Former Roehl Disposal Facility Pilot Test Evaluation and Remediation
City of Los Angeles Harbor Department (Port of Los Angeles) • Wilmington, CA
Solution Overview
Client:
City of Los Angeles Harbor Department (Port of Los Angeles)
Business Challenge:
- Chemicals of concern (COCs)—specifically, tetrachloroethene (PCE), lead, and arsenic—were found in the soil at the former Roehl Disposal Facility Site
Solution:
- Evaluated a previous pilot test to identify the cause of a rise in chemical agents
- Performed groundwater testing and recommended impacted soil and groundwater removal
Results:
- Developed a remediation system to reduce the concentration of chlorinated volatile organic compounds (CVOCs)
- Established a remedial strategy for long-term monitoring and sampling
Challenge
Spills and releases of chemicals from historical operations at the former Roehl Disposal Facility in Wilmington, CA migrated into the soil and the four stratigraphic groundwater zones beneath the property and neighboring parcels in its vicinity. The principal COCs identified to be present at the Site included CVOCs, primarily PCE, and metals (specifically, lead and arsenic) in shallow soil.
Solution
Apex evaluated a previous pilot test performed by another consultant involving in situ reactive zone (IRZ) injection of emulsified vegetable oil (EVO) and bacterial augmentation into the groundwater zone to reduce concentrations of PCE and other CVOCs. We identified the cause of previous injections to accommodate heterogeneity in subsurface permeability of the saturated zone which resulted in the apparent rise of post-injection vinyl chloride concentrations.
Apex performed additional groundwater testing that included specialized microbial analyses for dehalococcoides spp. bacteria. The results of the analyses indicated that although the EVO pilot test and subsequent groundwater monitoring data demonstrated the effectiveness of the EVO remedial approach, the limitations of the technology at the site (e.g., difficulty in introducing the EVO reagents into deeper sediments) and the potential deleterious unintended effects (including the generation of post‑treatment increases in vinyl chloride in areas within and outside of the treatment areas) present risks that argue against further use of EVO at the site.
Apex recommended revising the Remedial Action Workplan (RAW) to consider source removal as the primary remedy for impacted soil and groundwater at the site. The California Department of Toxic Substances Control (DTSC) provided its concurrence with this evaluation. To further define the lateral and vertical extent of high-VOC soil to be excavated, Apex conducted a membrane interface probe (MIP) investigation in conjunction with geophysical electrical conductivity measurements to provide definitive limits of impacted soil; these were in turn used in the preparation of a Corrective Measures Study (CMS) in accordance with the Consent Decree entered into by Roehl and the DTSC. As a pre-CMS investigation, Apex developed and implemented comprehensive groundwater and soil vapor sampling plans to delineate the extent of contamination offsite and fill in data gaps. Apex conducted groundwater and soil vapor investigations using Environmental Protection Agency (EPA) Triad principles to integrate data quality objectives, flexible work planning, direct push technology (DPT) with onsite analytical tools, and decision rules.
Results
Apex is currently working in concert with the City of Los Angeles and the DTSC to further evaluate the lateral limits of the groundwater and soil vapor CVOC plumes. This data is being used to develop risk-based models of potential exposure pathways and associated risks to receptors. To provide an immediate mitigation to the offsite receptors, Apex developed and installed an interim remediation system designed to reduce the concentration of CVOCs in soil vapors offsite and east of the property. Indoor air and subslab sampling methods will be used to evaluate the risk to offsite receptors. Concurrently, Apex is continuing to develop a remedial strategy which will entail source removal (to remove soils containing the highest CVOC concentrations), implementation of phytoremediation (to provide long‑term restoration of site soils and underlying shallow groundwater), and long-term monitoring and sampling to demonstrate groundwater dissolved CVOC plume stability and contaminant concentration reductions.