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Client:
Ephrata Landfill |
Background
Grant County operates the Ephrata Landfill, a historically unlined facility
that is now permitted under current state regulations. Although the landfill
is located in arid central Washington, excessive irrigation has raised
groundwater levels to near land surface.
Challenges
To design an effective monitoring system at this landfill, we needed to
understand groundwater flow patterns in three potentially connected aquifers.
When we discovered contamination in the uppermost aquifer during our initial
field explorations, we also needed to ensure that contaminants would not
migrate to a nearby supply well.
Approach
This project had several phases. First, we reviewed existing hydrogeologic
and water quality data to assess conditions at the site. Based on this
preliminary assessment, we installed 10 monitoring wells, completing many
of them in multiple aquifers. After detecting organic and inorganic contaminants
in the uppermost aquifer, we collected additional samples from nearby
supply wells as a precaution against health threats. We then investigated
this contamination—specifically, its source and ultimate fate. Finally,
we abandoned and replaced the landfill’s old water supply well.
Outcome
The landfill has continued to operate successfully during our involvement,
which has now spans more than 15 years. In fact, we recently assisted
with permitting efforts for a new lined cell and designed a monitoring
system that can distinguish between old and new contamination. This work
involved drilling two new groundwater extraction wells that will remove
some sources of contamination while we negotiate final corrective actions
with state regulators. We also designed a new supply well that will not
interfere with the landfill’s monitoring system. This well is over
600 feet deep and features extra-secure surface seals to prevent contaminant
migration.