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PUBLIC HEALTH ASSESSMENT

MESSER STREET MANUFACTURED GAS PLANT
LACONIA, BELKNAP COUNTY, NEW HAMPSHIRE


SUMMARY

The Messer Street Manufactured Gas Plant Site is located in Laconia, New Hampshire, just to the north of the Messer Street bridge over the Winnipesaukee River. Between approximately 1860 and 1952, the site was occupied by a facility that produced gas for lighting and heating from coal. Coal tar, a byproduct of this process, has been found beneath the site and in the sediments of the Winnipesaukee River. Since 1994, the New Hampshire Department of Health and Human Services (DHHS) has been providing advice to the Department of Environmental Services (DES) on questions of health risk at the site. During that time, a number of neighboring residents have expressed health concerns about the contamination at the site. To address these concerns, DHHS completed this public health assessment for the site under its cooperative agreement with the U.S. Agency for Toxic Substances and Disease Registry.

What kind of chemical contamination has been found on the site?

Coal tar contamination has been found beneath the site and in sediments of the Winnipesaukee River from the Messer Street bridge to a point 1,000 feet downstream. The coal tar contains primarily polycyclic aromatic hydrocarbons (PAHs), as well as some volatile organic compounds. PAHs are a class of over 100 different compounds that are found in and formed during incomplete combustion of coal, oil, wood, or other organic substances. Lesser amounts of these compounds have also been detected in water, sediment, and fish from areas of the Winnipesaukee River and Opechee Bay near the site. Surface soils on the site do not contain contamination at levels of health concern.

How might I be exposed to chemical contamination on the site?

There are three completed pathways by which people could be exposed to contamination at the site: (1) swimming and wading in the contaminated section of the Winnipesaukee River; (2) eating fish caught near the site; and (3) using the boat launch area on the site. Walking or playing on the banks of the river would not result in exposures to site contamination because these areas are not contaminated. Fishing using catch-and-release techniques would also not result in any exposure to site contaminants. Finally, simply living in the vicinity of the site would not result in exposures to site contamination unless someone engages in any of the three activities associated with completed exposure pathways.

What health effects might result from exposure to chemical contamination at the site?

  • People who swim or wade in the river would be at risk for short-term skin or eye irritation if they were to contact coal tar in the sediments. In 1995, DHHS issued an advisory against swimming in the contaminated stretch of river and arranged for permanent "No Swimming" signs to be installed. However, the neighboring residents report that some people still swim in the area.

  • Eating fish caught near the site is not expected to result in adverse health effects. Typically, fish do not accumulate PAHs in their tissues. Several site investigations have confirmed that the PAH concentrations are low in the tissues of fish collected near the site.

  • Using the boat launch area for recreation is also not expected to result in adverse health effects. The sediments of Opechee Bay near the boat launch area are much less contaminated than the sediments of the Winnipesaukee River downstream of the Messer Street bridge. Therefore, the likely exposures from using this area would be below levels of health concern.

Could exposures to chemical contamination at the site cause cancer?

The available evidence indicates that mixtures of PAHs and coal tars can cause cancer in humans. Therefore, chronic exposures to coal tars and PAHs while swimming or wading in the contaminated section of the river may increase an individual's risk of developing cancer, particularly skin cancer. Due to the possible carcinogenicity of the site contaminants and because of concerns expressed by local residents, DHHS reviewed and summarized cancer incidence data for Laconia between 1993 and 1997. No cancers were found to have significantly elevated rates among the people who live within one-quarter mile of the site.

What can I do to protect myself from being exposed to chemical contamination at the site?

There are three steps you can take to prevent exposures to chemicals on the site. First, do not swim or wade in the section of the Winnipesaukee River starting at the Messer Street bridge and extending 1,000 feet downstream to where the river narrows. Second, follow the recommendations of DHHS' state-wide fish consumption advisory. The general population is advised to limit their consumption of freshwater fish from New Hampshire waterbodies to four 8-ounce meals per month. Young children (6 years old or younger) and women of child-bearing age are recommended to eat only one 8-ounce meal per month. DHHS issued this advisory to protect the public from exposures to mercury in fish tissues, which is common throughout the state. Third, do not enter restricted areas of the site while remedial actions are underway.

Is the site being cleaned up?

Yes. Significant progress has been made by the parties who have assumed responsibility for the remediation of the site towards cleaning up the contamination on the site. A Remedial Action Plan for the site was approved by DES in March 1999. Under DES supervision, work began during the fall of 1999 and is scheduled for completion by the end of 2000. When the remedial actions are complete, DHHS believes that the public health hazards on the site will be eliminated.

Where can I get more information?

The text and appendices of the public health assessment for this site contain more information about the health issues discussed in this summary. To ask questions about this public health assessment or to obtain extra copies of this document, please contact Phil Trowbridge in the DHHS Bureau of Health Risk Assessment at (603) 271-4664 or (800) 852-3345 ext. 4664 (toll-free in N.H.). You can also send an email to the Bureau at healthrisk@dhhs.state.nh.us or visit its website at www.dhhs.state.nh.us/bhra. If you would like more information on the site cleanup efforts, please contact Bob Minicucci of the Department of Environmental Services at (603) 271-3503. Additional copies of this public health assessment will be available at the Laconia Public Library at 695 Main Street.


I. PURPOSE AND HEALTH ISSUES

At the request of the New Hampshire Department of Environmental Services (DES), the New Hampshire Department of Health and Human Services (DHHS) has been providing advice on health risk at the Messer Street Manufactured Gas Plant Site since 1994. During that time, a number of neighboring residents have expressed health concerns about the contamination at the site. To address these concerns, DHHS completed this public health assessment for the site under its cooperative agreement with the U.S. Agency for Toxic Substances and Disease Registry (ATSDR).

The objective of a public health assessment is to identify any public health actions that should be undertaken at the site. The public health assessment process is designed to complement the remediation of the site, but should not be confused with a risk assessment for remedial design purposes. This public health assessment includes: (1) the identification of pathways of exposure to site contaminants and an evaluation of their public health implications; (2) a summary of relevant and available health outcome data; and (3) responses to community concerns about the site.


II. BACKGROUND

(A) Site Description and History

The Messer Street Manufactured Gas Plant Site is located in Laconia, New Hampshire, just to the north of the Messer Street bridge over the Winnipesaukee River (Figure 1). It consists of two small parcels (3 acres in total) on a point of land that is bound by Opechee Bay to the west, the Winnipesaukee River to the south, the Boston & Maine Railroad to the east, and private property to the north (Figure 2). Currently, there are no buildings on either parcel. 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 [6].

Between approximately 1860 and 1952, the site was occupied by a manufactured gas plant (MGP). Using a process common during this period, the MGP heated coal or coal and oil feedstocks to produce gas for lighting and heating. Byproducts of this coal gasification process included: coal and oil ash, coke, coal tar, creosote, lubricating oils, solvents, ammonia, sulfur, and phenol. The main MGP production and waste storage facilities were located on the small parcel bound by Messer Street, the railroad, and the river. On the northern section of the property by Opechee Bay, there formerly was a small "tar pool" where coal tar waste was presumably stored. The plant ceased gas production operations in 1952 and was dismantled in 1981 [3].

In 1993, a local diver observed globules of black organic material in the sediments of the Winnipesaukee River near the Messer Street Site [5]. Following this discovery, the parties who have undertaken responsibility for the site cleanup, Northeast Utilities Service Company and EnergyNorth Natural Gas, Inc., have conducted several site investigations under state environmental rules and guidelines [1-7].

In 1999, a Remedial Action Plan for the site was produced by consultants for the parties who have assumed responsibility for the site cleanup [6]. DES approved the plan with input from DHHS [9] and work began in the fall of 1999. The first step of the remediation plan is to sink a sheetpile wall/collection trench into the soils along the edge of the river on the southern portion of the site. This wall will intercept and collect mobile coal tar near the southern edge of the property. Following the installation of the sheetpile wall, a vacuum will be used to remove distinct coal tar globules from the surface sediments near the site. These two steps, already ongoing and scheduled for completion during the winter of 1999-2000, will considerably reduce opportunities for exposures to coal tar in the sediments. In the fall of 2000, the remaining sediment contamination will be addressed by a combination of dredging in the most contaminated areas and capping in other areas. To prevent future exposures to contaminated groundwater and subsurface soils beneath the site, restrictions on the future use of the site will be written into the property deed and a groundwater monitoring program will be established [6]. In addition to these activities, a plan is being devised to remove up to 23,000 gallons of coal tar waste that was recently discovered in an old subsurface holding tank [7,10]. During the remedial operations, the site will be fully fenced to inhibit access by unauthorized persons [11]. Absorbent booms and silt curtains will be deployed in the river to minimize the mobilization of coal tar, soil, or sediments [6].

(B) Site Geology and Hydrology

Over much of the site area that was used in the MGP process, the native soils are covered by fill material made up of sand, gravel, and some debris. The fill layer is underlain first by a coarse-grained sand deposit and then by a coarser sand and gravel unit, both layers approximately 20 feet thick. Between these two layers, there is a relatively thin band of silt and fine-grained sand and clay. Bedrock, identified by the U.S. Geological Survey as heavily weathered, fractured, metamorphic rock of the Littleton Formation, was encountered in deep borings on the site between 54 and 80 feet below the ground surface [5].

In the vicinity of the site, the regional groundwater flow in the sand and gravel deposits is generally from the east to the west. Shallow groundwater on the site flows in a semi-radial pattern and discharges to both Opechee Bay and the Winnipesaukee River. During 1995-1996, the water table on the site was observed to be approximately 0.5-10 feet below the ground surface [5].

The source of the surface water in Opechee Bay and the Winnipesaukee River is Lake Winnipesaukee to the north. Surface water from Lake Winnipesaukee flows into Opechee Bay through the Lakeport Dam. At the southern end of Opechee Bay, the water enters the Winnipesaukee River and flows south for approximately one mile to Lake Winnisquam, passing through the Avery Dam in the middle of this stretch. Downstream of Lake Winnisquam, the Winnipesaukee River merges with the Pemigewasset River in Franklin, New Hampshire, to form the Merrimack River [5]. The Lakeport and Avery dams are operated by DES or DES contractors to maintain a constant water level in Opechee Bay and the Winnipesaukee River. However, for two weeks each October, the water levels in Opechee Bay and the river are lowered by approximately 3 feet to facilitate dam maintenance [5,6].

(C) DHHS Involvement

Throughout the environmental investigations at the site, DHHS has provided advice to DES on questions of human health risk, one of its primary roles as the state health department (RSA 125-H). DHHS staff have reviewed and commented on the three major site investigation reports, issued an advisory against swimming in the river near the site, performed several site visits, and conducted outreach activities to the community near the site to learn about any community health concerns.

  • In April 1995, DHHS reviewed and provided comments to DES [12] on the environmental data from the first site investigation [1-3].
  • In June 1995, DHHS issued an advisory against swimming in the Winnipesaukee River near the Messer Street MGP Site because of chemical contamination. Permanent "No Swimming" signs were posted in the affected area.
  • In June 1997, DHHS reviewed and provided comments to DES [13] on the results of the second major site investigation [5].
  • In August 1998, DHHS reviewed and provided comments to DES [14] on the proposed workplan for supplemental data collection in support of the remedial action plan [8].
  • In February 1999, DHHS reviewed and provided comments to DES [15] on the human health risk assessment associated with the third major site investigation [6].
  • In March 1999, DHHS held a public availability session in Laconia to provide residents with an opportunity to meet with health officials to discuss any health concerns in confidence. Several residents attended this session.
  • In July 1999, DHHS distributed a brief survey to residents in the immediate neighborhood around the Messer Street MGP Site to provide them with the opportunity to ask questions or communicate health concerns about the site. Forty-two (42) of the 113 surveys (37%) were completed and returned to DHHS. See Appendix D for a summary of responses to the survey.

(D) Demographics

Laconia is the thirteenth largest city in New Hampshire. According to U.S. Census data from 1990, the population of Laconia in 1990 was 15,743. Only 53% of the population reported living in the same house or apartment for more than five years. Children less than 5 years old and adults over 65 years old accounted for 23% of the population. The total number of people living within one-mile of the Messer Street MGP Site was 9,317 (Figure 1). Six hundred and eighty-one (681) of these residents lived within a quarter-mile of the site. The size of the populations living near the site were estimated using a geographic information system (ArcView v.3.1) and an area proportion spatial analysis technique.

(E) Quality Assurance/Quality Control (QA/QC)

In preparing this document, DHHS relied on the information provided in the referenced documents and contacts. Only data collected using appropriate sampling and laboratory methods were considered in this analysis. Data with demonstrated QA/QC problems were excluded from tables and calculations but may be discussed in the body of the text if they provide unique and relevant information. Whenever possible, data were taken directly from laboratory data sheets, not secondary source documents.


III. ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

An integral element of every public health assessment is a review of environmental contamination on the site. In the following section, the results from environmental assessments at the Messer Street MGP Site [1-7] are summarized for each different media (e.g., sediments, surface water, soils, etc.).

Concentrations of chemicals in each of the media have been compared to media-specific health-based comparison values to decide whether any of the compounds need further evaluation. Health-based comparison values are derived using information on the toxicity of the chemical and assuming frequent opportunities for exposure to the contaminated media (e.g., a residential setting). For non-cancer toxicity, DHHS typically uses ATSDR's minimum risk levels or the U.S Environmental Protection Agency's (EPA's) reference doses, which are estimates of daily human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects over a lifetime. Cancer risk comparison values are based on EPA's chemical-specific cancer slope factors and an estimated excess lifetime cancer risk of one in one million. Therefore, if the concentration of a chemical is less than its comparison value, it is unlikely that exposure would result in adverse health effects, and further evaluation of exposures to that chemical is not warranted. If the concentration of a chemical exceeds a comparison value, adverse health effects from exposure are not necessarily expected, but potential exposures to that chemical at the site should be evaluated. As a result, the following summary of environmental data highlights the chemicals that have been found on the site at concentrations above health-based comparison values. In the discussion section later in this document, exposures to these contaminants are evaluated in detail.

(A) Site Conceptual Model

A site conceptual model is a general description of the processes and the conditions that have been observed at a particular site. It is meant to provide the reader with an overview of the site so that the detailed information provided in the following sections can be taken in context.

Former MGP activities on the site produced coal tar waste, some of which was stored on the site. Soils beneath storage areas and other portions of the site have subsequently been found to be heavily contaminated with coal tar [5,7]. Coal tar is a complex mixture of organic compounds each of which has different properties and manners of behaving once released to the environment. At the Messer Street MGP Site, the more soluble compounds have dissolved into groundwater, which is discharging to the Winnipesaukee River and Opechee Bay. The remaining viscous coal tar is slowly flowing southwards through coarse sand lenses above the water table and seeping into the Winnipesaukee River downstream of the Messer Street bridge and on both sides of the railroad bridge. After entering the river, the mobile coal tar mixes with the river sediments and can be carried a short distance downstream by normal river transport processes [6]. The coal tar has been tested and found to contain primarily polycyclic aromatic hydrocarbons (PAHs) as well as some volatile organic compounds (VOCs) at concentrations of 130,000 and 18,900 milligrams per kilogram of sediment (mg/kg), respectively [5]. Therefore, environmental tests of sediments, surface water, fish tissue, and other media have focused on these contaminants.

PAHs are a class of over 100 different compounds that are found in and formed during incomplete combustion of coal, oil, wood, or other organic substances. In the environment, PAHs are found as complex mixtures of compounds, rarely as single compounds [17]. In the following sections of the document, the concentrations of PAHs in different media are typically reported as the sum of the concentrations of eighteen common PAH compounds, referred to as "total PAHs". Occasionally, the results for individual PAH compounds have been reported.

(B) Sediment

Following the discovery of coal tar material in the river in 1993, three separate investigations have collected 87 surface sediment samples (i.e., those from the top 4 feet or less of sediment) from areas near the site in Opechee Bay and the Winnipesaukee River [1,5,6]. All the sediment samples have been tested for PAHs, and some for metals, cyanide, VOCs, and polychlorinated biphenyls (PCBs).

PAHs were detected in 51 of the 81 samples from the Winnipesaukee River in the stretch of river starting at the Messer Street bridge and extending 1,000 feet downstream to the point where the river narrows. The range of total PAHs concentrations that was detected was considerable, with one sample containing 20,210 mg/kg but median concentrations for the different depth intervals being less than 25 mg/kg (Table 1, Figure 3). The highest concentrations of total PAHs (i.e., greater than 1,000 mg/kg) have been found along the north bank of the river between the Messer and railroad bridges as well as on the sandbar immediately downstream of the railroad bridge. Localized areas of contamination have been found as far as 1,000 feet downstream of the Messer Street bridge at the point where the river narrows (Figure 2). Farther downstream, sediment samples have not been found to be contaminated with PAHs or coal tar. Furthermore, a field investigation by DES and DHHS staff in 1997 probed the sediments all the way downstream to the Avery Dam and a section at the inlet of Lake Winnisquam to test for contamination [16]. Gross contamination with coal tar was not observed in these downstream areas.

Sediment contamination from the site in Opechee Bay is limited to areas adjacent to the site, near the boat ramp. Concentrations of total PAHs in these sediments are considerably lower than those found in the river, but still average 65 mg/kg and reach as high as 338 mg/kg in some areas (Table 1). For comparison, the concentrations of total PAHs in sediments from a part of Opechee Bay unaffected by the site (Opechee Cove on the west side of the bay) were approximately 1 mg/kg on average (Table 1).

Some of the VOCs that are present in the groundwater and coal tar have also been detected in the sediments but at concentrations below health-based comparison values (Table 2). No other target compounds were found in the sediments at levels above health-based comparison values.

(C) Surface Water

Six surface water samples have been collected and analyzed for PAHs [6]. Three PAHs (i.e., fluorene, phenanthrene, and pyrene) were detected at 0.019-0.020 micrograms per liter of water (ug/L) in one sample from near the boat ramp on Opechee Bay in 1998. No PAHs were detected in the other five surface water samples with detection limits of 0.011-10 ug/L. The surface water sampling results for PAHs are summarized in Table 3.

Four of these surface water samples were also analyzed for VOCs, but no VOCs were found at a detection limit of 5 ug/L. These results are supported by an estimate of loading to the Winnipesaukee River for the three VOCs (benzene, toluene, and styrene) whose concentrations exceed Ambient Groundwater Quality Standards in the groundwater beneath the site. Using the groundwater concentrations of these three compounds, the groundwater discharge to the river, and the average river flow from 1996, this model predicted that concentrations of these chemicals in the river would not be greater than approximately 0.1 ug/L [6] which is less than health-based comparison values for these compounds.

(D) Fish and Shellfish Tissue

Samples of fish fillets have been collected at the site during two investigations. In June 1996, 14 fish tissue samples were collected from three locations near the site: upstream of the site in Opechee Bay, in the Winnipesaukee River adjacent to the site, and downstream of the site [5]. In September 1998, 10 fish were collected from the Winnipesaukee River downstream of the railroad bridge and 3 fish were collected from a reference area in Opechee Bay [6]. Samples of shellfish were also collected from an area near the site (3 composite samples) and the reference area (2 composite samples).

The concentrations of total PAHs in fish fillet and shellfish samples from these two investigations have been summarized in Table 4. On average, the total PAH concentrations in fish and shellfish collected near the site (0.220 mg/kg) were higher than in fish and shellfish from the reference areas (0.046 mg/kg). These averages are likely to overestimate the actual PAH content of fish in the area because PAH compounds that were not detected were assumed to have a concentration of one-half the laboratory method detection limit.

During the June 1996 tests [5], PCBs, although not thought to be associated with the site, were also detected in fish at concentrations between 0.02 to 1.1 mg/kg and averaging 0.15 mg/kg. The concentrations of PCBs in popular finfish with moderate amounts of fatty tissues (0.03-6%) were all less than 0.1 mg/kg. PCB concentrations higher than this were only found in the three samples of American eel, which had higher fat contents (17-23%). This is consistent with our understanding that PCBs tend to accumulate in the fatty tissues of fish. The PCBs detected in these fish samples are indicative of regional conditions, not the coal tar waste at the site, and are not at levels of health concern in popular sport fish.

In addition to the fish fillet samples, whole body samples of five fish collected near the site were analyzed for site contaminants in 1994 and 1995 [2,4]. The results from these whole fish samples are not included on Table 4 because they are not representative of the fish tissue that people normally eat. For example, the samples include tissues from bone and internal organs.

(E) Surface Soil

In October 1994, 15 surface soil samples were collected on the Messer Street MGP Site [3]. These samples were analyzed for metals, cyanide, VOCs, and PAHs. The concentrations of the detected compounds are summarized in Table 5. No compounds were found above health-based comparison values, or in the case of arsenic, above expected background concentrations for New Hampshire. DHHS originally reviewed environmental data for surface soils in 1995 and concluded that the contaminant levels did not pose a public health risk [12].

(F) Subsurface Soil

Subsurface soils are contaminated with coal tar between 5 and 30 feet below the surface. In some areas, coal tar is present as a mobile non-aqueous phase liquid. Both the water table and the thin silt layer in the middle of the sand and gravel deposits appear to impede downward migration of coal tar. However, lateral migration of coal tar through the coarse upper sand layer to the Winnipesaukee River is likely. Discharges of coal tar to the river likely occur throughout the year but are accelerated by the annual draw down of water levels in October for dam maintenance. Subsurface soil is currently not accessible by people using the site for recreation [6].

(G) Groundwater

Groundwater beneath the site contains contaminants at concentrations above Ambient Groundwater Quality Standards, which are at least as strict as drinking water standards. Compounds exceeding these standards include several VOCs (benzene, toluene, ethylbenzene, styrene) and two PAHs (naphthalene and 2-methylnaphthalene). Two distinct plumes of contaminated groundwater are present on the site. One is in the northern section of the site and appears to discharge northwards to Opechee Bay. The second plume underlies the south half of the site and discharges southwards to the Winnipesaukee River [6]. No one is currently using the groundwater beneath the site for drinking, cooking, or other consumptive purposes because the surrounding neighborhoods receive drinking water from the municipal supply.

(H) Physical Hazards

There are no physical hazards on the site. During remedial operations, there will be heavy equipment operating on the site but site access will be restricted by a fence [11].



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