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Bank stable . Large deep lake at rear of bank . Dike at N. E . edge of l ake is 15 ft. wide, 8 ft . high. Could be overtopped and breached. Flood and debris would damage church and two or three houses downstream, cover road and wash out railroad . Gul ly at front covers road with wash regular l y. Lake contains about 5,000 cubic feet of water. The dike described in the USGS report is Dam No. 1. Dam Nos . 2 and 3 did not exist at the time of the survey . III. DESCRIPTIONOF DAMNO, 3 The centerline of Dam No. 3 was located approximately 2600 ft, upstream from the mouth of Middle Fork . The dam varied in height from approximate ly 45 ft. at the right abutment to 60 ft . at the left abut - ment. It is probable that the dam was trapezo i dal in shape, with side slopes determined by the ang l e of repose of t he refuse material . Mea- surements made by the Department of In t erior Task Force indicated a base width varying from 400 - 500 feet; the greater width existed at the left abutme nt and corresponded to the greater dam height . The dam spanned the entire width of the valley, which was approximately 400-500 feet at the location of the dam. As previously indicated , Dam No. 3 was con - structe d on a foundation of refuse sedimented from the impoundments pro - duced by Dam Nos. 1 and 2. Subsurface borings made recentl y indic ated t hat sediment deposits as great as 50 ft . in thickness existed beneath Dam No. 3. No information was obtained concerning the amount of freeboard that existed prior to the rain s torm preceding the failure. The crest width was estimated to be 100 - 200 ft . A 24- in. overflow pipe was placed 7
in the r i ght abutm e nt ar e a appro xi mately 7-10 f t. below the cr e st of the dam. However, under normal condi tio ns , flow would r each t he lowe r pond by see page through the dam rather than by fl ow through the pipe. From all indicatio ns, no provisi on s were made to prevent piping along the ove rflow pipe . In addition, none of the dams had emergency spillways. The coal mining refuse used to const ruc t the dam co nsis ts of a mi xture of clayey shale and low quality coal . Sources of refu se incl ude waste rock and other impurit i es generated during mine deve lo pment and operation and impurities sepa rated from th e "ru n of mine " or r aw coal at the pr eparation plant . General ly, most of the so lid waste is produced at the preparat ion pl ant. Coarse r e fus e (g reater th an 1 mm particles) is usually transported to the disposal site by conve yor s or trucks, whereas f ine refuse (less th an 1 mm pa rticles) is usually pumped to a settling pond in a sl urr y . Accordi ng to the Tas k Force Rep ort, refu se was continuou s l y dumped at Dam No. 3 following its inception. It was estimated t ha t appro ximately 1,000 tons of refuse wer e transported daily t o t he di s - posa l site by 30-to n trucks. The r ef use was dumped over th e ends of th e dam or on top of the dam. When dumped on top of the dam, layers as great as 5 ft. in thickness resulted. These l aye r s were spread with a bulldo zer to maintain a s urface for the haul trucks. No spec i al effort was made to compact the refuse material; however , some compact ion r e - sulted from the operation of the hauling and spreadin g eq uipment . 8
