2019-03-11_REPORT - C2009087 (2)

Home Browse Search

NPDES Discharge Point 003 (NPDES3). Hydrographs presented in Appendix D show that flow has increased at this site since September 18, 1984, when operation of the truck wash system began. During operation, water was siphoned from the Wadge Impoundment (NPDES2) into a holding pond. Overflow from the holding pond was diverted into the shop ditch, which flows into NPDES3. Water was pumped from the holding pond to the wash rack, drained into a settling pond, and then into the same shop ditch. This operation increased the flow at NPDES3 while decreasing the flow at NPDES2. Other events have affected the long-term hydrograph at NPDES3. They include the diversion away from NPDES3 of the runoff from an inactive fly ash pit (operated by the Hayden Station power plant) in October 1980 and the diversion away from NPDES3 of runoff contained in the Northwest Diversion Ditch (see the Seneca II Permit Application, Exhibit 7-7, Surface Water Hydrology Map and the 1982 Seneca II AHR) in April 1982. Discharge volumes at the site have also been affected by the reduction in diameter of the discharge culvert (36 -inches to 6 -inches) that occurred on July 19, 1988. A smaller volume pump and line from Pond 002 to the truck wash was installed in August 2001. The truck wash was last used in 2007. These pump lines, which were siphoning water out of Pond 002, were capped off on July 7, 2010. This year's average flow value, 0.010 cfs, is 940 lower than the historic (1980-2018) average flow value, 0.160 cfs. This year's below average value is due to retirement of the truck wash system. Review of the TDS plot indicates a decreasing trend, with the peak value occurring in September 2002. Surface Water Site SW -S2-2 (SSG2). This site exists on Grassy Creek downstream of discharges from PSCM Ponds 002 and 003, but upstream of Site SSG3 and Scotchman's Gulch (Yoast Mine NPDES Pond 010). Review of the TDS plot indicates an increasing trend, with the peak TDS occurring in August 2013. 14