Properties and variability of soil and trench fill at an arid waste-burial site

Arid sites commonly are assumed to be ideal for long-term isolation of wastes. Information on properties and variability of desert soils is limited, however, and little is known about how the natural site environment is altered by installation of a waste facility. During fall construction of two test trenches next to the waste facility on the Amargosa Desert near Beatty, NV, samples were collected to: (i) characterize physical and hydraulic properties of native soil (upper 5 m) and trench fill, (ii) determine effects of trench construction on selected properties and vertical variability of these properties, and (iii) develop conceptual models of vertical variation within the soil profile and trench fill. Water retention was measured to air dryness (ψ = 2 × 10⁶ cm water suction). The 15 300-cm pressure-plate data were omitted from the analysis because water-activity measurements showed the actual suction values were significantly less than the expected 15 300-cm value (avg. difference = 8550 ± 2460 cm water). Trench construction significantly altered properties and variability of the natural site environment. For example, water content ranged from 0.029 to 0.041 m³ m^-3 for fill vs. 0.030 to 0.095 m³ m^-3 for soil; saturated hydraulic conductivity was ≈ 10^-4 cm s^-1 for fill vs. 10^-2 to ≈ 10^-4 cm s^-1 for soil. Statistical analyses showed that the native soil may be represented by three major horizontal components and the fill by a single component. Under initial conditions, calculated liquid conductivity (K_l) plus isothermal vapor conductivity (K_v) for the upper two soil layers and the trench fill was ≈ 10^-13 cm s^-1, and K_l was ≤ K_v. For the deeper (2–5 m) soil, total conductivity was ≈ 10^-10 cm s^-1, and K_l was >K_v. This study quantitatively describes hydraulic characteristics of a site using data measured across a water-content range that is representative of arid conditions, but is seldom studied.