Construction Management Services for an Industrial Facility
Client: Industrial Business
Location: Portland, Oregon
About the Site
Our client’s industrial facility is located on 5 acres of the Columbia Slough, just over a mile from the Columbia River. Two settling ponds that were installed for the treatment of operational wastewater before discharge to the slough were used until the mid-1980s. The ponds were excavated, backfilled, and covered with asphalt.
History of Remedial Action
In 1997, the DEQ reviewed information for all sites in the Columbia Slough area and opened up this site for further investigation. During a Phase II environmental site assessment, a layer of residual sludge was found near the bottom of one of the former ponds.
Further investigation found links between this wastewater-pond residual sludge, high pH in soils, and elevated metal concentrations in the groundwater. The DEQ was concerned about the potential for metals in the groundwater impacting the adjacent Columbia Slough. MFA was engaged to assist with remediation.
The remedial action included excavation of aluminum sludge from the bottom of the historical settling pond; removal of high-pH soils; pH screening during excavation to assess whether soil at progressive elevations fell below the screening limit; backfilling the excavation; adding MetaFix™ soil amendment, in the configuration of a treatment wall on the groundwater-downgradient side of the excavation; and transporting the impacted material off site for disposal. The depth of the soil that had to be removed, combined with space constraints at the site, required sheet pile shoring to support excavation walls and provide stability to nearby buildings and structures. MFA oversaw the subcontractors implementing the shoring system and conducting the removal and backfill. Landscaping enhancements were also made along the bank of the Columbia Slough consistent with City of Portland tree-planting and erosion-control requirements.
As a result of the remediation, our client received a Source Control Decision from the DEQ in summer 2019. A DEQ No Further Action determination for the former ponds is pending.
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