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~. <br />Mr. Liddle: -2- June 1, 1983 <br />A culvert was installed to drain areas 1 and lA over the hill and into <br />the plunge pool. Reference for design was Handbook of Steel Drainage 6 <br />Highway Construction Products, copyrightt 1971. <br />Q=(1.486/N)AR2/3S1/2 ti'2/3011 (p. 190, 12"Helical) <br />AR 0.312 (p.192, 12") <br />5=0.55 (elope calculation) <br />Q1Z„=(1.486/0,011)0,312x0.55 <br />Q12,~ 31.3 cfa Therefore 12" is suitable to handle 21.1 efs req, <br />The dam on Pond 1 as well as on the other 3 Ponds was installed prior to <br />Blue Ribbon Coal Co, under the management of Western Associated Coal Co. <br />First-hand engineering judgements of the means and material is not avail- <br />able. Pond 1 has an area of 2 acres and an estimated depth of 4i,~ with <br />approximately 1'~' of this depth below drainage structures. This pond is <br />refered to as being capable of handling the lack of capacity in Pond 2( <br />App. C, page 8a Of 10). The numbers listed as required water and sediment <br />volumes is the excess volume required over the capacity of Pond 2. The <br />dam structure appears to be well compacted. Some of the material in the dam <br />is questionable as was illustrated in our May 1983 inspection where moving <br />a portion of the dam material was refered to as inadequate handling of <br />topsoil. With proper protection from erosion by Hubbard Creek the soil <br />should be adequate for the constructign material. Two concerns on the pond <br />are the erosion contrgl on [he north and west aides and the overflow cap- <br />acity. I would suggest additional rip-rap along portions of the north and <br />west sides and the installation of an emergency spillway on the south side, <br />Pond 2 was modified to have a freeboard of 2"rather than the 2.86" shown <br />on Exhibit G to allow for a larger water and sediment volume. (The 2.86 <br />appears to have been the measured freeboard when calulations were done <br />in 1982) The material and compaction used in the dam construction appear <br />to be good. Apossible problem with the pond is the slope stability of <br />the hillside behind it. Pond 1 would be capable of handling problems <br />with Pond 2. <br />Pond 3 was initially sized for a larger area therefore the only recent <br />modifications was the installation of different discharge structures. The <br />dam appears to be well compacted of suitable material. The width of the <br />dam might be questionable in places if larger volumes of water a~ sediment <br />were involved. Seeding of areas disturbed for construction will be done <br />in June 1983. <br />Pond 4 was modified recently by installation of different discharge <br />structures. The dam appears to be well compacted of suitable material. <br />Seeding will be done in June 1983 on areas affected by the construction. <br />This pond collects considerable amounts of coal fines and may require <br />more frequent clean-out then the other ponis. <br />If there are any further questions concerning the drainage and sediment <br />control system at Blue Ribbon Coal Co. please feel free to contact me <br />or bring them up in an on-site inspection. <br />