Seismic Reflection Survey At Douglas County Landfill, Nevada

In October 1992, a shallow high-resolution seismic reflection survey was performed at the Douglas County<br>Landfill near Gardnerville, Nevada as part of the site investigation (SI). The closed portion of the landfill<br>operated between 1963 and 1987. Presently five (5) monitor wells exist, two of which, including the<br>production well, are contaminated with solvents.<br>The site is located within the Basin and Range Province in the Carson Valley, a graben bounded by northsouth<br>trending mountains. The site is overlain by Tertiary sedimentary rocks and sediments of lacustrine and<br>fluvial origin. North-south trending normal faults are predominant, with a set of less prominent roughly eastwest<br>trending faults that present additional possible conduits for contaminant transport. The monitor wells<br>are typically 360 feet deep with the static water level about 200 feet beneath the surface. The stratigraphy,<br>according to the well logs, consists of older alluvium overlain by younger alluvium. Within the older alluvium<br>are thin flows of basalt and volcanic tuff. The older alluvium is layered sand, silty gravel, sandy silt, and silty<br>sand that is partially consolidated. The younger alluvium is unsaturated and consists of unconsolidated<br>coarse sand and gravel.