Projects > Hydrology and Water Quality Associated With The Midwestern Reclamation Site
Midwestern Reclamation Site Project
Final Report from the Indiana Geological Survey to the Indiana Division of Reclamation
Water Chemistry
Purpose:
Investigations were undertaken to evaluate the quality of ground and surface water in the vicinity of the site and to determine the effectiveness of the reclamation procedure on improving the chemistry of water discharging from the site.
Conclusions:
- Ground water in the ash fill has near-neutral pH and net alkalinity. Elements leached from the CCBs include potassium, chloride, boron, molybdenum, and arsenic. Antimony, silver, chromium, cadmium, selenium, copper, zinc, and mercury also were observed but occurred at values that fluctuated around the detection limit. Higher concentrations of leached components are associated with the FSS cap.
- Ground water in the refuse deposits remains highly acidic, but with increasing pH levels due to neutralization by the FSS cap. Concentrations of dissolved metals in refuse ground water remain high, including trace elements such as arsenic, cadmium, chromium, lead, and nickel.
- Water quality in the mine aquifer has not yet changed. The discharge of the spring that issues from the mine aquifer now passes through a PALD and is slightly alkaline.
- Water that discharges from the outlet pond during baseflow periods remains slightly acidic. However, there has been a reduction in the concentration of those elements that are derived primarily from the leaching of refuse. Elements derived from the leaching of CCBs have been observed in baseflow, but their concentrations are far less than those existing in ground water on the site. Chloride and potassium concentrations have increased only slightly. The concentrations of selenium, copper, and nickel have decreased. Chromium, cadmium, boron, and molybdenum concentrations show fluctuations corresponding to pH shifts. Lead and mercury concentrations have decreased to detection limits. Antimony and silver have not been detected in baseflow.
- Storm runoff, which has increased because of reclamation, is now of relatively good quality; net acidity of pre-storm baseflow declines to approximately zero during storms and remains low for several hours following storms.
- A five-fold reduction in total acid production from the site has resulted from reclamation. There has also been a five-fold reduction in the concentrations of iron and aluminum, while manganese concentrations remain relatively unchanged.
Graphical and Tabular Summaries of Results:
General Chemistry |
Effects of CCB Leachate |
Monitoring Sites
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Pre-reclamation Monitoring Sites |
Post-reclamation Monitoring Sites |
Monitoring sites labeled "SW" indicate surface-water sites. "SP" indicate springs. |
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Spreadsheets with Chemistry Data
The results of all chemical analyses through October 1998 are included in the spreadsheets whose links appear above.
All analyses except boron and mercury were performed by personnel of the Indiana Geological Survey Geochemistry Section. Mercury was analyzed by the Ball State University Chemistry Department. Boron was initially analyzed by the Indiana University Geological Sciences Department Analytical Laboratory, but after April 1996, this element was analyzed at Ball State.
Table rows are sorted by sampling site identification code and sampling date. In cases where pre-reclamation sampling site codes are different from post-reclamation codes, but represent sampling from essentially the same location and horizon, they have been combined, rather than alphanumerically separated (SW1 and MW09, for example). Columns contain all measured and calculated chemical parameters. Quality control checks are included to characterize the confidence limits one should place on the data collected for each sampling site and date. The symbol “NA” used in the table indicates no data is available. For measured values, this is due to a lack of sample, but for calculated values, the NA is the result of missing measured data needed for the calculation.
Units of measurements include milligrams per liter (mg/L) and parts per million (ppm), which are nearly equivalent units, differing only by a density value for water. Trace elements are measured in micrograms per liter (µg/L), which is nearly equivalent to parts per billion (ppb). Charge balances are calculated in milliequivalents per liter (meq/L) which is essentially milligrams per liter multiplied by a factor which combines molecular weight and valence charge for the chemical component of interest. Alkalinity and acidity are determined in milligrams per liter of equivalent calcium carbonate. This normalizes these parameters so that the acid-generating capacity and neutralizing potential of water samples can be compared directly. Detection limits for measured chemical parameters are derived from the instrument detection limit and calibration limits, and the dilution factor for each sample.
Acidity of Surface Discharge
The graph shows total alkalinity and potential acidity for water issuing from spring SP2A. PALD construction was completed prior to the October 1996 sampling, at which time alkalinity became sufficiently high enough to neutralize all the potential acidity. |
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The graph shows total alkalinity and potential acidity for water samples collected from surface discharge at site outlet (SW4/SW8). Pre-reclamation sampling occurred from April 1995 to October 1995. Sampling occurred during active reclamation from January 1996 through October 1996. Post-reclamation sampling began in November 1996. The discharge is currently net acidic, but with much less potential acidity than pre-reclamation levels. |
Total Acidity Reduction at Site Outlet
Analysis of water samples was used to determine the net reduction in acidity in
outflows from the site resulting from reclamation.
Hydrologic monitoring at the site indicates that surface discharge
(rather than ground-water flow) is the dominant means by which water leaves the site. Therefore, an
analysis of acidity reduction requires evaluation of streamflow at the site's outlet (SW8). Because
pre-reclamation monitoring was less than one year in duration, comparison of pre- and post-reclamation
conditions can only be evaluated for comparable durations and seasons. Data from 1997 were used as
representative of post-reclamation conditions. Rainfall and streamflow comparisons are made in the
physical hydrology section. Total outflows are tabulated below.
All available data on net acidity and alkalinity collected at the outlet were averaged for pre- and
post-reclamation periods. These average values of acidity and alkalinity concentrations were combined
with streamflow totals to determine the total outfalls of acidity during both periods.
| Tabulation of total outflows | ||
| Total precip. (cm) | 48.41 | 42.98 |
| Net acid/alk (mg/l) | 626 | 120 |
| Total outflow (l) | 3.4 x 10 8 | 1.4 x 10 8 |
| Total acidity (kg) | 2.1 x 10 5 | 1.7 x 10 4 |
| Net reduction (kg) | --- | 1.9 x 10 5 |
Both the total outflows of water and the concentrations of acidity were lower during the post-reclamation period, so that a net reduction of 1.9 x 10 5 kg of acidity (CaCO3 equivalent) has been realized. As shown in the section on quarterly sampling results, water quality tends to be at its worst during the warm season; therefore, this calculation probably represents a minimum estimate of the improvement of water quality at the site.
Analysis of Individual Storms
The relationship between stormflow and the quality of water that is being discharged from the site can be seen in this graph. As shown, specific conductance decreases while discharge increases during storms, indicating a reduction in the concentration of dissolved solids in the large outflows. |
The graphs below provide a comparison of water quality during two storms, one of which occurred before reclamation (graphs on the left) and another which occurred after reclamation (graphs on the right). It can be seen that, prior to reclamation, pH remained low and SpC remained high throughout the duration of the storm but acidity fluctuated over a range of high concentrations. In contrast, following reclamation, it can be seen that pH decreased briefly, then rose to near neutral value as the storm progressed. SpC plummeted to very low values as discharge increased. Acidity declined to near zero concentrations and remained low for several hours following the storm.
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Acidity of the Water-table Aquifer
The graph shows the effects of the cap of fixated scrubber sludge (FSS) on pH of ground water at MW5. The shallowest well (MW5S) is nearest to the FSS cap. FSS contains lime (CaO), which neutralizes H+ in water, forming hydroxide (OH-), which neutralizes additional H+. As a result, ground water closest to the FSS has nearly neutral pH, whereas ground water deeper below the FSS cap has more acidic pH. |
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The graph shows hydrogen ion activity calculated from pH for water samples collected at monitoring well MW7D. pH improvements appear to be slight, rising from a pre-reclamation low of 1.1 to a post-reclamation high of 3.0. However, since pH is a logarithmic scale, plotting the actual change in hydrogen-ion concentration (H+) illustrates a significant improvement in the concentration of H+ due to neutralization. Post-reclamation values show a trend toward reduction in free hydrogen ion activity (an increase in pH). |
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The graph shows potential acidity for water samples taken from monitoring well MW7D, screened into the refuse deposit. Pre- and post-reclamation acidity levels fluctuate considerably with no significantly sustained reduction occurring through time. Volume of highly acidic ground water exceeds neutralizing capacity of FSS cap so that potential acidity derived from dissolved metals is not appreciably reduced. Interaction of highly mineralized, acidic ground water with alkaline surface of impermeable FSS cap may eventually cause mineral buildup on FSS surface, thereby gradually reducing its capacity to neutralize acid. |
Summary Table 1. Acid Mine Drainage Parameters
("N" is the number of samples)
Effects of CCBs on Ground-water Chemistry
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The three graphs above show concentrations of FSS-leached components at various depths in water-table aquifer samples taken from the cluster of monitoring wells at MW5. Shown are concentration changes during pre- and post-reclamation monitoring for boron, potassium, and chloride. Boron and chloride show noticeable converging concentrations as components leached from the FSS cap attempt to equilibrate within the water column. Potassium attenuation is occurring at a much slower rate. Equilibration throughout the water column becomes more feasible as the amount of material being leached out of the FSS cap decreases, probably as a result of a combination of element depletion and reduced interaction between water and FSS. Such reduced interaction could be caused by mineral precipitation within the FSS (reducing permeability) and at the surface of the FSS (forming a barrier crust).
This graph shows molybdenum concentrations in ground water collected from the cluster of monitoring wells at MW5. Molybdenum in solution appears to be confined to the shallow zone of the aquifer nearest the FSS cap (MW5S). The lack of mixing, indicated by no increase in molybdenum concentrations in the deeper monitoring wells, is believed to be caused by a change in solubility of molybdenum at lower pH conditions. |
Effects of CCBs on Surface-water Chemistry
The four graphs below show concentrations of components leached from CCBs found at the reclamation site outlet (SW4/SW8) during pre- , active- , and post-reclamation. Components shown are chloride, potassium, boron, and molybdenum. Chloride peaked during pre-reclamation, boron peaked during active reclamation, and molybdenum peaked early in the post-reclamation phase. Potassium continues to show a slight increase in concentration. Additional sources of potassium contributing to surface discharge, such as fertilizer, may be responsible for the current pattern.
The concentrations of trace elements depend upon pH. As shown in the graphs below, molybdenum concentrations at the site outlet (SW8) are higher when pH is near neutral. However, most trace elements, such as chromium, have higher concentrations during periods when water pH is low.
Summary Table 2. CCB Leachate Parameters
- Study reveals few trace elements are leached from CCBs. Some major and minor inorganic
components are leached from CCBs.
- Leached from CCBs: Potassium, chloride, boron, molybdenum.
- Leached from either CCBs or AMD: arsenic, calcium, magnesium.
- Inconclusive based on available data: fluoride.
- Trace elements monitored for but not found leaching from CCBs: antimony, silver, chromium, lead, mercury, cadmium, nickel, selenium, copper, zinc.
- FSS leachate contains higher concentrations of molybdenum than ponded ash leachate.
- Monitoring well MW9 is screened in ponded ash, with spoil overlying the ash.
- Monitoring well MW8 is screened in ponded ash, with spoil and a FSS cap above the ash fill.
- Monitoring wells MW4D and MW5S are screened in spoil overlain by FSS.
- The mine aquifer is unaffected by CCB leachate.
- Water-table aquifer chemistry is attenuated in vertical dimension (MW5S, MW5M, and MW5D).
- CCB-derived components decrease in concentration with time at monitoring sites into water-table aquifer. General decrease occurs with some fluctuation attributed to seasonal variations in the water table.
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