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REV96866
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Last modified
8/25/2016 3:21:24 AM
Creation date
11/22/2007 12:04:07 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981032
IBM Index Class Name
Revision
Doc Date
11/18/1997
Doc Name
DEMONSTRATION FOR PHASE II BOND RELEASE ON N 1 AREA WITHHELD
From
GREG LEWICKI AND ASSOCIATES
To
MLRD
Type & Sequence
SL2
Media Type
D
Archive
No
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i <br />Sediment Loss Comparison Methodology <br />In order to compare the erosion from the pre-mine area to the post-mining <br />reclaimed area, a number of methods are potentially usable. First, sampling of <br />the reclaimed areas and pre-mining baseline data could be compared for a <br />particular storm event or number of storm events. This cannot be done, <br />however, since there are no data in the permit for the pre-mining slopes. Total <br />suspended solids data and total settleable solids data does exist for Curtis <br />Creek but for no other area. <br />Second, sampling of the reclaimed area and the adjacent undisturbed area <br />could be made for a particular storm event or number of storm events. After <br />reviewing the sites, maps, etc., we feel that it is not possible to pick locations <br />on the reclaimed areas and on adjacent areas that are equivalent in slope, <br />length of slope and control practices. For example, the Rienau #2 site contains <br />a permanent diversion immediately above the reclaimed area. The surrounding <br />undisturbed slopes have no such diversion. At the Northern #1 site, no sample <br />can be located in an area to solely measure the reclaimed area. All locations <br />will have some mixing of runoff from the reclaimed and the undisturbed areas. <br />Also, there are some serious questions about the mechanics of collecting valid <br />• samples on the ground. For these reasons, this alternative has been <br />abandoned. <br />Third, computer modelling techniques such as the SEDcad model could be used <br />to predict sediment loads for a particular storm. This technique is also flawed <br />because the modelling requires actual drainage basin parameters as input, and <br />as described above, the drainage basins are far from identical. There are no <br />points on the reclaimed and disturbed areas which are truly comparable. Also, <br />this model predicts the sediment concentration for one design storm only. <br />Fourth, an estimate of the annual sediment loss can be made for the <br />undisturbed areas using the Universal Soil Loss Equation and the baseline soil, <br />vegetation and topographic information. This calculation has a number of <br />advantages. Hydrologically, it is much better to compare sediment volumes on <br />an annual basis than for one particular storm. Many sources of error can be <br />eliminated in this way. The Soil Conservation Service office in Meeker also <br />agrees that this method is better suited for the reclaimed areas. Also, the <br />estimated soil losses for the undisturbed areas can be directly compared to the <br />reclaimed area using the vegetation conditions in both areas. <br />C, <br />
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