Laserfiche WebLink
<br />David Berry - 2 - January 26 2001 <br />if only the siphon was discharging and it was left unattended, flowing at full capacity, <br />the water level in the mine would; 1)remain stable for many years; 2) slowly <br />decrease to the point the siphon would break; or 3) slowly increase to the level of <br />the northwest intake portal. <br />A decrease in the water level in the mine below the intake of the siphon would <br />cause a siphon break or failure. After siphon failure the water level in the mine <br />would slowly increase. It would take 45 to 60 days for the water level in the mine <br />to reach the level of the Northwest Intake portal if the South Portal 4-inch pipe was <br />not flowing and about twice that long if the pipe was flowing. It is probable flow <br />would reestablish through the two 4-inch Northwest Intake pipes. I do not know if <br />the discharge would be free flow or siphon. The siphon can be reestablished after <br />a failure by pumping water from the river into the 6-inch discharge pipe. This action <br />purges air from 6 and 4-inch lines so the siphon is restarted. <br />4. The rate the siphon will discharge is a matter of historic record based on weekly <br />flow meter readings. However, this flow rate does fluctuate. A review of the data <br />in the 2000 AHR shows full flow rates that vary from 160 to 215 gpm. It is important <br />to note the purpose of the siphon is to keep the water level in the mine below the <br />level of the Northwest Intake portal. The siphon does not necessarily increase the <br />flow through the system. <br />The rate at which the Northwest Intake Portal pipe system (siphon) will discharge <br />under free flow is directly related to the amount of head on the pipes. The amount <br />of head on the pipes should nearly equal the depth of water impounded behind the <br />Northwest Intake seal. The attached calculations indicate that 2-feet of head on the <br />4-inch pipes results in a discharge of 200 gpm. <br />Designs presenting the hydraulic capacity of the North Decline dewatering system <br />are enclosed. I chose an S-inch diameter pipe to be ultra conservative. <br />6. Once the North Decline dewatering system is installed, the Roadside South portal <br />will have the following dewatering capacity in gallons per minute: <br />a. North Decline Dewatering System <br />b. Northwest Intake Siphon <br />c. South Portal 4-inch diameter pipe <br />Total <br />350 <br />220 <br />100 <br />670 <br />PCC will not discharge water from the North Decline discharge point until NPDES <br />approval is obtained. PCC has not initiated any activity regarding the acquisition of <br />an amended NPDES permit. <br />8. PCC does not currently hold the necessary surface rights to immediately implement <br />the proposed North Decline dewatering system. The surface is owned by PCC but <br />most of the proposed disturbance is within Department of Highways (DOH) right-of- <br />