SHAWN NAYLOR GREG A. OLYPHANT TRACY D. BRANAM Pros and Cons of Using CCBs in Reclamation Pros: Cons: •Disposal of large volumes of byproducts associated with energy.
Download ReportTranscript SHAWN NAYLOR GREG A. OLYPHANT TRACY D. BRANAM Pros and Cons of Using CCBs in Reclamation Pros: Cons: •Disposal of large volumes of byproducts associated with energy.
SHAWN NAYLOR GREG A. OLYPHANT TRACY D. BRANAM Pros and Cons of Using CCBs in Reclamation Pros: Cons: •Disposal of large volumes of byproducts associated with energy production •Contains potentially toxic metals •Minimal disturbance of adjacent areas for fill materials •Introduce alkalinity •Low permeability of some engineered CCBs prevents recharge and movement of groundwater •Poor understanding of leachate mobility in natural environments •Subsequent removal of these materials would present difficulties if such measures were ever deemed necessary Reclamation goal The Indiana Department of Natural Resources wanted to use CCBs to positively alter the hydrology of an AML site and improve chemistry of surface water exiting the site Purpose of study Although several researchers have used laboratory experiments to examine the physical and chemical characteristics of CCBs, studies that comprehensively examine the impacts of CCBs in applied settings are few. To determine the long-term physical and chemical effects of CCBs on a reclaimed AML site, baseline data are compared with post-reclamation data from several unique monitoring sites where CCBs were emplaced. History of Midwestern AML site •Surface and underground coal mining, 1895 to 1983 •Pyrite / associated weathering products were distributed among a large pyritic refuse pile in a central lowland area, underground mine workings, and highwall ponds (total area ~50 hectares) •AMD issued from a spring draining the underground mine workings and as baseflow from the central lowland aquifer 1996, ~450,000 m3 of CCBs were used as cap and fill material during reclamation •In Midwestern AML study area CCBs Utilized at Midwestern Site Cap: Fixated scrubber sludge (FSS) Structural fill: Ponded ash 3:2 ratio, fly ash : bottom ash 1:1 ratio, fly ash : FGD sludge with 1.5 - 2% quicklime 900 Concentration (mg/kg) 800 FSS Bottom Ash Fly Ash 700 600 500 400 300 200 100 0 As Ba B Cd Cr Cu Pb Hg Mo Ni Se Trace element concentrations for FSS and component CCBs used to produce FSS and ponded ash (analyses conducted prior to CCBs being wet sluiced) Midwestern site prior to and during reclamation Central refuse area prior to reclamation North highwall pond prior to reclamation Emplacement of ash fill at south pond Central refuse area prior to reclamation Midwestern site prior to and during reclamation Central refuse area prior to reclamation North highwall pond prior to reclamation Emplacement of ash fill at south pond North highwall pond prior to reclamation Midwestern site prior to and during reclamation Central refuse area prior to reclamation North highwall pond prior to reclamation Emplacement of ash fill at south pond Emplacement of ash fill at south pond Final reclamation steps Final grading and emplacement of soil cap (1m of reworked spoil and animal waste) Rip rap channels installed to divert runoff followed by revegetation Final grading and emplacement of soil cap Final reclamation steps Final grading and emplacement of soil cap (1m of reworked spoil and animal waste) Rip rap channels installed to divert runoff followed by revegetation Rip rap channels installed to divert runoff followed by revegetation Post-reclamation monitoring (November 1996 – November 2009) Methods: Physical hydrology Water levels Evapotranspiration Soil moisture profiles •Measured using a neutron probe •Estimated using a weighing lysimeter •Continuous data recorded using pressure transducers Discharge •Measured using a vnotch weir at the site outlet (SW4 / SW8) Chemical analyses Major cations Field chemistry •pH •Eh •SpC •Temperature •Acidity •Alkalinity •Ca Trace elements •Mg •As •F •K •Sb •Cl •Na •Ba •NO3 •Fe2+ •B •HCO3 •Fe3+ •Cd •SO4 Minor cations •Cr •Al •Cu •Mn •Pb •Ni •Se •Sr •Ag Major anions •Zn Water balance used to indicate relative pre- vs. post-reclamation rates of groundwater recharge R P ET S Ro R = groundwater recharge calculated as the residual ET = evapotranspiration P = precipitation S = change in unsaturated zone soil moisture storage Ro = runoff Water Balance Calculations Period P (cm) ET (cm) S (cm) Ro (cm) R (cm) 7/14/95 - 10/10/95 15.0 -8.8 (59%) NA 2.5 (17%) 3.7 (25%) 7/14/00 – 10/10/00 36.3 -24.5 (67%) -0.1 (0%) 6.2 (17%) 5.8 (16%) 7/14/00 - 7/18/01 94.1 -54 (57%) 1.9 (2%) 19.9 (21%) 18.3 (19%) Statistical analysis of refuse aquifer water level changes Statistical Model: WLt b0 b1Bt b2 Pt et t WLt = daily water level change in refuse aquifer (MW7) b0 = regression constant b1 = regression coefficient for barometric pressure (“barometric efficiency”) Bt = daily barometric pressure change (cm H2O) b2 = regression coefficient for precipitation Pt = daily precipitation (cm) et = autocorrelated error term ut = random error term Statistical analysis of refuse aquifer water level changes Pre-reclamation (1995) b1 (barometric press.) b2 (precipitation) parameter estimate standard error t-ratio -0.21 1.05 0.05 0.19 -4.55 5.48 Post-reclamation (1998) b1 (barometric press.) b2 (precipitation) standard error t-ratio -0.76 0.28 0.03 0.17 -28.9 1.70 n=282, R=0.84, =0.44 parameter estimate standard error t-ratio -1.23 0.25 0.05 0.27 -25.1 0.94 Post-reclamation (2008) b1 (barometric press.) b2 (precipitation) n=235, R=0.89, =0.00 parameter estimate Post-reclamation (2001) b1 (barometric press.) b2 (precipitation) n=140, R=0.56, =0.13 n=74, R=0.98, =0.49 parameter estimate standard error t-ratio -0.79 -0.04 0.02 0.18 -40.0 -0.20 Fluctuations in perched water overlying FSS cap Middle of cap Edge of cap Soil moisture data from former central lowland area MW7 Soil Moisture MW 4 Soil Moisture 0.3 0.3 Top of FSS layer 0.6 0.9 0.6 1.2 0.9 1.5 Top of FSS layer 1.2 Depth (m) Depth (m) 1.8 2.1 2.4 Spoil 2.7 3.1 3.4 3.7 1.5 1.8 2.1 2.4 2.7 4 N = 28 4.3 0 3 0.1 0.2 0.3 0.4 0.5 N = 27 3.3 0 Volumetric Moisture Content 0.1 0.2 0.3 Volumetric Moisture Content whiskers = min/max white line = median value bars = 25th/ 75th percentile red squares = mean value 0.4 0.5 Summary of chemical analyses SO4 (mg/l) Fe (mg/l) Acidity (mg/l) Alkalinity (mg/l) pH SpC (μmhos/cm) TDS (mg/l) Pre-reclamation water chemistry (April through August 1995) Site outlet (pre-rec.) SP1 n=3 1380 1220-1540 76 65-82 369 193-720 11 0-34 4.1 3.7-5.1 1958 1927-1988 2033 1900-2100 MW7 n=3 12967 8200-17500 4433 2800-5700 11732 7507-15817 0 0-0 1.4 1.1-1.8 22093 13700-32800 23333 12000-35000 SW4 n=4 2353 2280-2500 243 190-330 714 451-901 0 0-0 2.9 2.8-3.1 3215 3030-3350 3650 3300-3900 SW2 n=4 550 370-690 34 6-80 278 92-523 0 0-0 2.7 2.6-3.1 1479 930-1758 848 600-970 SW1 n=4 186 94-240 6 1-18 104 11-350 0 0-0 4.2 4.0-5.3 460 392-508 338 230-420 MW5 n=4 2695 2520-2880 285 250-320 885 825-979 0 0-0 3.1 3.0-3.4 3555 3390-3790 4275 3700-4700 Post-reclamation water chemistry (November 1996 through June 2007) Site outlet (post-rec.) SP2A 1463 722-1680 n=20 86 64-120 n=19 159 122-217 n=20 267 218-323 n=20 6.4 6.0-7.3 n=20 2531 1836-2810 n=20 2632 2336-3000 n=17 MW7 8119 2192-15900 n=20 2421 785-5700 n=18 5839 1560-13413 n=20 0 0-0 n=20 2.3 1.6-4.0 n=20 8890 4103-20800 n=20 15122 6405-29000 n=17 SW8 1579 625-2360 n=20 28 2-83 n=19 139 0-350 n=19 32 0-140 n=20 3.5 2.7-7.0 n=20 2448 1408-3389 n=20 2452 1600-3600 n=17 MW8 1794 1650-2270 n=20 1 0-6 n=19 20 0-70 n=20 55 29-123 n=20 7.0 6.2-8.7 n=20 3014 2516-3269 n=20 4192 2686-6823 n=17 MW9 1687 1370-1972 n=18 145 16-197 n=18 372 43-578 n=17 234 104-460 n=18 6.0 5.6-7.1 n=18 2740 1832-3172 n=18 3009 2400-3600 n=17 MW5S 2745 2175-4740 n=17 275 46-482 n=17 524 110-913 n=17 110 0-330 n=16 5.2 4.3-6.8 n=17 3726 2872-4950 n=17 5019 3500-9100 n=15 Changes in refuse aquifer (MW 7) supported by field chemistry data 4.5 35 R² = 0.55 4 30 3.5 25 3 pH 20 2 pH SpC 15 1.5 10 1 0.5 0 R² = 0.50 5 0 SpC (mS/cm) 2.5 16000 8000 14000 7000 12000 6000 acidity arsenic 10000 5000 8000 4000 6000 3000 4000 2000 2000 1000 0 0 Arsenic (µg/L) Total acidity (mg/L) Refuse aquifer (MW 7) acidity and arsenic concentrations Boron concentrations in refuse aquifer and ash-filled ponds 40 35 Boron (mg/L) 30 25 20 15 10 5 0 MW7 FSS over refuse SW2/MW8 SW1/MW9 FSS over ashfilled pond Ashfilled pond Arsenic concentrations at ash-filled ponds (SW2/MW8 and SW1/MW9) 50 40 SW2/MW8 SW1/MW9 Arsenic (µg/L) 30 20 10 EPA max. cont. level (10 µg/L) 0 Conclusions – physical hydrology •There has been a reduction in groundwater recharge that is attributed to: 1. Effectiveness of FSS cap that is distributed over 15% of the study area 2. Re-vegetation efforts have increased evapotranspiration 3. Increased barometric efficiency of the refuse aquifer indicates that it is now behaving as a confined aquifer 4. Perched water atop the FSS and little fluctuation in soil moisture content within the cap indicate that direct recharge of the refuse aquifer with oxygenated meteoric water is no longer taking place Conclusions – hydrochemistry •Long-term general improvements in water quality can be seen at each monitoring site •Alkalinity is now intermittently present at the site outlet and most of the other sites now regularly contain alkalinity •Improving trends in pH and SpC at the refuse aquifer (MW7) coincide with decreases in sulfate, total iron, lead, and total acidity •Arsenic and Boron remain slightly elevated at ash-filled lakes although the most recent sampling event in November, 2009 resulted in nondetect results for Arsenic at these sites Acknowledgements •Much of this work was funded by grants from the Indiana Department on Natural Resources, Division of Reclamation •Field work, including instrumentation and data collection, was coordinated by Jack Haddan with assistance from Curt Thomas, Kevin Spindler, Dana Cannon, Jeff Olyphant, and Jimmy Boswell. Lab analyses were conducted by Peg Ennis and Ron Smith. Denver Harper played a vital role in the design of the monitoring network, interpretation of pre-reclamation mine features and hydrology, as well as the development of a site GIS database. Questions?