EVALUATION OF THE USE OF COAL MINE TAILINGS FOR ROADBED CONSTRUCTION AND FILL DIRT
HARTFORD, SEBASTIAN COUNTY, ARKANSAS
Hartford, Sebastian County, Arkansas, is located approximately 25 miles south of Fort Smith,Arkansas. According to the 1990 census, Hartford had a population of 762. There is an abandonedcoal mine located within the Hartford city limits that is bordered by East Second Street, Olive Streetand Broadway Street. A records search resulted in the discovery of limited historical records for thecoal mine. Exact dates of mine operations are unknown but the mine has been abandoned sinceabout 1942. On August 18, 1999, the Arkansas Department of Environmental Quality (ADEQ)requested that the Arkansas Department of Health (ADH) evaluate soil sample data to determine ifthe use of coal mine overburden and waste soils (commonly referred to as mine tailings) for roadbed material and as fill dirt posed a public health hazard.
A resident of Hartford had contacted ADEQ to inquire about the possible health implications that exposure to coal mine tailings could have on the residents of Hartford. ADH and representatives ofADEQ met with the complainant to ascertain the nature and extent of the complainant's healthconcerns. Concerns focused on the physical and chemical dangers of "gob" piles (mine overburdenor tailings), the potential for adverse health effects associated with run-off from the site tosurrounding yards, and the potential for adverse health effects associated with the use of coal minetailings in roadbed construction and as fill dirt.
On September 29, 1999, ADH conducted a site visit. The site was fenced except for one open areaalong the back side of the property and was covered with mixed vegetation. Mine tailings werescattered throughout the property. One large mine waste pile, approximately 30 feet high and 100feet long, was located near the center of the property. Approximately 10 residences surrounded theproperty. Based on the visual inspection of the site, there did not appear to be any abnormal physicaldangers on the site. ADEQ reports that there have been no significant changes in the site conditionssince the ADH site visit.
The purpose of this health consultation is to evaluate the coal mine tailings sample data and todetermine if using the mine tailings for fill dirt or as roadbed material would create a public healthhazard. The objective of the sampling was to determine concentrations of metals in and around thepiles of overburden and waste soils since the complainant had specified waste metals in the tailingsand acidic mine drainage caused by oxidation of the waste metals in the tailings as the contaminants of concern.
On 2 June 1999, ADEQ officials collected four samples and analyzed the samples for metals. Themedia collected and the analysis performed were in response to a community member's formalcomplaint. Three of the samples were taken directly from the mine waste pile and one sample wastaken from the soil adjacent to a waste pile. This limited number of samples and the limited analysisthat was conducted on the samples does not allow for an accurate characterization of the site. Sincethree of the samples came directly from the mine tailings piles, concentrations would be anticipatedto be greater than or equal to concentrations in the surrounding soils. To assess the potential health risks associated with contaminants at this site, we compared contaminant concentrations to healthbased screening values. Screening values are media specific contaminant concentrations. Whileexceeding a screening value does not necessarily mean that a contaminant represents a public healththreat, it does suggest that the contaminant warrants further consideration. The public healthsignificance of contaminants that exceed screening values may be assessed by reviewing andintegrating relevant toxicological information with plausible exposure scenarios. Estimatedexposures may be compared to reported "No Observable" and "Lowest Observable" Adverse EffectsLevels (NOAELs and LOAELs) and to known effect levels in humans, when available. The resultsof the analysis and the risk based screening value for the substance are presented in the followingtable:
|Analyte||Sample 1 |
|Sample 2 |
|Sample 3 |
|Sample 4 |
|Aluminum||2477||8560||7410||9910||78000 ppm (EPA)|
|Arsenic||10||20.5||21.8||19.2||20 ppm (ATSDR)|
|Barium||61||65||55||69||4000 ppm (ATSDR)|
|Cadmium||<0.5||<0.3||<0.3||<0.3||10 ppm (ATSDR)|
|Chromium||13.4||21.6||19.6||19.9||210 ppm EPA|
|Copper||20||35.5||17.8||27.5||2900 ppm EPA|
|Iron||13615||31300||32900||26200||23000 ppm EPA|
|Manganese||110||218||34||210||7,000 ppm (ATSDR)|
|Nickel||11.3||23||9.7||22.9||1000 ppm (ATSDR)|
|Selenium||7.8||<5||<5||7.7||300 ppm (ATSDR)|
|Lead||<3.1||<2||13.7||<2||400 ppm EPA|
|Zinc||51.8||38.4||15.4||41.2||20,000 ppm (ATSDR)|
|A. All results are reported as parts per million |
B. Bolded values indicate that concentration exceeded screening value
To determine if using the mine tailings for fill dirt or as roadbed material would create a publichealth hazard, ADH evaluated the likelihood that exposure to contaminants at the maximumconcentrations detected would result in adverse health effects. When people are exposed tochemicals, the exposure does not always result in adverse health effects. The type and severity ofhealth effects that may occur in an individual from contact with contaminants depend on thetoxicologic properties of the contaminants; the amount of the contaminant to which the individual isexposed; how often and how long exposure is allowed to occur; the manner in which thecontaminant enters or contacts the body (breathing, eating, drinking, or skin/eye contact); and thenumber of contaminants to which an individual is exposed (combinations of contaminants). Onceexposure occurs, characteristics such as age, gender, nutritional status, genetics, life style, and healthstatus of the exposed individual influence how the individual absorbs, distributes, metabolizes, andeliminates the contaminant. A unique combination of all these factors will determine the individual'sphysiologic response to a chemical contaminant and any adverse health effects the individual maysuffer as a result of the chemical exposure.
To determine whether health effects are likely to result from exposure, ADH estimates pathwayspecific exposure amounts (or doses) of contaminants of concern as part of the toxicologicevaluation. Inhalation and dermal exposures were considered in the evaluation, but doses were notcalculated for these routes. None of the samples contained contaminants that exceeded dermalexposure screening levels. No air samples were taken, but the exposure scenarios for inhalationexposure should be limited to occasional exposure to tailings piles and possible exposure to tailingsused for fill dirt and roadbed materials. The contaminants detected in the samples are not volatileand the potential for inhalation exposure should be limited to exposure of suspended particulate.With the exception of lead, the risk of inhalation exposures to the detected metals is based on afraction of total exposure to the contaminant . Since the concentrations of the metals detectedwere so low, the potential for inhalation exposures that could be harmful is negligible.
Exposure doses were estimated for those analytes that exceeded the ATSDR soil comparison valueand for those analytes that have no soil comparison value. The estimated doses for incidental soilingestion are presented in the following table:
|Analyte||Concentration(mg/kg)||Estimated Soil Ingestion Dose|
|Exposure dose = contaminant concentration x soil ingestion rate x Exposure factor (10 -6)/Body Weight|
The main issue addressed in this Health Consultation is whether exposure to the contaminantsdetected in the analysis of the coal mine tailings will adversely affect the health of the citizens in thesurrounding community. Exposure points should be limited to direct exposure to the mine tailings bytrespassers on the site, exposure to run-off points surrounding the site, and to potential locations where the tailings are used as fill dirt or roadbed material.
Arsenic is an element that is widely distributed in the earth's crust. Background arsenicconcentrations in soils in the United States range from about 1 to 40 parts per million (ppm) with amean value of about 5 ppm. It is not unusual for soils in Arkansas to exceed United Statesbackground levels for arsenic. The highest sampled arsenic concentration for the site was 21.8 ppmwhich falls within national background ranges. Arsenic in soil may be transported by wind, byrunoff, or by leaching into the subsurface soil. Because many arsenic compounds tend to partition tosoil or sediment, leaching usually does not transport arsenic to any great depth but tends toconcentrate and remain in upper soil layers indefinitely.
Analysis of the toxic effects of arsenic is complicated by the fact that arsenic can exist in severaldifferent valence states and as many different inorganic and organic compounds. Most cases ofhuman toxicity from arsenic have been associated with exposure to inorganic arsenic . Dataprovided in Table 1 was for total arsenic. For the purposes of this health consultation, theconservative approach of evaluating all arsenic concentrations as inorganic arsenic is utilized.
The minimal risk level (MRL) for arsenic is 0.0003 mg/kg/day for chronic oral exposure. An MRLis an estimate of the daily human exposure to a hazardous substance that is likely to be withoutappreciable risk of adverse non-cancer health effects over a specified duration of exposure. Theestimated soil ingestion exposure dose for the sample with the greatest concentration of arsenic is0.0004 mg/kg/day. This soil ingestion exposure dose slightly exceeds the MRL for arsenic. Thechronic MRL for arsenic of 0.0003 mg/kg/day was based on individuals exposed to high levels ofarsenic in well water. Under these conditions, a clear dose-response relationship was observed forcharacteristic skin lesions. Daily intake of water from a drinking water source is generally a moresevere oral exposure than incidental soil ingestion. The no observed adverse effect level (NOAEL)in this study was 0.0008 mg arsenic/kg/day. The NOAEL is the highest exposure level at which noharmful effects were seen in the organ systems of the individuals studied. The lowest observedadverse effect level (LOAEL) is the lowest dose used in a study that caused a harmful health effect. The LOAEL in this study was 0.014 mg arsenic/kg/day. At a dose of 0.014 mg arsenic/kg/day,hyper-pigmentation and keratosis of the skin were observed. This effect is considered a "lessserious" effect. The calculated soil ingestion exposure dose of 0.0004 mg/kg/day is not expected to result in any non-cancer adverse health effects.
There are conflicting reports on the risk of increased cancer incidence in populations exposed toarsenic in their drinking water. There is evidence from several epidemiological studies and casereports that ingestion of inorganic arsenic increases the risk of developing skin cancer in certainpopulations. In most cases, the skin cancer only develops after prolonged exposure to highconcentrations of arsenic in drinking water. In contrast, several epidemiologic studies performedin the United States have not detected increased frequency of skin cancer in small populationsconsuming water with concentrations of arsenic ten times greater than the Environmental ProtectionAgency (EPA) maximum contaminant level of 0.05 ppm. These data suggest that even thoughexposure to arsenic in water is not uncommon in the United States, arsenic associated skin cancer isnot a common problem in this country. Since public water is available to potentially exposedpopulations, and public water is required to maintain concentrations below risk concentrations, theoral exposure to arsenic at the Hartford site should be limited to incidental ingestion of soil. Anexposure scenario limiting arsenic exposures to soil ingestion at the concentrations detected shouldnot increase the risk of cancer incidence to potentially exposed populations.
The EPA screening level for residential soil is 23,000 mg/kg. The highest concentration of iron insite soil was 32,900 mg/kg. Adverse health effects associated with iron are generally restricted toprolonged inhalation exposure in occupational environments to highly concentrated iron oxides. Ironis an essential mineral. The recommended daily allowance is 10 mg for men and 18 mg for women. The calculated soil ingestion dose for iron was 6 mg/kg/day. This value falls below therecommended daily allowance. Iron is not expected to pose a public health hazard by the ingestionroute of exposure.
Magnesium is an essential metal found in all human tissues. There are no health based exposurerestrictions for magnesium in its elemental form. Most foods contain significant amounts ofmagnesium. Nuts, cereals, sea foods, and meats are particularly high. Magnesium is an essentialmineral. The recommended daily magnesium allowance is 350 mg for men and 300 mg forwomen. The calculated soil ingestion exposure dose for the site was 0.1 mg/kg/day. Thepresence of it in site soils is not expected to pose a public health hazard by the ingestion route ofexposure.
Lead is a naturally occurring bluish-gray metal found in small amounts in the earth's crust. Sourcesof lead in dust and soil include lead that falls to the ground from the air, and weathering andchipping of lead-based paint from buildings and other structures. Mining wastes that have been usedfor sandlots, driveways, and roadbeds can also be sources of lead .
Foods such as fruits, vegetables, meats, grains, seafood, soft drinks, and wine may contain lead. Lead gets into food from water during cooking and into foods and beverages from dust that containslead falling onto crops, from plants absorbing lead that is in the soil, and from dust that contains leadfalling onto food during processing. The calculated soil ingestion exposure dose based on thehighest concentration of lead found at the site was 0.003 mg/kg/day. There are currently no MRLsderived for lead. The LOAEL, in humans for acute and intermediate oral exposure is 0.02mg/kg/day and 0.01 mg/kg/day, respectively. Ingestion of lead from site soils is not expected to pose a public health hazard.
Run-off from the site to surrounding yards.
Mining accelerates natural processes. The development of underground workings, open pits, ore piles, mill tailings, spoil heaps, and the extractive processing of ores enhance the likelihood of releasing chemical elements to the surrounding area in large amounts and at increased rates. The site in question has been inactive since approximately 1942. A common process that results in dispersion of elements from a mineralized site is acid drainage, commonly referred to as acid mine drainage (AMD). AMD is the formation and movement of highly acidic water which is rich in heavy metals. This acidic water forms through the chemical reaction of surface water (rainwater, snow melt, pond water) and shallow subsurface water with rocks that contain sulfur-bearing minerals, resulting in sulfuric acid. Heavy metals can be leached from rocks that come in contact with the acid, a process that may be substantially enhanced by bacterial action. The resulting fluids may be highly toxic and when mixed with groundwater, surface water, and soil may have harmful effects on humans, animals, and plants.
Run-off from the site could impact the soil surrounding the site and groundwater beneath the site,but there are no visual indications that this is occurring and there were no samples collected tocharacterize the off site soil or groundwater. Based on the sample data from the tailings, potentialcontamination of soils by the detected metals is unlikely to occur at concentrations that would resultin hazardous exposures. There is insufficient data to assess the impact of leaching from the tailingson the groundwater beneath the site. The metals detected in the samples have a wide range of soil togroundwater transfer potential, but the impact of the tailings on groundwater could not be assessedsince no samples were available.
The use of coal mine tailings from the mine waste pile in roadbed construction and as fill dirt.
The analysis of the June 1999 samples indicate that the mine tailings contain metals, but the concentrations of the contaminants are below health risk concentrations. An accurate assessment of the potential risks is restricted by the limited number of samples taken. If the samples accurately characterize all of the tailings piles and the surrounding soil, use of the tailings as roadbed materials and fill dirt will not create a public health hazard.
Child Health Initiative
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and childrendemand special emphasis in communities faced with contamination of soil, water, air and food. Children are at a greater risk than adults from certain kinds of exposures to hazardous substances. They are more likely to be exposed because they play outdoors and they often bring food intocontaminated areas. They are more likely to come into contact with dust, soil, and heavy vaporsclose to the ground. Also, they receive higher doses of chemical exposure due to lower bodyweights. The developing body systems of children can sustain permanent damage if toxic exposuresoccur during critical growth stages. Exposure doses for children were calculated to determine ifexposures could result in adverse health effects. Any potential for child exposures to lead should berestricted. Even though the sampling indicates that the potential for exposure to lead is probably minimal, additional sampling will be needed to substantiate that assumption.
- Based on the limited data available, the mine tailings piles at the Hartford mine site pose nopublic health hazard. The sampled tailings piles contained metals, but not at concentrations that would pose a public health hazard. There are no indications that the tailings should be excluded from use as fill dirt or roadbed materials.
- There is insufficient data to determine if there is off site contamination or if groundwater has been adversely effected by the mine tailings. These pathways represent indeterminate public health hazards.
Additional sampling is recommended to characterize the site. Off-site soil, sediment, and groundwater samples are needed to confirm that the mine tailings have not contaminated exposure points in the community.
This is an initial consultation. No previous activities have occurred on the site or in the community.
ADH is preparing a needs assessment to determine if there are health education or community involvement needs.
Future Action Plans
ADH will conduct educational outreach based on the findings of the needs assessment.
This Health Consultation for the Use of Coal Mine Tailings in Hartford, Arkansas was prepared bythe Arkansas Department of Health under a cooperative agreement with the federal Agency forToxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was initiated.
Technical Project Officer, SPS, SSAB, DHAC
The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed this health consultation and concurs with its findings.
Richard E. Gillig
Section Chief, SPS, SSAB, DHAC, ATSDR
Arkansas Department of Health
ATSDR Regional Representative:
ATSDR Region VI
ATSDR Technical Project Officer:
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
- Calabrese, EJ, Kenyon EM. Air Toxics and Risk Assessment. Chelsea, Michigan: LewisPublishers Inc.; 1991
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Arsenic.Atlanta: US Department of Health and Human Services; 2000 Sep.
- Tseng WP, Chu HM, How SW, et al. Prevalence of skin cancer in an endemic area ofchronic arsenicism in Taiwan. J Natl Cancer Inst 1968; 40:453-463.
- U.S. Environmental Protection Agency Integrated Risk Information System (IRIS) [database online]. Washington, DC; 1999.
- Zenz, Carl. Occupational Medicine. 3rd ed. St. Louis: Mosby Year Book Inc. 1994. P. 604-605.
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Lead. Atlanta: US Department of Health and Human Services; 1999 Jul.