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V ') 3330 Cameron Park Drive Suite 550 Cameron Park CA 95682 Phone:(530)676-6004-Fax(530)676-6005 PUBLIC NOTICE FOR CLOSURE OF ENVIRONMENTAL CASE Knowles Property, 7835 Thornton Road (aka 1140 W. Hammer Lane),Stockton,California Background The subject property is a vacant lot located at the southwest corner of the intersection of West Hammer Lane and Thornton Road. Motor vehicle fuels were released to the subsurface at the subject property from a historical underground storage tank (UST) fuel storage system in the late 1980's, and San Joaquin County Environmental Health Department (SJCEHD) currently regulates an environmental case at the property relating to this condition. The USTs and fuel dispensers were removed in March 1987 and the service station was demolished. Since this time,numerous actions have been performed to investigate and monitor the extent of petroleum hydrocarbon impact to the subsurface. A relatively large excavation, extending to a maximum depth of approximately 35 feet below ground surface, was completed in order to remove impacted soils from by Stratus the subsurface.__Ap rro,�imately 358.5 pounds of total petroleum hydrocarbons as gasoline and 46.6 pounds of benzene are estimated to have been removed by excavation. Fuel contaminant impact was found to extend vertically to shallow groundwater and a plume of impacted groundwater affects the northeastern portion of the subject property, extending offsite beneath the City of Stockton's roadway. Based on available groundwater analytical data, the plume is not thought to have impacted other properties. Between September 2012 and April 2015, ozone, a strong oxidant, was injected into the shallow groundwater interval through a network of injection wells by Stratus Environmental, Inc. in order to mitigate the contaminant plume. Application of ozone results in a chemical reaction that can degrade petroleum hydrocarbons to carbon dioxide and water. Ozone was applied within the area of the site with the highest remaining concentrations of petroleum hydrocarbons in groundwater. Groundwater samples were collected from monitoring wells located near the injection area to evaluate remedial performance. This data has indicated a substantial reduction in the concentrations of fuel contaminants in groundwater. Based on available data, no water wells are known to be threatened and no other significant risks to human health from mwaiuing contaminants -snelr-as• dermal contact or inhalation,-appear to be present. residual through Proposed Closure of Environmental Case Based on a review of available data,the subject property has been remediated to a condition that will allow for-the SJCEHD to close out the environmental case on the property under the criteria of the State Water Resources Control Board's `Low Threat Underground Storage Tank Closure Policy' (LTCP). Given this condition, on April 9,2015, SJCEHD issued a letter to the owner of the subject property indicating that further remediation and testing of groundwater quality was no longer necessary. However, before the environmental case can be closed, comments from the public and otherinterested parties regarding the pending case closure are being solicited. Further Information and Public Comment Opportunity Between May 4-and June 3Ar 2015, SJCEHD will be accepting public comments regarding the proposed case Goffee6*a-Ae6eo-.. Comments should be submitted in writing to Mr. Gabriel Gonzalez, 1868 East Hazelton closure Avenue, Stockton, California 95205. Mr. Gonzalez may also be reached at gaaonzalez ,sjcehd.com or(209) 468-3442. For further information regarding the environmental case at 7835 Thornton Road,please reference the State of California's GeoTracker Website (geotracker.waterboards.ca.gov), site T0607700078. For further information regarding the State Water Resources Control Board's `LTCP', we suggest entering the words `Low Threat Closure Policy' into an internet search engine;this should provide a link to a PDF version of this document within a State of California website(waterboards.ca.gov).