Engineering & Mining Journal

JUL 2018

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Page 33 of 75

WATER REUSE STRATEGIES 32 E&MJ • JULY 2018 Mines around the world depend on a steady supply of relatively clean water for the extraction of resources and the subse- quent beneficiation of ore to manufacture products. These mines have an opportu- nity to obtain significant benefit by cap- turing excess water for reuse within their operations. Implementing strategies for discharge water reuse helps promote op- erational and environmental sustainabili- ty and provide overall economic benefits, but also helps keep mining operations ahead of water discharge regulations. In the U.S., the Clean Water Act is the most prominent piece of legislation that regulates the use of water in the country. However, the water situation has changed drastically since then, and laws promulgat- ed through the act have been adapted and changed to meet evolving challenges from increased water demand and water-scarci- ty concerns to declining water quality. One of the most significant changes to the Clean Water Act is the identification and publication of impaired waters and total daily maximum loads (TMDL) in ac- cordance with Section 303(d). According to the TMDL provision, water bodies that are classified as impaired do not meet the designated quality standards for specific waterbodies and do not provide all the water resource values upon which dis- charges are managed. The provision aims to provide states with assistance in developing their own TMDLs that set the maximum amount of pollutant that can be discharged into a particular waterbody. Furthermore, TMDL development provides states with a start- ing point from which they are able to plan water restoration strategies that will im- prove the quality of impaired waterbod- ies within their borders. Those planning efforts are implemented through basin management action plans (BMAPs), which establish strategies and projects for restoring water quality. Jon Dinges, senior water resources planning leader at Black & Veatch, pointed out that waters published as verified im- paired for pollutants, such as heavy metals, are typically expressed as a numeric val- ue, whereas waters impaired for nutrients have historically been expressed in a more narrative fashion. "On the one hand, you would have very specific discharge limits in place for pollutants, such as copper or mercury. On the other hand, nutrient dis- charges would be governed by a statement along the lines of: 'You can't discharge ni- trogen and phosphorous in amounts that would cause an imbalance in the flora and fauna in the water bodies,'" he explained. The narrative standards make imple- mentation of effective nutrient-discharge management difficult, as there is no spe- cific determination regarding the amount of nutrients that can be safely discharged into a specific waterbody without causing an imbalance. This subsequently led to the 1998 promulgation of the National Numeric Nutrient Criteria Strategy, which operates under the auspices of the Clean Water Act. Since then, a number of states have made noticeable strides in developing the criteria needed to effectively mitigate harmful nutrient discharges into water- bodies across the U.S. The strategy has been delegated to most states in the U.S., with the ex- ception of Idaho, Massachusetts, New Hampshire, New Mexico and the District of Columbia. This could be due to the fact that these states have been exclud- ed — either because delegation has not been completed in these states or their relevant state programs do not have regu- latory requirements equivalent to or more stringent than current federal regulations. Impact of Nutrient Discharges on Waterbodies In recent years, a number of waterbodies across the U.S. have experienced algal bloom growth caused by nutrient enrich- ment of surface waters. Algal blooms often form when water is overexposed to nitrogen and phosphorus, causing severe nutrient impairment known as eutrophication. Harmful algal blooms caused by nutrient enrichment often occur in estuarine and marine environments, as well as fresh water systems. "These sud- den plant growths can be extremely toxic and harmful to the environment. This has an economic and social knock-on effect, as industries and communities that are reliant on the good health of waterbodies are severely impacted by the poor health of these waterbodies," Dinges said. The pervasive growth of algal blooms in waterbodies across the U.S. and the overall negative impact of nutrient im- pairment on the environment has incen- tivized various states to establish their own numeric nutrient surface water cri- teria with the assistance of the Environ- mental Protection Agency (EPA). Harnessing Discharge Water for Sustainable Mining Mines need to find innovative ways to mitigate their impact, and water reuse strategies are a great approach for active operations An algal bloom grows at the eastern end of Lake Erie, which has a long history of contamination due to discharges.

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