Multiplicity (Available only in the Geoenvironmental Special Issue)

Landin, Birgit K.; ,

Multiplicity (Available only in the Geoenvironmental Special Issue)

by Birgit K. Landin, New Mexico Environment Dept., Santa Fe, NM,

Serial Information: Civil Engineering—ASCE, 1997, Vol. 67, Issue 2, Pg. 9A-11A

Document Type: Feature article

Abstract:

When it comes to tracking groundwater contaminant plumes, single completion monitoring wells are the standard choice, but they aren't the only one. After four years of trying to delineate the plume at a Superfund site outside of Albuquerque, N.M., engineers from Geoscience Consultants, Ltd., McLean, Va., found that single-port weren't up to tracking the lateral and vertical movement of the plume. Instead, GCL decided to try multiport wells, which can take readings and samples from up to 12 different depths at the same location. The MP System� multiport wells, manufactured by Westbay Instruments, Inc., Vancouver, Canada, were used to obtain valuable data for characterizing the aquifer's properties, including horizontal and vertical hydraulic head distributions, flow paths, detailed vertical groundwater chemistry and plume delineation. GCL wanted to use the wells to obtain data for the remedial action plan, but initially EPA Region VI was skeptical. They feared that the multiport wells would lead to cross contamination, where pollutants from one part of the aquifer would migrate to another through the well's multiple openings. The wells are specially designed to prevent cross-contamination, however, with inflatable packers, bentonite seals and concrete grouting to keep the different layers of the aquifer separate. After many tests, GCL was able to show that cross-contamination was not occurring and the multiport wells became an essential part of the remedial monitoring network. The wells were also used to test which zones within the aquifer could be used for the injection of treated groundwater and as observation wells during a large-scale pump and treat test. The detailed data they provided helped GCL develop an accurate and effective remedial system design. The wells were installed in 1994 and the remediation plan was put into action in May, 1996. Samples taken two months later indicated that the plume had been captured. GCL expects the bulk of the plume to be remediated in five years, with the residual contaminants being cleaned up over the next 30 years. The multiport monitoring wells will be an important part of monitoring this progress.

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