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PUBLIC HEALTH ASSESSMENT

AMERICAN LINEN (AMERIPRIDE)
(a/k/a AMERIPRIDE SERVICES, INCORPORATED)
HIBBING, ST. LOUIS COUNTY, MINNESOTA


FOREWORD

This document summarizes potential public health concerns at a hazardous waste site in Minnesota. It is based on a formal site evaluation prepared by the Minnesota Department of Health (MDH). A number of steps are necessary to do such an evaluation:

  • Evaluating exposure: MDH scientists begin by reviewing available information about environmental conditions at the site. The first task is to find out how much contamination is present, where it's found on the site, and how people might be exposed to it. Usually, MDH does not collect its own environmental sampling data. We rely on information provided by the Minnesota Pollution Control Agency (MPCA), U.S. Environmental Protection Agency (EPA), and other government agencies, businesses, and the general public.

  • Evaluating health effects: If there is evidence that people are being exposed—or could be exposed—to hazardous substances, MDH scientists will take steps to determine whether that exposure could be harmful to human health. The report focuses on public health—the health impact on the community as a whole—and is based on existing scientific information.

  • Developing recommendations: In the evaluation report, MDH outlines its conclusions regarding any potential health threat posed by a site, and offers recommendations for reducing or eliminating human exposure to contaminants. The role of MDH in dealing with hazardous waste sites is primarily advisory. For that reason, the evaluation report will typically recommend actions to be taken by other agencies—including EPA and MPCA. However, if there is an immediate health threat, MDH will issue a public health advisory warning people of the danger, and will work to resolve the problem.

  • Soliciting community input: The evaluation process is interactive. MDH starts by soliciting and evaluating information from various government agencies, the organizations responsible for cleaning up the site, and the community surrounding the site. Any conclusions about the site are shared with the groups and organizations that provided the information. Once an evaluation report has been prepared, MDH seeks feedback from the public. If you have questions or comments about this report, we encourage you to contact us.

Please write to:

Community Relations Coordinator
Site Assessment and Consultation Unit
Minnesota Department of Health
121 East Seventh Place/Suite 220
Box 64975
St. Paul, MN 55164-0975

OR call us at:

(651) 215-0916 or 1-800-657-3904
(toll free call—press "4" on your touch tone phone)


INTRODUCTION

This Public Health Assessment (PHA) evaluates potential exposures to contaminants found at the AmeriPride Services Inc. (AmeriPride; formerly American Linen Supply Co.) site, located at 519 East 19th Street in the City of Hibbing, Minnesota. This document examines contaminated media (water, air, and soil), transport mechanisms, and routes of exposure (ingestion, inhalation and dermal contact) to determine the likelihood of individuals being exposed to contamination. This Public Health Assessment contains a summary of information obtained from the Minnesota Pollution Control Agency (MPCA), AmeriPride and its contractor Braun Intertec Corporation (Braun), and the city of Hibbing. This document also presents conclusions and recommendations made by MDH. This Public Health Assessment discusses data collected prior to December 1999.


BACKGROUND

Site Description and History

The site currently occupies a full city block, bordered on the north by railroad tracks, to the east by 6th Avenue East, to the south by 19th Street, and to the west by 5th Avenue East. Commercial/industrial buildings occupy properties to the east and north (the Hibbing Public Utilities steam plant and warehouses). The city fire station lies to the west, while to the south across 19th Street lie residential properties. The location of the site is illustrated in Figure 1, and a site map is presented in Figure 2.

AmeriPride began commercial laundry operations at the site in the early 1920s, occupying the building on the southeastern corner of the block. Other businesses which have operated on the same block included warehouses, a jewelry shop, and an auto sales and service facility. The buildings on the block were originally separated by alleys. Over the years, AmeriPride acquired the other buildings on the block. In the 1980s the alleys were covered to form one large single story building. Three underground storage tanks (USTs), two containing fuel oil and one containing gasoline, were removed from the site in 1987. No testing of soil or groundwater was done at the time the USTs were removed (Braun 1995). A warehouse which occupied the northwest corner of the block was demolished in 1994 to make way for an expansion of the building.

During geotechnical drilling on the northeast portion of the site in 1994, petroleum contaminated soil was discovered. Approximately 1,400 cubic yards of soil previously removed from the site for geotechnical reasons was also suspected of being contaminated with petroleum products. AmeriPride hired Braun Intertec Corporation (Braun) to conduct an investigation of the extent of the remaining petroleum contamination. The investigation consisted of the advancement of fifteen soil borings and the installation of three monitoring wells.

The results of the investigation showed that low levels of petroleum products remained in soil in the central portion of the site. Analysis of groundwater samples also showed detectable levels of petroleum products. Volatile organic compounds (VOCs), primarily tetrachloroethylene (also known as perchloroethylene, or PCE), were also detected in soil and in groundwater at levels in excess of the MDH Health Risk Limit (HRL). PCE is a common dry-cleaning solvent. AmeriPride operated a commercial dry-cleaning machine at the site from 1976 to 1990.

Due to the detections of PCE in soil and groundwater at the site, in 1995 it was entered by the owner into the MPCA's Voluntary Investigation and Cleanup (VIC) Program. Investigation activities were subsequently initiated to determine the nature and extent of soil and groundwater contamination at the site from past use or from disposal of PCE. The MPCA staff requested that MDH review site documents prepared to date, along with the results of indoor air monitoring, and develop recommendations regarding public health impacts from the site.

Geology/Hydrogeology
The unconsolidated sedimentary deposits in the area of the site generally consist of a clayey till, which contains sand, silt, and clay with deposits of gravel and cobbles. Bedrock generally lies at a depth of 50 to 100 feet below grade. Soil borings at the site itself show it is underlain by a mixture of sandy lean clays, silts, small organic deposits, and fill to an approximate depth of fifteen to eighteen feet below grade. Underlying this is a thick (approximately fifteen feet) layer of gray fat clay, which appears to be continuous beneath the site. Beneath the clay layer are various poorly graded sands, silty sands, and sandy silts to depths of approximately 70 feet which is the depth of the deepest boring advanced on the site (Braun 1999).

Shallow groundwater beneath the site is found in the unconsolidated deposits, at a depth of approximately 10 feet below grade. The shallow groundwater flow direction is generally to the north-northeast, toward the adjacent Hibbing Public Utilities plant. The Hibbing Public Utilities plant has a foundation drain and sump system which appears to influence local groundwater flow. Regional groundwater flow in the deeper units (beneath the clay layer) is expected to be southeasterly based on published geologic information. Groundwater movement in the area may be influenced by iron mining operations to the north and west, however.

Soil Data
Environmental investigations at the site have identified several areas of soil contamination related to past activities. The majority of the petroleum contamination identified during the initial site investigation was subsequently removed from the site during construction of the addition on the northeast corner of the property. Some petroleum contamination remains under existing buildings, however. The petroleum release file has been closed by the MPCA Leaking Underground Storage Tank (LUST) Program, indicating the LUST Program no longer views the residual petroleum contamination alone as representing a threat to human health or the environment given the current property use.

Several investigations have been conducted in and around the site buildings to identify the extent of the PCE contamination in soil. The investigations have centered around the north wall of the southeast building, where the dry-clean laundry machine was located. According to employees of AmeriPride, the solvent tanks which fed the machine periodically were overfilled (Braun 1995). In addition, the floor in that area had been perforated to allow spilled process water and solvent to drain through the floor to the soil below (Braun 1997). Concentrations of PCE as high as 2,500 milligrams per kilogram (mg/kg) were found in the soil at a depth of 5 feet below the floor at the base of the north wall, in the area of the former dry-cleaning machine and floor drain. This location is the likely source of the PCE contamination to the soil and groundwater. The areal extent of the soil contamination does not appear to be extensive, and is contained beneath the site building. The locations of borings conducted in the suspected PCE source area are shown in Figure 3.

The VOC contamination in soil appears to extend to a depth of approximately 10 feet beneath the building, the approximate depth of the surficial water table. Soil samples taken from selected borings advanced to the approximate depth of the clay layer (fifteen feet below grade) did not identify high concentrations of VOCs. Table 1 lists the maximum levels of PCE and three of its common breakdown products detected in the source area, the location and depth of the sample, and the applicable MPCA residential and industrial Soil Reference Values (SRVs) and Soil Leaching Values (SLVs). The SRVs are soil evaluation criteria based on the protection of human health from direct contact with contaminated soil through ingestion, skin contact, and inhalation of vapors and/or dust particles. The SLVs are designed to be protective of groundwater from the leaching of contaminants from the soil.

Monitoring Well/Push Probe Data
A total of sixteen monitoring wells has been installed at the AmeriPride site and the adjacent Hibbing Public Utilities plant to the east since investigation activities began. The first three monitoring wells, which were installed during the investigation of the petroleum release at the site, were subsequently abandoned. Current monitoring wells MW-1S and -1D, MW-2S and -2D, and MW-3S and -3D were installed as well nests on the site to characterize shallow and deeper groundwater in the area around the southeast building. Monitoring wells MW-4, MW-5, and MW-6S and -6D were installed to the east and southeast of the site to characterize groundwater down-gradient at the Hibbing Public Utilities plant. Monitoring wells MW-5D, MW-6XD, MW-7, and MW-8 were installed west, east, northeast, and southeast of the AmeriPride building to characterize groundwater quality beneath the clay layer. Groundwater samples have also been collected from push probes on both properties and to the southeast, across 19th Street. Historical groundwater analytical results have been compiled by Braun and are presented in Table 2. Current monitoring well locations and the groundwater flow direction in the three sets of wells (shallow, intermediate, and deep) are depicted in Figures 4, 5, and 6 respectively.

The shallow monitoring wells (MW-1S, -2S, -3S, -4, -5, and -6S) are screened at a depth of approximately 10 feet below grade. The intermediate wells (MW - 1D, - 2D, - 3D, and -6D) are screened at a depth of approximately 25 feet below grade, within the clay layer. The deep wells are screened at depths of approximately 50 feet below grade. Conductivity tests show the flow rate in the shallow wells to be relatively typical of poorly graded sands, while the flow rate in the intermediate wells is characteristic of less transmissive clay formations. There is a clear downward vertical gradient between the shallow and intermediate layers; in fact it exceeds the horizontal gradient in the clay layer (Braun 1997). There is also a considerable vertical gradient between the shallow and deep units, although the clay layer may act to inhibit conductivity between the two units (Braun 1999). There is therefore the potential for groundwater, and contaminants in the groundwater, to flow downward through breaks or areas of higher permeability within the clay layer.

Shallow groundwater samples (approximately 12-14 feet below grade) collected from push probe borings in the vicinity of the source area detected PCE at levels as high as 3,000 micrograms per liter (µg/l), which is approximately 400 times the HRL of 7 µg/l. Concentrations of other VOCs in this area have ranged from several hundred to several thousand times their respective HRLs. PCE was detected at a concentration of 25 µg/l at a depth of 10 feet in one push probe advanced off the AmeriPride property, just across 6th Avenue East and immediately adjacent to the Hibbing Public Utilities plant. Other push probes advanced to the east and south of the Hibbing Public Utilities plant did not detect the presence of PCE or its breakdown products in groundwater.

Concentrations of PCE and its breakdown products in the permanent monitoring wells have been highest in MW-1S, -1D, and -2S, located nearest to and immediately north of the suspected source area. Levels of PCE have ranged 13 to 1200 µg/l in MW-1S, from 13 to 190 µg/l in MW-1D, and from non-detect to 80 µg/l in MW-2S. Levels of vinyl chloride, the most toxic breakdown product of PCE, have been as high as 330 µg/l in MW-2S and 540 µg/l in MW-4, both located downgradient of the source area. Overall, levels of VOCs in the shallow and intermediate monitoring wells have varied, and varied widely, with no clear trend upward or downward. Petroleum related compounds, including benzene, toluene, ethyl benzene, and xylenes (BTEX), gasoline range organics (GRO), and diesel range organics (DRO) have been detected in the wells located nearest the former USTs. Levels of benzene have exceeded the HRL of 10 µg/l in some samples from MW-1S, -1D, and -2S, as well as in two of the three shallow monitoring wells installed and subsequently abandoned during the investigation of the petroleum release. Levels of GRO and DRO in excess of the MDH Health Based Value (HBV) of 200 µg/l have been detected in MW-1S, -1D, -2S, -2D, and -4. There were no analyses conducted for GRO and DRO in groundwater samples collected after February 1997, however.

Given the downward vertical gradient in the clay layer, and concern over possible contamination of the regional aquifer below, four monitoring wells were installed in 1999 and 2000 to monitor groundwater quality in the regional aquifer. The wells were installed far enough outside of the source area to avoid the creation of a possible conduit for carrying the VOC contamination from the source area into the deeper units. The suspected groundwater flow direction was to the southeast, and the first three wells were installed accordingly to determine if groundwater downgradient of the site had been impacted. Based on groundwater elevation measurements taken after the wells were installed, the groundwater was in fact found to be moving to the northeast (Braun 1999). This may be due to the influence of dewatering operations at the local iron mines. The fourth monitoring well (MW-8) was installed northeast of the site (Braun 2000a). No VOCs have been detected in any of the four wells set in the regional aquifer to date, indicating that the contamination is so far confined to the upper groundwater units.

Indoor Air Samples
Due to the presence of high levels of VOCs beneath the building floor, screening of indoor air was conducted during the initial phases of investigation. This screening was conducted using direct reading instruments, namely a photoionization detector (PID) equipped with an 11.7 eV lamp. The PID is capable of detecting organic vapors in air at relatively low concentrations (in the part-per-million range), but the PID is not compound-specific. Ambient air in basement areas, as well as sewer lines, floor drains, and other potential entry routes were tested. No organic vapors were detected using the PID. Ambient air samples collected with a standard charcoal tube in the basement of the AmeriPride building also did not show detectable levels of organic vapors in the air. Passive organic vapor monitoring badges exposed to the basement air in both buildings over an 8-hour period detected only low levels of two VOCs. Using the maximum detected soil VOC concentrations as inputs to an analytical model, Braun predicted that the resulting indoor air concentrations would in any event be below permissible occupational limits (Braun 1997).

Because of continuing concerns over the possible infiltration of VOCs from the soil and groundwater into site buildings, and questions over the accuracy of the analytical model, MPCA staff directed AmeriPride to conduct additional air monitoring in the basement of the AmeriPride and Hibbing Public Utility buildings using a method capable of lower detection limits. SUMMA canisters, which consist of a non-reactive, coated stainless steel canister placed under a vacuum, were used to collect ambient air samples over an 8 hour period. The air samples were then analyzed by an out-of-state laboratory using approved methods (EPA Method TO-14). Very low detection limits of less than one part-per-billion (generally less than 10 µg/m3 for most compounds) are possible using this method.

The results of five rounds of SUMMA canister air sampling indicated VOCs are present in ambient air in the basements of the AmeriPride and Hibbing Public Utility buildings. Levels of PCE ranged from 27 to 63 µg/m3 in the basement of the AmeriPride building, and from 3.9 to 62 µg/m3 in the basement of the Hibbing Public Utility building over the five sampling events. A summary of the SUMMA canister monitoring data is presented in Table 3. The locations of the organic vapor monitoring badge and SUMMA canister samples can be found in Figure 2.

Site Visit

On October 25, 1999, Jim Kelly of MDH, and Mark Elliott and Jane Mosel of the MPCA visited the AmeriPride Services Inc. site. The following observations were made:

  • The majority of the site has been developed, and is occupied by a large, single story building. Truck loading docks are located along the west side of the building, as well as a truck maintenance bay. The truck bays are open to the building interior.

  • The groundwater monitoring wells are visible inside and outside the building, and appear to be in good condition. Five plastic pipes were observed along the exterior of the north wall of the building; their use is unknown. According to AmeriPride officials, they may be connected to venting pipes installed beneath the newest part of the building.

  • The interior of the building consists of several areas where clothing and towels are washed, dried, folded, sorted, and repaired. Large commercial washers and dryers are used for these activities. Five powered roof vents as well as passive venting is used for ventilation of the building. Air movement was noticeable inside the building.

  • The location of the former dry-cleaning machine is visible through marks left on the floor near the walls of the room which contained it. In addition, locations where borings penetrated the concrete during the investigation of the source area are visible. Some cracks were noticed in the floor in this area, but appeared to be relatively well sealed.

  • A floor drain was observed approximately 50 feet east of the source area, in the former truck loading area. According to the facility manager, the ceramic tile piping connecting many of the drains from the plant has collapsed. A freight elevator for carrying freight from the basement to the ground floor is also located in this area; the access cover over the shaft is not airtight.

  • The basement of the AmeriPride building contained several desks and records storage boxes. The desks are used by route drivers to do their daily paperwork, which was reported by company officials to take up to one hour per day at most. A bathroom and shower did not appear to be in regular use. According to the facility manager, water observed around a floor drain in the bathroom was from the testing of fire alarms and sprinklers. The basement is reached via an open stairwell. The air samples were collected in the middle of the basement area.

  • The basement of the Hibbing Public Utilities plant, located just across 6th Avenue East, was also visited. The plant generates steam for use in heating by local homes and businesses, including AmeriPride. Steam pipes from the plant are located beneath the streets, and lead in many directions. According to the steam plant manager, snow will often melt off the streets due to the heating action of the steam pipes. Steam was observed coming from the storm sewers despite an air temperature near 60 degrees.

  • The plant is five to six stories high, and is open from the basement through several stories upward. The basement is a filled with pipes, ducts, boilers, and other equipment. It is quite warm, and well ventilated through several ducts and open vents to the outside.

  • The air samples were collected in a small room on the west side of the basement where several cracks in the west wall appear to be seeping groundwater. There is also an overhead grate in this room, and air movement was noticeable. Several cans of spray lubricant were noted next to a large valve in the room; it was not clear from the label if the lubricant contained VOCs, or if it is regularly used.

  • Several unsealed sumps were observed. According to the plant manager, the sumps collect both drainage from the footing drains as well as plant process water. Several thousand gallons per day are discharged from the system to the sanitary sewer under a National Pollutant Discharge Elimination System (NPDES) permit.

  • No employees were observed in the basement. According to the plant manager, workers enter the basement for specific tasks only, such as adjusting valves, reading meters, or maintaining equipment. Cigarette butts were noticed in several areas of the basement, including near where the air monitoring was conducted.

Demographics, Land Use, and Natural Resources Use

The city of Hibbing in St. Louis County and has a population of 17,720, in an estimated 7,478 households (1998 estimates; MOP 2000). The site is located in a mixed use area, with commercial and industrial buildings to the east, north, and west, and residences to the south. Several parks are located within a few blocks of the site (see Figures 1 and 2).

A search of the MDH County Well Index data base has identified 12 water wells within a one mile radius of the site (MGS 1997). Eight of the wells appear to be public supply wells operated by the city of Hibbing. One of the wells is believed to be used for equipment cooling purposes. The remaining wells appear to be monitoring wells. None of the wells appears to be directly downgradient of the site based on the groundwater flow direction in the regional aquifer. Extensive iron mining operations have occurred to the east, west, and north of the site, and various dewatering systems may have been or are in use to keep the mine pits dry. The mining operations may affect local groundwater flow.

General Regional Issues

A search of state and federal records conducted by Braun located four small quantity hazardous waste generators and ten leaking UST sites within a one mile radius of the site (Braun 1995). Based on the locations of the leaking UST sites (which primarily were gasoline or other petroleum related fuel releases), Braun concluded that some of the leaking UST sites could have had the ability to adversely impact groundwater beneath the site. No direct evidence that this is in fact occurring was presented, however.

Community Involvement

At this point in the investigation of the AmeriPride site, there has been no community involvement. In the event that active remediation of the site is proposed, a community relations plan would be drafted for the site by the MPCAas required by VIC and Superfund Program policies.

A draft version of this Public Health Assessment was made available for public comment from March 15 to April 15, 2001. A press release was also issued. No comments were received from the public regarding the draft Public Health Assessment.

Agency For Toxic Substances and Disease Registry (ATSDR) Involvement

MDH, under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR), evaluated the public health significance of contamination associated with AmeriPride site. More specifically, MDH and ATSDR cooperated to determine whether health effects are possible and to make recommendations to reduce or prevent possible health effects. ATSDR, located in Atlanta, Georgia, is a federal agency within the U.S. Department of Health and Human Services. ATSDR is mandated by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 as amended by Superfund Amendments and Reauthorization Act (SARA 1986) to conduct public health assessments at contaminated sites. In cooperation with ATSDR, the MDH has evaluated the public health significance of the AmeriPride site.


EVALUATION OF CONTAMINATION AND EXPOSURE

Tetrachloroethylene (PCE) is a synthetic solvent widely used for fabric cleaning and degreasing of metal. It has been the solvent of choice for dry-cleaning operators for a number of years because it is nonflammable, and volatilizes (evaporates) quickly. In dry cleaning operations, PCE is used as a scouring solvent to remove oils, greases, waxes, and fats from both natural and man-made fabrics. Commercial dry cleaners often use relatively large quantities of PCE in their operations (ATSDR 1997).

Once released into the environment, PCE easily volatilizes from soil and water. Factors which can affect the rate of volatilization from soil include the soil type, organic content of the soil, and nature of the release. Volatilization will tend to be higher in sandy soils, and lower in denser, more organic soils where PCE may be adsorbed onto organic carbon particles. PCE also tends to move rapidly through soil, and can easily contaminate shallow groundwater. PCE is more dense than water. If present in sufficient concentrations in groundwater, it may 'sink' and form a pool at the base of the groundwater aquifer. This pool of dense, non-aqueous phase liquid (or DNAPL) can serve as a continuing source of groundwater contamination.

Soil Contamination
Low levels of petroleum related contaminants remain in soils at the AmeriPride site. Maximum levels of PCE in soil exceed the MPCA industrial SRV by a factor of eight, and the residential SRV by a factor of twenty-five. However, because the contaminated soil is contained under the site building, there is little possibility of regular direct contact with the soil by workers or visitors to the site. There is the potential for exposure by workers if the contaminated soil is excavated or disturbed for utility or other maintenance work below the building floor. The contaminated soil may also serve as a continuing source of both groundwater contamination and of VOC vapors in indoor air.

Groundwater Contamination
As stated previously, maximum levels of PCE in shallow groundwater on the AmeriPride property exceed the HRL by a factor of over 400. Levels of petroleum compounds, especially benzene, GRO, and DRO have exceeded HRLs and HBVs in the past. Levels of PCE in shallow groundwater across the street on the Hibbing Public Utilities property are lower; PCE levels exceed the HRL by a factor of 3.5 in one push-probe water sample. Detectable levels of benzene, GRO, and PCE and its breakdown products, including trichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and vinyl chloride have been found in monitoring well MW-4, downgradient from the source area and also on the Hibbing Public Utilities property. PCE typically dissolves into the groundwater as it moves downgradient from the source of the contamination. Dissolved PCE has been shown to be easily degraded under anaerobic conditions in the environment by microbes through a process known as reductive dehalogenation (ATSDR 1997). This process involves reactions where electrons are transferred between molecules, including contaminants and other molecules present in the aquifer, and are classified as oxidation/reduction (Redox) reactions. The mechanism under which PCE is biodegraded to vinyl chloride, and ultimately to ethene, is illustrated in Figure 7. Several of these breakdown products, including cis-1,2-dichloroethylene and vinyl chloride, are more toxic than PCE. It appears that the presence of steam pipes within the area of soil and groundwater contamination likely raises the average soil temperature. The effect of this elevated temperature on the biodegradation of PCE is unclear.

Levels of PCE in monitoring wells set in the clay layer (MW-1D, -2D, -3D, and -6D) have been as high as 190 µg/l in MW-1D, indicating that PCE is present at the base of the surficial aquifer. Petroleum related compounds have also been detected in these monitoring wells. The levels of PCE in the intermediate wells have at times slightly exceeded the levels in shallow wells, indicating a downward gradient may exist at least in the source area. PCE has not been detected in any of the intermediate wells outside of the source area. Low levels of PCE breakdown products have been detected in MW-3D, at the south end of the site, which is side-gradient to the assumed direction of groundwater flow.

As determined by groundwater elevation measurements, groundwater in the shallow aquifer appears to be moving in an east or northeast direction, toward the adjacent Hibbing Public Utilities plant. Underlying the basement of the plant is a drainage system consisting of perforated drain tile lines and sumps which is intended to prevent groundwater from infiltrating into the plant basement. The basement extends to a depth of 17 feet below grade, which is below the average surficial water table depth. Groundwater collected by the drain system is pumped to a sanitary sewer line. The system also collects process water from the utility operations, and it is not possible to separate the groundwater from the process water or determine the proportion of either in the discharged water (Braun 1998). The discharge is reportedly several thousand gallons per day according to the plant manager. One breakdown product of PCE, cis-1,2-dichloroethylene, was detected at a level of 5.8 µg/l in a sample collected from the drainage system. Groundwater samples collected from push probes and monitoring wells which are assumed to be downgradient from the utility plant (MW-6S and -6D, and probes DP-2 and -8) did not show detectable levels of PCE or its breakdown products in the shallow aquifer. Braun has concluded that, based on the groundwater data and the results of groundwater modeling they have conducted, that the basement drainage system beneath the Hibbing Public Utilities plant captures all of the groundwater flowing through the AmeriPride site in the shallow aquifer (Braun 1998). The system does not appear to be sealed; VOCs in groundwater collected by the system could volatilize into basement areas. Volatilization and simple dilution may account for the general lack of detection of VOCs in water samples collected from the sump.

Given the downward vertical gradient across the nested wells and the detections of PCE and its breakdown products in the wells screened in the clay layer, the potential exists for PCE to be present as a pool of DNAPL on the clay layer. Finding a DNAPL can be problematic. The lack of detection of PCE or its breakdown products in the regional aquifer indicates that even if DNAPL exists at the site, it is not impacting the regional aquifer.

Indoor Air Quality
The detection of VOCs in the indoor air of the AmeriPride building and adjacent Hibbing Public Utilities plant represent the main exposure pathway of potential concern at the site. Levels of VOCs, especially potentially carcinogenic VOCs, have been relatively consistent over the five monitoring events conducted to date. This appears to indicate that there is not much seasonal variation in the levels of VOCs entering the buildings. In most cases, the presence of frost in the winter months can greatly influence the migration of subsurface gases and vapors. Frost can act as a "cap," preventing VOCs from volatilizing from the soil surface and into the atmosphere. This can lead to a seasonal increase in VOC entry into buildings through such routes as foundation cracks, pipe entries, or floor drains. The drainage system beneath the Hibbing Public Utilities plant appears to be open to the indoor air in the plant basement, potentially allowing VOCs in the groundwater to volatilize to the indoor air.

The use of SUMMA canisters has been shown to be an effective method for the collection of ambient air samples for analysis of low levels of VOCs. The stability of collected mixtures of ambient gases can be affected by physical adsorption or absorption processes with the collection vessel, reactions with the chemicals in the collected sample, or instability of the compounds. The stainless steel construction of the SUMMA canisters minimizes physical adsorption and absorption processes. A recent study of the accuracy, precision, and storage stability of 194 VOCs collected in SUMMA canisters demonstrated percent mean recovery rates of 93.7% to123.8% for the eight carcinogenic VOCs of potential concern in indoor air at the site (Brymer et al 1996). The eight carcinogenic VOCs are benzene, chloroform, chloromethane, 1,2-dichloroethane, methylene chloride, PCE, trichloroethylene (TCE) and vinyl chloride.

To determine if the observed levels of carcinogenic VOCs observed in the basements of the AmeriPride and Hibbing Public Utilities buildings could represent an excess long-term cancer risk, MDH staff developed a set of screening criteria known as "acceptable air concentrations," or AACs. The AACs were developed using common risk assessment parameters. The equation, assumptions used, and results of the calculations are presented in Appendix 1. Standard workplace assumptions developed by the EPA were used, including a working day of 8 hours, a working year of 250 days, and a working lifetime of 25 years (EPA 1991). The acceptable lifetime excess risk level used was1 x 10-5, which is the default acceptable risk limit used in Minnesota. Due to the low concentrations of non-carcinogenic VOCs detected, AACs were not calculated for these compounds. The potential effects of exposure to these low concentrations of non-carcinogenic VOCs are expected to be minimal.

Toxicological data for the eight carcinogenic VOCs was obtained from standard reference sources, including the U.S. Environmental Protection Agency (EPA) Superfund Technical Support Center, and EPA's Integrated Risk Information System (IRIS) and Health Effects Summary Tables (HEAST). The standard measure of the potency of a potential human carcinogen is known as a "slope factor." The slope factors are normally based on toxicological information gathered through animal exposure studies, where specified doses of the contaminant are usually administered orally, rather than by inhalation. A number of adjustments are made to the slope factors to account for uncertainties and the differences between animals and humans. Oral slope factors were used in the calculation of the AACs due to a lack of available inhalation toxicity values. Because of the uncertainties involved, use of the AACs should be limited to simple screening for the identification of potential problem situations and not as a long-term air standard or site-specific criteria.

The average concentrations of the eight carcinogenic VOCs detected in indoor air in the basements of the two buildings over the five monitoring events conducted to date were used to calculate a potential lifetime cancer risk from exposure to the VOCs. The use of average concentrations is an appropriate approach given the relative consistency of the data over the five sampling events. The concentration of benzene was only measured over the first two sampling events, although again, levels of benzene were relatively consistent. Although not reported in the original data, upon further review Braun reported that vinyl chloride was not present in any of the five samples above the actual laboratory method detection limit for vinyl chloride of 0.5 µg/m3 (Braun 2000b). This value was used in the final calculation. Both benzene and vinyl chloride are included in the risk calculations due to the fact that there have been numerous detections of both benzene and vinyl chloride in soil and groundwater at the site, and due to their status as known human carcinogens.

The estimated excess lifetime cancer risk from exposure to VOCs in indoor air was 5 x10-5 for the AmeriPride basement, and 3 x 10-5 for the Hibbing Public Utilities plant basement. This indicates that a slight excess lifetime cancer risk may exist for workers who spend the majority of their workday in the basement spaces. Three VOCs, benzene, 1,2-dichloroethane, and vinyl chloride were responsible for the majority of the excess risk. The VOC samples were collected in the basements of the AmeriPride and Hibbing Public Utilities buildings over an 8-hour period to reflect the exposure of full-time workers in the basements. The basement of the AmeriPride building is used as a temporary office, and as such workers likely do not spend an entire shift there but use the area sporadically (Braun 1999). Workers in the Hibbing Public Utilities plant appear to spend only a limited time period per day in the basement areas. The estimated excess lifetime cancer risk likely therefore overestimates the actual risk depending on the amount of exposure occurring at the two buildings. It purposely represents a conservative, screening approach to account for the various uncertainties involved. An additional source of uncertainty is that the air samples could have picked up other sources of VOCs including truck exhaust in the AmeriPride building, and spray lubricants or cigarette smoke in the basement of the Hibbing Public Utilities plant, or other industrial products used at the two facilities.

Another consideration is the total amount of exposure by the general population to these contaminants. Exposure to these VOCs can occur through a number of pathways in a number of situations. They are present in the environment (in ambient air and water), and in our homes and workplaces (in products and building materials). Levels of PCE measured in ambient air have ranged from less than 1 µg/m3 to as high as 9.0 µg/m3, while levels above 100 µg/m3 have been measured in some industrialized areas (ATSDR 1997). Levels of PCE measured in indoor air in homes in Minnesota ranged from non-detect to 120 µg/m3 in a recent study conducted in part by MDH (Stroebel et al 1997).

For PCE especially, inhalation is the most critical exposure pathway (over water and soil) based on the behavior of PCE in the environment (McKone and Daniels 1991). Lifetime estimates of cancer risk from exposure to PCE in indoor air have been estimated to be as high as 1.4 x 10-2 based on measured concentrations in homes (Tancrede et al 1987). VOCs in indoor air may also contribute to respiratory hypersensitivity and be capable of triggering asthmatic symptoms, although this relationship is not well established (Becher et al 1996).

The exposure of workers at the two buildings to VOCs in and of itself may not represent an unacceptable risk. However, given the likely total exposure to these compounds by an individual on a daily basis, the additional involuntary exposure to the levels observed at the site could result in an individual's overall exposure exceeding an acceptable lifetime cancer risk level. In addition, there is some uncertainty over the presence of vinyl chloride at levels near its AAC (0.48 µg/m3). Workers exposed to levels of vinyl chloride at or just below the laboratory method detection limit for a full work shift may incur an excess potential lifetime risk of cancer from that exposure alone.

The workers at the site can do little to control or minimize their exposure if their work activities occur in the basement areas. In addition, because the VOCs are present in the building as a result of environmental contamination and not from commercial use, the employees have not received worker right-to-know training as specified by the Occupational Safety and Health Administration (OSHA). This training is designed to instruct workers on how to safely work with and minimize their exposure to chemicals in the workplace. Because the exposure is the result of environmental contamination, the use of occupational exposure limits is not appropriate at the site. OSHA's Permissible Exposure Limits (PELS) are included in Table 3 for comparison.

Due to their ability to migrate through soil in the vapor phase, especially in permeable soil or fill such as gravel, VOCs may have migrated some distance in directions from the site other than the direction of groundwater flow. Of special concern are the homes directly to the south of the AmeriPride property. Several sewer and utility lines run beneath the streets surrounding the site, to which the homes are likely connected. These utility lines are visible in Figure 2. Gravel or other permeable fill is often used as a base beneath and around utility lines to facilitate drainage and avoid frost damage. VOCs in the vapor state may be able to migrate along these utility lines and enter building basements through foundation cracks, pipe entries, or floor drains. Exposure to the levels of VOCs observed in indoor air at the site in a residential setting would very likely exceed the lifetime allowable cancer risk given the greater exposure frequency and duration. The high concentrations of known human carcinogens such as vinyl chloride in groundwater across a wide area of the site add to the concern that VOCs, volatilizing from the groundwater, could migrate along utility lines and reach other area homes or businesses. The source of the VOC vapors is not confined to the original VOC release site. In essence, the entire surface of the contaminated groundwater plume can act as a source of VOC vapors. The effective 'heating' of the soil by steam pipes radiating from the Hibbing Public Utilities plant may also increase volatilization of VOCs from the soil or groundwater.


AGENCY FOR TOXIC SUBSTANCE AND DISEASE REGISTRY (ATSDR) CHILD HEALTH INITIATIVE

ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children make them of special concern to communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances at waste disposal sites. They are more likely to be exposed because they play outdoors, and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children also weigh less, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification, management decisions, housing decisions, and access to medical care.

No exposure to VOCs in soil, groundwater, or indoor air by children is expected at the AmeriPride or Hibbing Public Utility buildings as they are primarily adult workplaces with little or no public spaces. Childhood exposure to VOCs in indoor air in residences located to the south of the AmeriPride property is possible if VOCs are volatilizing from contaminated soil or groundwater at the site, migrating through soil or along utility lines, and entering homes through pipe entries or foundation cracks.


CONCLUSIONS

  • Levels of VOCs in soil significantly exceed the MPCA's soil evaluation criteria for direct human contact. However, the contaminated soil is beneath the site building where the likelihood of human contact is minimal.

  • The shallow groundwater beneath the site is grossly contaminated with PCE and its breakdown products, at levels significantly in excess of the HRLs. Levels of vinyl chloride, a known human carcinogen, are many hundreds of times its HRL. Concentrations of VOCs in the shallow groundwater have varied widely, with no clear upward or downward trend. Petroleum related VOCs also continue to be detected at the site, although analyses for GRO and DRO have not been conducted since 1997.

  • The VOC contamination in the shallow aquifer appears to be intercepted by a sump system beneath the adjacent Hibbing Public Utilities plant, and is ultimately discharged to the sanitary sewer.

  • A downward vertical gradient across the aquifer units was found in nested wells installed at the site. Given the concentrations of PCE detected, and it's ability to sink within an aquifer, the presence of DNAPL cannot be ruled out. Sampling of the regional aquifer downgradient from the site has shown no contamination, however.

  • Indoor air samples collected using SUMMA canisters in the basements of the AmeriPride building and Hibbing Public Utilities plant show detectable levels of VOCs. Comparison of the maximum levels detected during five sampling events with conservative air screening concentrations developed by MDH demonstrates a lifetime cancer risk only slightly in excess of acceptable limits. Three compounds, benzene, 1,2-dichloroethane, and vinyl chloride were primarily responsible for the excess risk. Actual exposure to these levels of VOCs for an entire work day is likely not occurring given the reported and observed use of the basements. The source of some of the VOCs may be other processes or products in use at the two facilities.

  • The laboratory method detection limit for vinyl chloride was approximately equal to the air screening level developed by MDH. No detections of vinyl chloride above the method detection limit were observed. Thus, some uncertainty exists as to the risk from the presence of vinyl chloride in indoor air at the site.

  • The potential migration of gaseous VOCs along utility lines and/or through soil into other neighboring businesses or residences has not been evaluated.

  • For the reasons stated above, the site represents an indeterminate public health hazard.

RECOMMENDATIONS AND PUBLIC HEALTH ACTION PLAN

  • To help determine long-term trends in groundwater quality and verify that the sump system beneath the Hibbing Public Utilities plant is continuing to intercept the VOC contamination in the shallow aquifer, groundwater samples should be collected from the permanent monitoring wells installed at the site on a regular basis.

  • The construction of the footing drainage and sump system at the Hibbing Public Utilities plant should be evaluated to determine if it is indeed open to the indoor air, and if so it should be sealed if possible to limit volatilization of VOCs from the groundwater to indoor air.

  • The discharge of VOC contaminated water should be conducted according to state and federal regulations and according to the requirements of the local waste water treatment plant.

  • The basements and first floors of the AmeriPride and Hibbing Public Utilities buildings should be carefully inspected for cracks, broken floor drain pipes, or other potential points of vapor entry. All such entry points should be sealed, and inspected regularly. To determine if the sealing efforts are successful, continued monitoring of indoor air in the basements should be conducted.

  • All future indoor air sample analyses should include benzene, and detection limits for vinyl chloride should be as close to the AAC as possible.

  • At least one groundwater sample from each monitoring well should be analyzed for GRO and DRO to determine the extent of residual petroleum contamination.

  • To determine if VOC vapors are migrating along utility lines or other routes, at least one, and preferably several indoor air samples (using SUMMA canisters) should be collected in the basements of all structures immediately adjacent to the AmeriPride property. Alternately, soil gas samples could be collected to determine if vapor migration through soils near adjacent structures is actually occurring.

  • If the soil and groundwater contamination at the site is not remediated, land use restrictions should be considered to ensure that future exposures to VOCs in soil, groundwater, and indoor air at the site will continue to be limited.

  • MDH's Public Health Action Plan for the site consists of continued consultation with MPCA staff and representatives of AmeriPride and the city of Hibbing on the air and groundwater monitoring and the groundwater collection sump, as well as participation in any planned public outreach activities.

REFERENCES

Agency for Toxic Substance and Disease Registry (ATSDR) 1997. Toxicological Profile for Tetrachloroethylene. September 1997.

Becher, R., Hongslo, J.K., Jantunen, M.J., Dybing, E. 1996. Environmental chemicals relevant for respiratory hypersensitivity: the indoor environment. Toxicology Letters 86: 155-162.

Braun Intertec Corporation 1995. Phase I Environmental Site Assessment Update. September 13, 1995.

Braun Intertec Corporation 1997. Phase II Environmental Site Assessment. July 23, 1997.

Braun Intertec Corporation 1998. Results of Supplemental Investigation, Phase II Environmental Site Assessment. May 19, 1998.

Braun Intertec Corporation 1999. Annual Progress Report. October 11, 1999.

Braun Intertec Corporation 2000a. Annual Monitoring Report. November 8, 2000.

Braun Intertec Corporation 2000b. Correspondence from Don Huff to Jane Mosel and Mark Koplitz of the MPCA, dated January 27, 2000.

Brymer, D.A., Ogle, L.D., Jones, C.J., Lewis, D.L. 1996. Viability of using SUMMA polished canisters for the collection and storage of parts per billion by volume level volatile organics. Environmental Science & Technology 30: 188-195.

EPA 1991. Risk Assessment Guidance for Superfund, Volume I Supplemental Guidance on Standard Default Exposure Factors. Office of Emergency and Remedial Response. March, 1991.

McKone, T.E., Daniels, J.I. 1991. Estimating human exposure through multiple pathways from air, water, and soil. Regulatory Toxicology and Pharmacology 13: 36-61.

MGS 1997. Minnesota Geological Survey, County Well Index. November 1997.

MOP 2000. Minnesota Office of Planning, State Demographic Center. Online - http://www.mnplan.state.mn.us/demography/docu_est.html#download. February 2000.

Stroebel, C., Pellizzari, E., Quackenboss, J.J. 1997. Sources and concentrations of volatile organic chemicals in homes with children. Unpublished.

Tancrede, M., Wilson, R., Zeise, L., Crouch, E.A.C. 1987. The carcinogenic risk of some organic vapors indoors: a theoretical survey. Atmospheric Environment 21: 2187-2205.


PREPARERS OF THE REPORT

James Kelly, M.S.
Health Assessor
Site Assessment and Consultation Unit
Minnesota Department of Health
tel: (651) 215-0913

Alan W. Yarbrough
Technical Project Officer
State Programs Section
Superfund Site Assessment Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry


GLOSSARY

Absorption:
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.


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.


ATSDR:
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.


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


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


CERCLA:
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.


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.


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


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


Contaminant:
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.


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


Dose:
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.


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


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 chemcials 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.


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


Exposure:
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.


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


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).


HRL:
Health Risk Limit. Groundwater quality criteria developed by MDH. Represents the concentration of a single contaminant, or a mixture of contaminants, that can safely be consumed daily in drinking water for a lifetime.


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.


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


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


LOAEL:
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.


MDH:
Minnesota Department of Health. Minnesota's public health agency.


MPCA:
Minnesota Pollution Control Agency. Minnesota's environmental enforcement agency.


MRL:
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, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.


NOAEL:
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.


PHA:
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.


PID:
Photo Ionization Detector. A device for measuring the concentration of total organic vapors in air via ionization with ultra violet light.


Plume:
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.


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


PRP:
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.


Public Health Assessment(s):
See PHA.


Public Health Hazard Criteria:
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


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, life-time 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.


SARA:
The Superfund Amendments and Reauthorization Act in 1986 amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from chemical exposures at hazardous waste sites.


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


Sample:
A smallnumber 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.


SLV:
Soil Leaching Value. Estimated concentration of a contaminant in soil that will not likely, through typical leaching processes, contaminate underlying ground water.


SRV:
Soil Reference Value. Estimated concentration of a contaminant in soil that will not likely pose a potential human health concern through exposure via ingestion, inhalation, and dermal contact.


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


Survey:
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 effect of the chemicals acting together are greater than the effects of the chemicals acting by themselves.


Toxic:
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.


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


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


Uncertainty Factor:
See Safety Factor.


UST:
Underground Storage Tank. A large tank often used for the storage of gasoline, fuel oil, solvents or other liquids.


VOC:
Volatile Organic Compound. Generally, an organic compound that easily volatilizes from soil or water.

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