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3) Mr. Heffner also indicated that the planned use of rock dams as grade stabilization and sediment control structures in the drainage bottom separating Phases III and IV has now been abandoned, in favor of utilizing bench size and design in combination with strategically-placed silt fencing to minimize runoff and sediment load. He indicated this new approach would be explained at the upcoming June 21 meeting in Denver. Based on the bench design observed in the Phase I area near the front entrance to the quarry, this method may prove adequate on exposed quarry walls of native rock material. Sites which will consist of benched limestone processing waste do exhibit surface rill and gully erosion on the steep slope faces which will need to be stabilized, or else provide for sediment control structures in the drainage bottom in lieu of slope face stabilization. Hydrology studies on the watershed areas above the amendment ~ site are also underway by a separate engineering consulting firm, which have yet to be completed and submitted for review. As a result, no comment is submitted regarding engineering adequacy on erosion/sediment control structures pending final decisions by Castle Concrete. 4) The "sub-irrigation" concept on backfilled benches overlying bedrock would appear to be applicable and effective only where the backfill depth approximates the effective root zone of the seeded/planted species. For grasses in particular, the vast maJOrity of the active root area lies within the top 2-4 feet of the soil (growth medium) profile. Backfill depth in excess of this would tend to minimize any "sub-irrigation" effect for grasses, although root growth of shrubs and some fortis may be able to utilize this condition at deeper backfill depths. Grasses sF~ould continue to receive priority for erosion control effectiveness. 5) The concept that "porosity" of the growth medium enhances plant growth and vigor should be more specifically defined, and may be misleading in many cases. In our experience, soil "porosity" whicFi carries beyond (i.e. coarser than) sandy loam (or equivalent) soil texture tends to decrease plant establisF~ment and performance, particularly in regard to the grass species mix specified in the mining plan. It still appears that backfill derived from coarse limestone processing spoil material will offer minimal opportunity for vegetative establishment without topsoiling addition.