Abstract: A Comparison of Borehole and Monitoring Well Groundwater Sample Results Using Both Field and Certified Laboratories

Thomas L. Ervin, Mary Louise Moise

In order to strategically place wells at the edges of groundwater plumes, "groundwater samples while drilling" were collected and analyzed during three remedial investigations prior to committing to the construction of wells at potential locations. The sample results provided data used to determine if the lateral and vertical edges of the plumes had been reached. If chemicals were detected in a borehole, the hole was abandoned and a new location was selected that was farther from the source of contamination, saving the cost of constructing and sampling more wells than necessary to define a plume. These decisions were reached rapidly using field laboratories to analyze the samples while drilling proceeded.

The analytical results generated during the three investigations indicate that borehole sample results are similar to monitoring well results. Holding the laboratory constant, borehole and monitoring well sample results (detections and nondetections) agreed qualitatively 84 percent of the time. Field laboratory and certified laboratory results agreed qualitatively at least 77 percent of the time. When field laboratory results differed from certified laboratory results by more than 20 percent, the field laboratory results were generally higher, providing a conservative margin of safety.

Based on the sample data generated during the three investigations, the use of on-site field laboratories for analyzing groundwater samples "collected while drilling" is an efficient and cost-effective technique for locating wells.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California