 (61 ug/L); and a resultant human health hazard index of <0.0007, correlating to no elevated <br /> indoor air risk to occupants in a theoretical building located over the plume. The Report cautions that <br /> the modeling results are preliminary, due to averaging of input values over several years of monitoring <br /> and the lack of sensitivity testing for the model. <br /> The Report recommends: <br /> Restarting the ozone injections system, due to rebound of COCs, and <br /> • Continued groundwater monitoring under CAO No. 93-701. <br /> 1 concur to the recommendations listed above. Note that the requirements for a successful model <br /> include sensitivity testing (to show which input parameters cause the greatest variation in output <br /> results) and that the inputs and assumptions used for the model must be representative of actual <br /> known conditions, to the greatest degree possible, and be defensible to closure comments from other <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br />