P.O. Box 248294
Wilcox, Walter M.; Solo-Gabriele, Helena M.
Wilcox, Walter
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Solo-Gabriele, Helena M.
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Perlman, M. L.; Prosser, H. C.
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Mayeda, T.
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Hoefling, R.; Kowski, P.; Strauch, G.
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The full article is available via journal subscription or single article purchase. The abstract may be viewed on the website below by selecting the volume number.
Seepage meter tests were performed at 6 sites in the vicinity of the L-31N Levee. These sites were located from 1.5 miles west to 0.2 miles west of Levee 31N within northeast Everglades National Park.
Samples were collected during a period ranging from January 1996 to December 1998. The monitoring network was modified over time with an emphasis placed on sites within the focus area. Early during the sampling program only a few sites were tested on a non-regular basis. Beginning in February 1997, samples were collected on a regular monthly schedule. Furthermore, it is important to note that as the research continued, sites were continually added until the completion of sampling. Overall, 580 samples were collected at 26 different sites, which included the two lakes.
Sample Collection All samples were collected in duplicate using glass scintillation vials. These vials were filled to the top with sample water and sealed with a screw-on top. A layer of parafilm was then wrapped around the vials in order to prevent evaporation. Samples were collected from groundwater, municipal pumping wells, surface water (including lakes), and rainwater. Groundwater samples were collected using a portable pump connected to a 12-volt battery. The intake end of the pump hose was lowered into the well casing while the outflow end was allowed to flow into the scintillation vial for sample collection. For shallow wells, the pump was allowed to draw water from the well for five minutes prior to sample collection to assure that a representative sample was collected. For deep groundwater sites, the well was purged for fifteen minutes. The production well samples were taken directly from a spigot attached to the pumping well. These samples were obtained from either Well 29 or Well 30 at the West Wellfield, depending upon which pump was in operation on the day of sampling. Surface water samples from the Everglades and canal sites were collected by immersing the scintillation vials below the water surface. At the lakes, a submersible pump was used to collect water from ten-foot depth intervals from the approximate center of each lake.
Rainwater collection for isotope analysis provided a somewhat unique problem, as collected rainwater must be shielded from evaporation effects. In order to accomplish this, rainwater collection bottles were filled with a two inch deep layer of mineral oil prior to use. These bottles were fitted with a collection funnel and an air release port. As rain entered the collection apparatus, the buoyant mineral oil floated on top of the collected rain, preventing rainwater interaction with the air and insuring the isotopic integrity of the sample. Once the rainwater was collected, a syringe was used to transfer the rainwater from below the mineral oil layer into the scintillation vials.
Sample Analysis Oxygen-18 analysis included a CO2 equilibration procedure utilizing a syringe as described by Matsui, 1980. This syringe technique was compared with the more traditional CO2 equilibration procedure (Epstein and Mayeda 1953) with good results (Standard deviation 0.18). Samples for deuterium determinations were processed using one of two methods. The first method utilized a uranium furnace as outlined by Bigeleisen et al.1952. The second method involved the use of a chromium furnace (Gehre et al. 1996).
See Water-Resources Investigations Report 00-45066 for complete details of data collection and analysis.
P.O. Box 248294
U.S. Department of the Interior, U.S. Geological Survey
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