Case study

GWSDAT as a Resource for Site Closure: Plume Delineation, Trend, and Data Gap Analysis

Tom Daigle

P.G. Senior Project Manager

GEI Consultants, Inc.

Woburn, Massachusetts, USA

Utilizing GWSDAT to evaluate groundwater plume delineation and trends. Various sites in Michigan.

Routine groundwater monitoring at remediation sites often continues for many years longer than
needed resulting in unnecessary spending and consumption of resources. The reasons for prolonged
groundwater monitoring activities may include an inadequate well network, poor delineation, localized
plume dynamics, or monitoring data gaps. Many of these issues are readily identified and addressed
using GWSDAT.

GEI was approached by a client to perform an independent review of the groundwater conditions at five
‘corner gas station’ Sites in Michigan. Each Site included over 20 years of monitoring data, however, a
comprehensive plume stability analysis had never been conducted. Each plume was previously
interpreted to be delineated and decreasing; however, Site closure was elusive based on site-specific
access restrictions and regulatory framework.

GEI utilized GWSDAT at each Site to quickly identify several gaps in both the spatial and temporal extent
of data. GWSDAT spatiotemporal analysis and individual well trend analysis allowed us to optimize
future data collection to compliment the existing dataset and accelerate each Site to closure. The
GWSDAT model allowed us to make strategic recommendations for new wells or sampling in locations
that would be ideal to provide the necessary data to achieve closure. We then recommended minor
improvements to the groundwater monitoring programs and incorporated new data into the GWSDAT
model to determine when sampling could be complete.

GWSDAT allowed us to evaluate the plume and provide easy-to-understand visualizations for the client
and stakeholders to make informed decisions. Without GWSDAT analysis, each Site may have continued
sampling for several more years collecting inadequate data to achieve Site closure. At the time of this
case study, two of the five Sites have been closed and the other three are on a more certain path.

GEI Consultants, Inc.
400 Unicorn Park Drive, Suite 300
Woburn, MA 01801
Tom Daigle, P.G. Senior Project Manager