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to prepare those designs and submit them to the staff prior to their construction should be sufficient protection for the Board that the modifications will be done. DRAINAC~ CQf2SE: We like the idea of using a single sediment control structure near the bottom of the drainage between Phases III and IV in combination with silt fences at the ends of the benches. This would certainly help to even further reduce damage to the drainage course. We also like the idea of committing to the establishment of crossings using the culvert approach with adequate protection for the culvert inlet and outlet. We feel the culverted crossing design should be developed around a 25 year, 24 hour event. In our experience this area is rather prone to heavy thunderstorms and therefore designing the crossings for a smaller storm could result in the crossing being washed out, possibly a couple times a year. It should be understood the amount of runoff which will occur from the benches will be very limited. The gradients on the benches will be very gradual and the material very porous. It is expected most of the water falling on the benches will stay on the benches. Therefore, siltation into the drainage course should be minimal and should be controlled well with silt ,,fences placed at the ends of the benches and kept in place for the first two or three years after revegetation, assuming revegetation occurs at the expected rate. This rate is based on our experience in revegetating other portions of the quarry. The size of the setback from the centerline of the drainage is a matter of same concern. If the setback is established at too great a distance the loss of mineable rock would become highly significant. It should be recognized the watershed which feeds this drainage covers only about 20 to 25 acres. So, the amount of potential flow in the drainage is quite limited. This is clearly evidenced by the lack of erosion in the water channel. Trees estimated at 100 to 200 years of age and with diameters of 1.5 to 3.0 feet can be found growing in the bottom of the drainage. ~viously, huge flows down this drainage have not occurred for a very lrng time. In fact, since 1%9, flows greater than just a few inches deep have not been observed in this or other drainages of similar type on or adjacent to the property. The bottom of the drainage contains not only large trees, but also shrubs and a very thick grass cover. Such vegetation simply could not develop in a drainage which is subject to flood flows with a frequency of more than once in from 100 to 300 years. Therefore, we wish to keep our original setback distance at an elevation of 6 to 12 feet above the centerline elevation of the drainage. The horizontal distance that this represents largely depends an the grade of the adjacent slopes. A sampling of measurements taken from the topographic maps that an 8 foot vertical setback results in a horizontal setback of from 20 to 50 feet (20 feet in only a few locations), depending upon exactly where the measurements are made. To expand the setback to 100 feet horizontally would result in a loss of approximately 2S/. of the mineable rock. Considering the small size of this drainage and the lack of historical flow dawn this drainage a 100 toot setback seems excessive. This is especially true, it seems to us, when 100 foot setbacks are frequently considered to be adequate in most cases along the Arkansas or Colorado Rivers. EXHIBIT G - WATER IS• ITEM 3 We are sorry about this minor discrepancy. We intend to use the 6 to 12 foot figure. SfdYDEl2 t~W AhEPIDhIIVT ADE0.WCY RESPQ~L~S MAY 22, 1989 PAGE 13