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J U h~~ - 2 0- 8 S T U E 2 1 1 1 E U A N S ~ B R I G G S <br />~ ~ • <br />Mf M0. Snyder Asnenduiunt <br />hydrologic Suyplsm¢n! <br />June 20, IAAA W 9:r0 A.M. <br />ProJcct No, 89002 <br />ATTORNEYS P _ 0 3 <br />2 <br />The silt retent.lon facility eizlrtg includes art efflclet,cy factor (7096 <br />was used) and a partlcle a1~e 1n mlrronn (40 was used). What was the <br />source of these flgttres't <br />k1:SPUNSE: The partlcle size, witett orlelnally considered was <br />somewhat lnrger than the size used for tho deaign bxsvd on the <br />oyoratlon and specific gravity of the materlat. Upon further <br />conslderatlon we feel t),ere could be soma smaller yarilclcs of a r~lne <br />silt variety created, We selsat.nA the 40 micron size as the design <br />yartlcls to assure maximum removal. The 7096 officlency fa fair. to he <br />a reasonable performance level based on Lhe shape of t}to yortd (L=;} x <br />width). <br />The grading plan indicates same disturbance will occur below L11C silt <br />ret.entlen PAC111ty. A s11t Pence and possibly a berm is recosntnerlded <br />for areas below tllC silt pond. <br />1tESr~UNSE; A slit fence has boon shown below rite pond along <br />contour 7226. If disturbance occurs below this elevatlozl, t}lo silt <br />toscc would be moved to the interface. A berm to direcr.runoft from <br />the west boundary area to the silt retentivrt facility w111 be inatallcd. <br />Tttis is indicated in Btormwatnr Runoff Improvements, S1te tserntlrtg <br />subaoctlon Urt 1'ago 11/12 of the Supylclncnt. <br />'nc~ silt retention faculty indicates thr+, olatlec pipe wf11 go t.hrnugh the <br />e[nbankts,ertt which will ac:tually'be cr•eatvd by oxcavatlon Into the <br />llr[lestorle sttatarlxl. How la Lkte pipo proyosod iv be lrtsta11ed1 <br />kESYONSi;: We would propose to develop this cortatructlort detail as <br />part of the final deaign plans based on reeommendatfons from fife <br />OpCratvr, Castle Co»crnte. p»e point of rnminder, water will not be <br />retained in this facility, the maximum drain down time 1s 8 hours, tf <br />some seepage should occur, the result would yrubably bo one of <br />1'I l l.ratlnn, <br />10. The standpipe calculations se submitted are acceytable, I[ },as b¢ott <br />recommended that the riser be wrapped !n a filter fabric (at. lAaFr. the <br />lower porllvtt), thus yravuttLltlg arty ausyendod [natCr•la! from lcaVltlg <br />Llu•vugh t)i,: Ktltndplpe Loles. <br />itESI~ONSf; The pond design allows for adequate partlcle settlement <br />and the slit reaching the standpipe will ba very minor, The fabric <br />would have a t:endAncy to clog the outlet holes dnring a mayor event <br />r.ausl»g the orifice (standpipe top) t~o overflow and possibly flow over <br />the spillway. '1'llls may result in a poorer quality effluent dtschargs <br />then 1f the bolas operate. We do trot propose use of a filter fabric <br />around the standpipe holes. <br /> •,~ <br /> i <br />,; , <br />r• ; <br />1~.: <br />' <br />x-, <br />;,,• i ~ <br />~. <br />4 <br />ilrj <br />r. S , . ;% <br />~ , ~ .l <br /> <br />