John S. Gierke

Vapor transport in unsaturated soil columns: Implications for vapor extraction

A mathematical model was derived to examine the impact of gas advection, gas diffusion, gas-water mass transfer, gas-water partitioning, sorption, and intraaggregate diffusion on subsurface movement of organic vapors. Laboratory experiments were performed to determine the validity of the model and to investigate the impact of the various mechanisms on vapor transport. Columns were packed with a uniform Ottawa sand and an aggregated porous soil material (APSM) to compare transport in different soil structures. Toluene vapor transport was observed in the sand under dry and wet (27% water saturation) conditions. The experiments with the APSM were performed dry and at 67% water saturation. In all the sand and the dry APSM experiments, gas advection and diffusion had the greatest impact. In a wet APSM experiment, intraaggregate (liquid) diffusion was also important to consider for gas velocities greater than approximately 0.05 cm s−1. For both soil materials, sorption of toluene vapors occurred for dry conditions, while vapor sorption was negligible when liquid water was present. These findings imply that vapor extraction performance in moist, aggregated soils will be affected by nonequilibrium transport. Therefore models that are developed for predicting the complete removal of contaminants by vapor extraction must account for nonequilibrium.

Mineral carbonation for carbon sequestration in cement kiln dust from waste piles

Alkaline earth metals, such as calcium and magnesium oxides, readily react with carbon dioxide (CO(2)) to produce stable carbonate minerals. Carbon sequestration through the formation of carbonate minerals is a potential means to reduce CO(2) emissions. Calcium-rich, industrial solid wastes and residues provide a potential source of highly reactive oxides, without the need for pre-processing. This paper presents the first study examining the feasibility of carbon sequestration in cement kiln dust (CKD), a byproduct generated during the manufacturing of cement. A series of column experiments were conducted on segments of intact core taken from landfilled CKD. Based on stoichiometry and measured consumption of CO(2) during the experiments, degrees of carbonation greater than 70% of the materials potential theoretical extent were achieved under ambient temperature and pressure conditions. The overall extent of carbonation/sequestration was greater in columns with lower water contents. The major sequestration product appears to be calcite; however, more detailed material characterization is need on pre- and post-carbonated samples to better elucidate carbonation pathways and products.

Life cycle assessment of vertical and horizontal flow constructed wetlands for wastewater treatment considering nitrogen and carbon greenhouse gas emissions

Life cycle assessment (LCA) is used to compare the environmental impacts of vertical flow constructed wetlands (VFCW) and horizontal flow constructed wetlands (HFCW). The LCAs include greenhouse gas (N(2)O, CO(2) and CH(4)) emissions. Baseline constructed wetland designs are compared to different treatment performance scenarios and to conventional wastewater treatment at the materials acquisition, assembly and operation life stages. The LCAs suggest that constructed wetlands have less environmental impact, in terms of resource consumption and greenhouse gas emissions. The VFCW is a less impactful configuration for removing total nitrogen from domestic wastewater. Both wetland designs have negligible impacts on respiratory organics, radiation and ozone. Gaseous emissions, often not included in wastewater LCAs because of lack of data or lack of agreement on impacts, have the largest impact on climate change. Nitrous oxide accounts for the increase in impact on respiratory inorganic, and the combined acidification/eutrophication category. The LCAs were used to assess the importance of nitrogen removal and recycling, and the potential for optimizing nitrogen removal in constructed wetlands.

State of technology review : soil vapor extraction systems

Abstract Extracting vapor from soil is a cost-effective technique for the removal of volatile organic chemicals (VOCs) from contaminated soils. Among the advant Unfortunately, there are few guidelines for the optimal design, installation, and operation of soil vapor extraction systems. A large number of pilot- Soil vapor extraction can be effectively used for removing a wide range of volatile chemicals over a wide range of conditions. The design and Operation This Project Summary was developed by EPAs Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of the research project tha

Remediation of NAPL Source Zones: Lessons Learned from Field Studies at Hill and Dover AFB

Innovative remediation studies were conducted between 1994 and 2004 at sites contaminated by nonaqueous phase liquids (NAPLs) at Hill and Dover AFB, and included technologies that mobilize, solubilize, and volatilize NAPL: air sparging (AS), surfactant flushing, cosolvent flooding, and flushing with a complexing-sugar solution. The experiments proved that aggressive remedial efforts tailored to the contaminant can remove more than 90% of the NAPL-phase contaminant mass. Site-characterization methods were tested as part of these field efforts, including partitioning tracer tests, biotracer tests, and mass-flux measurements. A significant reduction in the groundwater contaminant mass flux was achieved despite incomplete removal of the source. The effectiveness of soil, groundwater, and tracer based characterization methods may be site and technology specific. Employing multiple methods can improve characterization. The studies elucidated the importance of small-scale heterogeneities on remediation effectiveness, and fomented research on enhanced-delivery methods. Most contaminant removal occurs in hydraulically accessible zones, and complete removal is limited by contaminant mass stored in inaccessible zones. These studies illustrated the importance of understanding the fluid dynamics and interfacial behavior of injected fluids on remediation design and implementation. The importance of understanding the dynamics of NAPL-mixture dissolution and removal was highlighted. The results from these studies helped researchers better understand what processes and scales are most important to include in mathematical models used for design and data analysis. Finally, the work at these sites emphasized the importance and feasibility of recycling and reusing chemical agents, and enabled the implementation and success of follow-on full-scale efforts.

Hazard assessment of rainfall-induced landslides: a case study of San Vicente volcano in central El Salvador

The San Vicente volcano in central El Salvador has a recurring and destructive pattern of landslides and debris flows occurring on the northern slopes of the volcano, and in recent memory, there have been at least seven major destructive debris flows. There has been no known attempt to study the inherent stability of these slopes and determine the factors that might lead to slope instability. Past events on the volcano were used to perform a 2D slope stability back analysis and to estimate the unknown model parameters. This analysis confirmed that the surface materials of the volcano are highly permeable and have very low shear strength. Additionally, the analysis provided insight into the groundwater table behavior during a rainstorm. Slope geometry, rainfall totals and initial groundwater table location were found to have the greatest effect on stability. A methodology is outlined for creating a stability chart to be used during rainfall events for monitoring slope stability. This chart could be used by local authorities in the event of a known extreme rainfall event to help make evacuation decisions. Finally, recommendations are given to improve the methodology for future application in other areas as well as in central El Salvador.

Laboratory Investigation of Ammonium and Nitrate Removal in Vertical-Flow Regimes in Planted and Unplanted Wetland Columns

AbstractVertical-flow constructed wetlands were investigated for ammonium and nitrate removal from synthetic wastewater in bench-scale wetland columns. Total ammonia and nitrate were measured as wastewater and fed through planted and unplanted columns over three 4-week phases: downflow, upflow, and downflow-upflow in series. Mass balance results showed that downflow columns removed >90% of influent ammonium, regardless of vegetation. Unplanted downflow columns removed 15% of nitrate and 14% of total nitrogen. Planted downflow columns removed only 1% of nitrate and total nitrogen. Unplanted upflow columns removed 55% of ammonium, 50% nitrate, and 31% of total nitrogen, whereas planted upflow columns removed 59, 60, and 40% of nitrogen species, respectively. For downflow-upflow columns in series, unplanted columns removed 79% of the ammonium, 1% of nitrate, and 4% of total nitrogen. In-series planted columns removed 93, 62, and 59%, respectively. These results suggest that downflow wetlands may be more appr...

Hydrologic performance monitoring of an underdrained low-impact development storm-water management system.

The use of low-impact development (LID) storm-water management facilities will grow with gains in understanding of their performance based on field tests. An innovative flow measurement system was designed and tested for monitoring of an interconnected system of underdrained LID components forming a site management strategy. Pressure transducers housed in stilling wells provided in-line flow measurements in pipes connecting the LID components. A combination of laboratory experiments, field measurements, and computer simulations was used to calibrate the flow measurement system to translate depth measurements to estimates of flow. The monitoring system is well suited for high-resolution temporal monitoring and provides important information for evaluating LID component performance. The measurement system is limited to open-channel flow, but calculations indicate that surcharge conditions are expected to occur at the case study site only under conditions more extreme than the 100-year storm event.

Decision making for social sustainability: A life-cycle assessment approach

The need for sustainable development requires organizations to consider the economic, environmental, and social repercussions of their actions. While the economic effects, and increasingly the environmental consequences, of engineering design and business decisions are evaluated, little attention has been devoted to understanding the social impacts. It has been recognized that corporate decisions are linked to social sustainability indicators, and the need exists to better understand these links. This research represents a first step toward modeling the relationships between corporate decision alternatives and lower-order human needs (e.g., physiological requirements) and higher-order needs (e.g., belonging).

In situ mixed region vapor stripping in low-permeability media. 2. Full-scale field experiments.

This paper is the second in a three-part series that describes mixed region vapor stripping (MRVS) for in situ treatment of fine-grained soils contaminated by volatile organic compounds (VOCs) including trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and related halocarbons. As described in this paper, MRVS processes were studied during full-scale field experiments wherein ambient or heated air was injected at high volumetric flow rates during in situ soil mixing, and VOCs were volatilized and advectively removed from the subsurface, captured in a shroud covering the mixed region, and then treated on-site. The field test was conducted at an inactive land disposal site in southern Ohio where dense silty clay soils were contaminated by VOCs at concentrations in the 10-500 mg kg -1 range. During the field studies, seven columns, each 3.0 m diameter and 4.6 or 6.7 m deep, were treated with ambient air (∼15-25°C) or heated air (∼120-130°C) injected at flow rates of 28-40 m 3 min -1 . Intensive monitoring and measurement activities defined contaminant behavior and key MRVS operation and performance parameters. The field testing revealed that MRVS could rapidly reduce the concentrations of VOCs (i.e., TCE, TCA,...) in dense silty clay soil by 88-98%. The rate and extent of reduction was somewhat higher with the injection of heated air as compared to ambient air. Regardless of injection air temperature, as treatment progressed, the rate of VOC removal became increasingly mass transfer limited.