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Client:
Confederated Tribes of the Chehalis Reservation |
Background
The Chehalis Tribe initiated a wellhead protection project to better manage
its water supply wells and understand the risks to these sources. Project
goals included assessing the contaminants present in groundwater beneath
the reservation, estimating aquifer properties, and using this data to
model capture zones for domestic and supply wells.
Challenges
The Tribe obtains most of its water supply from more than 100 low-capacity
domestic wells distributed over the 6.6-square-mile reservation. A few
larger-capacity wells exist at Lucky Eagle Casino, the tribal housing
facility, and various industrial facilities. The wells are completed in
a highly permeable aquifer, which makes aquifer testing difficult because
water level drawdowns are low.
Approach
To help protect the quality of tribe’s water, we developed a monitoring
system to provide an early warning of potential problems. This work involved
delineating capture zones for production wells and springs and identifying
sources of contamination—both potential and actual. We also designed
an extensive monitoring network for groundwater sampling.
Outcome
Our efforts produced a comprehensive, ongoing monitoring program that
will warn the Tribe of imminent water quality problems.