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Mr. Archer <br />13 July 90 <br />Page 4 <br />input end of the dewatering device; and 2) a 6 foot by 22.0 foot, rip- <br />rapped spillway located north of the discharge pipe on the west pond <br />• embankment. Specifications regarding these installations are not <br />available at this time. <br />Sun Coal Company has experienced difficulties with the position of the <br />discharge pipe. Apparently, freezing and thawing of the embankment <br />materials surrounding the pipe gradually elevate the pipe, Although <br />corrective measures have been made from time to time, the current position <br />of the pipe and riser is too high for adequate functioning during the 100 <br />year 24 hour storm event, It is recommended that the pipe be lowered 1.5 <br />feet maintaining suitable inclination for gravity flow to the outlet, thus <br />meeting the design specification of a one foot freeboard. <br />• The perforated, mesh-capped riser on the dewatering device will attenuate <br />water flow into the discharge pipe, particularly if the 100 year 24 hour <br />storm event carries floating debris into ESASP. Therefore, it is very <br />important that the rip-rapped spillway be ab1E to accommodate water flow <br />in excess of the dewatering device capacity, <br />• A low point on the southwest part of the embankment is almost level with <br />the rip-rap in the spillway. Therefore, it is recommended that the <br />spillway be lowered so that the top of the rip-rap in the spillway be at <br />least 0.5 foot below the lowest elevation on the pond embankment. <br />• <br />Respectfully submitted, <br />Eu " ne M. Shearer, P.E. <br />~ sulting Geologist <br />EMS:mjs <br />• Enc. <br />