# Presentation: 174876

## 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 **

## Production and Use of PCE

**  ****PCE use in dry cleaning began in 1940s**

**Production and Use of PCE**

**  ****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**

## Production of PCE

**Production of PCE**

## 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 **

## Behavior of PCE in Subsurface

## Data on PCE in Ground Water

## Data on PCE in Ground Water

**These data represent a**
**select subset of all wells**

## PCE in Ground Water

**3 – ranking of PCE among all**
**      ****detected  VOCs**

**(assessment level of 0.2 ********g/L)**

## Occurrence Using Uncensored

**Concentrations**

**detection frequency **
**using no assessment level**

## PCE Concentrations

## Quantified Concentrations

**median**

**25****th**** percentile**

**75****th**** percentile**

**outlier **
**(> 1.5 ******** IQR)**

**1.5 ******** IQR**

## Concentrations Relative to MCL

**Major aquifers**

**Urban land use**

**Domestic wells**

**Public wells**

## 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**

## 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**

## Associations With 

**PCE Occurrence**

**Major aquifers:**

**1. Redox conditions**

**2. RCRA facilities within 1 km**

**3. Depth to top of aquifer**

## 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**

## 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**

## 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**