A Case Study of A Civil ActionLEARN NC

A Case Study of A Civil Action• This is a short, culminating activity that

can be used to assess your students' understanding of the steps needed to determine if a water source is contaminated and how it got that way, and to suggest possible methods of cleanup or remediation.

Volatile Organic Compounds (VOCs)

Include solvents (degreasers) used in a variety of industrial, commercial, and residential applications

Examples include: Tetrachloroethylene (PCE or PERC) Trichloroethylene (TCE) Vinyl chloride

TCEs in the environment Soil & Sediment

Source: Improper use or disposal of materials containing TCE Entrapped as a non-aqueous phase liquid (DNAPL) in the pore spaces

in soils and sediments Dissolved TCE can adhere to soil and sediment particles Can move through soil to contaminate groundwater

Air Source: Evaporation during use or disposal of a product containing TCE Source: Evaporation from contaminated surface water

Water Source: Improper use or disposal of materials containing TCE Source: Breakdown of PCE in anoxic groundwater conditions

Source: ATSDR ToxFAQs

NPL Site: Wells G and H

Relative locations of wells H and G and potential sources of pollution at Woburn, MA. Leukemia cases were clustered in the Pine Street neighborhood south of the wells. Properties near the wells included: W.R. Grace, NEP (Plastics), Olympia (trucking), UniFirst (dry cleaning), Wildwood (tannery).

Cluster of Leukemia CasesSource: http://www.mhhe.com/earthsci/geology/mcconnell/demo/intro.htm

TCE and PCE in Wells G and H• Water from well G contained 267 parts per billion

(ppb) TCE and 21 ppb PCE. • Water from well H contained 118 ppb TCE and

13 ppb PCE. • The MCL for TCE and PCE dissolved in public

drinking water is 5 parts per billion (0.005 ppm).• “Detection of TCE, PCE, and other organic

solvents in water samples was not possible prior to about 1973 and the detection equipment (gas chromatograph/mass spectrometer) was not commercially available until the late 1970s.”

Source: http://serc.carleton.edu/woburn/issues/tce_toxicity.html

Contamination by DNAPLs is Encountered at many Superfund Sites • Entrapped droplets of DNAPLs, as well as large

pools of DNAPLs, often account for a far greater amount of contaminant mass at a site than that dissolved in the aqueous phase and sorbed to soils and sediments

• Clean up of DNAPLs is challenging due to the density and insolubility of the chemicals.

• The number of DNAPL contaminated sites in the United States is well over 10,000. Source: http://www.itrcweb.org/teampublic_BioDNAPLs.asp

DNAPLs sink to the bottom of an Aquifer

http://water.usgs.gov/nawqa/vocs/national_assessment/report/chapter5.html

ContaminantPlume

Entrapped PCE

Entrapped PCE

Entrapped Air

Dr. Cass Miller: Physical & Chemical Approach to Remediation of DNAPLs

Dr. Miller’s research team developed a remediation model that takes advantage of the different densities of solutions.

Can a brine solution with a density greater than a DNAPL be used to remove that DNAPL from an aquifer?

Modeling Remediation of DNAPL Contaminated Aquifers

Play Animation

Coarse Sand

Fine Sand

DNAPLs will preferentially flow to the areas containing coarse sand

Field Test: Remediation of a PCE Contaminated Aquifer

UNC SBRP researchers are injecting PCE into a sandy aquifer at a field site to test the effectiveness of their remediation approach.

Field Test Results: 7 month long experiment 15% recovery of PCE Results from the laboratory-scale

experiments were not duplicated at the field site

Next steps: Determine the fate of the unrecovered PCE.

Did it infiltrate the clay? Determine how the brine dispersed in the soil.

Soil cores were removed from the site for further investigation.