Upper Fall Brook Watershed
Acid Mine Drainage
and Acid Rain Impacts
Conceptual Treatment Approaches
Terry A. Rightnour
Water’s Edge Hydrology, Inc.
January 15, 2007
trighnour@wehydro.com, 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 Locations
AMD Source Characteristics
Parameters
DFB001
Units
Flow
gpm
pH
SU
Acidity
Alkalinity
Ave.
DFB002
95% CI
Ave.
Combined
Flows
DFB003
95% CI
Ave.
95% CI
Ave.
95% CI
19
49
43
67
62
104
124
215
3.52
NP
3.44
NP
3.47
NP
NP
NP
mg/L
102
92
158
108
143
91
143
97
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
0.48
0.17
11.52
9.31
0.62
0.71
4.45
3.44
mg/L
95% CI - 95% Confidence Interval Prediction or Design Maximum Value
NP - Not predictable with available information
Basic Treatment Alternatives
• Passive Treatment
– Uses natural contaminant removal processes with noncontinuous 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.
Conceptual
Passive System Components
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.
Typical OPB
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.
Typical Vertical Flow Wetland
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.
Typical Surface Flow Wetland
Conceptual
Passive System Components
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.
DFB001
Passive System Model
Initial OPB – 40,000 CF
Flow
Acid
Alk
Al
Fe
DFB002
Max.
Ave.
Max.
Ave.
Max.
19
102
0
2.05
0.48
49
92
0
0.83
0.17
43
158
0
3.45
11.52
67
108
0
2.80
9.31
62
143
0
5.64
0.62
104
91
0
5.34
0.71
Ave.
Max.
124
143
0
4.35
4.45
215
97
0
3.60
3.44
Flow
Acid
Alk
Al
Fe
Oxidation/
Precipitation
Basin
Paired VFWs Each at –
62,000 SF Surface Area
Det. Vol.
Det. Time
Flow
Acid
Alk
Al
Fe
71 ft x
149 ft =
0.24
ac
43,500 CF Detention
Polishing SFW – 27,000 SF
DFB003
Ave.
40000
Ave.
Max.
24
124
143
0
3.91
3.56
14
215
97
0
3.39
3.04
gpm
mg/L
mg/L
mg/L
mg/L
gpm
mg/L
mg/L
mg/L
mg/L
CF
hrs
gpm
mg/L
Cleaning
Cycle =
10.4
mg/L
mg/L
mg/L
yrs
Vertical Flow Wetlands
VFW 1A
Surface Area
Detention Volume
Acidity Loading
Detention Time
Flow
Acid
Alk
Al
Fe
VFW 1B
62001
43511
Ave.
Max.
8
35
62
0
67
0.39
0.71
10
20
107
0
52
0.34
0.61
Flow
Acid
Alk
Al
Fe
Surface Flow
Wetlands
Surf. Area
100 ft x
284 ft =
0.65 ac
Flow
Acid
Alk
Al
Fe
62001
43511
2
x
261 ft x
261 ft =
3.13 ac
Cleaning
Cycle =
4.1 yrs
Ave.
Max.
124
0
67
0.39
0.71
215
0
52
0.34
0.61
26880
Ave.
Max.
124
0
67
0.10
0.26
215
0
52
0.16
0.35
Ave.
Max.
8
35
62
0
67
0.39
0.71
10
20
107
0
52
0.34
0.61
gpm
mg/L
mg/L
mg/L
mg/L
SF
gpm
mg/L
mg/L
mg/L
mg/L
SF
CF
g/d-m2
hrs
gpm
mg/L
mg/L
mg/L
mg/L
Treated
Discharge
Conceptual Passive System Layout
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.
Conceptual
Chemical System Components
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.
Aquafix Pebble Quicklime Systems
• 1 Ton Hopper System
• 35 Ton Silo System
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
DFB001
Flow
Acid
Alk
Al
Fe
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.
DFB002
DFB003
Ave.
Max.
Ave.
Max.
Ave.
Max.
19
102
0
2.05
0.48
49
92
0
0.83
0.17
43
158
0
3.45
11.52
67
108
0
2.80
9.31
62
143
0
5.64
0.62
104
91
0
5.34
0.71
Ave.
Max.
124
143
0
4.35
4.45
215
97
0
3.60
3.44
Flow
Acid
Alk
Al
Fe
Pebble Quicklime
Addition Unit
Neutralization Factor
Purity
Material Cost
Daily Addition
Annual Addition
Annual Cost
gpm
mg/L
mg/L
mg/L
mg/L
0.56
90
$120
Ave.
Max.
173
179
32
$3,799
as CaCO3
%
$/ton
lbs/day
Area < 0.10 ac.
tons/yr
$/yr
Oxidation/
Precipitation
Basin
Treated
Discharge
Det. Vol.
86 ft x
194 ft =
0.38
ac
Det. Time
Flow
Acid
Alk
Al
Fe
Det. Vol.
86 ft x
194 ft =
0.38
gpm
mg/L
mg/L
mg/L
mg/L
ac
Det. Time
Flow
Acid
Alk
Al
Fe
70000
Ave.
Max.
85
62
0
45
0.10
0.10
49
107
0
15
1.04
0.10
70000
Ave.
Max.
85
62
0
45
0.10
0.10
49
107
0
15
1.04
0.10
CF
hrs
gpm
mg/L
mg/L
mg/L
mg/L
Cleaning
Cycle =
2.5
yrs
CF
hrs
gpm
mg/L
mg/L
mg/L
mg/L
Cleaning
Cycle =
2.5
yrs
Conceptual Chemical System Layout
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 Sample Points
Headwaters Tributary Characteristics
Parameters
Units
FBH1
Ave.
FBH2
95% CI
Ave.
FBH3
95% CI
Ave.
FBH4
95% CI
Ave.
FBH5
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
Aluminum
mg/L
Estimated
Alkaline
Deficiency
lbs/day
-38.63 -72.96 -30.98 -19.21 -29.60 -31.76 -18.31 -26.97
-4.08 -14.35
0.37
0.65
0.29
0.10
0.24
0.40
0.48
0.59
0.11
0.39
10
66
2
3
7
20
12
49
1
7
95% CI - 95% Confidence Interval Prediction or Design Maximum Value
NP - Not predictable with available information
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.