Search

Groundwater is used as a drinking-water supply by about one-half of the U.S. population, including almost all people residing in rural areas. As estimated by the U.S. Geological Survey (USGS) [...], BACKGROUND: As the population and demand for safe drinking water from domestic wells increase, it is important to examine water quality and contaminant occurrence. A national assessment in 2006 by the U.S. Geological Survey reported findings for 55 volatile organic compounds (VOCs) based on 2,401 domestic wells sampled during 1985-2002. OBJECTIVES: We examined the occurrence of individual and multiple VOCs and assessed the potential human-health relevance of VOC concentrations. We also identified hydrogeologic and anthropogenic variables that influence the probability of VOC occurrence. METHODS: The domestic well samples were collected at the wellhead before treatment of water and analyzed for 55 VOCs. Results were used to examine VOC occurrence and identify associations of multiple explanatory variables using logistic regression analyses. We used a screening-level assessment to compare VOC concentrations to U.S. Environmental Protection Agency maximum contaminant levels (MCLs) and health-based screening levels. RESULTS: We detected VOCs in 65% of the samples; about one-half of these samples contained VOC mixtures. Frequently detected VOCs included chloroform, toluene, 1,2,4-trimethylbenzene, and perchloroethene. VOC concentrations generally were < 1 µg/L. One or more VOC concentrations were greater than MCLs in 1.2% of samples, including dibromochloropropane, 1,2-dichloropropane, and ethylene dibromide (fumigants); perchloroethene and trichloroethene (solvents); and 1,1-dichloroethene (organic synthesis compound). CONCLUSIONS: Drinking water supplied by domestic wells is vulnerable to low-level VOC contamination. About 1% of samples had concentrations of potential human-health concern. Identifying factors associated with VOC occurrence may aid in understanding the sources, transport, and fate of VOCs in groundwater. KEY WORDS: domestic wells, drinking-water quality, human health, volatile organic compounds. Environ Health Perspect 115:1539-1546 (2007). doi:10.1289/ehp.10253 available via http://dx.doi.org/ [Online 20 August 2007]

Examines postprogram experiences of minority youth in the National Urban League Youth Career Development Project. Results confirmed the difficulties minority female teenagers have obtaining jobs. Found parents' employment status had little effect, and unemployed youth tended to rely on informal job search techniques. (Author/JAC)

Reviews the educational and legal history of Black education; criticizes the emphasis on achievement scores as a predominant variable in the measurement of such programs; and states that conclusions about Black enrollment, retention, and successful matriculation are generally positive. (Author/MLF)

In modern firms the use of contests as an incentive device is ubiquitous. Nonetheless, experimental research shows that in the laboratory subjects routinely make suboptimal decisions in contests even to the extent of making negative returns. The purpose of this study is to investigate how earning the endowment, demographic differences, and individual preferences impact behavior in contests. To this end, we conduct a laboratory experiment in which subjects expend costly resources (bids) to attain an award (prize). In line with other laboratory studies of contests, our results show that subjects overbid relative to theoretical predictions and incur substantial losses as a result. Making subjects earn their initial resource endowments mitigates overbidding and thus increases efficiency. Overbidding is linked to gender, with women bidding higher than men and having lower average earnings. Other demographic information, such as religiosity, and individual preferences, such as preferences toward winning and risk, also influence behavior in contests. [ABSTRACT FROM AUTHOR]

Chapter 7 - Web GIS has some interesting examples of how web maps actually work but also introduces higher-level applications, including Esri's ArcGIS Story Maps. PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING April 2021 229 BOOKREVIEW This book is a wide-ranging and wide-open introduction to geographic information systems technology appropriate for undergraduate and graduate courses or for professionals interested in getting started with this technology or broadening their knowledge of the field. Chapter 10 - Introduction to Health GIS Applications exposes the reader to public health and emergency management applications and touches on map accessibility. [Extracted from the article]

The effects of digital elevation model (DEM) map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for TOPMODEL, a topography-based watershed model. The effects of topography on watershed hydrology are represented in TOPMODEL as the distribution of ln ( a/tan B), where ln is the Napierian logarithm, a is the upslope area per unit contour length, and tan B is the gravitational gradient. The minimum, maximum, mean, variance, and skew values of the ln ( a/tan B) distribution were computed from 1:24,000-scale (24K) DEMs at 30- and 90-m resolutions and from 1:250,000-scale (250K) DEMs at 90-m resolution for 71 areas in Pennsylvania, New York, and New Jersey. An analysis of TOPMODEL showed that model predictions of the depth to the water table, the ratio of overland flow to total flow, peak flow, and variance and skew of predicted streamflow were affected by both the DEM map scale and data resolution. Further TOPMODEL analyses showed that the effects of DEM map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln ( a/tan B) distribution, which was affected by both DEM map scale and data resolution. DEM map scale affected the mean of the ln ( a/tan B) distribution through its influence on the mean of the ln ( a) distribution, which characterizes land-surface shape, and the mean of ln (1/tan B) distribution, which characterizes land-surface slope. DEM resolution, in contrast, affected the mean of the ln ( a/tan B) distribution primarily by its influence on the mean of the ln ( a) distribution. [ABSTRACT FROM AUTHOR]

BSTRACT: Parts of the Raritan River basin in central New Jersey have undergone increasing development over the last several decades. The increasing population relies on the region's ground water and surface water sources for its residential, commercial, and industrial water supply. Urbanization, regionalized wastewater-treatment facilities, stream channel alterations, and interbasin transfers of water can all affect water availability. This pilot study was conducted to determine whether significant trends exist in the base-flow and overland-runoff characteristics of streams in two subbasins with different percentages of urban/built-up land (Anderson et at., 1976). Changes in flow characteristics that could indicate future reductions in safe water yield of the Raritan River basin were examined. Flow and flow variability of the steams draining these two subbasins have increased over time. Many of the flow measures studied experienced pronounced trend shifts about 1960. The cause of these changes cannot be readily determined from the data, nor is it clear whether the increased flow variability lies outside the natural range of flow variability of the streams draining the subbasins. [ABSTRACT FROM AUTHOR]