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<br />The major use of surface water in El Paso County is for <br />irrigation of 55,000 to 58,000 acres in the El Paso and <br />Mesilla Valleys in the El Paso County Water Improvement District <br />No.1. During periods when surface water deliveries from Ele- <br />phant Butte Reservoir to these Valleys are low, groundwater from <br />the Rio Grande alluvium is used as a supplementary water supply. <br />In 1974, approximately 173,502 acre-feet of Rio Grande Project <br />surface water was used to irrigate 55,195 acres in the two <br />Valleys. In 19b4, during a period of low surface water delivery, <br />120,303 acre-feet of grou~dwater was pumped while only 20,378 <br />acre-feet of Project surface water was used. <br /> <br />Groundwater from the Hueco Bolson deposits is being "mined" <br />in El Paso County and the Ci ty of Juarez area. It has been <br />estimated, Lhrough the use of an aquifer model, that in 1903, <br />about 11.45 million acre-feet of fresh groundwater was in storage <br />in the Hueco Bolson deposits in El Paso County. In 1973, the <br />amount in storage had been reduced to 10.64 million acre-feet. <br />One application of the model indicates that by 1990 storage will <br />be decreased to about 9.84 million acre-feet. Depletions in <br />storage are causing saline water encroachment from aquifers and <br />degradation of groundwater quality. The amounts of fresh to <br />slightly saline water that can be removed under "safe yield" <br />conditions has not as yet been determined. In 1974, about 99,700 <br />acre-feet of water was pumped from the Hueco Bolson deposits in <br />El Paso County and by the City of Juarez in Mexico. Studies in- <br />dicate that the aquifer received about 6,000 acre-feet per year <br />of natural recharge and about 21,000 acre-feet per year of water <br />from induced recharge (leakage) from the Rio Grande alluvium. <br />Induced recharge or leakage from, the alluvium is slowly degrading <br />the quality of groundwater pumped from the Bolsondeposits. <br />Water quality degradation will also occur due to lateral and <br />vertical encroachment of saline water from adjacent saline water <br />sands in the Bolson deposits as the fresh to slightly saline water <br />in storage is depleted. <br /> <br />The El Paso area has surface water supply and quality degrada- <br />tion problems also. In the last 20 to 30 years, ElephanL Butte <br />Reservoir has been able to deliver about 65 percent of the water <br />originally planned for ,the Rio Grande Project. At the El Paso <br />Gaging Station, the rate of annual depletion in discharge of the <br />river averaged about '16,400 acre-feet over a 65 year period (1907- <br />1972). These types of water -shortages coupled with agricultural, <br />municipal, and industrial return flows have caused and will continue <br />to cause water quality degradation in the area. <br /> <br />68 <br /> <br />"', .- t r~ '\, ).... <br />l.,..,~. v, <br />