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Groundwater Pollution

Containment of Pollution

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What can we do with the pollutant?

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http://www.frtr.gov/matrix2/section3/figure3_1.html

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When pollutants are found in the soil and/or groundwater there are several choices:

1. Stop the pollution from moving (immobilization)

2. Remove the pollutant.

3. Destroy the pollutant.

4. Dilute the pollutant.

5. Do nothing.

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This week we will look at the immobilization of the pollutant.

This is also called containment.

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Advantages of containment:It is a simple and strong technology. It is low cost compared to many treatments, especially for large source areas. A well made containment system stops almost all contaminant movement to other areas.

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Containment can be combined with in situ treatment.

It stops contaminant moving during the treatment.

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Disadvantages of containment:

Containment does not reduce source zone mass, concentration, or toxicity unless it is used in combination with treatment technologies.

Containment systems such as slurry walls are not impermeable and so containment only works for a time.

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We don’t know how well they work over time.

Long-term monitoring of the containment system is essential to know that contaminants are not moving.

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These slides are adapted from: 1.34 Waste Containment and Remediation Technology , As taught in: Spring 2004, by Dr. Peter Shanahan , MIT OpenCourseWare, Creative Commons License, http://ocw.mit.edu/OcwWeb/Civil-and-Environmental-Engineering/1-34Spring2004/CourseHome/

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Capping of pollution sources

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Cover systems (“caps”)Stop contact and exposure to wasteStop humans or animals from digging into wasteReduce (or almost stop) infiltrationReduces/stops movement of contaminants to ground water by infiltrating water

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Landfill Cover Layers

http://www.frtr.gov//matrix2/section4/D01-4-27.html

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Cap layers: Plants (Vegetation)

Stops rain from washing away soil.Infiltration reduced byevapotranspiration

Use:Short rooted plantsLow nutrient needsCan live in dry and heat

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Cap layers: soil layer

Grows plants

Protects lower layers

Usually 60-cm thick

Crushed stone or rocks may be used in dry places

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Cap layers: Protection layer

90-cm layer of rocks to stop animals from digging.Sometimes stops long rootsNot always included

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Cap layers: Filter layer

Stops small particles from soil moving into drains

May be plastic or 30-cm sand

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Cap layers: Drainage layerStops infiltrated water moving don to low K layers below.Stops water making pools on geomembrane liner.Drains by gravity. At least 30 cm of sand or plastic withK = 10-2 cm/sec.

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Cap layers: Low K layerBoth plastic (geomembrane) and low-K soil (clay)Low K prevents infiltration of water into waste: hydraulic barrierGeomembrane: at least 0.5 mm (20-mil ) thickCompacted clay: at least 60 cm with K ≤ 10-7 cm/s

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Cap layers: Gas vent layerNeeded if waste will make methane or toxic gasLike drainage layer:30 cm of sand or other materialWith horizontal venting pipes (low number to keep cap impermeable)

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Geomembrane (or FML – flexible membrane liner) is impervious except at holes, tears, or seams.

Good FML has one hole per 0.4 hectare.

1 hectare = 10 000 m2

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http://www.groundwateruk.org/archive/industrial_and_urban_pollution_of_groundwater.pdf

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Capping is good for landfills, widespread soil contaminants

Costs ~

$440,000 per hectare for non-hazardous waste

$560,000 per hectare for hazardous waste

25http://www.fernald.gov/VImages/PhotoTour/2002/Aug02/pages/6319-D3684.htm

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Walls to stop groundwater flow.

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Vertical cut-off walls

Technologies include:Sheet-pile or geomembrane walls

Slurry walls

Grout curtains

In-situ soil mixing

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Sheet pile or geomembrane walls

These are put into the ground to stops the flow of groundwater.

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Interlocking Sheet Piles

http://www.waterloo-barrier.com/

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Sheet Pile Installation

http://www.oceta.on.ca/profiles/wbi/barrier.html

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Sheet Pile Grouting

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Slurry walls

Slurry is a mix of soil and other material to form a wall which stops the flow of groundwater.

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Slurry walls

Most common cut-off wall technology

Can use:Soil and bentonite clay (SB)

Cement-bentonite (CB)

Pozzolanic materials (type of cement - 접합제 )

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Trench for Slurry Walls

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Vertical section for slurry wall

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Vertical section for “hanging” slurry wall for LNAPLS

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Horizontal plans

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Materials for slurry walls

SB (soil-bentonite) have lower K, are less expensive

Usual K = 10-7 cm/sec

Reported K’s as low as 5 x 10-9 cm/sec

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CB (cement-bentonite) have more strength

Use on slopes where strength is important

Use in areas where there is not good soils (for SB)

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Other things can be added to make better CB and SB:

Fly ash ( 재 ) to increase carbon for adsorptionLiners or sheet pile put inside slurry wall to decrease K

These things cost moreApproximate costs:$540 to $750 per m2 (1991 dollars)

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Slurry wall performancePerformance has been mixed:

Slurry walls leakConstruction can be difficultWaste may compromise wallRequires long-term pumping in slurry wall enclosures

Slurry walls are good barriers to advection, but not to diffusion

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EPA review of slurry wall successReviewed 130 sites – 36 had adequate data:

8 of 36 met remedial objective4 met objective except not yet for long term13 appear to have met objective4 appear not to have met objective7 are uncertain

4 of 36 leaked and required repairs(leaks most often at “key” with floor)

http://www.epa.gov/swertio1/download/remed/subsurf.pdf

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Grout ( 그라우트 , 시멘트 [모르타르 ] 풀 ) curtainsPut grout to form containmentInstallation methods:

Jet grouting – inject grout into soil, mixing soil and groutPressure grouting – forces grout into fractures in rockDeep-soil mixing – grout-bentonite slurry mixed into soils to create wall

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Grouting Patterns

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Grout materials

Solid suspensions:Clay, bentonite, cement, and combinations

Chemical grouts:Silica- or aluminum-based solutions

Polymers