viding lake access, storage facilities, and security. The authors also acknowledge the following U.S. Geological Survey staff for their substantial contributions: Tim Oden for project management through June 2008 and for overall technical guidance throughout the study; Jennifer Graham for guidance in sampling design and limnology; Richard Kiesling and William Asquith for developing the initial "pump-and-switch" sampling system design for continuous, real-time water-quality monitoring; Ken VanZandt and Jason Ramage for gage house and platform design and construction; and Jeff East for technical direction and programming during the development and testing of the new data-collection and transmission system. Finally, because of unique challenges involving the application of new technology and the labor-intensive nature of the study, essentially everyone in the Gulf Coast Program Office of the U.S. Geological Survey Texas Water Science Center deserves recognition for contributing to the success of the study.

Front cover: Background, Photograph showing a mobile, multi-depth continuous water-quality monitoring station, Lake Houston, January 2010. Top, Photograph showing field personnel servicing a water-quality-monitoring sonde that is attached by a data cable to an automated reel, part of a mobile, multi-depth continuous water-quality monitoring station, Lake Houston, May 2008. Back cover, Photograph showing field personnel collecting water from Lake Houston using a peristaltic pump (pump not shown) through Teflon-lined tubing into various water-quality-sample bottles, Lake Houston, April 2006.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C=(°F-32)/1.8Vertical coordinate information is referenced to the World Geodetic System of 1984 (WGS 84).Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).Elevation, as used in this report, refers to distance above the vertical datum.Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C).Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (µg/L). AbstractIn cooperation with the North Plains Groundwater Conservation District (NPGCD), the U.S. Geological Survey collected and analyzed water-quality samples at 30 groundwater monitor wells in the NPGCD in the Texas Panhandle. All of the wells were completed in the Ogallala Formation of the central High Plains aquifer. Samples from each well were collected during February-March 2012 and in March 2013. Depth to groundwater in feet below land surface was measured at each well before sampling to determine the water-quality sampling depths. Water-quality samples were analyzed for physical properties, major ions, nutrients, and trace metals, and 6 of the 30 samples were analyzed for pesticides. There was a strong relation between specific conductance and dissolved solids as evidenced by a coefficient of determination (R 2 ) value of 0.98. The dissolved-solids concentration in water from five wells exceeded the secondary drinking-water standard of 500 milligrams per liter set by the U.S. Environmental Protection Agency. Water from 3 of these 5 wells was near the north central part of the NPGCD. Nitrate values exceeded the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter in 2 of the 30 wells. A sodium-adsorption ratio of 23.4 was measured in the sample collected from well Da-3589 in Dallam County, with the next largest sodium-adsorption ratio measured in the sample collected from well Da-3588 (12.5), also in Dallum County. The sodium-adsorption ratios measured in all other samples were less than 10. The groundwater was generally a mixed cation-bicarbonate plus carbonate type. Twentythree trace elements were analyzed, and no concentrations exceeded the secondary drinking-water standard or maximum contaminant level set by the U.S. Environmental Protection Agency for water supplies. In 2012, 6 of the 30 wells were sampled for commonly used pesticides. Atrazine and its degradate 2-Chloro-4-isopropylamino-6-amino-s-triazine were detected in two samples. Tebuthiuron was detected in one sample at a detection level below the reporting level but above the long-term method detection lev...