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o OJ to 1_: .-- ~ . ,-.. ..- Evapotranspiration Deep percolation Effective precipitation Total soil intake Leaching percentage 5/37 = 28 Inches 5 Inche s 4 Inches 37 Inches 13 percent Two farms studied by the ARS in the Reed Wash study area showed a lower leaching percentage of less than 5 percent. With only these two farms available for comparison, however, the leaching percentage was assumed to be 13 percent, the same as estimated by the ARS for the entire valley. Storage An aquifer composed of clay particles and under art,esian pressure, such as the Mancos Shale aquifer in Grand Valley, should have a small storage coefficient. The results of the two pump tests made by the Water and Power Resources Service showed the storage coefficient to be in the magnitude of 10 (0.00001). With a mean aquifer thickness of about 1.5 feet over an area of 5,000 acres and with a porosity of 40 percent, the artesian aquifer could store 3,000 acre-feet of water. The winter flows in Reed Wash show a loss of about 350 acre-feet per month from the ground-water syst,em. It would therefore take less than a year for a volume equal to th,e artesian volume to be released. Because the artesian aquifer is predominantly recharged from canal and lateral seepage, construction of same will shmtl a response at the outlet within a year. To evaluate the loading mechanism in the Reed Wash study area, computer modeling of the salt system was performed using the Water and Power Resources Service saturated chemistry portion of the return flow model. A variety of soil types was analyzed and compared to the field data collected in the wells and drains. These soils included various weathered shale samples taken in the area and compared with unweathered shales. There 19