Removal Action Workplan, Former Ketema A&E Facility

Removal Action Workplan, Former Ketema A&E Facility

The California Department of Toxic Substances Control (DTSC) approved a Removal Action Workplan (RAW) that describes sequential implementation of passive ventilation, active ventilation, air purification, and soil vapor extraction (SVE) to mitigate potential vapor intrusion of volatile organic compounds (VOCs) to residences originating from the Former Ketema Facility (Site). In addition, the RAW describes placing GAC socks within concrete culvert boxes to intercept water flow from a Pump House. Background: The Former Ketema Facility is located at 790 Greenfield Drive in the city of El Cajon. Highway 67 is located approximately 0.5 mile to the northwest followed by commercial/industrial properties and Gillespie Field, and Interstate 8, located approximately 0.75 mile south of the facility. Magnolia Elementary School (MES) is located adjacent to the western property boundary of the facility. Residential developments are located to the north and east of the facility and further downgradient, northwest of MES, including the Starlight, Greenfield, and Villa Cajon Mobile Home Park (MHP) communities. Industrial and commercial developments are located south of the facility and further downgradient of the site in the area adjacent to Highway 67. The nearest mapped surface water body is Forrester Creek, a concrete-lined, intermittent drainage channel that flows westerly approximately 0.7 mile south of the Site, before turning and flowing north-northwesterly approximately 1.2 miles west of the Site. The California Department of Transportation (Caltrans) operates the Highway 67/Bradley Avenue Overpass Pump House located at the southwestern corner of Highway 67 and East Bradley Avenue. The Pump House is designed to prevent flooding of Highway 67 by pumping stormwater into the adjacent drainage channel. The Site has been used as an aerospace manufacturing plant since the 1950s. In 1987, contamination of groundwater with chlorinated solvents was discovered underlying the Site, resulting from past operations. Groundwater investigation and monitoring conducted at the Site since 1987 indicated concentrations of VOCs in groundwater above State of California Maximum Contaminant Levels (MCLs) in both on- and off-site monitoring wells. The Site-related COCs include: - Trichloroethene (TCE), - Tetrachloroethene (PCE), - 1,1-Dichloroethene (1,1-DCE), - 1,1-Dichloroethane (1,1-DCA), - 1,1,1-Trichloroethane (1,1,1-TCA), and - 1,4-Dioxane (a semi-volatile organic compound). Downgradient migration of contaminated groundwater resulted in a shallow groundwater plume extending approximately 1.5 miles northwest off-Site. Groundwater off-gassing in the downgradient plume resulted in potential vapor intrusion risk to residences located in MHP; and groundwater intercepted at the HWY 67/Bradley Avenue Pump House, when discharged into the tributary of Forester Creek, could pose risk to the ecological receptors in the creek. Project Activities: To remediate impacted soil vapor, the removal action will involve sequential implementation of passive ventilation, active ventilation, air purification, and SVE to mitigate potential vapor intrusion to residences downgradient of the Site. If passive/active ventilation and indoor air purification does not effectively mitigate vapor intrusion in the off-site residences, SVE will be implemented to capture potentially impacted soil vapors from the subsurface beneath and in the vicinity of the residence(s) of concern. SVE, also known as soil venting or vacuum extraction, is an in situ remedial technology that reduces concentrations of volatile contaminants adsorbed to soils in the unsaturated (vadose) zone. In this technology, a vacuum will be applied through existing wells near the source of contamination in the soil. Volatile constituents of the contaminant mass vaporize, and the vapors are drawn toward the extraction wells. Extracted vapor is then treated as necessary (typically by carbon filtration for chlorinated VOCs), before being released to the atmosphere. The increased air flow through the subsurface can also stimulate biodegradation of some of the contaminants, especially those that are less volatile. To treat surface water discharges from the Pump House, the removal action consists of placing two clusters (five sets of granular activated carbon (GAC) socks per cluster) within concrete culvert boxes, each set consisting of three socks (total of 30 socks) stacked in a pyramid-like shape, in series across the V-ditch. The proposed GAC socks will be placed perpendicular to and will intercept water flow in the V-ditch to adsorb and remove Site-related COCs (and other dissolved organic compounds) from infiltrated groundwater discharged from the Pump House to the tributary of Forester Creek and other ecological receptors present downgradient.

El Cajon

San Diego

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San Diego