What Are the Environmental and Health Effects Associated with Disposing of CCRs in 

Landfills and Surface Impoundments? 

EPA has evaluated potential human and ecological risks from exposure to CCR chemical 

constituents for more than twenty years. The following section summarizes the our work, from 

the mid-1990s until the present and includes descriptions of damage cases found and risk 

assessment work conducted to identify the most likely combinations of chemical constituents and 

organisms that may be at risk. EPA’s risk assessment work includes four analyses: 1) U.S. EPA 

1998, “Draft Final Report: Non-groundwater Pathways, Human Health and Ecological Risk 

Analysis for Fossil Fuel Combustion Phase 2 (FFC2)” (June 5, 1998) referred to hereafter as the 

1998 Non-groundwater risk assessment (available in docket # F-1999-FF2P-FFFFF in the RCRA 

Information Center, and on the EPA website at 

http://www.epa.gov/osw/nonhaz/industrial/special/fossil/ngwrsk1.pdf); 2) preliminary 

groundwater and ecological risk screening of selected constituents in U.S. EPA 2002, 

“Constituent Screening for Coal Combustion Wastes,” (contractor deliverable dated October 

2002, available in docket EPA-HQ-RCRA-2006-0796 as Document # EPA-HQ-RCRA-2006-

0796-0470); referred to hereafter as the 2002 screening analysis; 3) U.S. EPA 2009a, “Human 

and Ecological Risk Assessment of Coal Combustion Wastes” (September 2009) available in the 

docket for this proposed rule, and referred to hereafter as the 2009 risk assessment; and 4) U.S. 

EPA 2009b, “Inhalation of Fugitive Dust: A Screening Assessment of the Risks Posed by Coal 

Combustion Waste Landfills” available in the docket for this proposed rule. 

Human Health Risks
Individuals can be exposed to the constituents of concern found in CCRs through a number of 

exposure routes. Potential contaminant releases from landfills and surface impoundments 

include: leaching to ground water; overland transport from erosion and runoff; and air emissions. 

The potential of exposure from any one of these exposure pathways for a particular chemical is 

dependent on the physical and chemical characteristics of the chemical, the properties of the 

waste stream, and the environmental setting. EPA has conducted a peer-reviewed risk 

assessment of potential human health risks from CCR constituents leaching to groundwater that 

subsequently migrate either to a nearby drinking water well, or to nearby surface water, and is 

ingested as drinking water or through fish consumption (U.S. EPA 2009a). EPA has also 

performed preliminary analyses of human health effects from constituents that have eroded or 

have run off from waste management units (U.S. EPA 2002), and of human health effects from 

breathing windblown particulate matter from landfill disposal operations (the 1998 risk 

assessment and U.S. EPA 2009b). 

Longstanding EPA policy is for EPA risk assessments to include a characterization of the risks at 

two points on a distribution, or range, of risk estimates: a central tendency estimate that 

represents conditions likely to be encountered in a typical exposure situation, and a high end 

estimate that represents conditions likely to be encountered by individuals with higher exposures 

(U.S. EPA 1995).1

 Examples of factors that would influence a nearby resident’s exposure are 

 

1 Guidance for Risk Characterization, U.S. Environmental Protection Agency, 1995; accessible at 

http://www.epa.gov/OSA/spc/pdfs/rcguide.pdf, which states that “For the Agency's purposes, high end risk 

descriptors are plausible estimates of the individual risk for those persons at the upper end of the risk distribution,” 

or conceptually, individuals with “exposure above about the 90th percentile of the population distribution”). As 
the residence’s distance from a CCR waste management unit, and an individual’s behavior or 

activity patterns. In the 2009 risk assessment, the high end risk estimates are the 90th percentile 

estimates from a probabilistic analysis. 

The comparisons that EPA uses to judge whether either a high end or central tendency estimated 

risk is of concern are the risk criteria. For an individual’s cancer risk, the risk criteria are in the 

range of 1 x 10-6, or one in one million “excess” (above and beyond pre-existing risk) probability 

of developing cancer during a lifetime, to 1 x 10-4 (one in ten thousand),2 with 1 x 10-5 (one in 

one hundred thousand) being the “point of departure” for listing a waste as hazardous. For 

human non-cancer hazard, the risk criterion is an estimated exposure above the level at which no 

adverse health effects would be expected to occur (expressed as a ratio of the estimated exposure 

to the exposure at which it is likely that there would be no adverse health effects; this ratio is also 

called a hazard quotient (HQ), and a risk of concern equates to a hazard quotient greater than 

one), or, in certain cases of drinking water exposure, water concentrations above the MCL 

established under the Safe Drinking Water Act. 

 

The exposure pathways for humans that EPA has evaluated for CCR landfills and surface 

impoundments are nearby residents’ groundwater ingestion and air inhalation, and fish 

consumption by recreational fishers: 

Ground Water Ingestion 

 suggested in the Guidance, we also provide 50th percentile results as the central tendency estimate of that risk 

distribution. 

2

 See 40 CFR 300.430. 
Contaminants can leach from CCRs in landfills and surface impoundments into the groundwater 

and subsequently be ingested by individuals who use groundwater as a source of drinking water. 

A detailed discussion of the modeling and risks from this pathway can be found in U.S. EPA 

2009a (available in the docket for this proposal). This report presents the methodology, results, 

and uncertainties of EPA’s assessment of human health risks resulting from groundwater 

contamination from coal-fired electric utilities. 

Under the assumptions used in this risk assessment, some of the constituents that were modeled 

exceeded the risk criteria for listing as a hazardous waste (1 x 10-5 or one in 100,000). Regarding 

high-end risks estimated from surface impoundment management: 

• Unlined surface impoundments managing CCRs had estimated arsenic cancer risks of 2 

x 10-3 (two in one thousand), while nitrate/nitrite was estimated to exceed the MCL by a 

factor of 20 and lead by a factor of 3; molybdenum had an estimated hazard quotient of 

8, boron had an estimated hazard quotient of 7, and selenium had an estimated hazard 

quotient of 2. 

• Unlined surface impoundments co-managing CCRs with coal refuse had estimated 

arsenic cancer risks of 2 x 10-2 (two in one hundred), while lead was estimated to exceed 

the MCL by a factor of 9, cobalt was estimated to have a hazard quotient of 500, 

cadmium an estimated hazard quotient of 9, and molybdenum an estimated hazard 

quotient of 3. 

• Clay-lined surface impoundments managing CCRs had estimated arsenic cancer risks of 

9 x 10-4 (nine in ten thousand), an estimated nitrate/nitrite exceedance of the MCL by a 
factor of 10, an estimated hazard quotient for molybdenum of 5, and an estimated hazard 

quotient for boron of 4. 

• Clay-lined surface impoundments co-managing CCRs with coal refuse had estimated 

arsenic cancer risks of 7 x 10-3 (seven in one thousand), an estimated cobalt hazard 

quotient of 200, an estimated cadmium hazard quotient of 3, and an estimated 

molybdenum hazard quotient of 2. 

• Composite-lined surface impoundments co-managing CCRs with coal refuse had 

estimated arsenic cancer risks of 4 x 10-6, which is less than the risk criterion. 

The central tendency estimates for surface impoundments were: 

• For unlined surface impoundments managing CCRs, estimated arsenic cancer risks 

of 1 x 10-4 (one in ten thousand). 

• For unlined surface impoundments co-managing CCRs with coal refuse, estimated 

arsenic cancer risks of 6 x 10-4 (six in ten thousand), and an estimated cobalt hazard 

quotient of 20. 

• For clay-lined surface impoundments managing CCRs, estimated arsenic cancer risks 

of 6 x 10-5 (six in one hundred thousand); 

• For clay-lined surface impoundments co-managing CCRs with coal refuse, estimated 

arsenic cancer risks of 2 x 10-4 (two in ten thousand), and an estimated cobalt hazard 

quotient of 6; 

• For composite-lined surface impoundments managing CCRs, or co-managing CCRs 

with coal refuse, estimated risks either did not exceed the risk criteria or the modeled 
infiltration rate was too low for the contaminant plume to reach the nearby resident’s 

well during the time period of analysis (10,000 years). 

One aspect of the modeling work that is important to note is the differing arrival times of various 

constituents, at the modeled well locations. Due to differences in behaviors when interacting in 

soil, some chemical constituents move more quickly than others through the subsurface 

environment. For unlined surface impoundments, the median number of years until peak well 

water concentrations would occur was estimated to be 74 years for boron and selenium, 78 years 

for arsenic, and 97 years for cobalt. For clay-lined surface impoundments, the median number of 

years was estimated to be 90 years for boron and selenium, 110 years for arsenic, and 270 years 

for cobalt. Of the plumes that did reach the receptor wells from composite-lined units,3

 the 

median number of years was estimated to be 4,400 years for boron, 4,600 years for selenium, and 

8,600 years for arsenic. The median number of years until peak well water concentrations for 

cobalt did not occur in the 10,000 year time period that was modeled. 

 For the high end risk estimates from landfills: 

• For unlined landfills managing CCRs, arsenic was estimated to have a cancer risk of 4 x 

10-4 (four in ten thousand), while thallium was estimated to have a HQ of 3 and antimony 

and molybdenum both had an estimated HQ of 2. 

• For unlined landfills that co-dispose CCRs with coal refuse, arsenic was estimated to 

have a cancer risk of 5 x 10-4 (five in ten thousand), while thallium and molybdenum 

were estimated to have a HQ of 2. (EPA recognizes that the industry has developed 

 

3

 In other words, based on the results from this subset of the total number of Monte Carlo realizations 
guidance to improve CCR management when coal refuse is present to prevent the 

generation of acidic conditions. EPA solicits information on how the constituent 

concentrations may have changed based on current practices.) 

• For unlined landfills managing FBC, arsenic was estimated to have a cancer risk of 3 x 

10-5 (three in one hundred thousand). 

• For clay-lined landfills managing CCRs, arsenic was estimated to have a cancer risk of 2 

x 10-4 (two in ten thousand), while thallium was estimated to have a HQ of 2. 

• For clay-lined landfills co-managing CCRs with coal refuse, arsenic was estimated to 

have a cancer risk the same as for clay-lined landfills managing CCRs—that is 2 x 10-4

(two in ten thousand). 

• For clay-lined landfills managing FBC waste, arsenic was estimated to have a cancer risk 

of 6 x 10-5 (six in one hundred thousand), while thallium was estimated to have a HQ of 

4, and antimony was estimated to have a HQ of 3. 

• For composite-lined landfills that managed CCRs or FBC waste, or that co-managed 

CCRs with coal refuse, the contaminant infiltration rates were generally too small for the 

contaminant plume to reach the receptor well during the 10,000 year period of the 

analysis. 

The central tendency estimates for landfills were: 

• For unlined landfills managing CCRs, arsenic was estimated to have a cancer risk of 6 x 

10-6 (six in one million), which is less than the risk criterion. 

• For unlined landfills co-managing CCRs with coal refuse, arsenic was estimated to have 

a cancer risk of 2 x 10-5 (two in one hundred thousand). 
• For unlined landfills managing FBC waste, the modeled contaminant infiltration rates 

were too low to cause the arsenic contaminant plume to reach the nearby resident’s well 

during the time period of the analysis (10,000 years). 

• For clay-lined landfills managing CCRs, arsenic was estimated to have a cancer risk of 4 

x 10-6 (four in one million), which is less than the risk criterion. 

• For clay-lined landfills co-managing CCRs with coal refuse, arsenic was estimated to 

have a cancer risk of 6 x 10-6 (six in one million), which is less than the risk criterion. 

• For clay-lined landfills managing FBC waste, arsenic was estimated to have a cancer risk 

of 4 x 10-7 (four in ten million), which is less than the risk criterion. 

• For composite-lined landfills managing FBC waste, modeled infiltration rates were too 

low for the arsenic contaminant plume to reach the nearby resident’s well during the 

10,000 year time period of the analysis. 

As with surface impoundments, the constituents in CCRs managed in landfills did not all arrive 

at the drinking water well at the same time. For unlined landfills, the median number of years 

until peak well water concentrations were estimated to occur was approximately 2,000 years for 

boron, 2,300 years for thallium, 2,800 years for arsenic, 2,600 years for selenium, and 7,800 

years for cobalt. For clay-lined landfills, the median estimated time until peak well 

concentrations was approximately 4,000 years for arsenic, 5,100 years for selenium, 4,300 years 

for thallium, 5,600 years for boron, and 10,000 years for cobalt. Of the plumes that did reach the 

receptor wells from composite-lined units, the constituent concentrations did not yet peak in the 

10,000 year time period that was modeled. 
As discussed in Appendix I, the Agency has evidence that such potentially toxic constituents 

have leached from CCRs into groundwater from landfills and surface impoundments at levels 

exceeding the primary drinking water standards (see 

www.epa.gov/safewater/contaminants/index.html for EPA’s drinking water standards). 

Comparing the results of the 2009 risk assessment with the damage cases, EPA notes that the 

estimates for groundwater exceedances for many of the constituents in the risk assessment are 

the same as those found in the damage cases (arsenic, boron, cadmium, lead, molybdenum, and 

selenium). The differences in estimated time-to-peak-well-concentrations between unlined 

versus clay-lined or composite lined waste management units that are apparent for some 

constituents, suggest that the damage cases involving contaminated drinking water may occur 

sooner with unlined waste management units than with clay-lined or composite-lined waste 

management units. This expected outcome would be consistent with the damage cases observed 

to date, which have been primarily found in instances where waste management units are 

unlined. If the groundwater modeling in the 2009 risk assessment is accurate, it may be possible 

to see similar damages developing from clay-lined units, in the coming decades. 

Air Inhalation 

Air emissions from CCR disposal sites can originate from waste unloading operations, spreading 

and compacting operations, the re-suspension of particulates from vehicular traffic, and from 

wind erosion. Air inhalation exposures may cause adverse human health effects, either due to 

inhalation of small-diameter (less than 10 microns) “respirable” particulate matter that causes 

adverse effects, such as triggered asthma attacks or increased mortality (and for which the 
NAAQS for particulate matter has been established, under the CAA), or due to the toxic effects 

of these respirable particles. 

 Potential adverse health effects from particulate matter inhalation: 

To evaluate the potential exposure of residents to particulate matter that live near landfills that 

have disposed of CCRs, EPA has performed a screening-level analysis using the SCREEN3 

model. This analysis, in Inhalation of Fugitive Dust: A Screening Assessment of the Risks Posed 

by Coal Combustion Waste Landfills (US EPA 2009b, copy of which is in the docket for this 

proposed rule), indicates that, without fugitive dust controls, there could be exceedances of the 

NAAQS for fine particulate matter in the air at residences near CCR landfills. EPA requests 

comment and data on the screening analysis, on the results of any ambient air monitoring for 

particulate matter that has been conducted, where air monitoring stations are located near CCR 

landfills, along with information on any techniques, such as wetting, compaction, or daily cover 

that may be employed to reduce such exposures. 

 Potential adverse health effects from toxic constituents present in particulate matter: 

A description of the modeling and risks from this pathway for disposal of CCRs in landfills and 

surface impoundments can be found in the Draft Final Report: Non-ground Water Pathways, 

Human Health and Ecological Risk Analysis for Fossil Fuel Combustion Phase 2 (FFC2); June 

5, 1998.4

 This analysis did not address the issue of enrichment of toxic constituents present in 

 

4

 www.epa.gov/epawaste/nonhaz/industrial/special/fossil/ngwrsk1.pdf 
the finer, inhalable fraction of the overall particulate matter size distribution,5

 but used the total 

constituent concentrations to represent the concentrations of constituents present on the inhaled 

particulate matter. Based on the analysis, at landfills, the highest estimated risk value was an 

individual excess lifetime risk of 4 in one million for the farmer, due to inhalation of chromium 

(all chromium present in the particulate matter was assumed to be in the more toxic, hexavalent 

form). For surface impoundments, the highest risk value was 2 in one million for the farmer 

(again assuming all chromium present was hexavalent). The Agency requests comment on the 

analysis, as presented in the draft final report, as well as any data, including air monitoring data 

that may be available regarding the potential for residents to be exposed to toxic constituents by 

this exposure pathway. 

Fish Consumption 

Exposure for this pathway stems from human consumption of fish that are caught in surface 

water bodies, such as streams or rivers, located near CCR landfills or surface impoundments. 

There are several ways in which a nearby water body and, consequently, the fish in that water 

body, could become contaminated due to waste management activities: runoff and erosion from 

the landfill or surface impoundment, direct deposition of airborne particles, the migration of 

contaminated groundwater from underneath the waste management unit into the nearby surface 

water, or even direct discharge of surface impoundment effluent. Once the constituents are in 

the surface water, fish may absorb the dissolved constituents during normal respiration across the 

 

5

 See, for example, Vouk, V. and Piver, W. “Metallic Elements in Fossil Fuel Combustion Products: Amounts and 

Form of Emissions and Evaluation of Carcinogenicity and Mutagenicity.” Env Health Perspec 1983: 47(201-225). 
gills. In addition, contaminants that concentrate in the sediments may be introduced into fish 

through the food chain. Contaminants can accumulate in fish from either or both of these 

exposure mechanisms depending on the chemical’s potential for bioconcentration and 

bioaccumulation. 

The 2009 risk assessment addresses potential human health risks from eating fish that are 

contaminated due to the migration of contaminated groundwater that migrates from underneath 

the landfill or surface impoundment and affects nearby surface water bodies. Regarding highend risk estimates from surface impoundment management:6

• Unlined surface impoundments managing CCRs had an estimated arsenic cancer risk of 

8 x 10-6 (eight in one million), which is less than the risk criterion, and an estimated HQ 

for selenium of 3. 

• Unlined surface impoundments co-managing CCR with coal refuse had an estimated 

arsenic cancer risk of 3 x 10-5 (three in one hundred thousand). 

• Clay-lined surface impoundments managing CCR had an estimated arsenic cancer risk of 

4 x 10-6 (four in one million), which is less than the risk criterion, and an estimated HQ 

for selenium of 2. 

• Clay-lined surface impoundments co-managing CCR with coal refuse had an estimated 

arsenic cancer risk of 8 x 10-6 (eight in one million), which is less than the risk criterion. 

• For composite-lined surface impoundments managing CCR, or co-managing CCR with 

coal refuse, estimated risks either did not exceed the risk criteria or the modeled 

 

6

 Central tendency estimates either did not exceed the risk criteria or the modeled infiltration rate was too low for the 

contaminant plume to reach the surface waterbody during the time period of the analysis (10,000 years) 
infiltration rate was too low for the contaminant plume to reach the nearby surface 

waterbody during the time period of analysis (10,000 years). 

 

The central tendency estimates for landfills were: 

• For unlined landfills managing CCR, the arsenic cancer risk was estimated to be 1 x 10-6

(one in one million). 

• For unlined landfills co-managing CCR with coal refuse, the arsenic cancer risk was 

estimated to be 2 x 10-6 (two in one million), which is less than the risk criterion. 

• Unlined landfills managing FBC waste had modeled contaminant infiltration rates that 

were too low to cause the arsenic contaminant plume to reach the nearby surface 

waterbody during the time period of the analysis (10,000 years). 

• For clay-lined and composite-lined landfills managing CCR, or co-managing CCR with 

coal refuse, estimated risks either did not exceed the risk criteria or the modeled 

infiltration rate was too low for the contaminant plume to reach the nearby surface 

waterbody during the time period of analysis (10,000 years). 

• Central tendency estimates either did not exceed the risk criteria or the modeled 

infiltration rate was too low for the contaminant plume to reach the surface waterbody 

during the time period of the analysis (10,000 years). 

 

Ecological Risks

For ecological non-cancer hazards that are modeled, the risk criterion is a hazard quotient that 

represents impacts on individual organisms, with a risk of concern being an estimated hazard 
quotient greater than one. In some instances, EPA also considered documented evidence of 

ecological harm, such as field studies published in peer-reviewed scientific literature. Such 

evidence is often sufficient to determine adverse ecological effects in lieu of or in addition to 

modeling potential ecological risks. 

Two types of exposures can occur for ecological receptors: exposures in which ecological 

receptors inhabit a waste management unit directly, and exposures in which CCRs or its 

chemical constituents migrate, or move, out of the waste management unit and contaminate 

nearby soil, surface water, or sediment. 

For exposures in which ecological receptors directly inhabit a waste management unit, the 1998 

risk assessment indicated that several chemical constituents present in CCRs managed in surface 

impoundments may pose adverse effects on organisms that inhabit those impoundments: 

aluminum (amphibians), arsenic (birds), boron (amphibians), cadmium (mammals), lead 

(mammals), mercury (birds) and selenium (mammals and amphibians). Because of the large size 

of these waste units, many being 100’s of acres to one that is about 2600 acres, receptors can 

often inhabit these waste management units. There are a number of recent references in the peerreviewed scientific literature specific to CCRs managed in surface impoundments that confirm 

the 1998 risk assessment results and provide additional pertinent information of potential 

ecological damage. Hopkins, et al. (2006)7

 observed deformities and reproductive effects in 

 

7

 Hopkins, W.A., S.E. DuRant, B.P. Staub, C.L. Rowe, and B.P. Jackson. 2006. Reproduction, embryonic 

development, and maternal transfer of contaminants in the amphibian Gastrophryne carolinensis. Environmental 

Health Perspectives. 114(5):661-666. 
amphibians living on or near CCR disposal sites in Georgia. Rowe, et al. (2002)8

 provided a 

thorough review of laboratory and field studies that relate to the impact of CCR surface 

impoundment management practices’ on aquatic organisms and communities. Examples of 

studies cited in Rowe, et al. (2002) that illustrates the impact of CCRs on aquatic organisms in 

direct contact with surface impoundment waters and/or sediments include Benson and Birge 

(1985),9 Coutant, et al. (1978)10 and Rowe, et al. (2001),11 while examples of studies cited in 

Rowe, et al. 2002 that illustrates the impact of CCRs on aquatic organisms in water bodies near 

CCR surface impoundments include Lemly (1993)12 and Sorensen, et al. (1982)13 and (1988).14 

This latter category may reflect CCR impacts attributable to three constituent migration 

mechanisms: 1) NPDES-permitted discharges from impoundments; 2) overtopping of 

 

8

 Rowe, C., Hopkins, W., Congdon, G. “Ecotoxicological Implications of Aquatic Disposal of Coal Combustion 

Residuals in the United States: A Review.” Env Monit Assess 2002: 80(270-276). 

9

 Benson, W. and Birge, W. “Heavy metal tolerance and metallothionein induction in fathead minnows: results from 

field and laboratory investigations.” Environ Toxicol Chem 1985:4(209-217). 

10 Coutant, C., Wasserman, C., Chung, M., Rubin, D., Manning, M. “Chemistry and biological hazard of a coal-ash 

seepage stream.” J. Water Poll. Control Fed. 1978:50(757-743). 

11 Rowe C., Hopkins, W., and Coffman, V. “Failed recruitment of southern toads (Bufo terrestris) in a trace-element 

contaminated breeding habitat: direct and indirect effects that may lead to a local population sink.” Arch. Environ. 

Contam. Toxicol. 2001:40(399-405). 

12 Lemly A., “Guidelines for evaluating selenium data from aquatic monitoring and assessment studies.” Environ. 

Monit. Assess. 1993:28(83-100). 

13 Sorensen, E., Bauer, T., Bell, J., Harlan, C. “Selenium accumulation and cytotoxicity in teleosts following 

chronic, environmental exposure.” Bull. Environ. Contam. Toxicol. 1982:29(688-696). 

14 Sorenson, E. “Selenium accumulation, reproductive status, and histopathological changes in environmentally 

exposed redear sunfish.” Arch Toxicol 1988:61(324-329). 
impoundments; and 3) groundwater-to-surface-water discharges (modeled in US EPA 2009a), as 

well as other, non-CCR-related, sources of pollutants. 

The 2009 risk assessment addresses potential ecological risks from aquatic receptors living in 

nearby surface waterbodies. Regarding risk estimates from surface impoundments: 

• For high-end risks, unlined surface impoundments were estimated to have HQs of 2,375 

for boron, 22 for lead, 13 for arsenic V, 12 for selenium VI, 6 for cobalt, and 3 for 

barium. 

• For high-end risks, clay-lined surface impoundments were estimated to have HQs of 854 

for boron, 7 for lead, 4 for arsenic V, 4 for selenium VI, and 3 for cobalt. 

• For high-end risks, composite-lined surface impoundments were estimated to have HQs 

of 257 for boron, 2 for lead, 5 for arsenic V, and 5 for cobalt. 

• Central tendency estimates for unlined surface impoundments showed an HQ of 7 for 

boron. 

• Central tendency estimates for clay-lined and composite-lined surface impoundments 

were either below the risk criteria, or the modeled infiltration rate was too low for the 

contaminant plume to reach the nearby surface waterbody during the time period of the 

analysis (10,000 years). 

Regarding risk estimates from landfills: 

• For high-end risks, unlined landfills were estimated to have HQs of 281 for boron, 8 for 

lead, 2 for selenium VI, 2 for arsenic V, and 2 for barium. 

• For high-end risks, clay-lined landfills were estimated to have an HQ of 78 for boron. 
• For high-end risks in composite-lined landfills, the estimated risks either did not exceed 

the risk criteria or the modeled infiltration rate was too low for the contaminant plume to 

reach the nearby surface waterbody during the time period of analysis (10,000 years). 

• Central tendency estimates for landfills of all liner types were either below the risk 

criteria, or the modeled infiltration rate was too low for the contaminant plume to reach 

the nearby surface waterbody during the time period of the analysis (10,000 years). 

The 2009 risk assessment addresses potential ecological risks from sediment receptors living in 

nearby surface waterbodies. Regarding risk estimates from surface impoundments: 

• For high-end risks, unlined surface impoundments were estimated to have HQs of 311 

for lead, 127 for arsenic III, and 30 for cadmium. 

• For high-end risks, clay-lined surface impoundments were estimated to have HQs of 58 

for lead, 55 for arsenic III, and 9 for cadmium. 

• For high-end risks, composite-lined surface impoundments were estimated to have HQs 

of 4 for lead, 31 for arsenic III, and 2 for cadmium. 

• Central tendency estimates for all surface impoundments were either below the risk 

criteria, or the modeled infiltration rate was too low for the contaminant plume to reach 

the nearby surface waterbody during the time period of the analysis (10,000 years). 

Regarding risk estimates from landfills: 

• For high-end risks, unlined landfills were estimated to have HQs of 58 for lead, 11 for 

arsenic III, 5 for cadmium, and 2 for antimony. 

• For high-end risks, clay-lined landfills were estimated to have an HQ of 3 for arsenic III. 
• For high-end risks in composite-lined landfills, the estimated risks either did not exceed 

the risk criteria or the modeled infiltration rate was too low for the contaminant plume to 

reach the nearby surface waterbody during the time period of analysis (10,000 years). 

• Central tendency estimates for landfills of all liner types were either below the risk 

criteria, or the modeled infiltration rate was too low for the contaminant plume to reach 

the nearby surface waterbody during the time period of the analysis (10,000 years). 

While the 2009 risk assessment addresses exposure to aquatic and sediment receptors in surface 

waterbodies impacted by groundwater, EPA had not collected new data on impoundment water 

samples. Therefore, the direct exposure pathway for ecological risk was addressed through 

discussion of the results of the CCW risk assessment conducted in 1998 (U.S. EPA, 1998a,b). 

This assessment did consider direct exposure of ecological receptors to surface impoundment 

waters. The approach in the 1998 study restricted the analysis to terrestrial receptors that obtain 

food and prey directly from the surface impoundments. The 1998 direct exposure results show: 

• HQs greater than 1 for antimony, molybdenum, thallium, chromium III, zinc, beryllium, 

chromium VI, and arsenic III. 

• HQs greater than 10 for silver, nickel, vanadium, copper, aluminum, and arsenic V. 

• HQs greater than 100 for selenium IV, selenium VI, cadmium, total selenium, barium, 

lead, mercury, and boron. 

Seven of the proven damage cases to surface water identified in the damage case assessment 

were ecological in nature and reflect damages to fish, frogs, and other wildlife as a result of 

discharges from surface impoundments. The Agency notes that these discharges are regulated by 

the NPDES program under the CWA and are not within the authority of RCRA. We are 
presenting these cases here simply to provide information on this potential for risk to the 

environment. 

In five cases, lakes constructed as cooling water sources for coal-fired power plants received 

discharges from the plants’ ash-settling ponds containing elevated levels of selenium resulting in 

elevated levels of selenium in fish in the lakes. The states issued fish consumption advisories 

and set new discharge limits for selenium. These advisories have since been lifted based on 

results of fish tissue studies. Similarly, a fish-consumption advisory was issued by the 

Tennessee Wildlife Resources Agency (TWRA) in January 2009 in response to the coal ash spill 

at the TVA Kingston power plant. TWRA plans to resample fish tissue on a semiannual basis 

and expects that the assessment of the impact of this release on wildlife resources and habitat 

will require repeated sampling and evaluation over the next three to five years. In another case, 

coal ash was disposed of in a nearby quarry from 1967 to 1990. Concentrations of selenium, 

arsenic, and possibly thallium were elevated in largemouth bass from the quarry relative to bass 

from another nearby site, and some fish from the quarry had deformed bony structures. Higher 

concentrations of arsenic, selenium and lead were also found in small animals around a coal ash 

pond than in animals from a reference site. Finally, at another site, fly ash was sluiced 

(transported in water) to settling basins. A continuous flow of sluice water exited the basins into 

a swamp, which discharged into a stream. Observations of bull frog tadpoles inhabiting the 

settling basins and swamp revealed deformities and impaired swimming and predator avoidance 

abilities. 
For the risk analysis conducted for the March 1999 Report to Congress,15 a number of 

publications were identified linking adverse effects in amphibians (and other biota) with 

exposure to sluiced ash pumped into a series of settling basins and, ultimately, into a two hectare 

drainage swamp. This site is one of the seven proven ecological damage case sites identified by 

EPA. The drainage swamp at the Savannah River Project in South Carolina historically received 

effluent from other coal ash settling basins that are no longer in use (Rowe, et al., 1996). Various 

studies related to this site (e.g., Cherry, et al., 1984; Guthrie and Cherry, 1979; Hopkins, et al., 

1997) have demonstrated that effects ranging from mortality to sublethal effects, such as 

developmental anomalies, are causally linked to the presence of elevated concentrations of trace 

elements found in coal ash residuals. In particular, selenium has been shown to be toxic to 

amphibians at relatively low levels of exposure (e.g., Browne and Dumont, 1979). In addition, 

accumulation of selenium (a common trace metal in CCRs) has been demonstrated in both 

terrestrial (e.g., Carlson and Adriano, 1993) and aquatic ecosystems (e.g., Lemly, 1985; 

Ohlendorf, et al., 1990; Saiki, et al., 1993). Many studies suggested that the effects were caused 

by the properties of combustion ash (e.g., low pH; siltation; high soluble salts concentration; 

pozzolanic action), as well as the trace metals in the ash. 

 

15 Non-ground water Pathways, Human Health and Ecological Risk Analysis for Fossil Fuel Combustion Phase 2 

(FFC2); Draft Final Report, June 5, 1998 available at 

www.epa.gov/epawaste/nonhaz/industrial/special/fossil/ngwrsk1.pdf