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M - 1117 Lone Palm Avent e, Suite 201 M �� Modesto, California 95351 ( 209-579-2221 Fax: 209-579-2225 ASSOCIATES INC . The samples will be analyzed for GRO utilizing EPA Method 8015B; BTEX and selected fuel oxygenates MTBE, ethyl tertiary butyl ether (ETRE) di-isopropyl ether (DIPE), tertiary amyl ether (TAME), tertiary butyl ether (TBA), 1 ,2-DCA, and 1 ,2-dibronioethane (EDB) utilizing EPA Method 826013 . The groundwater samples will also be analyzed for total chromium by EPA 6020, hexavalent chromium by EPA Method 7199, and broinate by EPA Method 300. Ozone Sparge Pilot Testing A mobile ozone generator will be connected to the ozone sparging wells to inject ozone into the saturated zone. Ozone will be injected into each sparge well for approximately 15 to 20 minutes per hour over a period of four weeks at a rate of approximately 2 to 3 cubic feet per minute. This "micro-sparge approach will provide information to evaluate the effectiveness of an ozone sparge system (low airflow and low pressure). The duration and rate of ozone injection can be adjusted downward or upward as desired, The sparging wells will alternately be used as observation wells when not being actively utilized as the ozone injection well . Monitoring parameters will be periodically measured in nearby monitoring wells two to three times a week during the test. If periodic monitoring in tine observation wells identifies the presence of hexavalent chromium, the ozone injection rate can be lowered or terminated to slow the formation of hexavalent chromium. CONTINGENCY PLAN FOR POTENTIAL HEXAVALENT CHROMIUM ABATEMENT The results of a recent bench scale treatability study for reducing petroleum hydrocarbon concentrations in groundwater indicate ozone sparging would be effective in remediating petroleum impacted groundwater at the site. Undesirable secondary effects of ozone sparging include the formation of hexavalent chromium and bromate. The bench scale study indicates bromate will naturally attenuate in both the ozone treatment zone and in areas beyond the treatment zone, i.e. downgradient. Consequently, the bromate issue is not viewed as a significant concern. Hexavalent chromium will likely be formed in the ozone treatment zone and will persist for an unknown period of time before natural attenuation begins. Should periodic monitoring indicate hexavalent chromium is not naturally attenuating at an acceptable rate, a contingency plan to remediate the hexavalent chromium will be implemented . Under the contingency plan, calcium polysulfide or other material that has been proven to convert dissolved hexavalent chromium to trivalent chromium will be injected into the groundwater. Downgradient monitoring wells MW I , MW5, and MW8 (and possibly MW6 and MW9) will be used to inject calciuria polysulfide or other materials to limit the lateral migration of dissolved hexavalent chromium. It is anticipated that a solution of calcium polysulfide or other material will be injected into the wells via gravity feed, During the pilot testing, ATC will communicate weekly with the SJCEHD. Should the decision be made to implement the contingency plan, ATC will submit a brief workplan to the SJCEHD describing the injection procedures and materials and proposed injection wells. Ozone Pilot l esling Workplan — FCnlle! Stockton TVW Compmty ATC Associates Inc. St...\28349\ Reporti.Ozone Pilot l esting RP AFC Project No. 54.28349.00011 6