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Bulldo,¢ Mine Tailings Ponds Evaluation <br />location. The depth of the unsaturated zone was estimated from the hand augured holes and <br />probe depth locations chosen to provide at least three or four oxygen measurements above the <br />saturated zone. Pore gas was measured by pulling gas samples from the pore space with a <br />vacuum pump and through a portable oxygen meter. The first site chosen at the Lower Pond for <br />oxygen profile and flux measurements, labeled LPO,(A) on Figure 3.2, was abandoned afrer it <br />was determined that the tailings were too fine grained and neaz saturation for evacuation of gas <br />from the pore spaces. The measurements were then made at a second location, labeled LPOz(B) <br />on Figure 3.2, where the tailings were drier and more coazse. Tailings samples were obtained by <br />hand augering at each of the probe locations, for measurement of the tailings moisture profile in <br />the unsaturated zone. A Sand Cone Density Test (ASTM D1556) was also performed at each <br />location, to estimate the bulk tailings density. This measurement provides information needed to <br />evaluation of oxygen diffusivity and sulfate production if oxygen consumption is observed. <br />Oxygen flux measurements were made immediately adjacent to the oxygen probe measurement <br />locations. Oxygen flux measurements were made using a method similar to that described by <br />Nicholson et al. (1995). The flux measurement sites were prepazed by excavating through the <br />cover soil and below the depth of significant root penetration (typically about six inches) to <br />reduce the effect of oxygen consumption from decomposition of organic material. The tailings <br />surface was then leveled and athin-walled cylinder, with a diameter of approximately nine <br />inches (20 cm) and capped on the top end, was inserted into the tailings, leaving a small, air- <br />filled head space above the tailings surface. An oxygen sensor was installed in the sealed head <br />space and the decay in oxygen concentration was measured and recorded to determine the <br />oxygen flux into the tailings over periods of 17 hours to several days. <br />Tailings pore water samples were obtained from temporary piezometers installed in the Upper <br />Tailings Pond. The temporary piezometers consisted of 2-inch diameter slotted PVC pipe <br />wrapped in a filter cloth and installed in holes UPTH-la, UPTH-16, and UPTH-2. These drill <br />holes were completed with ahand-auger at the approximate locations shown on Figure 3.1. The <br />temporary piezometers were lefr open overnight and backfilled afrer sampling of pore waters. <br />Grab samples of soil for attenuation testing were excavated by hand from near-surface soils <br />below the impoundments and cut-banks immediately adjacent to [lte impoundments. Attenuation <br />Nomesmke :Llinmg Company ShepGerd ,Ili/fer, lnc. <br />p.ir-~inmdiy~R..p~ 9 April l~t. 1997 <br />