ORCO Stanton Revised Removal Action Workplan

ORCO Stanton Revised Removal Action Workplan

The project consists of excavation of soil to address volatile organic compound (VOC) impacts, specifically tetrachloroethene (PCE) on the approximately 10.66-acre property (Site) located in an area of mixed residential and commercial use. Project activities include the excavation and off-Site disposal of approximately 75 cubic yards of soil and installation of a passive vapor intrusion mitigation system [VIMS]. In addition, a land use covenant (LUC) will be recorded with the County of Stanton and Operation, Maintenance, and Monitoring (OM&M) Plan will be developed to monitor VIMS effectiveness and condition. The project is estimated to take approximately 1 week (5 days) and about 7 trucks. Background: The entire Site consists of five parcels (Assessor Parcel Numbers [APNs] 131-101-01 (Parcel A), 131-101-16 (Parcel B), 131-101-15 (Parcel C), 131-101-21 (Parcel D), and 131-101-18 (Parcel E). From approximately 1954 to the early 1970s, Parcel A used as a gasoline service station and then an automobile sales operation in the 1970s, before being redeveloped and used by a flower shop from approximately 1981 until 2018. Parcel B was developed and occupied by a restaurant from approximately 1962 until 2018. By 2020 all structures on Parcel A and B had been demolished except the concrete foundation and asphalt parking area. Parcels C, D, and E are part of the active on-Site ORCO Block manufacturing facility, which has been in operation since 1954; an office building was constructed in the southwest corner of Parcel D in 2005. Stanton Land entered into a Standard Voluntary Agreement (SVA) with the DTSC, Docket Number HSAFY23/24-131, executed between Stanton Land, LLC and DTSC on June 20, 2024. Adjacent property uses are detailed below: • North – Katella Avenue, followed by retail building (10972 Katella Avenue), single-family residences, MS Landscape and Gardening Services (10951 Court Ave), and Katella Plywood & Lumber Co. (8121 Katella Avenue) • East – Caltrans maintenance yard (8122 Katella Avenue) • South – Southern California Edison easement with high-voltage transmission lines and is also used by ORCO as a block storage yard, followed by mobile home park (11250 Beach Boulevard) • West – Beach Boulevard, followed by dental office (11001 Beach Boulevard), bank (11051 Beach Boulevard), restaurant (11097 Beach Boulevard), and Stanton Park • Northwest – Intersection at Beach Boulevard and Katella Avenue, followed by Chevron gasoline station (10961 Beach Boulevard) Stanton Land intends to redevelop the Site with multi-tenant residential housing and mixed-use commercial buildings, with the exception of the existing office building, which will remain. The City of Stanton has determined that the redevelopment of the property qualifies for an exemption from the California Environmental Quality Act under Assembly Bill 130. Previous Investigations: Beginning in 2013, subsurface investigations were conducted at the Site to assess potential impacts from historical features located on Parcel E of the Site, including the mechanic pit, former oil use area (weed abatement), hazardous waste storage area, forklift steam cleaning pit and maintenance area, a former 10,000-gallon diesel underground storage tank (UST), and vehicle washdown area. The 2013 investigation analyzed soil and groundwater with results indicating isolated areas of total-petroleum hydrocarbon (TPH)-impacted soil and TPH-diesel and the chlorinated solvent, tetrachloroethene (PCE) in groundwater at concentrations slightly above the applicable screening levels. The detections of PCE in groundwater were reported near the former forklift steam cleaning pit. In 2023, 2024, and 2025, additional investigations further investigated and delineated VOC impacts, specifically PCE, in soil vapor and groundwater. The source areas of VOC impacts appear to be localized near the former forklift steam cleaning and maintenance pits area in the northeast portion of the Site and near a storage area in the southwest portion of the Site. Project Activities: Based on subsurface investigations performed at the Site, soil vapor concentration results indicated that there are two areas with elevated residual VOC impacts. These areas are generally located near the former forklift steam cleaning and maintenance pit area in the northeast portion; and a storage area in the southwest portion. Following removal of aboveground features (which is not part of this project), an approximately 10 feet long by 10 feet wide area is proposed to be excavated at both areas. Based on the depth to groundwater (18 feet bgs) and the proposed grading depth (minimum 5 feet over excavation), the limited excavations are proposed to go down 10 feet bgs. Approximately 37.5 cubic yards are proposed to be excavated from each source area, for a total of 75 cubic yards. All excavated soils from within the two limited excavation areas will be disposed off-Site. All soil loads will be transported under proper waste manifests by licensed and insured transporters. A VIMS will be designed and installed beneath the entire footprint of the proposed buildings to minimize the potential exposure of vapor intrusion of VOCs to future occupants. The VIMS design for the proposed building structures will include the following key components: • A sub-slab vapor barrier, which will consist of a spray-applied geomembrane (e.g., EPRO E.Spray, or equivalent) and a cushion geotextile installed beneath all slabs and footings of the proposed structures; • A passive ventilation system, which will include a perforated flat vent piping network embedded in a minimum 2-inch thick layer of rock course. The vent pipes will capture the potential vapors and direct them into vent risers that will terminate above the roofline of the structures; • Trench dams and conduit seals, for all utilities penetrating the slab of the proposed structures (if applicable) in order to prevent VOCs from migrating into the structure; • Soil vapor probes, installed in conjunction with the vapor barrier system may include horizontal soil vapor probes beneath the building and vertical soil vapor probes located outside the building; and • An optional active ventilation system may be implemented via the installation of mechanical blowers if deemed necessary. Based on soil vapor data generated at the Site, a passive ventilation system is expected to be sufficient to mitigate vapor intrusion at the Site. Although not anticipated, in the event biological, cultural or historical resources are discovered in the course of project activities, work will be suspended while a qualified biologist, cultural or historical specialist makes an assessment of the area and arrangements are made to protect or preserve any resources that are discovered. If human remains are discovered, no further disturbance will occur in the location where the remains are found, and the County Coroner will be notified pursuant to the Health and Safety Code, Chapter 2, Section 7050.5.

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