Treatment of Arsenic and Metals in Ground Water Using a
Compost/ZVI PRB
Ralph Ludwig, David Jewett, Ann Keeley,Frank Beck, Patrick Clark, Steve Acree,
Randall Ross(EPA ORD-NRMRL)
David Blowes, Laura Spink, David Smyth(University of Waterloo)
Columbia Nitrogen Site
tidal marsh
Columbia Nitrogen Site • Site impacted by former phosphate fertilizer
manufacturing operations • Pyrite and elemental sulfur used in production of
sulfuric acid • Sulfuric acid stored in Pb-lined concrete vats
• Site extensively filled with operational materials and debris
• Ground water impacted by heavy metals (Pb, Cd), arsenic, and low pH
Current Scenario
sulfide/sulfur oxidation iron oxidation
ground surface
FeS2 + 7/2O2 + H20 Fe2+ + 2SO4
2- + 2H+
Fe2+ + 1/4O2 + 5/2H2O Fe(OH)3 + 2H+
tidal marsh
So + 3/2O2 + H2O SO4 2- + 2H+
H2SO4 SO4 + 2H+
As Pb Cd Fe2+
H+
PRB Treatment Objectivepromote sulfate reduction
ground surface
Fe2+
SO4 2-
H+
Me2+
As
net acid producing water
net acid consuming water
flow
HCO3 -
HCO3 -
PRB HCO3 - tidal marsh
HCO3 -
-SO42- + 2CH2O H2S + 2HCO3
Me2+ + HS- MeS + H+
Fe2+ + HS- FeS + H+
PRB Treatment Objectives
• Raise pH of ground water• Promote sulfate reduction to remove heavy
metals, arsenic, and ferrous iron • Prevent additional down-gradient ecosystem
impacts by preventing acid production associated with ferrous iron oxidation
• Contribute to ecosystem restoration by converting ground water from acid producing to acid consuming system (i.e. generate an alkalinity plume)
PRB Design Tests/Studies
• Laboratory column tests� Focused on optimizing reactivity and hydraulic
conductivity � Mixture of 30% compost, 20% ZVI, 5% limestone
and 45% pea gravel selected
• Permeameter tests� Three samples from final mixture tested for
permeability to ensure permeability greater than that of aquifer
� Result of permeability testing: K = 6.7E-02 cm/s
Plastic Sheet
Limestone
Granite
Reactive Material
6 ft
West East South 27 ft
Vertical X-Section of Pilot PRB
compost/ZVI/limestone + pea gravel
Crush and Run
Gravel ~4 ft
~0.5 ft
~7.5 ft
North
compost
1 3
5
7 9
11 13
15
12 ft
6 ft
27 ft NOT TO SCALE
a
b
c
d
e
f
2 4
6 8
10
12 14
16
ground water flow
Multi-Level Monitoring System Layout
Performance Monitoring
• Chemical monitoring conducted 1, 3, 8, 13, and 18 months after installation
• Chemical parameters evaluated: Pb, As, Cd, Fe, pH, Eh, alkalinity, cations, anions, TOC/DOC, sulfide
• Microbial parameters: MPN sulfate reducers
• Hydraulic monitoring – slug tests
10.12
10.91
7.13
6.87
6.47
10.29
10.59
7.70
6.69
6.65
10.95
10.89
6.85
5.29
4.37
5.42
5.95
5.36
3.36
2.56
2.45
5.10
4.06
2.62
2.21
2.25
5.33
3.82
2.90
2.26
2.31
2.57
2.54
2.70
2.50
2.45
2.81
2.37
3.36
2.69
2.73
pH profile – 8 months
ground water flow
pH 1210 86 42 0
5.29
5.70
4.52
3.67
2.63
2.36
4.60
3.76
2.87
2.40
2.39
4.77
3.54
2.74
2.28
2.27
10.18
10.54
8.63
7.52
7.22
10.50
10.73
9.31
7.43
6.89
10.79
10.67
6.18
4.05
3.81
2.30
2.51
3.08
2.70
2.60
2.81
2.27
3.25
2.90
2.51
pH profile – 13 months
ground water flow
pH 1210 86 42 0
6.36
4.98
3.82
3.11
2.80
5.78
4.04
3.31
2.72
2.74
5.36
3.59
2.97
2.55
2.41
10.18
10.60
10.23
7.00
6.23
10.03
10.28
10.25
8.68
6.36
10.60
10.68
7.23
4.21
3.96
2.50
2.64
3.17
2.80
2.57
3.38
3.67
3.49
2.91
2.88
pH profile – 18 months
ground water flow
pH 1210 86 42 0
511
565
404
364
373
422
408
298
282
389
-171
-457
-445
-306
-114
-201
-417
-549
-215
-182
-225
-384
-139
84
194
101
96
343
369
359
132
250
377
398
397
151
330
386
422
400
250
0
Eh profile – 8 months
ground water flow
Eh (mV)
-300-150
150300450600
106
230
329
385
383
242
363
385
385
377
88
128
328
388
372
152
-195
-282
-630
-284
-141
-26
-233
-471
-367
-201
-357
-387
-139
141
160
249
289
110
138
168
457
426
346
333
363
0
Eh profile – 13 months
ground water flow
Eh (mV)
-300-150
150300450600
616
530
427
395
384
486
452
376
366
407
166
110
172
-69
51
181
99
159
-486
61
97
74
-106
322
301
126
351
372
358
371
175
368
371
373
382
244
396
394
392
391
0
Eh profile – 18 months
ground water flow
Eh (mV)
-300 -150
150300450600
0.083
0.575
2.76
3.18
3.23
0.060
0.823
0.931
0.132
1.57
0.004
0.004
0.0004
0.004
0.003
0.004
0.004
0.004
0.003
0.004
0.003
0.005
0.005
0.000
0.008
0.006
0.037
1.50
2.28
2.38
0.007
0.289
2.63
2.45
2.84
0.006
0.508
1.08
0.676
0.304
Pb concentration profile – 18 months
ground water flow
Pb (mg/L)
00.0150.100.501.002.00>3.00
0.177
0.917
27.0
133
137
0.794
4.06
36.7
96.3
126
4.97
5.06
161
261
234
3.98
7.51
202
281
243
3.79
12.4
117
283
265
0.037
0.056
0.036
0.015
0.158
0.024
0.029
0.032
0.013
0.009
0.046
0.050
0.022
1.25
11.7
As concentration profile – 18 months
ground water flow
As (mg/L)
0 0.01 0.10 1.00 10.01001,000
0.008
0.010
0.089
1.58
2.10
0.008
0.014
0.060
0.200
0.892
0.001
0.001
0.0005
0.001
0.001
0.001
0.001
0.002
0.001
0.001
0.001
0.002
0.001
0.0009
0.001
0.001
0.001
0.002
2.64
3.24
0.001
0.005
0.445
3.43
3.95
0.001
0.036
0.757
3.50
4.58
Cd Profile – 18 months
ground water flow
Cd (mg/L) 00.0150.101.02.03.04.0
0
0
0
0
0
0
0
0
0
0
264
643
381
133
130
147
227
457
147
79
418
630
300
18
0
180
22
0
0
0
67
12
0
0
0
50
0
0
0
0
Alkalinity profile – 18 months
ground water flow
Alkalinity (mg/L CaCO3)
>500400400200100500
5385
28650
62130
3020
1970
59960
34875
8610
3080
2000 5.70
239
884
3960
9270
62.7
54.8
511
3310
10390
<0.10
89.3
1800
24600
60220
894
2920
12745
35800
70180
1200
3340
14245
55080
67940
1060
3230
11180
46920
71390
Sulfate profile – 18 months
ground water flow
SO4 (mg/L)
0 5,000 10,000 20,000 40,000 60,000 80,000
Iron profile – 18 months
ground water flow
Fe (mg/L)
0 1005001,0005,00010,00020,000
142
616
2410
2760
2390
138
602
2470
5690
2390
198
389
1800
2710
2510
0.154
0.140
0.119
218
2140
<0.035
<0.035
<0.035
32.7
1570
0.189
0.168
82.4
3850
2560
70.9
213
1240
2430
2450
106
282
1190
3170
2650
DGIWUG AN
0
4.5
3.1x103
3.3x101
4.0x102
6.8x101
2.2x104
2.8x104
1.6x105
1.1x103 1.1x105
5.4x102
1.3x103
5.4x106
7.0x104
Sulfate reducers (MPN)
Groundwater flow direction
East West Ground Surface
Clay Aquitard
Phylogenetic Tree Display
Neighbor Joining Tree
Alignment: 13.55 % 502 Clostridium tertium14.34 % 502 Clostridium chauvoei14.74 % 502 Eubacterium multiforme14.75 % 517 Eubacterium limosum14.84 % 516 Clostridium purinolyticum15.00 % 500 Clostridium paraputrificum15.54 % 502 Clostridium histolyticum15.54 % 502 Clostridium fallax
Clostridium perfringensClostridium paraputrificum
Clostridium chauvoeiClostridium tertiumClostridium fallax
N Join: 8.976 %
Clostridium gasigenes
Eubacterium multiforme
Clostridium histolyticum
Eubacterium limosum
15.74 % 502 Clostridium perfringens Clostridium scatologenes Clostridium purinolyticum
16.20 % 500 Clostridium scatologenes
Summary• 18-month data indicates effective removal of
Pb, Cd, and As to date • pH of influent ground water is increased from
< 4 to > 6 • Ground water is converted from acid
producing potential to acid consumingpotential
• Sulfate reducers are present in PRB in significant numbers
• 34S enrichment being observed in PRBground water
Issues
• Hydraulics through PRB not yet fully resolved
• Ground water flow through much of site is very slow
• Upper part of aquifer appears to exhibit higher hydraulic conductivity than PRB
Future Work
• Continue semi-annual monitoring to assess performance and longevity ofPRB
• Conduct tracer test to better evaluate hydraulics through PRB
• Evaluate solid phase chemistry within PRB
• Refine design of PRB for potential full-scale implementation
