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Client:
Clark Public Utilities |
Background
In an effort to supply water to the rapidly growing population of Clark
County, Washington, Clark Public Utilities (CPU) has explored many possible
new groundwater sources. Unfortunately, the availability of suitable development
sites continues to decrease. One possible water source is a highly productive
aquifer system along the Columbia River near Vancouver Lake. This system,
however, not only supports local wetlands but it also includes areas where
historic industrial uses have contaminated the aquifer with chlorinated
solvents.
Challenges
Although the contaminant plume is currently contained, operating a high-capacity
wellfield could mobilize it. Before developing such a wellfield, CPU needed
to understand how pumping will affect plume migration. A complicating
factor is the area’s complex groundwater conditions; water level
gradients are very low (and therefore difficult to measure) and groundwater
levels are strongly influenced by flow variations in local surface water
features. For instance, Columbia River levels vary daily in response to
tidal influences but vary seasonally according to upstream dam operations.
Approach
Typically, we assess groundwater flow patterns using measurements of water
levels obtained in the field. In this case, however, such a traditional
approach was infeasible. Instead, we constructed a groundwater flow model
that incorporates known hydrogeologic information and surface water variation.
This model was also designed to evaluate the significance of unknown information
by running an uncertainty analysis.
Outcome
The contaminant distribution predicted by our model was a good match to
observed conditions, indicating that our design and calibration were successful.
We used the model to evaluate the how pumping at the proposed wellfield
site would alter the spreading of contamination from the source areas.
Related Projects
Groundwater Development / Clark Public Utilities: Water Supply Development
Watershed
Assessments / Clark Public Utilities: Salmon Creek Basin Management Plan