Case study - Westbay System delivered cost effective groundwater monitoring in mountainous region

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Multilevel well network provided high-density data at a reduced cost

CHALLENGE

After installing a number of traditional  monitoring wells at the site, it became  clear to the project scientists that more  and better data would be necessary  to properly characterize the complex  groundwater flow system.

SOLUTION

The high cost (measured in both time  and money) of installing conventional  well clusters at high-elevation locations  caused DCRG to consider other options.

RESULTS

Westbay System wells enabled DCRG  to monitor the large number of zones  required by the complexity of the site at  a greatly reduced cost in comparison to  other technologies.

High resolution data was needed to properly characterize complex flow system

In 1988, DuPont was tasked with completing a groundwater investigation at the DuPont  Belle, West Virginia, facility, as required by the U.S. Environmental Protection Agency’s site  Resource Conservation and Recovery Act (RCRA) Corrective Action permit. The focus of the  investigation was a number of historically utilized solid waste management units in the 600  acre mountain area adjacent to the plant. The work was carried out by the DuPont Corporate  Remediation Group (DCRG) and URS consultants.

After installing a number of traditional monitoring wells at the site, it became clear to the  project scientists that more and better data would be necessary to properly characterize the  complex groundwater flow system.

The plant is located in south-central West Virginia, a region with steep mountainous terrain  and heavily dissected valleys. The 100 acre main plant, where agricultural and special  chemicals are manufactured, lies on an alluvial terrace along the Kanawha River. The 600  acre mountain area is a contiguous property north of the main plant, characterized by bedrock  consisting of multiple layers of interbedded sandstone, shale, coal, and claystone.

The monitoring program faced multiple challenges:
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  • The groundwater system in the area was impacted with low  concentrations of site-related and naturally occurring semivolatile  and volatile organic chemical constituents.
  • Monitoring had to be carried out in five different aquifers, all  separated by shale aquitards.
  • ƒThe monitoring well locations were primarily on the tops of  mountains, which required wells as deep as 920 ft. ƒ
  • Also, the steep topography and layered stratigraphy was expected  to result in exceptionally high differential pressures over very short  distances in the boreholes.

Conventional well clusters proved costly and inefficient

The high cost (measured in both time and money) of installing  conventional well clusters at high-elevation locations caused DCRG  to consider other options. In addition to the need for cost-effective  monitoring, the special site conditions required a monitoring system  that was reliable and robust. After considering all of the available  options, DCRG decided to install Westbay Systems.

In 1994, the Westbay System was installed in five open bedrock  boreholes to depths of over 880 ft, with up to 40 monitoring zones in  each well.

Westbay Systems can be installed directly into open bedrock  boreholes, with Westbay System packers providing annular seals at  pre-determined locations. The Westbay System casing components  can be arranged in a wide variety of configurations, providing the  ability to monitor virtually any borehole feature and an unlimited  number of monitoring zones. The systems can also be installed  through a removable protective guide tube for installation in boreholes  of uncertain rock quality.

The water chemistry and hydraulic data from the first five wells at  the Belle site proved to be invaluable. As a result, an additional six  Westbay Systems were installed at the site in 2000, and one more well  was installed in 2005.

Westbay multilevel well system delivered high-density data  at a reduced cost

Westbay System wells enabled DCRG to monitor the large number of  zones required by the complexity of the site at a greatly reduced cost  in comparison to other technologies.

DCRG was able to detect and continue to monitor the presence of low  concentrations of site-related and naturally occurring semivolatile  and volatile organic chemical constituents present at the site. The  increased data density provided by Westbay System multilevel  technology also enabled them to delineate the horizontal and vertical  extent of the impact of these constituents on the multiaquifer  system. The Westbay System provided DCRG with the ability to add  monitoring zones for a fraction of the cost of the well, enabling them to  establish the areal extent of groundwater constituents efficiently and  cost effectively.

The hydraulic data supplied by the Westbay Systems was used to  help develop a three-dimensional conceptual hydrogeologic model  of groundwater flow at the site. DCRG could not have created such  an accurate predictive model without the data density provided by  the Westbay System wells. The model has since been accepted by  the regulatory agency that originally directed DuPont to carry out the  work.

Thus, at the same time DuPont was collecting and using the valuable  data provided by the Westbay System, they were also realizing  savings in well costs, field oversight costs, and waste treatment  costs.

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