PERMFILE57953 - Laserfiche WebLink

Home Browse Search

consists of igneous and metamorphic gravels and cobbles from the Raggeds and the West Elk moun- tains upstream from the site. During high flow conditions in eazly June, the river flows approxi- mately 2500 cfs maximum during an average yeaz and can flow 6,000 to 11,500 cfs fora 100 year event. During non-peak flow conditions, most of the water flow in the river is from groundwater and the flow rate is only 8 to 100 cfs. To ensure that the river never captures the lake made from mining, an embankment protection plan is outlined in the Mining Plan section. The entire permit area is within the 100 yeaz floodplain of the River. Details of river flow and qual- ity are presented in Appendix B, from 2 USGS Gages near Paonia. Suspended solids range from ap- proximately 20 mg/liter to 4000 + mg/liter, demonstrating the same wide variability of the sediment load in the stream as shown for the River, depending upon the time of year, spring thaw and summer thundershowers. During peak flow in spring thaw, the river is extremely muddy. The Paonia Reser- voir, upstream from the permit area, has severe sediment deposition problems from the upper parts of the watershed. The pH of the River is fairly steady from 8.1 to 8.5. Selenium.is a dissolved ion of concern in the area, especially to fish populations. The CDPHE determined that the level of sele- nium chronic to aquatic life is 4.6 µg/liter. The acute level is 18.4 µg/liter. The USGS gage down- stream of the junction of the North Fork with Leroux Creek showed a level of is 4.0 µg/liter in Sep- tember of 2002. Considerable agricultural water moving through irrigated fields dissolves some sele- nium from contact with the Mancos Shale and increases its dissolved concentration. Since this oper- ation is so small and so close to the river (within 100 feet), it is not expected to have any impact on the selenium concentrations in the River. Due to its proximity to the river, this area has been flushed with water since the last ice age and does not contribute additional selenium. Selenium loading in the river comes from a vast area of exposed Mancos Shale in the watershed and the irrigation canals providing new contacts for water with the shale. It is expected that the water quality of the pumped water for the 3-4 years that this operation will exist will be approximately the same as that of the river itself. Past surface irrigation of the site has produced runoff which either directly enters either the River, the small depression or the existing pond on the site. An incised man-made ditch called the Farnsworth Collection Ditch begins near the southeast corner of the permit area at a spring for which the Farnsworth's have adjudicated water rights. This spring flows water year round and the water currently is delivered to the small pond near the southwest corner of the permit area. An overflow from this pond returns the water to the ditch downstream, which enters the river shortly thereafter. See Map B-1. An existing small irrigation return immediately south of the Farnsworth Collection Ditch gathers any irrigation water from the orchard to the south, thus effectively isolating the site from runoff entering from the south. North Fork Pit Mazch 04