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ENVIRONMENT, INC. ~aApE 7 BILDAM BTONE - BEDROCK MINE M.L.R.B. PERMIT i~ M-97-OH6 JANUARY 7, 1998 that there is no aquifer within 100 feet of the sur- face. (c) As stated earlier a small berm or ditch will be con- structed around the upgradient side of each excavation area to prevent surface runoff from entering the dis- turbed areas. Where rain water or snowmelt accumulates in the excavated area it will be directed to a low point in the excavation and retained until it soaks in or evaporates. Since the slab rock area will be de- pressed no sediment traps will be needed. There is no bridge at the point where the tributary canyon enters the site. This is a mistake on the map that I just found out about. There are corrugated metal culverts under the road at this point and the easiest way to assure water continues to flow in the tributary water- way will be to avoid changing the character of the water course until it reaches a deeper part of the canyon. This may mean we have to limit slab rock mining immediately adjacent to the water course. The removal of surface stone in this area will not affect the natural flow of water so that could continue. This same plan would work on the north end as well. The only stormwater that we have to retain on the site is that water that comes in contact with disturbed areas (process water). By allowing it to accumulate in the bottom of the mine, we can control the quality of water leaving the mined area. Once reclamation is complete and the site is revegetated, any water leaving the site would be the same quality as it is now so no permit is needed. Since no structures need to be built to retain the process water no designs are necessary. No long term accumulation will occur in the mined area. To find out if water will accumulate in the excavation I used the same analyses method dictated by the State Engineers guidelines for lake evaporation. In that analysis 708 of the average precipitation is used by plants and 30~ returns to the system as evaporation or soak in. You then subtract yearly precipitation from the average pan evaporation numbers from NOAA Technical Report 33 to get the net evaporation from the lake surface. Assuming, the accumulated water is like a lake you can find whether water will accumulate in the mined area. In this case, the NOAH report shows there is 47.5 inches of surface evaporation per year and we have 13.1 inches of average rain fall. The net result is a negative number {(13.1"*0.7)-47.5" _ -38.33")} so no water will accumulate in the mine for any extended period. This is true, since during the last 20 years there have been no problems with appreciable amounts of water accumulating in the Siloam Mine that this permit area surrounds.