Protecting Water Resources during Mining with a Ditch and Berm System
Updated: May 9, 2019
HPS plans to protect vital water resources in several ways. The most visible and versatile of these efforts will be a ditch and berm system that will surround each mining area.
Mining activities will be set back from property lines and on-site avoided wetlands and waters. Inside those setbacks, HPS will build a silt fence to control erosion. Once the silt fence is installed around a given mine area (“mine block”), and prior to mining, HPS will construct a ditch and berm system averaging 150 feet wide inside the fence around the mine block. The recharge ditch and berm are recognized best management practices (BMPs) routinely utilized in the industry to control stormwater and prevent flooding; reduce erosion; provide surficial aquifer recharge; and facilitate recycling of water for mining purposes.
The berm will be constructed of material generated excavated from the ditch. Berms have an minimum height of four feet above ground elevation, with sloping sides to direct rainfall into the adjacent ditch, which will be dug deep enough to intersect the surficial aquifer to allow for recharge. Actual mining will occur approximately 60 feet beyond the ditch. The land between the mine cut and the recharge ditch will be occupied by a material transport conveyor and stockpiles of the dirt that overlies the phosphate matrix (“overburden”), which must be removed so phosphate can be extracted.
The ditch and berm will capture stormwater falling within the mine block, protecting adjacent properties, wetlands, and surface waters like the New River from inundation, flooding, and the introduction of sediments or other contaminants that can accumulate within stormwater as it flows across the land. The HPS team knows limiting runoff is critical to ensuring the continued water quality of adjacent wetlands and surface waters. As a result, the proposed stormwater system—of which the ditch and berm is a crucial piece—is designed to exceed regulatory requirements and will control the water produced by a 500-year, 24-hour storm event, even if the earth is already fully saturated.
In addition to stormwater, the ditch holds water that is removed from the mining area to allow the dragline and other equipment to access the area. The water in the ditch helps to maintain the level of the surficial aquifer in three ways. First, it creates a hydraulic barrier between mining activities and adjacent property. Modeling and industry experience show that a recharge ditch helps to confine any drawdown of the surficial aquifer to the limits of the mining area. Second, as water flows into the ditch it can percolate into the surficial aquifer to help replenish it. Third, water from the ditch is circulated and used in the pre-washing and beneficiation process, limiting the need to draw additional water from outside sources, or pump from the Floridan aquifer.
Return to this space in the coming weeks to learn more about HPS’s efforts to protect water quality and water quantity during the proposed mining.