MIXED CONTRIBUTIONS OF LOCAL AND REGIONAL GROUNDWATER AT THE MIDWAY FISH HATCHERY WATER SUPPLY

During the past fifty years Myxobolus cerebralis, a parasite that causes whirling disease in salmonid fish, has spread to hundreds of streams in the northeastern and western United States. The disease results in deformities and premature death. There is now evidence that the parasite can contaminate shallow groundwater systems. In 2000, the Utah State fish hatchery at Midway, Utah, which relied on shallow groundwater that discharged at the down gradient end of a tufa platform, was closed due to M. cerebralis contamination.

To reopen the hatchery, a non-contaminated groundwater source had to be found. Confined aquifer groundwater beneath the hatchery was identified as a possible source. Three alluvial aquifer systems have been identified at the hatchery, all of which contribute to the hatchery springs: a shallow unconfined aquifer, a intermediate semi-confined aquifer, and a deep confined aquifer. The aquifers are separated by tufa layers. The solute content and groundwater age unexpectedly decrease with depth.

In this investigation we have used we used multiple tools -solute, isotopic, physical, geophysical methods to evaluate flow paths and groundwater recharge histories which contribute to the inverted chemical and age relationships. Up gradient in the tufa platform the unconfined aquifer is recharged by upwelling thermal water (>6,000 14C years), which is diluted along the flow path by downward moving modern recharge in the tufa platform. Upper and lower confined alluvial systems, which flow beneath the tufa platform, are recharged up gradient with both old, but not thermal, (> 2,000 14C years) and modern stream waters. At the base of the tufa platform much of the unconfined aquifer water discharges, but down gradient of tufa platform appreciable confined aquifer waters mix with the unconfined aquifer. Thus at the down gradient end of the tufa platform most of the discharge is from the unconfined aquifer and down gradient of the platform most of the unconfined aquifer discharge is from the underlying confined systems.

Once the lower confined aquifer system (about 60 m below ground surface) was identified as a potential M. cerebralis free aquifer a new hatchery design was completed and full fish production is anticipated in 2009.