Abstract

As part of a multidisciplinary U.S. Geological Survey study of water resources in Upper Kittitas County, Washington, chemical and isotopic data were collected from groundwater, surface-water, and atmospheric precipitation sites from 2010 to 2012. These data are documented here so that interested parties can quickly and easily find those chemical and isotopic data related to this study. The locations of the samples are shown on an interactive map of the study area. This report is dynamic; additional data will be added to it as they become available.

Introduction

The U.S. Geological Survey (USGS), the Washington State Department of Ecology, and Kittitas County are cooperating in a study to (1) define the hydrogeology of Upper Kittitas County, (2) provide information regarding groundwater occurrence and availability, (3) describe the potential extent of groundwater and surface-water continuity in the area, and (4) determine the extent of potential impacts to surface and groundwater resources resulting from groundwater withdrawals from wells. This report presents chemical and isotopic data from groundwater, stream, and precipitation samples collected during USGS field visits in the Upper Kittitas County study area (fig. 1) between 2010 and 2012. The chemical and isotopic character of water can be used to develop an understanding of the origin, direction of movement, and rate of movement of water.

Chemicals of interest are selected dissolved gases and a suite of inorganic constituents that are commonly present in natural waters. Natural waters obtain dissolved gases and inorganic constituents as a result of interactions with gases, fluids, soils, and rocks. Dissolved gases (see Glossary) such as nitrogen (N₂), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used to characterize recharge conditions such as recharge temperature; dissolved oxygen (O₂) and methane (CH₄) provide information about the oxidation-reduction state; and dissolved sulfur hexafluoride (SF₆) can be used to estimate the residence time of groundwater (“age dating”). Inorganic constituents include major rock-forming elements that are commonly found in groundwater (for example, calcium and sodium) as well as other naturally occurring constituents that are typically detected in groundwater at trace concentrations (for example, arsenic and nickel). The inorganic chemistry of groundwater reflects the soils and rocks through which the groundwater has passed, and to some extent the amount of time that groundwater has resided in those geologic compartments.

Isotopes are atoms of an element that are distinguished by having different numbers of neutrons. Isotopes can be stable or radioactive (decaying or changing from one isotope to another over time). The isotopes of interest for this project include:

• stable isotopes of water (¹⁶O and ¹⁸O, expressed as δ¹⁸O, and ¹H and ²H, expressed as δ²H);
• tritium (radioactive ³H) in water;
• stable isotopes of helium (³He and ⁴He, expressed as δ³He) dissolved in water;
• the common stable isotope of carbon, ¹³C (expressed as δ¹³C) of dissolved inorganic carbon; and
• the common radioactive isotope of carbon, ¹⁴C (expressed as percent modern carbon, or PMC) in dissolved inorganic carbon.

As water moves through atmospheric, surface, and subsurface environments, the ratios of the stable isotopes of water can change, imparting different isotopic signatures to those various waters. Thus, water provenance often can be identified on the basis of the stable isotopic composition of the water. The other common isotope of water, tritium, serves a different purpose in groundwater studies. Tritium decays to ³He. Water recharging aquifers contains tritium derived from atmospheric sources. Time elapses as groundwater moves along flowpaths in aquifers, and as time passes, tritium decays. Thus, tritium concentrations can be used to characterize general timeframes of groundwater age. The decay of tritium to ³He allows hydrologists to combine measurements of tritium and ³He to date groundwater with greater clarity than can be done solely with tritium. Finally, because groundwater contains dissolved inorganic carbon, the radioactive decay of ¹⁴C allows hydrologists to use carbon isotopes to place constraints on groundwater age.

Sample Collection and Analysis

Consistent sample collection and processing protocols were used (U.S. Geological Survey, variously dated). Groundwater samples were collected in Upper Kittitas County primarily from domestic wells, although other well types, such as irrigation wells, also were included. Groundwater samples for stable isotopes of water and tritium were collected in-line (that is, not exposed to the atmosphere) from existing plumbing. Groundwater samples for other chemical and isotopic analyses were collected in-line, upgradient from pressure tanks, and upgradient from any treatment systems such as water softeners. Stream samples were collected as grab (single-point) samples from the centroid (center) of flow in well-mixed streams. For springs, grab samples were collected as close as possible to the spring orifice or spring discharge zone. Stagnant springwater was avoided where possible; five samples from springs were collected from stagnant zones and these five sets of results are identified with comments noting this limitation in appendix A. Precipitation samples were collected as cumulative point samples designed to avoid evaporation (Friedman and others, 1992).

Samples for inorganic constituents were analyzed at the USGS National Water Quality Laboratory in Lakewood, Colorado. Trace elements in filtered water were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and collision-reaction cell inductively coupled plasma-mass spectrometry (cICP-MS), as described by Fishman and Friedman (1989), Garbarino (1999), and Garbarino and others (2006). Major ions, silica, and minor elements in filtered water were analyzed as follows: most anions, by ion chromatography (Fishman and Friedman, 1989; Fishman, 1993); most cations, silica, and minor elements, by inductively coupled plasma-atomic emission spectrometry (Fishman and Friedman, 1989; Fishman, 1993); fluoride, by ion selective electrode (Fishman and Friedman, 1989); and potassium, by inductively coupled plasma-atomic emission spectrometry (Clesceri and others, 1998).

Samples for major dissolved gases (N₂, O₂, Ar, CH₄, and carbon dioxide [CO₂]) were analyzed by the USGS Chlorofluorocarbon Laboratory in Reston, Virginia, by gas chromatography with flame ionization detection and gas chromatography with thermal conductivity detection; these methods are described in Busenberg and others (1998) and U.S. Geological Survey (2012). Samples for SF₆ were analyzed by the USGS Chlorofluorocarbon Laboratory by purge and trap gas chromatography with an electron capture detector, as described in Busenberg and Plummer (2000) and U.S. Geological Survey (2012). SF₆ data were scaled to the National Oceanic and Atmospheric Administration 2000 scale of atmospheric SF₆ mixing ratios (National Oceanic and Atmospheric Administration, 2008). Noble gases (He, Ne, Ar, Kr, Xe) were analyzed by mass spectrometry at Lamont-Doherty Earth Observatory, Palisades, New York (Lamont-Doherty Earth Observatory, 2013).

Stable isotopes of hydrogen (H) and oxygen (O) in water (H₂O) were analyzed by mass spectrometry at the USGS Reston Stable Isotope Laboratory (U.S. Geological Survey, 2013). Water samples were analyzed for δ¹⁸O and δ²H by CO₂ and hydrogen (H₂) equilibration, respectively (McCrea, 1950; Coplen and others, 1991), and the data were normalized to the scale defined by Vienna Standard Mean Ocean Water (VSMOW) (δ¹⁸O = 0.00‰, δ²H = 0.0‰) and Standard Light Antarctic Precipitation (SLAP) (δ¹⁸O = –55.50‰, δ²H = –428.0‰) (Gonfiantini, 1978; Coplen, 1988).

Samples for tritium were analyzed by electrolytic enrichment and liquid scintillation (Thatcher and others, 1977) at the USGS Tritium Laboratory, Menlo Park, California.

Samples for δ³He were analyzed by mass spectrometry at Lamont-Doherty Earth Observatory, Palisades, New York (Plummer and Mullin, 1997).

Samples for δ¹³C and ¹⁴C were analyzed by mass spectrometry and by accelerator mass spectrometry, respectively, at the National Ocean Sciences Accelerator Mass Spectrometry Facility at the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts.

Chemical and Isotopic Data

Chemical and isotopic data are available in appendix A of this report as Microsoft© Excel 2007 (.xlsx) files and as comma-delimited files (.csv). Locations of these sites are shown on an interactive map of the study area available at http://wa.water.usgs.gov/projects/kittitasgw/sites.htm. This interactive map can be navigated by using the buttons in the upper-left corner, or by clicking the mouse to pan and double-clicking the mouse to zoom. When the cursor is placed over a sampling site, a message box appears that displays the well number and provides a link to data for that site. The link leads to the USGS National Water Information System, where additional information such as well construction data or water level data can be found. Additional data will be added as they become available.

References Cited

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First posted March 7, 2013