2016-01-22_REVISION - C1981014 (4)

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Sediment Demonstration — Mine Site - revised 1/22/2016 w/ 1/8/2016 addendum Page 1 Section 3.03.1 SOUTHFIELD MINE FACILITY AND RDA PHASE II BOND RELEASE RECLAIMED AND NON -MINED LANDS SEDIMENT ANALYSIS This mine site sediment demonstration was originally submitted with the bond release application SL -03. It has been revised and/or amended on two occasions. This document is the second revision to the original and retains only information that EFCI believes is valid and appropriate given the concerns expressed by the DRMS. Selection of I -S factors in somewhat subjective. The length and the slope % are related and must be selected with care and a good understanding of sediment detachment principles and theory. EFCI has taken great care to ensure that LS factor information has been selected and believes that information and parameters selected are appropriate. Averaging all the values from the three sediment demonstrations conducted by EFCI is likely the most accurate over the long term. Predictions from RUSLE represent soil loss averaged over many storms andyears. It also represents averages over a total field or disturbed area. Average sedirnentyield values for the three demonstrations are presented below in Table 5. The first DRM,S' concern was documented below on page 4 and dated 11812016. This revision to the original analysis evaluated the LS' factor in more detail, specific to the RDA. Additional information was incorporated to develop Demonstration # 1 and Demonstration #2. Explanation of modifications for the LS' factor and the cover factor are presented in the 11812016 response. Table 5, as submitted in the 11812016 response, was then averaged with the original mine site sedimentyield value presented with the two new demonstrations to calculate a mine site average sedimentyield, for the adjacent un -mined condition and the reclaimed condition. On January 21, 2016, the DBMS expressed concern about the value used for the LS factor in the original sediment demonstration. Therefore, this revised analysis (112112016) modifies the original sediment demonstration with regard to the I -S factor. Afore information and input were used to develop the new LS factors for the mine site. The LS' factors used for the revised original calculation are shown in detail on page 3 in the table titled LS' Factor Table. Four rallies were used to determine an average value for the surrounding non -ruined area. This value was then averaged with the assumed pre -mine value of the portal area, which results in a LS' factor of 3.755. Four measurements were included for the reclaimed area and averaged, resulting in an LS' factor of 3.14. The cover factor used is the average site -wide value as shown in Table 1. The final.redirnentyield values of this modified original sediment calculation is shown in Table 2 below. Ueruonstrations # 1 and #2 remain unchanged from // 812016. However, since Table 5 averaged the three demonstrations, Table 5 has now been revised to reflect the average of the three, including this revision to the original calculation. INTRODUCTION As part of Phase I1 bond release for the Southfield Mine Facility and RDA, a sediment yield analysis was developed to determine if the sediment yield from the existing reclaimed condition is comparable or better than the non -mined condition. The Facility area was reclaimed and seeded in 2003. The RDA was reclaimed progressively over the life of the mine and seeded in various phases beginning in 1983 through the final seeding in 2003. Rule 3.03.1(3)(b) requires that "No more than sixty (60) percent of the bond shall be released so long as the lands to which the release would be applicable are contributing suspended solids to streamflow or runoff outside the permit area in excess of premining levels as determined by baseline data or in excess of levels determined on adjacent nonmined areas; until soil productivity for prime farmlands has returned to equivalent levels of yield as nonmined land of the same soil type on the surrounding area under equivalent management practices as determined from the soil survey performed under 2.04.12 and 2.06.6 and the success determination methodology of 4.25.5(3)(a); or, on alluvial valley floors, until the essential hydrologic functions and agricultural productivity have been reestablished."