Groundwater Sampling Devices
13
onto surfaces. Initial concentrations were approximately 500 g/L for lindane,
and 3045 g/L for aldrin and dieldrin.
Two VOC solutions were used in this study. In the low-level study, the test
solution contained trans-1,2-dichloroethylene (TDCE), benzene (BENZ), tri-
chloroethylene (TCE), o-dichlorobenzene (ODCB), m-xylene (M-XYL), and
tetrachloroethylene (PCE). Initial concentrations ranged from 100 g/L to 700
g/L. In the high-level study, initial concentrations of BENZ, M-XYL, and PCE
were approximately 130 mg/L.
For the metals study, the test solution was prepared by adding 37 mL of
certified (GFS Chemical) metal standards (1,000 mg/L) directly to the standpipe.
The solution was then mixed by recirculating it several times. Cd and Pb were in
solution as cations, while Cr (as dichromate) and As (as arsenite or arsenate)
were anions. Initial concentrations in the standpipe were approximately 70 g/L
for Pb, 50 g/L for As and Cr, and 30 g/L for Cd.
All the standpipes were filled with the test solution to within ~45 inches of
the top. This allowed room to place the test device in the standpipe without
spilling the test solution. During the initial equilibration period (prior to testing)
and while the PDB samplers were left in the standpipe, the top of the standpipe
was covered with a thin plastic disc that was held in place with duct tape and
covered tightly with aluminum foil to reduce losses caused by volatilization from
the standpipe.
TCE-contaminated monitoring well
The groundwater monitoring well used in this study had four-inch-diameter
PVC casing and screen. The well is screened from 126.5 to 136.5 feet; the static
water level was 125 feet. Concentrations of TCE in this well were around 130
mg/L. A dedicated Grundfos pump with Teflon-lined polyethylene tubing was
used to retrieve the control samples from this well (pump intake was at a depth of
133 feet). Samples were taken using low-flow sampling (Puls and Barcelona
1995, USEPA 1996) at a flow rate of approximately 200 mL/min. No drawdown
of the water level has been observed in this well at this rate of pumping.
Experimental design
For the standpipe experiments, the entry port for each sampling device was
placed at the same depth as the sampling port on the standpipe. For the field
study, the placement of the samplers in the well was matched in a similar fashion
with the entry port of the groundwater pump. Each sampler went through the
complete series of tests before the next type of sampler was tested. For the Kabis,
Previous Page
