8.2. SR 11-07-2016 - Laserfiche WebLink

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Industrial wastewater will be generated seasonally during operation of the washplants. It is anticipated that aggregate washing will be conducted at both mine sites. Each wash plant will discharge up to approximately 1,200-1,500 gpm of process water into on-site sedimentation basins for treatment and reuse back to the washplant. The composition of the industrial wastewater is naturally occurring fine grained sediment that has washed off the larger sand and gravel components of the deposit. 3) If the wastewater discharge is to surface water, identify the wastewater treatment methods and identify discharge points and proposed effluent limitations to mitigate impacts. Discuss any effects to surface or groundwater from wastewater discharges. Wastewater will not be discharged to surface water. Washwater from the wash plant contains suspended solids that are treated in a series of sedimentation ponds and reused. The sedimentation ponds are designed to allow fine particles to settle out of the water. The ponds are built in series so the initial pond removes the majority of the sediment and additional settling occurs throughout the series to the final pond where it is pumped back to the washplant. The sedimentation ponds are cleaned out on a periodic basis to remove the accumulated sediment and maintain treatment efficiency and pond volumes. The sediment, which is composed of naturally occurring silt and clay that has been rinsed off the surface of the aggregates, is allowed to dry. The dried sediment is typically blended with other overburden soils and used in Site reclamation activities. Once sufficient settling has occurred, the water is clean enough to be used in the wash plant again. Washwater is not discharged off-site or to surface water; rather it is recirculated back to the wash plant and recycled. ii. Stormwater- Describe the quantity and quality of stormwater runoff at the site prior to and post construction. Include the routes and receiving water bodies for runoff from the site (major downstream water bodies as well as the immediate receiving waters). Discuss any environmental effects from stormwater discharges. Describe stormwater pollution prevention plans including temporary and permanent runoff controls and potential BMP site locations to manage or treat stormwater runoff. Identify specific erosion control, sedimentation control or stabilization measures to address soil limitations during and after project construction. Prior to construction the majority of stormwater drains internally to low areas, located throughout the Site. The very northern portion of the Site drains off-site. However, due to the rapid permeability of the on-site soils the quantity of runoff is small. During active mining, all stormwater contacting exposed soils within the active mining area will be handled internally and will not be discharged off-site. As mining progresses over the Site, drainage will be directed to low areas within the mine floor where it will temporarily collect, infiltrate through the granular soils or evaporate. Perimeter berms will be constructed within setback areas, shaped, and stabilized with vegetation. Mining activity will create steep slopes on a temporary basis. The active mine face is typically at a slope that ranges from 1:1 to 2:1 (horizontal to vertical). The active face is not vegetated and therefore is subject to erosion. The active face always slopes towards the interior of the mining operation and sedimentation from any erosion of these slopes is Environmental Assessment Worksheet Page 15 Elk River Sand and Gravel Mines:Tiller Corporation and Max Steininger, Inc.