Engineered covers were constructed during the summer of 1997 in northwest Eagle Flat Basin southeast of El Paso, Texas. We are evaluating two different cover designs in this program: a GCL on asphalt barrier at 1.3-m depth and a capillary barrier at 2.0-m depth. Each design consists of vegetated topsoil underlain by compacted native sediments and an asphalt or a capillary barrier. The two cover designs will be subjected to ambient and enhanced precipitation resulting in four plots (17 x 17 m each). These covers have been vegetated and may also be considered evapotranspiration (ET) covers. If water movement is restricted to the shallow part of either cover, the designs may be considered similar to monolithic covers. The objectives of the engineered cover studies are to compare the performance of the different designs, optimize monitoring of engineered covers, and provide data to validate numerical models of flow and transport. We are conducting detailed monitoring of the various components of the water balance. We are monitoring precipitation, surface runoff, water storage changes, lateral flow on the GCL/asphalt layer, and deep drainage. We installed pan-type lysimeters beneath each plot to monitor drainage. In addition to water balance parameters, we are also monitoring soil water matric potential. Preliminary results indicate that most instrumentation systems are performing well and that water moves through these systems predominantly by piston-type flow. Thus far, there has been no significant movement of water through either cover.

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Environmental Quality