Scientific Investigations Report 2008–5071
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5071
Conceptual Model of Hydrologic and Thermal Conditions
All available monitoring and pumping wells in the study area were inventoried by the USGS and their locations were determined using a hand-held GPS unit. Altitudes of wells were based on a survey conducted by Horton Dennis & Associates, Inc. in 1998 (S. Dilly, written commun., 2007) and spot-checked and expanded on by PUD surveyors. Surveyed altitudes were reported to the nearest 0.01 ft and, for the purpose of this study, were considered accurate to ±0.05 ft. Water levels were measured using an electrical or steel tape that was read to the nearest 0.01 ft. Water levels were considered accurate to ±0.1 ft. Vertical temperature profiles in wells were measured using a recently verified electrical tape and water temperatures were read to the nearest 0.1°C. The time of all measurements was recorded in local time, which is either Pacific Standard Time or Pacific Daylight Time, depending on the time of year. Continuous water levels measured during several hours on July 18, 2007, were made using electrical and steel tapes that had been verified to give the same results. The times of the continuous water-level measurements were read from cellular phones that were verified to match the times recorded by the continuous monitoring network run by the PUD within 1 minute.
All ground-water samples, with the exception of the sample collected from well TH4, were collected following protocols described by Wilde (1999) in order to ensure representative samples of ground water. Clean-sampling protocols, as described by Wilde and others (2002), were used to process the samples. Sampling equipment consisted of polyethylene tubing with Teflon® or stainless-steel fittings that were attached to a faucet at the well head. The tubing was then connected directly to a flow chamber to monitor physical properties (water temperature, pH, specific conductance, and concentrations of dissolved oxygen) and through a splitter to provide either raw or filtered water samples. Existing pumps were active in all wells that were sampled except for well TH4. An equivalent volume of purge water had already been pumped during the previous 24 hours, therefore, the sampling equipment was flushed with ground water and samples were collected after ensuring that physical properties measured in the flow chamber had stabilized. All lines and processing equipment that came in contact with the sample water after the point of attachment to the well discharge structure were composed of Teflon®, polyethylene, or stainless steel. Ground-water samples were pumped directly through a line or a filtration cartridge into sample bottles and samples were preserved or stored on ice and shipped for analysis to the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado and Pacific Analytical Laboratory in Corvallis, Oregon. Because there was no pump in well TH4, a 2-L Kemmerer© sampler was lowered into the well to obtain a grab sample of water from the upper 10 ft of the perforated interval. The sampler was retrieved from the well and water was then pumped from the Kemmerer© sampler with a peristaltic pump and processed like all other samples. The Columbia River sample was collected with the Kemmerer© bottle near the location labeled RIV in figure 2. The sampler was lowered through the water column to about 3 ft above the riverbed before the sampling mechanism was triggered. Water from the Kemmerer© bottle was withdrawn from the sampler using a peristaltic pump and processed like the ground-water samples. Aseptic techniques were used in the collection of samples for bacterial enumeration.
Laboratory analyses were performed for common ions and bacteria enumeration. Water samples for the analysis of nitrate plus nitrite were received at the NWQL and stored at less than 4°C prior to analysis. Samples were analyzed for nitrate plus nitrite using a cadmium reduction-diazotization colorimetric method described by Fishman (1993). Samples were analyzed for chloride and sulfate using ion chromatography (Fishman and Friedman, 1989); calcium, magnesium, sodium, and iron were analyzed using inductively coupled plasma (Fishman, 1993); and potassium was analyzed using flame atomic absorption (Fishman and Friedman, 1989). Manganese was analyzed using inductively coupled plasma detected with a mass spectrometer (ICP/MS) (Faires, 1993). Variability in reported concentrations due to variability in laboratory analytical processes was expected to be less than 2 percent.
Bacterial enumerations were done using fluorescent counting techniques (Hurst and others, 1997). Bacterial-enumeration samples were sent to Pacific Analytical Laboratory in Corvallis, Oregon, where enumerations were conducted using Moleculer Probes BacLight viability and counting stains with a fluorescent microscope. The 95-percent confidence interval for enumerations provided by the laboratory was about 10 percent.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2008/5071
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