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Client:
Regional Disposal Company |
Background
The Roosevelt Regional Landfill is located in southeastern Washington,
on the Columbia Plateau. The site features a shallow, flood-basalt aquifer
underlain by 340 feet of clay. As a solid waste facility, the landfill
has been subject to two important state environmental regulations in recent
years—the Minimal Functional Standards and the newer WAC 173-351.
Our hydrogeologic characterization efforts have yielded information that
has been vital to meeting the requirements of both.
Challenges
Our main challenge was to characterize this regionally extensive project
area in a cost-effective manner. Although geologic and water quality data
were adequate in the immediate landfill vicinity, little information was
available for areas outside the landfill footprint.
Approach
Our characterization efforts involved extensive field work. We drilled
more than 10,000 feet using air-rotary methods, designed and installed
more than 50 monitoring wells, mapped local geologic features, and conducted
hydraulic tests to assess aquifer parameters. In addition, we collected
water samples for analysis of typical chemical constituents. To reduce
the number of boreholes required for this characterization, we used two
innovative approaches: groundwater isotope analyses and time-domain electromagnetic
techniques. Our assessment of carbon-14, tritium, and stable isotopes
provided information about the age and origins of groundwater. This assessment,
in conjunction with traditional hydraulic approaches, gave us valuable
insights into the complex groundwater flow patterns and potential contaminant
transport pathways within the regional aquifer system.
Outcome
Our resulting conceptual geologic model provided a strong basis for designing
and implementing an effective groundwater monitoring program. We use our
environmental database to import, manage, evaluate, and report on this
monitoring data.