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<br />a <br /> <br />.. <br />~ <br />-~- <br />~ <br /> <br />FY 1972. Based on information obtained from this test, exploratory and <br />ovservation wells were drilled to acquire additional knowledge about <br />subsurface water conditions. In FY 1973, twelve exploratory wells were <br />drilled along both sides of the river in unconsolidated riverfill material. <br />Perforated casings were installed so that water quality samples could be <br />obtained and the water table elevation and brine interface observed during <br />a subsequent well pumping program. Also during FY 1973, five locations <br />on the east side of the river were core drilled into the consolidated <br />residual rocks of the valley floor at depths ranging from 74 to 200 feet. <br />These locations are shown in Figure 6. <br /> <br />. <br /> <br />Data obtained during the studies indicate that the shallow overburden of <br />alluvial deposits along the flood plain of the river covers a brecciated <br />gypsiferous formation which is rich in sodium chloride salt. This for- <br />mat ion is believed to be the residual cap of a collapsing salt anticline, <br />,. - . <br /> <br />or dome, which underlies the valley. Saturated brine lies within a few <br />feet of the sruface along the east side of the river and plunges to a <br />depth of about 100 feet about a mile to the west of the river. A <br />layer of relatively fresh ground water overlies the brine on the west <br />side of the stream. <br /> <br />The alluvial materials are shallow on the sides of the valley and in- <br />crease to a depth of from 100 to 150 feet near the middle. Consisting <br />of sand and silt near the surface grading to coarser gravel near the bottom, <br />these deposits have replaced salts which have been leached from the <br />underlying breccia, probably by ground water moving along the fresh <br />water-brine interface and surfacing to the river near mid-valley. Figure <br />6 also shows the area along the stream where brine is found on the surface. <br />.The western margin of the area represents the surfacing line of the brine, <br />and the remainder is essentially a stable impoundment. <br /> <br />In FY 1974, pump tests were conducted on a well drilled to the west of <br />the river through 100 feet of lensatic river deposits and 200 feet of <br />the brecciated gypsum cap of the anticline. These involved two brine- <br />producing aquifers: a zone of sand, silt and gravel deposits from 8 to <br />97 feet deep and a zone of fractured gypsum breccia from 230 to 250 feet <br />oor5Jl <br />