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 lead 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 prepared the remedial design, which includes chemical isolation cap modeling, dredge prism design, CDF geometry and volume estimates, waterway reconfiguration, and material handling. Spatial modeling, slope stability analysis, groundwater modeling, and hydrodynamic modeling were prepared as part of the remedial design evaluations. After completing preliminary remedial design, EA planned and led a vapor extraction study that identified close to $9 million in potential savings. A cost-benefit evaluation was performed to optimize the balance between thicker isolation caps, deeper dredging, limited CDF space, and habitat requirements for specific water depths.
EA played 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. Our 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.
