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Review of 2002-2003 Air Monitoring Data



This health consultation has been prepared while data is being gathered for the Public Health Assessment for the Merrimack Station Power Plant in Bow, New Hampshire. The following document was prepared by the New Hampshire Department of Health and Human Services, Office of Community and Public Health, Bureau of Environmental and Occupational Health (BEOH), through a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). This health consultation reviews air monitoring data that were collected around the Suncook Village area during 2002 and 2003, near the Merrimack Station power-generating facility, for the purpose of identifying current public health implications associated with exposure to sulfur dioxide and particulate matter.

BEOH has been involved with the Merrimack Station since 2001, in response to community health concerns. This health consultation, as well as the Public Health Assessment, is being prepared as a result of a petition presented to ATSDR. The Public Health Assessment is pending completion due to the current collection of air quality monitoring data. This document presents current air quality conditions, as well as presents a plan for future activities.

This health consultation (and future Public Health Assessment), address the environmental medium of air quality only. This was the primary concern presented in the petition to ATSDR.

When reading this document, it is important to note that BEOH's role at the Merrimack Station site as a public health agency is considerably different from the roles of other agencies, particularly those charged with addressing environmental issues. In this document, BEOH evaluates the public health implications of the levels of air quality in the Merrimack Station study area. These evaluations are not meant to address the region's compliance with state and federal environmental standards, such as the Environmental Protection Agency's (EPA) National Ambient Air Quality Standards (NAAQS), even though this health consultation uses the NAAQS as a means for evaluating air monitoring data collected near the Merrimack Station site. State and federal environmental agencies are responsible for evaluating a region's attainment status with the NAAQS and other environmental standards. Please see Appendix C for a glossary of environmental terms.


2.1 Site Description and History

The Merrimack Station Power Plant is located along the eastern edge of Bow, New Hampshire. It is on the west bank of the Merrimack River, across from Suncook Village, a residential area that straddles the towns of Pembroke and Allenstown (Figure 1).

Merrimack Station is the largest coal-fired electrical generating station owned by Public Services of New Hampshire (PSNH). It generates 478 megawatts (MW) of electrical output, supplying power to 189,000 residential, commercial and industrial customers. Its primary source of generation is through two coal-fired utility boilers. The boiler stacks are 225 and 317 feet high. During periods of peak power demand, Merrimack Station also uses two jet-fuel combustion turbines.

Under the Clean Air Act, power plants are required to measure and report stack emissions of criteria air pollutants, such as sulfur dioxide (SO2), nitrogen oxides and carbon monoxide, as well as opacity (a means of determining the amount of particulate matter). In addition, ambient air monitoring is often required to determine the potential impacts to the surrounding areas that may require measures for emissions reductions (e.g., observation of elevated SO2 concentration that may indicate a need to switch to lower sulfur fuel). In the early 1980s, New Hampshire Department of Environmental Services (DES) began monitoring SO2 in the ambient air surrounding the power plant to ensure that National Air Ambient Air Quality Standards (NAAQS) were not being exceeded. Ambient air monitoring has been conducted at the Brickett Hill Road monitoring station since that time. In 2002, DES set up another SO2 monitoring station on Exchange Street, in the town of Pembroke. These ambient air monitoring data reflect emissions from both Merrimack Station and a variety of other sources (e.g., cars, businesses, home heating) in the area.

Over the past several years, there have been air quality concerns raised by residents of Pembroke and the adjacent town of Allenstown. Some area residents have complained of health problems, such as respiratory illness. In 2001, a petition to examine environmental data and health effects of the Merrimack Station power facility was presented to ATSDR. As a result, BEOH began collecting environmental, epidemiological and community health concerns in order to complete a Public Health Assessment of Merrimack Station.

2.2 Site Visit

On July 10 2003, BEOH staff conducted a site visit at the Merrimack Station Power Generating Facility. The site visit included a tour of the plant and associated facilities, a drive through the surrounding area, and a meeting with the Operational and Environmental Managers. BEOH representatives included Dennis Pinski, Chunfu Liu, Vickie Shallow, and Todd Hudson. Additionally, a representative from DES Air Resources accompanied BEOH on the site visit. Approximately 3 hours were spent on and around the site.

All facilities associated with the operation of Merrimack Station are contained within a fence that has guarded gates. Public access to the site is restricted. The plant consists of two separate steam-generating boilers, which operate independently. Each unit burns ground coal in a cyclone boiler that heats water to generate steam. The steam is used to spin a turbine, creating electricity. The two coal-fired boilers operate based on electrical demand within the New England region; usually, each boiler is operating near its capacity. The jet-fired turbines are used during periods of extreme electrical demand (e.g., hot days) on the New England power grid, i.e., demand is based on electrical use throughout the region (a "grid"). These turbines operate only when the coal-fired turbines are unable to meet the operational demands of the plant.

Coal is unloaded from railcars, inside a large enclosure. During this process, the coal is sprayed with water to prevent fugitive dust releases. The coal is then loaded on to hoppers, where it is transported inside the facility's boilers. On average there is enough coal sitting outside the facility to operate the plant for 1-2 days.

Stack emissions are monitored by real-time devices that measure emissions of criteria air pollutants and opacity. According to PSNH, these monitoring devices operate full time and are continually monitored by power station personnel.

2.3 Demographics and Land Use

The population center of the towns of Pembroke and Allenstown is Suncook Village. Approximately half of Pembroke's residents and one-quarter of Allenstown's residents live in this area. The center of Suncook Village is slightly less than 2 miles from the Merrimack Station power facility.

The population of Suncook Village was estimated from census blocks since it has no defined boundaries and is actually part of these two larger towns. Data from the 2000 census indicate that the area has an estimated population of 5,032. Approximately 1,677 residents live within the Allenstown boundary and 3,385 residents live in Pembroke.

There are approximately 2,126 people living within a 1-mile radius of Merrimack Station (Figure 1). This includes people outside of Suncook Village, such as people living in the town of Bow and the greater areas of the towns of Pembroke and Allenstown. It is estimated that the majority of this population lives in Suncook Village since all areas within the 1-mile radius are of relatively low population density, and much of Suncook Village has a population density greater than 2,000 people per square kilometer.

Of particular interest are the populations of children and senior citizens. These are groups of people that can be considered "sensitive" to air pollution, i.e., they may be affected by lower levels of pollution or they may have more serious reactions to pollutants. Children less than 5 years old and adults over 65 years old accounted for approximately 16.7% of the population of Suncook Village (Table 1). Since the area is split between two towns and demographics data were only available at the town level, BEOH estimated the age distribution for Suncook Village based on demographic data from the entire populations of Pembroke and Allenstown. The percentage of children less than 5 years old is slightly more than the statewide percentage (6.1%); the percentage of adults over 65 years old is slightly less than the statewide average (12%) (Table 1).

Suncook Village is mostly residential, with a small commercial district. There is a small amount of industry in the surrounding towns of Pembroke, Allenstown and Bow (Bow is across the river from Suncook Village, where Merrimack Station is located) including several facilities that generate some of the same pollutants generated by Merrimack Station. According to DES, there are 19 industrial operations within 5 miles of Merrimack Station that hold air permits for emissions of Criteria Air Pollutants or Air Toxics similar to the pollutants emitted by Merrimack Station (DES, 2003). Many of these businesses release small amounts of contaminants while Merrimack Station is a much larger source of pollutants such as sulfur dioxide, particulate matter and certain air toxics. Near Merrimack Station, there are several sand and gravel operations, and at least two cement processing/loading facilities.

Many schools are located in Suncook Village. Pembroke Academy and Three Rivers School are approximately one mile from the power station. Pembroke Village School, Armand Dupont School and Allenstown Elementary School are approximately two miles from the power station. Several parks and churches are also located in Suncook Village.

There are four main roads in or near Suncook Village. Route 3 is a thoroughfare road that passes through the village, and it is a major route for traffic going between Concord and Manchester. Routes 3A and 28 are also nearby. Interstate 93, the main artery for traffic going from Boston to northern New Hampshire, is less than 2 miles from Suncook Village.

2.4 Local Meteorology

This section reviews meteorological data to characterize how Merrimack Station's emissions are carried away from the facility's smokestacks. This summary focuses on meteorological data from three sources. These sources establish regional wind patterns for this area of the Merrimack Valley as well as observed wind patterns for the area around the power station.

  • Concord Airport Automated Surface Monitoring System. This station is run by the National Weather Service and is part of the nation's primary surface weather observing network. This station monitors wind speed and direction on an hourly basis. Both ground and upper air measurements are taken and used to create a summary of regional wind patterns.
  • Figures 2 and 3 present wind roses for Concord Municipal Airport, north of Merrimack Station and Suncook Village. The meteorological station is in an area of similar topography and no significant terrain features are located between Concord Municipal Airport and Merrimack Station. These observations were taken approximately 5 miles from Merrimack Station and Suncook Village and are representative of wind patterns for the region (DES, Personal Communication, 2003). The wind roses represent measurements taken from 1993 through present day. These figures present the statistical distribution of wind speed and wind direction for that period. The wind rose indicates that prevailing winds most frequently blow roughly from northwest to southeast. In fact, winds originating from between the directions of west-northwest (WNW) and north-northwest (NNW)--directions that blow from the power station to Suncook Village) accounted for 21% to 36% of the hourly observations (the percentage varied from season to season). During the months of December, January and February, winds blowing from between WNW and NNW were most frequent (Figure 2), while they were least frequent during the months of June, July and August (Figure 3). On average, winds blew from a northwest to southeast direction approximately 28% of the time. Hourly observations that recorded calm, or no wind, were recorded on an average of approximately 22% of the time.

  • Merrimack Station's on-site meteorological station. From January 1994 to November 1995, wind direction and wind speed were measured on-site and recorded on an hourly basis. These data, although only for a short period, are useful since they demonstrate regional wind patterns and corroborate the wind patterns measured at Concord Airport. Figure 4 presents a wind rose for hourly observations taken at Merrimack Station for 1994 (the only full year of data). The prevailing wind directions are similar to that seen in the wind roses from Concord Airport (Figures 2 and 3), blowing roughly from northwest to southeast. Winds originating from the directions between WNW and NNW accounted for approximately 44% of the hourly observations recorded at this meteorological station.

  • Exchange Street monitoring station. In addition to measurements of sulfur dioxide and particulate matter, the air quality monitoring station on Exchange Street also measured wind direction and speed. Table 2 summarizes the wind direction measurements from October 2002 through May 2003. These wind direction frequency charts are used to demonstrate localized wind movement at the surface.

As the wind direction frequency data in Tables 2 indicates, ground level wind direction patterns are similar to the wind rose charts for Concord Airport and Merrimack Station meteorological in Figures 2, 3 and 4. Prevailing winds originated from northwesterly (i.e., north-north-west and west-north-west) directions, accounting for approximately 34% of all measurements taken at the Exchange Street station. In the 6 months that these observations were taken, this station recorded valid measurements of wind direction for 99.2% of the hours, suggesting that the station rarely experienced operational difficulties.

Not surprisingly, wind direction plays an important role in air quality issues. According to the wind direction measurements at Concord Airport, the Merrimack Station site and Suncook Village, the prevailing wind direction is from the northwest to the southeast. Somewhat consistent with this prevailing wind direction is the fact that community members, through the DES Air Quality complaint log and community meetings with BEOH, have often reported seeing a "plume" extend from near the Merrimack Station to Suncook Village; some have reported seeing it as far as Bear Brook State Park in Allenstown. These comprehensive data suggest that there is potential for emissions from the Merrimack Station to blow from the direction of the site to Suncook Village.


3.1 Assessment Methodology

It should be noted that attributing air exposures to individual sources is often an extremely difficult task, especially in areas with many different sources, like the Suncook Village area. A number of local residents believe that their health problems are related to exposure to air pollutants emanating from the Merrimack Station electrical generating facility. Although it has been established that Merrimack Station has historically been a source of various air emissions, many other sources of emissions are found in this area of the Merrimack Valley. These sources include, but are not limited to, industrial plants, waste incinerators, residential fireplaces, heating oil use, automobiles and gravel/granite/sand operations. Due to the uncertainty in determining the extent to which each individual source contributes to inhalation exposures, the health consultation does not provide quantitative estimates of each source's impact on levels of air pollution. Rather, this health consultation attempts to determine if persons have been exposed to contaminants at levels that might be associated with adverse health effects.

BEOH generally follows a two-step methodology to comment on public health issues related to air pollution. First, BEOH obtains representative environmental monitoring data for the site of concern and compiles a comprehensive list of site-related contaminants. Second, BEOH uses health-based comparison values to identify those contaminants that do not have a realistic possibility of causing adverse health effect. For the remaining contaminants, BEOH reviews recent scientific studies to determine whether the extent of environmental contamination indicates a public health hazard.

The health-based comparison values used in this report are concentrations of contaminants that the current public health literature suggest are "safe" or "harmless". That is, comparison values (CVs) are concentrations of contaminants that are considered to be levels of exposure at which health effects are not expected to occur. The derivation of a comparison value uses conservative (i.e., "worst case") exposure assumptions, resulting in values that are much lower than the actual exposure concentrations observed to cause adverse health effects. Therefore, comparison values are protective of public health in most exposure situations. That is, if the concentrations in the exposure medium are less than the CV, the exposures are not of health concern and no further analysis of the pathway is required. However, while concentrations below the comparison value are not expected to lead to any observable health effect, a concentration above this level doesn't automatically indicate a public health hazard. Depending on site-specific environmental exposure factors (for example, duration of exposure) and activities of people that result in exposure (time spent in area of contamination), exposure to levels above the comparison value may or may not lead to a health effect. Therefore, ATSDR's comparison values are not used to predict the occurrence of adverse health effects, but rather a mechanism to determine whether or not to further examine exposure to a chemical through a specific pathway.

The following analysis identifies air pollutants for the Merrimack Station study area, describes the known levels of air pollutants in the area, reviews site specific studies that have measured levels of air pollution, and finally, comments on the public health implications of inhalation exposures to air pollution in the Merrimack Station study area.

3.2 Chemicals of Concern

This section contains site-specific information about potential chemicals of interest associated with the site; however, inclusion in this section does not imply that a particular chemical represents a threat to public health. It is well known that the burning of fossil fuels can result in the generation of air pollutants such as particulate matter (PM2.5, PM10) and sulfur dioxide (SO2). These compounds are known as Criteria Air Pollutants, because EPA has regulated them by first developing health-based criteria (science-based guidelines) as the basis for setting permissible levels. One set of limits (primary standard) protects health; another set of limits (secondary standard) is intended to prevent environmental and property damage. BEOH obtained local air monitoring data for sulfur dioxide and particulate matter from the air monitoring stations around Suncook Village. Sulfur dioxide and particulate matter is commonly associated with coal-fired electrical generating facilities. They are also products of automobile emissions, small and large industrial operations and the use of firewood and home heating fuels.

3.3 Ambient Air Monitoring Data

DES has been monitoring sulfur dioxide, at two stations simultaneously, since September 2002. The Brickett Hill Road station has been operating for several years (older data from this station and other past monitoring stations will be used in evaluating past exposures). The Exchange Street station, which is approximately 3/4 of a mile from the power plant, has been monitoring sulfur dioxide, wind speed, wind direction and temperature since September 2002. Particulate matter monitoring began at this station in October 2002, with PM10 samples being taken every 12 days. Both stations were placed in their locations based on the prevailing wind directions and the location of the nearest population concentration (Suncook Village).

3.3.1 Sulfur Dioxide

Air monitoring data were available from September 2002 through May 2003. Most of the time the sulfur dioxide levels were below ATSDR's health guideline (for acute exposures) of 10 parts per billion (ppb). This level is set by ATSDR as in indication that further examination of chemical concentrations and health effects should be investigated and is based on an averaging period of up to 14 days. Periodically, however, hourly sulfur dioxide levels at the Exchange Street monitoring station, and to a lesser extent at the Brickett Hill Road monitoring station, showed levels of sulfur dioxide above this comparison value. The highest average sulfur dioxide level detected in a one-hour monitoring period was 147 ppb.

BEOH was unable to calculate a true annual average for these stations since 365 days of monitoring has not taken place at both monitoring stations. An "overall average" was used in lieu for the annual average, under the assumption a true annual average would be obtained at a future date. Air monitoring for the Brickett Hill and Exchange Street stations showed an overall average of 2.9 ppb and 6.3 ppb, respectively (Table 4). These levels are well below the EPA's health based air quality standard (an annual average concentration of 30 ppb). In addition to cumulative sulfur dioxide levels being below the annual NAAQS annual average, all 24-hour averages, from both stations, for this entire period (the daily average from June 2002 to May 2003) were below the EPA 24-hour standard of 140 ppb. The highest 24-hour averages for the Brickett Hill monitoring station and the Exchange Street monitoring station were 25.9 ppb and 58.9 ppb, respectively (Table 4). These data indicate that the average ambient air concentrations do not exceed the NAAQS regulatory limits for SO2.

Although there were no documented exceedences of health-based air-quality standards, there were large variations in sulfur dioxide levels during the monitoring period. For any given hourly observation, sulfur dioxide levels were as low as zero or not detected, and at one point as high as 147 ppb. During the entire monitoring period, there were approximately nineteen hourly observations of sulfur dioxide above 100 ppb (Table 5a and 5b). All but three of these occurred at the Exchange Street monitoring site. At that location, relatively strong winds were blowing from the general direction of the power plant in nearly each instance. For the two occasions where Brickett Hill had observations over 100 ppb, winds again were blowing from the direction of Merrimack Station, though at lower speeds.

Elevated pollution levels can be caused when relatively strong winds blow directly from a source (or sources) to a monitor site, or when meteorological conditions cause pollutants to accumulate due to a lack of dispersion. Examples of the latter are thermal inversions in the colder months and periods of air stagnation during hot, humid summer months, both of which can trap existing pollution in an area. Though high concentrations of pollutants frequently occur under these conditions, the elevated levels of SO2 observed during the period appear to be more a result of direction transport from a source or sources to the monitors.

Hot summer weather is another factor that contributes to poor air quality. Although "air quality action days" are commonly associated with elevated ozone levels, sulfur dioxide levels can climb due to power generating facilities responding to an increased electrical demand. In addition to this, air stagnation can occur during these conditions. Air stagnation is a condition where there is little to no air movement, thus pollutants are not dispersed from their sources. It is possible the that Merrimack Station contributes to increased sulfur dioxide levels during these times, but there are multiple other sources that can contribute as well, including vehicular traffic, other nearby industrial facilities and other power generating facilities. In addition to other nearby sources, air quality in the summer can be affected via pollution from other regions of the United States and Canada. Increased power demand over a large region results in increased production at power generating facilities all over the region, resulting in increased ambient sulfur dioxide levels. On days with high temperatures over the region, most power plants in New England, as well as much larger power plants in neighboring regions, can contribute to poor air quality for the entire region.

3.3.2 Particulate Matter Particulate Matter Less Than 10 Microns (PM10)

Monitoring for particulate matter is available from October 2002 through June 2003. Individual samples of PM10 ranged from 2.6 to 47.0 µg/m3 (Table 6). All individual 24- hour average values were below the NAAQS limit for 24-hour averages (150 µg/m3). The overall averages (for the entire sampling period) from both stations were 13.9 µg/m3 (Brickett) and 15.9 µg/m3 (Exchange), three times below the NAAQS limit for the annual average (50 µg/m3). Again, as with annual sulfur dioxide levels, the levels of PM10 will be revisited once a full year of monitoring has taken place. Particulate Matter Less Than 2.5 Microns (PM2.5)

Monitoring stations in Suncook Village did not monitor for PM2.5, also known as fine particulate matter. PM2.5 is an important component since recent studies show that many health effects are associated with PM2.5 exposures. These health effects include respiratory-related hospital admissions and emergency room visits, aggravated asthma, chronic bronchitis and decreased lung function. Since PM2.5 is actually a subset of PM10, levels of PM2.5 can be estimated from PM10 measurements, based on scientific literature.

To characterize the overall average of PM2.5, BEOH multiplied the PM10 overall averages (13.9 and 15.9 µg/m3) by the mean percentage (70% or 0.7) of PM2.5 that comprises PM10 (EPA, 2002). The resulting estimated levels of PM2.5 are 9.7 µg/m3 and 11.1 µg/m3 for the Brickett Hill Road and Exchange Street monitoring stations, respectively. These estimated overall averages are below the NAAQS standard for PM2.5 (15 µg/m3)

To characterize 24-hour averages of PM2.5, BEOH multiplied the highest recorded PM10 level (47 µg/m3) and multiplied it by the 95th percentile value for the fraction of PM2.5 that is in PM10. This represents a "worst-case scenario" in terms of short-term levels of PM2.5. The resulting estimated 24-hour average of PM2.5 is 45.6 µg/m3. This estimated level is below the NAAQS standard for PM2.5 (65 µg/m3).

Even though current particulate matter data indicate that particulate matter levels are below levels at which health effects occur, BEOH and ATSDR consider the current frequency of particulate matter monitoring to be insufficient. When a plume of particulate matter passes through an area, the levels are likely to fluctuate. The current sampling frequency, once every 12 days for a 24-hour period, may not be adequate to reflect actual levels. For example, no particulate matter sample was taken during the inversion event that occurred on December 26. Sampling at a greater frequency increases the probability that a sample will be taken during an event such as an inversion. This increases the probability that the yearly averages will reflect long-term exposures.

3.4 Pathways of Exposure

This section summarizes exposure pathways. BEOH's first goal in this process is to identify exposure pathways. Exposure pathways are studied to understand the different ways that contaminants move within and from a site and the different ways that people might come into contact with those contaminants. The purpose of the exposure pathway investigation is to determine if anyone might come into contact with the environmental media under study, when (how often, over what time period), where and how. This information alone does not define exposure - it simply helps us to better understand the likelihood of exposures. The exposure pathway information is used together with the environmental data to support the health effects evaluation.

Exposure pathways are categorized as completed, potential, or eliminated. For a person to be exposed to a contaminant, the exposure pathway must be completed. An exposure pathway is considered completed when five pathway elements are present and exposure has occurred, is occurring, or will occur in the future. These elements include: (1) a source of contamination, (2) transport through an environmental medium, (3) a point of exposure, (4) a route of human exposure and (5) a potentially exposed population. A pathway is considered to be a potential pathway when at least one of the five elements is missing and may or may not be present in the future. An exposure pathway is eliminated when one or more of the elements is missing and will never be present to complete the pathway. An evaluation of the pathways for public health significance will be presented in the following section.

3.4.1 Breathing Outdoor Air

As mentioned previously, breathing ambient air is the only completed exposure pathway in Suncook Village. Much of the health consultation focuses on Merrimack Station, primarily because it is a very large, highly visible industry in the area, and because it has been the center of considerable public concern. Because emissions from the power station blow off-site, people living, working and playing in downwind locations come in contact with emissions. It is difficult to know, however, how the quantity of emissions from a particular source affects the overall ambient air quality. Quantifying the sources of air emissions typically only becomes necessary when it is found that ambient air levels are above health-based criteria.

The ultimate measure of the effect of air pollutant exposures to the residents of a community is the measurement of actual pollutants where people live, work, or play. For public health assessments, these environmental monitoring stations are assumed as the human "receptor" that completes the environmental human exposure pathway.

3.4.2 Analysis of Transport of Air

This section analyzes measurements of wind direction and ambient air concentrations of sulfur dioxide. These two factors, when measured simultaneously, allow for detailed analysis of the sources that most likely contribute to air pollution. The most difficult aspect of air emissions exposure is demonstrating that contaminants are actually transported from their source to an actual point of exposure, i.e., sulfur dioxide moving from Merrimack Station's stacks to areas in Suncook Village. As previously discussed, meteorological data from 1993-2003 show that prevailing winds blew roughly from northwest to southeast. This trend suggests that long-term pollutant impacts from Merrimack Station would likely be greatest at locations southeast of the facility. Merrimack Station emissions may have short-term air quality impacts in all compass directions around the site, with the extent of these impacts determined by how often a location was downwind from the facility. Therefore, BEOH assumes that air quality impacts in other areas around the facility are likely to be lower (on a long-term basis) than what is monitored at the location(s) most downwind from the facility.

BEOH examined trends in wind direction from October 24, 2002 to May 6, 2003. Sulfur dioxide levels were monitored from September 9, 2002 to May 6, 2003. This is a relatively short period in terms of comparing overall air quality, especially since both wind and sulfur dioxide monitoring from summer months are not included. Sulfur dioxide measurements are continuously being recorded at both Brickett Hill Road and Exchange Street Monitoring Stations, and wind direction is continuously being monitored at the latter. Since measurements are being recorded past the writing and publication of this document, additional air data past these dates will be analyzed and addressed in the final Public Health Assessment.

The air monitoring stations recorded 4,648 hours of wind direction observations. 4,557 and 7,437 hours of sulfur dioxide observations were recorded for the Exchange Street and Brickett Hill locations, respectively. Table 3 illustrates how the sulfur dioxide concentrations, on average, varied with wind direction during this time frame. When sulfur dioxide levels were above 10 ppb (the level established by ATSDR that indicates further environmental analysis is required), winds blew from between the directions of north north west (NNW) or west north west (WNW) approximately 48% of the time (Table 3). When sulfur dioxide levels were above 100 ppb (the level at which actual health effects begin to occur), winds blew from these directions approximately 80% of the time (Table 3). Fine particulate matter from the power plant would be expected to be transported and dispersed in a similar way as SO2.

Although Figures 2-4 along with the analysis of Suncook Village monitoring data provide evidence that Merrimack Station's emissions may account for some sulfur dioxide in the ambient air, it is still possible that emissions from other nearby sources may have also contributed to recorded levels of sulfur dioxide. Suncook Village is approximately 7 miles from Concord and 11 miles from Manchester. These two cities have a combined population of nearly 150,000. Large populated areas can have several sources of sulfur dioxide, including boilers and furnaces, industrial processes, and combustion in motor vehicle engines. In addition to these non-point sources, DES has identified at least 19 known point sources of criteria air pollutants (the same pollutants associated with Merrimack Station) in a five-mile radius of Merrimack Station.


4.1 Introduction

BEOH has reviewed the scientific literature while conducting the evaluation of exposure to sulfur dioxide and particulate matter. BEOH relies on the ATSDR Toxicological Profiles, which summarize pertinent toxicity data from animal and human studies.

To evaluate exposure from breathing contaminants in air, ATSDR develops inhalation Minimal Risk Levels (MRLs) when sufficient human or animal studies are available. MRLs are available for three exposure periods: acute for exposure periods up to 14 days, intermediate for exposure periods of 15 to 364 days, and chronic for exposure periods greater than 1 year. Therefore, a chemical can have acute, intermediate and chronic MRLs if sufficient scientific studies are judged to be available for those periods. An inhalation MRL is the concentration of a chemical in air below which non-cancerous harmful effects are unlikely. The concentration unit for an inhalation MRL is either in parts of a chemical per billion parts of air (parts per billion, ppb), or it is measured in micrograms per cubic meter (µg/m3). For example, ATSDR has developed an acute, inhalation MRL of 10 ppb for sulfur dioxide. If the level of sulfur dioxide in air is 5 ppb (or any level under 10 ppb), then people exposed to this level are not likely to experience harmful effects.

Exceeding an MRL, however, does not mean that harmful effects will occur, but that a more thorough toxicological evaluation is necessary. Examples of some factors that are considered as part of a more thorough evaluation include the following:

  • Comparing the chemical concentration in air to concentrations that cause harmful effects to determine how close the concentrations are,
  • Determining who is exposed and if they are more sensitive to the chemical,
  • Evaluating the location of the air sample in relation to where people live,
  • Determining if the toxicological effect in study is applicable to the people who are exposed,
  • Considering different aspects of exposure in the study (e.g. dosing period, amount, frequency of exposure) and the applicability of those aspects to people who live near the site and their exposure,
  • Considering the effect of uncertainty in exposure estimates, and
  • Considering the effect of uncertainty in deciding possible harmful effects.

After conducting its site-specific toxicological evaluation, ATSDR describes whether or not people who are exposed to site contaminants might experience harmful effects from that exposure. As part of this discussion, ATSDR also describes the uncertainty that usually exists in making these decisions.

BEOH has outdoor air measurements for sulfur dioxide in the Suncook Village area from June 2002 to May 2003, as well as several years of data from Brickett Hill. These data form the basis of BEOH's evaluation of the recorded levels of sulfur dioxide.

4.2 Sulfur Dioxide and NAAQS Standards

In general, the ambient air monitoring data described in the previous section indicate that there were no exceedences of NAAQS regulatory limits in the areas around Suncook Village. The EPA sets NAAQS standards to protect the entire population, including the most sensitive receptors, such as asthmatics, children, and the elderly. It is important to note that the outdoor air monitoring results are used in this health consultation as a surrogate for exposure to air pollutants in the area of the Suncook Village. Actual individual exposure to air pollutants is determined by a complex interplay among human activity, such as the locations where time is spent and housing characteristics (as they influence penetration of outdoor pollutants).

The overall averages observed in the Suncook Village area (Table 4) were far below the NAAQS level of 30 ppb. The averages recorded at the Brickett Hill Road and Exchange Street monitoring stations were approximately 2.9 ppb and 6.3 ppb, respectively. These averages are 5 to 10 times lower than the NAAQS standard.

In regard to the 24-hour averages, all 24-hour averages from June 2002 to May 2003 were below the NAAQS standard of 140 ppb. The highest recorded 24-hour average was 59 ppb (this is from the December 26 inversion event). The median 24-hour levels for the Brickett Hill Road and Exchange Street locations were 1.0 ppb and 3.8 ppb, respectively, far below the NAAQS standard.

Since neither of the health-based NAAQS limits were exceeded, it is highly unlikely that any resident would suffer adverse health effects at the observed levels of sulfur dioxide. However, BEOH uses EPA's health-based standards as a first step in evaluating the public health implications of pollutants. Therefore, BEOH will evaluate other available health-based guidelines from other government agencies to make a thorough detailed public health analysis.

4.3 Sulfur Dioxide and ATSDR's MRL

At this time, we will focus on the average sulfur dioxide levels for a one-hour period. There is no 1-hour standard for EPA NAAQS limits and all exposure periods, including very short periods, must be evaluated in the in-depth analysis. Tables 5a and 5b highlight the number of hourly measurements, 24-hour averages and days that sulfur dioxide levels were above ATSDR's acute MRL (10 ppb). This acute MRL is used to determine whether sulfur dioxide levels should be evaluated further. Tables 5a and 5b show that over this period of monitoring:

  • Exchange Street Station: Average hourly air levels exceeded the acute MRL of 10 ppb for 892 hours out of a possible 4557 hours of monitoring activity, or about 1 out of every 5 hours.
  • 148 days (out of a possible 240 days) had at least one hourly air sample that exceeded the acute MRL of 10 ppb.
  • 48 days (out of a possible of 240 days) had a 24-hour average at or above 10 ppb.

  • Brickett Hill Road Station: Average hourly air levels exceeded the acute MRL of 10 ppb for 573 hours out of a possible 8160 hours of monitoring activity, or about 7% of all hours monitored.
  • 122 days (out of a possible 340 days) had at least one hourly air sample that exceeded the acute MRL of 10 ppb.
  • 27 days (out of a possible of 240 days) had a 24-hour average at or above 10 ppb.

To conduct this more thorough toxicological evaluation, ATSDR used data from its Toxicological Profile for Sulfur Dioxide (ATSDR, 1998), which includes recently published human and animal studies to determine whether or not people in the Suncook Village area might experience harmful effects from sulfur dioxide.

A review of the toxicological literature for sulfur dioxide shows that the lowest level known to cause harmful effects in humans is 100 ppb after exposures of just a few minutes. At 100 ppb, these harmful effects have only been observed in people with asthma who were exercising and breathing (and receiving sulfur dioxide) through a mouthpiece. The only effect observed in exercising asthmatics was increased airway resistance in the lungs (also known as bronchoconstriction). It should be noted that these effects are temporary and go away after the exposure stops. This increase can be detected in a clinical setting and is not likely to cause overt symptoms in exercising asthmatics in an outdoor setting.

According to Tables 5a and 5b, there were 18 hourly observations that were above 100 ppb, 3 observations from the Brickett Hill station and 15 taken from the Exchange Street station. Most of the time, these elevated levels occurred separately from one another, although there is one exception from December 26, 2002 (Table 4). During this day, there were 5 consecutive hours of sulfur dioxide levels above 100 ppb, with a peak of 147 ppb (the highest hourly average recorded during the observation period). During this time, hourly sulfur dioxide levels were above 100 ppb from 4:00am through 8:00am. Sulfur dioxide levels were not recorded at the Brickett Hill location because the station was not operating from December 24 through January 14.

4.4 Summary of Exposure Findings

Based on the review of sulfur dioxide monitoring data, there is little possibility of residents in the Suncook Village area experiencing adverse health effects as a result of exposure to long-term or short-term levels of sulfur dioxide. The recorded levels are well below than national pollution standards and also below levels (as documented in scientific literature) in which health effects occur.

There are other triggers that also exist for asthma, in addition to sulfur dioxide. For example, air pollution (such as fine particulate matter and ozone), tobacco smoke, dust mites, animal (pet) dander, molds and pollen are a few triggers listed at the following websites for the American Lung Association:


To ensure that the health of New Hampshire's children is protected, BEOH follows ATSDR's Child Health Considerations requiring that Public Health Assessments and health consultations specifically evaluate the potential for children being exposed to site-related hazardous waste and whether or not the health of children might be affected.

This health consultation reflects ATSDR's and BEOH's concern about protecting children's health from toxic chemicals in the environment. Specifically, BEOH evaluated the potential for harmful effects occurring in children in the following scenarios:

  • Children being exposed to sulfur dioxide and particulate matter in the air, and the possibility of harmful effects;
  • Children with asthma as a sensitive subpopulation.

All health-based standards and guidelines used in this evaluation take children into consideration. Since young children are often the most sensitive receptor in a population, NAAQS standards and ATSDR MRLs were developed with this group in mind.


On September 11, 2003, BEOH released the Draft Health Consultation for Review of 2002-2003 Air Monitoring Data for public comment. In addition to mailing the draft document to 15 local residents, government officials, and interested parties, the availablity of the draft health consultation was announced in a press release to local media. BEOH also offered to make hard copy and electronic versions of the draft document available to the public upon request.

The public comment period on the draft document lasted for 1 month (September 11, 2003 to October 12, 2003). No written comments were received by BEOH during this time period.


There currently is no one source (or multiple sources) of sulfur dioxide or particulate matter that result in unhealthy exposures to the residents of Suncook Village, based on the data collected. These levels are significantly below levels in which known adverse health effects occur in sensitive groups such as asthmatics, young children and the elderly. Current ambient levels of sulfur dioxide and particulate matter are not expected to cause adverse health effects, including people with asthma and other respiratory conditions.

Monitoring data does show however, that elevated levels of SO2 can be expected in the area and may occur when the wind blows from the general direction of the power plant. Temperature inversion events and air stagnation episodes also occur periodically in this region of the Merrimack Valley and these can also cause high pollution levels. Both scenarios can result in levels of sulfur dioxide, which can cause slight irritation in exercising asthmatics.

Ambient levels of sulfur dioxide and particulate matter in Suncook Village are no apparent public health hazard. BEOH considers the overall status of the Merrimack Station power generating facility to be an indeterminate public health hazard because BEOH has not completed evaluating other aspects of the Public Health Assessment including: annual levels of sulfur dioxide levels and particulate matter, air toxics measurements, community health concerns and health outcome data. Upon evaluation of these outcomes, BEOH will issue a final public health status for the site.


An important part of this health consultation is that BEOH makes recommendations, to other agencies or groups, about public health actions that the bureau thinks should be conducted at a hazardous waste site or in the community. In developing these recommendations, BEOH looks to identify an appropriate agency or other entity to follow up on these recommendations. The results of these discussions are presented in the Public Health Action Plan section. The following are BEOH's recommendations for Suncook Village.

  1. Collect and review new site data, as they become available.

  2. Provide health education to area residents regarding air quality action days, asthma/respiratory triggers, as well an explanation of thermal inversions, air quality action days and their effect on air quality.

  3. Monitoring for fine particulate matter (PM2.5) should be performed on a continuous basis.


The Public Health Action Plan for Suncook Village contains a description of actions that have been or will be taken by BEOH and other government agencies at the site. The purpose of this plan is to ensure that this health consultation not only identifies potential public health hazards associated with the site, but also provides a plan of action to prevent or minimize the potential for adverse human health effects from exposure to site-related hazardous substances.

9.1 Completed, Current and Ongoing Actions

  1. DES is currently monitoring for sulfur dioxide, particulate matter and air toxics in Suncook Village, at two locations. Air monitoring is expected to continue.

  2. BEOH will continue to evaluate all air quality data in regard to public health.

  3. BEOH is currently preparing a Public Health Assessment of the Merrimack Station, which incorporates community health concerns and health outcome data with air quality data.

  4. In 2002, BEOH performed a community needs assessment in and around Suncook Village.

9.2 Actions Planned

  1. BEOH will complete a Public Health Assessment for the Merrimack Station in the future. This document will include:

    • Past sulfur dioxide and total suspended particulate (TSP) levels,
    • Air toxics evaluation,
    • Community health concerns, and
    • An evaluation of health outcome data.

  2. BEOH will continue to conduct health education/outreach activities in the Suncook Village area.

  3. BEOH will evaluate measurements of air toxics that are currently being monitored at the Exchange Street monitoring station.

  4. BEOH will reevaluate and expand the Public Health Action Plan when needed. New environmental, health outcome data, or the results of implementing the above actions may warrant additional actions at this site.


Todd C. Hudson
Environmental Health Risk Analyst
Bureau of Environmental and Occupational Health
New Hampshire Department of Health and Human Services

ATSDR Regional Representative:

Gary Perlman
Public Health Advisor
ATSDR Region I

Technical Consultation provided to ATSDR by:

Gregory V. Ulirsch
Technical Project Officer/Environmental Health Scientist
Superfund Site Assessment Branch
Division of Health Assessment and Consultation, ATSDR


The Health Consultation for the Merrimack Station Power Plant, Bow, New Hampshire was prepared by the New Hampshire Department of Health and Human Services under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was initiated.

Gregory V. Ulirsch
Technical Project Officer, SPS, SSAB, DHAC

The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed this Health Consultation and concurs with its findings.

Roberta Erlwein


Agency for Toxic Substances and Disease Registry (ATSDR). 1998. Toxicological Profile for Sulfur Dioxide. Atlanta: US Department of Health and Human Services.

New Hampshire Department of Environmental Services. 2003. Memorandum Regarding Other Air Pollution Sources in Vicinity of Pembroke.

U.S. Environmental Protection Agency (EPA). Air Quality Criteria for Particulate Matter (Third External Review Draft). 2002. U.S. Environmental Protection Agency, Office of Research and Development, National Center For Environmental Assessment, Research Triangle Park Office, Research Triangle Park, NC.


Table 1.

Estimated age distribution for the Suncook Village area, based on 2000 Census data from Pembroke and Allenstown.
Age (years) Persons Percentage
Less than 5 332 6.6%
5 to 9 years 386 7.6%
10 to 14 years 414 8.2%
15 to 19 years 359 7.1%
20 to 24 years 226 4.5%
25 to 34 years 693 13.7%
35 to 44 years 1004 19.8%
45 to 54 years 725 14.3%
55 to 69 years 240 4.7%
60 to 64 years 172 3.4%
65 to 74 years 281 5.6%
75 to 84 years 176 3.5%
85 years and over 54 1.1%

Table 2.

A summary of hourly wind direction measurements, taken from October 24 through May 6, at the Exchange Street monitoring station.
Direction Observations Percent
ENE 552 12.4%
ESE 759 17.0%
NNE 621 13.9%
NNW 807 18.1%
SSE 299 6.7%
SSW 184 4.1%
WNW 712 16.0%
WSW 482 10.8%
Missed Observations 36 0.8%
Total Observations 4452

Table 3.

Analysis of wind direction frequencies when hourly sulfur dioxide levels exceeded 10 ppb and 100 ppb.
Direction 10 ppb 100 ppb
ENE 64 7.7% 0  
ESE 130 15.6% 0  
NNE 40 4.8% 1 6.7%
NNW 160 19.2% 7 46.7%
SSE 68 8.2% 2 13.3%
SSW 64 7.7% 0  
WNW 244 29.3% 5 33.3%
WSW 61 7.3% 0  
No wind measurement 1 0.1% 0  
ENE 64 7.7% 0  

The ATSDR Minimal Risk Level.
The level at which health effects have been documented.
Sulfur dioxide NAAQS:
    annual = 30 ppb
    24-hour = 140 ppb
    3-hour = 500 ppb

Table 4.

A summary of overall averages of sulfur dioxide, 1-hour measurements and 24-hour averages, in parts per billion (ppb).
Station "overall" average maximum 1-hour average maximum 24-hour average median 24-hour average
Brickett Hill Road 2.9 135 25.9 1.0
Exchange Street 6.3 147 58.9 3.8

"Overall" average refers to the average of the sampling period of October, 2002 to June 2003.

Table 5a.

Hourly Sulfur Dioxide Levels at the Exchange Street Monitoring Station. Number of Samples Greater than (ATSDR's Acute Inhalation MRL) 10 ppb, 100 ppb and 24-Hour averages.
Month Hourly Concentrations
Number of 1-hour Samples Number of 1-hour Samples Greater Than Number of Days With 24-Hour Averages Greater Than 10 ppb
10 ppb 100 ppb
September 2002* 513 42 1 3
October 741 37 0 3
November 713 66 0 4
December 730 215 8 11
January 856 206 1 8
February 644 102 0 5
March 794 86 0 4
April 698 119 5 9
May 2003* 125 19 0 1

* Monitoring did not take place for the entire month.

Table 5b.

Hourly Sulfur Dioxide Levels at the Brickett Hill Road Monitoring Station. Number of Samples Greater than (ATSDR's Acute Inhalation MRL) 10 ppb, 100 ppb and 24-Hour averages.
Month Hourly Concentrations
Number of 1-hour Samples Number of 1-hour Samples Greater Than Number of Days With 24-Hour Averages Greater Than 10 ppb
10 ppb 100 ppb
June 2002* 710 71 0 3
July 739 63 1 4
August 735 43 0 1
September 708 35 0 1
October 726 9 0 0
November 708 73 0 5
December 550 49 0 2
January 438 47 0 2
February 662 51 2 2
March 727 102 0 7
April 711 14 0 0
May 2003* 123 16 0 0

Table 6.

PM10. Summary of overall averages and 24-hour averages, in g/m3. Values from PM2.5 have been extrapolated from PM10 data using most recent scientific literature.
Station PM10 PM2.5 (estimated)
"overall" average maximum measurement "overall" average maximum measurement
Brickett Hill Road 13.9 44.0 9.7 45.6
Exchange Street 15.9 47.0 11.1

"Overall" average refers to the average over the sampling period of October, 2002 to June, 2003


General location and demographic information of the Merrimack Station and surrounding areas
Figure 1. General location and demographic information of the Merrimack Station and surrounding areas.

Wind roses from Concord Municipal Airport, calculated from 1993-2003 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing.
Figure 2. Wind roses from Concord Municipal Airport, calculated from 1993-2003 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing.
Data Source: National Climactic Data Center.

Wind roses from Concord Municipal Airport, calculated from 1993-2003 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing.
Figure 3. Wind roses from Concord Municipal Airport, calculated from 1993-2003 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing.
Data Source: National Climactic Data Center.

Wind Rose from Merrimack Station, calculated from 1994 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing
Figure 4. Wind Rose from Merrimack Station, calculated from 1994 meteorological monitoring. Bars in the figure indicate from which direction the wind was blowing.
Data Source: NH Department of Environmental Services.


How a chemical enters a person's blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.

Acute Exposure:
Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.

Additive Effect:
A response to a chemical mixture, or combination of substances, that might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

Adverse Health Effect:
A change in body function or the structures of cells that can lead to disease or health problems.

Ambient Air Monitoring:

Antagonistic Effect:
A response to a mixture of chemicals or combination of substances that is less than might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.

Background Level:
An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific-environment.

The goal of the Bureau of Environmental and Occupational Health is to protect the health and well being of NH citizens by reducing the prevalence of lead poisoning, providing free safety and health consultations for employers, regulating the lead and asbestos abatement industries, and by evaluating the health risk associated with exposure to chemical contaminants in the environment. The Bureau has three component sections: the Childhood Lead Poisoning Prevention Program, the Occupational Health Program and the Health Risk Assessment Program.

Used in public health, things that humans would eat - including animals, fish and plants.

See Community Assistance Panel.

A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control.

Any substance shown to cause tumors or cancer in experimental studies.

See Comprehensive Environmental Response, Compensation, and Liability Act.

Chronic Exposure:
A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.

Completed Exposure Pathway:
See Exposure Pathway.

Community Assistance Panel (CAP):
A group of people from the community and health and environmental agencies who work together on issues and problems at hazardous waste sites.

Comparison Value (CVs):
Concentrations or the amount of substances in air, water, food, and soil that is unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment, and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.

A belief or worry that chemicals in the environment might cause harm to people.

How much or the amount of a substance present in a certain amount of soil, water, air, or food.

See Environmental Contaminant.

Delayed Health Effect:
A disease or injury that happens as a result of exposures that may have occurred far in the past.

Relating to the statistical study of human populations to include such characteristics and factors as population counts, births, deaths, migration, sex, age, and related statistics

Dermal Contact:
A chemical getting onto your skin. (see Route of Exposure).

The mission of the Department of Environmental Services is to help sustain a high quality of life for all citizens by protecting and restoring the environment and public health in New Hampshire.

The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".

Dose / Response:
The relationship between the amount of exposure (dose) and the change in body function or health that result.

The amount of time (days, months, years) that a person is exposed to a chemical.

To come or send forth.

Releases of gases to the atmosphere (e.g., the release of carbon dioxide during fuel combustion). Emissions can be either intended or unintended releases.

Environmental Contaminant:
A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.

Environmental Media:
Usually refers to the air, water, and soil in which chemicals of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.

U.S. Environmental Protection Agency (EPA):
The federal agency that develops and enforces environmental laws to protect the environment and the public's health.

The Environmental Protection Agency mission is to protect human health and to safeguard the natural environment - air, water, and land - upon which life depends.

The study of the different factors that determine how often, in how many people, and in which people will disease occur.

Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)

Exposure Assessment:
The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.

Exposure Pathway:
A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:

  1. Source of Contamination,
  2. Environmental Media and Transport Mechanism,
  3. Point of Exposure,
  4. Route of Exposure, and
  5. Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.

How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.

Volatile; apt to flee away; readily wafted by the wind.

Hazardous Waste:
Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.

Health Effect:
ATSDR deals only with Adverse Health Effects (see definition in this Glossary).

To put into practical effect; carry out.

Indeterminate Public Health Hazard:
The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.

Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).

Breathing. It is a way a chemical can enter your body (See Route of Exposure).

Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused harmful health effects in people or animals.

See Cancer.

The science that deals with the phenomena of the atmosphere, especially weather and weather conditions.

Means, technique, or procedure; method.

Minimal Risk Level. An estimate of daily human exposure - by a specified route and length of time -- to a dose of chemical that is likely to be without a measurable risk of adverse, no cancerous effects. An MRL should not be used as a predictor of adverse health effects.

The Clean Air Act requires EPA to set National Ambient Air Quality Standards for pollutants considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

The National Priorities List. (Which is part of Superfund.) A list kept by the U.S. Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or is being looked at to see if people can be exposed to chemicals from the site.

No Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, that did not cause harmful health effects in people or animals.

No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.

No Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.

Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.

Particulate Matter:
Material suspended in the air in the form of minute solid particles or liquid droplets, especially when considered as an atmospheric pollutant.

A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).

Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). For examples: the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.

A group of people living in a certain area; or the number of people in a certain area.

Potentially Responsible Party. A company, government or person that is responsible for causing the pollution at a hazardous waste site. PRP's are expected to help pay for the clean up of a site.

Most common or conspicuous; main or prevalent.

Public Health Assessment(s):
See PHA.

Public Health Hazard:
The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.

PHA categories given to a site, which tell whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:

- Urgent Public Health Hazard
- Public Health Hazard
- Indeterminate Public Health Hazard
- No Apparent Public Health Hazard
- No Public Health Hazard

Have or relating to number or quantity.

Receptor Population:
People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).

Reference Dose (RfD):
An estimate, with safety factors (see safety factor) built in, of the daily, lifetime exposure of human populations to a possible hazard that is not likely to cause harm to the person.

Route of Exposure:
The way a chemical can get into a person's body. There are three exposure routes:

- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- or getting something on the skin (also called dermal contact).

Safety Factor:
Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.

Sample Size:
The number of people that are needed for a health study.

A small number of people chosen from a larger population (See Population).

Source (of Contamination):
The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.

Special Populations:
People who may be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older people are often considered special populations.

A branch of the math process of collecting, looking at, and summarizing data or information.

Superfund Site:
See NPL.

A way to collect information or data from a group of people (population). Surveys can be done by phone, mail, or in person. ATSDR cannot do surveys of more than nine people without approval from the U.S. Department of Health and Human Services.

Synergistic effect:
A health effect from an exposure to more than one chemical, where one of the chemicals worsens the effect of another chemical. The combined effects of the chemicals acting together are greater than the effects of the chemicals acting by themselves.

A main road or public highway.

Graphic representation of the surface features of a place or region on a map, indicating their relative positions and elevations.

Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.

The study of the harmful effects of chemicals on humans or animals.

Abnormal growth of tissue or cells that have formed a lump or mass.

Uncertainty Factor:
See Safety Factor.

Urgent Public Health Hazard:
This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.

Wind Rose:
A meteorological diagram depicting the distribution of wind direction and speed at a location over a period of time.

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