Evaluation of an In Situ,On-Line Purging System for the Cone Penetrometer

Abstract

Materials that will be used to construct an in situ, on-line purging system for the cone penetrometer were evaluated. Transfer efficiencies for volatile organic compounds (VOCs) through stainless steel, nickel, aluminum, and Teflon® tubings were determined using a gas-phase mixture of VOCs containing trichloromethane, tetrachloromethane, 1,1,1- trichloroethane, tetrachloroethene, hexane, benzene, toluene, and 1,2-dimethylbenzene. The water content of the gas stream had an insignificant effect on the quantitative transfer of VOCs through Teflon® tubing but was critical to efficiently transfer the compounds through metal tubing, particularly nickel. Transfer efficiencies for all eight analytes in moist gas streams through stainless steel were greater than 95%. Toluene, tetrachloroethene, and 1,2-dimethylbenzene were transferred with 93%, 81%, and 80% efficiency, respectively, when they were drawn through Teflon® PFA (perfluoroalkoxy) tubing. In general, the retention of the VOCs by Teflon® increases with decreasing aqueous solubility of the analyte. The efficiencies at which VOCs were purged from aqueous standards in Teflon® PFA, Type 304 stainless steel, and glass vessels were similar. Stainless steel was superior to nickel, aluminum, and the Teflon® polymers as a material for an in situ, on-line purging system for the cone penetrometer.     

Comparison of PCE and TCE disappearance in heated volatile organic analysis vials and flame-sealed ampules

The rates of hydrolysis reported for tetrachloroethylene (PCE) and trichloroethylene (TCE) at elevated temperatures range over two orders-of-magnitude, where some of the variability may be due to the presence of a gas phase. Recent studies suggest that volatile organic analysis (VOA) vials provide a low-cost and readily available zero headspace system for measuring aqueous-phase hydrolysis rates. This work involved measuring rates of PCE and TCE disappearance and the corresponding appearance of dechlorination products in water-filled VOA vials and flame-sealed ampules incubated at 21 and 55 °C for up to 95.5 days. While PCE and TCE concentrations readily decreased in the VOA vials to yield first-order half lives of 11.2 days for PCE and 21.1 days for TCE at 55 °C, concentrations of anticipated dechlorination products, including chloride, remained constant or were not detected. The rate of PCE disappearance was 34 times faster in VOA vials at 55 °C compared to values obtained with flame-sealed ampules containing PCE-contaminated water. In addition, the concentration of TCE increased slightly in flame-sealed ampules incubated at 55 °C, while a decrease in TCE levels was observed in the VOA vials. The observed losses of PCE and TCE in the VOA vials were attributed to diffusion and sorption in the septa, rather than to dechlorination. These findings demonstrate that VOA vials are not suitable for measuring rates of volatile organic compound hydrolysis at elevated temperatures.     

A carbon balance method for paper and wood products

The approach used to track the flow of carbon sequestered in the forest through harvest, processing into products, and final disposition of products is described. The methodology is broadly flexible and applicable to forest-based carbon balance assessments. A carbon balance is computed across all forestland ownerships for the production facility of interest. The balance considers forest uptake, harvest, combustion of fuels, emissions from process steps and losses from product use, disposition and recycling. The method also allows for sensitivity and marginal assessments of a variety of real and hypothetical situations using variable assumptions. Example results for a vertically integrated pulp and paper mill are presented. Results suggest that integrated forest products facilities drawing their raw material from sustainably managed forests can achieve a net positive carbon balance over the product cycle. The amount of net carbon sequestration attributable to such facilities depends upon a number of factors. The most critical of these include net forest growth, the method for allocating the growth in forest carbon among all of those harvesting from the drain area of a given facility, and the use and disposal patterns for the paper or wood products manufactured.     

Effectiveness of nanoscale zero-valent iron for treatment of a PCE-DNAPL source zone

Nanoscale zero-valent iron (nZVI) has received considerable attention as a potential in situ remediation technology for treating chlorinated solvent source zones. Experimental and mathematical modeling studies were conducted to investigate the performance of nZVI in the transformation of tetrachloroethene (PCE) entrapped as a dense nonaqueous phase liquid (DNAPL). Injection of a 60 g/L suspension of nZVI into a column containing 20-30 mesh Ottawa sand and PCE-DNAPL at a residual saturation of 5.5% resulted in a uniform distribution of nZVI and minimal displacement of PCE. Subsequent flushing with 267 pore volumes of water containing 3mM CaCl(2) at a Darcy velocity of 0.75 m/day resulted in steady-state effluent concentrations of PCE near the solubility limit (ca. 200mg/L) and production of dissolved-phase ethene (10-30 mg/L). Over the duration of the experiment, approximately 30% of the initial PCE-DNAPL mass reacted to form ethene, 50% was eluted as dissolved-phase PCE, and 20% remained in the column as PCE-DNAPL. To further explore the implications of the nZVI column results, a multiphase transport model was developed that incorporated rate-limited PCE-DNAPL dissolution and reactions with nZVI. Using a fitted pseudo first-order transformation rate coefficient of 1.421/h, the model accurately captured observed trends in effluent concentrations of PCE and ethene and overall mass balance. A model sensitivity study reveals a strong dependence of treatment effectiveness on system characteristics. The sensitivity analysis suggests that an increase in the extent of PCE transformation is facilitated by decreasing flow rate, emplacement of nZVI down-gradient of the DNAPL source zone, and decreasing length of the DNAPL source zone. These findings indicate that, although emplacement of high concentrations of nZVI within a PCE-DNAPL source zone can result in substantial transformation of the parent compound, careful attention to design parameters (e.g. flow rate, location and amount nZVI delivered) will be required to achieve complete conversion to benign reaction products.     

Sustainability or collapse: what can we learn from integrating the history of humans and the rest of nature?

Understanding the history of how humans have interacted with the rest of nature can help clarify the options for managing our increasingly interconnected global system. Simple, deterministic relationships between environmental stress and social change are inadequate. Extreme drought, for instance, triggered both social collapse and ingenious management of water through irrigation. Human responses to change, in turn, feed into climate and ecological systems, producing a complex web of multidirectional connections in time and space. Integrated records of the co-evolving human-environment system over millennia are needed to provide a basis for a deeper understanding of the present and for forecasting the future. This requires the major task of assembling and integrating regional and global historical, archaeological, and paleoenvironmental records. Humans cannot predict the future. But, if we can adequately understand the past, we can use that understanding to influence our decisions and to create a better, more sustainable and desirable future.     

Therapeutic uses of edible plants in Bangalore city, India: combining health with cooking practices through home herbal gardens

This article examines the therapeutic uses and perceptions of edible plants cultivated in home herbal gardens in the city of Bangalore, Southern India. We suggest that an examination of edible plants within a therapeutic context facilitates a more comprehensive understanding of the role that plants play both in the diet and in the health of urban populations such as in Bangalore. We conclude by reinforcing the importance of promoting awareness of the combined value of medicinal and edible plants through their cultivation in home gardens and the role of local health knowledge in health promotion.     

Measures of energy cost and value in ecosystems

The physical output of ecological processes have different values even though they may be measured in the same physical units. Using linear input-output theory, we derive a set of weights based on direct and indirect energy requirements for ecosystem commodities which uniquely converts them into commensurable unit costs. Under certain conditions, these costs are equal to values or prices. Using this system, behavioral theories can be better posed for experimental verification.