Projects Hydrology and Water Quality Associated With The Midwestern Reclamation Site (Site No. 1087) Pike County, Indiana by Denver Harper and Greg Olyphant
	Maps showing location of the study site. Right-click on the map to zoom in.

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PROJECT SUMMARY

In cooperation with the Indiana Division of Reclamation (IDOR) of the Indiana Department of Natural Resources (IDNR), the Indiana Geological Survey (IGS) and the Department of Geological Sciences of Indiana University (IU) undertook an investigation to provide quantitative information concerning the beneficial effects of reclamation involving the emplacement of a cap containing coal combustion byproducts (CCBs) across a deposit of pyritic coarse-refuse that is currently generating contaminated drainage. The term of the study was from March 1995 to February 1999.

PROJECT SCOPE AND CHRONOLOGY

Acid-generating refuse from an abandoned coal-preparation facility.

The study area is Abandoned Mine Land Site No. 1087 ("Midwestern"), located in the uplands of the Patoka River watershed, in Section 22, T. 2S, R. 7W, Pike County, Indiana. This site was a source of acidic mine drainge (AMD), virtually all of which exited the site as surface discharge through a single outlet into a tributary of the Patoka River. During surface mining of the Springfield Coal, widespread layers and ridges of overburden spoil had been deposited. In addition, pyritic coal preparation refuse had been deposited over approximately 7.9 acres in the central part of the site.

Surface runoff was acidified by dissolution of iron sulfate salts, which were abundant across the surface of the exposed refuse. Rainfall that infiltrated the refuse also resulted in the generation of acidic ground water (from pyrite oxidation); this infiltrated rainfall represented a great store of acidity which was continuously being discharged as baseflow into a central trunk stream. Several highwall pits along the periphery of the refuse area contained ponds, some of which were interconnected to a mine aquifer consisting of flooded underground mines. The uppermost elevation of the water in this mine aquifer was fixed by the elevation of a spillway associated with one of the ponds. A small levee and impoundment raised the level of a spring that issued from the mine aquifer, thereby limiting its discharge. Thus, baseflow of the principal stream exiting the site came mainly from the shallow water-table aquifer in coarse-grained refuse. Because both baseflow and storm runoff was derived primarily from the central refuse area, discharge from the site—regardless of season or prevailing weather conditions—was extremely acidic.

View of a water-filled pit that was pumped and then filled with coal-combustion byproducts.

In Indiana, there has been limited use of coal combustion byproducts in the reclamation of active surface mines. Although such byproducts had not previously been utilized in the reclamation of abandoned mine land (AML) sites, the Indiana Division of Reclamation (IDOR) was interested in demonstrating the suitability of these materials for use as alkaline cover and structural fill in AML settings, because good borrow materials are often scarce in surface-mined areas, and because mine spoil, which is abundant, often has undesirable physical and chemical properties. ATEC Associates, Inc. (ATEC), determined that AML Site No. 1087 (“Midwestern”) was well situated to demonstrate the use of ponded ash and fixated scrubber sludge (FSS), which is a mixture of fly ash, gypsiferous flue-gas desulphurization sludge, and agricultural limestone. Because FSS has a very low saturated hydraulic conductivity (10^-6 and 10^-9 cm/sec), it was proposed to use such material as a cap over the pyritic refuse to prevent percolation of infiltrated rain water into the refuse deposit. ATEC created a reclamation design that involved utilization of fly ash and FSS from the Petersburg Generating Station of Indianapolis Power and Light (IPL) to backfill highwalls and to construct cover over exposed coal refuse.

Perspective views of the reclamation site, before and after reclamation.

Reclamation commenced on October 10, 1995. Highwall lakes were drained and backfilled, as were other low-lying areas. By late autumn 1996, all the ash had been delivered to the site and emplaced. A passive anoxic limestone drain (PALD) was constructed to capture and treat flow from the spring that issues from the abandoned underground mines. A network of riprap drainage channels was created to capture surface runoff and direct it into sediment ponds at the outlet from the site. Wetland cells were installed to passively treat a zone of seeps located in the southern part of the site. By late September of 1997, revegetation and grading was finished and reclamation was complete.

On April 1, 1995, the Indiana Geological Survey (IGS) and the Department of Geological Sciences of Indiana University (IU) began to monitor baseline conditions. This included rainfall, evaporation, soil moisture, stream flow and stream chemistry leaving the site, and water levels and associated chemistry in monitoring wells across the site. Pre-reclamation monitoring continued through mid-October 1995.

Monitoring activities being conducted by personnel of the IGS at the Midwestern Reclamation Site.

During reclamation, several monitoring installations were destroyed. Following reclamation in spring 1997, IGS re-installed monitoring stations where necessary and continued to monitor the hydrological and geochemical aspects of the site in order to draw conclusions about the reclamation.

SUMMARY OF RESULTS

Prior to reclamation, acidic mine drainage (AMD) was being derived from a contaminant plume in the central refuse area and from a spring that discharged from abandoned underground mines. This problem drainage was addressed by a combination of the following techniques: (1) FSS was placed over the refuse deposit to prevent vertical recharge of the shallow water table, (2) surface-mine highwall pits were filled and capped, (3) a Passive Anoxic Limestone Drain (PALD) was installed to treat a spring that discharges from the underground workings, and (4) final treatment of surface waters was accomplished through a series of wetland cells and settling ponds.

View of a constructed wetland on part of the Midwestern Reclamation Site.

A comparison of data collected before and after reclamation indicates that total acidic outfall from the site during the critical period of April through October (which is the season when AMD is typically most concentrated) has experienced a five-fold reduction. This reduction represents a net gain of about 2 x 10⁵ kilograms of alkalinity (CaCO₃ equivalent) in the acid-base balance of the site. This was accompanied by a five-fold reduction in the concentrations of iron and aluminum. Among trace elements, the concentrations of boron, molybdenum, selenium, copper, and chromium increased for a brief period either during reclamation or shortly after, but have since decreased. Nickel and cadmium concentrations continue to show fluctuations corresponding to pH shifts but at lower concentrations than before reclamation. Lead and mercury concentrations have decreased to detection limits since reclamation. Antimony and silver have not been detected at all. Chloride and potassium concentrations have increased only slightly.

Hydrologic monitoring and geophysical investigations indicate that the preexisting contaminant plume within the refuse is being effectively isolated from vertical recharge by the FSS. Also, the proportion of rainfall that leaves the site as direct runoff has increased. This increased storm runoff has not caused any erosion on the site, and sufficient moisture is being retained in the soil cover to insure healthy vegetation.

Continuous monitoring of water quality at the outlet indicates that the storm runoff is much more dilute than baseflow. Also, simultaneous monitoring of discharge at the site's outlet and at the outlet of the PALD indicated that most of the baseflow from the site is now being derived from the flooded underground workings. The PALD is effectively treating the mine water, so that even the baseflow is more dilute and less acidic that it was prior to reclamation.

The results of our investigation show that this reclamation approach has favorably altered the hydrologic and hydrochemical conditions on the site in such a way that rainwater has a shorter residence time and is less exposed to acid-generating conditions. This has been achieved without any significant leaching of detrimental trace elements from the CCBs.

For a detailed technical report on the investigation, go to the Midwest Reclamation Project Web page. NOTE: Because it contains a number of graphics with large files, the technical report is best viewed with a high-speed internet connection.

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For additional information, you may contact either Greg Olyphant (e-mail: olyphant@indiana.edu) at the Department of Geological Sciences, Indiana University, Bloomington, IN 47405, or Denver Harper (e-mail: dharper@indiana.edu) at the Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47405