REP38877 - Laserfiche WebLink

Home Browse Search

Kathy Welt and Christine Johnston March 7, 1997 (DRAFT) Page 4 MCC worked quickly to contain and control the inflow for the safet}' of the miners and to restore mining in the section. Pumps and piping were installed to dischazge the flows from the mine. All discharges from the mine were contained and treated (chemical addition, flocculation, sedimentation) in ponds MB-1 and MB-2R before being released in accordance with NPDES/CDPS permit requirements. The ground surface above the fault is in the upper reaches of Sylvester Gulch. Several days of investigations were made during the spring of 1996 to assess whether there was any surface evidence of the fault or surface impacts from the fault inflows. No evidence of the fault was observed. Many of the spring and seep locations in the valley were also visited to observe flows and assess the general temperature (by touch) of the spring water. In all cases, the waters encountered in Sylvester Gulch were observed to be considerably colder than the water emanating from the fault, and the observed surface flows in Sylvester Gulch were considerably less (<] cfs) than those observed flowing into the mine (>4.5 cfs) up chazmel from the fault location. There was no change in the flow regime of Sylvester Gulch in the vicinity of the fault. Previous work by the USGS in 1989 suggests that Sylvester Gulch is afracture-controlled drainage along its north-south reach prior to its confluence with the North Fork. The N60°E orientation of the B East Mains fault is counter to this and crosses the drainage with no obvious surface evidence (stratigraphic or topographic). MCC had not observed the fault or groundwater in previous exploration in the azea or from lineament or geotechnical evaluations of the surface lands. On April 8, 1996, MCC encountered the same fault in the #4 Entry (the next entry to the north). Approximately 30 minutes after first encountering the fault in the #4 Entry, a considerable increase in flow occurred, predominately from the Floor, with sufficient pressure to lift several blocks of floor coal several cubic feet in size. Based on visual observations and pumping capacities and piping required to keep up with the flow, the maximum flow from this fault zone was estimated to be 2,SOOt gpnt. As with inflows from the #5 Entry, the flow from [he #4 Entry began to diminish within three to four days. On May 7, 1996, the estimated flow rate from the fault was 240f gpm. Figure 1 is a graphical representation of the observed and measured inflow from the B East Mains fault since encountering it in March 1996. In May and early June 1996, MCC mined up to and through the fault in the #0 and #1 Entries only to find that no water was produced. This "hit-and-miss" encounter with water in the fault system indicates the difficulty in anticipating its presence. On June 20, 1996, MCC entered the fauli via the #2 Entry. Within two weeks after mining through the #2 Entry, water was again encountered at a rate in excess of 1,OOOt gpm while flows from the #4 Entry ceased. Within 15 days this flow had diminished to approximately 120 gpm. By the middle of August 1996, the Flow had decreased to approximately 85 gpm, exclusively through the #2 Entry, and has remained so through to the present. The present flow rate (as of late January 1997) of 85 gpm may be the constant recharge rate into the fault system from a continual source of unknown but significant magnitude, although continued monitoring during 1997 will be necessary to confirm this. As of the end of 1996, approximately 100 million gallons or 300 acre-feet of water had entered the mine via the B East Mains fault. Assuming that 85 gpm is the constant rechazge rate, approximately 190 acre-feet of water was released from storage during the 9 months following the initial inflows