Environmental Dredging Services to remediate contaminated sediment associated with the Callahan Mine Superfund Site in Brooksville, Maine.

Description

Environmental Dredging Services to remediate contaminated sediment associated with the Callahan Mine Superfund Site in Brooksville, Maine. The work consists of providing Environmental Remediation Services for dredging approximately 6,000 to 10,000 cubic yards of sediment from Goose Cove and covering an area of approximately 1.5 acres. The Goose Cove sediment removal area is located on the Penobscot Bay side of the former Goose Falls Dam with a tidal range of approximately 10 feet and a Mean Lower Low Water (MLLW) depth of approximately 4 to 6 feet. A maximum removal depth of 2-4 ft is required based on the requirements of the Record of Decision and Remedial Design. Tidal surface elevations in this area will provide unimpeded barge access; however, mobilization to this area presents several challenges. Structures within the proposed sediment removal area such as a steel pipe, chains, and moorings, will be removed by the Contractor prior to dredging, and moorings will be replaced after remediation is complete. Unauthorized boat access to Goose Cove will be controlled during remediation activities.Goose Cove sediment removal can be completed using mechanical or hydraulic methods. Sediment removed from Goose Cove will be hydraulically pumped approximately 1,500 feet to a CAD cell (former mine pit) for tremie placement. Real time hydrogen sulfide air monitoring will be required at the disposal location following an approved UFP-QAPP prepared by the Contractor. To protect against unintended releases of excessive sediment plumes, a turbidity curtain and turbidity monitoring may be required.The former Callahan Mine was a hard-rock, open-pit mine developed in Goose Pond, a shallow tidal estuary of approximately 75 acres in the Town of Brooksville, Maine. The Site is located approximately 15 miles west of the town of Blue Hill and 35 miles west of the town of Bar Harbor on the northwest side of the Cape Rosier peninsula on Penobscot Bay.Goose Cove is a narrow 15.5-acre inlet located adjacent to the northwestern end of Goose Pond, immediately north of Goose Falls. During early mine operations, groundwater seepage into the pit and entrained rock dust were pumped to an outfall in Goose Cove. This effluent likely contained fine grained drilling and blasting waste. Because of concerns about sediment accumulation in Goose Cove, an embayment within Goose Pond (Dyer Cove) was dammed off and used as a settling pond to remove a portion of the sediment (rock flour and silt) prior to discharge to Goose Cove. In addition, berms were constructed across portions of Goose Pond to separate surface water flows from mine operating areas and provide a sedimentation basin for overflow and decant discharge from the Tailings Impoundment. As a result of these operations, deposits of light gray, talcose sediment (termed mine waste) accumulated in portions of Goose Cove, Dyer Cove, and South Goose Pond. Areas of mapped mine waste (MACTEC, 2009) coincide with areas used as effluent settling ponds, effluent discharge locations, and sumps. There is an approximate 1.5-acre area (MACTEC, 2009) in Goose Cove coinciding with mine waste deposits like those in Goose Pond.