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ITEM 1 -_ In the 1984 amendment that added the Phase IV area, the reclamation plan stated "the depth of material used for subsoil should be at least 12 inches and preferably 14 to 18 inches." The plan later states "Soil depth will be between B and 15 inches, depending upon the subsoil depth and properties. We found on the visual berm that 10 to 12 inches of soil was excellent and 8 inches almost as good. Below 8 inches, though, the quality of growth declined rapidly until soil depth was about three inches, at which point there was little difference between that and bare waste." In the new application, you state on page 30 that "A minimum depth of two to three inches of soil is required, but about four inches seems to produce the best cost/benefit ratio. Soil depths greater than four inches tend to experience a decreasing value relative to the amount of soil." Please explain this discrepancy. From "Revegetatim Guidelines for Surface Mined Areas" (C. Wayne Cook, et. al., CSU Range Science Department, December 1974), "it is strongly recommended that at least ten inches of topsoil be saved and distributed over the subsoil material or mixed with the solid material surface for a plant growth medium" for Mountain Brush vegetation expressions and for Foothills Juniper vegetation expressions "it may be necessary to save soil from three to four feet where it occurs in order to have 18 to 24 inches to serve as a plant growth medium over the entire area to be rehabilitated." It appears that a 4-inch topsoil replacement depth will be insufficient for reclamation purposes. I recommend based on past Board approval and literature, that topsoil be replaced to no less than 8 inches and that this be placed over the backfilled materials. Please discuss why replacement topsoil depths should not be a minimum of B inches. RE~.POVSE: Camille Farrell asked a very similar question several years ago. First of all, the visual berm soil depth determination for adequacy was based on the first growing season. In later growing seasons this preliminary assessment was modified as a result of shallow depth soil growth rapidly catching up with the deeper soil growth. Thus after two growing seasons, there was essentially no difference between areas with 4 inches and areas with B or more inches. This means that, except in the first growing season, soil depths of more than about 4 inches does not appear to result in any better growth in later years. Secmd, when placing soil over depths of backfill that range from about 1 foot to as much as 6 to 8 feet near the backwall of the benches, mly a thin veneer of soil is needed. This is highly representative of the natural Paunsaugunt Series where there is from 2 to 6 inches of A horizon resting directly an tap of about 10 to 16 inches of C horizon which rests directly on tap of bedrock. The C horizon in the Paunsaugunt series is almost indistinguishable from quarry rubble. In this typical depth of native soil (18 inches) grasses, shrubs, and trees grow. Third, expecting us to put 8 inches of topsoil when there is only 6 inches at best, and same areas have less than 2 inches, is asking us to irtport soil. The native vegetation grows in less favorable conditions than what you are recommending we do. That does not seem reasonable. Fourth, our reclamation efforts at this quarry and at other operations have clearly demonstrated that highly successful growths can be established in mly one season with the replacement of 4 inches of soil on tap of backfill. If mly 4 inches of soil was placed on tap of the bench we would agree that failure was the effort's destiny. But 4 inches of soil on top of 1 to B feet of backfill is actually better than what Mother Nature provided this area with. Therefore, because SNVDER NW AhE]~IDh~VT ADEG1lIACY RESPONSES MAY 22, 1989 PAGE 5