T156 Identification and Quantification of Groundwater Flow Using Heat as a Tracer

Tuesday, 11 October 2011
8:00 AM - 12:00 PM
Room M100HI

GEOTHERMAL SURVEYS REVEAL EXOTHERMIC REACTIONS 27 YEARS FOLLOWING ACID ABATEMENT, OLD FORTY MINE, CLARION CO, PA

Paper number: T156-5
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

Limeplant flue dust (108.9 to 362.9 mt/.40ha) and quarry fines (362.9 to 36.3 mt/.40ha) were incorporated 15 to 45cm deep in a reclaimed surface mine, Clarion Co. PA to determine if alkaline top dressings might slow or abate pyrite oxidation. Two 1.0 ha treatment and a control plot were established, mulched, seeded and fertilized during 1984. Vadose water-quality responses were monitored in nested lysimeters and temperatures measured in 16 deep wells (16.7m average) and along 4 traverses at 30- and 60cm- depths to detect reductions in pyrite oxidation rates. Months to years might be required for buffered waters to permeate unsaturated spoil, neutralize acidic pore waters, raise pH and slow catalytic bacterial reactions. Temperature surveys were expected to reveal acid hot spots and areas with decreasing exothermic reactions brought about by the addition of lime plant flue dust and quarry fines.

Ten of 16 deep wells were cooler in April 2011 than 1988, 5 showed slight cooling and one was warmer in an untreated area. Eight wells were cooler when minimum v maximum temperatures were measured between Nov. 1987 to Oct. 1988 and were compared with April 2011 values, four showed some and four even less cooling during the period.

Shallow temperatures were obtained along four traverses crossing outslopes, the mine crest, treated, untreated and control plots. Nearly all April 2011 temperatures were cooler than April 1988 values. Outslopes were cooler than the mine crest. This supports a buoyancy-driven air circulation model over a diffusion model. Cooling was more pronounced in treated v control and untreated plots, but were widely variable in both. Tipple waste hotspots remained following 27 years of treatment. Neutralization benefits extended to 4.9m by the 17th year: pH remained low (3.0 to 4.4) within the upper 4.9m within control and untreated areas. Loading rates of flue dust and limestone quarry fines applied to the Old Forty Mine were not adequate to offset the 28% total sulfur content contained within the spoil and 2.6% pyritic sulfur content for tipple refuse.