Abstract

Public-supply springs are included in Utah’s Drinking Water Source Protection Program because about 785 springs supply water to 325 public water-supply systems in the State. The program specifies three protection zones with higher levels of management in zones closer to the spring or well. Zone 1, the closest zone, is an arbitrary 100-foot fixed radius around the well or spring. Zones 2 and 3 are based on groundwater time-of-travel (250 days, zone 2; 15 years, zone 3) or flow boundaries.

We used hydrogeologic mapping, physical and chemical properties of the spring water, catchment-area calculations, dye-tracer studies, and aquifer tests to delineate protection zones around Olsens Spring in Box Elder County. Olsens Spring discharges from a relatively small surface-drainage basin underlain by fractured dolomite. West Hallings Spring also discharges from this surface-drainage basin. Hydrogeologic mapping was useful for developing a conceptual model of ground-water conditions and delineating likely zones of contribution for Olsens Spring and West Hallings Spring, but the zones of contribution to each spring could not be differentiated using these techniques. The combined zone of contribution to these springs encompasses at least the entire surface drainage, an area of approximately 17 km² (6.5 mi²) above the springs. Although catchment-area calculations indicate that the zone of contribution may be significantly larger than the surface-drainage area, the surface-drainage area is likely within the margin of error in the catchment-area calculations. Delineation of protection areas for springs is a complex process requiring the interpretation of data from many sources. In this case, additional subsurface investigations, including extensive aquifer testing and potentiometric-surface mapping, would be needed to further test the boundary delineated using hydrogeologic mapping, calibrate catchment-area calculations, and, if necessary, refine the protection areas.