Geology topics

Terry L. Schertz

Publications and source records attributed to Terry L. Schertz.

13 recordsLinked to original sources

USGS2015

Design, analysis, and interpretation of field quality-control data for water-sampling projects

The process of obtaining and analyzing water samples from the environment includes a number of steps that can affect the reported result. The equipment used to collect and filter samples, the bottles used for specific subsamples, any added preservatives, sample storage in the field, and shipment to the laboratory have the potential to affect how accurately samples represent the environment from which they were collected. During the early 1990s, the U.S. Geological Survey implemented policies to include the routine collection of quality-control samples in order to evaluate these effects and to ensure that water-quality data were adequately representing environmental conditions. Since that time, the U.S. Geological Survey Office of Water Quality has provided training in how to design effective field quality-control sampling programs and how to evaluate the resultant quality-control data. This report documents that training material and provides a reference for methods used to analyze quality-control data. Quality-control data are those generated from the collection and analysis of quality-control samples, and are used to estimate the magnitude of errors in the process of obtaining environmental data. “Bias” and “variability” are the terms used in this report for the two types of errors in environmental data that are quantified by the data from quality-control samples. Bias is the systematic error inherent in a method or measurement system. Variability is the random error that occurs in independent measurements. The types of field quality-control samples discussed in this report include blanks, spikes, and replicates. Blanks are samples prepared with water that is intended to be free of measurable constituents that will be analyzed by the laboratory; blanks are used to estimate bias caused by contamination. Spiked samples are modified by addition of specific analytes; spikes are used to determine the performance of analytical methods and to estimate the potential bias due to matrix interference or analyte degradation. Replicate samples are two or more samples that are considered to be essentially identical in composition. Replicates are used to evaluate variability in analytical results. Various sub-types of these quality-control samples are defined and discussed in this report, and guidance is provided for incorporating the proper samples into the design for a project. The concept of inference space is introduced to help determine where and when quality-control samples should be collected as well as which environmental samples are related to a set of quality-control samples. The recommended basic quality-control design incorporates project-specific considerations, such as the objectives and scale of the study, and hydrologic and chemical conditions within the study area. The report provides extensive information about statistical methods used to analyze quality-control data in order to estimate potential bias and variability in environmental data. These methods include construction of confidence intervals on various statistical measures, such as the mean, percentiles and percentages, and standard deviation. The methods are used to compare quality-control results with the larger set of environmental data in order to determine whether the effects of bias and variability might interfere with interpretation of these data. Examples from published reports are presented to illustrate how the methods are applied, how bias and variability are reported, and how the interpretation of environmental data can be qualified based on the quality-control analysis.

Techniques and Methods↗

USGS2006

User's manual for the National Water Information Systemof the U.S. Geological Survey Water-Quality System

This user documentation is designed to be a reference for the Water-Quality System (QWDATA) within the National Water Information System (NWIS). For the new user, the 'Introduction' and 'Getting Started' sections are the recommended places to begin. The experienced user may want to go straight to the details provided in the program section (section 3). Code lists and some miscellaneous reference materials are provided in the Appendices. The last section, 'Tip Sheets,' is a collection of suggestions for accomplishing selected tasks, some of which are basic and some of which are advanced. Where appropriate, these Tip Sheets are referenced in the main text of the documentation.

Open-File Report↗

USGS2005

User's manual for the National Water Information System of the U.S. Geological Survey (USGS), Water-quality System (QWDATA)

Open-File Report↗

USGS1999

Summary and evaluation of pesticides in field blanks collected for the National Water-Quality Assessment Program, 1992-95

Field blanks are quality-control samples used to assess contamination in environmental water samples. Contamination is the unintentional introduction of a chemical (pesticides in this instance) into an environmental water sample from sources such as inadequately cleaned equipment, dirty hands, dust, rain, or fumes. Contamination causes a positive bias in analytical measurements that may need to be considered in the analysis and interpretation of the environmental data. Estimates of pesticide contamination in environmental water samples collected for the National Water-Quality Assessment (NAWQA) Program are used to qualify, where needed, interpretations of the occurrence and distribution of pesticides in the surface and ground waters of the United States. Field blanks collected from 1992 to 1995 as part of the NAWAQA Program were analyzed for 88 pesticides and pesticide metabolites. Of 47 pesticides determined by gas chromatography/mass spectrometry, 23 were detected at least once in 175 surface-water field blanks and 15 were detected at least once in 145 ground-water field blanks. The most frequently detected pesticides in surface-water field blanks were atrazine (in 10.9 percent of blanks), simazine (9.1 percent), and metolachlor (4.6 percent). The most frequently detected pesticides in ground-water field blanks were p,p' -DDE (4.1 percent) and atrazine (2.8 percent). The maximum pesticide concentration detected by gas chromatography/mass spectrometry in a surface-water field blank was 0.120 microgram per liter (µg/L) for pronamide; the maximum concentration detected in a ground-water field blank was 0.013 µg /L for chlorpyrifos and prometon. Of 41 pesticides determined by high-performance liquid chromatography, diuron and 2,4-D were detected once in 109 surface-water field blanks and bromacil, diuron, and fenuron were detected once in 104 ground-water field blanks. Except for a detection of 2,4-D at 0.230 µg /L, the detectable concentrations of these pesticides were less than or equal to 0.020 µg /L. Field blanks showed no evidence of contamination by most pesticides. Of the 88 pesticides for which the field blanks were analyzed, 63 were not detected in field blanks from surface-water sites and 70 were not detected in field blanks from ground-water sites. Therefore, environmental data for the pesticides not detected in field blanks can be interpreted without qualification for contamination. Field blanks did show evidence of contamination by some pesticides. Most of the pesticides detected in field blanks, however, were detected more frequently and at higher concentrations in environmental water samples. Two criteria were used to evaluate the need to consider contamination in water-quality assessments: (1) a ratio of the frequency of pesticide detection in environmental water samples to the frequency of detection in field blanks of 5.0 or less and (2) a ratio of the median concentration detected in environmental water samples to the maximum concentration detected in field blanks of 2.0 or less. These criteria indicate that contamination, for the majority of the pesticide data collected for the NAWQA Program, probably does not need to be considered in the analysis and interpretation of (1) the frequency of pesticide detection or (2) the median concentration of pesticides detected. Contamination must be considered, however, in detection frequency for cispermethrin, pronamide, p,p' -DDE, pebulate, propargite, ethalfluralin, and triallate in surface water and fenuron, benfluralin, pronamide, cis-permethrin, triallate, chlorpyrifos, trifluralin, propanil, p,p' -DDE, bromacil, dacthal, diazinon, and diuron in ground water. Contamination also must be considered in median concentrations detected for pronamide, p,p' -DDE, propargite, napropamide, and triallate in surface water and benfluralin, cis-permethrin, triallate, chlorpyrifos, trifluralin, p,p' -DDE, dacthal, and diazinon in ground water.

Open-File Report↗

USGS1998

Data from selected U.S. Geological Survey National Stream Water Quality Monitoring Networks

A nationally consistent and well-documented collection of water quality and quantity data compiled during the past 30 years for streams and rivers in the United States is now available on CD-ROM and accessible over the World Wide Web. The data include measurements from two U.S. Geological Survey (USGS) national networks for 122 physical, chemical, and biological properties of water collected at 680 monitoring stations from 1962 to 1995, quality assurance information that describes the sample collection agencies, laboratories, analytical methods, and estimates of laboratory measurement error (bias and variance), and information on selected cultural and natural characteristics of the station watersheds. The data are easily accessed via user-supplied software including Web browser, spreadsheet, and word processor, or may be queried and printed according to user-specified criteria using the supplied retrieval software on CD-ROM. The water quality data serve a variety of scientific uses including research and educational applications related to trend detection, flux estimation, investigations of the effects of the natural environment and cultural sources on water quality, and the development of statistical methods for designing efficient monitoring networks and interpreting water resources data.

Water Resources Research↗

USGS1998

A workbook for preparing a district quality- assurance plan for water-quality activities

APPEARS TO BE A REPORT ON HOW TO WRITE REPORTS --THE 'ABSTRACT' THAT FOLLOWS IS JUST THE GENERIC ABSTRACT TO BE USED FOR WATER USE REPORTS: In accordance with guidelines set forth by the Office of Water Quality in the Water Resources Division of the U.S. Geological Survey, a quality-assurance plan has been created for use by the [State name] District in conducting water-quality activities. This quality-assurance plan documents the standards, policies, and procedures used by the [State name] District for activities related to the collection, processing, storage, analysis, and publication of water-quality data. The policies and procedures that are documented in this quality-assurance plan for water-quality activities are meant to complement the District quality-assurance plans for surface-water and ground-water activities and to supplement the [State name] District quality-assurance plan.

Open-File Report↗

USGS1997

User's manual for the National Water Information System of the U.S. Geological Survey; Chapter 2, Water-quality system

Explore the source record for details and available documents.

Open-File Report↗

USGS1991

The computer program estimate trend (ESTREND), a system for the detection of trends in water-quality data

Computerized statistical and graphical procedures were developed for use in U.S. Geological Survey (USGS) investigations of trend in stream water-quality data. These procedures, identified as EStimate TREND (ESTREND), are described in this paper to assist USGS investigators involved in multiple-station studies of water-quality trends. Additional discussion focuses on certain statistical and operational decisions required in multiple-station analysis of trends. The statistical methods used in ESTREND overcome common statistical problems encountered by conventional statistical trend techniques in the analysis of water-quality data. The problems include data that are non-normal and seasonally varying and water-quality records with missing values, 'less-than' (censored) values, and outliers, all of which adversely affect the performance of conventional statistical techniques. Parametric and nonparametric statistical trend tests are used in ESTREND. A nonparametric method, the Seasonal Kendall test, is used for data that have few less-than values or data that have been censored at only one reporting limit. A parametric test for trend involving a maximum likelihood estimation method is used for data that have been censored at multiple reporting limits. The Seasonal Kendall test for uncensored data allows for the removal of flow variability in water-quality data which improves the performance of the statistical trend tests. Menu-driven procedures in ESTREND allow the user to easily retrieve water-quality data, analyze data for trend, and view tabular and graphical results of analyses.

Water-Resources Investigations Report↗

USGS1986

Statistical summary and evaluation of the quality of surface water in the Colorado River basin, 1973-82 water years

Significant upward trends in dissolved-solids concentrations were detected with the Seasonal Kendall Test for trends at three stations in the upper basin during the study period. The increases exceeded 270 milligrams per liter per year at two stations and 165 milligrams per liter per year at the third station. The composition of dissolved constituents in the Colorado River basin changes from predominantly sodium and chloride ions in the upper basin to predominantly calcium and bicarbonate ions in the lower basin. The U.S. Environmental Protection Agency secondary drinking-water regulations of 500 milligrams per liter for total dissolved solids was exceeded 95 percent of the time at each station on the main stem of the Colorado River in the upper basin. In the middle Colorado River basin, the Environmental Protection Agency secondary drinking-water regulations for total dissolved solids was exceeded approximately 95 percent of the time at most stations. Nutrient concentrations in the Colorado River basin generally were low. Only one sample exceeded the level set for nitrate nitrogen, and no other nutrient species exceeded Environmental Protection Agency levels. A general upward trend was detected in organic nitrogen and total nitrogen, but concentrations still remained low. Densities of fecal-col iform and fecal-streptococcal bacteria ranged from less than 1 colony per 100 milliliters to 26,000 colonies per 100 milliliters and 1 colony per 100 milliliters to 50,000 colonies per 100 milliliters, respectively. Fecal-coliform densities exceeded Environmental Protection Agency criteria for public water supply (2,000 colonies per 100 milliliters) at several stations during the study. Biochemical oxygen demand concentrations ranged from 0.00 to 34 milligrams per liter. Only one mean biochemical oxygen demand concentration exceeded 8 milligrams per liter, the upper range of concentration common in moderately contaminated streams. Trace elements and pesticides were detected in many samples throughout the basin. The concentrations generally were low, and maximum contaminant levels rarely were exceeded.

Texas↗

USGS1985

Trend analysis of weekly acid rain data, 1978-83

There are 19 stations in the National Atmospheric Deposition Program which operated over the period 1978-83 and were subsequently incorporated into the National Trends Network in 1983. The precipitation chemistry data for these stations for this period were analyzed for trend, spatial correlation, seasonality, and relationship to precipitation volume. The intent of the analysis was to provide insights on the sources of variation in precipitation chemistry and to attempt to ascertain what statistical procedures may be most useful for ongoing analysis of the National Trends Network data. The Seasonal Kendall test was used for detection of trends in raw concentrations of dissolved constituents, pH and specific conductance, and residuals of these parameters from regression analysis. Forty-one percent of the trends detected in the raw concentrations were downtrends, 4 percent were uptrends, and 55 percent showed no trends at a = 0.2. At a more restrictive significance level of a = 0.05, 24 percent of the trends detected were downtrends, 2 percent were uptrends, and 74 percent showed no trends. The two constituents of greatest interest in terms of human generated emissions and environmental effects, sulfate and nitrate, showed only downtrends, and sulfate showed the largest decreases in concentration per year of all the ions tested.

Water-Resources Investigations Report↗

USGS1984

Computation and use of volume-weighted-average concentrations to determine long-term variations of selected water-quality constituents in lakes and reservoirs

A computer program using the Statistical Analysis System has been developed to perform the arithmetic calculations and regression analyses to determine volume-weighted-average concentrations of selected water-quality constituents in lakes and reservoirs. The program has been used in Texas to show decreasing trends in dissolved-solids and total-phosphorus concentrations in Lake Arlington after the discharge of sewage effluent into the reservoir was stopped. The program also was used to show that the August 1978 and October 1981 floods on the Brazos River greatly decreased the volume-weighted-average concentrations of selected constituents in Hubbard Creek Reservoir and Possum Kingdom Lake.

Water-Resources Investigations Report↗

USGS1984

Effects of October 1981 flood on the quantity and quality of water in selected streams and reservoirs in the Brazos River basin, Texas

The storm that moved across north-central Texas during October 11-13, 1981, produced intense rainfall along a line extending from east of Abilene, Texas to Breckenridge, Texas to north of Mineral Wells, Texas. Rainfall in excess of 20 inches was recorded near Clyde. Texas and in several locations near Breckenridge, Texas. The large quantity of rainfall in the Hubbard Creek drainage basin caused the water level in Hubbard Creek Reservoir to rise by 13.33f feet and the storage contents of the reservoir to increase from 233,000 to 441,000 acre-feet during 56 hours. Large quantities of inflow into Possum Kingdom Lake from the Brazos River, Big Cedar Creek basin, and ungaged inflow from the Big Caddo Creek basin, and Rock Creek basin caused the water level to rise 7.54 feet and the storage contents to increase from 505,000 to 653,000 acre-feet during 48 hours.

Water-Resources Investigations Report↗

USGS1984

Effects of storm-water runoff on water quality of the Edwards Aquifer near Austin, Texas

Analyses of samples collected from Barton Springs at approximately weekly Intervals and from Barton Creek and five wells in the Austin area during selected storm-runoff periods generally show that recharge during storm runoff resulted in significant temporal and area! variations in the quality of ground water in the recharge zone of the Edwards aquifer. Recharge during storm runoff resulted in significant increases of bacterial densities in the ground water. Densities of fecal coliform bacteria in samples collected from Barton Springs, the major point of ground-water discharge, ranged from less than 1 colony per 100 milliliters during dry weather in November 1981 and January and August 1982 to 6,100 colonies per 100 milliliters during a storm in May 1982. Densities of fecal streptococcal bacteria ranged from 1 colony per 100 miniliters during dry weather in December 1981 to 11,000 colonies per 100 miniliters during a storm in May 1982. Recharge during storm runoff resulted in significant decreases in the specific conductance and the concentration of total nitrate nitrogen in the ground water. Specific-conductance values of samples from Barton Springs ranged from 438 micromhos per centimeter at 25° Celsius after a storm in October 1981 to 682 micromhos after a relatively long period of deficient rainfall in September 1982. The specific-conductance values and, thus, the mineralization of the ground water in the recharge zone generally were inversely related to the quantity of recharge. Nitrate nitrogen was the most prevalent form of nitrogen in the ground water. Concentrations of total nitrate nitrogen in samples from Barton Springs ranged from 0.51 milligram per liter after a storm in October 1981 to 1.6 milligrams per liter during dry weather in February and September 1982. Although the values of these and other properties or constituents in ground water varied temporally and areally, available data indicate that the values of most of the major and minor elements in ground water in the recharge zone of the Edwards aquifer were significantly less than the primary maximum or secondary maximum contaminant levels set by the U.S. Environmental Protection Agency for public water systems. Bacteriological data for Barton Springs and selected wells indicate that the ground water in the aquifer is susceptible to bacterial pollution, especially during storm runoff. The water may require disinfection if used for drinking or culinary purposes.

Water-Resources Investigations Report↗