Spirit Lake is a complex site where 700,000 cubic yards of metals and PAH contaminated sediments are targeted for a combined dredging, capping, monitored natural recovery/enhanced monitored natural recovery remedy where sediments will be placed in onsite confined disposal facilities (CDFs). EA is leading the design and permitting for the project partnership of EPA and US Steel. Remedial design began with extensive sediment chemical and geotechnical characterization studies to provide key data for dredge prism and CDF berm design and with treatability studies to inform dewatering and material handling. EA is preparing the remedial design, which includes chemical isolation cap modeling, dredge prism design, CDF geometry and volume estimates, waterway reconfiguration, and material handling. EA led spatial modeling, slope stability analysis, groundwater modeling, and hydrodynamic modeling as part of the remedial design evaluations. After completing preliminary remedial design, EA planned and led a vapor extraction study that has identified close to $9 million in potential savings. EA has performed cost-benefit evaluations to optimize the balance between thicker isolation caps, deeper dredging, limited CDF space, and habitat requirements for specific water depths.
EA plays an essential role coordinating with over 25 representatives from state regulators, natural resources agencies, indigenous peoples, community groups, municipalities, and a historic railroad as part of permitting and design approvals. EA’s ability to build strong relationships between clients and regulators was key to performing interactive weight of evidence evaluation to set the remedial footprint effectively and efficiently. EA has led public meetings and stakeholder round tables, coordinating with the State Historic Preservation Office on cultural resources issues associated with indigenous peoples.
