SITE INFORMATION AND CORRESPONDENCE_FILE 2

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�SJ EuouuNOp G. Bao x JR. exrironwix ',e�'{_, vaxx n yr Water Boards Mv,nxw xp��RnT.n,lbx Central Valley Regional Water Quality Control Board 21 August 2014 Jennifer Sedlachek ExxonMobil Environmental Services Company 4086 Piedmont Avenue, #199 Oakland, CA 94611 REVISED NOTICE OF INTENT, FORMER EXXON SERVICE STATION #73942, 4444 PERSHING AVENUE, STOCKTON, SAN JOAQUIN COUNTY On 4 March 2014, Cardino ERI submitted a Notice of Intent (NOI) and supporting technical information to operate under Waste Discharge Requirements of General Order R5-2008-0149 (General Order) on your behalf for your site at 4444 Pershing Avenue in Stockton. Cardno ERI is proposing to inject up to 15,500 pounds of the chemical oxidizer PersulfOx into groundwater to reduce concentrations of petroleum hydrocarbons detected in shallow groundwater found at about 20 feet below ground surface. In our comments addressing the NOI, Central Valley Water Board staff requested a proposed Monitoring and Reporting Program (MRP) and Contingency Plan to monitor effectiveness and address adverse impacts if they are observed in transition and compliance wells. The revised NOI received 30 June 2014 does not adequately address background levels of naturally occurring inorganic compounds and does not appropriately propose Contingency Plan actions that would address deleterious by-products mobilized as a result of injection of the proposed strong oxidizer in the subsurface. Background levels of inorganic constituents must be developed using wells outside the impacts of petroleum hydrocarbons released at this Site. The revised NOI includes baseline data from the monitoring wells that currently are impacted, or historically have been impacted, by petroleum hydrocarbons. The geochemistry in these wells is not representative of naturally occurring conditions in the area of the Site. Background data could be established from monitoring wells MW-11 and MW-12 because these wells do not appear to have been impacted by the release from this site. Background levels of metals and salts will be used to establish permit limits and action levels for implementing the Contingency Plan. Once background is established for; sodium, sulfate, nitrate, ammonium, iron, manganese, cadmium, chromium, hexavalent chromium, bromate and total dissolved solids, we can determine if any water quality objectives are already exceeded in this area or if there is capacity to allow an increase up to 20% of background, without exceeding water quality objectives. Under the General Permit, any constituent that already exceeds water quality objectives cannot be increased in compliance wells by the injection project. If the constituent is below water quality objectives then the water quality in the compliance zone wells may be increased up to 20 % KARL E. LONOLEY ScD, P.E.. GNAIn [ PAMELA C. CREEDON P.E. BCEE, E%ECIITIVE o,r GER 11020 Sun Center Drive#200.Rancho Cordova,CA 95670 ww.waterboardS Ca.gov/Centralvalley �)rrcl u"o ecn