PUBLIC HEALTH ASSESSMENT
DAVIS PARK ROAD TCE
GASTONIA, GASTON COUNTY, NORTH CAROLINA
The Davis Park Road Trichloroethene (TCE) site is located in the southwestern part of Gastonia, North Carolina, along Davis Park Road, south of Hudson Boulevard and north of Blackwood Creek. Groundwater at the site was contaminated with volatile organic compounds (VOCs), including TCE and tetrachloroethene (PCE). These compounds reportedly originated from contaminated soil behind a local auto repair shop. Groundwater contamination was detected in a number of private wells in the area. Residents have been provided with filters for their private wells or put on the municipal water system.
Based on available information, the Agency for Toxic Substances and Disease Registry has concluded that the Davis Park Road TCE site warrants no health concerns at this time. Residents are no longer drinking contaminated water, and levels of contaminants in soil are too low to cause health effects. In the past, the maximum levels of TCE detected in well water exceeded regulatory standards and could have increased the risk of health effects if that water was used for drinking for many years.
ATSDR recommends that the Environmental Protection Agency (EPA) continue monitoring the groundwater at the site to confirm that contaminant levels are decreasing.
The Davis Park Road Trichloroethene (TCE) site was proposed for the National Priorities List (NPL) on July 28, 1998 and listed on January 19, 1999. The Agency for Toxic Substances and Disease Registry (ATSDR) is required by Congress to conduct public health assessments on all sites proposed for the NPL. In this public health assessment, ATSDR evaluates the public health significance of the Davis Park Road TCE site. ATSDR has reviewed available environmental data, potential exposure scenarios, and community health concerns to determine whether adverse health effects are possible. In addition, this public health assessment recommends actions to prevent, reduce, or further identify the possibility of site-related adverse health effects.
This site description comes from reports provided by the Environmental Protection Agency (EPA) [1,2,3]. The Davis Park Road TCE site ("the site") includes approximately 20 acres of residential homes and private businesses in unincorporated Gaston County, southwest of the city of Gastonia, North Carolina. The site consists of contaminated soil behind an automobile transmission shop (Davis Park Auto Repair) located at 2307 Davis Park Road, and contaminated groundwater emanating from this property and extending south along Davis Park Road to Blackwood Creek. Another potential source of contamination is gasoline leaking from underground storage tanks at Godwin Refrigeration, located approximately 150 feet north of Davis Park Auto Repair. Residences are present above the entire extent of contaminated groundwater. A majority of the houses within the site area obtained water from private or community wells. Tetrachloroethene (PCE), TCE, 1,1-dichloroethene (1,1-DCE), chloroform, and methyl tert-butyl ether (MTBE) are the groundwater contaminants of concern identified in EPA's record of decision (ROD) for this site. [3].
The topography of the area is slightly sloped to the west toward Crowders Creek and to the east and south towards Blackwood Creek. Both creeks are receiving streams for groundwater in the area.
Contamination at the site was discovered in March 1990, when a routine groundwater sample collected from the Cedar Oak Park community well by the Gaston County Environmental Health Department (GCEHD) was found to contain volatile organic compounds (VOCs), including TCE, PCE, and chloroform. Follow-up sampling of community and private wells confirmed the contamination and showed that the highest TCE concentrations were near Davis Park Auto Repair [1].
From May 1990 to January 1994, a series of soil and groundwater investigations were conducted at the site by EPA, North Carolina Department of Environment, Health and Natural Resources (DEHNR), and Gaston County [1,3,4]. The results suggested that PCE, and possibly TCE, had been released sometime in the past through a drainpipe behind Davis Park Auto Repair and that these contaminants and their breakdown products had moved through the soil into the underlying groundwater [1,3,4].
From May 1996 through April 1998, EPA conducted a remedial investigation (RI) to assess the nature and extent of site contamination. Results indicated minimal soil contamination (primarily petroleum-related VOCs) behind Davis Park Auto Repair. In addition, VOCs in area wells were found to be less numerous and at generally lower levels than in the previous studies. In the wells closest to the auto shop, which initially had the highest contaminant levels, VOCs were no longer detectable [1,3].
In September 1998, EPA issued a ROD for the site. In the ROD, EPA presented its selected remedial alternative for the site. The remedy included connection of homes, churches, and businesses in the site area to the Gastonia municipal water system, optional installation of carbon filters on private wells that have been affected by site contamination, and monitored natural attenuation of the groundwater contamination, which is decreasing through dispersion and intrinsic biodegradation (breakdown by naturally occurring microorganisms). The groundwater will be tested for contamination on a quarterly basis for 3 years and annually for 27 years. Monitoring will be discontinued when groundwater contamination has declined to below drinking water standards as specified in the ROD [3].
During the remedial design, a natural attenuation study was conducted to confirm that the contaminant plume is naturally attenuating. A contingency remedy for active pumping and treatment of the contaminated groundwater plume was provided for in the ROD, should the results of groundwater sampling fail to confirm natural attenuation. In a September 25, 2000, memorandum report, EPA confirmed that natural attenuation was occurring at the site and that remedial goals would be achieved [5].
On-site construction was initiated on May 15, 2000. A total of 63 residences were connected to the Gastonia municipal water system and are now receiving water from that system. EPA installed carbon filters at 5 residences where the homeowners did not agree to be connected to the public water supply system. Two residents with private wells in the affected area chose not to receive either public water or a carbon filter. EPA also physically abandoned 19 private wells by plugging them with a cement grout. Construction was determined to be complete on September 27, 2000 [5].
Demographic information is shown in Figure 1. The population of Gaston County was estimated to be approximately 178,000 in 1995, with a 1990 population density of about 490 persons per square mile. From 1980 until 1990, the county experienced a population increase of 15.3%. The city of Gastonia, the largest municipality in Gaston County, had a 1990 population of nearly 55,000 [1,3].
According to 1990 U.S. Census information, an estimated 5,264 people lived within a one-mile radius of Davis Park Auto Repair. Approximately 69% of the population was white, 30% was black, and less than 1% was of another racial or ethnic group.
The predominant land use in the immediate vicinity of the site is residential. Two of the larger neighborhoods are the Cedar Oak Park subdivision and the Hedgewood Circle area. Although most of the site is outside the Gastonia city limits, it is still under city jurisdiction. The only commercial operations within the site boundary are Davis Park Auto Repair and Godwin Refrigeration. Several churches are also located within the site boundary [1,3,5].
Before the remedial action, approximately 120 residences in the Davis Park Road area were served by the Gastonia municipal water system. These 120 residences included 26 homes in the Cedar Oak Park subdivision that were served by two community supply wells until February 1998, when they were connected to the municipal water system. The water source for the municipal system is Mount Island Lake, located east-northeast of the city [1].
The remaining 170 residences in the site area used private or community wells for their household water needs. These wells range from 80 to over 250 feet in depth [1,4]. Groundwater is present in a deep aquifer in fractured bedrock more than 80 feet below ground surface (bgs) and in a shallow aquifer above a weathered rock layer ranging from 10 to 80 feet bgs. Because interconnection is likely, groundwater (and contaminants) can be transferred from one aquifer to the other [1,4].
At the site, groundwater generally flows toward the south or southeast and discharges to Blackwood Creek along the eastern and southeastern edge of the site. However, local groundwater flow, and therefore movement of contaminants, is also influenced by fractures in the rock layers and operation of area water supply wells. Measurements of hydraulic conductivities suggest that groundwater moves most easily in the weathered rock of the shallow aquifer [1]. Davis Park Auto Repair is believed to be located within a localized groundwater high area so that groundwater flows away from the property in a semi-circular pattern [1].
The nearest surface water to the site is Blackwood Creek, located about 2,500 feet south of Davis Park Auto Repair. The creek flows along the south and southeast borders of the site and into Crowders Creek, approximately 3,500 feet south of Davis Park Auto Repair. According to published reports, Crowders Creek is not used for recreational purposes, except for very limited bridge fishing several miles downstream of the site [1].
Several investigations of groundwater and soil from the site have been conducted. The data evaluated in this report include results from the following studies.
Appendix A contains details on the groundwater and soil samples evaluated. ATSDR's review of the data reports indicated that appropriate quality control measures were taken in the preparation of the analytical data. The conclusions reached in this document are based on the data listed above and may be modified if new environmental data become available.
ATSDR visited the site(1) to better understand the physical setting of the site and its relationship to the people living and working nearby. During the site visit, the following observations were made:
The process by which ATSDR evaluates the possible health impact of contaminants is summarized here and described in more detail in Appendix B. ATSDR uses comparison values (CVs) to determine which chemicals to examine more closely. CVs are concentrations of chemicals in the environment (air, water, or soil) below which no adverse human health effects should occur. Exceeding a CV does not mean that health effects will occur, just that more evaluation is needed.
If the level of contamination at the site is greater than the CV, further evaluation will focus on identifying which chemicals and exposure situations could be a health hazard. Child and adult exposure doses are calculated for the exposure scenario of interest. Exposure doses are the estimated amounts of a contaminant that people come in contact with under specified exposure situations. These exposure doses are compared to appropriate health guidelines for that chemical. Health guideline values are considered safe doses; that is, health effects are unlikely below this level. If the exposure dose for a chemical is greater than the health guideline, then the exposure dose is compared to known health effect levels identified in ATSDR's toxicological profiles. If the chemical of concern is a carcinogen, the cancer risk is also estimated. These comparisons are the basis for stating whether or not the exposure presents a health hazard. More information on these calculations is provided in Appendix C.
Exposure Pathways and Contaminants of Concern
The following sections describe the various ways people could come into contact with contaminants at the site. Each of these is called an exposure pathway. Appendix D summarizes the possible exposure pathways. If people are unlikely to be exposed to contaminants in a given pathway, then that pathway will not be evaluated further for human health risks.
Contaminants have been detected in the groundwater beneath the site. People drinking this groundwater could be exposed to these contaminants. For this analysis, we considered water sampling results from private wells and from converted former residential wells collected during the RI [1]. The converted residential wells were included with the monitoring well section of the RI, but we treated them as drinking water wells in this document since people once used them for drinking purposes. Data from the other monitoring wells were not considered since contaminant concentrations measured in monitoring wells were in the same range as the drinking water wells and people do not generally drink water from monitoring wells. Table 1 lists the contaminants of concern, compounds that were detected at least once above the corresponding CV.
Table 1. Well Water Contaminants Detected Above Drinking Water Comparison Values
| Contaminant | Concentration Range in parts per billion (ppb) | Frequency of Detection / Total | Comparison Value (CV) in ppb | CV Source1 |
| Benzene | ND - 26 | 3 / 97 | 5 / 0.6 | MCL2 / CREG3 |
| Bromodichloromethane | ND - 6 | 1 / 97 | 200 / 0.6 | EMEG4 / CREG |
| Chloroform | ND - 40 | 1 / 97 | 100 / 6 | EMEG / CREG |
| Dibromochloromethane | ND - 0.6 | 1 / 97 | 300 / 0.4 | EMEG / CREG |
| Dichloroethane | ND - 0.6 | 2 / 97 | 2000 / 0.4 | EMEG / CREG |
| 1,1-DCE | ND - 4 | 3 / 97 | 90 / 0.06 | EMEG / CREG |
| MTBE | ND - 5096 | 5 / 97 | 200 | LTHA5 |
| PCE | ND - 24 | 18 / 97 | 5 | MCL |
| TCE | ND - 134 | 43 / 97 | 5 | MCL |
| Source: [1] 1 These comparison values are described in Appendix B. 2 MCL = maximum contaminant level 3 CREG = cancer risk evaluation guide. 4 EMEG = environmental media evaluation guide. 5 LTHA = lifetime health advisory |
||||
Next, exposure doses were calculated for the contaminants of concern in Table 1. The worst case was assumed to be a one-year-old child weighing 11 kilograms (kg) drinking one liter per day of water containing the maximum concentration of each contaminant for 350 days out of the year [7]. The exposure dose estimated through this procedure was compared with health guideline values and toxicological information for the contaminant of concern. For evaluating the risk of cancer, we assumed that adults weighing 70 kg would be exposed to the maximum concentration of each contaminant for 350 days a year for the 34 years that contamination was possible (from 1966, when the auto repair shop opened, to 2000, when homes were connected to the municipal water system). This dose was multiplied by 2 to account for additional dermal and inhalation exposure during showering [8]. When this analysis was performed, doses for benzene, bromodichloromethane, chloroform, dibromochloromethane, 1,1-DCE, and PCE were found to be lower than the applicable noncancer health guidelines and/or within EPA's acceptable cancer risk range (less than 1×10-4) and were dropped from further consideration [9,10,11,12,13,14,15,16,17,18].
Details of the calculations and tables containing the calculated exposure doses and excess cancer risks are included in Appendix C. The following sections describe the evaluation of the remaining contaminants of concern from Table 1.
MTBE
The child exposure dose calculated using the highest concentration of MTBE measured in drinking water is 1.5 times higher than the intermediate oral minimal risk level (MRL) [16]. This MRL is based on a lowest observed adverse effect level (LOAEL) of 100 mg/kg/day in studies on rats [16]. At the LOAEL, kidney function effects were observed. No health effects are expected from this exposure because the calculated dose is 250 times smaller than the LOAEL. However, people drinking water containing MTBE at levels higher than about 20 parts per billion (ppb) might detect unpleasant tastes and odors from the MTBE in their water [19].
The International Agency for Research on Cancer (IARC) has determined that MTBE is not classifiable as a human carcinogen [20]. There is insufficient evidence that it causes cancer in humans and only limited animal data [20]. No evaluation of cancer risk was performed.
TCE
The child exposure dose calculated using the highest concentration of TCE measured in drinking water is 0.01 milligrams per kilogram per day (mg/kg/day). Animal studies have shown effect levels several orders of magnitude higher than this dose [18]. However, some epidemiologic studies have suggested that drinking TCE at levels similar to the maximum at this site for long periods is associated with skin problems, liver and kidney damage, impaired immune system function, and impaired fetal development in pregnant women [18]. These studies are controversial because there were other contaminants present in the water which may have caused the observed health effects, some studies had too few people in them, and TCE effect levels were not well-defined [18]. Although still unlikely, if people drank the most highly contaminated water at the site for several years, they may have an increased risk of the above health effects.
The International Agency for Research on Cancer (IARC) has determined that TCE is a probable human carcinogen [20]. EPA is currently reviewing the cancer slope factor for this substance [21]. Assuming a person drank 2 liters of water containing TCE at the maximum concentration every day for the entire 34 years that contamination was possible (from 1966 to 2000), and assuming a conservatively high cancer slope factor of 0.4 (mg/kg/day)-1, the predicted increased risk of cancer would be low to moderate.
ATSDR also considered how concurrent exposure to the other chemical contaminants in addition to TCE in well water may have affected people. Because the worst case scenario (long-term exposure to the maximum level) showed no adverse health effects were expected for the other individual contaminants, the presence of other contaminants is not expected to have a significant additive effect to the risk of health effects from TCE. In addition, the increased risk of cancer from cumulative exposures is not considered to be of concern because of the low risks calculated for the individual contaminants and the conservative assumptions described above.
Many wells on the site had contaminant levels much lower than the maximums discussed above, too low to cause health effects. Homeowners at the site have been informed of the results of testing of their wells, and all but two homes were connected to the Gastonia municipal water system or had carbon filters installed on their wells, effectively disrupting this exposure pathway [5]. It is impossible to tell whether past exposures could lead to the above long-term health effects without more specific information about how long people were drinking contaminated water and the levels of contaminants in each well over time. The risk to the residents who chose not to receive either public water or a carbon filter depends on the actual contaminant levels in their wells and their specific exposure scenario. Sampling by EPA showed reductions of contaminants in the groundwater over time, indicating that these contaminants are being naturally attenuated [5]. Therefore, while the well water pathway could have posed a public health hazard in the past, since the pathway has been disrupted it is not considered to pose a current public health hazard.
People on the site could come into direct contact with contaminants in soil. They could get contaminated soil on their skin, or they might accidentally eat or breathe in soil particles. Table 2 lists the contaminants that were found in the soil on site at levels above soil CVs. Only surface soil samples were considered, since people would not normally come in contact with soil beneath the ground surface.
Table 2. Soil Contaminants Above Soil Comparison Values
| Contaminant |
Concentration Range in parts per million (ppm) |
Frequency of Detection / Total | Comparison Value (CV) in ppm | CV Source1 |
| Arsenic | ND - 15 | 7 / 7 | 20 / 0.5 | EMEG2 / CREG3 |
| Lead | 20 - 630 | 7 / 7 | 400 | SSL4 |
| Source: [1,3,4] 1 These comparison values are described in Appendix B. 2 EMEG = environmental media evaluation guide. 3 CREG = cancer risk evaluation guide. 4 SSL = EPA soil screening level. |
||||
Although initial investigations had shown significant levels of PCE, TCE, and DCE (a PCE/TCE breakdown product) in soils behind the auto repair shop, all data presented in the RI report showed nondetectable levels of these contaminants in surface soils, indicating that they had already broken down or volatilized [1]. In addition, the below ground surface samples showed significant reductions in contaminants over time, indicating that these contaminants were being naturally attenuated [1]. None of the volatile contaminants were present at levels above CVs [1].
Exposure doses were calculated for the contaminants of concern in Table 2. The worst case was assumed to be a 10-year-old child (36.3 kg average weight) contacting the maximum concentration of each contaminant all day for 52 days out of the year (once a week) [7]. The exposure dose estimated through this procedure was compared with health guideline values and toxicological information for the contaminant of concern. For evaluating the risk of cancer, we assumed adults weighing 70 kg would be exposed to the maximum concentration of each contaminant for 52 days a year for a lifetime (70 years). When this evaluation was performed, the exposure dose for arsenic was below applicable cancer and noncancer health guidelines and it was dropped from consideration [22]. For lead, the blood lead level increase predicted in a worst-case scenario was below health guidelines, and it was also dropped from consideration [23]. Therefore, the surface soils are not considered to pose a health hazard. Details of the calculations and tables containing the calculated exposure doses and excess cancer risks are included in Appendix C.
Water from surface runoff on the site may pick up contaminants from soils, sediments, or groundwater. No use of this water for drinking water purposes was identified, but people who live on or visit the site might accidentally ingest some of the surface water or get it on their skin while wading or swimming in the creeks or ponds on site. Nine surface water samples were collected from Blackwood Creek and Crowders Creek downstream of the auto repair shop during the RI. No contaminants were detected in any surface water sample [1,3]. Because there are no contaminants present, the surface water pathway is considered incomplete.
People who live on or visit the site might accidentally ingest some of the sediments from the ponds or streams on the site or get them on their skin while wading or swimming there. Six sediment samples were collected from the creek near the site. No compounds were detected above screening levels [1]. The sediment pathway is therefore considered incomplete.
ATSDR recognizes that infants and children may be more vulnerable to exposures than adults in communities faced with contamination of their air, water, soil, or food. This vulnerability is a result of the following factors:
Because children depend completely on adults for risk identification and management decisions, ATSDR is committed to evaluating their special interests at the site as part of the ATSDR Child Health Initiative.
The major exposure routes for children living on the site are ingestion of drinking water and ingestion of surface soil. Please refer to the appropriate sections of this report for discussions of the possible health effects for children.
The Superfund law requires that health outcome data be considered in a public health assessment. Health outcome data may include mortality information (the number of people dying from a certain disease) or morbidity information (the number of people in an area getting a certain disease). In order to thoroughly evaluate health outcome data as it relates to a hazardous waste site, the following elements are necessary: (1) the presence of a completed human exposure pathway, (2) sufficiently high contaminant levels to result in measurable health effects, (3) sufficient number of people in the completed pathway for the health effect to be measured, and (4) a health outcome database in which disease rates for populations of concern can be identified.
The site does not meet the requirements for including an evaluation of health outcome data in a public health assessment. Although completed human exposure pathways existed at this site, those pathways have been disrupted and the former contaminant levels, exposures, and exposed population are not great enough to result in a meaningful measurement of health outcome data.
Community Health Concerns and Public Comments
On March 25, 1999, ATSDR staff held a public availability session at the Taylor Memorial Baptist Church to gather community concerns about the Davis Park Road TCE site. Approximately 21 people attended the session, including 18 residents and 3 city or county officials. Most of the residents were interested in finding out what ATSDR was doing at the site and in getting information about TCE and PCE, two of the major groundwater contaminants associated with the site. Some of the residents asked whether their well water was safe and some suggested that we contact the Gaston County Health Department or EPA to obtain the sampling data for their wells. Residents who asked about the status of EPA's plans and activities for the site were referred to the EPA remedial project manager.
A few of the residents indicated that they were experiencing health problems and wondered if they were related to the site. The specific concerns raised and ATSDR's responses are detailed below.
Concern: What are the long-term health effects for children and adults who drank private well water shown to contain site-related contaminants?
Response: It is unlikely that people will exhibit health effects from drinking well water from the site. If a person drank water with the highest concentration of TCE for several years, they would have an increased, although still very small, risk of health effects. See the discussion of the well water pathway on page 7 of this document.
Concern: Did the contaminants in private well water cause brain tumors, lung cancer, and other health problems, including headaches, chronic cough, sinusitis, bronchitis, cysts, skin and intestinal disorders in residents at the site?
Response: Some epidemiologic studies have suggested that exposure to TCE in drinking water can cause health effects, but the studies are controversial because of their limitations. In addition, we do not know enough about past contaminant levels in people's well water and how much well water those people were drinking to determine the risk for health effects. Based on the available data, however, it is unlikely that any people were exposed to contaminants at high enough levels for a long enough time to result in health effects.
Concern: Can't the government close down the Davis Park Auto Repair shop and remove the junk cars leaking oil in my neighbor's backyard?
Response: ATSDR is a non-regulatory, public health agency and does not have any authority to close down the auto repair shop or remove junk cars from residential properties. ATSDR suggests that these issues be discussed with the local zoning authority.
During the March 1999 site visit, ATSDR staff also contacted local health officials to gather additional information regarding health concerns about the site. These officials indicated that few residents had expressed health concerns about the Davis Park Road site contamination.
In addition to the March 1999 availability session, the Davis Park Road TCE Public Health Assessment was available for public review and comment from August 23 to March 25, 2002, at the Gaston County Public Library in Gastonia, NC. The public comment period was announced in local newspapers, and fact sheets announcing the availability of the public health assessment were mailed to residents near the site. The PHA was also sent to several federal, state, and local officials. The following written comments were received.
(from North Carolina Department of Environment and Natural Resources)
Comment:
Page 8, first paragraph, last line: The statement that the risk calculations are overly conservative is too strong based on the arguments that follow. The arguments that "most wells did not contain the maximum concentration contaminants", and "contaminant levels probably varied over time" ignore the fact that contaminant levels were only monitored at this site for 12 of the 34 years of its potential existence. Prior to contamination discovery in 1990, there may have been periods when people were exposed to water from these wells that had contaminant levels greater than have been detected in the last 12 years. While there are many other areas in risk assessment that are biased towards conservatism, there is too much uncertainty in the two arguments presented above to support such a strong statement. A similar argument is made on page 9, TCE, end of second paragraph.
Response:
ATSDR agrees that there is not enough past information to make the statements listed in the above comment. These statements have been removed from the document.
(from a former site resident, paraphrased)
Comment:
Concerns expressed over contaminated well water causing stomach, muscle, bone, and heart problems.
Response:
Some epidemiologic studies have suggested that exposure to TCE in drinking water can cause health effects, but the studies are controversial because of their limitations. In addition, we do not know enough about past contaminant levels in people's well water and how much well water those people were drinking to determine the risk for health effects. Based on the available data, however, it is unlikely that any people were exposed to contaminants at high enough levels for a long enough time to result in health effects.
People may have been exposed in the past to levels of TCE that exceeded regulatory guidelines and may have slightly increased the risk of health effects. Therefore, ATSDR considers the Davis Park Road TCE site a past public health hazard (as defined in Appendix E).
Because people are no longer drinking contaminated water from the site and because contaminant levels in soil are too low to cause health effects, ATSDR considers the Davis Park Road TCE site to currently pose no apparent public health hazard (as defined in Appendix E).
The public health action plan for the Davis Park Road site contains a description of actions that have been or will be taken at the site by ATSDR and/or other government agencies. The purpose of the plan is to ensure that this public health assessment not only identifies public health hazards at the site, but also outlines a plan of action to prevent or minimize the potential for adverse human health effects from exposure to site-related hazardous substances. ATSDR will follow up on this plan to ensure that it is implemented.
Actions Completed
Planned Actions
ATSDR will reevaluate and expand the public health action plan if needed. New environmental, toxicological, or health outcome data or the results of implementing the above proposed actions may determine the need for additional actions at this site.
Authors of Report
Jill J. Dyken, Ph.D., P.E.
Environmental Health Scientist
Division of Health Assessment and Consultation
Moses Kapu, Ph.D.
Environmental Health Scientist
Division of Health Assessment and Consultation
Stephen Richardson, P.E.
Environmental Health Engineer
Division of Health Assessment and Consultation
Regional Representative
Robert Safay
Senior Regional Representative
ATSDR Region IV
Community Involvement
Youlanda Outin
Community Involvement Specialist
Division of Health Assessment and Consultation
Health Educator
Stephen Blackwell
Health Education Specialist
Division of Health Education and Promotion
..APPENDIX A. GROUNDWATER AND SOIL SAMPLING DETAILS
Private well sampling
From May 1990 to July 1993, approximately 26 private and community wells in the site area, including the Cedar Oak Park community well, were sampled by EPA, the state of North Carolina, and Gaston County. At least 14 of the samples contained detectable levels of TCE and/or PCE. The highest TCE and PCE levels were generally found in the Cedar Oak Park community well and in wells close to and down gradient (south and southeast) of the Davis Park Auto Repair shop. VOCs normally associated with gasoline contamination, such as benzene and MTBE, were found in two wells just west of the auto repair shop. The presence of benzene and MTBE in these wells may be attributed to gasoline contamination from the Godwin Refrigeration property, which is located within a few hundred feet of the wells [1,4,6].
During the January 1994 expanded site investigation by the state of North Carolina, 5 private wells near the auto repair shop that had previously been found to contain VOCs were sampled. The sampling results showed TCE and PCE, along with traces of other VOCs, in several of the wells. The highest TCE and PCE levels were found in the Cedar Oak Park community well. In general, the contaminant levels were lower than those found in previous years [4].
In May 1996, during Phase I of the RI field activities, groundwater samples were collected for VOC analysis from 29 residential wells in the site area. The well locations are shown in Figure 5. VOCs were detected in several of the wells, including the Cedar Oak Park community well, which again had the highest levels of TCE and PCE. Most of the wells closest to the auto shop (historically among the most contaminated area wells) showed little contamination. Samples from 4 of the wells were also analyzed for metals. A number of metals were detected in these samples, but the levels do not exceed health CVs [1,3].
In February 1998, during Phase III of the RI, groundwater samples were collected from 3 private water supply wells in the site area. PCE was detected in 1 well, and TCE was found in all 3 wells. Among the 3 wells, the lowest TCE level (about half the May 1996 level) was found in the well closest to the auto shop. No other VOCs were detected in the 3 wells [1,3].
Monitoring Well Sampling (includes converted former residential wells)
In May 1996, during Phase I of the RI field activities, groundwater samples were collected from 2 existing monitoring wells at the Davis Park Auto Repair shop. No VOCs, pesticides, or PCBs were detected in either of the wells. Various metals were detected in both wells, but the levels do not exceed health CVs [1,3]. RI Phase II groundwater samples were collected in October 1996 from temporary monitoring wells installed at 3 locations on the Davis Park Auto Repair property and at one location southeast of the shop near Blackwood Creek. Low levels of TCE and toluene were detected in 2 of the monitoring wells on the auto shop property [1,3].
In January 1998, during Phase III of the RI, groundwater samples were collected from the 2 existing monitoring wells at the Davis Park Auto Repair shop; 9 newly installed monitoring wells southeast, south, southwest, and west of the auto shop; and 6 former residential wells which had been converted to monitoring wells. Several VOCs, including PCE, TCE, and MTBE, were detected in the wells. The highest PCE and TCE levels were detected at the former Cedar Oak Park community well, while the highest MTBE concentrations were found in a former residential well west of the auto shop. MTBE in the former residential well may have been associated with gasoline contamination from the nearby Godwin Refrigeration operation, located about 150 feet north of the auto shop. According to published documents, releases from the Godwin Refrigeration property, where two underground storage tanks (USTs) were used to store gasoline until 1992, were responsible for contamination of nearby private wells with gasoline-type contaminants [1].
In April 1998, during Phase III of the RI, an additional groundwater sample was collected from a soil boring adjacent to the auto shop. Only low levels of MTBE were detected [1,3].
Soil
From May 1990 to August 1992, the NCDENR sampled soils around the Davis Park Auto Repair shop several times. These samples showed significant levels of PCE, TCE, and DCE (a PCE/TCE breakdown product) in soils behind the shop near a drainpipe that exited the shop's service bays [1].
During a January 1994 expanded site investigation, the State of North Carolina sampled soils near the drainpipe behind the Davis Park Auto Repair shop. The sampling results showed TCE, DCE, and petroleum-type VOCs (toluene, ethyl benzene, and xylene) in the soils around the drainpipe. However, the TCE and DCE soil levels were significantly lower than the 1990-1992 levels [1,3,4].
In May 1996, during Phase I of the EPA RI field activities, 6 surface soil (0 to 6 inches below ground surface [bgs]), and 9 subsurface soil samples were collected from the auto shop property and analyzed for VOCs, semi-volatile organic compounds (SVOCs), pesticides, PCBs, and metals. No organic contaminants were detected in the surface samples except low levels of the pesticide dieldrin in one sample. Petroleum-type VOCs (ethyl benzene, toluene, and xylene) and a number of SVOCs were detected in 2 of the subsurface soil samples, and the pesticide toxaphene was detected in one subsurface sample. Various metals were detected in both surface and subsurface sample. Metals levels were generally consistent with local background levels, with the exception of lead, which was found at elevated levels in several samples [1,3].
In October 1996, during Phase II of the RI field activities, 9 subsurface soil samples were collected from 8 locations around the auto repair shop; 3 of the samples were taken from areas behind the shop where soil contamination was previously found. No VOCs were detected except bromoform, which was detected in only one sample [1,3].
In December 1997, during Phase III of the RI field activities, 10 subsurface soil samples were collected from a single boring behind the auto repair shop, and 4 subsurface samples were collected during installation of 4 monitoring well boreholes southeast, south, and southwest of the auto shop. No VOCs were detected in any of the samples except benzene, which was found in one soil sample (39 to 41 feet bgs) from behind the auto shop. In April 1998, an additional 9 subsurface soil samples were collected from 7 borings around the auto shop. No VOCs were found in any of these samples [1,3].
APPENDIX B. EXPLANATION OF EVALUATION PROCESS
Screening Process
In evaluating these data, ATSDR used comparison values (CVs) to determine
which chemicals to examine more closely. CVs are the contaminant concentrations
found in a specific media (air, soil, or water) and are used to select contaminants
for further evaluation. CVs incorporate assumptions of daily exposure to the
chemical and a standard amount of air, water, or soil that someone may inhale
or ingest each day.
As health-based thresholds, CVs are set at a concentration below which no known or anticipated adverse human health effects are expected. Different CVs are developed for cancer and noncancer health effects. Noncancer levels are based on valid toxicologic studies for a chemical, with appropriate safety factors included, and the assumption that exposure occurs every day. Cancer levels are the media concentrations at which there could be a one in a million excess cancer risk for an adult eating contaminated soil or drinking contaminated water every day for 70 years. For chemicals for which both cancer and noncancer numbers exist, the lower level is used to be protective. Exceeding a CV does not mean that health effects will occur, just that more evaluation is needed.
CVs used in this document are listed below:
Environmental Media Evaluation Guides (EMEGs) are estimated contaminant concentrations in a media where noncancer health effects are unlikely. The EMEG is derived from ATSDR's minimal risk level (MRL).
Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one additional excess cancer in one million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors.
Lifetime Health Advisories (LTHAs) are derived by EPA from a drinking water equivalent level below which no adverse noncancer health effects are expected to occur over a 70-year lifetime.
Maximum Contaminant Levels (MCLs) are enforceable drinking water regulations established by EPA under the Safe Drinking Water Act that are protective of human health to the extent feasible both technologically and economically. The MCL assumes exposure over a 70-year lifetime and ingestion of 2 liters of water per day.
Reference Media Evaluation Guides (RMEGs) are estimated contaminant concentrations in a media where noncancer health effects are unlikely. The RMEG is derived from EPA's reference dose (RfD).
EPA Soil Screening Levels (SSLs) are estimated contaminant concentrations in soil at which additional evaluation is needed to determine if action is required to eliminate or reduce exposure.
Evaluation of Public Health Implications
The next step is to take those contaminants that are above the CVs and further identify which chemicals and exposure situations are likely to be a health hazard. Child and adult exposure doses are calculated for the site-specific exposure scenario, using our assumptions of who goes on the site and how often they contact the site contaminants. The exposure dose is the amount of a contaminant that gets into a person's body. Appendix C details how exposure doses were calculated for this site.
Noncancer Health Effects
The calculated exposure doses are then compared to an appropriate health guideline for that chemical. Health guideline values are considered safe doses; that is, health effects are unlikely below this level. The health guideline value is based on valid toxicologic studies for a chemical, with appropriate safety factors built in to account for human variation, animal-to-human differences, and/or the use of the lowest adverse effect level. For noncancer health effects, the following health guideline values are used.
Minimal Risk Level (MRLs) - developed by ATSDR
An estimate of daily human exposure - for a specified route and duration - to a dose of chemical that is likely to be without a measurable risk of adverse, noncancer effects. An MRL should not be used as a predictor of adverse health effects. A list of MRLs is available at http://www.atsdr.cdc.gov/mrls.html.Reference Dose (RfD) - developed by EPA
An estimate of the daily, life-time exposure of human populations to a possible hazard that is not likely to cause noncancer health effects. The RfDs is available at http://www.epa.gov/iris/
If the estimated exposure dose for a chemical is less than the health guideline value, then the exposure is unlikely to cause a noncancer health effect in that specific situation. If the exposure dose for a chemical is greater than the health guideline, then the exposure dose is compared to known toxicological values for that chemical and is discussed in more detail in the public health assessment. These toxicological values are doses derived from human and animal studies which are summarized in the ATSDR toxicological profiles. A direct comparison of site-specific exposure and doses to study-derived exposures and doses found to cause adverse health effects is the basis for deciding whether health effects are likely or not.
Calculation of Excess Cancer Risk
The estimated risk of developing cancer from exposure to the contaminants is calculated by
multiplying the site-specific adult exposure dose by EPA's corresponding cancer slope factor
(available at http://www.epa.gov/iris/ ). For the air pathway, the maximum air concentration is
multiplied by the corresponding cancer slope factor. The results estimate the maximum increase in
risk of developing cancer after 70 years of exposure to the contaminant.
The actual risk of cancer is probably lower than the calculated number. The method used to calculate the cancer slope factor assumes that high-dose animal data can be used to estimate the risk for low dose exposures in humans. The method also assumes that there is no safe level for exposure. Little experimental evidence exists to confirm or refute those two assumptions. Lastly, the method computes the 95% upper bound for the risk, rather than the average risk, suggesting that the cancer risk is actually lower, perhaps by several orders of magnitude.(2)
Because of uncertainties involved in estimating cancer risk, ATSDR employs a weight-of-evidence approach in evaluating all relevant data(3). Therefore, the cancer risk is described in words (qualitatively) rather than giving a numerical risk estimate only. The numerical risk estimate must be considered in the context of the variables and assumptions involved in their derivation and in the broader context of biomedical opinion, host factors, and actual exposure conditions. The actual parameters of environmental exposures must be given careful consideration in evaluating the assumptions and variables relating to both toxicity and exposure.
APPENDIX C. RESULTS OF EXPOSURE DOSE CALCULATIONS
Well Water Pathway
The ATSDR exposure dose formula used for the well water pathway is:
where:
ed = exposure dose in milligrams per kilogram per day (mg/kg/day);
c = maximum concentration in water in micrograms per liter (µg/L);
ir = ingestion rate in liters per day (L/day);
ef = exposure factor, days of exposure divided by 365 days per year (unitless);
1000 = conversion factor of micrograms per milligram (µg/mg);
bw = body weight in kilograms (kg).
Assumptions used were based on default values and/or professional judgment [7]. The incidental drinking water ingestion rate for adults was 2 L/day and for children was 1 L/day. For average body weight, 70 kg and 11 kg was used for adults and 1-year-old children, respectively. The exposure factor was 350/365, because the exposure was assumed to occur 350 days a year. The adult exposure was multiplied by 2 to account for dermal and inhalation exposure during showering [8]. The child doses were larger and were used for initial screening.
The doses for children resulting from this calculation for well water contaminants of concern are shown in Table C1. Child doses for benzene, bromodichloromethane, chloroform, dibromochloromethane, dichloroethane, 1,1-DCE, and PCE were below the health guidelines. MTBE and TCE were retained for further analysis in the document text.
Table C1. Child Exposure Doses Calculated for Well Water Pathway
| Contaminant | Maximum concentration, micrograms per liter (µg/L) | Child dose, milligrams per kilogram per day (mg/kg/day) | Health guideline (HG), mg/kg/day | HG source |
| benzene | 26 | 0.002 | 0.003 | Oral RfD |
| bromodichloromethane | 6 | 0.0005 | 0.02 | MRL1 |
| chloroform | 40 | 0.003 | 0.01 | MRL1 |
| dibromochloromethane | 0.6 | .00005 | 0.03 | MRL1 |
| dichloroethane | 0.6 | .00005 | 0.2 | MRL2 |
| 1,1- DCE | 4 | 0.0003 | 0.009 | MRL1 |
| MTBE | 5096 | 0.4 | 0.3 | MRL2 |
| PCE | 24 | 0.002 | 0.01 | Oral RfD |
| TCE | 134 | 0.01 | none3 | - |
| 1 chronic oral minimal risk level. 2 intermediate oral minimal risk level. 3 no health guideline available. |
||||
Excess cancer risk is estimated by multiplying the adult exposure dose by the cancer slope factor. This is then multiplied by the fraction 34/70, because the cancer slope factor assumes a 70-year lifetime of exposure, whereas the maximum time anyone at this site could have been exposed was 34 years (from 1966 when the auto repair shop opened to 2000 when homes were connected to the municipal water system). Table C2 tabulates the results of this calculation for the well water contaminants of concern. The excess cancer risk for benzene, bromodichloromethane, chloroform, dibromochloromethane, dichloroethane, 1,1-DCE, and PCE is within EPA's acceptable risk range of 1×10-6 to 1×10-4. MTBE is not classifiable as to its potential to cause cancer in humans and is discussed further in the document. TCE was also retained for further evaluation. The oral cancer slope factor has been withdrawn for review at the time of the writing of this document.
Table C2. Excess Cancer Risk Calculation Results for the Well Water Pathway
| Contaminant | Maximum concentration, micrograms per liter (µg/L) | Cancer slope factor, 1 / milligrams per kilogram per day (mg/kg/day)-1 | Adult dose, mg/kg/day | Excess cancer risk |
| benzene | 26 | .055 | 0.001 | 4×10-5 |
| bromodichloromethane | 6 | 0.062 | 0.0003 | 1×10-5 |
| chloroform | 40 | 0.0061 | 0.002 | 6×10-6 |
| dibromochloromethane | 0.6 | 0.084 | 0.00003 | 1×10-6 |
| dichloroethane | 0.6 | 0.091 | 0.00003 | 1×10-6 |
| 1,1-DCE | 4 | 0.6 | 0.0002 | 6×10-5 |
| MTBE | 5096 | none1 | 0.3 | - |
| PCE | 24 | 0.052 | 0.001 | 3×10-5 |
| TCE | 134 | none1 | 0.007 | - |
| 1 no cancer slope factor available. | ||||
Soil Pathway
The ATSDR exposure dose formula used for the soil pathway is:
where:
ed = exposure dose in milligrams per kilogram per day (mg/kg/day);
c = maximum concentration in soil in milligrams per kilogram (mg/kg);
ir = ingestion rate in milligrams per day (mg/day);
ef = exposure factor, days of exposure divided by 365 days per year (unitless);
1×10-6 = conversion factor of kilograms per milligram (kg/mg);
bw = body weight in kilograms (kg).
Assumptions used were based on default values and/or professional judgment [7]. The incidental soil ingestion rate for adults was 100 mg/day and for children was 200 mg/day. For average body weight, 70 kg and 36.3 kg was used for adults and 10-year-old children, respectively. Children younger than 10 years old are assumed to not access the site. The exposure factor was 52/365, because the exposure was assumed to occur on average once a week throughout the year.
The doses for children resulting from this calculation for soil contaminants of concern are shown in Table C3. The child dose for arsenic was below the health guideline. For lead, we used the most protective correlation between blood lead levels and soil concentration found in epidemiological studies, 0.0068 microgram per deciliter (µg/dL) increase in blood lead level per mg/kg of lead in soil. For the maximum lead concentration measured in soil, blood lead levels could be expected to increase by 4.3 µg/dL. Because this is a protective calculation (i.e., children would be exposed to an average rather than the maximum concentration) and blood lead levels are not considered elevated until they reach 10 µg/dL, lead exposure is not considered a problem for this site.
Table C3. Child Exposure Doses Calculated for Soil Pathway
| Contaminant | Maximum concentration, milligrams per kilogram (mg/kg) | Child dose, milligrams per kilogram per day (mg/kg/day) | Health guideline (HG), mg/kg/day | HG source |
| arsenic | 15 | 0.00001 | 0.0003 | MRL1 |
| lead | 630 | 0.0005 | none2 | - |
| 1 chronic oral minimal risk level. 2 no health guideline available. |
||||
Excess cancer risk is estimated by multiplying the adult exposure dose by the cancer slope factor; Table C4 tabulates the results of this calculation for the soil contaminants of concern. The excess cancer risk for arsenic is within EPA's acceptable risk range of 1×10-6 to 1×10-4. Lead is a probable human carcinogen, but no cancer slope factor is available so it was impossible to quantitatively assess risk.
Table C4. Excess Cancer Risk Calculation Results for the Soil Pathway
| Contaminant | Maximum concentration, milligrams per kilogram (mg/kg) | Cancer slope factor, 1 / milligrams per kilogram per day (mg/kg/day)-1 | Adult Dose, mg/kg/day | Excess cancer risk |
| arsenic | 15 | 1.5 | 0.000003 | 5×10-6 |
| lead | 630 | none1 | - | - |
| 1 no cancer slope factor available. | ||||
APPENDIX D. EXPOSURE PATHWAYS FOR DAVIS PARK ROAD TCE SITE
| Source for all pathways: Solvent and/or petroleum disposal, spillage, and/or leakage at auto repair shop | |||||||
| PATHWAY NAME | ENVIRONMENTAL MEDIA & TRANSPORT MECHANISMS | POINT OF EXPOSURE | ROUTE OF EXPOSURE | EXPOSURE POPULATION | TIME | NOTES | Complete? |
| Well Water | Infiltration to groundwater | Residences with contaminated drinking water wells | Ingestion, inhalation, dermal exposure | Residents | Past, Present | Population may include young children. | Y |
| Soils | Disposal, spillage, or leakage of waste materials | Auto shop property, especially near the old drainpipe | Incidental Ingestion, inhalation, dermal exposure | Site workers, trespassing children and adults | Past, Present | Population may include children 10 years and older. | Y |
| Surface Water | Surface water runoff over contaminated soil to creek | Along Blackwood Creek | Incidental ingestion, dermal exposure | Residents and site visitors wading or playing in creek | Past, Present | Population may include children 10 years and older. | N |
| Sediment | Surface water runoff over contaminated soil to creek | Along Blackwood Creek | Incidental ingestion, dermal exposure | Residents and site visitors wading or playing in creek | Past, Present | Population may include children 10 years and older. | N |
APPENDIX E. ATSDR PLAIN LANGUAGE GLOSSARY OF ENVIRONMENTAL HEALTH TERMS
ATSDR defines an exposure pathway as having 5 parts:
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.
