Figure 17. Locations of areas frozen into bedrock, areas where permafrost is underlain by unfrozen sediments

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Drilling Through Weathered Bedrock

Speculative; Data Lacking

Surface; Locally Sporadic and

Discontinuous Thaw Zones may

Permafrost Present to

be Present at the SedimentBedrock

Unspecified Depth

Interface, Especially Near Unfrozen

Areas and Adjacent to the

Active Landfill Area

Sediments Thawed Between

Subpermafrost Aquifer

Permafrost and Bedrock;

Subpermafrost Aquifer Present

Figure 17. Locations of areas frozen into bedrock, areas where permafrost is underlain by unfrozen sediments

that overlie unfrozen bedrock, and unfrozen zones that penetrate the permafrost completely. Unfrozen zones

generally are within former sloughs or channels, and permit communication between supra- and subpermafrost

aquifers. The large areas of materials that are frozen into bedrock constrain ground water interactions among

aquifers in Birch Hill and the Tanana Valley alluvium; they also modify flow patterns by their impermeability. A

bedrock aquifer in Birch Hill may communicate through fractures, such as the thaw zone associated with Finnegan's

Pond (upper right of landfill). Subpermafrost aquifers communicate with the large unfrozen area of alluvium

beneath and south of the Chena River. Data are practically nonexistent, however, on permafrost and bedrock

depths east of Ski Hill Road, an area critical to understanding ground water conditions north of the Chena River.

The mapping of unfrozen zones and aquifers beneath the landfill is based on our interpretations of subsurface

conditions surrounding it, which were obtained from historical aerial photographs.