SITE INFORMATION AND CORRESPONDENCE

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• RECEIVED • Ee�.l„a c. BF.—JF.. MAY 0 3 2012 n r M—ii Rbneibuez Water Boards ENVIRONMENTAL HEALTH PERMIT/SERVIq Central Valley Regional Water Quality Control Board 2 May 2012 Mr. Arnold Hof 28537 E. River Road Escalon, CA 95320-9629 REVIEW OF OCTOBER 2011 GROUNDWATER MONITORING REPORT, FORMER CAL FARM SUPPLY, 2040 W. WASHINGTON STREET, SAN JOAQUIN COUNTY On behalf of Mr. Arnold Hof, owner of land formerly occupied by Cal Farm Supply, JD Smith Consulting conducted groundwater monitoring in October 2011 and prepared the 6 December 2011 Groundwater Monitoring Report. California Regional Water Quality Control Board, Central Valley Region, (Central Valley Water Board) staff reviewed the report, which presents groundwater quality information and proposes that the site may be ready for environmental closure. The groundwater monitoring data shows that by October 2011, concentrations of diesel and gasoline have declined from greater than 10,000 ug/L to 260 and 140 ug/L, respectively, and are present in only one well, near the former underground fuel tank. The water quality objective for diesel is 100 ug/L and for gasoline is 5 ug/L. Nitrate has similarly declined, and exceeds water quality objectives in only two wells at 54 mg/L and 69 mg/L (MW-3 and MW-4). The water quality objective for nitrate is 45 mg/L. These monitoring wells are located towards the upgradient portion of the property, where nitrate has been observed to be migrating onto the property from an upgradient source. The other historical constituent of concern, beta-benzene hexachloride, was not detected in 2011 at a detection limit of 0.10 ug/L. Benzene hexachloride has been slowly declining in concentration, and was detected at 0.08 ug/L in 2005. The water quality objective for beta-benzene hexachloride is 0.023 ug/L, based on the Cal/EPA Cancer Potency Factor as a drinking water level. In the Monitoring Report, the history of the Central Valley Water Board directives correctly states that the site will qualify for closure review when the constituent concentration trends are declining, and that the underground tank case will be closed concurrently with the closure of the nitrate and benzene hexachloride pollutants. Since the October 2011 monitoring event was the first monitoring event since 2005, another monitoring event should take place in either the spring or the fall, in order to have two KARL E. LONCLEv SOD, P.E., CHAIR I PAMELA C. CRECDON P.E.. BCEE, EXECUTIVE OFFICER 11020 Sun Center Drive N200,Rancho Cordova.CA 95670 1 w—waterboards.ca.goWcenhalvalley C"FELrf.rEo'A"F