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

2. PCE use in dry cleaning began in 1940s PCE use in dry cleaning began in 1940s Production and Use of PCE Production declined after peak in 1970s Production declined after peak in 1970s As of 2002, PCE was primary solvent for 85% of drycleaners 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 Denser than water High solubility relative to MCL High solubility relative to MCL Moderate organic carbon partitioning Moderate organic carbon partitioning Relatively high Henry’s coefficient Relatively high Henry’s coefficient Relatively long half-life in water Relatively long half-life in water

5. Behavior of PCE in Subsurface

6. Data on PCE in Ground Water

7. 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 median 25 th percentile 75 th percentile outlier (> 1.5  IQR) 1.5  IQR

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

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

14. Occurrence of TCE With PCE PCE occurred more frequently in PCE occurred more frequently in oxic ground water compared to anoxic oxic ground water compared to anoxic Molar concentration ratios of PCE/TCE Molar concentration ratios of PCE/TCE were 3 times higher in oxic ground water were 3 times higher in oxic ground water compared to anoxic 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 3. Proximity to dry-cleaner LUST 2. Well depth

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

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