Evidence for water contamination by effluents 

from steam- and coal-fired power plants:

the need for zero liquid discharge limitation

Avner Vengosh and Laura Ruhl

Nicholas School of the Environment, 

Duke University 

http://sites.nicholas.duke.edu/avnervengosh/
Energy production in the USA (2011)

EIA- US Energy Information Administration

Total production= 78 quadrillion Btu

Renewable 

(12.3%)
Electricity production in the USA (2011)

EIA- US Energy Information Administration

Renewable 

(8%)
Five hundreds power plants nationwide generate 

approximately 130 million tons of coal ash each year
As, B, 

Se, Hg

Combustion

Volatilization Retention of gases and 

volatiles by fly ash and 

treatment (FGD)

Storage of coal 

ash in ponds

leaching

Contamination of 

water resources

The cycle of contaminants: from fossil 

swamps to today waters 

coal
The Roxboro Coal fired plant, North Carolina 

1513 MCM

(~New York city)

(2558 megawatts)

Contaminants discharge to the environment

Cooling water

Source: CCR effluents Water quality

NPDES outfall
Evidences for water contamination from coal 

combustion products

• Extensive literature on laboratory coal ash leaching experiments 

has demonstrated the high mobilization of contaminants such as 

arsenic and selenium from coal ash.

• Specific case studies of spills or accidents (e.g., TVA coal ash 

spill, Kingston, TN).

• Monitoring the water quality of outfalls and downstream lakes 

and rivers in NC (Ruhl et al., 2012)
Experimental leaching of TVA coal combustion products:

High levels of As and Se upon leaching with water

bulk fly ash bottom ash
Coal Combustion Residues

As

Se

Hg

B

Sr

Li

Ra

SO4

Cr

Pb

Pollutants from coal combustion residues 

that could be released to the environment 
December 22, 2008: retaining walls broke on a waste retention pond at the Kingston 

coal Plant, Tennessee, and an estimated 4.1 million m3 of coal ash slurry was spilled 

onto the land surface and into the adjacent Emory and Clinch Rivers

The 2008 TVA coal ash spill

Accumulation of coal combustion products in the river bottom
Subsurface ash/ sediments;

Pore water

River water

(As <10 ppb)

Discovery of hot spots: arsenic contamination in pore water from 

buried ash deposits within river sediments in the spill area

15-50 cm

River sediments

Ecological threshold

(150 ppb)

From Ruhl et al., 2010
A national-level issue
Roxboro 

Plant at 

Hyco Lake

Mayo Plant 

at Mayo 

Lake

Belews Plant 

at Belews Lake Dan River 

Plant on the 

Dan River

Asheville Plant at Lake 

Julian and the French 

Broad River

Riverbend

Plant at 

Mountain 

Island Lake

Marshall Plant 

at Lake 

Norman

Allen Plant 

at Lake 

Wylie

Reference 

Lake Jordan 

Lake

Buck Plant at 

High Rock 

Lake 

9 sites, 1 reference lake
Investigated coal-fired electrical power plants, CCR effluent 

discharge through NPDES outfalls, and associated waterways in 

North Carolina 

• Large 

variability in 

effluent flux

• With and 

without FGD 

scrubber 

system
High As concentrations in some of the 

effluents from coal combustion residues 

ponds

Hyco Lake Outfall

Effluents from coal ash ponds

FGD FD No FGD
Enrichment factors of CCR effluents relative to upstream waters

As

Se

Tl

B

Two- to three-orders of magnitude of contaminants enrichment;

Support EPA modeling for high contaminants levels in CRR effluents
Conservative variations : Dilution in some cases can 

mitigates contamination

• The size of the water 

resource – massbalance between CRR 

discharge flux and 

natural water flows;

• The nature of the 

contaminants (e.g., its 

solubility);
Lake level

Redox-sensitive contaminants are enriched in deep water 

associated with lake thermal stratification

oxic

anoxic
Recycling of arsenic: long-term accumulation in 

lake sediments: dilution cannot be the solution

Coal 

Adsorption

to particulates

accumulation Pore water

Discharge of CRR effluents
Recycling of arsenic: long-term accumulation in 

lake sediments: high As in pore water even in 

systems where As in CRR effluent is low

Pore water in lake sediments

FGD FDNo FGD

Implications: reduction of 

contaminants level in CRR outfall is 

not sufficient to prevent contaminants’ 

accumulation in lake sediments and 

ecological food-chain  zero liquid 

discharge is needed.
Charlotte water treatment 

Outfall

(As=56 ppb)

Mountain Island Lake

Surface water=1 ppb;

Pore water =100 ppb

Suspended 

solids

drinking water

sludge (30-70 mg/kg)

soil amendment

?

The larger scale arsenic impact

Riverbed Steam Station
Arsenic in sludge from Charlotte-Mecklenburg treatment plant 

Data from Sam Perkins, Catawba Riverkeeper Foundation 

Arsenic levels in sludge 

from treatment facilities in 

NC not associated with 

coal ash disposal  zero

Results and implication

• This study shows that coal-fired power plants and FGD wastewaters have 

significant high levels of contaminants and directly effect the water quality of 

receiving waters of North Carolina. 

• We show that even low concentrations of some contaminants, such as As with 

concentrations below health benchmarks at the NPDES outfalls, could become 

problematic as As is retained in suspended sediments and remobilized with 

environmental changes in reduced bottom and pore waters. Dilution cannot be a 

solution.

•In every NPDES outfall we investigated we found elevated levels of contaminants; 

the test that was conducted in North Carolina applies to similar hundreds of coal ash 

ponds in the USA - this is a national level problem. 
Results and implications (continued)

• The results of this study have significant implications for hundreds of similar sites 

across the US given that CCR storage facilities continuously generate contaminants 

via leaching and transport to nearby hydrological systems. While this study focused 

on surface waters near CCR facilities, groundwater may have similar effects. Many 

CCR disposal ponds and landfills are not lined and, in many instances, are neither 

adequately monitored, nor regulated with respect to their effects on groundwater 

and surface waters. 

• The evidence for direct contamination of water resources directly from NPDES 

outfall of CCR effluents highlights the need for rigorous monitoring and clear 

regulations for limiting the CCR contaminants that are being discharged into US 

waterways. Zero liquid discharge is the only solution that can stop the buildup 

of coal contaminants in the environment.
Further reading:

Ruhl, L., Vengosh, A., Dwyer, G.S., Hsu Kim H., Schwartz, G., Romanski, A., and 

Smith, S.D. (2012). The impact of coal combustion residue effluent on water resources: 

A North Carolina example. Environmental Science & Technology, 46, 12226-12233.

Ruhl, L., Vengosh. A., Dwyer, G.S., Hsu-Kim, H., Deonarine, (2010). The 

Environmental Impacts of the Coal Ash Spill in Kingston, Tennessee: An EighteenMonth Survey. Environmental Science and Technology, 44, 9272–9278.

Ruhl, L., Vengosh. A., Dwyer, G.S., Hsu-Kim, H., Deonarine, A., Bergin, M., 

Kravchenko, J. (2009). Survey of the potential environmental and health impacts in the 

immediate aftermath of the coal ash spill in Kingston, Tennessee. Environmental Science 

and Technology, 43, 6326–6333.

http://sites.nicholas.duke.edu/avnervengosh/
Acknowledgements

•Nicholas School of Environment, Duke University

•National Science Foundation, Geobiology & Low-Temperature 

Geochemistry Program