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Contamination of Ground Water by Perchloroethene (PCE) – A National Perspective

Contamination of Ground Water by Perchloroethene (PCE) – A National Perspective. By Michael Moran U.S. Geological Survey. Ground Water Resources Association of California, 13th Symposium Series on Groundwater Contaminants Conference, Newport Beach, California, November 10, 2004 .

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Contamination of Ground Water by Perchloroethene (PCE) – A National Perspective

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  1. Contamination of Ground Water by Perchloroethene (PCE) – A National Perspective By Michael Moran U.S. Geological Survey Ground Water Resources Association of California, 13th Symposium Series on Groundwater Contaminants Conference, Newport Beach, California, November 10, 2004 U.S. Department of the Interior U.S. Geological Survey

  2. Production and Use of PCE • PCE use in dry cleaning began in 1940s • Production declined after peak in 1970s • As of 2002, PCE was primary solvent for • 85% of drycleaners - this constitutes 25% of PCE production - remainder is used as industrial solvent

  3. Production of PCE

  4. Physicochemical Properties of PCE • Denser than water • High solubility relative to MCL • Moderate organic carbon partitioning • Relatively high Henry’s coefficient • Relatively long half-life in water

  5. Behavior of PCE in Subsurface

  6. Data on PCE in Ground Water

  7. Data on PCE in Ground Water These data represent a select subset of all wells

  8. PCE in Ground Water 3 – ranking of PCE among all detected VOCs (assessment level of 0.2 g/L)

  9. Occurrence Using Uncensored Concentrations detection frequency using no assessment level

  10. PCE Concentrations

  11. Quantified Concentrations outlier (> 1.5  IQR) 75th percentile median 25th percentile 1.5  IQR

  12. Concentrations Relative to MCL Domestic wells Public wells Urban land use Major aquifers

  13. Occurrence of TCE With PCE • Among 4 solvents in ground water, • PCE-TCE was most common mixture • TCE may be daughter product of • reductive dechlorination of PCE

  14. Occurrence of TCE With PCE • PCE occurred more frequently in • oxic ground water compared to anoxic • Molar concentration ratios of PCE/TCE • were 3 times higher in oxic ground water • compared to anoxic

  15. Associations With PCE Occurrence Major aquifers: 1. Redox conditions 2. RCRA facilities within 1 km 3. Depth to top of aquifer

  16. Associations With PCE Occurrence Domestic wells: 1. Population density 2. RCRA facilities within 1 km Public wells: 1. Population density 2. Well depth 3. Proximity to dry-cleaner LUST

  17. Dry Cleaners as RCRA Facilities  Most dry cleaners that use PCE are probably regulated under RCRA  We estimate that about 30% of RCRA sites are dry cleaning facilities   6,000 RCRA-regulated dry cleaners

  18. Summary and Conclusions • At a national scale, PCE is one of the most • frequently detected VOCs in ground water • PCE concentrations exceed the MCL more • frequently than most other VOCs • RCRA facilities and dry cleaners are • associated with PCE occurrence

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