MESSER STREET MANUFACTURED GAS PLANT
LACONIA, BELKNAP COUNTY, NEW HAMPSHIRE
In January 2000, the New Hampshire Department of Health and Human Services (DHHS) completed a Public Health Assessment for the Messer Street Manufactured Gas Plant site in Laconia, and released it for public comment . The Public Health Action Plan at the end of this document called for DHHS to continue to advise the New Hampshire Department of Environmental Services (DES) on questions of health risk during the full remediation of the site. Shortly after this document was completed, DES requested that DHHS review and comment on the proposed plan for additional remediation of the site . This Health Consultation summarizes DHHS' comments on the plan and compares new environmental testing results with the data reviewed for the Public Health Assessment. DHHS completed the Public Health Assessment and this Health Consultation under its cooperative agreement with the U.S. Agency for Toxic Substances and Disease Registry (ATSDR).
Site Description and History
The Messer Street Manufactured Gas Plant site is located in Laconia, New Hampshire, north of the Messer Street Bridge over the Winnipesaukee River. Currently, there are no buildings on the site. There is a boat launch and parking lot along the Opechee Bay shore and an electrical substation near the Messer Street Bridge. The remainder of the site consists of undeveloped grassy areas. The area surrounding the site is a combination of commercial and residential properties .
From the late 1800's to 1952, the site was occupied by a manufactured gas plant (MGP). Byproducts of this coal gasification process included: coal and oil ash, coke, coal tar, creosote, lubricating oils, solvents, ammonia, sulfur, and phenol. The plant ceased gas production operations in 1952 and was dismantled in 1981 [2,3].
Between 1993 and 1999, the parties who have undertaken responsibility for the site, Northeast Utilities Service Company and EnergyNorth Natural Gas, Inc., have conducted several site investigations under state environmental rules and guidelines. In 1999, these parties produced a Remedial Action Plan for the site and began remedial work .
Most of the first phase of the remediation was completed between September 1999 and January 2000. It began with the installation of a sheetpile wall/collection trench into the soils along the edge of the river to intercept and collect mobile coal tar. Following this, a vacuum was used to remove 300 gallons of coal tar globules from the surface sediments near the site. Finally, a large subsurface holding tank containing coal tar waste, presumably a major source of contamination, was discovered and the coal tar removed. Work is also underway to restrict the use of the site to prevent future exposures to contamination in subsurface soils and groundwater .
Summary of Proposed Work
While the first phase of remediation stopped discharges of coal tar to the river, the second phase aims to clean up the tarry sediments that remain in the Winnipesaukee River and Opechee Bay .
Remediation is planned for all contaminated, shallow sediments in sections of the river accessible to swimmers or waders (i.e., where the water is less than five feet deep). This will consist of either dredging the contaminated sediments, covering them with a layer of clean granular material, or a combination of both. Some contamination in deeper sections of the river will also be remediated to address risks to ecological receptors or to prevent future mobilization of contamination by hydraulic scour. Overall, between 6,200 and 13,000 cubic yards of sediment will be removed and 2.5 acres will be capped. The capping material is not expected to erode, even under 100 year flood conditions.
A barge-mounted clamshell bucket will be used to dredge the contaminated sediments. Dredged sediments will be deposited directly into metal containers where they will be dewatered. Water from the dredged material will be treated on-site and then discharged to the municipal sewer. To minimize downstream releases of contaminants during the operations, silt curtains and other barriers will be installed in the waters around work zones. Containers holding the sediments will be covered with tarps to minimize air emissions and odors, and regular air monitoring will be performed. On-site equipment traffic will be minimized to the extent possible and the terrestrial work zone will be kept wet to prevent dust from being stirred up.
In order to prevent exposures to contaminants during the operations, the remedial work will occur in fall and winter, not the busy summer season. Boat traffic in the river will be restricted, and "No Swimming" signs around the site will be maintained. However, the plan indicates that the boat launch on Opechee Bay could be kept open if requested by the town. Heavy truck traffic will be routed away from residential areas to the extent possible. A meeting will be held before the work begins to explain the short-term risks and the long-term benefits of the work to the public.
Summary of New Environmental Data
Four new sediment samples have been collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) and other contaminants . The new data, along with comparable summary data from the Public Health Assessment, are shown in Table 1. The new results are consistent with the data on which the conclusions of the Public Health Assessment are based. In fact, the newer data show contaminant concentrations lower than those found previously. This is likely because the new samples were composites of sediments from many locations and depths. The data reviewed for the Public Health Assessment were predominantly from grab samples of surface sediments.
In the Public Health Assessment for this site, DHHS found that people who swim or wade in the contaminated sections of the river would be at risk for adverse health effects . DHHS supports the proposed remedy because it should remove this public health hazard. In particular, the proposal calls for remediation of all contaminated, shallow sediments in areas where swimmers or waders might contact them (i.e., where the water is less than 5 feet deep). The remedy will be built to withstand a 100 year flood so future exposures to any coal tar buried in the sediments are not likely.
DHHS also supports the plan to remediate areas of the river at risk for ecological receptors and the sediments in Opechee Bay. These actions will further reduce exposures to people who fish in the area and who use the boat launch, respectively.
The proposal calls for air monitoring around the site to address concerns about air emissions and odors. DHHS supports this plan but feels that some additional surface water sampling would be beneficial. In particular, surface water samples should be collected downstream of the dredging activity (and any temporary barriers) during periods of heavy operation to confirm that large amounts of contamination are not being mobilized by the work. In addition, sediment quality in the contaminated area should be monitored after the remedial action to verify that cleanup goals have been attained.
Many steps are planned to prevent exposure to contaminants and worksite hazards during the cleanup. Given this effort, it is inconsistent to allow use of the boat launch while the cleanup operations in Opechee Bay are ongoing. Therefore, DHHS recommends that boat launch be closed during this stage of the work.
When DHHS conducted a survey of the neighborhood near the site, we learned that most of the neighboring residents prefer to receive information in the mail rather than at public meetings. As a result, DHHS developed a mailing list of interested parties. We would recommend that, in addition to the planned public meeting, materials on the cleanup and the short-term hazards be mailed to the people on DHHS' mailing list. People who live on properties abutting the river between the site and Avery Dam should be identified and added to the list. Many of these residents who abut the river have docks extending out into the water and would be at risk for exposure if contaminants were mobilized during the cleanup.
Children are at a greater risk than adults from certain kinds of exposure to hazardous substances emitted from waste sites. They are more likely to be exposed for several reasons (e.g., they play outdoors more often than adults thus increasing the likelihood that they will come into contact with chemicals in the environment). Due to their smaller stature, children may breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if certain toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.
The Messer Street MGP site may pose a significant health hazard to children and young adults since people in these age groups are more likely to swim or wade in the river and, therefore, would have an increased opportunity for exposure to coal tar in the sediments. Therefore, DHHS strongly supports the plan for remediation at the site. We also support additional safeguards during the cleanup operations to verify the efficacy of methods, prevent off-site releases, and prevent short-term exposures.