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Soil Water Balance Changes in Engineered Soil Surfaces

Westinghouse Hanford Company, P.O. Box 1970, Richland, WA 99352;

S. O. Link

Pacific Northwest Lab., P.O. Box 999, Richland, WA 99352;

W. J. Waugh

Environmental Sciences Lab., U.S. Dep. of Energy Grand Junction Projects Office, P.O. Box 14000, Grand Junction, CO 81503.

^* Corresponding author.

ABSTRACT

Permanent disposal of radioactive waste requires the construction of isolation barriers that minimize both recharge and erosion. Recharge can be prevented by storing precipitation near the surface so that it will be returned to the atmosphere via evapotranspiration. Erosion can be reduced with gravel mulch, but thick gravel layers may increase recharge. Gravel mixed into the surface soil may provide erosion protection without increasing recharge. To compare the effects that erosion control has on infiltration, two lysimeter experiments were conducted to examine the effects of sand and gravel mulches and gravel admixtures, using two precipitation regimens and with or without vegetation. Sand and gravel mulch increased soil-column water storage and decreased evapotranspiration compared with a plain soil surface. Gravel admixtures did not significantly affect the soil water balance compared with plain soil surfaces. Vegetation increased evapotranspiration and decreased soil moisture storage compared with nonvegetated treatments. Irrigation greatly increased evapotranspiration but had little effect on soil water storage. Drainage was detected from sand and gravel-mulch lysimeters, but not from lysimeters with a plain-soil or gravel-admixture surface. Results are significant for isolation barrier designs in arid sites: (i) a nonvegetated gravel-mulch surface eventually will result in recharge, even under low precipitation (160 mm/yr); and (ii) a soil column with a plain-soil or gravel-admixture surface is capable of recycling all water back to the atmosphere, even under high-precipitation (450 mm/yr).

M.R. Sackschewsky, present address: Pacific Northwest Lab., P.O. Box 999, Richland, WA 99352.

C.J. Kemp, present address: IT Hanford Company, Richland, WA 99352.

Received for publication March 25, 1994.