A large international ore refining and metals processing company was faced with mounting operational costs associated with stormwater management at its Texas facility. Stormwater runoff from extensive ore piles conveyed large quantities of ore fines into the storm sewer system resulting in continuous clogging, loss of 5000 tons of ore annually, and periodic flooding of the facility. In addition, the facilities stormwater management lake was at capacity with little provision for expansion to meet increasing management needs. The combination of continuous maintenance needed to keep the storm sewer system open, in conjunction with the loss of eroded ore was estimated to cost the company over $650,000 annually in lost revenues. A cost-effective and sustainable solution was needed to minimize stormwater management costs, eliminate ore losses and provide additional management capacity in the stormwater management lake.
Roux Associates was retained to design a multi-faceted Engineered Natural System (ENS) that would provide recovery of eroded ore fines, reduce suspended solids and other trace constituents in stormwater runoff, eliminate flooding potential, consumptively use excess stormwater, and provide runoff treatment to the levels needed to re-use stormwater at the site. After completion of a pre-design treatment needs and siting investigation, Roux Associates developed an ENS design that would passively and cost-effectively meet these objectives. Major elements of the system included five large sedimentation trenches designed to capture and retain ore fines from intense stormwater runoff events, grassed conveyance swales to further reduce TSS loadings, a staged 8-acre constructed treatment wetland (CTW) designed to treat inflows from the sedimentation trenches and swales to re-use water quality levels, and a 8-acre “Phyto plot” to consumptively eliminate excess stormwater runoff from the ore storage area of the site.
Construction and activation of the project was completed in March, 2008. The final system included 2,200 linear feet of sedimentation trenches installed around the perimeter of the ore piles; 3,500 linear feet of vegetated swales; a multi-staged CTW containing a 1-acre sediment forebay, 5 acres of high marsh/low marsh wetlands, and a 2-acre micro-pool. Also included was an 8-acre Phyto plot containing 7,000 hybrid poplar trees. The Phyto plot is equipped with a spray irrigation system for the consumptive use of excess stormwater. The trees are expected to mature in 4 years and, at maturation, will provide the capacity to consume up to 41 million gallons of excess stormwater per year. The capital cost of the project was $2.1 Million with a projected O&M cost of less than $100 K annually. The system is fully functional with performance data currently being collected.