AS 22: Some animal crossings in permafrost areas will not be mechanically refrigerated, but will consist of about 150 feet of buried insulated pipe and free standing heat pipes to draw off heat from the soil. Casing pipe to hold the heat pipes is being driven here, at an animal crossing north of Glennallen., 1976-03, PCA0002-1a-27, Folder: PCA0002-1a. Alyeska Pipeline Service Company : Trans-Alaska Pipeline Construction Collection, 1976-1977, PCA 2. Alaska State Library - Historical Collections Finding Aids. https://alaska.libraryhost.com/repositories/2/archival_objects/17303 Accessed February 22, 2025.