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Noel S.
Philip Ground penetrating radar (GPR) and seismic refraction surveys were conducted
at a critical location on a glacial moraine near Yakutat, Alaska, and
at several road culvert sites prior to their excavation near Petersburg,
Alaska. The subsequent exposure at the culvert locations allowed the hydrogeologic
properties and aquifer geometry (including depth to water table and bedrock)
to be observed and measured. Calculating the velocities of electromagnetic
and seismic waves from both machines using known geometry of the subsurface
provided constraints on hydrogeologic properties. Observations of the
aquifer material on the moraine were made from exposures at the surface
and from shallow excavation. The near-subsurface moraine material is composed
of clean sand and poorly sorted gravel, and the culvert locations are
filled with uniform gravel, clay and sand. The geology of the two locations
varies, but the heterogeneity of the unconsolidated material comprising
the substrate in both is quite similar. Seismic data acquired at the moraine
show a subsurface depth to bedrock of 25 meters at the moraine. The expected
results from the surveys should allow a reasonable geometric model of
the subsurface to be made within a 10% estimated resolution of depth.
Further applications of the data set and extrapolated properties of the
subsurface should lead to reasonable models of hydrogeologic substrate
and general flow regime. The subsurface model will prove valuable during
the next cyclical closure of Russell Fjord by Hubbard Glacier, the body
of water bordering the glacial moraine to the north. |
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