GEOHYDROLOGY OF THE TELEGRAPH HILL AREA, ST. PAUL ISLAND, ALASKA

A MODFLOW-2000 ground-water-flow model was developed for the Telegraph Hill area on St. Paul Island, Pribilof Islands, Alaska and simulates steady-state ground-water-flow conditions. The model was constructed using an unconfined aquifer, a confining unit, and a basal aquifer that simplify several Pleistocene- to Recent-Age volcanic and aeolian water-bearing strata and the coastline and the Ghyben-Herzberg freshwater-saltwater interface were used as boundary conditions.

Simulated ground-water altitudes for the basal aquifer show flow radiating outward from higher heads near the island's center toward lower-head coastal-discharge areas. In contrast, the simulated altitude of ground-water in the unconfined aquifer is a subdued expression of the topography. Water in the unconfined aquifer discharges to coastal areas, surface-water bodies, evaporates, and (or) flows vertically through the confining unit to the basal aquifer. With acceptable error, the model reasonably simulates steady-state ground-water flow, but cannot be used to assess the migration of contaminants or the intrusion of saltwater.