https://phys.org/news/2018-05-steel-chips-coli-storm.html

E. coli contamination is one of the major water quality impairments of the Big Sioux River according to South Dakota Department of Environment and Natural Resources. Testing at several storm water drainage sites at Brookings showed that E. coli concentrations at these drainage sites after a summer storm can be as high as 2,000 colony forming units (cfu) per 100 milliliters (mL).

Hua explained that a previous graduate student had tested zeolite, limestone and steel slag, a byproduct of the mining industry, as well as steel chips. Those results led to Dai's study focusing on steel chips.