SUSTAINABLE LANDFILLING: EVALUATING THE POTENTIAL … SoukupS.pdf · Conclusions • The impact to groundwater quality from landfill mining depends primarily on: •Size and duration

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SUSTAINABLE LANDFILLING: EVALUATING THE POTENTIAL IMPACT OF LANDFILL MINING ON GROUNDWATER QUALITY

May 2017

Speaker:

William G. Soukup, P.G.

Presentation Goals

• Understand Risk

• Reduce Risk

• Manage Risk

© 2017 Cornerstone. All rights reserved.

Advantages of Mining MSW

• Gain landfill space

• Remediation of a

poorly-functioning landfill

• Side Benefits • Recovery of soil for reuse as daily cover

• Optional recovery of metals, combustibles, etc.


MSW operational face


Trommel Screen Rotating Drum


Trommel Rig


Potential Downsides of Landfill Mining

• Time and costs

• Exposure to wastes and landfill gas

• Odors

• Impacts to groundwater quality


Typical Mining Sequence


Limited leachate generation on side slopes

No further leachate generation on bottom

MSW

Natural Formation GW Table

Cap

Factors for Leachate Generation


Moisture Content (MC): the amount of water per unit volume of waste. (% volume/volume)

10 to 20 %

Field Capacity (FC): the moisture holding capacity of waste under gravity drainage. (% volume/volume)

30 to 40 %

Leachate Generation: occurs when moisture content exceeds field capacity

Example Leachate Generation


Assumed Waste thickness = 27’

1’ 1’

Waste Volume = 27 ft3 = 1 yd3

35 gallons of recharge = 56 inches of precipitation

Up to 30% of recharge due to “channeling”

Groundwater Model Simulation


• 80 acres, 50 feet of waste

• Underlying sand; k=50’/d

• Uniform groundwater horizontal gradient

• Leachate generation rate 48 inches per year

• Steep side slopes

• Non-reactive, conservative solute

• Leachate concentration = 100 m/v units

Groundwater Model Simulations


Simulated operational factors

1. Mining areas (phases) 2. Sequencing phases 3. Steepness of side slopes 4. Mining rate

Metrics used to evaluate results

1. Maximum concentration beneath excavation 2. Maximum concentration at downgradient boundary 3. Total mass-flux at downgradient boundary


Discharge Boundary

Mined Area

Scale:

48’

38’

40’

42’

44’

46’

0’ 2,000’

Model Domain - Single Phase Scenario

Predicted Concentrations – Single Phase


10 years

40 years 30 years

20 years

100

30

1

50+

Predicted Concentrations - Single Phase


Source Area Concentration

Discharge Area Concentration

Normalized Total Mass Flux = 100 mass-units

10-year Mining period

0 10 20 years 30 40 50

Three Phase Scenario


Discharge Boundary

Mined Area

Scale:

48’

38’

40’

42’

44’

46’

0’ 2,000’

Phase 1

Phase 2

Phase 3

Predicted Concentrations – 3 Phases


3.3 years

30 years 10 years

6.6 years

40+

70+

90+

80+

20+

60+

Predicted Concentrations - 3 Phases






0 10 20 years 30 40 50

9 Phases (upgradient sequencing)


Discharge Boundary

Scale:

48’

38’

40’

42’

44’

46’

0’ 2,000’

1 3 2

5

8

6

7

4

9

Predicted Concentrations – 9 Phases


1.1 years

4.4 years 3.3 years

2.2 years

Predicted Concentrations - 9 Phases upgradient sequencing






0 10 20 years 30 40 50

9 Phases (downgradient sequencing)


Discharge Boundary

Scale:

48’

38’

40’

42’

44’

46’

0’ 2,000’

1 3 2

5

8

6

7

4

9

Predicted Concentrations – 9 Phases downgradient sequencing






0 10 20 years 30 40 50

Steep Sidewalls


6% 6%

88%

Shallow Sidewalls


33% 33%

33%

0

20

40

60

80

100

120

One Phase 3 Phases 9 PhasesUG

9 PhasesDG

9 PhasesShallowSides

9 Phases15 years

Nor

mal

ized

mas

s un

its

Max Conc.

Max Conc.

Total

12 17 10 11

100

Summary of Model Results


32

In-situ Groundwater Sample Collection


Validation Sampling Sequence


Conclusions

• The impact to groundwater quality from landfill mining depends primarily on:

• Size and duration of the open excavation

• Precipitation rate

• Operational modifications that can reduce impacts include:

• Mining in smaller sub-areas

• Reaching waste bottom more quickly

• Keeping side slopes relatively steep


Conclusions

• Groundwater travel time is slow allowing early warning of pending groundwater impacts.

• The pro-active evaluation of potential groundwater impacts (through modeling and validation sampling) is a cost effective means of reducing long-term risks.


Contact Information


William G. Soukup, P.G. Cornerstone Environmental Group, LLC

[email protected]

Phone: (845) 695-0202

Cell: (201) 274-6863

mailto:[email protected]

Predicted Concentrations – 9 Phases Shallow Side slopes






0 10 20 years 30 40 50

Predicted Concentrations - 9 Phases 15-year Operation






0 10 20 years 30 40 50

Documents

SUSTAINABLE LANDFILLING: EVALUATING THE POTENTIAL … SoukupS.pdf · Conclusions • The impact to groundwater quality from landfill mining depends primarily on: •Size and duration