2010-10-06_REVISION - C1981010 (2)

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C_Iqla/_0/0 S L__ 1;7 Zuber, Rob From: Graham Roberts [graham @trappermine.com] Sent: Wednesday, October 06, 2010 5:44 PM To: Zuber, Rob Subject: RE: SL12 USLE Hey Rob, Had to do some research on this. After digging into this I am going to revise my numbers for the LISLE calculations. The conclusions will be the same, that post-mining ground cover will produce less run-off, but the tons will change. Most of the factors used in the USLE are generic for our area or based on historic data at the min-site. The only factors that change is the LS factor, depending on the slope of the parcels, and the C factor in the post-mining calculation. They are chosen to most accurately reflect the condition of the parcels and practices performed on them during reclamation. The calculation has become fairly routine as the landscape varies little from one side of the mine to the other. We did average the blocks together as they are all very similar, aspect wise, vegetation wise, etc... The one C parcel is so small we just lumped it together, it has little effect on any of the calculations. I took slope measurements. in various positions on the parcels to get an average length and slope for all of the parcels. These measurements were taken from the topo on the ARR Maps. As has been determined with past bond release applications, we cannot effectively break these calculations out by watershed, or sub-watershed. All we can do is evaluate each parcel within the parcel boundaries. The pre-mining C values are exactly as you deduced. I have been sticking with those values as they are a good historic representation of the cover for the majority of the mine site. Little changes with the pre-mine calculations when dealing with parcels located on the long and fairly uniform slopes of the upper reaches of the hillside. The post-mining C value is a mistake, I will revise that, it should have been 66.6% herbaceous cover, which, extrapolated from the SCS Table for C factors for Permanent Pasture, Rangeland, Idle Land and Grazed Woodland, No Canopy would net a C factor of 0.032. This factor was used in the SedCad runs. As previously stated I will revise this value in the equation to return a more accurate number. The conclusion will remain the same, but the margin of decreased sediment movement will shrink with the lesser cover. The vegetation sampling results this year were somewhat lower than previous years and previous bond release applications. It was kind of slow year for vegetative growth this year. In the findings document and a field study conducted by Tom Kaldenbach for SL-1 the division made the assumption that pre-mining lands would produce 10% less soil loss than post mining lands. I'm not entirely sure what this was based on. However, that was the template laid before us on the first bond release we attempted. The assumption was not necessarily justified as Tom did extensive work on-site, determining that post-mining sediment yields were indeed equal or lesser than pre-mining through sediment surveys of ponds in reclaimed areas on the western side of the mine. We have continued to use the assumption of 10% to modify the LISLE to favor the pre-mining soil loss. You can see the total tons per acre amount is modified at the end of the equation by multiplying by 0.90 to reduce the yield. His findings can be found in the findings document and some correspondence detailing his excursion prior to approving the bond release I will send you amended pages 11 and 12 as I tweak the numbers in those two tables. I will also be sending the certification to you at that time. Let me know if you have any other questions. Graham