USACE, New England District

Overview:

• Geological, Geotechnical, Geothermal, and Geophysical Investigations
• Groundwater Investigation and Modeling
• Soil and Sediment Investigation
• Environmental Chemistry, Data Collection, Management and Interpretation
• Human Health Risk Assessment
• Baseline Ecological Risk Assessment (BERA)
• Sediment Toxicity Testing

Description:

Hingham Former Burning Grounds (FBG) is a former open burning/open detonation (OB/OD) munitions disposal area at the former Hingham Naval Ammunition Depot Annex. On 1 January 2019, Bluestone acquired Avatar Environmental, LLC. Bluestone (Avatar) is currently completing the RI/FS for CENAE under its FUDS program. Technical tasks have been conducted as multiphase investigations based on an initial data gaps analysis.

All work performed by Bluestone at this FUDS has been conducted in accordance with CERCLA. The RI along with the risk assessments are CERCLA-compliant. Prior to initiation of field work, the Team prepared all required Quality Assurance Project Plans in accordance with UFP.

The team completed geophysical and intrusive investigations to identify geo-anomalies to determine the presence of ordnance and explosives (OE) and MEC in the vicinity of a 1.25-acre portion of the former burning ground. These data are being used to evaluate whether OE or MEC are creating a hazard to human health and the environment. Over 1,300 anomalies were identified and investigated using manual excavation. Although many metal items were found, no MEC were found, confirming previous findings.

Bluestone installed seven bedrock well and six overburden wells under an accelerated schedule to supplement the existing network of 19 monitoring wells. The accelerated schedule implemented soon after TO award allowed for new wells to be installed in time to be sampled as part of the already-planned Spring groundwater sampling event, eliminating a separate field mobilization effort and saving money. In addition to slug tests performed on existing and new wells to inform related hydrogeological fate and transport groundwater models, we have conducted three rounds of groundwater sampling.

To augment soil monitoring results collected previously, we collected an additional ~125 surface and subsurface soil samples throughout the 7-acre investigation area. Soil sampling included the use of Incremental Sampling Methodology (ISM) at four areas of suspected explosives contamination. In addition, soil sampling was also conducted at several slag piles using ISM.

Located adjacent a large wetland complex containing regulatory-sensitive vernal pools and 350 ft upslope of the Aaron River, the FBG has been shown to be a source of runoff and groundwater discharge of contaminants to the wetlands and the river. Prior to the investigations conducted by Bluestone, no data were available to determine the extent to which the OB/OD operations may have contributed to contamination of the surrounding wetlands. As part of the ecological investigation, we surveyed the adjacent wetlands, identified potential vernal pools, and mapped groundwater seeps that serve as a source of water to wildlife. Approximately 25 surface water and sediment samples were collected from these habitats. Based on the results and the presence of amphibians in the pools, 10-day sediment bioassays will be conducted with amphibians (wood frog or spotted salamander) of the vernal pools. In addition, 28-day amphipod tests will be performed to assess the potential risk to fairy shrimp. Amphipod assays are also planned for the sediments of the Aaron River where elevated levels of lead and possibly other chemicals may represent an ecological risk.

More recently, there is some indication that the wetlands may have been contaminated from dispersion and deposition of airborne particulate contamination originating from the burning of munitions. To address this possibility, an extensive background monitoring program of wetland hydric soils and sediments from vernal pools will be conducted. These data will be compared with site data and evaluated as part of the Uncertainty Analysis of the Human Health and Ecological Risk Assessments. Moreover, should remediation be required, these background data will serve to inform remedial action requirements.

This project to date has included multiple rounds of sampling. Media have included overburden and bedrock groundwater, surface and subsurface soils, hydric soils, and surface water and sediments. In addition to discrete sampling, an ISM approach was used for the soil investigations of suspected OB/OD areas and four slag piles. Water was also collected from Mount Blue Springs, a free and popular public source of spring water that has been in use since the mid-19th century. All analytical data underwent Tier 2 and Tier 3 (explosives) chemistry validation to meet data requirements for use in the risk assessments. All environmental chemistry data were incorporated into a project database that allowed for a streamlined approach for management and interpretation.

As with the wetlands investigation, an extensive background monitoring program of surface soils will be conducted. These data will be compared with site soil data and evaluated as part of the Uncertainty Analysis of the Human Health and Ecological Risk Assessments. Moreover, should remediation be required, these background soil data will serve to inform remedial action requirements.

Bluestone is currently preparing human health and ecological risk assessments for the FBG to inform risk management decisions in the FS in accordance with requirements under CERCLA. The HHRA evaluates the risk associated with potential multi-media exposure to contaminants under the current recreational use as well as potential future residential use. The SLERA evaluates the potential risk to fish and wildlife from exposure to contamination in terrestrial, wetland, and aquatic habitats. In addition, the SLERA incorporates the use of the site-specific sediment bioassays for amphibians and invertebrates.

The Human Health and Ecological Risk Assessments will incorporate innovative spatial-weighting of the contaminant distributions to better estimate potential exposure instead of deferring to the more typical conservative approach used in most risk assessments.

The RI/FS is being conducted under regulatory requirements of CERCLA and in close cooperation with Massachusetts Department of Environmental Protection (MassDEP) and Massachusetts Department of Conservation and Recreation (MassDCR). The project team includes a MA Licensed Site Professional, with extensive experience of MassDEP and MCP requirements.