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Torrey Harding - 2 - 26 March 2015 Contingency Plan: In-situ remediation for reducing hexavalent chromium concentrations in groundwater can be an effective remediation alternative. Secondary effects of injection may include an elevation of pH and the formation of by-products. However, these secondary effects are generally limited in duration and/or in a relatively small portion of the aquifer. Groundwater limitations require pH of the groundwater, at the compliance points, downgradient and outside the treatment zone to shift outside the range of 6.5 to 8.5. The addition of Cascade® in bench scale testing has shown that the potential to elevate the pH of the groundwater exists. However, elevated pH levels generated during application of Cascade®was also observed to decrease over time. Should periodic monitoring indicate the pH or any other detected by-products are not naturally attenuating at an acceptable rate (a downward trend over the six-month monitoring period), a contingency plan will be implemented. Under the contingency plan, if pH at compliance points is measured using portable monitoring equipment to exceed 8.5, then efforts will be made to reduce the pH to within the approved range by adding an appropriate acid into the injection well following consultation with Central Valley Water Board staff. Monitoring and Reporting Program: The Discharger will be conducting sampling during the period of the pilot test and reporting the results as described in the attached Groundwater Monitoring and Reporting Program. General Information: 1. The project will be operated in accordance with the requirements contained in the General Order and in accordance with the information submitted in the completed Notice of Intent. 2. The required annual fee (as specified in the annual billing you will receive from the State Water Resources Control Board) shall be submitted until this Notice of Applicability is officially revoked. 3. Injection of materials other than water and calcium polysulfide into the subsurface is prohibited. 4. Failure to abide by the conditions of the General Order could result in an enforcement action as authorized by provisions of the California Water Code. 5. The Discharger shall comply with the attached Monitoring and Reporting Program, Order No. R5-2015-0012-003, and any revisions thereto as ordered by the Executive Officer. If you have any questions regarding this matter, please call Bill Brattain at (916) 464-4622. Original signed by Duncan Austin, for PAMELA C. CREEDON Executive Officer Attachment cc: Jeanne Homsey, P.E., Cardno ATC, Modesto