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Jrr~~ 1999 Srnecr Cool Con~pmrp r Surcm fI Il%~ ~tlurr Sedmunolion Pand O1T S/atiiii~ Aua/r ri/ ~ I . 1.0 INTRODUCTION 1.1 PURPOSE The purpose of this stability analysis is to calculate the salety factor (SF) under static conditions for the Sedimentation Pond 017 embankment in order to document design compliance with applicable regulatory standards under Rule 4.05.6(1 I)(j) or (k). 1.2 METHODOLOGY The static SF for Sedimentation Pond Ol7 was calculated using a basic, one-dimensional equilibrium analysis program called XSTABL (v5.2). "Ihe calculated SF is the ratio of those resisting forces that would prevent embankment movement or failure to the corresponding driving forces. Resisting forces include the internal strength parameters for both the soil materials used in the construction of the embankment and the underlying base materials en which the facility will he constructed. Potential dnving forces include gravitational forces on the embankment and foundation materials and the gravitational and lateral forces associated with the water volume that could be impounded behind the embankment. For this analysis, a circular failure mode was assumed, and the SF was calculated using the Bishop method. 1.3 PROCEDURE The embankment cross-section shown on Exhibit 13-SB of the Seneca Ii W Permit, (Leidich. 1999). was used to evaluate embankment stability. For the analysis, a water surface elevation behind the embankment of 7,483 feet above mean sea level (amsl) was used. This water surface elevation is equivalent to the elevation of the invert to the principal spillway. The embankment is designed with upstream and downstream slopes of 3H:1 V. The design width of the embankment crest is IS feet. Total height from the bottom of the pond to the top of the embankment is 13 feet. The emereency spillway invert is ?.~ Feet below the embankment crest. The base of the embankment is designed to be on a flat surface with no slope Gom the upstream embankment toe to the downstream embankment toe. The potential phreatic surface for the stability analysis' is based on a water surface elevation of 7.483 ft- amsl corresponding to the invert elevation of the principal spillway. The phreatic aureate through the embankment was estimated based on Darcy's law and Casagrande's procedure as outlined by Huang (1983). The resulting surface is shown on the XSTABL computer printouts contained in Appendix B. Based on soil surveys the soils in the area are defined as a Silas loam. A complete soil description of this soil type can he found in Appendix A. Properties for [his soil type are shown on Table I Sedimentation Pond 017 Soil Data. TABLEI SED(M1tENTATiON POND 017 SOIL DATA SOIL No. SOIL NAh1E ATTERBERG PARTICLE S12E USCS LR19iTS DATA CLASSIFICATION fLL-Pq (9o assin No. 200) 28A Silas- Venable Loam (20-35)-(5-IS) 35-5?~a SC. CL-ML. CL The soil strength properties for the natural soils were obtained from published data for common soils (Luo • and Peng, 1999). The soil information can be found in Appendix A. According to the published data for a Alom/gamrr3~ Itiohon.'Lnenmt, Lir. !GS Soulb Uulan Baukrard. Srile -F70 "L.'kemooA, Colorado 80??8 • 130iJ IGi-i l-JO J~\8i I \rr[~/~oedl7ualn'Gry 0:/7//79 r.'A