CERCLA RI and IRM Modification
Location: Northern New Jersey
Regulatory Program: CERCLA
Duration: September 2008 to Present
Summary: Designed, managed, and conducted multi-media Remedial Investigation to assess the horizontal and vertical extent of VOCs and metals impacts originating at two adjacent sites; collaborated with the project engineer to evaluate and optimize the performance of an interim remedial measure; developed and implemented modifications to a groundwater performance monitoring program initiated in the 1990s, to reflect investigative findings supporting a more focused scope for sampling and reporting; supported client’s internal assessment of site re-use options by identifying and resolving data gaps, informing area-specific assessments made by the project engineer and risk assessor.
This site consists of two adjacent properties (Sites A and B; see figure below) on which chemical production and recycling activities took place beginning in the 1960s. In the early 1970s, shallow municipal wells were found to be impacted by metals attributed to discharges at Site B. This prompted the closure of the shallow wells and the installation of a new series of deeper wells at locations about 2,000 feet further from Site B.
Beginning in the early 1980s, owners of Sites A and B conducted investigative and remedial activities aimed at characterizing sources of VOC impact related to Site A and of metals impact related to Site B, and protecting the new municipal supply wells. By the early 1990s, a “first generation” pump and treat system was in place in the municipal watershed area downgradient of the two industrial sites, collecting and treating VOC- and metals-impacted groundwater, and performance monitoring programs (PMPs) were underway. By the late 1990s, plume remediation had been accomplished such that NJDEP approved shut-down of the first generation system coincident with the startup of “second generation” pump and treat systems to maintain hydraulic control at sources on Sites A and B until source remedies could be implemented. These Interim Remedial Measures (IRMs) remain in operation today.
EPA took over as the lead regulatory agency in 2005, signing an administrative order with the owner of Site A (a recent corporate successor to the company that historically operated the site) to complete the RI/FS for Site A and to complete a comprehensive RI/FS for groundwater. The Site A owner developed and obtained EPA and NJDEP approval of Supplemental RI (SRI) Workplan documents and in 2008 hired Princeton Geoscience to assist their in-house EH&S staff with implementation of the project field activities, preparation of project field sampling plans and reports.
Between 2009 and 2013, we implemented the SRI in two phases, assuming additional project scoping and management responsibilities after our client merged with another company, focusing internal EH&S efforts on overall project management.
Activities performed during SRI Phase 1 included:
- VOC source area soil investigation on Site A
- Plume transect groundwater sampling at the Site B downgradient property boundary for VOCs and metals
- Soil sampling to assess re-use potential of a historically unused portion of Site A
- Vapor Intrusion (VI) studies on Sites A and B (with risk assessment contractor)
Findings of SRI Phase 1 were summarized in technical memoranda which were used as basis for the SRI Phase 2 Field Sampling Plan. SRI Phase 2 tasks included:
- Offsite VOC and metals plume delineation along three cross-plume transects in the watershed area upgradient of the municipal wells
- Assessing discharge/recharge relationships between groundwater and local surface water bodies and potential for ecological risk in areas where groundwater discharges to surface water
- Evaluating metals concentrations detected in Site A soils vs. natural geologic background conditions
- Revising the PMP monitoring network, and focusing the PMP sampling and reporting efforts, based on SRI findings
- Supplemental soil sampling on Site A to support Human Health Risk Assessment (HHRA) and the client’s internal EH&S strategy for site redevelopment
- Delineating the extent of 1,4-dioxane in groundwater and identifying and delineating the extent of the 1,4-dioxane source area
During and following SRI Phase 2, Princeton Geoscience collaborated with the project engineering consultant in their execution of several tasks conducted to assess and, if necessary, improve performance of the IRM on Site A. IRM Assessment tasks included:
- Shallow piezometer installation and hydraulic conductivity testing
- Groundwater chemical profiling
- Pumping test and hydraulic capture assessment
- Geotechnical and waste characteristics analysis
- In addition, Princeton Geoscience prepared a groundwater flow model, which was used to support design of a modified groundwater recovery system for Site A.
Throughout the SRI, we interacted with the project risk assessor to focus investigative activities as needed to fill relevant data gaps.
Findings of the SRI were included in a Site Characterization Summary Report (SCSR) and draft RI Report, which also incorporated the interim findings of the IRM Assessment and risk assessment activities. Major findings included:
- Soils beneath the former location of a tank farm and process area on Site A constitute the main source of VOC impacts to groundwater; soil in this area is impacted to a depth of about 30 feet, approximately 25 feet below the water table
- A separate area on Site A contributed to limited 1,4-dioxane impacts in groundwater
- The historically unused portion of Site A exhibits no contaminant impact that would preclude redevelopment
- A separate VOC plume originating at an upgradient Superfund site has diminished in response to source remediation efforts at the site; dilute remnants of the plume are expected to continue to attenuate
- The IRM on Site A captures most of the VOC impacted groundwater, but some VOC mass bypasses the system locally and periodically
- The IRM on Site B captures metals-impacted groundwater and functions as a backup for the Site A IRM, capturing most of any VOC mass bypassing the IRM on Site A
- VOCs do not discharge to surface water at concentrations posing risk to receptors
- VOC concentrations in groundwater on the watershed property upgradient of the municipal wells are low and decreasing, municipal wells are not impacted or at risk of being impacted by VOCs
- Metals impacts to groundwater resulted from historical operations on Site B and from past water treatment sludge management operations at the municipal wellfield
- Metals impacts to groundwater attenuate within distances of 200 to 800 feet of the property line such that municipal wells are not impacted above drinking water standards, either in raw or treated water
- Operation of the Site B IRM is effective in limiting flux of metals contamination from historical release areas on Site B
Princeton Geoscience is currently working with the client and the project engineering consultant as they develop plans for a near-term modification of the Site A IRM and prepare deliverables for the Feasibility Study. The modified IRM will incorporate four recovery wells to replace two existing wells, more robust treatment to handle the increased flow and VOC loading, and permitted surface water discharge of the treated effluent, to eliminate currently incurred POTW discharge fees. As noted, the IRM is being upgraded to improve control of VOC impacted groundwater associated with Site A and eliminate reliance upon the Site B IRM as a backup. Another reason for making the Site A IRM more robust is to ensure a high degree of source control during a future source remedy currently anticipated to consist of in-situ chemical oxidation.
Based on an extensive record of PMP monitoring which documents stable or decreasing VOC concentrations, Princeton Geoscience expects that Monitored Natural Attenuation (MNA) will function as a near-term remedy component for the offsite portion of the plume, and following source remediation, as a site-wide groundwater remedy. Key elements for the FS will include 1) enhancing the weight of evidence supporting MNA, and 2) defining endpoints for source treatment based on VOC mass flux from the source area, as measured by sampling at the expanded recovery wells, which will capture all VOC mass emanating from the source area on Site A.
To further support MNA, Princeton Geoscience has developed plans for conducting compound-specific isotope analysis (CSIA) to quantify contaminant degradation rates. Results of the CSIA study will be utilized with groundwater flow and transport modeling to define source remediation endpoints, the achievement of which will allow the pump and treat system on Site A to be shut down, with a change to MNA as the site-wide groundwater remedy for VOCs.
The SRI evaluated metal impacts to groundwater based on EPA’s request because the Site B owner was in bankruptcy proceedings when EPA assumed regulatory responsibility for this project. The owner of Site B subsequently emerged from bankruptcy and continues remediation of metals impacts related to their past operations.
Princeton Geoscience is currently preparing a final text, figures, and tables for site characterization related portions of the RI Report and coordinating with the project risk assessor as they prepare the ecological and human health risk assessments. Upon completion of those assessments, a Final RI Report will be submitted to EPA and NJDEP.