Abstract

Drinking Water Source Protection (DWSP) zones were delineated for the Willard City Well Nos. 1 and 2 using a combination of computer modeling and watershed approaches. These wells derive water from unconsolidated valley-fill sands and gravels of the East Shore aquifer system, and are located near a major mountain front creek, and the bedrock of the Wasatch Range. Unconsolidated valley fill that consists of interfingering bodies of gravel, sand, silt, and clay, with coarser grained intervals composes a local, principal aquifer of relatively high transmissivity. Bedrock in the Wasatch Range is cut by the Willard thrust fault system, Wasatch normal fault zone, and spatially variable fracture systems. Willard Creek loses significant flow to valley-fill sands and gravels to the west of the mouth of Willard Canyon. Thus, recharge to the principal aquifer includes significant seepage of surface water from streams near the mountain front, and a poorly constrained component of subsurface inflow across the Wasatch fault zone. DWSP zones in the valley fill, numerically simulated using available hydrologic data and treating the Wasatch fault zone as a low permeability boundary, have semielliptical shapes around Well Nos. 1 and 2. However, because Willard Creek provides significant recharge to the principal aquifer, the Willard Creek watershed was included in the delineation. Regional hydraulic relationships between surface water and groundwater resources along parts of the Wasatch Front indicate that other mountain-front watersheds located near groundwater-based public water systems also may need to be included in local DWSP plans to comply with the Source Water Protection Program outlined in the 1996 amendments to the Safe Drinking Water Act.