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Upper Fall Brook WatershedAcid Mine Drainage
and Acid Rain Impacts
Conceptual Treatment Approaches
Terry A. Rightnour
Water’s Edge Hydrology, Inc.
January 15, 2007
[email protected], http://wehydro.com
Upper Fall Brook Watershed
• Problems:– The upper Fall Brook watershed is impacted by acidification from
natural and man-made sources.– The majority of acidification and metals contamination comes
from acid mine drainage (AMD) sources DFB001, DFB002, & DFB003.
– Additional acidification comes from acid rain and natural wetland (bog) acidity in the headwaters.
• Goals:– Treat the three AMD sources above Fall Brook Road.– Reduce non-AMD impacts in the Fall Brook headwaters.– Establish good water quality in upper Fall Brook as justification
for treating other downstream AMD sources in lower Fall Brook.
AMD Source Analyses
• Sampled by TCCCC from June to November 2006 – 8 rounds to date on DFB001, DFB002, and DFB003.
• Analyzed for average conditions and 95% confidence interval (CI) flows.
• Plotted concentrations versus flow to predict conditions at 95% CI flows.
• 95% CI values are usually design maximums for stream restoration systems.
• Conditions were predicted for combined flows to represent the system influent.
• Previous SRBC sampling was not included due to possible climatic and analysis method differences.
AMD Source Characteristics
Units Ave. 95% CI Ave. 95% CI Ave. 95% CI Ave. 95% CI
Flow gpm 19 49 43 67 62 104 124 215
pH SU 3.52 NP 3.44 NP 3.47 NP NP NP
Acidity mg/L 102 92 158 108 143 91 143 97
Alkalinity mg/L 0 0 0 0 0 0 0 0
Aluminum mg/L 2.05 0.83 3.45 2.80 5.64 5.34 4.35 3.60
Iron mg/L 0.48 0.17 11.52 9.31 0.62 0.71 4.45 3.44
95% CI - 95% Confidence Interval Prediction or Design Maximum ValueNP - Not predictable with available information
FlowsDFB001 DFB002 DFB003
CombinedParameters
Basic Treatment Alternatives• Passive Treatment
– Uses natural contaminant removal processes with non-continuous addition of power or reagents.
– Most applicable to low to moderate contaminant loadings.– Suited to sites with a low availability of access or O&M labor.– Best technologies for this site are oxidation/precipitation basins
(OPBs), vertical flow wetlands (VFWs), and surface flow wetlands (SFWs).
• Chemical Treatment– Involves continuous controlled application of a neutralizing
reagent, with or without need for power.– Most applicable to moderate to high contaminant loadings.– Suited to accessible sites with readily available O&M labor.– Best technology for this site is pebble quicklime addition.
Oxidation/Precipitation Basins
• Remove iron and aluminum by forming precipitate sludge through oxidation.
• Usually have little effect on acidity or manganese.• Work best with 24 hours or more detention time.• Additional volume needed to store accumulating sludge – typically
40% of total volume.• 24 hour removal rates in alkaline water are approx. 35% for
aluminum and 65% for iron; rates decline in acidic waters.• Sludge generated at approx. 1 liter per 5 grams of aluminum or 10
grams of iron removed.• Require periodic cleaning to remove sludge as detention capacity is
approached.
Vertical Flow Wetlands
• Deep basins filled with a bottom layer of limestone aggregate and an upper layer of spent mushroom compost.
• Influent migrates down through both layers, neutralizing acidity and generating alkalinity.
• Acidity capacity based on loading over surface area of compost (25 g/day-m2 average, 50 g/day-m2 maximum)
• Alkalinity generation based on detention time in limestone (18 hours average, 12 hours minimum).
• Remove metals based on percentage of influent concentration (90% of aluminum, 80% of iron, 10% of manganese).
• Metals precipitates eventually clog substrates, requiring flushing or substrate replacement.
• Usually applied in pairs, with one cell able to maintain treatment while the other is off-line for maintenance.
Surface Flow Wetlands
• Vegetated basins with shallow surface flow (1 – 6 inches).• Work best for polishing metals from alkaline waters at the discharge
end of treatment systems.• Metals removal rates are directly related to influent concentration:
– Aluminum rate approx. 0.21 x (Inf. Conc.) g/day-m2
– Iron rate approx. 0.17 x (Inf. Conc.) g/day-m2
• Cells may require periodic water level adjustment and vegetative management, but seldom major substrate maintenance if influent metals are low.
Conceptual Passive Treatment Plan
• Collect and combine AMD sources in an OPB for initial aluminum and iron removal.
• Split flow to two parallel VFWs for acidity removal and alkalinity generation.
• Pass VFW discharges through an SFW for final polishing, with target aluminum < 0.1 mg/L on average.
• A site-specific model was run for basic sizing considerations.
Passive System Model
Initial OPB – 40,000 CF
Paired VFWs Each at –
62,000 SF Surface Area
43,500 CF Detention
Polishing SFW – 27,000 SF
Flow gpm
Acid mg/L
Alk mg/L
Al mg/L
Fe mg/L
Flow gpm
Acid mg/L
Oxidation/ Alk mg/L
Precipitation Al mg/LBasin Fe mg/L
Det. Vol. CF
Det. Time hrs
71 ft x Flow gpm Cleaning149 ft = Acid mg/L Cycle =
ac Alk mg/L yrs
Al mg/L
Fe mg/L
Vertical Flow Wetlands
Surface Area 2 x SF
Detention Volume 261 ft x CF
261 ft =
Acidity Loading ac g/d-m2
Detention Time hrs
Flow gpm
Acid mg/L
Alk mg/L
Al yrs mg/L
Fe mg/L
Flow gpm
Acid mg/L
Alk mg/L
Surface Flow Al mg/L TreatedWetlands Fe mg/L Discharge
Surf. Area SF
Flow gpm100 ft x Acid mg/L
284 ft = Alk mg/L
ac Al mg/L
Fe mg/L
62
124
4.354.45
35
143
03.913.56
3.13
11.52
14215
Max.
0.62
124 21597
0
0.390.71
0.71
1240
10.4
40000
0.48
24
0.17
0.24
Ave.
97
0
143
1580
3.45
62
5.64
19102
02.05
62
8
0.61
Cleaning
Cycle =
4.1
35
067
0.39
49920
0.83
Ave. Max.
DFB001Ave.
9.31
DFB002Ave.Max.
67108
01430
43
Ave.
5.340.71
DFB003
Max.
Max.
104910
2.80
0.34
03.603.44
0.39
067
3.393.04
8
VFW 1A VFW 1B
Ave. Max. Ave. Max.
6200143511
1020
107052
0.340.61
6200143511
0.71
107
1020
052
Ave. Max.
0.65
052
0.340.61
215
67
0.160.35
Ave. Max.
0
670.100.26
26880
2150
52
124
Passive System Model Results
• Overall system size estimated at ≈ 6 acres with earthwork• OPB cleaning cycle predicted at ≈ 10 years• VFW cleaning cycle predicted at ≈ 4 years• Construction cost estimated at ≈ $810,000• Annualized O&M estimated at ≈ $64,000• 15-Year total cost estimated at ≈ $1.8 million
• Depending on effluent metals goals, the SFW size could be reduced.
Pebble Quicklime Treatment Systems
• Based on a waterwheel-driven applicator.• Pebble quicklime has about twice the neutralization capacity and
reactivity of limestone.• Easily scaleable to flow increases.• Provide a consistent neutralization delivery rate.• Aquafix systems available in scalable sizes between small hoppers
(1/2 – 1 ton) to silos (up to 100 ton).• Bulk delivery approx. $120/ton for pebble quicklime.• Metals are removed as sludge in an OPB similar to passive
systems.• Sludge generation tends to be greater than passive sludge,
estimated at 1 liter for 2.5 grams of aluminum or 5 grams of iron removed.
Conceptual Chemical Treatment Plan
• Collect and combine AMD sources in a single channel.• Apply pebble quicklime using a flow split to drive an Aquafix system.• Precipitate sludge in paired downstream OPBs, with one OPB
capable of maintaining 24 hour detention while the other is offline for cleaning.
• Site-specific model was run for basic sizing requirements using specifications of pebble quicklime and Aquafix systems.
Chemical System Model
Aquafix 35 ton silo system for 1 year storage capacity.
Approx. 175 lbs/day addition yields discharge alkalinity of 45 mg/L on average and 15 mg/L at 95% CI flow.
Paired OPBs each at 70,000 CF total volume.
Flow gpm
Acid mg/L
Alk mg/L
Al mg/L
Fe mg/L
Flow gpm
Acid mg/L
Alk mg/L
Al mg/L
Pebble Quicklime Fe mg/L
Addition Unit
Neutralization Factor as CaCO3
Purity %
Material Cost $/ton
Daily Addition lbs/day Area < 0.10 ac.
Annual Addition tons/yr
Annual Cost $/yr
Oxidation/Precipitation TreatedBasin Discharge
Det. Vol. CF
Det. Time hrs
86 ft x Flow gpm Cleaning194 ft = Acid mg/L Cycle =
ac Alk mg/L yrs
Al mg/L
Fe mg/L
Det. Vol. CF
Det. Time hrs
86 ft x Flow gpm Cleaning194 ft = Acid mg/L Cycle =
ac Alk mg/L yrs
Al mg/L
Fe mg/L
0.10 1.040.10 0.10
0.38 45 15 2.5
62 1070 0
Ave. Max.
85 49
90
Ave. Max.
70000
03.603.44
173 179
$120
32
0.56
Ave.
1.040.10
Ave.
49107
Max.
0.62
215
$3,799
1080
DFB003
Max.
Max.
104910
2.809.31
1430
43Ave. Max.
00
62Max.
67
DFB001Ave.
4992
19102
DFB002
5.64
2.5
5.340.71
2.05
1580
3.450.830.48
85
0.17
0.38
Ave.
143
11.52
124
0
450.100.10
970
62
4.354.45
70000
0
15
Chemical System Model Results
• Overall system size estimated at ≈ 1.5 acre• Silo refilling cycle estimated at ≈ 1 year• OPB cleaning cycle predicted at ≈ 2.5 years• Construction cost estimated at ≈ $300,000• Annualized O&M estimated at ≈ $35,000• 15-Year total cost estimated at ≈ $820,000
Conclusions
• Chemical treatment with pebble quicklime appears to be the more cost-effective alternative.
• Both alternatives will require establishment of long-term O&M funds.• Chemical treatment will require more frequent supervision by skilled
mechanical labor, potentially adding to long-term costs.• There may not be sufficient area to construct an adequately sized
passive treatment system capable of receiving gravity flow from all AMD sources.
• Reducing the size of the passive system would result in shorter longevity, a lesser degree of treatment, or both.
• Chemical treatment is recommended as the most viable option for this site.
Fall Brook Headwaters
• Impacted by non-AMD acidity from acid rain and bog tannin.• TCCCC has sampled five tributaries between June and October,
2006, with 5 rounds to date.• Acid Neutralization Capacity (ANC) was used instead of acidity and
alkalinity as a better measure of non-AMD acidification.• Results were analyzed for average and 95% CI conditions, and
alkaline deficiency.• Objective is to locate and design an alkalinity-generating VFW to
improve headwaters conditions above AMD impacts.
Headwaters Tributary Characteristics
Units Ave. 95% CI Ave. 95% CI Ave. 95% CI Ave. 95% CI Ave. 95% CI
Flow gpm 450 1514 96 231 403 1051 1094 3022 359 865
pH SU 4.46 NP 4.58 NP 4.66 NP 5.42 NP 5.15 NP
ANC meq/L -38.63 -72.96 -30.98 -19.21 -29.60 -31.76 -18.31 -26.97 -4.08 -14.35
Aluminum mg/L 0.37 0.65 0.29 0.10 0.24 0.40 0.48 0.59 0.11 0.39
Estimated Alkaline Deficiency
lbs/day 10 66 2 3 7 20 12 49 1 7
95% CI - 95% Confidence Interval Prediction or Design Maximum ValueNP - Not predictable with available information
FBH5FBH4Parameters FBH1 FBH2 FBH3
Preliminary Conclusions
• A standard VFW for non-AMD application (approx. 1 acre size) will produce about 50 lbs/day alkalinity.
• The combined alkaline deficiency in the five sample points is 32 lbs/day on average and 145 lbs/day under 95% CI conditions.
• One VFW would be adequate to correct average deficiencies, but up to three VFWs may be needed to correct high flow conditions.
• FBH1, FBH3, and FBH4 appear to be the best candidates for VFWs based on deficiencies and flow volumes.
• FBH5 may also be considered due to its location near the top of the watershed to maximize main stem restoration length.