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Project ID: 2004CT45B

Title: Investigating the Influence of Purging on Long-Term Remediation Compliance Monitoring

Project Type: Research

Focus Categories: Groundwater, Water Quality, Toxic Substances

Keywords: groundwater, purging, monitoring well, water quality

Start Date: 03/01/2004

End Date: 02/28/2005

Federal Funds: $24,907

Non-Federal Matching Funds: $41,753

Congressional District: second

Principal Investigator:
Gary A. Robbins


Monitoring wells are used for remediation compliance monitoring across the country at contamination sites. Typically, the wells are sampled on a quarterly basis. The common sampling procedure is to purge 3-5 casing volumes of water before obtaining the sample. Most often, purging is performed using a bailer. Technical objections to the use of bailers have led to regulatory adoption of low flow purging and sampling with pumps. However, low flow purging and sampling increases the cost and time for sampling relative to the use of a bailer. Moreover, a number of recent studies question the need for purging prior to sampling at all. The high cost of disposal of purge water and the variability in results are issues that have forced examination of purging and sampling practices. Several studies have concluded that samples obtained without purging provide comparable data to that obtained with purging. Even if the data do not agree, one may argue that data obtained without purging may still be used for evaluating spatial and temporal trends in water quality for the purposes of remediation monitoring and regulatory compliance. Constituent concentrations obtained in monitoring wells represent averages of the vertical concentration distribution outside the well. Even with purging, the data obtained from wells is qualitative rather than quantitative. As such, this supports the use of no-purge sampling for compliance monitoring. In fact, some regulatory authorities have started accepting data from non-purged samples for compliance monitoring. The objective of this study is to assess the validity of the no-purge sample option for regulatory compliance monitoring. To meet this objective a field study will be performed at the University of Connecticut Motor Pool, which has a history of gasoline contamination and remediation. Site hydrogeology has been well characterized in three-dimensions in numerous past research projects. At the site, two locations with existing monitoring wells in close proximity to clusters of multilevel samplers will be used for sampling. Along with the study wells, other wells at the site will be used for evaluating changes in water table level and flow direction. The field tests will entail performing monitoring in wells and multilevel samplers of select water quality parameters (e.g., T, EC, pH, ORP, DI, DO, turbidity, MTBE and BTEX) on a monthly basis for one year. Following water level measurement, small grab samples will be taken to develop profiles of the water quality in the well. The well will then be sampled at three depths using a bailer (no–purge samples). Afterwards, the wells will be purged with a bailer and resampled. Then the wells will be purged and sampled using low flow methods. The multilevel samplers will also be sampled using low flow techniques. The data from the multilevel samplers, along with previously determined hydraulic conductivity determinations, will permit estimation of well concentrations based on concentration averaging models to help evaluate factors influencing data derived from the wells. Well data will be compared statistically using ANOVA testing. We will also examine how the well and multilevel sampling data vary temporally using time series trend analysis. The results of this study will aid in resolving the issue as to whether purging is needed for compliance monitoring. Furthermore, it will aid in helping to interpret monitoring data obtained from wells in consideration of concentration averaging.

Progress/Completion Report PDF

U.S. Department of the Interior, U.S. Geological Survey
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Last Updated: Tuesday July 12, 2005 3:04 PM
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