bluuebunny/crossref_metadata_2025 huggingface dataset:
Using accelerated life testing procedures to compare the relative sensitivity of rainbow trout and the federally listed threatened bull trout to three commonly used rangeland herbicides (Picloram, 2,4-D, and clopyralid)
Authors: Fairchild James F , Allert Ann , Sappington Linda S , Nelson Karen J , Valle Janet
Published: February 2008

We conducted 96-h static acute toxicity studies to evaluate the relative sensitivity of juveniles of the threatened bull trout (Salvelinus confluentus) and the standard cold-water surrogate rainbow trout (Onchorhyncus mykiss) to three rangeland herbicides commonly used for controlling invasive weeds in the northwestern United States. Relative species sensitivity was compared using three procedures: standard acute toxicity testing, fractional estimates of lethal concentrations, and accelerated life testing chronic estimation procedures. The acutely lethal concentrations (ALC) resulting in 50% mortality at 96 h (96-h ALC50s) were determined using linear regression and indicated that the three herbicides were toxic in the order of picloram acid > 2,4-D acid > clopyralid acid. The 96-h ALC50 values for rainbow trout were as follows: picloram, 41 mg/L; 2.4-D, 707 mg/L; and clopyralid, 700 mg/L. The 96-h ALC50 values for bull trout were as follows: picloram, 24 mg/L; 2.4-D, 398 mg/L; and clopyralid, 802 mg/L. Fractional estimates of safe concentrations, based on 5% of the 96-h ALC50, were conservative (overestimated toxicity) of regression-derived 96-h ALC5 values by an order of magnitude. Accelerated life testing procedures were used to estimate chronic lethal concentrations (CLC) resulting in 1% mortality at 30 d (30-d CLC1) for the three herbicides: picloram (1 mg/L rainbow trout, 5 mg/L bull trout), 2,4-D (56 mg/L rainbow trout, 84 mg/L bull trout), and clopyralid (477 mg/L rainbow trout; 552 mg/L bull trout). Collectively, the results indicated that the standard surrogate rainbow trout is similar in sensitivity to bull trout. Accelerated life testing procedures provided cost-effective, statistically defensible methods for estimating safe chronic concentrations (30-d CLC1s) of herbicides from acute toxicity data because they use statistical models based on the entire mortality:concentration:time data matrix.
The Evaluation, Classification and Reporting of Unconventional Resources
Authors: Elliott David C.
Published: February 2008

The evaluation of unconventional resources presents many challenges, one of which is a need to evaluate all resource classes, not only Proved reserves. The evaluation of hydrocarbons is described as consisting of three steps: Estimation, Classification, and Reporting, with a concomitant requirement for auditing. The nature of estimates is discussed, in particular, that there is always an associated uncertainty and some fundamental principles of classification are reviewed. The classification of unconventional hydrocarbons is discussed, with an emphasis on Discovered Petroleum Initially-In-Place and Contingent Resources, which are formulated as a series of Decision rules. Information on production potential, either from tests or analogs, is of particular importance when classifying unconventional hydrocarbons, and the typical lack of defined pool boundaries requires that careful consideration be given to the area assigned to various resource categories, both of which points emphasise the need for an understanding of the detailed reservoir geology.

The Petroleum Resource Management System (PRMS), supplemented by the Canadian Oil and Gas Handbook (COGEH), has provided the basis for the discussion in this paper, but it is impossible in a short paper to capture these systems in full, and reference should be made to the original source documents for details. The emphasis in this paper is on recovery through wells, but some brief mention of mined hydrocarbon recovery is made. The exploitation of unconventional hydrocarbons is in its early stages, and evaluation procedures, including classification, are still under development. Many aspects of the evaluation process are not addressed in this paper, and those that are, are likely to require further development and modification.
Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Model-Based Evaluation of Technology and Potential
Authors: Moridis George J. , Collett Timothy S. , Boswell Ray , Kurihara M. , Reagan Matthew T. , Koh Carolyn , Sloan E. Dendy
Published: February 2008

Gas hydrates are a vast energy resource with global distribution in the permafrost and in the oceans. Even if conservative estimates are considered and only a small fraction is recoverable, the sheer size of the resource is so large that it demands evaluation as a potential energy source. In this review paper, we discuss the distribution of natural gas hydrate accumulations, the status of the primary international R&D programs, and the remaining science and technological challenges facing commercialization of production. After a brief examination of gas hydrate accumulations that are well characterized and appear to be models for future development and gas production, we analyze the role of numerical simulation in the assessment of the hydrate production potential, identify the data needs for reliable predictions, evaluate the status of knowledge with regard to these needs, discuss knowledge gaps and their impact, and reach the conclusion that the numerical simulation capabilities are quite advanced and that the related gaps are either not significant or are being addressed. We review the current body of literature relevant to potential productivity from different types of gas hydrate deposits, and determine that there are consistent indications of a large production potential at high rates over long periods from a wide variety of hydrate deposits. Finally, we identify (a) features, conditions, geology and techniques that are desirable in potential production targets, (b) methods to maximize production, and (c) some of the conditions and characteristics that render certain gas hydrate deposits undesirable for production.
Rock Typing — Keys to Understanding Productivity in Tight Gas Sands
Authors: Rushing J. A. , Newsham K. E. , Blasingame T. A.
Published: February 2008

This paper presents a work-flow process to describe and characterize tight gas sands. The ultimate objective of this work-flow is to provide a consistent methodology to systematically integrate both large-scale geologic elements and small-scale rock petrology with the physical rock properties for low-permeability sandstone reservoirs. To that end, our work-flow integrates multiple data evaluation techniques and multiple data scales using a core-based rock typing approach that is designed to capture rock properties characteristic of tight gas sands.

Fundamental to this process model are identification and comparison of three different rock types — depositional, petro-graphie, and hydraulic. These rock types are defined as:

Depositional — These are rock types that are derived from eore-based descriptions of genetic units which are defined as collections of rocks grouped according to similarities in composition, texture, sedimentary structure, and stratigraphic sequence as influenced by the depositional environment. These rock types represent original large-scale rock properties present at deposition. Petrographie — These are rock types which are also described within the context of the geological framework, but the rock type criteria are based on pore-scale, microscopic imaging of the current pore structure — as well as the rock texture and composition, clay mineralogy, and diagenesis. Hydraulic — These are rock types that are also defined at the pore scale, but in this case we define "hydraulic" rock types as those that quantify the physical flow and storage properties of the rock relative to the native fluid(s) — as controlled by the dimensions, geometry, and distribution of the current pore and pore throat structure.

Each rock type represents different physical and chemical processes affecting rock properties during the depositional and paragenetic cycles. Since most tight gas sands have been subjected to post-depositional diagenesis, a comparison of all three rock types will allow us to assess the impact of diagenesis on rock properties. If diagenesis is minor, the depositional environment (and depositional rock types) as well as the expected rock properties derived from those depositional conditions will be good predictors of rock quality. However, if the reservoir rock has been subjected to significant diagenesis, the original rock properties present at deposition will be quite different than the current properties. More specifically, use of the depositional environment and the associated rock types (in isolation) to guide field development activities may result in ineffective exploitation.
Tight Gas Surveillance and Characterization: Impact of Production Logging
Authors: McCracken Michael E. , Fitz Dale , Ryan Tom
Published: February 2008

In this paper, we discuss the importance of production logging in tight gas reservoirs due to the large number of commingled entries that are typically associated with tight gas wells. We discuss the challenges associated with obtaining high quality production log data in tight gas reservoirs and the subsequent production log interpretation. Along with addressing these challenges, some initial production logging results are presented that highlight the importance of geology. These results include: 1.) Most of a well's production comes from a few zones, 2.) Some observed production rates are substantially higher than anticipated based on matrix properties, and 3.) In a few cases, sands that can be locally correlated between wells may be associated with anomalously high production rates.
Impact of Stress Sensitive Permeability on Production Data Analysis
Authors: Archer Rosalind
Published: February 2008

The dependence of reservoir permeability and porosity on pressure can have a significant impact on well performance. This paper addresses this issue theoretically, via reservoir simulation, and via production data analysis type curves. This paper presents the single phase fluid flow equation for a slightly compressible fluid in a stress sensitive reservoir in a form which can be solved in Laplace space to generate profiles of well flow rate versus time (for constant bottomhole pressure production). This is achieved by writing the flow equation in terms of the derivatives of a function involving the sum of pressure and pressure-squared terms. Reservoir simulation results concur with the theoretical prediction that depletion in a stress sensitive reservoir will be slower than in a non-stress sensitive reservoir, however ultimate recovery in the simulation cases was not affected by stress sensitivity. p/z plots for stress sensitive reservoirs show volumetrics are unaffected by stress sensitivity. Analysis of simulated production data from stress sensitive reservoirs shows that drainage area is likely to be underestimated by this approach. Permeabilities predicted from analysis using standard type curves are lower than the permeability at initial reservoir pressure. The magnitude of the reduction in the interpreted permeability naturally depends on the magnitude of the stress sensitivity.
Importance of Fabric on the Production of Gas Shales
Authors: Bustin A. M. M. , Bustin R. M. , Cui X.
Published: February 2008

The heterogeneity and complexity of gas shales cause substantial and often inexplicable variability in the production histories of gas wells. A major factor contributing to this variability is the microfabric of the matrix and the fracture network of the reservoir. It is widely postulated, although not proven, that the gas production from shales is controlled principally by Darcy flow through the fracture system and the matrix is considered important principally for gas storage. In order to gain insight and test the relative importance of fracture spacing and matrix diffusion/flow on the production of gas shales, we have developed a 2-dimensional numerical simulation model, which considers the flow of gas through both the shale matrices and the fractures for varying fabrics utilising experimental data obtained from a variety of important gas shales. The results of initial, constant parameter, numerical simulations showed that for a wide range of relative fracture permeability, matrix permeability/diffusivity and fracture spacing, the productivity of a gas shale reservoir is dependent on matrix diffusion rates. The diffusion rates and stress dependent fracture permeability data when integrated into the numerical simulator can be tested against measured production histories leading to more accurate production forecasts of new reservoirs and optimisation of field design.
The Characteristic Flow Behavior of Low-Permeability Reservoir Systems
Authors: Blasingame T. A.
Published: February 2008

This paper considers the mechanisms and characteristic flow patterns of low permeability reservoir systems. In this paper we focus on the issue of low permeability in conjunction with reservoir heterogeneity (as these often go hand in hand). Generally speaking, we focus on the single-phase gas flow case as this is most relevant — and we avoid concerns related to multiphase flow.

Low permeability reservoir systems exhibit unique flow behavior for the following reasons:

Low permeability (which yields poor utilization of reservoir pressure), this is caused in part by: –Depositional issues: very small grains, mixed with detrital muds (clays).–Diagenetic issues: clay precipitation, massive cementation, pressure compaction, etc. Reservoir heterogeneity — dictated by deposition and post-deposition (diagenetic) events, including: –Vertical heterogeneity: layering, laminae, etc.–Lateral heterogeneity: medium to large scale geologic features (e.g., turbidite deposition, faults, etc.).–Differential diagenesis, including hydrocarbon generation and migration.

These characteristics lead us to the relatively simple observation that low permeability reservoirs are simply poor conductors offluids. As a matter of background, this work discusses the issues relevant to the origin of low (and ultra-low) permeability reservoirs, but our primary focus is flow at macro- and mega-scales (as would be observed at a well). An obvious comment at this point is that the reservoir permeability and the reservoir heterogeneity are fixed constants that we can not change. While true, we can change our mechanism for accessing the reservoir (i.e., the well) and we can change our development strategy to ensure optimal performance and recovery of a particular reservoir.

As for changing our access to the reservoir, we can utilize hydraulic fracture stimulation techniques to create a conductive pathway into the reservoir from the well. This is and will be implicit in the continued development of low and ultra-low permeability reservoirs — regardless of the well type (vertical or horizontal). In this work, our emphasis is to consider the relatively simple case of a single vertical well with a hydraulic fracture and the resulting flow behavior that this type of well will experience. It is our contention that the elliptical flow regime dominates reservoir performance in low/ultra-low permeability reservoirs, and we apply both analytical and numerical solutions to a typical field case to illustrate the validity of the elliptical flow regime.
Design and Life Cycle Considerations for Unconventional Reservoir Wells
Authors: Miskimins Jennifer L.
Published: February 2008

This paper provides an overview of design and life cycle considerations for certain unconventional reservoir wells. An overview of unconventional reservoir definitions is provided. Well design and life cycle considerations are addressed from three aspects including up-front reservoir development, initial well completion, and well life and long-term considerations.

Up-front reservoir development issues discussed include well spacing, well orientation, reservoir stress orientations, and tubular metallurgy. Initial well completion issues include maximum treatment pressures and rates, treatment diversion, treatment staging, flowback and clean-up, and dewatering needs. Well life and long-term discussions include liquid loading, corrosion, refracturing and associated fracture reorientation, and the cost of abandonment.

These design considerations are evaluated using case studies for five unconventional reservoir types including shale gas (Barnett shale), tight gas (Jonah Field), tight oil (Bakken play), coalbed methane (San Juan basin), and tight heavy oil (Lost Hills Field). In evaluating the life cycle and design of unconventional reservoir wells, "one size" definitely does not fit all and valuable knowledge and a shortening of the learning curve can be achieved for new developments by studying similar, more mature fields.
Unconventional Resource Play Evaluation: A Look at the Bakken Shale Play of North Dakota
Authors: Cox Stuart A. , Cook David M. , Dunek Ken , Daniels Reagan , Jump Connie , Barree Bob
Published: February 2008

Unconventional resource plays can provide a long-term supply of oil and gas to help supplement the North American energy demands. However, obtaining a good economic return from these developments can be challenging. A successful entry into an unconventional play requires careful pre-entry analysis in order to develop meaningful production profiles and set realistic expectations. Wells completed in unconventional plays typically exhibit limited drainage areas and produce a majority of recoverable reserves at low rates. Due to the limited flow capacity of these reservoirs typical development strategies include some form of horizontal completion.

When considering a potential entry into a "new" resource play there are a number of important questions that must be answered such as "What is an appropriate range of initial production rates and reserves for the development?" or "What is the most cost effective completion method?" and "How will post drill completion efficiency be determined?". This paper will present one operator's approach to answer these questions for its entry into the Bakken Shale development of North Dakota. The paper focuses on the effective use of existing public information to frame expectations for the development. It will also present the completion design considerations and initial implementation results from the development.
Stimulating Unconventional Reservoirs: Lessons Learned, Successful Practices, Areas for Improvement
Authors: Cramer David D.
Published: February 2008

The term "unconventional reservoir" has different meanings to different people. Certain reservoirs termed unconventional have a rock matrix consisting of inter-particle pore networks with very small pore connections imparting very poor fluid-flow characteristics. Abundant volumes of oil or gas can be stored in these rocks, and often the rock is high in organic content and the source of the hydrocarbon. Yet because of marginal rock matrix quality, these reservoirs generally require both natural and induced fracture networks to enable economic recovery of the hydrocarbon. Rock types in this class include shale and coalbed methane (CBM.) The term shale is a catchall for any rock consisting of extremely small framework particles with minute pores charged with hydrocarbon and includes carbonate and quartz-rich rocks. Another type of unconventional reservoir is stacked pay units exhibiting somewhat better pore characteristics than in the case outlined above but with the individual units tending to be lenticular in shape and having an extremely small size or volume. These two classes of unconventional reservoirs are amenable to well stimulation and will be the focus of this paper.

The above rock types when commercially exploited are known as resource plays. Once a low-priority, the depletion of conventional reservoirs and improving price for oil and gas has driven unconventional reservoirs to an important place in the oil and gas industry. In some regions (i.e., Rocky Mountain province), unconventional reservoirs represent the primary target of current activity and remaining hydrocarbon development. Given their unique petrophysical properties, each type of unconventional reservoir requires a unique approach to well stimulation, with often differing objectives than exist with conventional reservoir types. This paper reviews the characteristics of the basic unconventional reservoir types, lessons learned and successful stimulation practices developed in completing these reservoirs, and areas for improvement in treatment and reservoir characterization and treatment design.
Stimulating Unconventional Reservoirs: Maximizing Network Growth while Optimizing Fracture Conductivity
Authors: Warpinski N. R. , Mayerhofer M. J. , Vincent M. C. , Cipolla C. L. , Lolon E. P.
Published: February 2008

Unconventional reservoirs such as gas shales and tight gas sands require technology-based solutions for optimum development. The successful exploitation of these reservoirs has relied on some combination of horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping to engineer economic completions. However, the requirements for economic production all hinge on the matrix permeability of these reservoirs, supplemented by the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations demonstrate that ultra-low shale permeabilities require an interconnected fracture network of moderate conductivity with a relatively small spacing between fractures to obtain reasonable recovery factors. Microseismic mapping demonstrates that such networks are achievable and the subsequent production from these reservoirs support both the modeling and the mapping. Tight gas sands, having orders of magnitude greater permeability than the gas shales, may be successfully depleted without inducing complex fracture networks, but other issues of damage and zonal coverage complicate recovery in these reservoirs. As with the shales, mapping has proved itself to be valuable in assessing the fracturing results.
Role of Natural Fractures and Slot Porosity on Tight Gas Sands
Authors: Aguilera Roberto
Published: February 2008

Naturally fractured tight gas sands have come of age in the United States. They will also come of age in Canada within the next few years and in the rest of the world within the next few decades.

This work discusses the role of natural fractures and slot porosity on tight gas sands as they relate to geoscience, drilling, completion, stimulations, petrophysics, well testing, and reservoir engineering.

It is concluded that natural fractures and/or slot porosity play, and will continue to play, an important role in the successful and economic production of gas from tight sands. Research leading to innovating technologies that presumably will reduce capital and operating costs will play a key role in the development of this resource. Understanding the rocks and the regional variability of fracture distribution and diagenesis is the cornerstone of this research.
Modeling of Mixed-Gas Adsorption and Diffusion in Coalbed Reservoirs
Authors: Shi J. Q. , Durucan S.
Published: February 2008

Commercial CBM production is almost exclusively through reservoir pressure depletion (primary recovery). Enhanced coalbed methane recovery (ECBM), involving injection of pure N2/CO2 or a mixture of the two, such as power plant flue gas, is a technology that has the potential to recover a larger fraction of methane in place without excessively reducing the reservoir pressure. CO2-ECBM has an added benefit that a potentially large volume of greenhouse gas can be stored in deep coal seams globally. The use of numerical models is essential in the development of the ECBM and CO2 storage technology. The quasi-steady state Fickian diffusion equation, together with the Langmuir equation, has been almost exclusively used in numerical simulation of primary coalbed methane production. Assuming that the individual gas component in a multicomponent system diffuses independently, the quasi-steady state Fickian diffusion equation can be readily extended to model mixed-gas diffusion. In the recent years, attempts have been made to use this approach, in conjunction with the extended Langmuir equation, to model ECBM/CO2 storage field pilots as well as laboratory flooding tests. However, this modelling approach for mixed-gas diffusion lacks theoretical rigour as the interaction between different gas components is not accounted for, though the practical significance of doing so in coalbeds is not well understood at present.

A reservoir simulation sensitivity study on the Yubari CO2 storage pilot project, Japan, is presented. The sensitivity study with CO2 and CH4 sorption times indicates that the sorption time for CO2 has a much pronounced impact on the back-produced gas composition. The study has also highlighted the limitation of the extended Langmuir equation for ternary system predictions. Although inconclusive, the sensitivity results suggest that the N2 component sorption in the coalbed reservoir is over-estimated by at least 20% by the model.
Identifying Bypassed and Ineffectively Stimulated Layers in a Well With Commingled Production From Multiple Layers: Mesaverde Case History
Authors: Craig David P. , Odegard Chad E.
Published: February 2008

In an effort to examine well and reservoir connectivity for wells drilled through multiple low-permeability stacked lenticular reservoirs, we present case histories from the Piceance basin of Western Colorado. We review the completion and subsequent abandonment of an air-drilled high-angle slant hole through the Williams Fork sandstones in Grand Valley field as well as a high-angle slant hole drilled through and completed in two Williams Fork Mesaverde sandstones. We also review a case history describing single-entry-point fracture treatments in vertical wells designed to "frac into" sandstones near the entry point, and we describe a post-frac evaluation of propped fracture communication with sandstones adjacent to the single entry point. Lastly, we present a case history showing the results of a refracture-candidate evaluation and isolated-layer restimulation pilot program in the Piceance Basin where it is known that between 10% and 30% of the Meseverde layers targeted for fracturing are ineffectively stimulated or inadvertently bypassed during primary fracturing operations. The refracture-candidate pilot program provided the following.

An evaluation of production logs as a refracture-candidate diagnostic. An evaluation of short-term pressure buildup tests as a refracture-candidate diagnostic. An evaluation of fracture-injection/falloff tests as a refracture-candidate diagnostic.

Four discrete Mesaverde sandstones were tested as part of the refracture-candidate pilot program. Of the four layers selected for testing, numerous microseismic events were mapped during the initial fracture treatments in two, and no events were recorded in the other two. The refracture-candidate pilot program included recording a new production log and completing short-term pressure buildup and nitrogen fracture-injection/falloff tests in each isolated layer. The nitrogen fracture-injection/falloff tests confirmed the microseismic mapping during the original completion, that is, layers without microseismic events did not have a conductive hydraulic fracture based on the nitrogen-injection/falloff analysis. Consequently, bypassed or ineffectively stimulated layers can be identified with refracture-candidate diagnostics.
Nitrate in Tile Drainage of the Semiarid Palouse Basin
Authors: Keller C. Kent , Butcher Caroline N. , Smith Jeffrey L. , Allen‐King Richelle M.
Published: February 2008

Topographically heterogeneous agricultural landscapes can complicate and accelerate agrochemical contamination of streams due to rapid transport of water and chemicals to poorly drained lower‐landscape positions and shallow ground water. In the semiarid Palouse region, large parts of these landscapes have been tile drained to enhance crop yield. From 2000–2004 we monitored the discharge of a tile drain (TD) and a nearby profile of soil water for nitrate concentration ([NO3]), electrical conductivity level (EC), and water content to develop a conceptual framework describing soil nitrate occurrence and loss via subsurface pathways. Tile‐drain baseflow [NO3] was consistently 4 mg N L−1 and baseflow EC was 200 to 300 μS cm−1 Each year sudden synoptic increases in TD discharge and [NO3] occurred in early winter following ∼150 mm of fall precipitation, which saturated the soil and mobilized high‐[NO3] soil water throughout the profile. The greatest TD [NO3] (20–30 mg N L−1) occurred approximately contemporaneous with greatest TD discharges. The EC decrease each year (to ∼100 μS cm−1) during high discharge, a dilution effect, lagged ∼1 mo behind the first appearance of high [NO3] and was consistent with advective transport of low‐EC water from the shallow profile under saturated conditions. Water‐budget considerations and temporal [NO3] patterns suggest that these processes deliver water to the TD from both lower‐ and upper‐slope positions, the latter via lateral flow during the high‐flow season. Management practices that reduce the fall reservoir of soil nitrate might be effective in reducing N loading to streams and shallow ground water in this region.
Impact of Glyphosate‐Tolerant Soybean and Glufosinate‐Tolerant Corn Production on Herbicide Losses in Surface Runoff
Authors: Shipitalo Martin J. , Malone Robert W. , Owens Lloyd B.
Published: February 2008

Residual herbicides used in the production of soybean [Glycine max (L.) Merr] and corn (Zea mays L.) are often detected in surface runoff at concentrations exceeding their maximum contaminant levels (MCL) or health advisory levels (HAL). With the advent of transgenic, glyphosate‐tolerant soybean and glufosinate‐tolerant corn this concern might be reduced by replacing some of the residual herbicides with short half‐life, strongly sorbed, contact herbicides. We applied both herbicide types to two chiseled and two no‐till watersheds in a 2‐yr corn–soybean rotation and at half rates to three disked watersheds in a 3‐yr corn/soybean/wheat (Triticum aestivum L.)‐red clover (Trifolium pratense L.) rotation and monitored herbicide losses in runoff water for four crop years. In soybean years, average glyphosate loss (0.07%) was ∼1/7 that of metribuzin (0.48%) and about one‐half that of alachlor (0.12%), residual herbicides it can replace. Maximum, annual, flow‐weighted concentration of glyphosate (9.2 μg L−1) was well below its 700 μg L−1 MCL and metribuzin (9.5 μg L−1) was well below its 200 μg L−1 HAL, whereas alachlor (44.5 μg L−1) was well above its 2 μg L−1 MCL. In corn years, average glufosinate loss (0.10%) was similar to losses of alachlor (0.07%) and linuron (0.15%), but about one‐fourth that of atrazine (0.37%). Maximum, annual, flow‐weighted concentration of glufosinate (no MCL) was 3.5 μg L−1, whereas atrazine (31.5 μg L−1) and alachlor (9.8 μg L−1) substantially exceeded their MCLs of 3 and 2 μg L−1, respectively. Regardless of tillage system, flow‐weighted atrazine and alachlor concentrations exceeded their MCLs in at least one crop year. Replacing these herbicides with glyphosate and glufosinate can reduce the occurrence of dissolved herbicide concentrations in runoff exceeding drinking water standards.
Phosphorus Fertilizer and Grazing Management Effects on Phosphorus in Runoff from Dairy Pastures
Authors: Dougherty Warwick J. , Nicholls Paul J. , Milham Paul J. , Havilah Euie J. , Lawrie Roy A.
Published: February 2008

Fertilizer phosphorus (P) and grazing‐related factors can influence runoff P concentrations from grazed pastures. To investigate these effects, we monitored the concentrations of P in surface runoff from grazed dairy pasture plots (50 × 25 m) treated with four fertilizer P rates (0, 20, 40, and 80 kg ha−1 yr−1) for 3.5 yr at Camden, New South Wales. Total P concentrations in runoff were high (0.86–11.13 mg L−1) even from the control plot (average 1.94 mg L−1). Phosphorus fertilizer significantly (P < 0.001) increased runoff P concentrations (average runoff P concentrations from the P20, P40, and P80 treatments were 2.78, 3.32, and 5.57 mg L−1, respectively). However, the magnitude of the effect of P fertilizer varied between runoff events (P < 0.01). Further analysis revealed the combined effects on runoff P concentration of P rate, P rate × number of applications (P < 0.001), P rate × time since fertilizer (P < 0.001), dung P (P < 0.001), time since grazing (P < 0.05), and pasture biomass (P < 0.001). A conceptual model of the sources of P in runoff comprising three components is proposed to explain the mobilization of P in runoff and to identify strategies to reduce runoff P concentrations. Our data suggest that the principal strategy for minimizing runoff P concentrations from grazed dairy pastures should be the maintenance of soil P at or near the agronomic optimum by the use of appropriate rates of P fertilizer.
Evaluation of Fumigation and Surface Seal Methods on Fumigant Emissions in an Orchard Replant Field
Authors: Gao Suduan , Trout Thomas J. , Schneider Sally
Published: February 2008

Soil fumigation is an important management practice for controlling soil pests and enabling successful replanting of orchards. Reducing emissions is required to minimize the possible worker and bystander risk and the contribution of fumigants to the atmosphere as volatile organic compounds that lead to the formation of ground‐level ozone. A field trial was conducted in a peach orchard replant field to investigate the effects of fumigation method (shank‐injection vs. subsurface drip‐application treatments) and surface treatments (water applications and plastic tarps) on emissions of 1,3‐dichloropropene (1,3‐D) and chloropicrin (CP) from shank‐injection of Telone C‐35 and drip application of InLine. Treatments included control (no water or soil surface treatment); standard high‐density polyethylene (HDPE) tarp, virtually impermeable film (VIF) tarp, and pre‐irrigation, all over shank injection; and HDPE tarp over and irrigation with micro‐sprinklers before and after the drip application. The highest 1,3‐D and CP emission losses over a 2‐wk monitoring period were from the control (36% 1,3‐D and 30% CP) and HDPE tarp (43% 1,3‐D and 17% CP) over shank injection. The pre‐irrigation 4 d before fumigation and VIF tarp over shank injection had similar total emission losses (19% 1,3‐D and 8–9% CP). The HDPE tarp and irrigations over subsurface drip‐application treatments resulted in similar and the lowest emission losses (12–13% 1,3‐D, and 2–3% CP). Lower fumigant concentrations in the soil‐gas phase were observed with drip‐application than in the shank‐injection treatments; however, all treatments provided 100% kill to citrus nematodes in bags buried from 30 to 90 cm depth. Pre‐irrigation and drip application seem to be effective to minimize emissions of 1,3‐D and CP.
When Does Nitrate Become a Risk for Humans?
Authors: Powlson David S. , Addiscott Tom M. , Benjamin Nigel , Cassman Ken G. , de Kok Theo M. , van Grinsven Hans , L'hirondel Jean‐Louis , Avery Alex A. , van Kessel Chris
Published: February 2008

Is nitrate harmful to humans? Are the current limits for nitrate concentration in drinking water justified by science? There is substantial disagreement among scientists over the interpretation of evidence on the issue. There are two main health issues: the linkage between nitrate and (i) infant methaemoglobinaemia, also known as blue baby syndrome, and (ii) cancers of the digestive tract. The evidence for nitrate as a cause of these serious diseases remains controversial. On one hand there is evidence that shows there is no clear association between nitrate in drinking water and the two main health issues with which it has been linked, and there is even evidence emerging of a possible benefit of nitrate in cardiovascular health. There is also evidence of nitrate intake giving protection against infections such as gastroenteritis. Some scientists suggest that there is sufficient evidence for increasing the permitted concentration of nitrate in drinking water without increasing risks to human health. However, subgroups within a population may be more susceptible than others to the adverse health effects of nitrate. Moreover, individuals with increased rates of endogenous formation of carcinogenic N‐nitroso compounds are likely to be susceptible to the development of cancers in the digestive system. Given the lack of consensus, there is an urgent need for a comprehensive, independent study to determine whether the current nitrate limit for drinking water is scientifically justified or whether it could safely be raised.
Land Management Impacts on Dairy‐Derived Dissolved Organic Carbon in Ground Water
Authors: Chomycia Jill C. , Hernes Peter J. , Harter Thomas , Bergamaschi Brian A.
Published: February 2008

Dairy operations have the potential to elevate dissolved organic carbon (DOC) levels in ground water, where it may interact with organic and inorganic contaminants, fuel denitrification, and may present problems for drinking water treatment. Total and percent bioavailable DOC and total and carbon‐specific trihalomethane (THM) formation potential (TTHMFP and STHMFP, respectively) were determined for shallow ground water samples from beneath a dairy farm in the San Joaquin Valley, California. Sixteen wells influenced by specific land management areas were sampled over 3 yr. Measured DOC concentrations were significantly elevated over the background as measured at an upgradient monitoring well, ranging from 13 to 55 mg L−1 in wells downgradient from wastewater ponds, 8 to 30 mg L−1 in corral wells, 5 to 12 mg L−1 in tile drains, and 4 to 15 mg L−1 in wells associated with manured fields. These DOC concentrations were at the upper range or greatly exceeded concentrations in most surface water bodies used as drinking water sources in California. DOC concentrations in individual wells varied by up to a factor of two over the duration of this study, indicating a dynamic system of sources and degradation. DOC bioavailability over 21 d ranged from 3 to 10%, comparable to surface water systems and demonstrating the potential for dairy‐derived DOC to influence dissolved oxygen concentrations (nearly all wells were hypoxic to anoxic) and denitrification. TTHMFP measurements across all management units ranged from 141 to 1731 μg L−1, well in excess of the maximum contaminant level of 80 μg L−1 established by the Environmental Protection Agency. STHMFP measurements demonstrated over twofold variation (∼4 to ∼8 mmol total THM/mol DOC) across the management areas, indicating the dependence of reactivity on DOC composition. The results indicate that land management strongly controls the quantity and quality of DOC to reach shallow ground water and hence should be considered when managing ground water resources and in any efforts to mitigate contamination of ground water with carbon‐based contaminants, such as pesticides and pharmaceuticals.
Environmental Impacts of Training Activities at an Air Weapons Range
Authors: Bordeleau Geneviève , Martel Richard , Ampleman Guy , Thiboutot Sonia
Published: February 2008

Within Canada, it has been recognized in the last decade that military training activities may have impacts on the environmental quality of training ranges. However, impacts of activities specific to Air Force Bases have not yet been intensely documented. A hydrogeological study was accomplished at the Cold Lake Air Weapons Range, Alberta, to evaluate the environmental impacts of using bombs, rockets, strafing, and open burning/open detonation (OB/OD) on the quality of soil, ground water, surface water, and lake sediments. Samples were analyzed for metals, anions, ammonium perchlorate (NH4ClO4), and energetic materials (EM). It was found that training activities did not result in measured values being exceeded on the basis of guidance values for surface water and lake sediments. Contamination by metals was mostly limited to soils, and some metals may be related to the use of bombs (Cd, Cu, Pb), strafe (Cu), and rockets (As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, U, V, Zn). TNT (2,4,6‐trinitrotoluene) was the main EM found in soils, while RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine) was more common in ground water. Both are related to live bombing, while nitroglycerine (NG) is related to rocket use and was detected in soils only. Aluminum, nitrate, and ammonium perchlorate detected in ground water may be related to live bombing or rockets. OB/OD operations resulted in the presence of various EM in soils, and of perchlorate and nitrate in ground water. Contamination by metals and explosives in soils was localized around the targets and varied significantly in time; however, in ground water it was more constant and may persist for a period of several years after a target has been removed.
Metal Release from Bottom Sediments of Ocoee Lake No. 3, a Primary Catchment Area for the Ducktown Mining District
Authors: Lee Giehyeon , Faure Gunter , Bigham Jerry M. , Williams David J.
Published: February 2008

Ocoee Lake No. 3 is the first reservoir receiving suspended sediments contaminated with trace metals discharged by acid mine effluents from the Ducktown Mining District, Tennessee. Bottom sediments (0–5 cm) from the lake were sampled to assess the potential for future adverse environmental effects if no remediation controls or activities are implemented. The sediments were found to include a major component (173 ± 19 g kg−1) that dissolved in 6 mol L−1 HCl within 24 h. This acid‐soluble and relatively labile fraction contained high concentrations of Fe (460 ± 40 g kg−1), Al (99 ± 11 g kg−1), Mn (10 ± 8 g kg−1), Cu (2000 ± 700 mg kg−1), Zn (1300 ± 200 mg kg−1), and Pb (300 ± 200 mg kg−1). When the pH of water in contact with the sediment was decreased experimentally from 6.4 to 2.6, the concentrations of dissolved trace metals increased by factors of 2200 for Pb, 160 for Cu, 21 for Zn, 9 for Cd, 8 for Ni, and 5 for Co. The order in which metals were released with decreasing pH was the reverse of that reported for pH‐dependent sorption of these metals in upstream systems. Substantial release of trace metals from the sediment was observed even by a modest decrease of pH from 6.4 to 5.9. Therefore, the metal‐rich sediment of the lake should be considered as potentially hazardous to bottom‐dwelling aquatic species and other organisms in the local food chain. In addition, if the reservoir is dredged or if the dam is removed, the accumulated sediment may have to be treated for recovery of sorbed metals.
Water Quality Modeling of Fertilizer Management Impacts on Nitrate Losses in Tile Drains at the Field Scale
Authors: Nangia V. , Gowda P. H. , Mulla D. J. , Sands G. R.
Published: February 2008

Nitrate losses from subsurface tile drained row cropland in the Upper Midwest U.S. contribute to hypoxia in the Gulf of Mexico. Strategies are needed to reduce nitrate losses to the Mississippi River. This paper evaluates the effect of fertilizer rate and timing on nitrate losses in two (East and West) commercial row crop fields located in south‐central Minnesota. The Agricultural Drainage and Pesticide Transport (ADAPT) model was calibrated and validated for monthly subsurface tile drain flow and nitrate losses for a period of 1999–2003. Good agreement was found between observed and predicted tile drain flow and nitrate losses during the calibration period, with Nash‐Sutcliffe modeling efficiencies of 0.75 and 0.56, respectively. Better agreements were observed for the validation period. The calibrated model was then used to evaluate the effects of rate and timing of fertilizer application on nitrate losses with a 50‐yr climatic record (1954–2003). Significant reductions in nitrate losses were predicted by reducing fertilizer application rates and changing timing. A 13% reduction in nitrate losses was predicted when fall fertilizer application rate was reduced from 180 to 123 kg/ha. A further 9% reduction in nitrate losses can be achieved when switching from fall to spring application. Larger reductions in nitrate losses would require changes in fertilizer rate and timing, as well as other practices such as changing tile drain spacings and/or depths, fall cover cropping, or conversion of crop land to pasture.
The Impact of Alum Addition on Organic P Transformations in Poultry Litter and Litter‐Amended Soil
Authors: Warren Jason G. , Penn Chad J. , McGrath Joshua M. , Sistani Karamat
Published: February 2008

Poultry litter treatment with alum (Al2(SO4)3·18H2O) lowers litter phosphorus (P) solubility and therefore can lower litter P release to runoff after land application. Lower P solubility in litter is generally attributed to aluminum‐phosphate complex formation. However, recent studies suggest that alum additions to poultry litter may influence organic P mineralization. Therefore, alum‐treated and untreated litters were incubated for 93 d to assess organic P transformations during simulated storage. A 62‐d soil incubation was also conducted to determine the fate of incorporated litter organic P, which included alum‐treated litter, untreated litter, KH2PO4 applied at 60 mg P kg−1 of soil, and an unamended control. Liquid‐state 31P nuclear magnetic resonance indicated that phytic acid was the only organic P compound present, accounting for 50 and 45% of the total P in untreated and alum‐treated litters, respectively, before incubation and declined to 9 and 37% after 93 d of storage‐simulating incubation. Sequential fractionation of litters showed that alum addition to litter transformed 30% of the organic P from the 1.0 mol L−1 HCl to the 0.1 mol L−1 NaOH extractable fraction and that both organic P fractions were more persistent in alum‐treated litter compared with untreated litter. The soil incubation revealed that 0.1 mol L−1 NaOH–extractable organic P was more recalcitrant after mixing than was the 1.0 mol L−1 HCl–extractable organic P. Thus, adding alum to litter inhibits organic P mineralization during storage and promotes the formation of alkaline extractable organic P that sustains lower P solubility in the soil environment.
Rhamnolipid Morphology and Phenanthrene Solubility at Different pH Values
Authors: Shin Kyung‐Hee , Kim Kyoung‐Woong , Kim Ju‐Yong , Lee Kyung‐Eun , Han Sung‐Sik
Published: February 2008

The effect of pH and rhamnolipids on the solubility of phenanthrene was investigated in a sand–water system. Batch phenanthrene solubilization experiments in this system showed that the highest phenanthrene solubility occurred at pH 5 in the presence of 240 and 150 mg L−1 rhamnolipids. As the pH was increased from 5 to 7, the apparent solubility of phenanthrene decreased and then stabilized from pH 7 to 8. At pH 4, a dramatic decrease in phenanthrene solubility was observed. This result is in contrast to previous findings obtained in an aqueous system without soil particles. To investigate the reason for this decrease, the critical micelle concentrations (CMCs) were measured in the presence or absence of sand particles, and the maximum amount of sorbed biosurfactant at each pH was calculated based on the differences of the two CMC values. More rhamnolipid molecules were lost by the sorption into sand particles at pH 4 than at other pH values; this explains the dramatic decrease of solubility at pH 4 in the sand–water system. To confirm the explanation for the different solubilizing capacity that results from the structural change of biosurfactant aggregate, cryo‐transmission electron microscopy was used. Micrographs showed that the rhamnolipid morphology changed from large lamellar sheets, to vesicle, and then to micelle as the pH increased. The large and multilamellar vesicles at pH 5 were considered to be the most effective structure for the solubilization of phenanthrene.