FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: Monitoring Mines Reclaimed with Mixtures of Spoil and Coal Combustion Residues

ICCI Project Number: 96-1/7.1A-3

Principal Investigator: Dr. Steven P. Esling, Department of Geology, Southern Illinois University

Other Investigators: Dr. Bradley C. Paul, Department of Mining Engineering, Southern Illinois University

Project Manager: Dr. Daniel Banerjee, ICCI

Abstract

Three separate large-scale field demonstration projects begun within the last five years at abandoned mines, have involved in one way or another, the application of both flue gas desulferization (FGD) and fluidized bed combustion (FBC) residues in mine land reclamation. The first, at Forsythe-Energy, used FGD residues as well as fly ash as substitute fill to a surface mine pit; the second, at Thunderbird, created seven caps composed of varying proportions of FBC fly and bottom ashes; and the third, at Harco, involved amending coal processing waste with FGD residues to control infiltration and to induce alkaline recharge. Previous studies monitored all three demonstration sites for short term performance, and in general, no significant environmental impacts were detected. The long-term capacity of the residues to control acid mine drainage and their long-term impact on the environment, however, are unknown. Changes in regulations that would allow the widespread application of the residues in reclamation as well as industry acceptance of these methods hinges on the long-term behavior. The first year of this two year project continued monitoring the performance and environmental impacts of the different reclamation strategies applied at the three sites. Geochemical results collected over the past year suggest that the residues can ameliorate groundwater impacted by mining activities. In addition, to date, leachate generated by the residues has not degraded groundwater or surface water quality. The final analysis of the data collected over the two year project period will include an evaluation of the effectiveness of each reclamation technique, as well as environmental impacts originating with the FBC and FGD residues, if any. In addition, data collected will be used to adjust groundwater flow and contaminant transport models at each site. The final report will synthesize the results with earlier research at all three sites.

Executive Summary

Three separate large-scale field demonstration projects begun within the last five years at abandoned mines, have involved in one way or another, the application of both flue gas desulferization (FGD) and fluidized bed combustion (FBC) residues in mine land reclamation. The first, at Forsythe-Energy, used FGD residues as well as fly ash as substitute fill to a surface mine pit; the second, at Thunderbird, created seven caps composed of varying proportions of FBC fly and bottom ashes; and the third, at Harco, involved amending coal processing waste with FGD residues to control infiltration and to induce alkaline recharge. Previous studies monitored all three demonstration sites for short term performance, and in general, no significant environmental impacts were detected. Long-term impacts and long-term performance of FBC and FGD residues in preventing acid mine drainage, on the other hand, are unknown. Industry and regulatory agency acceptance of new reclamation strategies employing FGD or FBC residues hinges on an analysis of long-term environmental impacts. This report summarizes continued environmental monitoring for the past year at all three demonstration sites.

The monitoring network at the Forsythe-Energy site has only monitoring wells (including a drain beneath the residues). The network at Thunderbird includes a rain gauge, monitoring wells, survey points, lysimeters and surface water sampling points along Briar Creek. The network at Harco, once reclamation work is completed, will include a rain gauge, monitoring wells, suction and free-drainage lysimeters, infiltrometers, tensiometers, and TDR probes. Progress made this past year can be divided into work completed in order to prepare a site for long-term sampling and a preliminary analysis of surface and groundwater quality at the Forsythe-Energy and Thunderbird sites.

Site Preparation Work

Reclamation has altered groundwater flow directions away from wells originally installed to monitor downgradient groundwater quality at the Forsythe-Energy site. Other wells now downgradient are too far from the residue fill to detect leachate. A new well was installed immediately downgradient of the fill in December, 1996 following accepted standard practices. Groundwater sampling at the Forsythe-Energy began once this well was installed.

The dedicated sampling system originally intended for the wells at the Thunderbird site requires access to the well head with a vehicle that can carry the heavy and bulky gas cylinders used to drive the pumps. Access roads to the Thunderbird site were removed just before the start of this project. A wet autumn then prevented access to the monitoring wells with a vehicle. Fortunately, an alternative sampling system became an option when another project, funded by the US Department of Energy, allowed the Department of Geology to acquire an actuator for driving inertial pumps. The relatively light weight actuator can be carried to remote sites. Dedicated inertial pumps were installed at Thunderbird after acquisition of the actuator in the spring, 1997. Groundwater sampling began at Thunderbird in June, 1997.

At the time this project began, the contractor retained by the Illinois Abandoned Mine Land Reclamation Division of the Illinois Department of Natural Resources to reclaim the Harco site still had not completed the work. Because of this, groundwater monitoring wells still needed to be installed, a task not originally planned for this project. Three groundwater monitoring wells were installed at the site in May and July, 1997; one upgradient and two downgradient of soil amendments with FGD residues. Additional wells will be installed as the contractor completes reclamation adjacent to the test plot in the coming year. No groundwater samples were collected at Harco. The first set of samples will be collected the first quarter of the second year of the project.

Geochemistry

Water quality sampling for this project followed accepted standard practices to effectively guarantee reliable field geochemical and hydrologic data. In the course of the past year, 68 samples were collected at the three sites from surface and groundwater monitoring points. Three samples were collected from each field instrument during a sampling event; one for cations, one for anions, and one for alkalinity. The alkalinity tests were performed using a Mettler Auto Titrator in the Mining Engineering Environmental Laboratory. The remaining tests were performed in the Mining Engineering Carterville Laboratories, or the joint water chemistry lab operated by Mining Engineering and Geology. Anions were determined potentiometrically or by Liquid Ion Chromatography using a Dionex 10. Cations were determined by ICP with more precise measurements for lead, arsenic and selenium made by graphite furnace or hydride formation AA.

An analysis of the samples collected at each site seeks an answer to two questions; Does leachate generated by the FBC and FGD residues impact groundwater or surface water quality? and, Do these residues mitigate acid mine drainage? The critical indicators of acid mine drainage are elevated concentrations of iron, magnesium, manganese, and sulfate. The fly ash which composed part of the fill at the Forsythe-Energy site generates high concentrations of boron in its leachate. The FBC residues at Thunderbird and the FGD residues at Forsythe-Energy and Harco produce high concentrations of sodium and potassium in their leachate.

Samples at the Forsythe-Energy site collected from a sand filter installed horizontally at the base of the residue fill consistently contain high concentrations of boron, and reduced levels of iron, manganese, magnesium, and sulfate relative to the native groundwater. Boron is the best indicator of residue leachate at this site. This constituent, however, is not detected in wells located downgradient at concentrations significantly different than those in wells upgradient of the residue fill. In addition, iron, magnesium, manganese, and sulfate, traditional indicators of acid mine drainage, have reduced levels in downgradient wells when compared to upgradient wells.

The Thunderbird site also showed positive effects of the FBC caps, both in groundwater and stream samples. Many factors can influence the geochemistry of stream water other than drainage across the reclaimed mine site, including the duration and intensity of recent storm events. The concentration of some constituents tends to fluctuate from one sample event to another because of these factors. Certain trends in the Briar Creek data, however, are evident. Sodium and potassium, indicators of leachate generated by the FBC residues at this site, are not detected in concentrations downstream from the test plots in levels significantly different than those upstream.

Upgradient wells at the Thunderbird site have high concentrations of iron, manganese, magnesium and sulfate and low pH levels relative to the wells located downgradient of the residues. Preliminary groundwater data, therefore, suggests some ameliorating effects of the residues. Sodium and potassium concentrations in the downgradient wells also do not exceed those detected in the upgradient wells, indicating that at the present time leachate generated by the residues has not reached groundwater.

Plans for the Second Year of the Project

Environmental monitoring will continue during the second year of the project. The final analysis of the data collected over the two year project period will include an evaluation of the effectiveness of each reclamation technique, as well as environmental impacts originating with the FBC and FGD residues, if any. In addition, data collected will be used to adjust groundwater flow and contaminant transport models at each site. The final report will synthesize the results with earlier research at all three sites.