Revised Explanation of Significant Differences Trader Joe’s Company – Rancho Cordova Logistics Center

Revised Explanation of Significant Differences Trader Joe’s Company – Rancho Cordova Logistics Center

The proposed project activities involve design and installation of vapor mitigation systems (VMS) as part of new building construction. Project activities would be accomplished through a long-term Trader Joe’s development plan for a 55-acre site located at 12100 Atlanta Circle in the city of Rancho Cordova (Site). Background: The project applicant, Trader Joe’s, plans to develop a portion of the Site. The Site is an approximately 55-acre area of land within the northwestern portion of Rancho Cordova Logistics Center (RCLC). The Site is currently developed with one unoccupied warehouse building (Building 1), paved asphalt areas, and lined stormwater features. The Site was formerly used by Aerojet for manufacturing and chemical storage. Portions of the Site are located within the limits of the Perimeter Groundwater Operable Unit Five (OU-5) of the Aerojet Superfund Cleanup Area, and are subject to Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) requirements. The larger Aerojet facility was placed on the National Priorities List (NPL) in December 1983 and contains soil, soil vapor, and groundwater impacts with primary compounds of concern (COCs) including, but not limited to, trichloroethene (TCE), perchlorate, and N-nitrosodimethylamine (NDMA). In February 2011, the U.S. Environmental Protection Agency (EPA) issued a Final Record of Decision (ROD) for soil for OU-5, which recommended installation and operation of a soil vapor extraction (SVE) system and temporary asphalt cap to improve capture of the volatile organic compounds (VOCs), institutional controls in the form of a land use covenant (LUC), and engineering controls via VMS for areas where neither soil excavation nor soil vapor extraction would be protective due to VOC migration onto OU-5 from upgradient sources. Because of the environmental conditions, the Site includes two LUCs with restrictions, prohibitions, and requirements related to groundwater (groundwater LUC) and soil vapor quality (vapor mitigation LUC). In September 2021, a subsurface investigation was performed to evaluate soil and soil vapor that would be potentially encountered in the project area. As described in the 2023 DTSC-approved Remedial Action Plan (RAP) and consistent with the 2011 ROD, the selected remedial action for the RCLC project consisted of the installation of a passive VMS underneath the concrete slabs of the proposed buildings (RCLC Buildings 1 and 2) to mitigate potential vapor intrusion risk. The selected remedial action alternative aligns with the Site being subject to the DTSC remedial action agreement (RAA) and the vapor mitigation LUC, which restricts development to industrial, commercial, and office space, and requires any new buildings to include vapor mitigation measures. As a result of Aerojet’s previous remediation (completion of SVE) and due to the lack of impacts in on-Site soils identified during the 2021 subsurface investigation, no soil remediation was required as part of the 2023 RAP. However, soils were required to be managed consistent with the DTSC approved Site Management Plan (SMP). The overall basis for the Explanation of Significant Differences (ESD) is that residual VOCs remain in soil vapor beneath the Site, and the vapor intrusion LUC requires the installation and operation of VMS as part of new building construction. Project Activities: As described in the ESD, the project activities will involve changes to the remedy selected in the 2023 RAP to accommodate the proposed Trader Joe’s development project. To address potential vapor intrusion risks from VOCs, the installation of a passive VMS underneath the concrete slabs of the proposed buildings will be included as part of the development to mitigate potential vapor intrusion risk. The following changes will be made to the remedy in conjunction with the Trader Joe’s development project: • As required by the vapor mitigation LUC, the Building 1 Expansion and construction of new buildings will include the design and installation of a VMS to mitigate the potential for vapor intrusion from soil vapor beneath the buildings. The VMS for the Building 1 Expansion and Maintenance Building will consist of a vapor barrier membrane located immediately beneath the structural building slab combined with a horizontal collection and venting system installed below the vapor barrier membrane. The objective of the VMS for each building is to allow soil vapors that would otherwise collect beneath the slab to migrate and vent to the atmosphere outside the building. In the event it is necessary, each building’s VMS will be designed with the capability to operate as an active system. Upon completion of construction and VMS performance monitoring, if concentrations or system performance indicate active extraction is necessary, in-line mechanical blowers will be installed on the roof level to provide active extraction of the soil vapor from beneath the Building 1 Expansion and Maintenance Building. • The VMS for the three Guard Houses will include a subgrade gravel layer and vapor barrier membrane located beneath the concrete island where the Guard Houses will be placed. The Guard Houses are prefabricated structures constructed of aluminum with operable doors and windows and heating, ventilation, and air conditioning (HVAC) systems. Therefore, passive horizontal collection and venting of soil vapor is not currently recommended or practical as part of the VMS design for the Guard Houses. Post-construction and long-term VMS performance monitoring requirements for the new buildings intended for occupancy will be generally consistent with the approved RAP. • The VMS for a future freezer building and freezer building expansion will also include passive VMS with the capability to operate as active; however, the freezer building and freezer building expansion will be constructed at a later date yet to be determined. The remedy implementation timeline for the first phase of the Trader Joe’s development project (Building 1 Expansion, Maintenance Building, and Guard Houses) is anticipated to start in October 2025 and be completed in May 2026 (eight months). A similar remedy implementation timeline of eight months is estimated for the second phase of the Trader Joe’s development project (Freezer Building and Freezer Building Expansion). DTSC utilized information and analysis in the Easton Research Park West Tentative Subdivision Map Project Initial Study/Mitigated Negative Declaration (MND) to support a final determination about the type of environmental document required to be prepared for the proposed Revised Explanation of Significant Differences Trader Joe’s Company – Rancho Cordova Logistics Center as provided by Sections 15162, 15163, and 15164 of the CEQA Guidelines. The City of Rancho Cordova, as the Lead Agency pursuant to the CEQA, approved the MND on November 15, 2021 (State Clearinghouse Number 2021090544). The Project consisted of a Tentative Subdivision Map to subdivide an existing 178.50-acre parcel into ten parcels for future development of an industrial warehouse campus and one landscape/right-of-way lot. Improvements would include grading the entire site along with tree and vegetation removal, demolition of existing buildings, structures, foundations, and pavement with off-site demolition debris disposal, construction of associated stormwater detention basins, parking lots, and interior private streets and involve off-site construction and reconfiguration of overhead and underground utilities to serve the Project Site on adjacent and nearby roadways and Aerojet property.

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