Department of Interior (1998) aquatic selenium toxicity threshold (>2 μg/L) and were greater than ten times the predam
breach levels. However, the highest selenium concentration detected in Hailstone Creek (11 μg/L) was still close to seven times less than the highest concentration detected in Hailstone Reservoir (73 μg/L) before it was dewatered. There are no clear trends with groundwater selenium data, although some of the wells were slightly
elevated compared to pre‐dam breach levels. The only post‐dam breach macroinvertebrate site that was sampled
prior to the breach is at Hailstone Creek. In 2012, the selenium concentration in benthic macroinvertebrates in
Hailstone Creek (15 mg/kg dw) was three times higher than the maximum macroinvertebrate selenium
concentration detected at that same location prior to the dam breach (3 mg/kg dw). However, the 2012 Hailstone
Creek macroinvertebrate selenium concentration was still almost two times less than the average selenium
macroinvertebrate concentration detected in Hailstone Reservoir prior to the dam breach (24 mg/kg dw). Selenium
concentrations were also quantified in macroinvertebrates sampled from Halfbreed, Goose, Grass, and Big Lakes.
Macroinvertebrate selenium concentrations at these sites followed a similar pattern as their respective surface water
samples. Concentrations were elevated to levels slightly above a toxicity threshold (>3 mg/kg dw ) in 2011 but
decreased to levels below that threshold in 2012. The dam was removed to reduce mortality to waterfowl and
shorebirds exposed to elevated levels of salts and selenium. A condition of the MOA (USFWS and MTDEQ 2009)
between the U.S. Fish and Wildlife Service and the Montana Department of Environmental Quality allowing the
Service to open up Hailstone dam and release water was to monitor surface water quality and groundwater quality
for multiple years following the dam breach. A plan designed to monitor the surface water and groundwater quality
and biota at Hailstone and Halfbreed NWRs was also a component of the Hailstone dam removal EA (U.S. Fish and
Wildlife Service 2010). Costs were previously covered by Refuge Cleanup funds; however, the refuge has reached the limit of requesting funds and must seek funds from other sources. This inventory is designed to meet the
requirements of the MOA and the EA.
