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8.1 Underground Water— Underground water in Las Vegas Valley occurs, so far as is presently known, in four horizons or zones, the surface or near-surface water, the shallow zone between a depth of 200 to 450 feet, the middle zone which underlies the blue clay in the valley and which ranges in depth from 500 to 700 feet, and the deep zone which in­cludes all waters encountered below a depth of 700 feet. All zones are recharged by water falling as rain or snow in portions of the Spring and Sheep Mountains above the 6,000-foot elevation on the Spring Mountains and the 6,500- foot elevation on the Sheep Mountains. The near-surface aquifer is not recharged by direct precipitation but is recharged directly or indirectly from the deeper aquifers. Geological faults, imperfect separation of the aquifers, cooling water, irrigation water, and sewage recharge the near-surface aquifer. Draft from the near-surface aquifer is largely by transpiration and evaporation. The nature of the aquifer does not lend Itself to other development such as wells. Since the annual average water levels have re­mained reasonably constant with an estimated discharge of 8,000 acre-feet per year, the recharge is estimated at a like figure. Based on the rainfall, area and nature of the out­croppings, itis estimated that 50,000 to 35,000 acre-feet 49.