bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Speed Civil Transport Hybrid Laminate Sandwich Fuselage Panel Test
Authors: Miller M , Rufin AC , Westre WN , Samavedam G
Published: March 2009

Hybrid laminates consisting of interspersed titanium foils and carbon fiber-reinforced polymer-matrix composite (PMC) plies are among the leading material candidates for High-Speed Civil Transport (HSCT) primary structure. To demonstrate the feasibility of fabricating large adhesive bonded honeycomb sandwich subcomponents with hybrid laminate facesheets, a 1.9-meter radius × 3.0-meter long curved panel representative of the HSCT forward fuselage was built and tested. The subcomponent was first tested to twice the equivalent constant-load amplitude fatigue design service objective (66 000 cycles). The panel ran for another full design service objective with longitudinal notches, plus an additional 2 500 cycles with a circumferential notch. Finally, the panel was successfully tested to approximate regulatory residual strength load requirements (1.15 × max. fatigue loads). These tests demonstrated at a subcomponent level the durability of titanium/carbon fiber-reinforced PMC laminates and confirmed the hypothesis that fiber bridging can significantly retard the rate at which damage progresses from a crack-like defect in these materials.
Prediction of Fatigue Life Under Helicopter Loading Spectra for Safe Life and Damage Tolerant Design
Authors: Irving PE , Buller RG
Published: March 2009

Variable amplitude loading spectra have been developed from service data gathered on a helicopter rotor head. Over 90% of the cycles have r values between 0.7 and 0.9. Variable amplitude fatigue crack growth tests have been performed using the modified rotorcraft spectra on CT specimens of 10-2-3 β-titanium alloy and a 7010 aluminium alloy. Samples were subjected to variations on the original loading spectrum where smaller load cycles had been progressively removed. Crack closure was monitored at intervals throughout selected load sequences. The results showed that the small range, high mean cycles originating in rotor vibrations contributed over 80% of the crack growth damage. In the titanium samples the contribution of the different parts of the spectrum could be predicted using a simple summation of constant amplitude crack growth increments, without load interaction effects. In the aluminium alloy, the situation was more complicated, with a reduced contribution of the small cycles. The implications for damage tolerance in helicopter components are discussed.
Mixed-Mode Fatigue Failure in Structural Adhesives
Authors: Sancaktar E
Published: March 2009

Fatigue data obtained under biaxial loading conditions for adhesively bonded joints are used to plot S-N type diagrams to assess the effects of biaxiality in loading. Independently Loaded Mixed-Mode Specimens (ILMMS) are used for data collection purposes. These specimens are basically two (steel) beams bonded together to be fatigue loaded under cantilever (opening) mode while a simultaneous but physically separate inplane (static) shear load is also induced with the aid of a small hydraulic piston embedded in the specimen. Application of such static shear loads on the bonded joint results in S-N behavior different than that obtained with opening load only. The model adhesives used are Metlbond 1113-2 and Metlbond 1113 solid film thermoset adhesives similar to those commonly used in aircraft and aerospace industries. The former is an elastomer-modified epoxy adhesive and the latter is identical except that it contains a synthetic carrier cloth. Thus, the effect of carrier cloth in adhesive's S-N behavior is also assessed. Analytically, the classical linear log-log representation of the adhesive S-N data in log PImax versus log Nc or log PII versus log Nc formats is explored. The modifications necessary to reflect the effects of biaxiality in loading and also the presence of a carrier cloth are assessed. The fatigue failure results are also compared with the results obtained under monotonic biaxial loading conditions.
Ductile Crack Growth from Simulated Defects in Strength Overmatched Butt Welds
Authors: Nishioka OS , Panontin TL
Published: March 2009

Defects that develop in welds during the fabrication process are frequently manifested as embedded flaws from lack of fusion or lack of penetration. Fracture analyses of welded structures must be able to assess the effect of such defects on the structural integrity of weldments; however, the transferability of R-curves measured in laboratory specimens to defective structural welds has not been fully examined.

In the current study, the fracture behavior of an overmatched butt weld containing a simulated buried, lack-of-penetration defect is studied. A specimen designed to simulate pressure vessel butt welds is considered; namely, a center crack panel specimen, of 1.25 inch by 1.25 inch cross section, loaded in tension. The stress-relieved double-V weld has a yield strength 50% higher than that of the plate material, and displays upper shelf fracture behavior at room temperature. Specimens are precracked or notched, loaded monotonically while load-CMOD measurements are made, then stopped and heat tinted to mark the extent of ductile crack growth.

These measurements are compared to predictions made using finite element analysis of the specimens using the fracture mechanics code Warp3D, which models void growth using the Gurson-Tvergaard dilitant plasticity formulation within fixed sized computational cells ahead of the crack front. Calibration data for the finite element analyses, namely cell size and initial material porosities, are obtained by matching computational predictions to experimental results from tests of welded compact tension specimens. The calibrated methodology is then used to predict ductile crack growth in defective welds in a structural crack geometry. The R-curves measured in compact tension specimens are compared to those obtained in multi-specimen weld tests, and conclusions as to the transferability of R-curves are discussed.
Predicting Extensive Stable Tearing in Structural Components
Authors: Dexter RJ , Gentilcore ML
Published: March 2009

Cracked structural components fabricated from relatively thin sections (less than 26 mm thick) of common structural steels and weld metals (with minimum Charpy toughness requirements) will fail by ductile tearing at service temperatures. In order to estimate the residual ductility of cracked structural steel members; it is necessary to predict hundreds of millimeters of crack extension as a function of applied displacement. A number of problems with application of the J-R curve approach to cases of such extensive crack growth are described. A very simple approach, i.e. predicting crack extension using a constant crack-opening angle, is shown to be reasonably accurate. Over 30 large-scale welded steel members containing fatigue cracks were loaded under displacement control. These members, fabricated from HSLA-80 steel and EH-36 steel, exhibited a crack-opening angle of 0.24 radian for both steels in tension and in bending.
Volatile Organic Compounds in the Environment: A Multimedia Perspective
Authors: Cohen Y
Published: March 2009

The environment is a complex system of interacting environmental media. Pollutants do not stay in the medium where they originate but move across environmental phase boundaries. The distribution of pollutants throughout the various environmental compartments (for example, air, water, soil, and biota) is the result of complex physical, chemical, and biological processes. The resulting environmental and human health risks depend upon the degree of exposure of human and ecological receptors, via multiple pathways, to these chemicals. Thus, environmental pollution is a multimedia problem. Volatile organic compounds (VOCs), in particular, are very mobile in the environment. For example, VOCs which are initially present in the soil or water media can readily volatilize to the atmosphere where they can be transported over significant distances from the source location. In this paper an overview is presented of VOC sources, VOC ambient levels, the multimedia distribution of VOCs in the environment, and multipathway exposure to VOCs.
Taking Inventory on VOC Releases from Amoco's Yorktown Refinery
Authors: Klee HH , Schmitt RE , Podar MK , Harrass MC
Published: March 2009

Amoco's Yorktown, Virginia, refinery is a 35-year-old, 53 000 bbl/day facility that manufactures gasoline, heating oil, liquid petroleum gas, sulfur, and coke. In a cooperative and voluntary effort, Amoco Corporation and the U.S. Environmental Protection Agency conducted a joint project to study polluation prevention opportunities at an operating industrial facility.

Source reduction efforts—key to pollution prevention strategies—require knowledge of specific sources of releases. However, data on releases from individual process units are limited in favor of data to monitor existing end-of-pipe pollution control requirements. The study's sampling program sought to portray the distribution of releases within the refinery, their management within the refinery, and ultimate releases leaving the refinery. Subsequent tests of blowdown stack and fugitive emissions further improved total release estimates.

The initial study estimated that the refinery generates about 25 000 metric tons (t)/year of potential pollutants. Of these, about half are released from the refinery as airborne, waterborne, or land-disposed releases. Airborne releases comprise the majority of releases by mass, about 12 000 t/year. Most of the airborne releases are volatile organic compound hydrocarbons. The inventory sampling project and subsequent work identified differences with Toxic Release Inventory (TRI) values and standard emission factors (AP-42). The inventory and other data provided an opportunity to consider options for, and limitations of, specific pollution prevention or source reduction strategies.
Estimation of Emissions of Volatile Organic Compounds (VOCs) from Canadian Residences
Authors: Davis CS , Otson R
Published: March 2009

Estimates of emissions of ten VOCs from Canadian residences based on Eq 1, where Ci and Co, respectively, are the indoor and outdoor concentrations, ach is the number of air changes per hour, V the average house volume, and N the number of houses, ranged from 14 tonnes/y (benzene) to 227 tonnes/y (toluene). E=(Ci−Co)×ach×V×N Measured ambient benzene concentrations in Metropolitan Toronto (annual mean of 2 to 3 μg/m3) were within a factor of 10 of box model predictions based on a benzene emission inventory. Predicted ambient concentrations for the VOCs with the three highest residential emissions (toluene, decane, and 1,4-dichlorobenzene) were a negligible fraction of measured ambient concentrations in Metropolitan Toronto. Canadian indoor emissions for selected VOCs found in household solvents were a small fraction (0.2 to 2.3%) of the residential solvent usage. Indoor and outdoor VOC concentration data in conjunction with air exchange rates are useful in estimating VOC emissions from residences.
Vapor-Phase Organic Compounds in Canadian Residences
Authors: Otson R
Published: March 2009

A national average of 0.464 mg/m3 was calculated for the total concentration of 40 organic compounds detected previously in 757 randomly selected Canadian homes. Reanalysis of a composite sample representative of all the homes by gas chromatography/mass spectrometry allowed quantitation of 52 additional compounds. Overall, the total of concentrations for the 92 vapor-phase organic compounds (VPOCs) averaged 0.829 mg/m3 in the homes. The average total VPOCs burden was estimated to be at least 1.4 mg/m3, and probably >2 mg/m3, when extraction recoveries and unidentified organics in the composite sample were considered. Factor analysis of data for 26 VOCs and other variables collected in the national pilot study indicated associations between some variables (for example, hydrocarbons, season, temperature, humidity). Possible sources (fuels, carpets, paints, etc.) of the 26 VOCs were identified by comparison of the factor analysis results with information in the Canadian Indoor Source Profile database and the scientific literature.
Sensory Irritation in Mice Exposed to VOC Emissions from Indoor Products
Authors: Muller WJ , Black MS
Published: March 2009

An ASTM standard method for estimation of sensory irritation (SI) in mice of airborne chemicals (E 981-84) was modified and applied to the estimation of irritation caused by volatile organic compound (VOC) emissions of products used in indoor environments. This method has the potential ability to relate the results from animal studies to expected human responses. VOC emissions of indoor products are commonly tested using small environmental chambers, according to ASTM standard guide D 5116-90. This standard guidance was used as the basis for generating airborne VOCs emitted from samples of carpet, ceiling tile, wall-covering, resilient flooring, and veneer. Four mice in each test were exposed to these emissions. The changes in the respiratory waveform and respiratory frequency of exposed mice were used to determine the relative irritancy during each exposure. Experimental variables included the product chamber air temperature and the construction material of the environmental chambers (glass or stainless steel) that were used to generate the exposure atmosphere. Increased temperature was found to induce the irritation response; however, chemical analysis indicated that the relative concentrations of major VOCs in product emissions also change in response to elevated temperature. The type of construction material of the environmental chamber was not found to affect the response of the animals above biological variability, although a trend toward increased irritation was observed using glass chambers. The chemical atmospheres were comparable for the two chamber types.
A Modified Gravimetric Method for Measuring Rates of Vapor Adsorption and Desorption on Soils. Kinetics of Toluene Adsorption/Desorption on Bentonite
Authors: Grismer ME , Labolle E , Raihala T , Eweis J
Published: March 2009

In arid and semi-arid regions where net infiltration and soil moisture are relatively low, movement of volatile organic compounds (VOC) in the vadose zone may be dominated by vapor transport and adsorption mechanisms. The objective of this study is to develop the experimental methods necessary to determine the rate of isothermal adsorption and desorption, and the adsorption capacity of toluene (and other VOCs) onto different soils and minerals subject to a range of initial water contents and temperatures. The proposed method is a modification of the gravimetric method described by both Brooks and Grismer. A stainless steel chamber houses a load cell connected through a serial interface to a computer. After sealing the dry adsorbent (soil) in the chamber, the chamber air is purged using dewatered nitrogen gas before introduction of the adsorbate (VOC). The computer, through the interface, directs the load cell and records sample mass at preselected time intervals without additional supervision. The method is applied to measure rates of adsorption and desorption of toluene on bentonite. Toluene sorption rates are modeled using a second-order rate equation described by Grismer that yielded an initial rate parameter equivalent to that for water vapor adsorption despite the toluene having a much smaller adsorption capacity. The results illustrate the simplicity of the proposed method.
The Fate And Behavior of Volatile Aromatic Hydrocarbons in Sewage Sludge-Amended Soil
Authors: Wilson SC , Jones KC
Published: March 2009

The fate and behavior of five commonly occurring aromatic volatile organic compounds (VOCs), namely toluene, ethyl benzene, and o-, m-, and p-xylene, were investigated in sewage sludge-amended soil. Laboratory experiments were conducted to investigate VOC concentrations in sludge-amended soil for different soils and at different sludge application rates over 31 days. Results indicated that VOC loss rates decreased with increased soil organic matter content and increased sludge application rate. VOC loss rates in spiked samples were found to be comparable to those in unspiked samples over 31 days. Results from laboratory experiments also indicated that abiotic loss processes were more important than biological degradation for the removal of VOCs from sewage sludge-amended soil. VOC loss rates were also compared in a field study where sludge was applied to grassed and plowed plots.
Solid-Phase Microextraction of VOCs in Water
Authors: Pratt K , Shirey R , Mani V
Published: March 2009

The measurement of very low concentrations of organic compounds in the environment has been a subject of research for many years. Recently, the sample preparation in the analysis of aqueous samples has been achieved by solid phase microextraction (SPME). This method has been shown to be fast, inexpensive, solventless, portable and automatable. SPME has several advantages over conventional liquid-liquid extraction. SPME has been shown to be a quantitative technique for volatile and semivolatile compounds from gaseous and liquid samples. The quantization by SPME is also linear over four orders of magnitude. As this method can reach a detection limit of 15 ppt (parts per trillion) for several compounds and can be easily automated, the analysis of volatile organic compounds (VOCs) in the environment, in particular, water samples, is highly advantageous by this method. This study will describe the analysis of volatile organics, BTEX, and halogenated organics in water. The lowest limit of detection, linearity, and other parameters will be discussed. The analysis of a soil sample taken near an oil storage tank for VOCs by SPME will be described. A comparison between different fibers (different types of coating materials and film thickness) using different columns will be described in this work.
Estimating VOC Emissions from Waste Water Treatment Units Using a Flow-Through Flux Chamber and Chemdat7
Authors: Rabideau CG , Comey KR
Published: March 2009

There is increasing concern in the petroleum industry for a practical method of accurately quantifying refinery volatile organic compound (VOC) emissions. The U.S. Environmental Protection Agency (EPA) developed the Chemdat7 emission rate model to predict VOC emissions from surface impoundments, waste-water treatment plants, and land farms for regulatory purposes. Previous studies have indicated that Chemdat7 significantly overpredicted VOC emissions. Much of the model evaluation of Chemdat7 used the EPA isolation environmental flux chamber. There are some concerns in using the EPA isolation flux chamber for measurement of fugitive emissions from surface impoundments due to its effect on ambient wind velocity, temperature, and solar radiation. This paper discusses an alternative method for quantifying VOC emissions from waste-water treatment units using a flow-through environmental flux chamber, and includes a comparison of the results from the flow-through chamber with that of the Chemdat7 model.
Preparation and Analysis of Dry VOC-Fortified Soils
Authors: Minnich MM , Zimmerman JH , Schumacher BA
Published: March 2009

Studies were performed to assess the practicality of using dry VOC-fortified soils as performance evaluation materials (PEMs) and also to compare the effectiveness of EPA's low- and high-level purge-and-trap procedures [SW-846 Method 5030A (EPA 1992)]. Desiccator-dried soils were fortified in large batches with a combination of eight neat VOCs at 1000 ng each VOC/g soil. Three studies were performed on each of three soil types, namely, Hayesville (0.2% organic carbon, 32% clay), Kyle (0.6% organic carbon, 9% clay), and Charleston (3.8% organic carbon, 8% clay). VOC recoveries by the high-level procedure were good to excellent for all soils and compounds (98% mean recovery) and only fair by the low-level procedure (71% mean recovery). The mean relative standard deviation for all soil/compound/procedure combinations in the first study was 11%. Soil and compound properties influenced the VOC recoveries and rates of vapor losses from dry VOC-fortified soils. The poorest recoveries by the low-level procedure occurred on the soil with the highest proportion of organic matter. Rapid volatilization losses of 1,1,1-trichloroethane, benzene, trichloroethene, toluene, and tetrachloroethene were observed from 1-g samples of Kyle soil. In contrast, only trichloroethene was observed to volatilize from the Hayesville soil and no decreases in VOC concentrations were observed on the Charleston soil from 1-g samples that sat open for 20 min. No volatile losses were observed from any of the soils when dry 20-g soil samples were left open for 20 min. The technique of fortifying large batches of dry soils for PEMs as used in these studies provides good precision, but some modifications are suggested to improve the recoveries of compounds with low GC retention times on some of the soils. Also, further studies are needed to evaluate the influence of soil properties on VOC recoveries.
Characterizing a VOC Site Through On-Site Analysis of Soil Gas
Authors: Ardito CP , Duval TA , Reaber DW
Published: March 2009

An alternative approach for characterization of sites contaminated by volatile organic compounds (VOCs) has been employed at Sandia National Laboratories, Albuquerque, New Mexico (SNL/NM), in order to characterize a plume from a chemical waste landfill (CWL). The characterization approach is designed to maximize the use of soil gas analysis for definition of the nature and extent of contamination and for validation of the conceptual model of contaminant transport. Comparison of the soil gas data analyzed at an on-site laboratory with those data generated by an EPA-approved analytical laboratory indicates that soil gas data provide a much more representative picture of site conditions. To assist in the validation of our conceptual model of contaminant transport for the CWL, we employed an approach developed at SNL/NM that allows for assessment of nonaqueous phase liquids (NAPLs) through equilibrium testing of the soil gas data.

Ground water beneath the CWL, approximately 146 m below ground surface (BGS), has been impacted by low levels of VOCs. Laboratory data from soil samples collected through split-spoon sampling techniques revealed detectable contaminants to a maximum depth of approximately 6 m BGS. However, soil gas concentrations revealed a contaminant plume at concentrations in the range of 100 ppmv at depths greater than 60 m BGS. We demonstrate in this paper that soil gas data can provide a much more accurate picture of site conditions.
Overview of Transboundary Pollution Issues Along The Mexico-US Border
Authors: Medina EJ
Published: March 2009

This paper presents an overview of pollution issues affecting the Mexico-US border region, and briefly traces the development of the international legal framework which covers Mexico-US border relations on environmental issues. Examples from different border areas are used to illustrate surface water, groundwater, air pollution, and hazardous waste problems associated with the rapid growth and industrialization of areas along the border. Some of the specific issues presented include the Tijuana-San Diego sewage problem, the New River toxic discharges, Nogales Wash groundwater pollution, air pollution in Cd. Juarez-El Paso, and the Alco-Pacifico lead contamination case in Tijuana, B.C. Additional research to characterize the extent of border area pollution and resultant ecological impacts is fundamental in the development of binational policies to deal with these problems. Another priority need is the application of risk assessment models, which will help policy makers on both sides of the border to coordinate efforts and allocate resources to solve this crisis. Immediate attention should be directed toward acquiring information necessary to evaluate the impacts of border-area pollution on natural ecosystems.
Use of Artificial Lighting in Environmental Assessment Studies
Authors: Greenberg BM , Dixon DG , Wilson MI , Huang X-D , McConkey BJ , Duxbury CL , Gerhardt K , Gensemer RW
Published: March 2009

Artificial lighting is often required to study toxicant impacts on biological systems in the laboratory. Since light can effect the responses of both the organism and the toxicant, care must be taken to ensure that the laboratory lighting mimics the light conditions in the relevant compartment of the natural environment with respect to both intensity and spectral output. Photoinduction of toxicant action and responses of plants to UV-B provide examples of the need to control lighting in environmental testing. It is possible to simulate sunlight with respect to the visible:UV-A:UV-B ratio using a variety of lamps. The types of lights that are useful for building such sources are fluorescent, metal discharge, incandescent and microwave lamps. The methods of quantification of light that best fit environmental research are radiometric and quantum methods. This paper focuses on the types of artificial light sources that are commonly used in the laboratory and the quantification of light.
Integrated Ecological Hazard Assessment of Waste Site Soil Extracts Using FETAX and Short-Term Fathead Minnow Teratogenesis Assay
Authors: Fort DJ , Stover EL , Bantle JA
Published: March 2009

Frog Embryo Teratogenesis Assay — Xenopus (FETAX) is a 96-h whole embryo-larval assay designed to detect environmental developmental toxicants for use in ecological hazard assessment. FETAX offers several advantages in integrated biological hazard assessment including, time- and cost-effectiveness, technical ease, and versatility. FETAX has undergone extensive intra- and more recently interlaboratory validation with known mammalian teratogens and non-teratogens. Ecological hazard evaluations of contaminated sediments, waste site soils, and complex surface and groundwaters have also been performed. An integrated hazard assessment study using FETAX, the conventional, Pimephales promelas 7-d teratogenecity test, and an abbreviated P. promelas teratogenecity test utilizing the general FETAX protocol was conducted with specific reference toxicants and aqueous extracts of contaminated hazardous waste site soils. Results from the studies indicated that FETAX can be used as a component of a battery of bioassays designed to assess potential ecological hazard. Furthermore, the generalized FETAX protocol may be useful with other species in evaluating developmental toxicity hazard.
Plant Ecotoxicology: The Design and Evaluation of Plant Performance in Risk Assessments and Forensic Ecology
Authors: Kapustka LA
Published: March 2009

Since the emergence of ecology as a serious discipline, debates on the relevance of laboratory studies including toxicology have been prominent. Standardized phytotoxicity tests are often challenged due to the limited range of test species and the narrow range of environmental conditions proscribed in the tests. This paper discusses the uncertainty currently associated with lab-to-field extrapolations and other aspects of standardized tests. Characterization of test parameters is critical as a first step to quantification and, ultimately, reduction of uncertainty. A conceptual context for designing studies to quantify and reduce uncertainty is presented. A step-wise procedure based on Koch's postulates is offered as the best way to bolster linkage of toxicity data to predictions of risk and characterization of posts incidents (forensic ecology).
The Development of Generic Industrial Cleanup Criteria in the State of Michigan
Authors: Berger RS , Barkach JH , Kuhn WF
Published: March 2009

On July 11, 1990, the Michigan Department of Natural Resources (MDNR) promulgated administrative rules to implement a uniform hazardous waste site cleanup program in Michigan. These MDNR Administrative Rules (Act 307) establish a process for calculating risk-based cleanup levels for soil and groundwater affected by carcinogenic and noncarcinogenic hazardous chemicals which pose a threat to human health and the environment.

The MDNR periodically publishes guidance documents that provide interpretation and procedures for implementation of the Act 307 Rules. The MDNR recently published a guidance document which presents generic risk-based cleanup criteria for industrial sites. The purpose of this paper is to provide background on the Act 307 rules, and to describe the algorithms used to calculate this cleanup criteria. In addition, this paper provides background on the MDNR's selection of standardized exposure variables for industrial land use.
A Methodology to Identify Safer Chemical Products
Authors: Quan B
Published: March 2009

Pollution Prevention has become a hot topic in the last few years and it is being touted as a way of achieving “sustainable development”. Many experts claim that the best way to achieve pollution prevention is to not use hazardous materials in the first place or use safer substitutes. However, it is unclear at this time what safer substitutes really means except that sometimes products are tagged with this label simply because they are water-based or come from nature. The City and County of San Francisco has developed a methodology to identify safer or non hazardous products. The initial purpose of the methodology was to help and encourage City agencies to use less hazardous products and to minimize the number of products that the City's Purchasing Department would have to keep in inventory. However, the methodology may be used to identify safer household products as well. For example, one set of criteria that is used is the occupational exposure standards, in which they are compared to the equilibrium vapor pressures for the ingredients in the product. The purpose of this paper is to discuss the quantitative approach that the city has developed to screen products and the effect that this methodology will have in helping and encouraging City agencies and the general public to use less hazardous products. Also, there will be a discussion on what impact this might have on the amount of hazardous waste generated.
Strategy for Developing Remediation Target Concentrations Based on Human Exposure Duration Considerations
Authors: Nielsen JM , Washburn ST , Keoughan KM
Published: March 2009

A risk-based strategy for calculating remediation target concentrations (RTCs) has been developed based on (1) the toxicity of the substances of primary concern, (2) the exposure period considered when evaluating different types of potential health effects, and (3) the timeframe of potential exposures. In developing RTCs, it is important to consider the likely period of human exposure and the potential for natural attenuation to reduce residual contaminant concentrations over time. Thus, RTCs to be achieved at the completion of active site remediation may be higher than the cleanup goals that must be met, on average, during the period of potential post-remedy exposure.

This methodology for developing RTCs has received acceptance by USEPA for soil cleanup at a Superfund site. For this site, USEPA required that soils be remediated to a level that will protect ground water (i.e., residual soil concentrations that will not result in leachate concentrations that exceed specified ground water cleanup goals) and that ground water contamination be addressed using a pump and treat remedy. An important component of the remedy ultimately adopted at the site is continued monitoring of the ground water to ensure that chemical concentrations in ground water are reduced below the cleanup goals. Soil sampling at the completion of the ground water remedy may also be required to demonstrate that chemical concentrations in soil at the end of the ground water cleanup are also at acceptable levels. Using a leaching model, the soil RTCs were defined as the concentrations remaining in soil after active soil remediation that would not result in leachate concentrations that exceed the ground water cleanup goals, on average, after completion of the ground water remedy.
Current Status of Environment Canada's Guidance on Control of Test Precision Using a Spiked Sediment Toxicity Test: What to Spike and How?
Authors: Stephenson GL , Day KE , Scroggins R , Kirby RS , Hamr P
Published: March 2009

A draft of Environment Canada's “Guidance on Control of Test Precision Using a Spiked Control Sediment Toxicity Test” was reviewed by an international technical subcommittee. Comments were received, assessed, and discussed by members of the project steering committee, at which time, it was decided that in order to accommodate the recommendations of the subcommittee members, the revision of the document would be delayed until the results of some major sediment spiking and sediment formulation research initiatives were available.

A minimum of ten critical issues were identified by the reviewers and these issues have been summarized and briefly discussed in light of the consensus reached by the subcommittee. The data published in recent months in the scientific literature have helped to resolve some of the issues, or at least provide supporting evidence for some of the decisions that have been reached. However, one of the most contentious and critical issues that has not been resolved is the type and nature of the test medium to be spiked. In order to expand the scope beyond assessment of test precision to include interlaboratory comparisons and performance evaluation, it was decided that a formulated or artificial sediment option would be recommended as an alternative to field-collected sediments. This approach appears germane to several regulatory programs and there are currently a number of on-going research initiatives that are in the process of developing and testing the use of formulated sediments. Results of some recent experiments designed to study the effects of different formulations of sediment on survival and growth of the amphipod, Hyalella azteca, the chironomid, Chironomus riparius, and the mayfly, Hexagenia spp., as well as reproduction in the oligochaete worm, Tubifex tubifex, are presented and the implications for guidance development discussed.
Perspectives in Avoidance-Preference Bioassays
Authors: Steele CW , Taylor DH , Strickler-Shaw S
Published: March 2009

Although behavioral endpoints are used in hazard assessment, establishment of water quality criteria and assessment of a contaminant's hazard to aquatic life rely primarily on standard acute and chronic toxicity tests. Sublethal effects of pollutants should, however, be of major concern because more organisms experience sublethal rather than acutely or chronically lethal exposures of contaminants. The avoidance-preference approach to behavioral bioassays is very useful in screening pollutants for which the mechanisms of perception or response are largely unknown. The underlying philosophy of these studies is that an animal which perceives a chemical can be “attracted” or “repulsed” by it. No response is frequently assumed to indicate lack of perception. All three responses have broad ecological implications. We discuss the conditions required for performing avoidance-preference bioassays, as well as their sensitivities, advantages, and limitations. In this regard, a comparative approach is used in examining the results of avoidance-preference bioassays with zebrafish in two different apparatuses. Finally, we compare the results of avoidance-preference studies with other measures of the behavioral toxicity of lead to tadpoles.
Behavioral Avoidance as Evidence of Injury to Fishery Resources: Applications to Natural Resource Damage Assessment
Authors: DeLonay AJ , Little EE , Lipton J , Woodward DF , Hansen JA
Published: March 2009

Natural Resource Damage Assessment (NRDA) provisions enacted under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) and the Oil Pollution Act (OPA) empower natural resource trustees to seek compensation for environmental injury resulting from the release of oil or hazardous substances. Under NRDA regulations promulgated under CERCLA, fish avoidance behavior is recognized as an accepted injury, and may be used to support damage claims. In support of an ongoing damage assessment, tests were conducted to determine if avoidance of ambient metals concentrations may contribute to reductions in local salmonid populations. In laboratory tests, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) avoided mixtures of metals (Cd, Cu, Pb, and Zn) at concentrations that occur in impacted river reaches at a contaminated site (Clark Fork River, MT). Avoidance of metal contamination may contribute to population reductions and preclude restoration of instream populations by prohibiting movement of fish into contaminated areas of the river from uncontaminated tributaries. Laboratory avoidance tests were performed at two testing facilities. The similar avoidance responses observed at the two laboratories demonstrated the reproducibility of avoidance measures.
Determination of the Pore Size Distribution of Nonwoven Geotextiles by a Modified Capillary Flow Porometry Technique
Authors: Vermeersch OG , Mlynarek J
Published: March 2009

The capillary flow porometry(CFP)technique, known as the bubble point method, has been applied to measure the entire pore size distribution (PSD)of nonwoven geotextiles.

The classical technique is based on the differential analysis of two test runs: a wet run, during which the specimen is saturated by a wetting fluid, and a dry run, carried out on a non-saturated specimen. In the wet run, a saturated specimen allows the passage of air through pores when the capillary attraction of the wetting fluid is exceeded by the air pressure. As the air pressure is increased, smaller and smaller pores will pass air. In the dry run, air will flow through all pores when any amount of air pressure is applied to one side of the specimen. Both runs are performed in a sealed chamber. The flow rate through the sample from zero pressure to a maximal pressure is measured during each run. Assuming a cylindrical shape of pores, the pore size distribution is then computed.

Needle-punched and heat-bonded, polypropylene continuous filament nonwoven geotextiles have been tested during the program. The geotextiles were selected based on manufacturing process and their basic physical properties, mass per unit area and thickness.

Results, in terms of indicative pore sizes obtained from the pore size distribution are compared to the selected properties of geotextile products (thickness, mass per unit area and mass per unit volume), and the filtration opening size (FOS), determined by the hydrodynamic sieving technique (CGSB 148.1, method 10–94).

Relationships between measured pore sizes and selected properties of geotextiles have been found.

Research is presently in progress to widen the application of the CFP technique to measure the pore sizes up to 300 micrometers by using a non-zero contact angle wetting fluid and to verify the CFP technique applicability for other types of geotextiles, as well.

Knowledge of the PSD will be helpful in filter design because it focuses on new structural parameters of geotextiles, not presently considered by conventional design procedures.
Wet Sieving as a European EN-Standard for Determining the Characteristic Opening Size of Geotextiles
Authors: Dierickx W , Myles B
Published: March 2009

Three different sieving methods were put forward by national delegations to determine the characteristic opening size of geotextiles. A comparison of these methods was carried out by laboratories in Europe together with laboratories in China and North America.

The interlaboratory trials showed that wet sieving gave results with good agreement within narrow limits in all involved laboratories. The dry sieving procedure showed a larger spread of results, mainly due to several laboratories not respecting the rules laid down in the test procedure, moreover dry sieving is not appropriate for very fine textured geotextiles (O90 less than 100 μm). The results of the inter-laboratory hydrodynamic sieving showed a somewhat larger variation than the wet sieving procedure although sets of results were more or less of the same order.

The main constraints of the hydrodynamic sieving procedure were that before any results are available one or more days must pass (sieving time is 24 hours) and the apparatus which is not commercially available, is expensive and non-standard. As a result apparatus used for the hydrodynamic sieving all had slightly different constructions while for the wet sieving complying sieve apparatus was used by most laboratories.

Wet sieving has therefore been put forward as the preferred method for a European EN-standard. A detailed description of the advantages and some constraints of the wet sieving procedure and analysis will be given. Also the acceptance of the O90 as the determination criteria for pore size rather than the O95 is discussed.
Permeameter Research to Evaluate Geotextile Performance
Authors: Dierickx W
Published: March 2009

The evaluation of the hydraulic performance of geotextiles from field experiments is not an easy task as it takes a long time before conclusions can be drawn. Laboratory research is the only possibility to evaluate the performance of various geotextiles in a relatively short period.

Permeameters with upward flow are used to achieve that purpose. As the flow of water through a soil is not a static process, an increasing hydraulic gradient is applied. Tests normally last three weeks. They allow the prediction of the risk of particle passage as well as the risk of blocking and clogging. However, results cannot be expressed as a gradient ratio only. The gradient ratio just gives an overall picture of the behavior of soil and envelope. To evaluate the hydraulic performance of the envelope, a comparison must be made between the evolution of the hydraulic gradient in the soil and the hydraulic gradient across the geotextile.

Permeameter tests designed to evaluate the performance of geotextiles require careful preparation and accurate execution. Not only soil types but also soil conditions may influence the final results. The experience with permeameter research is described and results are presented.
Evaluation of Geotextile Filter in a Collection System at Fresh Kills Landfill
Authors: Corcoran BW , Bhatia SK
Published: March 2009

The New York City Department of Sanitation has retained consultants to design a leachate collection system for the Fresh Kills Landfill in New York City. Fresh Kills Landfill is regarded as the world's largest landfill. Because of an Order on Consent the landfill is required to have a leachate collection system by 1996. Design of the collection system includes a trench backfilled with granular material wrapped in a geotextile filter. The geotextile filter will be a critical component of the collection system and will be designed to meet soil retention and permeability requirements for the system. An existing leachate collection trench with a non-woven geotextile filter was constructed at the landfill in 1988. This collection trench and geotextile filter were exhumed, sampled and analyzed in 1993 to determine the effectiveness of the geotextile filter. Information gained from this study was utilized for the design of future leachate collection systems. Results of this study will be the subject of this paper.

This study was unique in the sense that a geotextile filter was used for the first time in the collection trench at the Fresh Kills Landfill. In addition an evaluation of its performance had not been investigated before. The geotextile filter was analyzed to determine the impacts of burial and filtration of leachate in a landfill environment on the hydraulic and mechanical properties of the material. Also, the potential for biological growth on the geotextile filter was investigated. Results of this study identified minor clogging of the geotextile filter due to soil particle retention within the pores of the non-woven material. A slight reduction in permittivity was observed due to particulate clogging.
Use of Geosynthetics in the Uplift Pressure Relief System for a Raft Foundation
Authors: Chang DT-T , Wu JY , Nieh Y-C
Published: March 2009

Deep raft foundations below a high groundwater table always have hydrostatic uplift pressure problems. Conventional solutions such as dead weight, tension pile, or anchors are costly, inefficient, and time-consuming. This paper presents a rational approach by using a geosynthetic system to control and relieve the hydrostatic uplift force within the impervious strata. Filtration, clogging, transmissivity, and other pertinent properties of geosynthetic materials are specified to assure the dissipation of uplift hydrostatic pressure in the long run. The design concept was applied in practice to a multi-story commercial complex. Based on the site experience, the installation of this system was found to be rapid, simple, and cost effective. The results of long-term (3 years) site monitoring made to date have shown good performance of this system.
Behavior of Nonwoven Geotextiles under Pumping Loads
Authors: Lafleur J , Assi M , Mlynarek J
Published: March 2009

Dynamic consolidation tests were carried out to simulate the pumping loads acting on road foundations where coarse aggregates are separated from fine subgrade soils by nonwoven geotextiles. The tests were performed in a cylindrical 108 mm diameter consolidation cell loaded at a frequency of 1 Hz, with vertical stresses oscillating between 12 and 48 kPa. Combinations involved two aggregates, two subgrade soils and five nonwoven needle-punched geotextiles. The pore pressure dissipation and the settlements of the soil/geotextile systems were recorded as a function of the number of cycles to evaluate the time for stabilization, ts. The amounts of subgrade particles trapped into the geotextiles and migrating into the aggregates were evaluated at the end of each test. The results disclosed that the systems were sensitive to the filtration opening size O95 of the geotextiles and to the size of the aggregates. Although products with smaller O95 adequately prevented piping into the subbase, entrapment of particles into the geotextile contributed to a 12 to 17% increase in their mass per unit area. The resulting reduction in porosity however, is not believed to reduce substantially the filter permeability. Finally, the larger aggregates were also associated with an increase in subgrade particle entrapment within the geotextile structure.
Recombination Lifetimes in Silicon
Authors: Schroder DK
Published: March 2009

The recombination lifetime τr is a very effective parameter to characterize the purity of a material or a device, because it is sensitive to very low densities of contamination. Impurity densities as low as 1010 cm−3 can be detected. τrhas become a process and equipment characterization and evaluation tool. The various recombination mechanisms are discussed here. We show that surface recombination plays an important role in today's high purity Si and will become yet more important as bulk impurity densities in Si are reduced further. The dependence of lifetime on impurity energy level and minority carrier injection level is discussed. Concepts are stressed in the paper, with the necessary equations to clarify these concepts. Wherever possible, the concepts are augmented with experimental data, with particular emphasis on iron in silicon, because Fe is one of the most important impurities in Si today.
Minority Carrier Diffusion Length Degradation in Silicon: Who is the Culprit?
Authors: Weber ER , Istratov AA , McHugo SA , Hieslmair H , Flink C
Published: March 2009

The influence of transition metals on minority carrier diffusion length in silicon is discussed. It is shown that transition metals easily precipitate on silicon lattice microdefects. These precipitates can not be easily dissolved, which makes gettering procedure ineffective. This conclusion is confirmed by experiments on FZ, CZ and photovoltaic silicon, discussed in this paper. The recombination activity of interstitial copper and its capture cross-section for electrons are determined. The recombination activity of interstitial and precipitated copper and iron are compared. It is shown that the precipitates of copper have much higher recombination activity than the interstitial copper, whereas iron is very active in both precipitated and interstitial form.