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-4110 Californi,- ilegional Water Quality Con*rol BoardC411't-----'�it)) <br /> Central Valley Region Robert Schneider,Chair <br /> Linda S.Adams Arnold <br /> Secrerat7 for Sacramento Main Office Schwarzenegger <br /> Environmental 11020 Sun Center Drive#200.Rancho Cordova.California 95670.6114 Governor <br /> Protection Phone(916)464-3291 •FAX(916)464-4641 <br /> litip://%%,Nvw.waterboards.ca.gov/centralva]IW <br /> 'n"EC OV D <br /> 2 October 2006 <br /> OCT 5 2006 <br /> Sandy Galganski ENVIRONMENT HEALTH <br /> The Dow Chemical Company PERMIT/SERVICES <br /> P.O. Box 1398 <br /> Pittsburg, CA 94565 <br /> REVIEW OF 2005 ANNUAL GROUNDWATER MONITORING REPORT, DOW CHEMICAL <br /> FACILITY, 400 WEST GANDY DANCER DRIVE, TRACY, SAN J^vAQUIN COUNTY <br /> Staff of the Regional Water Quality Control Board, Central Valley Region (Regional Water <br /> Board) has reviewed the 1 February 2006 2005 Annual Groundwater Monitoring Report <br /> (Annual Report) submitted by URS Corporation (URS) on behalf of The Dow Chemical <br /> Company (Dow). The Annual Report describes annual groundwater monitoring activities <br /> performed during the fourth quarter 2005. <br /> Groundwater flow was to the northwest in December 2005 similar to historical conditions. <br /> Groundwater samples collected from the four existing monitoring wells were analyzed for <br /> volatile organic compounds (VOCs) using EPA Method 8260B. Trichlorofluoromethane (Freon <br /> 11) was reported in two samples at concentrations of 1.5 micrograms per liter (ug/L) at well <br /> TW-3 and 13 ug/L at well TW-2 (14 ug/L in duplicate sample). Dichlorofluoromethane (Freon <br /> 12) was reported in all four samples at concentrations ranging from 10 ug/L (TW-4) to 29 ug/L <br /> (32 ug/L in duplicate sample, TW-2). 1,1-dichloroethene (1,1-DCE) was reported at well TW-2 <br /> at a concentration of 4.9 ug/L (5.7 ug/L in duplicate sample). No other VOCs were detected in <br /> the groundwater samples. The next monitoring event is scheduled for December 2006. <br /> Site groundwater quality in the fourth quarter 2005 did not exceed water quality objectives <br /> established in the Central Valley Basin Plan. The maximum concentration of 1,1-DCE <br /> decreased significantly from 39 ug/L at well TW-2 in March 2005 to 4.9 ug/L in December <br /> 2005. Regional Water Board staff recommends that the site be considered for case closure if <br /> water quality objectives are not exceeded during the December 2006 monitoring event. The <br /> next annual groundwater monitoring report is due to this office by 1 February 2007. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4719 or by <br /> email at mclardy@waterboards.ca.gov <br /> Mark W. Clardy, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br /> California Environmental Protection Agency <br /> Za Recycled Paper <br />