The client operated a large wood preserving and storage facility next to a river from 1913 until the 1980s. Industrial practices of the day resulted in treatment product losses to the ground’s surface and underlying fractured limestone bedrock.

A risk assessment conducted in 2007 identified no ecological risk in the river, but recommended contaminant source reduction. The client voluntarily maintained this project and contracted us to complete a detailed sediment characterization and oversee an environmental remediation program.

A series of groundwater and free-treatment product interceptor trenches and wells were installed along the river shore by other consultants on the team to capture historical creosote and associated dense non-aqueous phase liquids (DNAPL) in fractured bedrock.

HESL implemented runoff controls on the site, to prevent contaminated runoff from reaching the river.

We placed sediment capture barriers in the river and profiled the sediment captured up to twice per year. We used the captured sediment to:

• Create 3D models and evaluate barrier capture effectiveness and sediment accumulation patterns over time.
• Analyze for contaminants and co-factors which affect the distribution of the contaminant complexes.
• Conduct spatial-temporal statistical analyses to improve sediment capture effectiveness and identify changes over time.

Following sampling, the accumulated sediment was suction-dredged annually from the river by divers for disposal to a licensed receiving facility.

Downstream river sediments are sampled every three years to compare current to historic sediment distribution patterns.

The program results, combined with a broader sampling program conducted at the river’s mouth, tracked the contaminants removed from the river by the program.

Contaminants have decreased in sediment, and the program has reduced aquatic risk.

Annual reports and meetings with regulators document a strategy of continuous improvement of site conditions and maintaining no ecological risk in the river.