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Clayton Wein -2- October 31, 2017 <br />4. DRMS: On Figure 1 it appears that the label for the old underdrain location was left on the drawing <br />by accident. Please explain or revise your submittal. <br />BRL: Please see revised Figure 1. <br />5. DRMS: <br />a. Why is the new cross section smaller than the existing one? (Three square feet rather than four <br />square feet). <br />b. Please elaborate on the location of the proposed upper end of the underdrain. <br />c. Explain why the last 20 feet of the underdrain pipe will not be solid as in the previous design. <br />d. Please explain the slope used in the calculation. Is it based on the slope of Ditch AN <br />BRL: (a) Both seeps as discussed in the text do not have a perceptible flow, they are seeps, or small <br />leaks from the Fire Mountain Canal, so the estimated flow for both designs are an estimate. <br />The revised cross section is smaller than the existing one in order to make the underdrain re-route <br />feasible for construction. It is desirable to have at least two feet of common fill between the <br />designed underdrain and Ditch J10 and J11 in order to protect the underdrain during clean out of <br />Ditch J10. The section could have been increased to four feet under the Ditch J11 section, but for <br />consistency and ease of construction was kept at three feet. The cross section of three feet is <br />adequate to pass the estimated flow from the East seep and therefore a cross section of four feet is <br />not necessary. <br />(b) The upper end of the East underdrain will be constructed much like the upper end of the west <br />underdrain. A point survey has been performed on the seep, but the extents have not been <br />delineated. Prior to construction of the underdrain, another survey will be conducted that <br />delineates the entire seep area. The upper end will be a rectangular area where native material will <br />be dug out, and backfilled with clean gravel. The intent of the large upper end is to ensure the <br />entire seep area is captured and directed into the underdrain and away from the coal mine waste <br />pile. A perforated pipe will then be placed in the bottom of the trench. <br />(c) The East underdrain's last twenty feet will be solid pipe. Please see revised Volume XI, page 8. <br />(d) The slope used in the underdrain is based on the actual slope of the designed underdrain, not <br />based on a surface ditch slope. <br />Feel free to contact me if you have any questions. <br />Sincerely, <br />Tamme Bishop, P.E. <br />Project Engineer <br />Cc: Bill Bear <br />