4 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.
5 This week we will look at the immobilization of the pollutant. This is also called containment.
6 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.
7 Containment can be combined with in situ treatment. It stops contaminant moving during the treatment.
8 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.
9 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.
10 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/ http://ocw.mit.edu/OcwWeb/Civil-and- Environmental-Engineering/1- 34Spring2004/CourseHome/
12 Cover systems (“caps”) Stop contact and exposure to waste Stop humans or animals from digging into waste Reduce (or almost stop) infiltration Reduces/stops movement of contaminants to ground water by infiltrating water
15 Cap layers: Plants (Vegetation) Stops rain from washing away soil. Infiltration reduced by evapotranspiration Use: Short rooted plants Low nutrient needs Can live in dry and heat
16 Cap layers: soil layer Grows plants Protects lower layers Usually 60-cm thick Crushed stone or rocks may be used in dry places
17 Cap layers: Protection layer 90-cm layer of rocks to stop animals from digging. Sometimes stops long roots Not always included
18 Cap layers: Filter layer Stops small particles from soil moving into drains May be plastic or 30- cm sand
19 Cap layers: Drainage layer Stops 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 with K = 10 -2 cm/sec.
20 Cap layers: Low K layer Both plastic (geomembrane) and low- K soil (clay) Low K prevents infiltration of water into waste: hydraulic barrier Geomembrane: at least 0.5 mm (20-mil ) thick Compacted clay: at least 60 cm with K ≤ 10 -7 cm/s
21 Cap layers: Gas vent layer Needed if waste will make methane or toxic gas Like drainage layer: 30 cm of sand or other material With horizontal venting pipes (low number to keep cap impermeable)
22 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 m 2
45 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
46 CB (cement-bentonite) have more strength Use on slopes where strength is important Use in areas where there is not good soils (for SB)
47 Other things can be added to make better CB and SB: Fly ash ( 재 ) to increase carbon for adsorption Liners or sheet pile put inside slurry wall to decrease K These things cost more Approximate costs: $540 to $750 per m 2 (1991 dollars)
48 Slurry wall performance Performance has been mixed: Slurry walls leak Construction can be difficult Waste may compromise wall Requires long-term pumping in slurry wall enclosures Slurry walls are good barriers to advection, but not to diffusion
49 EPA review of slurry wall success Reviewed 130 sites – 36 had adequate data: 8 of 36 met remedial objective 4 met objective except not yet for long term 13 appear to have met objective 4 appear not to have met objective 7 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
50 Grout ( 그라우트, 시멘트 [ 모르타르 ] 풀 ) curtains Put grout to form containment Installation methods: Jet grouting – inject grout into soil, mixing soil and grout Pressure grouting – forces grout into fractures in rock Deep-soil mixing – grout-bentonite slurry mixed into soils to create wall