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lexan pipe
Core sample acquisition and processing. One hundred twenty-two
continuous meters of rock was cored with conventional rotary methods
over a 2-week period in February 1995. Cores (1.5 m long, 6.11
cm in diameter) were retrieved by wireline. Groundwater pumped
from the downgradient Sacramento Valley regional aquifer was amended
with sodium hypochlorite to a concentration of 60 mg liter?1 and
used as drilling fluid. Drilling fluid was continually discharged
(not recirculated) during coring. Nineteen of the seventy-six
cores required to advance the hole past the surface casing to
total depth were processed for microbiological analyses (every
fourth core). Sixteen of these cores could be closely matched
in depth with groundwater samples obtained by straddle packer
sampling (described below) (Fig. 2). No groundwater samples could
be taken to compare with three cores taken between 102.7 and 122.0
m because of the length of the straddle packer sampler and accumulated
debris in the corehole. Control and assessment of contamination
introduced during coring were consistent with procedures reviewed
by Fredrickson and Phelps (11) and Griffin et al. (15), including
the use of carboxylated, fluorescent microspheres (0.9-?m diameter;
Polysciences, Inc., Warrington, Pa.) (38) and soluble perfluorocarbon
tracers (30) to assess drilling fluid intrusion. New drilling
rods were purchased and dedicated to this project. All drill steel
was steam cleaned prior to insertion into the corehole, and the
inner core barrel was similarly cleaned prior to each trip downhole.
The inner barrel was handled only with clean cotton gloves by
researchers and drillers, and no lubricant was used on the pipe
threads. For microbiological cores, a Lexan liner that had been
cleaned with 10% bleach solution, rinsed with distilled water,
and air dried was placed inside the inner core barrel.
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