Integrated Environmental Assessment and Management — Volume 12, Number 2—pp. 353–363 © 2015 SETAC
353
Assessment of Trace Element Impacts on Agricultural Use of Water from the Dan River following the Eden Coal Ash Release Dean Hesterberg,*y Matthew L Polizzotto,y Carl Crozier,y and Robert E Austiny yDepartment of Soil Science, North Carolina State University, Raleigh, North Carolina, USA
(Submitted 29 September 2014; Returned for Revision 9 February 2015; Accepted 14 May 2015)
ABSTRACT
Keywords: Coal ash
Trace elements
Soil contamination
INTRODUCTION Catastrophic releases of potentially toxic substances into the environment require rapid assessments of impacts and prioritization of mitigating actions by a diverse array of responders. Recent, large-scale releases of coal ash into river systems have focused attention on the issue of safe management of this energy byproduct. Approximately 120 million tonnes of solid-phase coal ash combustion products are produced annually in the United States as a result of electric power generation (Rowe 2014). Nearly 60% of these materials are stored in more than 1000 wet surface impoundments of landfills (Ruhl et al. 2012), and failure of wet impoundments can result in release of coal ash containing potentially toxic trace elements into the environment. The largest such incident in the United States occurred on December 22, 2008 when 3.8 million cubic meters of coal ash slurry were released into the Clinch and Emory Rivers after a dike failed at a 34-hectare impoundment at the Tennessee Valley Authority (TVA) Kingston Fossil Plant (Ruhl et al. 2010). Another historically large incident in the United States involved a 1.1-million cubic meter release of ash sludge and black water in Martin County, Kentucky in 2000 (Wigginton et al. 2007). A rapid and judicious response is critical for mitigating environmental * Address correspondence to [email protected] Published online 2 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ieam.1669
Rapid assessment
Water quality
Mass-balance calculation
damages in the event of any coal ash release from its containment area. The research described here illustrates a mass–balance approach for assessing environmental impacts of potentially toxic trace elements contained within coal ash. We demonstrate the approach in an assessment of agricultural impacts of the February 2, 2014 failure of a stormwater discharge pipe at an ash storage site at Duke Energy’s Dan River Steam Station in Eden, North Carolina. This impoundment failure led to an estimated 35 000 tonnes of coal ash and more than 100 000 cubic meters of ash water being released into the Dan River. The ash was distributed across nearly a 120-km stretch of river, and an estimated 90% of ash remains in the river system following cleanup operations. Coal ash commonly contains elevated concentrations of trace elements such as As, Ba, Cu, Pb, and Se (Vejahati et al. 2010). “Trace elements” are chemical elements that occur at very low (parts-per-million) concentrations compared with major elements found at percentage-level concentrations in rocks and minerals (Sparks 2003). Either particulate or dissolved forms of trace elements can pose risks to human and ecosystem health. Between the Steam Station release site in Eden and the John H. Kerr Reservoir 120 km downriver, the Dan River serves as a source of drinking water for people and livestock, a source of irrigation water for agriculture, and a resource for recreation. Accordingly, mobilization of trace element contaminants from the released coal ash could lead to significant impacts to a wide variety of stakeholders within the region.
Environmental Management
Catastrophic events require rapid, scientifically sound decision making to mitigate impacts on human welfare and the environment. The objective of this study was to analyze potential impacts of coal ash-derived trace elements on agriculture following a 35 000-tonne release of coal ash into the Dan River at the Duke Energy Steam Station in Eden, North Carolina. We performed scenario calculations to assess the potential for excessive trace element loading to soils via irrigation and flooding with Dan River water, uptake of trace elements by crops, and livestock consumption of trace elements via drinking water. Concentrations of 13 trace elements measured in Dan River water samples within 4 km of the release site declined sharply after the release and were equivalent within 5 d to measurements taken upriver. Mass–balance calculations based on estimates of soil trace-element concentrations and the nominal river water concentrations indicated that irrigation or flooding with 25 cm of Dan River water would increase soil concentrations of all trace elements by less than 0.5%. Calculations of potential increases of trace elements in corn grain and silage, fescue, and tobacco leaves suggested that As, Cr, Se, Sr, and V were elements of most concern. Concentrations of trace elements measured in river water following the ash release never exceeded adopted standards for livestock drinking water. Based on our analyses, we present guidelines for safe usage of Dan River water to diminish negative impacts of trace elements on soils and crop production. In general, the approach we describe here may serve as a basis for rapid assessment of environmental and agricultural risks associated with any similar types of releases that arise in the future. Integr Environ Assess Manag 2016;12:353–363. © 2015 SETAC
354
One particular challenge in responding to such a coal ash release is making timely decisions about potential environmental risks based on minimal or imperfect data. With regard to the Dan River release, this challenge was manifested in terms of agricultural use of river water. Whereas river water used as a source for human drinking water is routinely monitored and treated, river water for agricultural purposes is accessed at a variety of locations, applied to land in varying amounts depending on rainfall, and provided to livestock without monitoring water quality. Irrigation and flooding with contaminated river water can load toxic trace elements to soils, potentially causing excessive accumulation of these elements in food crops. Similarly, consumption of contaminated water by livestock could result in adverse health impacts and possibly transfer trace elements through the food chain to humans. Following the ash release to the Dan River, timely decision making guidance was needed by farmers to determine if, when, and how river water could be used to avoid land degradation, economic loss, and exposure of toxic trace elements to people and livestock. These decisions were essential for determining whether to invest in planting crops soon after the ash release and how to manage livestock on lands that could be impacted by the release. The objectives of our research were to evaluate potential impacts of ash-derived trace element contaminants on agriculture in the Dan River basin and to determine which potentially toxic elements are of most concern. We analyzed available water chemistry data and used knowledge of agricultural practices in the Dan River basin to assess potential soil-loading rates of trace elements via irrigation and flooding, crop uptake of these elements, and the potential threat of trace elements to livestock. Evaluating these data with respect to pathways for trace element transfer between residual coal ash in the Dan River and agricultural soils, crops, and livestock led to practical guidelines for diminishing any impacts of the ash release on agricultural production. The approach and scenarios described here can be adopted to support timely analyses by regulatory agencies and extension services who advise farmers and citizens on environmental and agricultural risks associated with any similar types of contaminant releases that arise in the future.
Integr Environ Assess Manag 12, 2016—D Hesterberg et al.
MATERIALS AND METHODS Location The coal ash release occurred at Duke Energy’s Dan River Steam Station in Eden, North Carolina (Figure 1). The majority of ash has been dispersed throughout the river between the release site and the Kerr Reservoir downriver. Dan River water is used for irrigation in the river floodplain, and common crops include tobacco, corn, wheat, soybeans, and forage-type fescue. River water is also used as a drinking water source for livestock. Data sources Mass–balance calculations were developed based on measurements of total concentrations of various trace elements reported by US Environmental Protection Agency (USEPA) or Duke Energy for up to 449 unfiltered, acidified samples of Dan River water collected between February 2 and March 19, 2014 at multiple locations downriver and upriver of the coal ash release site. Additional water quality data included turbidity and trace element concentrations in suspended solids from the USEPA, and dissolved concentrations of Zn in filtered samples from Duke Energy. The USEPA samples were collected at multiple locations between the coal ash release site and the South Boston, Virginia water intake located approximately 110 km downriver (Figure 1). Duke Energy samples were taken between the release site and the Henderson, North Carolina water intake in the John H. Kerr Reservoir. The USEPA data collected over time are available on their web site (USEPA 2014), and the remaining data were provided by Duke Energy Corporation. As discussed below, data from both sources showed consistent trends. Samples containing trace elements at concentrations below reportable concentrations (“practical quantitation limits” for USEPA data or “detection limits” for Duke Energy data) were plotted at these limits in our trend graphs. These limits varied between the two data sources and sometimes across data sets from different sampling times, apparently because of different laboratories or techniques used to perform the analyses. The total number of samples in which specific elements were
Figure 1. Field map of a section of the Dan River showing the coal ash release (“spill”) site, selected water quality sampling sites, and other reference points.
Impacts of the Dan River Coal Ash Release on Agriculture—Integr Environ Assess Manag 12, 2016
analyzed by either or both USEPA and Duke Energy was 449 for As, Cr, Cu, Pb, Se, and Zn; 445 for Cd; and between 29 and 60 for Ba, Hg, Ni, Sr, V, and Y. Elemental compositions for four coal ash samples collected February 6-12, 2014 from the primary ash basin at the Dan River Steam Station were also obtained from USEPA (Table 1, discussed below). Scenario calculations Temporal trends in water quality data following the Eden coal ash release were used to determine potential impacts of the release on agricultural operations in the Dan River basin. We assessed potential impacts based on four pathways: 1) deposition and buildup of trace elements in soils from irrigation water; 2) uptake of trace elements from irrigation water into crops; 3) deposition of trace elements to soils from flooding; and 4) exposure of livestock to trace elements in drinking water. For pathways 1 to 3, we used a mass–balance approach to assess potential impacts based on a nominal concentration of 5 mg/L and a worst-case concentration of 50 mg/L of any trace element in Dan River water. Details, assumptions, and example calculations are given below for each of the pathways. The principles described can be adopted to specific pathways and conditions by which other chemical releases into the environment can impact agriculture. Trace element deposition to soils from irrigation water. We used the 5 and 50 mg/L water concentrations to assess the annual deposition of trace elements to soils with 25.4 cm
355
(10 inches) of irrigation water. According to growers in the Dan River basin, annual water needs of crops are approximately 25.4 cm (10 inches) for wheat, 40.6 cm (16 inches) for tobacco, and 43.2 cm (17 inches) for soybeans. The assumption of 25.4 cm used in our calculations represents between 60% and 100% of the annual water needs of wheat, tobacco, and soybeans. Results of our calculations can be scaled proportionately to other irrigation-water applications, which depend on rainfall levels for a given year. Changes in soil trace element concentrations following deposition depend on the mass of soil used in the calculation. For example, if trace elements added with irrigation water were assumed to accumulate only in the top 1 cm of soil, then the estimated buildup would be 30-fold greater than if the trace elements were assumed to be distributed by tillage within the top 30 cm of soil where the majority of crop roots reside. Because most trace elements have limited mobility in soils and some mixing of soil is expected even in no-till systems, we assumed for our calculation that any trace elements applied with irrigation water from the Dan River would be distributed evenly throughout the top 10 cm of soil. The results of our calculations can be proportionately scaled to other soil depths. To illustrate our calculation, we assumed a topsoil bulk density of 1.3 tonnes/m3 (50% porosity). Thus, the top 10 cm of soil would weigh 1300 tonnes/ha. Applying 1 cm of water per hectare (105 L) containing 50 mg/L of a given trace element would add 5.0 g of the trace element. Distributing this 5.0 g of trace element into 1300 tonnes of soil would increase the soil
Table 1. Ranges and mean concentrations of trace elements in coal ash samples from the failed ash pond at the Dan River Steam Station, compared with concentration ranges reported for soils and fertilizers Range of ash conc. (mg/kg)a
Mean SD ash conc. (mg/kg)a
Soil conc. range (mg/kg)b
Fertilizer conc. range (mg/kg)c
As
17–61
48 21
4.4–7.2
2.7–120
Ba
210–1110
680 460
580
no data
Cd
353
Assessment of Trace Element Impacts on Agricultural Use of Water from the Dan River following the Eden Coal Ash Release Dean Hesterberg,*y Matthew L Polizzotto,y Carl Crozier,y and Robert E Austiny yDepartment of Soil Science, North Carolina State University, Raleigh, North Carolina, USA
(Submitted 29 September 2014; Returned for Revision 9 February 2015; Accepted 14 May 2015)
ABSTRACT
Keywords: Coal ash
Trace elements
Soil contamination
INTRODUCTION Catastrophic releases of potentially toxic substances into the environment require rapid assessments of impacts and prioritization of mitigating actions by a diverse array of responders. Recent, large-scale releases of coal ash into river systems have focused attention on the issue of safe management of this energy byproduct. Approximately 120 million tonnes of solid-phase coal ash combustion products are produced annually in the United States as a result of electric power generation (Rowe 2014). Nearly 60% of these materials are stored in more than 1000 wet surface impoundments of landfills (Ruhl et al. 2012), and failure of wet impoundments can result in release of coal ash containing potentially toxic trace elements into the environment. The largest such incident in the United States occurred on December 22, 2008 when 3.8 million cubic meters of coal ash slurry were released into the Clinch and Emory Rivers after a dike failed at a 34-hectare impoundment at the Tennessee Valley Authority (TVA) Kingston Fossil Plant (Ruhl et al. 2010). Another historically large incident in the United States involved a 1.1-million cubic meter release of ash sludge and black water in Martin County, Kentucky in 2000 (Wigginton et al. 2007). A rapid and judicious response is critical for mitigating environmental * Address correspondence to [email protected] Published online 2 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ieam.1669
Rapid assessment
Water quality
Mass-balance calculation
damages in the event of any coal ash release from its containment area. The research described here illustrates a mass–balance approach for assessing environmental impacts of potentially toxic trace elements contained within coal ash. We demonstrate the approach in an assessment of agricultural impacts of the February 2, 2014 failure of a stormwater discharge pipe at an ash storage site at Duke Energy’s Dan River Steam Station in Eden, North Carolina. This impoundment failure led to an estimated 35 000 tonnes of coal ash and more than 100 000 cubic meters of ash water being released into the Dan River. The ash was distributed across nearly a 120-km stretch of river, and an estimated 90% of ash remains in the river system following cleanup operations. Coal ash commonly contains elevated concentrations of trace elements such as As, Ba, Cu, Pb, and Se (Vejahati et al. 2010). “Trace elements” are chemical elements that occur at very low (parts-per-million) concentrations compared with major elements found at percentage-level concentrations in rocks and minerals (Sparks 2003). Either particulate or dissolved forms of trace elements can pose risks to human and ecosystem health. Between the Steam Station release site in Eden and the John H. Kerr Reservoir 120 km downriver, the Dan River serves as a source of drinking water for people and livestock, a source of irrigation water for agriculture, and a resource for recreation. Accordingly, mobilization of trace element contaminants from the released coal ash could lead to significant impacts to a wide variety of stakeholders within the region.
Environmental Management
Catastrophic events require rapid, scientifically sound decision making to mitigate impacts on human welfare and the environment. The objective of this study was to analyze potential impacts of coal ash-derived trace elements on agriculture following a 35 000-tonne release of coal ash into the Dan River at the Duke Energy Steam Station in Eden, North Carolina. We performed scenario calculations to assess the potential for excessive trace element loading to soils via irrigation and flooding with Dan River water, uptake of trace elements by crops, and livestock consumption of trace elements via drinking water. Concentrations of 13 trace elements measured in Dan River water samples within 4 km of the release site declined sharply after the release and were equivalent within 5 d to measurements taken upriver. Mass–balance calculations based on estimates of soil trace-element concentrations and the nominal river water concentrations indicated that irrigation or flooding with 25 cm of Dan River water would increase soil concentrations of all trace elements by less than 0.5%. Calculations of potential increases of trace elements in corn grain and silage, fescue, and tobacco leaves suggested that As, Cr, Se, Sr, and V were elements of most concern. Concentrations of trace elements measured in river water following the ash release never exceeded adopted standards for livestock drinking water. Based on our analyses, we present guidelines for safe usage of Dan River water to diminish negative impacts of trace elements on soils and crop production. In general, the approach we describe here may serve as a basis for rapid assessment of environmental and agricultural risks associated with any similar types of releases that arise in the future. Integr Environ Assess Manag 2016;12:353–363. © 2015 SETAC
354
One particular challenge in responding to such a coal ash release is making timely decisions about potential environmental risks based on minimal or imperfect data. With regard to the Dan River release, this challenge was manifested in terms of agricultural use of river water. Whereas river water used as a source for human drinking water is routinely monitored and treated, river water for agricultural purposes is accessed at a variety of locations, applied to land in varying amounts depending on rainfall, and provided to livestock without monitoring water quality. Irrigation and flooding with contaminated river water can load toxic trace elements to soils, potentially causing excessive accumulation of these elements in food crops. Similarly, consumption of contaminated water by livestock could result in adverse health impacts and possibly transfer trace elements through the food chain to humans. Following the ash release to the Dan River, timely decision making guidance was needed by farmers to determine if, when, and how river water could be used to avoid land degradation, economic loss, and exposure of toxic trace elements to people and livestock. These decisions were essential for determining whether to invest in planting crops soon after the ash release and how to manage livestock on lands that could be impacted by the release. The objectives of our research were to evaluate potential impacts of ash-derived trace element contaminants on agriculture in the Dan River basin and to determine which potentially toxic elements are of most concern. We analyzed available water chemistry data and used knowledge of agricultural practices in the Dan River basin to assess potential soil-loading rates of trace elements via irrigation and flooding, crop uptake of these elements, and the potential threat of trace elements to livestock. Evaluating these data with respect to pathways for trace element transfer between residual coal ash in the Dan River and agricultural soils, crops, and livestock led to practical guidelines for diminishing any impacts of the ash release on agricultural production. The approach and scenarios described here can be adopted to support timely analyses by regulatory agencies and extension services who advise farmers and citizens on environmental and agricultural risks associated with any similar types of contaminant releases that arise in the future.
Integr Environ Assess Manag 12, 2016—D Hesterberg et al.
MATERIALS AND METHODS Location The coal ash release occurred at Duke Energy’s Dan River Steam Station in Eden, North Carolina (Figure 1). The majority of ash has been dispersed throughout the river between the release site and the Kerr Reservoir downriver. Dan River water is used for irrigation in the river floodplain, and common crops include tobacco, corn, wheat, soybeans, and forage-type fescue. River water is also used as a drinking water source for livestock. Data sources Mass–balance calculations were developed based on measurements of total concentrations of various trace elements reported by US Environmental Protection Agency (USEPA) or Duke Energy for up to 449 unfiltered, acidified samples of Dan River water collected between February 2 and March 19, 2014 at multiple locations downriver and upriver of the coal ash release site. Additional water quality data included turbidity and trace element concentrations in suspended solids from the USEPA, and dissolved concentrations of Zn in filtered samples from Duke Energy. The USEPA samples were collected at multiple locations between the coal ash release site and the South Boston, Virginia water intake located approximately 110 km downriver (Figure 1). Duke Energy samples were taken between the release site and the Henderson, North Carolina water intake in the John H. Kerr Reservoir. The USEPA data collected over time are available on their web site (USEPA 2014), and the remaining data were provided by Duke Energy Corporation. As discussed below, data from both sources showed consistent trends. Samples containing trace elements at concentrations below reportable concentrations (“practical quantitation limits” for USEPA data or “detection limits” for Duke Energy data) were plotted at these limits in our trend graphs. These limits varied between the two data sources and sometimes across data sets from different sampling times, apparently because of different laboratories or techniques used to perform the analyses. The total number of samples in which specific elements were
Figure 1. Field map of a section of the Dan River showing the coal ash release (“spill”) site, selected water quality sampling sites, and other reference points.
Impacts of the Dan River Coal Ash Release on Agriculture—Integr Environ Assess Manag 12, 2016
analyzed by either or both USEPA and Duke Energy was 449 for As, Cr, Cu, Pb, Se, and Zn; 445 for Cd; and between 29 and 60 for Ba, Hg, Ni, Sr, V, and Y. Elemental compositions for four coal ash samples collected February 6-12, 2014 from the primary ash basin at the Dan River Steam Station were also obtained from USEPA (Table 1, discussed below). Scenario calculations Temporal trends in water quality data following the Eden coal ash release were used to determine potential impacts of the release on agricultural operations in the Dan River basin. We assessed potential impacts based on four pathways: 1) deposition and buildup of trace elements in soils from irrigation water; 2) uptake of trace elements from irrigation water into crops; 3) deposition of trace elements to soils from flooding; and 4) exposure of livestock to trace elements in drinking water. For pathways 1 to 3, we used a mass–balance approach to assess potential impacts based on a nominal concentration of 5 mg/L and a worst-case concentration of 50 mg/L of any trace element in Dan River water. Details, assumptions, and example calculations are given below for each of the pathways. The principles described can be adopted to specific pathways and conditions by which other chemical releases into the environment can impact agriculture. Trace element deposition to soils from irrigation water. We used the 5 and 50 mg/L water concentrations to assess the annual deposition of trace elements to soils with 25.4 cm
355
(10 inches) of irrigation water. According to growers in the Dan River basin, annual water needs of crops are approximately 25.4 cm (10 inches) for wheat, 40.6 cm (16 inches) for tobacco, and 43.2 cm (17 inches) for soybeans. The assumption of 25.4 cm used in our calculations represents between 60% and 100% of the annual water needs of wheat, tobacco, and soybeans. Results of our calculations can be scaled proportionately to other irrigation-water applications, which depend on rainfall levels for a given year. Changes in soil trace element concentrations following deposition depend on the mass of soil used in the calculation. For example, if trace elements added with irrigation water were assumed to accumulate only in the top 1 cm of soil, then the estimated buildup would be 30-fold greater than if the trace elements were assumed to be distributed by tillage within the top 30 cm of soil where the majority of crop roots reside. Because most trace elements have limited mobility in soils and some mixing of soil is expected even in no-till systems, we assumed for our calculation that any trace elements applied with irrigation water from the Dan River would be distributed evenly throughout the top 10 cm of soil. The results of our calculations can be proportionately scaled to other soil depths. To illustrate our calculation, we assumed a topsoil bulk density of 1.3 tonnes/m3 (50% porosity). Thus, the top 10 cm of soil would weigh 1300 tonnes/ha. Applying 1 cm of water per hectare (105 L) containing 50 mg/L of a given trace element would add 5.0 g of the trace element. Distributing this 5.0 g of trace element into 1300 tonnes of soil would increase the soil
Table 1. Ranges and mean concentrations of trace elements in coal ash samples from the failed ash pond at the Dan River Steam Station, compared with concentration ranges reported for soils and fertilizers Range of ash conc. (mg/kg)a
Mean SD ash conc. (mg/kg)a
Soil conc. range (mg/kg)b
Fertilizer conc. range (mg/kg)c
As
17–61
48 21
4.4–7.2
2.7–120
Ba
210–1110
680 460
580
no data
Cd
