In the Fall of 2002, EPA Region 1 requested the assistance of the EPA Brownfields Technology Support Center (BTSC) in developing a strategy for site characterization and reuse. The BTSC assisted Region 1 with systematic project planning (SPP) for the Site, revising the existing Targeted Brownfields Assessment (TBA) Work Plan to incorporate a Triad Approach-based HRSC. Following approval of the revised TBA Work Plan in December 2002, a field investigation was conducted over the course of 1 week in February 2003 that effectively characterized the Site for all constituents of concern (COCs).
The investigation revealed widespread contamination in soils at the Site, quickly leading the project team to conclude that complete remediation or removal of soil to residential standards was cost prohibitive. In 2007, Phase I Remediation was completed, which included the removal of soils contaminated with polychlorinated biphenyls (PCBs). In 2012, the first portion of Phase II Remediation was completed, which included the relocation of soil and ash, installment of a geotextile fabric cover, placement of a cap (clean fill), and construction of a stone revetment along the waterside perimeter of the Site. The final grades were dictated by the Site's proposed use. The purchase agreement for the property mandated that the Site be converted into a public park.
Highlights of the project from a Triad and HRSC perspective include:
|Site Name||Former Cos Cob Power Plant|
|Site Type||Power Plant|
|Project Lead Organization||Town of Greenwich, with support from EPA Region 1|
|Project Lead Type||Municipal/Local Lead|
|Regulatory Lead Program||Targeted Brownfields Assessment|
|Triad Project Status||Field Program Completed|
|Reuse Objective Identified||Yes|
The Site occupies approximately 9 acres and operated as a coal-fired power plant from 1907 until the mid-1960s. The plant was decommissioned in 1986 and the property deeded to the Town of Greenwich in 1987. The COCs were primarily associated with fly ash that was used as fill across the Site, and with leaks from electrical transformers. All buildings at the Site have been demolished and the transformers formerly stored at the Site have been removed.
The Town planned to redevelop the property as a community recreational area, including walking trails and playing fields. At the time of the field investigation, a detailed reuse plan for the property or redevelopment timeline had not been developed.
The DWS field program rapidly clarified the principal reuse questions and remedial options for the project team and the Town. Field-based technologies were used in an HRSC format to increase site coverage (that is, data density) and limit decision uncertainty. Key ranges of concentrations and safety factors were identified and refined to guide data interpretation and decision-making in the field using real-time methods, and these ranges also became the focus of collaborative data collection using off-site methods to increase decision confidence. Although concentrations of some COCs (TPH, PAHs, and arsenic) at the Site were above Connecticut residential criteria across large areas of the Site, findings showed that a sound investigation approach, limited remediation in impacted areas, and careful evaluation of cleanup criteria and reuse alternatives would support reuse.
Arsenic concentrations in soil/fill across the Site were in the range of 10 to 150 milligrams per kilogram (mg/kg). Total PAH concentrations across the Site were commonly in the range of 100 to 700 mg/kg and ranged as high as 1,900 mg/kg. TPH concentrations were greater than 1,000 mg/kg over a large portion of the Site. In addition, PCB hotspots with concentrations ranging from 1 to 10 mg/kg were delineated over limited areas of the Site.
A consultant has been retained by the Town in 2012 to commence the design of the construction plans for the proposed park. The construction of the park will be the last step in the Phase II Remediation process. The State of Connecticut requires the use of residential cleanup standards for recreational reuse scenarios; however, results of the TBA indicated that removal of contaminated soil exceeding residential direct contact criteria would not be cost-effective. Remedial alternatives considered feasible for the Site included removal of limited PCB hotspots, and placement of clean fill material over portions of the Site to prevent exposure in conjunction with deed restrictions to prohibit digging into contaminated media.
The Town was deeded the property in 1987 from the Connecticut Department of Environmental Protection (CDEP) with the understanding that eventually the property would be open to all residents of the State. Several previous investigations at the property indicated the presence of PAHs and other petroleum constituents, PCBs, and metals (mainly arsenic) in soil above Connecticut residential direct contact criteria.
The Town received a TBA grant in 2002 to characterize the Site and assess potential reuse options.
Project objectives included use of the Triad Approach to collect a high-density data set using HRSC strategies, limit decision uncertainty, and in a single mobilization, sufficiently characterize the nature and extent of site contaminants to allow the Town to evaluate reuse scenarios and remedial options. The scope of the project also included evaluation of feasibility of potential cleanup options.
The SPP effort and DWS field effort applied at the Site established the principal contamination issues and reuse options for the Site without the need for additional mobilizations. Time was also saved because the project was completed in a single mobilization and TBA funding cycle.
Overall cost savings for the project were estimated at 35 percent when compared to a "conventional approach" to site characterization. The project team assessed these savings even after accounting for the additional upfront SPP efforts, revised Work Plan preparation, and the DMA that was performed under the Triad.
Costs for the conventional approach assumed two mobilizations and accompanying sampling and analysis plans. Lower data density and higher analytical costs were also assumed when using a conventional approach with exclusive use of fixed-base laboratory analyses.
The project team further estimated a time savings of approximately 1 year, assuming that a conventional approach would have required at least two mobilizations performed over two 1-year TBA funding cycles.
The BTSC assisted the project team (EPA Region 1 and its contractor) during the SPP effort to develop a preliminary CSM and frame the principal study questions and decisions based on data from previous investigations. The CSM indicated that potential threats to human health and the environment were essentially limited to direct contact with contaminated surface soil and sediment at the site. Much of the contamination was predicted to be related to releases to surface soils from stored transformers (PCBs), and the use of fly ash from coal combustion as fill across the site (petroleum-related contaminants and arsenic).
The initial work plan developed by EPA Region 1's contractor was based on a conventional approach to site characterization, involving limited sampling at locations where historical releases were expected along with fixed-base laboratory analysis. With BTSC's assistance, the project team revised the sampling approach into an HRSC based on use of the Triad Approach DWS. The approach called for random grid sampling and field-based measurement technologies to expand the extent and density of sampling for TPH, PAH, and PCBs.
The strategy for uncertainty management included the use of field-based analytical technologies to increase data density and DWS to support adaptive and focused sampling. BTSC conducted statistical data analysis and used decision support tools (DSTs) to provide preliminary field-based action levels.
The revised TBA Work Plan incorporating the Triad Approach was accepted by the project team and the stakeholders for the project.
The project manager for the Town was the principal decision maker for the Site, with assistance from EPA Region 1's Remedial Project Manager (RPM). Other stakeholders with input to Site decisions included the BTSC and EPA Region 1's technical support contractor, Metcalf and Eddy, Inc. (M&E). BTSC's support was provided in the areas of chemistry, statistics, geoscience, and engineering. A BTSC chemist also provided oversight of the field-based analytical program during the investigation. M&E provided the field investigation team and overall project management and coordination. Additional valuable technical support assistance and training was provided by the test kit vendor, siteLAB.
Recommendations were provided for real-time analysis of TPH and PAHs in the field using UVF test kits and PCBs using on-site laboratory gas chromatograph/electron capture detector (GC/ECD). A DMA study was completed before the field investigation to ensure the usability of the UVF test kits and to develop preliminary field-based action levels correlated with fixed-base laboratory analyses.
The field effort at the Site was completed in 1 week in February 2003. Direct-push technology (DPT) methods were used to collect soil samples at depths up to 4 feet below ground surface (bgs) from a 70 foot X 70 foot sampling grid placed across the Site. The sample location within each grid element was selected randomly unless a specific area of potential contamination was identified, whereupon a judgmental (biased) sample was collected. Initially, samples from only the top two 1-foot intervals at each location were analyzed in the field, and a percentage of the samples collected were sent for off-site collaborative analyses. Field analyses were performed for PAH and TPH at all locations using the UVF test kits, whereas PCB analyses were performed only in grid elements where PCB releases were possible based on historical information. A total of 93 samples were collected for PAH and TPH analysis using the test kits, and 103 samples were collected for PCB analyses by the Region 1 mobile laboratory. In addition, 112 samples were collected for fast turnaround arsenic analyses at a fixed-base laboratory.
As the initial data were collected, it became clear that concentrations of TPH, PAHs, and arsenic that consistently exceeded Connecticut's reuse criteria in the top 2 feet of soil across a significant portion of the Site. Acknowledged past disposal and fill practices at the Site suggested that similar concentrations could extend to as deep as 30 feet bgs, making the analysis of deeper samples unnecessary and rendering removal or remediation options to residential standards cost prohibitive for these COCs. For PCBs, additional step-out sampling in grid elements where detections of PCBs were reported by the mobile laboratory delineated additional localized areas of PCB contamination in the surface and near-surface soil.
Decision logic diagrams were incorporated into the revised DWS work plan to allow maximum use of TPH and PAH values from the UVF test kits and PCB values based on on-site laboratory analysis (using GC/ECD). The decision logic assisted the project team in assessing "clean" and "dirty" areas using the UVF test kits, and other areas where additional samples or collaborative analyses from fixed-base laboratory analyses were necessary before the clean/dirty designation could be made. The selection of samples for off-site analysis in this manner allowed for refinement of field-to-laboratory correlations and of the field-based action levels as the investigation progressed.
Additional step out sampling protocols were outlined in the decision logic to focus additional sampling in areas where tentative PCB identifications were made. The decision logic diagrams are available in the BTSC Case Study that can be accessed from this profile.
Due to the relatively low residential direct exposure criteria (DEC) for arsenic of 10 mg/kg all samples collected for arsenic were analyzed off-site using EPA SW-846 method 3050B/6010B. Results were provided within several days. A field portable x-ray fluorescence (FP-XRF) unit was used by the EPA Region 1 mobile laboratory to screen metals samples and confirm assumptions that additional metals were not present in quantities exceeding Connecticut residential DECs. A subset of the samples sent for offsite analysis of arsenic were also analyzed for the entire suite of metals using SW-846 method 3050B/6010B.
Analyses for TPH and total PAHs were performed in the field using a micro extraction prior to test kit analysis. Collaborative off-site laboratory methods for the test kit data included TPH by SW-846 Method 8015 (gas chromatograph/flame ionization detector/photoionization detector [GC/FID/PID]) and PAHs by SW-846 method 8270 (gas chromatograph/mass spectrometer [GC/MS]) performed in the selective ion monitoring (SIM) mode.
Samples collected for the analysis of PCBs were conducted on-site by EPA's Region 1 mobile laboratory with off-site collaborative analyses performed for any tentatively identified PCBs at the EPA Region 1 fixed-base laboratory.
TQRSs provided for the siteLAB® test kits and the Shimadzu GC/ECD in the Case Study prepared by BTSC for the site (see below for link).
BTSC provided support in developing correlations between UVF test kits results for TPH and total PAHs with offsite analyses for TPH by SW-846 method 8015 and PAHs by SW-846 method 8270 operated in the SIM mode. The field- and fixed-based laboratory methods together produced a high quality, high-density data set that managed sampling as well as analytical uncertainty and was suitable for decision making at the Site.
Data quality review also included review of chromatograms from off-site laboratory analyses. These reviews were performed to better assess the comparability of the field UVF data to the fixed-base laboratory GC methods that were used on a subset of the samples to establish a collaborative data set. The chromatogram review revealed that uncertainties in chromatogram interpretation at the fixed-base laboratory were the major source of comparability issues between the field and laboratory data.
Spreadsheets and commercial statistical software packages were used to manage and assess field data. These packages were also used to develop and refine field action levels for the TPH and PAH test kits.
DMA samples were collected on December 9, 2002 and analyzed under a training session conducted by siteLAB for M&E and EPA personnel on December 12, 2002.
Field work was conducted from February 3 through February 7, 2003.
|Cos Cob Site Case Study (9 MB)|
To update this profile, contact Cheryl T. Johnson at Johnson.Cheryl@epa.gov or (703) 603-9045.