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Mr. Clapper and Mr. Romig <br /> September 24, 1996 <br /> Page 4 <br /> gpm when the reservoir is full. The actual embankment seepage will most likely be <br /> somewhat less than this, and probably within an order of magnitude. <br /> Seepage through the foundation of the dam embankment is potentially a significant <br /> source of inflow to the collection system. It is nearly impossible to estimate the expected <br /> foundation seepage increase. Historically, it does not appear that foundation seepage has <br /> been significant. However, the possibility exists that there are more permeable zones in <br /> the bedrock above the historic water levels in the reservoir, or that there are <br /> undocumented flowpaths that were historically sealed by the fairly impermeable tailing <br /> material. The original design reports for the embankment state that a fractured zone of <br /> clay shale was encountered near the emergency spillway. A silt-clay blanket seat was <br /> placed over the fractured zone. The water level In the Impoundment has not historically <br /> been high enough to test the effectiveness of this seal. <br /> Based on the items discussed above the modified seepwater return system was <br /> designed for a maximum pumping capacity of 650 to 650 gpm. This flowrate seemed <br /> reasonable considering the likelihood that the seepage rate will increase, and that the <br /> magnitude of the increase is somewhat uncertain at this time. <br /> A new pipeline will be required to deliver water from the toe of Dam 4 to Robinson <br /> Reservoir. We propose that 8-inch diameter HDPE pipe with butt-fused joints be used for <br /> the pipeline. The pressure rating of the pipe would decrease as the pipeline elevation <br /> Increases up the hill. The route of the pipeline would basically follow existing roadways <br /> for the most part (ref. dwgs D4.2-01 to 03). Beginning at the pump station, the pipeline <br /> would follow the road up the south groin of the dam,extend through the embankment, and <br /> cross under the emergency spillway. The pipeline would then follow the road along the <br /> SO' d NO' ON 2b: T T 96 bZ daS NK-T9Z-S�02-T : 131 aOSSd -8 .jai aaym - m. m <br />