Relief wells at Garrison and Snake Creek dams were installed to control seepage and to prevent piping through pervious sands and gravels in the foundations.

A detailed investigation that included geologic mapping, exploratory borings, peg-model studies, water-level readings, pump tests, resistivity surveys, and laboratory tests was necessary to determine the most desirable location, spacing, and depth at which to install the relief wells.

Inspection during construction and pump testing after construction were necessary to evaluate the satisfactory completion of the wells. Data collected during the geologic investigation and construction of the wells, along with measurements of the piezometric head and flow into the wells, are recorded on a drawing that assists in determining seepage conditions through the dam foundation at various reservoir stages.