FIELD DOCUMENTS AND WORK PLANS 2004-2014

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State of California—California Environmental Protection Agency Department of Toxic Substances Control NEGATIVE DECLARATION Department of Toxic Substances Control Site Mitigation&Brownfields Reuse Program 8800 Cat Center Drive Sacramento, CA 95827 Subject: Z DRAFT❑ FINAL ❑ MITIGATED Project Title:Former Marley Cooling Tower Corporation Facility State Clearinghouse No.: Project Location: SPK, formerly MCTC is located at 200 North Wagner in Stockton; Califomia 95205 in the County of San Joaquin. Former operations were performed on two adjacent properties (referred to as North & South Yard) that are bisected by the Stockton Terminal & Eastern rail line. The facility Is bounded on the north and east by light industry and the Stockton Diverting Canal, on the west by Franklin High School's athletic field, and on the south and southeast by residential areas. Project Description: The Department of Toxic Substances Control is proposing to approve a Remedial Action Plan Amendment (RAP Amendment) pursuant to the authority granted under Chapter 6.8, Division 20, California Health & Safety Code (H&SC) at the Marley Cooling Tower Company (MCTC)Site, The objective of this remedial action is 1) to modify the current groundwater remedy to implement in-situ chromium reduction through injection of calcium polysulfide and ethanol (reductant solution); and 2) install horizontal welts and re-initiate flushing of deep soils to flush chromium to groundwater, where [t will encounter the reductant solution. if groundwater data suggests favorable site-wide results, phase out groundwater extraction, treatment,and discharge to the Stockton Diverting Canal. Remediation of subsurface soils beneath the retort pit area and the underlying groundwater has not been completed and is the subject of this RAP Amendment. While the dissolved chromium plume has reduced from the maximum extent (August 1989) in the shallow and intermediate zone with the operation of the groundwater pump and treat system, remediation time is uncertain. A solution containing potable water, calcium polysulfide that Is approved by State of Callfomia water agencies for well head rehabilitation activities and groundwater treatment of metals-impacted sites, and ethanol will be injected into groundwater to physically change the hexavalent chromium contamination in groundwater to the trivalent form, which is less toxic and not mobile in the subsurface environment. The approach proposed in the RAP Amendment has been successfully pilot-tested at the Site and is expected to clean up the groundwater in approximately three years as opposed to the current 17-year estimated cleanup time for the existing pump and treatment system. The injection solution application pilot-tested at the Site has been used at other multiple sites and has not displayed adverse effects on the long-term groundwater quality, Project activities include the following: 1. Enhance the existing soil flushing system which operated underneath the former retort pit area between 1992 and 2003. This enhanced system will be accomplished by the installation of an estimated 5 horizontal wells approximately 15 to 20 feet below the top of the retort pit cap, which is below the zone of the most significant arsenic-impacted sail. Two wells will be located in the area of the former retort pit with well screen lengths extending approximately 160 feet. Three wells will be located east of the former retort pit, in an area formerly used for solution storage in aboveground storage tanks. The screen length of the three wells will be approximately 85 feet. Drilling angles and horizontal directional drilling technology will be employed. This will enable better distribution of flushing water without disturbing the existing retort pit cap or the near surface arsenic/copper contamination underneath. 2. Flush all wells with reductant solution to mobilize and treat the chromium from the vadose zone to groundwater. The effluent water from the treatment plant will be piped to a holding tank for use as the reductant solution. From the holding tank the effluent water will be piped in parallel by manifold directly to the horizontal wells at specified rates. The two deep horizontal wells will deliver the reductant solution in the low part of the vadose zone and groundwater beneath the retort pit area. An initial dosing of reductant solution will be utilized in the two deep wells and will be determined when specific volumes and concentrations are fully evaluated. If necessary, periodic redosing would be performed. 3. Routine operations and monitoring inspections will be performed weekly to ensure that the system is functioning correctly. Personnel will inspect all aboveground piping, fittings, and all other associated equipment and make repairs as needed. DTSC 1327(110&06)