Bob Hedin, Hedin Environmental, "Effective Passive Treatment of Coal Mine Drainage"

Effective Passive Treatment of Coal Mine Drainage

Bob Hedin, Ted Weaver, Neil Wolfe, George Watzlaf, Kim Weaver

Hedin EnvironmentalPittsburgh, PA

Components of Installation of an Effective Passive Treatment System

• Characterization of AMD• Proper selection of technology• Proper sizing• Trouble-shoot design• Proper construction• Routine maintenance and sampling• Major maintenance

Anoxic Limestone Drain

Ponds Vertical Flow Pond

Oxic Limestone Bed

Wetland Ponds Ponds

Oxic Limestone Bed (drainable)

NetAlkaline

Net alkaline Net acid

Net acid

DO, Fe3+, Al all < 1 mg/L(high Fe2+)

Characterize Mine Water

Wetland

Final Discharge

Mn

DO, Fe3+, Al any > 1 mg/L DO, Fe3+, Al any > 1 mg/LFe < 10 mg/L

High Fe2+

Ponds

Repeat As Needed

Mn

Passive Technologies Used by HE

• Ponds – oxidize Fe, settle solids, mixing

• Wetlands – polishing , Mn and solids removal

• Anoxic limestone drains – alkalinity generation

• Oxic limestone beds– alkalinity generation, metal removal, polishing

• Vertical flow ponds (SAPS, Anaerobic Wetlands)– alkalinity generation and metal removal

Four Examples of the Effective Use of these Technologies



Oxic Limestone Bed

Wetland Ponds Ponds


NetAlkaline


Net acid



Wetland

Final Discharge

Mn


High Fe2+

Ponds

Repeat As Needed

Mn

Marchand Mine Passive System

Ponds and Wetlands

influentSewickley Creek

Pond A

Pond B

Pond C

Pond D

Pond E

Pond F

Wetland

Wetland

Wetland

Fe2+ + HCO3- + O2 FeOOH + H2O

FeOOH(ss) FeOOH(ps)

Sizing: 90th percentile flow conditions30 g d-1m-2 Fe removal in ponds5 g d-1m-2 Fe removal in wetland

Marchand system, average conditions, 2006 - 2014

Flow pH Alk FeT Mn Al SO4TSS

gpm ----------------mg/L---------------

Influent 1,876 6.3 335 72.4 1.2 <0.1 1,136 25

Pond F out 7.1 230 12.4 1.1 <0.1 1,117 16

Effluent 7.8 216 1.0 0.5 <0.1 1,160 <6

Dec-

06

Jun-

07

Dec-

07

Jun-

08

Dec-

08

Jun-

09

Dec-

09

Jun-

10

Dec-

10

Jun-

11

Dec-

11

Jun-

12

Dec-

12

Jun-

13

0

1

2

3

4

5

6

7

influent effluent

Fe, m

g/L

Maintenance of the Marchand System

Fe sludge accumulation• 575,000 gallons/yr Fe sludge• 7.5% loss of storage volume per year• In June 2012 the system’s theoretical

retention had decreased from 74 hr to 46 hr• June 2012 sludge in first three ponds was

removed


Pond A

Pond B

Pond C

Pond D

Pond E

Pond F

Wetland

Wetland

Wetland

FeOOH recovered in 2012

Cost Effective? To date calculation

• Construction: $1,250,000 (2006)• Maintenance: $150,000• Total cost: $1,400,000• Fe removal, 4,100,000 lb Fe• Unit Cost: $0.35/lb Fe• Unit Cost: $0.19/1000-gallons

Cost Effective? 20 year calculation

Fe solids are used• Construction: $1,250,000 (2006)• Maintenance: $585,000• Total cost: $1,835,000• Fe removal, 11,700,000 lb Fe• Unit Cost: $0.16/lb Fe• Unit Cost: $0.09/1000-gallons


Fe solids are landfilled @ $50/ton• Construction: $1,250,000 (2006)• Maintenance: $585,000• Sludge disposal at landfill: 23,000 ton, $1,170,000• Total cost: $3,005,000• Fe removal, 11,700,000 lb Fe• Unit Cost: $0.26/lb Fe• Unit Cost: $0.15/1000-gallons



Oxic Limestone Bed

Wetland Ponds Ponds


NetAlkaline


Net acid



Wetland

Final Discharge

Mn


High Fe2+

Ponds

Repeat As Needed

Mn

SR-114D Passive System


1,300 ton limestone120 gpm flow with 35 mg/L Fe2+

SR-114D System,Butler County, PAAugust 1995

SR-114D System,Butler County, PA

Fe2+ + Mn2+ + H+ Fe2+ + Mn2+ + Ca2+ + HCO3-

limestoneanoxic


Sizing: minimum of 12 hour retention for high flow plus20 years of LS dissolution = 1,800 + 600 = 2,400 tons


Sizing: minimum of 12 hour retention for high flow plus20 years of LS dissolution = 1,800 + 600 = 2,400 tons

Budget allowed 1,750 tons of LS for two systems:• SR-114B 450 tons• SR-114D 1,300 tons


Fe2+ + Mn2+ + H+ Fe2+ + Mn2+ + Ca2+ + HCO3-

limestoneanoxic

Jun-

94

Jun-

96

Jun-

98

Jun-

00

Jun-

02

Jun-

04

Jun-

06

Jun-

08

Jun-

10

Jun-

12

Jun-

14

0

10

20

30

40

50

60Fe

, mg/

L

Jun-

94

Jun-

96

Jun-

98

Jun-

00

Jun-

02

Jun-

04

Jun-

06

Jun-

08

Jun-

10

Jun-

12

Jun-

14

0

50

100

150

200

250

Alk fldAlk Lab

Alka

linity

, mg/

L Ca

CO3

Original Alkalinity

Limestone Dissolution in ALD1995-2014

• ALD has generated 375 ton CaCO3

• ALD has dissolved 416 tons limestone • 32% of original 1,300 tons• Theoretical average retention time has

decreased from 10.8 hr to 7.4 hr

SR-114D ALD Maintenance

• No maintenance to date (19 years)• ALD will need rehabilitated in next 5-10 years– Clean remaining limestone– Replaced dissolved limestone


Twenty Year Calculation• Construction: $65,000 (2014)• Maintenance: $0• Total Cost: $65,000• Alkalinity generation: 395 ton CaCO3

• Unit cost: $165/ton CaCO3

• Unit cost: $0.05/1000-gallons



Oxic Limestone Bed

Wetland Ponds Ponds


NetAlkaline


Net acid



Wetland

Final Discharge

Mn


High Fe2+

Ponds

Repeat As Needed

Mn

Anna S Mine Passive Treatment Complex

Vertical Flow Ponds

Anna S passive systems, 2004 - 2014

Flow pH Alk Acid Fe Al Mn SO4

gpm s.u. mg/L CaCO3 mg/L mg/L mg/L mg/L

Anna System S1 influent 216 3.1 0 145 7 13 8 356S2 influent 31 3.8 0 33 <1 2 6 134Final na 7.4 129 -99 1 <1 4 316

Hunters Drift SystemHD influent 234 2.8 0 354 35 34 7 556Final na 7.4 144 -112 <1 <1 2 509

Ja

n-0

4

Ja

n-0

5

Ja

n-0

6

Ja

n-0

7

Ja

n-0

8

Ja

n-0

9

Ja

n-1

0

Ja

n-1

1

Ja

n-1

2

Ja

n-1

3

Ja

n-1

4

-

50

100

150

200

250

300 Hunters system final discharge

Anna System final discharge

Alk

ali

nit

y,

mg

/L

Major Maintenance

• Rehabilitate substrates that contribute to system’s effectiveness (alkalinity generation)

• Alkaline Organic Substrate: replenish• Limestone Underdrain: clean and replenish

Cost Effective? To Date (10 years)

• Construction: $2,500,000 (2004)• Maintenance: $300,000• Total cost: $2,800,000• Alkalinity generation: 3,472 tons CaCO3

• Unit Cost: $806/ton CaCO3

• Unit Cost: $1.10/1000-gallons


• Construction: $2,500,000 (2004)• Maintenance: $900,000• Total cost: $3,400,000• Alkalinity generation: ~6,800 tons CaCO3

• Unit cost: $500/ton CaCO3

• Unit cost: $0.67/1000-gallons



Oxic Limestone Bed

Wetland Ponds Ponds


NetAlkaline


Net acid



Wetland

Final Discharge

Mn


High Fe2+

Ponds

Repeat As Needed

Mn

Tangascootack #1 Passive System


Solar PanelComputerWater Level Control box with bottom gate valve

Tangascootack #1 system, 2010 – 2014

Flow pH Alk Acid Fe Al Mn SO4

Inflow na 4.0 0 89 0.2 11.1 25.9 927

DLB out 45 7.3 197 -169 0.1 0.2 1.7 968

Au

g-1

0

De

c-1

0

Ap

r-1

1

Au

g-1

1

De

c-1

1

Ap

r-1

2

Au

g-1

2

De

c-1

2

Ap

r-1

3

Au

g-1

3

De

c-1

3

Ap

r-1

4

Au

g-1

4

-250

-200

-150

-100

-50

0

0

20

40

60

80

100

120DLB InfluentDLB EffluentFlow rate

Ac

idit

y,

,mg

/L

Flo

w R

ate

, g

pm

Aug-

10

Dec-

10

Apr-1

1

Aug-

11

Dec-

11

Apr-1

2

Aug-

12

Dec-

12

Apr-1

3

Aug-

13

Dec-

13

Apr-1

4

Aug-

14

0

5

10

15

20

25InfluentDLB effluent

Mn,

mg/

L

Solids Management

• Effective limestone beds retain 99% of Al and Fe3+

• Decades of experience find that solids plug the bed and decrease effectiveness

Solids accumulate in pores

Solids form scale on LS aggregate

Solids Management

• Routine draining removes suspended solids in pores

• Infrequent cleaning of stone removes scale

Pittsburgh Botanic Garden DLBsolids basin during end of draining

Pittsburgh Botanic Garden DLBsolids basin during end of draining

70% of the Al retained in the DLB during routine operations released during draining

Major Maintenance

• Clean limestone aggregate every 3-10 years• Established procedures and costs

Limestone cleaning cost: $5/ton

Cost Effective? To Date (3.5 years)

• Construction: $80,000 (2010)• Maintenance: $8,000• Total cost: $88,000• Alkalinity generation: 90 tons CaCO3




• Construction: $80,000 (2010)• Maintenance: $1,000/yr (inspection) +

$5,000/3-year (cleaning) + $2,500/3-yr LS replacement= $70,000

• Total cost: $150,000• Alkalinity generation: 515 tons CaCO3



Summary

• Highly successful passive treatment of discharge with large range of flow rates and chemical conditions

• Effective treatment obtained year-round• All systems require O&M, but the needs are

modest and with planning can be implemented cost-effectively

• Cost of effective passive treatment is much less than conventional chemical treatment

Summary: 20 year treatment estimates

$/1000 gallons

$/ton CaCO3

$/lb Fe

Marchand (FeOOH) $0.09 ---- $0.16Marchand (landfill) $0.15 $0.26Lancashire $0.44 --- $1.32SR 114D ALD $0.05 $165 ---Aquafix CaO $421Scootac #1 $0.30 $291 ---Anna S $0.67 $500 ---Lime – AMD Treat $1,200


Pond A

Pond B

Pond C

Pond D

Pond E

Pond F

Wetland

Wetland

Wetland

Questions or Comments?

Al Fe Mn Al Fe Mn

Routine

Influent 13.0 0.5 0.8 13.8 0.44 0.93

Effluent 0.7 0.1 0.2 0.4 0.09 0.14

Retained 13.4 0.35 0.79

Draining

Removal 12-239 0.6-8.1 0.2-0.8 9.5 0.35 0.10

% removed 71% 99% 13%

% retained 29% 1% 87%

Routine conditions

In out

Flow, gpm na 4-11

pH 3.3 7.6

Acidity 130 -188

Alkalinity 0 221

Al, mg/L 13.0 0.7

Mn, mg/L 0.8 0.2

Fe, mg/L 0.5 <0.1

Pittsburgh Botanic Garden DLB

Poured concrete tank

100’ X 20’ X 5’

450 ton limestone

Agri Drain SDS system

Drains empty once/week

Concrete tank