2005-05-23_REVISION - M1977424 - Laserfiche WebLink

Home Browse Search

Logan Wash Mine TR No. 6 portal is approximately the same elevation as the east portal and was sealed with an earth plug during previous reclamation activities in the early 1990's. During construction of the west adit plug, a small bentonite dike was placed in front of the underground face of the plug to limit potential water contact with the plug. The west drift inclines with an 11 % grade (as shown on mine maps) and therefore lies above the workings in the east drift. A summer inspection of the upper (west drift) workings showed the accumulation of water in some locations and the incline portion of the west drift was contributing a small amount (estimated to be less than 0.5 gpm) to the lower workings near the cross drift. On the basis of mine maps (Attachment A), the east or lower drifr is 1,300 ft long and 10 ft wide. An underground inspection showed the drift to be 8 to 9 ft high. The east drift declines with distance from the portal. Based on previous underground observations, it is the east drift that floods during spring runoff and, in some cases, would discharge water from the portal by way of a 6-inch diameter steel pipe that originated approximately 50 feet inside the portal behind a small earth/bentonite dike. The incised gulley located immediately the east of the east portal typically exhibits spring runoff flows, some of which emanate from strata bedding or other spring openings on the surface. It is likely that some of this surface water infiltrates the outcrop and contributes to flooding of the mine workings. The main source of mine flood water is interpreted to be groundwater originating from infiltrating snow melt. OOSI has monitored flow from the Research Mine since 1993. The monitoring data are presented in Attachment B. No flow occurred from the mine during the yeazs 2003 and 2004. This was because of the construction of a retention dam inside the portal in the spring of 2003 (see Section 2.3) that retained a minor surge in the mine pool, and although the retention dam has remained in place, there was insufficient snow pack to create a mine pool surge in 2004. The normal period of discharge from the Research Mine is during spring runoff, which usually begins in April and ends by July. During abnormally wet years, some discharge has extended into December. During the monitoring period 1993 to 2002, discharge consisted of flows ranging from 0 to over 50 gallons per minute (gpm) during the months of April through July. The average and median flow rate from the portal during flow periods are 1.13 and 1.18 gpm, respectively. Annual flow volumes range from 0 to 288,500 cubic feet (ft3), for the period of record. The discharge of 288,500 ft3 was in 1997, an abnormally wet year for western Colorado. The average volume of discharge for this period is 73,740 ft3. The maximum daily discharge was approximately 78,545 gallons in Apri11998, and the median daily discharge is 1,700 gallons. 2.2 Evaluation of Mine-Water Storage and Portal Closure Integrity Within the period of record monitored by OOSI, the maximum total seasonal volume of water that discharged from the Research Mine was calculated to be 288,500 ft3 in 1997. The estimated storage volume of the lower workings is 298,930 ft3. The estimated storage volume is the volume available for mine flood water storage if the mine was flooded to the back of the workings behind secure portal plugs. This includes the main north-trending drift, side drifts, and rooms, and the workings at the same level associated with the west drift. Although it is evident Western Water & Land, lnc.