A southeastern Massachusetts property is associated with a now-demolished chemical plant where a variety of industrial chemicals and pesticides were manufactured for many years. The client has been conducting environmental remediation activities at the property since the plant ceased operations in the early 2000’s. The contamination at the site affects multiple media, including soil, groundwater, surface water, and sediment. In 2004, our client signed a consent order with U.S. EPA under the Resource Conservation and Recovery Act (RCRA) to complete a detailed site investigation and conduct any required remediation. Several prior consultants conducted investigation activities at the site and identified chlorinated benzenes, arsenic, lead, mercury, and polychlorinated biphenyls (PCBs) as the primary constituents of potential concern (COPCs). Our client’s goal in retaining Geosyntec was to address significant comments provided by U.S. EPA on the deliverables prepared by a prior consultant, complete the RCRA Facility Investigation (RFI), and develop and implement a remedial strategy to achieve site closure.
Geosyntec’s Scope of Services
Geosyntec began work on the project by providing an independent third-party review of the previous consultant’s proposed approach for addressing U.S. EPA’s comments updating the conceptual site model. Geosyntec subsequently developed and implemented a Supplemental Field Work Plan (SFWP) to complete the RFI which included additional characterization at the site to better understand the complex hydrogeology. An RFI report summarized the investigation results and the revised conceptual site model.
Revising the conceptual site model included the use of several lines of evidence to create a model describing the geologic and hydrogeologic site conditions. Geosyntec’s supplemental investigation included surficial geophysical testing, installation of monitoring wells and streambed piezometers, hydraulic conductivity testing, and tracer injection testing. The three major water-bearing units at the site consist of shallow overburden, deep overburden/weathered bedrock, and fractured bedrock. The weathered bedrock zone has localized areas of high transmissivity and is hydraulically continuous with the deep coarser-grained overburden deposits. By characterizing vertical hydraulic gradients throughout the site, Geosyntec developed a conceptual model to demonstrate the influence of hydraulically conductive zones and vertical gradients on groundwater flow and contaminant transport. Additionally, streambed piezometers were used to evaluate the potential for groundwater containing COPCs to be discharged to sediment and surface water. These conceptual modeling efforts have resulted in identifying effective methods of groundwater treatment, and what is needed to address ecological and human health risk pathways at the site.
As part of the RFI, Geosyntec demonstrated that the transmissivity of the overburden aquifer at the site is less than would be needed to support drinking water wells. A discussion with EPA and MassDEP concluded that the site should not be considered a potential drinking water source area under State regulations. As a result, drinking water standards are no longer being considered as potential Media Cleanup Standards (MCS).
Geosyntec has been assisting in preparing updated human health and ecological risk assessments and supporting our client in ongoing regulatory negotiations on the risk assessment documents. Geosyntec provided technical expertise to review and update the existing risk assessments for the site to minimize rework for our client. We have also worked with the client to develop conceptual remedies for the site to prepare for the upcoming work including developing MCS and performing a Corrective Measures Study (CMS). Our review of the conceptual remedies for the site allowed the client to prepare for costs associated with site remediation and to identify site activities that could be completed during regulatory negotiations on the risk assessments to help the overall project schedule continue to move forward.
Geosyntec’s expertise allowed us to evaluate a complex site with a substantial data set quickly and to provide our client with a scientifically-defensible response to U.S. EPA’s comments. We conducted over 900 person-hours of field work to complete the RFI and produced a report that was approved by U.S. EPA with no additional comments. We also used our understanding of the Massachusetts regulations to eliminate drinking water standards from consideration as MCS, significantly reducing the likely remediation cost for the client.
- Location: Dighton, Massachusetts
- Client: Zeneca
- Project Practice Areas: Contaminated Sites
- Type of Facility: Former Manufacturing Facility
- Services Provided: Conceptual site model preparation; RCRA facility investigation; Risk assessment; Regulatory interaction; Pre-design investigation; Remedial strategy
- Type of Work: Remedial Investigation
- Governing Regulation: Federal, State and Local