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I. INTRODUCTION This report consists of a brief analysis of the time elapsed to fill the mine workings at the Powderhorn Coal Company Roadside Mine, if the Northwest Intake Portal siphon ceases to function. II. DESCRIPTION OF CONDITIONS Water from natural sources is entering the Roadside Mine Northwest Intake Pool. The water level is currently within approximately ~ feet of the e]evation of the back-filled Northwest Intake Portal (the portal floor elevation is 4762 feet). The water level is controlled by discharge through a siphon arrangement at that NW portal. As long as water level is maintained, the suction in the siphon is also maintained and water is discharged through the pipe preventing the Level from rising. Because of variations and uncertainty in the rate of inflow, the water level is monitored and the flow in the siphon adjusted to maintain the level below the portal level but high enough to avoid breaking the suction and losing the siphon effect. The working range of the water level is considered to be 7 feet -between the elevations of 475 and 4762 feet (Attachment 1). If the water level rises to the floor of the mine portal (4762 feet elevation), it will begin to infiltrate the backfill of the portal. If the water level were to rise to the level of the portal roof (4770 feet elevation), a significant pressure (as hydraulic head) would be imposed on the unconsolidated backfill of that portal. III. POTENTIAL SITUATIONS FOR FILLING THE POOL Situation I : siphon break. To break the siphon, the water level must fall beneath 4755 feet. This can occur because the unmaintained siphon outflow dischazge may exceed the mine water inflow rate (Attachment 2). As inflow proceeds within the mine, the water level would rise 7 feet to reach the level of the portal. At that point, assuming the pipe lies at the bottom of the back-filled portal and its crest (highest point in elevation) is 4762 feet, when the water reached the level of the portal, it will discharge through the pipe by gravity flow but would also begin to infiltrate the backfill of the portal. Situation 2: siphon blockage. If the existing dewatering device becomes clogged, the water will continue to fill the pool. The vertical distance the water rises before reaching the level of the portal would be less than in the first situation, and would depend on the water level at the time of the blockage. Water will begin to infiltrate the backfill material and the level will rise, depending upon the transmissivity of the backfill material (how quickly and easily the water can flow through the material). The water level could conceivably reach the roof of the portal - 4770 feet -eight feet higher than the portal floor.