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June 15, 2015 <br />Mr. Marcus Pierce, Engineering Geologist <br />Central Valley Regional Water Quality Control Board <br />11020 Sun Center Drive, #200 <br />Rancho Cordova, CA 95670-6114 <br />Subject: Addendum Work Plan for Supplemental ISCO Injections <br />California Army National Guard Field Maintenance Shop #24 <br />Stockton, California <br />Contract W912P7-12-D-0001, Task Order CQ01 <br />Dear Mr. Pierce: <br />Environmental Cost Management, Inc. (ECM) is submitting this Addendum Letter Work Plan for <br />Supplemental ISCO Injections (Work Plan) to the Central Valley Regional Water Quality Control <br />Board on behalf of the California Army National Guard (CA ARNG), under U.S. Army Corps of <br />Engineers (USACE) Los Angeles District Contract W912P7-12-D-0001, Task Order CQ01, <br />Amendment 0001. This Work Plan represents an addendum for the Work Plan for Implementing <br />Remedial Action by In -Situ Chemical Oxidation (ISCO) submitted by ECM on June 2014. <br />This Work Plan is a formal request to continue injection of PersulfOx and ORC-A in accordance <br />with the approved 2014 Work Plan and the Notice of Applicability (NOA) of General Order No. <br />R5-2008-0149-045 (CVRWQCB, 2013). The ISCO injection will occur within the 2,500 square <br />foot area and injection interval as the prior 2014 injection. <br />The work will include injection of PersulfOx and ORC-A by Regenesis through direct push <br />technology (DPT) over an area of approximately 2,500 square feet. ECM will advance a total of <br />twenty-eight (28) injection points over two injection events of fourteen (14) injections each. At five <br />(5) locations we will core and inject beneath the existing UST concrete anchor slab. The proposed <br />locations for the injection points are provided in Figure 1 attached. ECM will deliver the injectants <br />between 35 feet (ft.) to 55 ft. below ground surface (bgs). The 2015 ISCO injection is scheduled <br />for the week of July 6th thru July 101h and August V thru August 7th 2015. <br />ECM proposes to collect a soil sample near MW -5 that is within the center of the contaminant <br />area and additional groundwater samples from MW -5, MW -6 and MW -7 using passive diffusion <br />bags (PDBs) at various depths. These samples will be analyzed for TPH-g, BTEX, and VOCs <br />(naphthalene and fuel oxygenates) by USEPA Method 8260B. The analytical results of these soil <br />and groundwater samples will be used for internal purposes only to further define injection interval <br />volumes and target areas. The soil and groundwater sampling activities are scheduled for June <br />30, 2015. <br />ECM will perform this work in accordance with the June 2014 Work Plan for Implementing <br />Remedial Action by In -Situ Chemical Oxidation (ISCO), including the Quality Assurance Project <br />Plan (QAPP) and the project Accident Prevention Plan/Site Safety and Health Plan (APP/SSHP). <br />