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INTRODUCTION <br />Sediment Fond 006 was constructed in the NW4 fIW~ of Section .2, Township 5 No ct h, Range <br />BR West in a tributary to HubGerson ,inch. The pond and embankment was constructed to <br />control runoff and sediment from a watershed disturbed by mining activities. Fhase I <br />construction was completed in 19b 9. Fhase II consisted ~~f modifyr ng the existing <br />principal spillway to increase the active storage rapa city of [he pond and lowers nq [he <br />emergency sprllwa y. A drop inlet C11F was installed to •ron[n~1 and meat the runoff from <br />the watershed. Fhase III :nnsisted ~~f constru Icing a clean Wate[ Di version in the <br />southeast f•o ci con of [he watershed which dive r[s R1.-0 acres away from Fond u06. The <br />principal spillway was also m~~dified by cutting a a-i m:h diameter dewatering ciifice ai <br />an elevation of 7066.0. In late September ~;f 1997, the mine received approximately J.7 <br />inches of precipitation over a four day pe aod, with orie day _..ceeding the 10-year, Z!- <br />hour event. This event happened right after Wpsoil was re mo'+ed from a large portion of <br />the mining area directly uF~scr=_am frnm pond 006. Given ct~~ large amount of pie-shipped <br />area and the unusually la rye sto rrn =vent pond 1105 filled with sediment r.o its maximum <br />capacity. I[ should be nosed that pond 005 was dredged in the summer of L96 and had <br />10,000 cubic yards of se=ii moor removed from i[ then. Due to chose <+ents, Seneca has <br />reevaluated the pond and is submitting ttii.. PI',ase IV d=sign. <br />The sediment basi•=ally filled the incised pn rt ion of the E~o nd. The e>:i sting =merger c; <br />spi ilway is app ro:a mately seven fee[ deep. So, rather than removing the sediment in the <br />incised portion of the pond, Seneca will ca ise [he in•: eit of the principal and emergency <br />spillways. The new bottom cf the pc nd +levacien is 7nri?, which is also the original <br />~J <br />upstream toe of the ertibankme nt. The inverC of the emergency spillway will be less than ~0 <br />feet in height above the upstream tee and the po rid will still have a capacity of less <br />than 20 acre-feet. Because the 005 wareished is ar. the maximum disturbs n~.-e, and to <br />prevent thls from happening again, r~ L?wer portion of the existing B pit will be <br />utilized as a Fre-Settling Basin, see E.=.h slit 1~ This Gasin is completely incised and <br />does r.oC require an embankme r.t. Th.is will be accoreplished by ccnst root ir,g an inlet <br />channel which will divert ru ncff from the 006 Gulch inb; the B pit and an outlet channel <br />which will return the runoff bast to the ~3u 1ch just aGove culvert A1. This will <br />effectively deposit Lhe majority of the sedime nr ,n [he pre-settling basin and 4:ems-i:ond_ <br />006 as free of sediment as possible, while Seneca can do additional reclamation of the <br />dis[urbwi porn en •-.f Vie watershed to further minimi_e [he amount of sediment being <br />• 9enera[ed. <br />1 Revised 03i ii[/9~3 <br />