Well-Purging Protocols for Sampling Dissolved Petroleum Hydrocarbons

Abstract

Traditionally, most guidelines for sampling contaminated ground water recommend purging wells prior to sampling. Recently, however, many environmental professionals are questioning the need for, and/or the desirability of, purging wells prior to sampling ground water for dissolved petroleum hydrocarbons. In an attempt to balance the costs associated with monitoring against the costs associated with the actual remedial activities at contaminated sites, several regulatory agencies are now permitting use of a no-purge sampling protocol under certain circumstances. This article summarizes the current controversy that exists with regard to well-purging protocols, and describes a project that was initiated in the state of Massachusetts to assess the issue. This assessment was primarily based upon comparison of BTEX levels (determined via traditional laboratory methods) in ground-water samples obtained both before and after purging. Data for this project were also obtained using an innovative field-screening tool called the “ChemSensor.” The results of this project suggest that, under certain conditions, a no-purge method of sampling may be appropriate during the long-term monitoring phases on sites contaminated with dissolved petroleum hydrocarbons. Although the data set obtained to date in Massachusetts is limited to three different geologic formations, it represents a useful extension of similar work completed in California and in New York, which is discussed herein. It is anticipated that this work will be useful to the profession as a starting point for examination of this timely issue.