To maintain mining operations at a limestone quarry in California, the mine operator must continually dewater the open pit and treat the stream for selenium and nickel prior to discharge. The first of two plants, a 500 gpm facility was designed and built in 2014 under an expedited timeline. The compact footprint, modular plant was built within the confines of the mine pit, requiring only a level gravel surface for installation. Since installation, the SeHAWK® bioreactors have been operational to achieve a stringent discharge limit of 4 ppb selenium.