Applied tracer tests in fractured rock: Can we predict natural gradient solute transport more accurately than fracture and matrix parameters?

Applied tracer tests provide a means to estimate aquifer parameters in fractured rock. The traditional approach to analysing these tests has been using a single fracture model to find the parameter values that generate the best fit to the measured breakthrough curve. In many cases, the ultimate aim is to predict solute transport under the natural gradient. Usually, no confidence limits are placed on parameter values and the impact of parameter errors on predictions of solute transport is not discussed. The assumption inherent in this approach is that the parameters determined under forced conditions will enable prediction of solute transport under the natural gradient. This paper considers the parameter and prediction uncertainty that might arise from analysis of breakthrough curves obtained from forced gradient applied tracer tests. By adding noise to an exact solution for transport in a single fracture in a porous matrix we create multiple realisations of an initial breakthrough curve. A least squares fitting routine is used to obtain a fit to each realisation, yielding a range of parameter values rather than a single set of absolute values. The suite of parameters is then used to make predictions of solute transport under lower hydraulic gradients and the uncertainty of estimated parameters and subsequent predictions of solute transport is compared. The results of this study show that predictions of breakthrough curve characteristics (first inflection point time, peak arrival time and peak concentration) for groundwater flow speeds with orders of magnitude smaller than that at which a test is conducted can sometimes be determined even more accurately than the fracture and matrix parameters.     

Book reviews

Our Stolen Future. How man-made chemicals are threatening our fertility, intelligence and survival. T. Colborn, J. P. Myers & D. Dumanoski, 1996, Boston, Little, Brown, 306 pp. ISBN 0 316 87546, £18.99

Environmental Sociology: a social constructionist perspective. John Hannigan, 1995, London, Routledge, ISBN 0 415 112 559, £12.99

Citizen Science: a study of people, expertise and sustainable development. Alan Irwin, 1995, London, Routledge, ISBN 0 415 130 107, £13.99

The True Costs of Road Transport. David Maddison, David Pearce, Olof Johansson, Edward Calthrop, Todd Litman & Eric Verhoef, 1996, London, Earthscan, 242 pp. ISBN 185 383 2685, £10.95

Car Dependence: a report for the RAC Foundation for Motoring and the Environment. RAC Foundation for Motoring and the Environment, 1995, London, 154 pp. ISBN 086211355 5

Local Sustainability: turning sustainable development into practical action in our communities. Roger Few (Ed.), Leicester Environment City Trust, 1996, Leicester, Environ Trust, 100 pp., £28.00, [Available from: Environ Parkfield, Western Park, Leicester, LE3 6HX, UK]

Successful Environment Management in a Week. Mark Yoxon, 1996, London, Hodder & Stoughton, 96 pp. ISBN 0 340 66374 X, £6.99

Principles of Environmental and Resource Economics. H. Folmer, H. Landis Gabel & H. Opschoor (Eds), 1995, Aldershot, Edward Elgar, 512 pp. ISBN 1 85898 224 3, £85.00

The Contingent Valuation of Environmental Resources: methodological issues and research needs. David Bjornstad & James R. Khan (Eds), 1996, Cheltenham, UK and Brookfield USA, Edward Elgar, ISBN 1 858983215

Towards Sustainability. Peter Martin & Colin Hutchinson, 1996, London, Office for Public Management, £5.45

Conservation and the Consumer: understanding environmental concern. Paul Hackett, 1995, London, Routledge, 229 pp. ISBN 0 415 08096 7, £45.00     

GROUNDWATER DISCHARGE AND ITS IMPACT ON SURFACE WATER QUALITY IN A CHESAPEAKE BAY INLET1

ABSTRACT: Surface water, groundwater, and groundwater discharge quality surveys were conducted in Cherrystone Inlet, on Virginia's Eastern Shore. Shallow groundwater below agricultural fields had nitrate concentrations significantly higher than inlet surface waters and shallow groundwater underlying forested land. This elevated nitrate groundwater discharged to adjacent surface waters. Nearshore discharge rates of water across the sediment-water interface ranged from 0.02 to 3.69 liters·m^?2·hr^?1 during the surveys. The discharge was greatest nearshore at low tide periods, and decreased markedly with increasing distance offshore. Vertical hydraulic heads, E_h, and inorganic nitrogen flux in the sediments followed similar patterns. Nitrate was the predominant nitrogen species discharged nearshore adjacent to agricultural land use, changing to ammonium farther offshore. Sediment nitrogen fluxes were sufficient to cause observable impacts on surface water quality; nitrate concentrations were up to 20 times greater in areas of groundwater discharge than in the main stem inlet water. Based on DIN:DIP ratios, nitrogen contributions from direct groundwater discharge and tidal creek inputs appear to be of significant ecological importance. This groundwater discharge links land use activity and the quality of surface water, and therefore must be considered in selection of best management practices and water quality management strategies.     

PERMEABILITY OF AIR AND IMMISCIBLE ORGANIC LIQUIDS IN POROUS MEDIA1

ABSTRACT: The conductivity of air, mineral oil (relative viscosity 77), and a light nontoxic oil (relative viscosity 4.7) was measured in three porous media: a sand, loamy sand, and a silt loam. The measurements were made over a range of water contents for each porous medium. Small volumes of air were present as well as significant amounts of water during most of the oil conductivity measurements. The results were compared to two methods for calculating conductivities of immiscible fluids in water-wet porous media. A new equation that accounts for swelling and for the gas slippage effect in very small pores was formulated for use with these methods The observed conductivities, spanning seven orders of magnitude, agree reasonably well with calculated values. Only three soil parameters are required to calculate the conductivities: (1) the saturated conductivity of water, (2) the saturated conductivity of the immiscible fluid of interest, and (3) a pore size index value that is obtained from an estimate from the water release curve of the porous material. Remediation of organic liquid spills is briefly discussed to illustrate the practical applications of gas phase conductivities, as well as those for immiscible organic liquid phases. It is concluded that, in light of spatial variation under field conditions, the method presented for calculating values of three-phase conductivities will be useful in the management of immiscible organic liquid spills and leaks.     

Noninvasive fetal genome sequencing: a primer

We recently demonstrated whole genome sequencing of a human fetus using only parental DNA samples and plasma from the pregnant mother. This proof-of-concept study demonstrated how samples obtained noninvasively in the first or second trimester can be analyzed to yield a highly accurate and substantially complete genetic profile of the fetus, including both inherited and de novo variation. Here, we revisit our original study from a clinical standpoint, provide an overview of the scientific approach, and describe opportunities and challenges along the path toward clinical adoption of noninvasive fetal whole genome sequencing. © 2013 John Wiley & Sons, Ltd.     

The acetochlor registration partnership: prospective ground water monitoring program

The Acetochlor Registration Partnership conducted a prospective ground water (PGW) monitoring program to investigate acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide] transport to ground water at eight sites. The distribution of soil textures among these sites was weighted toward coarser soil types, while also including finer-textured soils that dominate most corn (Zea mays L.)-growing areas of the United States. Each site consisted of a 1.2-ha test plot adjacent to a 0.2-ha control plot. Suction lysimeters and monitoring wells were installed at multiple depths within each test and control plot to sample soil-pore water and near-surface ground water. Irrigation was applied to each site during the growing season to ensure water input of 110 to 200% of average historical rainfall. Acetochlor dissipated rapidly from surface soils at all sites with a DT(50) (time for 50% of the initial residues to dissipate) of only 3 to 9 d, but leaching was not an important loss mechanism, with only 0.25% of the 15,312 soil-pore water and ground water samples analyzed containing parent acetochlor at or above 0.05 microg L(-1). However, quantifiable residues of a soil degradation product, acetochlor ethanesulfonic acid, were more common, with approximately 16% of water samples containing concentrations at or above 1.0 microg L(-1). A second soil degradation product, acetochlor oxanilic acid, was present at concentrations at or above 1.0 microg L(-1) in only 0.15% of water samples analyzed. The acetochlor PGW program demonstrated that acetochlor lacks the potential to leach to ground water at detectable concentrations, and when applied in accordance with label restrictions, is unlikely to move to ground water at concentrations hazardous to human health.     

Acid-base accounting to predict post-mining drainage quality on surface mines

Acid-base accounting (ABA) is an analytical procedure that provides values to help assess the acid-producing and acid-neutralizing potential of overburden rocks prior to coal mining and other large-scale excavations. This procedure was developed by West Virginia University scientists during the 1960s. After the passage of laws requiring an assessment of surface mining on water quality, ABA became a preferred method to predict post-mining water quality, and permitting decisions for surface mines are largely based on the values determined by ABA. To predict the post-mining water quality, the amount of acid-producing rock is compared with the amount of acid-neutralizing rock, and a prediction of the water quality at the site (whether acid or alkaline) is obtained. We gathered geologic and geographic data for 56 mined sites in West Virginia, which allowed us to estimate total overburden amounts, and values were determined for maximum potential acidity (MPA), neutralization potential (NP), net neutralization potential (NNP), and NP to MPA ratios for each site based on ABA. These values were correlated to post-mining water quality from springs or seeps on the mined property. Overburden mass was determined by three methods, with the method used by Pennsylvania researchers showing the most accurate results for overburden mass. A poor relationship existed between MPA and post-mining water quality, NP was intermediate, and NNP and the NP to MPA ratio showed the best prediction accuracy. In this study, NNP and the NP to MPA ratio gave identical water quality prediction results. Therefore, with NP to MPA ratios, values were separated into categories: <1 should produce acid drainage, between 1 and 2 can produce either acid or alkaline water conditions, and >2 should produce alkaline water. On our 56 surface mined sites, NP to MPA ratios varied from 0.1 to 31, and six sites (11%) did not fit the expected pattern using this category approach. Two sites with ratios <1 did not produce acid drainage as predicted (the drainage was neutral), and four sites with a ratio >2 produced acid drainage when they should not have. These latter four sites were either mined very slowly, had nonrepresentative ABA data, received water from an adjacent underground mine, or had a surface mining practice that degraded the water. In general, an NP to MPA ratio of <1 produced mostly acid drainage sites, between 1 and 2 produced mostly alkaline drainage sites, while NP to MPA ratios >2 produced alkaline drainage with a few exceptions. Using these values, ABA is a good tool to assess overburden quality before surface mining and to predict post-mining drainage quality after mining. The interpretation from ABA values was correct in 50 out of 52 cases (96%), excluding the four anomalous sites, which had acid water for reasons other than overburden quality.     

Observer reactions to interpersonal injustice: The roles of perpetrator intent and victim perception

The present research contributes to a growing literature on observer reactions to injustice experienced by others. In particular, we separated two variables that have previously been confounded in prior research, namely perpetrator intent to cause harm and victim perception of harm. We expected that injustice intent and injustice perceptions would have both unique and joint effects on observer reactions. The results of three experiments in which we manipulated perpetrator injustice intent and victim injustice perceptions supported our predictions. First, we found that observers had more negative reactions toward superiors who intended to inflict high versus low levels of interpersonal injustice toward a subordinate. Second, the injustice intent of the superior influenced observers' reactions more than did victim perceptions of injustice. Third, most novel, we found that the mere intent to cause injustice generated negative reactions in observers, even in the absence of a “true” victim—that is, when the subordinate perceptions of injustice were low. Together, our results emphasize the importance of examining observers' reactions to injustice and incorporating perpetrator intentions into the study of organizational justice. Copyright © 2012 John Wiley & Sons, Ltd.     

Chronic institutional failure and enhanced vulnerability to flash‐floods in the Cuenca Altadel Río Lerma,Mexico

The dominant paradigm in disaster risk reduction (DRR) policies has been seriously contested because of its reliance on interventions based on technocratic expertise. In the Mexican context, the influence of informal practices such as clientelism and cartelisation of the political system produces environmental degradation and vulnerability to disasters within the communities in the study site. This paper contributes to understanding of failed institutional processes and parallel practices that intensify vulnerability to disasters by contrasting the discourses of agents within a peri‐urban community in central Mexico. Employing the Situational Analysis Approach as a methodological framework, the study identifies divergent views and practices within the community, leading to different responses to disasters and to different perceptions regarding institutional performance. In addition, it finds that institutional decision‐making, based only on scientific and technical expertise, has resulted in unintended consequences that influence ongoing vulnerability to floods in the site under review.