PERMFILE100658 - Laserfiche WebLink

Home Browse Search

Also prior to mining Phase 1, a 2.0 high berm of 2.SH:1 V sideslopes will be constructed of existing earth azound the entire perimeter of the site. This will prevent any runoff from entering the site and the berm will also be placed immediately outside (above) the 100 year floodplain to further prevent that any flood waters could enter the pit. The existing berm on the south edge of the permit area is already more than 2.0 feet high. No additional work will be done to improve this berm. The 2.0 feet high specification is meant to be a minimum specification for the berm azound the permit area. This berm will be left after reclamation to also prevent flood water from entering the lake. Since known petroleum hydrocazbon contamination exists on the top of the groundwater north of the staging area, and since the mining of the designated azeas requires pumping of the groundwater, there is some risk that the free product from the azea north of the permit area could be drawn down to the mining pit as a result of pumping. Although levels aze low and the risk may be low, it has been decided to insta112 trenches as shown on Map C-2 which will be kept at a water level eleva- tion of 4452' or higher and dug to 5' below normal ground water level (4449') in order to provide positive hydraulic gradient against the ground water to the north to keep any contamination from entering the pit azea. Therefore, the trenches will be dug to an elevation of 4444'. The sideslopes will be 1.5H:1 V. See Map C-3 for a cross section of the trench details in relation to the staging area and the mining pit. As described in the Water Information section, this level will initially be kept low but can be modified up or down in response to what is being seen at the monitoring wells. The trench may have a low spot in the furthest point of the southeast corner. If this is encountered, clean fill will be used to build up the embankment to the required level above the water, as shown on the Cross Section of Map C-3. This embankment portion will not be steeper than 2.SH1.OV. It will be built in lifts not to exceed 8" and will be compacted to 95% maximum dry density as tested with a standazd Troxler densitometer on site. The overburden material from the majority of the excavation of Trench # 1 may need to be treated in the off site contaminated overburden farming area. This is also shown on Map C-2. The gravel should not be contaminated and will be placed in the staging azea for processing. The overburden material from Trench #2 should not be contaminated and will be placed in the substitute soil stock- Gilsonite Pit 9/03