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At least 1,117 records · Page 62Linked to original sources
USGS2007

Surface-Water Quality-Assurance Plan for the USGS Wisconsin Water Science Center

This surface-water quality-assurance plan documents the standards, policies, and procedures used by the Wisconsin Water Science Center of the U.S. Geological Survey, Water Resources Discipline, for activities related to the collection, processing, storage, analysis, management, and publication of surface-water data. The roles and responsibilities of Water Science Center personnel in following these policies and procedures including those related to safety and training are presented.

Open-File Report↗
USGS1955

Ground water and the law - some selected annotated references

The strictly "legal" literature of ground-water use and control -except for a few essays in certain of the law reviews- is quite limited. A larger and more pointful source of information and analysis is the legal-scientific writings of the geologists, hydrologists, meteorologists, engineers and others. When new statutes are to be drafted by legislatures, and new decisions are to be made by courts on this subject, such literature may well be of far greater importance than legal precedents unfounded on scientific fact. This may be demonstrated by the character and scope of the legal-scientific literature of ground water, just one branch of water science, but one which is of major importance to any thoughtful consideration of water use and control.

Open-File Report↗
USGS2015

A quarter century of research on the Colorado Plateau: A compilation of the Colorado Plateau Biennial Conference Proceedings for 1993-2015

This Open-File Report is a compilation of the work published in the Colorado Plateau Biennial Conference book series over the span of the past nearly quarter century (conferences held between 1991–2011). The primary focus of the conferences has been to work toward integrating new science findings into management of the region’s natural and cultural resources. This conference and book series has begun a tradition of cooperation and community, bridging cultural, social, and biophysical research interests and addressing the needs of scientists and land managers working in a complex geographic area. We include here the abstracts for each of the 11 books in the series, as well as links to files with comprehensive literature citations and author listings. The goal of this compilation is to encourage further cooperation and communication on research and management issues of the Colorado Plateau among researchers, land managers, Native American tribes, and the public.

Open-File Report↗
USGS2024

California community Earth Models for Seismic Hazard Assessments workshop report

The California Community Earth Models for Seismic Hazard Assessments Workshop (https://www.scec.org/workshops/2024/california-community-models) was held online March 4–5, 2024, with more than 200 participants over the two days. In this report, we provide a summary of the key points from the presentations and discussions. We highlight three use cases that drive the development of community Earth models, present an inventory of existing community Earth models in California, summarize a few techniques for integrating and merging models, discuss potential connections with the Cascadia Region Earthquake Science Center, and discuss what “community” means in community Earth models.

California↗
USGS2014

Riparian restoration framework for the Upper Gila River, Arizona

This technical report summarizes the methods and results of a comprehensive riparian restoration planning effort for the Gila Valley Restoration Planning Area, an approximately 53-mile portion of the upper Gila River in Arizona (Figure 1-1). This planning effort has developed a Restoration Framework intended to deliver science-based guidance on suitable riparian restoration actions within the ecologically sensitive river corridor. The framework development was conducted by a restoration science team, led by Stillwater Sciences with contributions from researchers at the Desert Botanical Garden (DBG), Northern Arizona University (NAU), University of California at Santa Barbara (UCSB), and U.S. Geological Survey (USGS). All work was coordinated by the Gila Watershed Partnership of Arizona (GWP), whose broader Upper Gila River Project Area is depicted in Figure 1-1, with funding from the Walton Family Foundation’s Freshwater Initiative Program.

Arizona↗
USGS2023

Ecological effects of pinyon-juniper removal in the Western United States—A synthesis of scientific research, January 2014–March 2021

Executive Summary Increasing density of pinyon ( Pinus spp. ) and juniper ( Juniperus spp. ) woodlands (hereinafter “pinyon-juniper”), as well as expansion of these woodlands into adjacent shrublands and grasslands, has altered ecosystem function and wildlife habitat across large areas of the interior western United States. Although there are many natural and human-caused drivers of woodland infilling and expansion, restoration of sagebrush ( Artemisia spp. ) habitat through removal of pinyon-juniper is considered an urgent management objective in many locations, particularly in support of sagebrush-dependent wildlife species of conservation concern. In December 2020, the Bureau of Land Management (BLM) established the Pinyon-Juniper Management Categorical Exclusion (PJCX) to expedite the regulatory process for pinyon-juniper removal projects on public lands, largely intended to benefit mule deer ( Odocoileus hemionus ) and greater sage-grouse ( Centrocercus urophasianus ) habitats. During final preparation of this report, the BLM discontinued use of the PJCX (as of November, 2022), but the pinyon-juniper tree removal techniques assessed in this report are commonly used and understanding their effects remains relevant to land use planning. To address areas of uncertainty relative to potential ecological effects of the PJCX, we conducted a review of the peer-reviewed science literature to better understand the likely responses of vegetation, environmental (for example, soils), and wildlife variables to specific tree removal techniques permitted by the PJCX. In brief, the PJCX permitted removal of trees by either manual cutting, mechanical cutting, or mastication; allowed certain methods to redistribute or remove resulting tree biomass after treatment; and prohibited broadcast burning, roadbuilding, removal of old-growth, and seeding of non-native species. Specifically, we conducted our review to address the following questions: How will PJCX removal techniques affect plant communities, soils, and abiotic resources? How do these pinyon-juniper removal techniques affect wildlife communities, including both woodland- and sagebrush-dependent species? What are the potential ecological implications of different pinyon-juniper removal treatment types and implementation strategies (for example, treatment sizes) over time? What are the most important gaps in our scientific understanding of how treatments might affect targeted ecosystems over space and time (for example, potential effects of climate change)? To answer these questions, we considered studies related to pinyon-juniper ecosystems, focusing on research that occurred over a large portion of the interior western United States that is the primary focus of the PJCX. We also focused on papers published from 2014 onward, to avoid excessive overlap with other recent reviews on pinyon-juniper management effects. Using strict criteria, including only considering research that tested responses for statistical significance, we identified 48 papers that primarily examined treatment effects on vegetation and other environmental variables (1,709 responses), and 11 papers that addressed effects on wildlife (132 responses). Responses to the PJCX-permitted treatments were summarized as either positive (that is, a significant increase), negative (that is, a significant decrease), or non-significant (that is, no significant difference). Responses were assigned to categories (for example, Native Annual Grass/Forb Abundance) and hierarchical treatment levels. We found that there were large proportions of non-significant responses among all categories combined, with roughly half or more of all responses non-significant (48 percent for wildlife, 60 percent for vegetation-environmental), comparable to other recent systematic reviews of pinyon-juniper treatment effects. However, we also found that when there were significant responses, some important trends potentially emerged. Important undesirable outcomes included far more positive than negative responses of exotic grass and forb abundance among nearly all treatment types. Cutting treatments were also more likely to decrease biocrust cover and microbial activity. Potentially beneficial outcomes included mostly positive responses among sagebrush obligate species, including more positive than negative responses for mule deer and sage-grouse. Some treatment types (for example, mastication) also resulted in more positive than negative responses for native grasses and forbs (although, non-significant responses were the majority). We also highlighted many limitations of this review, including how responses often come from few studies, and how some response-treatment category combinations lack adequate response data. Moreover, the existing research is often insufficient to address many key questions about treatment effects, largely owing to short time-scales and limited spatial extents of observations, which do not match the size of treatments being implemented by land managers, nor capture long-term, post-treatment ecological dynamics. We also identify a lack of research that addresses key interactions that could undermine restoration objectives, including potential effects of climate change and grazing on post-treatment environments. Thus, we emphasize the importance of integrating these factors into future pinyon-juniper treatment research, and we stress the need for use of monitoring programs and research studies that partake in data collection and analysis over long durations and broad spatial scales.

Open-File Report↗
USGS2017

Deep-sea coral research and technology program: Alaska deep-sea coral and sponge initiative final report

Deep-sea coral and sponge ecosystems are widespread throughout most of Alaska’s marine waters. In some places, such as the central and western Aleutian Islands, deep-sea coral and sponge resources can be extremely diverse and may rank among the most abundant deep-sea coral and sponge communities in the world. Many different species of fishes and invertebrates are associated with deep-sea coral and sponge communities in Alaska. Because of their biology, these benthic invertebrates are potentially impacted by climate change and ocean acidification. Deepsea coral and sponge ecosystems are also vulnerable to the effects of commercial fishing activities. Because of the size and scope of Alaska’s continental shelf and slope, the vast majority of the area has not been visually surveyed for deep-sea corals and sponges. NOAA’s Deep Sea Coral Research and Technology Program (DSCRTP) sponsored a field research program in the Alaska region between 2012–2015, referred to hereafter as the Alaska Initiative. The priorities for Alaska were derived from ongoing data needs and objectives identified by the DSCRTP, the North Pacific Fishery Management Council (NPFMC), and Essential Fish Habitat-Environmental Impact Statement (EFH-EIS) process. This report presents the results of 15 projects conducted using DSCRTP funds from 2012-2015. Three of the projects conducted as part of the Alaska deep-sea coral and sponge initiative included dedicated at-sea cruises and fieldwork spread across multiple years. These projects were the eastern Gulf of Alaska Primnoa pacifica study, the Aleutian Islands mapping study, and the Gulf of Alaska fish productivity study. In all, there were nine separate research cruises carried out with a total of 109 at-sea days conducting research. The remaining projects either used data and samples collected by the three major fieldwork projects or were piggy-backed onto existing research programs at the Alaska Fisheries Science Center (AFSC).

NOAA Technical Memorandum↗
USGS2016

Groundwater quality, age, and susceptibility and vulnerability to nitrate contamination with linkages to land use and groundwater flow, Upper Black Squirrel Creek Basin, Colorado, 2013

The Upper Black Squirrel Creek Basin is located about 25 kilometers east of Colorado Springs, Colorado. The primary aquifer is a productive section of unconsolidated deposits that overlies bedrock units of the Denver Basin and is a critical resource for local water needs, including irrigation, domestic, and commercial use. The primary aquifer also serves an important regional role by the export of water to nearby communities in the Colorado Springs area. Changes in land use and development over the last decade, which includes substantial growth of subdivisions in the Upper Black Squirrel Creek Basin, have led to uncertainty regarding the potential effects to water quality throughout the basin. In response, the U.S. Geological Survey, in cooperation with Cherokee Metropolitan District, El Paso County, Meridian Service Metropolitan District, Mountain View Electric Association, Upper Black Squirrel Creek Groundwater Management District, Woodmen Hills Metropolitan District, Colorado State Land Board, and Colorado Water Conservation Board, and the stakeholders represented in the Groundwater Quality Study Committee of El Paso County conducted an assessment of groundwater quality and groundwater age with an emphasis on characterizing nitrate in the groundwater. Groundwater-quality samples were collected from 50 randomly selected wells between May and June 2013. The samples were analyzed for major ions, nutrients, dissolved gases, tritium ( 3 H), chlorofluorocarbons (CFC-11, CFC-12, and CFC-113), and fuel products (such as benzene, toluene, ethylbenzene, and xylenes). None of the groundwater samples exceeded the U.S. Environmental Protection Agency (EPA) National Primary Drinking Water Regulations for primary maximum contaminant levels (MCL) for major ions. Secondary maximum contaminant levels, which are not health concerns and affect mainly taste, color, or odor of the water, were observed in rare instances for pH (2 samples), chloride (1 sample), iron (3 samples), and manganese (8 samples). The secondary maximum contaminant level for total dissolved solids was also exceeded for two samples. Nitrate (nitrite plus nitrate as nitrogen in groundwater) was elevated above the estimated background concentration of natural recharge waters of 1 milligram per liter (mg/L) in 44 of the 50 wells sampled and showed a median concentration of 5.4 mg/L. Nitrate concentrations were above the MCL of 10 mg/L in 5 of the 50 wells sampled and above half of the EPA MCL (5 mg/L) in 27 of the 50 wells sampled, which included samples above the MCL. Dissolved-oxygen concentrations exceeded 0.5 mg/L in 95 percent of reported values (40 of 42 samples) and exceeded 2.0 mg/L in 90 percent of reported values (38 of 42 samples). The oxidized conditions observed in most areas indicate that nitrate from fertilizers and animal or human waste was geochemically stable and could persist in the groundwater for decades or perhaps longer. A historical analysis of median nitrate concentrations over nearly three decades showed an increase in nitrate of approximately 1 mg/L from 4.3 to 5.4 mg/L, although the increase was not determined to be significantly different using nonparametric statistical methods. Major-ion data indicate that groundwater representative of the primary aquifer was classified as calcium-sodium bicarbonate type water. Other water samples from wells located mainly along the periphery of the primary aquifer had cation-anion compositions consistent with distinct water sources, including groundwater contributions from the underlying bedrock aquifers. The areas with differentiable water sources were located mainly where alluvial deposits were thin and geologic contacts to the underlying bedrock aquifers were relatively shallow. Nitrate concentrations in the groundwater were evaluated for relations to land use. An agricultural region was defined using a sequence of land satellite imagery. Groundwater flow directions interpreted from median water-table elevations measured from 2000 to 2013 were used in conjunction with cropland locations to define the agricultural region boundaries by encompassing potential pathways of nitrate transport in the groundwater from nitrogen-based fertilizers. A statistically significant higher median nitrate concentration was observed for areas inside the agricultural region (6.7 mg/L) compared to areas outside the agricultural region (2.3 mg/L), although median concentrations in both areas were below the MCL (10 mg/L). Median nitrate concentration was also significantly greater in land parcels with septic use (4.9 mg/L) compared to nonseptic parcels (1.7 mg/L). In general, agriculture or septic use was identified as the primary source of nitrate, depending on location, while commercial, county, grazing, and residential land uses were generally secondary sources of nitrate. Apparent groundwater ages were estimated from chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium ( 3 H) data using models that assumed piston flow and binary mixing (dilution of a young component with old, tracer-free water). The mean and median groundwater ages were about 30 years and the standard deviation was 6 years, indicating that most groundwater in the primary aquifer was “young” water that had recharged to the aquifer over the last few decades (post-1950s). The median fraction of young water was about 71 percent, and the standard deviation was 29 percent. The remaining water predated the 1950s, which may have originated from deeper geologic formations or may represent slow moving groundwater within the primary aquifer. Some of the oldest groundwater ages (older than 30 years) were observed in the upper reaches of the aquifer to the northwest where the primary aquifer is thin and intersects bedrock, supporting the hypothesis of geochemically distinct groundwater entering the primary aquifer from below. Groundwater that had reached the central part of the aquifer from upgradient areas of the basin was variable in age because of differences in flow paths and travel velocities. The groundwater age analysis showed that current (2013) land-use practices could affect water quality over decades to come, and that responses to remedial actions could be slow, especially for constituents, such as nitrate, that are stable under oxidized conditions. Fuel products (including acetone, benzene, diisopropyl ether, ethylbenzene, methyl acetate, methyl tertiary butyl ether (MTBE), methyl tert-pentyl ether, m- + p-xylene, o-xylene, tert-amyl alcohol, tert-butyl alcohol, tert-butyl ethyl ether, and toluene) were analyzed in groundwater from 49 of the 50 wells. Water from seven sites had detections for fuel compounds; all concentrations were below MCL. The results provided assurance of water quality and a valuable baseline to evaluate future trends of fuel constituents as the region is further developed. Probability maps were developed from logistic regression models to examine the likelihood that nitrate concentrations in groundwater exceeded specified levels. Susceptibility analysis examined relations between mid-level (5.0 mg/L) nitrate concentrations and climatic, hydrologic, and geologic variables; the significant variables were identified as depth to groundwater, soil organic matter, and soil water storage to 25-centimeter (cm) depth. The vulnerability assessments included natural factors driving susceptibility but also human factors related to land use and septic use. Vulnerability to low-level (2.5 mg/L) nitrate was related to depth to groundwater, septic zoning, and soil organic matter. The results highlighted that septic zoning affected low-level nitrate concentrations. Vulnerability to mid-level (5.0 mg/L) nitrate was examined using all 50 samples and also with two data outliers removed, which showed relatively high nitrate concentrations but also anomalous water chemistry or were located beyond the primary study area. Vulnerability to mid-level (5.0 mg/L) nitrate using all 50 samples was related to depth to groundwater, land use, septic use within a 500-meter (m) radius, soil water storage to a 25-cm depth, soil organic matter, and whether a location was within the agricultural region. The mid-level (5.0 mg/L) vulnerability model using 48 samples (two outliers removed) produced the best overall fit and was related to the same variables as when using all samples except septic use. The results for mid-level vulnerability provided additional support that septic use was associated with low levels of nitrate in the groundwater. Soil properties and land use were identified as the main drivers of moderate nitrate concentrations. Probabilities of exceeding low-level nitrate concentrations were high in most areas with the lowest probabilities usually to the northwest along thin geologic deposits in the upper part of the basin. The results of this investigation offer the foundational information needed for developing best management practices to mitigate nitrate contamination, basic concepts on water quality to aid public education, and information to guide regulatory measures if policy makers determine this is warranted. Science-based decision making will require continued monitoring and analysis of water quality in the future.

Colorado↗
USGS1995

The surface of crystalline basement, Great Valley and Sierra Nevada, California: A digital map database

Crystalline basement in central California extends westward from the exposed Sierra Nevada beneath the sedimentary fill of the Great Valley and under the eastern edge of the Coast Ranges at mid-crustal depth. The surface of this basement is defined from three types of control: in the Sierra Nevada from the topography itself, beneath the eastern two thirds of the Great Valley in considerable detail from numerous wells drilled for oil and gas, and beneath the western San Joaquin Valley in less detail from seismic reflection and refraction profiles. Together, these data demonstrate that the surface of crystalline rock is continuous from the exposed rock in the mountains to the top of high-velocity rock buried deep beneath the eastern front of the southern Coast Ranges. This report presents a compilation of data through 1985 that define the surface of this crystalline basement, a contour map of the surface, and the lithology of the basement rock sampled by many of the wells. The compilation was begun as part of the investigation of the 1983 Coalinga earthquake, and was subsequently converted to digital form and extended to the whole of the Great Valley and Sierra Nevada. The main purpose was to explore and document the shape and continuity of the basement surface and to determine the relation of the surface to the tectonic wedge hypothesis (Wentworth and others, 1984; Wentworth and Zoback, 1989). Available basement samples from wells - principally the thin-section collection of May and Hewitt (1948) preserved by the California Academy of Sciences - were also reexamined by cooperating petrologists in an effort to distinguish wells that bottomed in ophiolitic rocks.

California↗
USGS2022

Measuring and attributing sedimentary and geomorphic responses to modern climate change: Challenges and opportunities

Today, climate change is affecting virtually all terrestrial and nearshore settings. This commentary discusses the challenges of measuring climate-driven physical landscape responses to modern global warming: short and incomplete data records, land use and seismicity masking climatic effects, biases in data availability and resolution, and signal attenuation in sedimentary systems. We identify opportunities to learn from historical and paleo data, select especially sensitive study sites, and report null results to better characterize the extent and nuances of climate-change effects. We then discuss efforts to improve attribution practices, which will lead to better predictive capabilities. We encourage the earth-science community to prioritize scientific research on climate-driven physical landscape changes so that societies will be better prepared to manage the effects on health and safety, infrastructure, water–food–energy security, economics, and ecosystems that follow from climate-driven physical landscape change.

Earth's Future↗
USGS2005

Host Fish Identification and Early Life Thermal Requirements for the Federal Endangered Winged Mapleleaf Mussel

The winged mapleleaf mussel (Quadrula fragosa, WML) is a Federal endangered species historically inhabiting at least 34 river systems in 12 Midwestern states. Only four populations are currently known to exist, including one confirmed reproducing population in the St. Croix National Scenic Riverway (NSR) bordering Minnesota and Wisconsin. Recovery efforts are limited by a lack of life history information, particularly which species of fish serve as host to the mussel's parasitic larvae (glochidia). Since 1997, biologists at the University of Minnesota have tried to identify host fish for the WML. Department of the Interior colleagues working in western Wisconsin at the U.S. Fish and Wildlife Service's La Crosse Fishery Resources Office and Genoa National Fish Hatchery, the National Park Service's St. Croix NSR, and the U.S. Geological Survey's Upper Midwest Environmental Sciences Center (UMESC) in La Crosse joined the team in 2001 to expand and accelerate the laboratory host fish identification program by making use of the well-equipped aquatic research facilities at UMESC. We report on several WML early life history investigations conducted at UMESC since autumn 2003 to identify suitable host fish species and evaluate thermal requisites for the development of glochidia into free-living juvenile mussels.

Fact Sheet↗
USGS2008

Water-Quality and Lake-Stage Data for Wisconsin Lakes, Water Year 2007

The U.S. Geological Survey (USGS), in cooperation with local and other agencies, collects data at selected lakes throughout Wisconsin. These data, accumulated over many years, provide a data base for developing an improved understanding of the water quality of lakes. To make these data available to interested parties outside the USGS, the data are published annually in this report series. The locations of water-quality and lake-stage stations in Wisconsin for water year 2007 are shown in figure 1. A water year is the 12-month period from October 1 through September 30. It is designated by the calendar year in which it ends. Thus, the period October 1, 2005 through September 30, 2007 is called 'water year 2007.' The purpose of this report is to provide information about the chemical and physical characteristics of Wisconsin lakes. Data that have been collected at specific lakes, and information to aid in the interpretation of those data, are included in this report. Data collected include measurements of in-lake water quality and lake stage. Time series of Secchi depths, surface total phosphorus and chlorophyll a concentrations collected during non-frozen periods are included for all lakes. Graphs of vertical profiles of temperature, dissolved oxygen, pH, and specific conductance are included for sites where these parameters were measured. Descriptive information for each lake includes: location of the lake, area of the lake?s watershed, period for which data are available, revisions to previously published records, and pertinent remarks. Additional data, such as streamflow and water quality in tributary and outlet streams of some of the lakes, are published in another volume: 'Water Resources Data-Wisconsin, 2007.'

Open-File Report↗
USGS2004

Strategic plan for the U.S. Geological Survey status and trends of Biological Resources Program: 2004-2009

The mission of the USGS Status and Trends of Biological Resources Program is to measure, predict, assess, and report the status and trends of the Nation's biological resources to facilitate research, enable resource management and stewardship, and promote public understanding and appreciation of our living resources. Determining the status (abundance, distribution, productivity, and health) and trends (how these variables change over time) of our living natural resources is critical for their Trumpeter swan with numbered wing tags. This tech- protection or restoration. The Progg ran nique allows birds to he monitored remotely without the provides the USGS, other agencies of need for recapture to identify individuals. Photo by the Department of the Interior (DOI), Wayne Miller. other federal and state agencies, and the public with science-based monitoring data and information for local, regional, and national assessment of biological resources and the ecosystems that support them.

Circular↗
USGS2024

Novel quantitative methods to enable multispectral identification of high-purity water ice exposures on Mars using High Resolution Imaging Science Experiment (HiRISE) images

Reliable detection and characterization of water ice on the Martian surface is pivotal to not only understand its present and past climate, but to also provide valuable information on in-situ resource availability and distribution for future human exploration missions. Ice-rich features are currently identified with visible/near-IR (VNIR), thermal IR and radar data. However, their coarse spatial scale sometimes limits confident characterization of small (i.e., meter-scale) icy exposures resulting from recent activity like new impacts. Water ice bearing materials possess weaker spectral characteristics at wavelengths shorter than ∼1030 nm that may be resolved by VNIR imaging instruments like the High Resolution Imaging Science Experiment (HiRISE) and the Colour and Stereo Surface Imaging System (CaSSIS). Our study assesses the spectral capability of HiRISE colour observations to help distinguish high purity water ice exposures from ice-poor materials. We report detailed methodologies for reliable colour characterization of icy surface using unfiltered HiRISE images. We present the first quantitative approach to uniquely characterize high-purity ice-rich materials through spectral shape and spectral parameterization methods at high spatial resolution (∼50 cm/pixel). We also present three spectral parameters to aid detection of pure water ice features, while also providing statistical constraints to enable a quantitative interpretation scheme. Our methods are observed to work well in characterizing and separating ice-rich features uniquely from ice-poor and ferrous materials. However, we do observe that these methods have a lower grain size detection limit of ∼250–300 μm, and may not be able to uniquely separate frosts from ground ice exposures. We also apply these methods to better constrain the composition of bright materials exposed by recent impacts identified in previous surveys, where substantial evidence for ice-bearing materials was previously unavailable. Overall, our work proposes HiRISE colour-based methods as a novel approach for high-resolution multispectral characterization of ice-rich features on the Martian surface, which is of particular value since the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has ceased operations.

Icarus↗
USGS2006

Response to comment on “Persistence of pharmaceutical compounds and other organic wastewater contaminants in a conventional drinking-water-treatment plant”

The U.S. Geological Survey (USGS) and the Centers for Disease Control thank Dr. Till for her comments concerning our research ( Till, 2005 ) and welcome the opportunity to respond. The primary objective of our study was to evaluate the potential for organic wastewater-related contaminants (OWCs), including pharmaceuticals, to survive a conventional drinking-water-treatment process and persist in potable-water supplies ( Stackelberg et al., 2004 ). Our study was supported by two USGS laboratories: the National Water Quality Laboratory (NWQL), which provided the HPLC/ESI-MS and CLLE GC/MS data and the Ocala Water Quality and Research Laboratory (OWQRL), which provided the LC/MS data ( Stackelberg et al., 2004 ). Although discussed as distinct techniques by Dr. Till and indicated by differing acronyms to distinguish the laboratories producing the data, as described in our paper, the two LC/MS methods are very similar; they consist of a solid-phase extraction method with analysis of the extract produced using high-performance liquid chromatography coupled to an electrospray ionization mass spectrometer operated in the positive mode. The NWQL and OWQRL report ‘trace’ and ‘ultratrace’ determinations of analytes that provide significant benefit for describing the presence and fate of low-level contaminants. For mass spectral methods, an analyte is qualitatively identified by its retention time on the chromatographic column as well as the presence of two or more confirming ions with area ratios that match that of the reference standard compounds. Because of a recognized increased risk of false positives, these qualitative identification criteria are used in conjunction with abundant quality-control samples (detailed below) to confirm detection prior to making an estimate of the concentration. These qualitative identification criteria must be met before a compound is considered present (or detected) in a sample ( Oblinger Childress et al., 1999 ). When a compound has been qualitatively identified in an environmental sample (whether above or below its reporting level [RL]), it is assessed in context with associated field and laboratory blanks, field and laboratory replicates, and other data, such as appropriate laboratory reagent spikes. An environmental concentration is calculated only after determining that field and laboratory procedures did not contaminate the samples. The concentrations are then calculated from 5- to 8-point calibration curves using internal standard quantitation. Our lowest calibration standard is intentionally much lower than the RL, typically 10 times lower. The most abundant molecular or fragment ion is used for quantitation, and, for the two LC/MS methods, at least one, and where possible two, qualifier ions are used for confirmation. For the GC/MS method, with its greater degree of fragmentation, one quantitation and two qualifier ions are used. When any of the abovementioned qualitative identification criteria are not met, the analyte is considered not present and is reported as “less than” the RL.

Science of the Total Environment↗