Nancy J. Hayden

Evaluating the efficiency and temporal variation of pilot-scale constructed wetlands and steel slag phosphorus removing filters for treating dairy wastewater

The performance and temporal variation of three hybrid and three integrated, saturated flow, pilot-scale constructed wetlands (CWs) were tested for treating dairy farm effluent. The three hybrid systems each consisted of two CWs in-series, with horizontal and vertical flow. Integrated systems consisted of a CW (horizontal and vertical flow) followed by a steel slag filter for removing phosphorus. Time series temporal semivariogram analyses of measured water parameters illustrated different treatment efficiencies existed over the course of one season. As a result, data were then divided into separate time period groups and CW systems were compared using ANOVA for parameter measurements within each distinct time period group. Both hybrid and integrated CWs were efficient in removing organics; however, hybrid systems had significantly higher performance (p<0.05) during peak vegetation growth. Compared to hybrid CWs, integrated CWs achieved significantly higher DRP reduction (p<0.05) throughout the period of investigation and higher ammonia reduction (p<0.05) in integrated CWs was observed in late summer. Geochemical modeling demonstrates hydroxyapatite and vivianite minerals forming on steel slag likely control the fate of phosphate ions given the reducing conditions prevalent in the system. The model also demonstrates how the wastewater:slag ratio can be adjusted to maximize phosphorus removal while staying at a near-neutral pH.

Microscopic observation of a NAPL in a three-fluid-phase soil system

Abstract The focus of this study was to observe the location and form of a NAPL in a three-fluid-phase (air-NAPL-water) soil system utilizing an advanced microscopic technique, cryo-scanning electron microscopy (cryo-SEM) with X-ray analysis. A sandy aquifer material was brought to residual water (NaCl saturated) saturation (∼4% by pore volume) followed by NAPL (iodobenzene) saturation, ranging from ∼1% to 80%, using modified Tempe® pressure cells. A small intact soil core was obtained from the pressure cell and quickly frozen in liquid nitrogen. The core was fractured and chromium coated at a high vacuum and −130°C. Secondary electron images (SEI) and X-ray dot maps (Si, Cl and I) were made of samples with different NAPL saturations. Photomicrographs and X-ray dot maps confirmed the existence of continuous NAPL films on soil (containing a residual water saturation) at high NAPL saturations. Photomicrographs revealed v-shaped wedges, pendular rings and films on irregular shaped sand grains. At low NAPL saturations (∼1% by pore volume), iodine was virtually nondetectable in the overall X-ray analysis of the sample. This suggests that the small quantity of NAPL present in the sample probably existed as thin films or small isolated lenses or blobs.

Mobilization of residual tetrachloroethylene during alcohol flushing of clay-containing porous media

Mobilization of residual DNAPL in a contaminated aquifer may be problematic for the application of enhanced dissolution remediation techniques such as alcohol or surfactant flushing. The objective of this study was to investigate the effects of clay fines on residual saturation, permeability and the onset of mobilization of PCE during alcohol flushing. Column experiments were conducted with soils containing 0%, 2%, 5%, 10%, and 20% clay that was completely mixed within a well-sorted Ottawa sand. Column characterization included pressure-saturation relationships, pore-size distribution, permeability, and residual saturation. The columns were flushed with isopropyl alcohol (IPA) in concentration increments to determine when mobilization of PCE occurred. Trapping numbers were calculated. Results showed that increasing amounts of clay resulted in decreased hydraulic conductivity, increased residual PCE saturation and a larger pore size distribution. Residual PCE was found to begin to mobilize in the clay-mixed media at a range of trapping numbers below those reported in the literature for homogeneous well-sorted sand. This suggests that the potential to mobilize the residual PCE is greater in the mixed media. This may be explained by the formation of multi-pore branched ganglia in the clay-containing media as opposed to singlet formation in a well-sorted media. The multi-pore ganglia may mobilize more readily than singlets due to the added force of head acting on the PCE interface where the trapping is occurring. Using a narrow range of trapping numbers determined in homogeneous media to predict mobilization may not be appropriate in mixed media because mobilization was noted at a variety of trapping numbers. However, relationships between the trapping number at mobilization and various soil parameters such as the amount of clay, residual DNAPL saturation, and pore size distribution, indicate that these, coupled with the trapping number, may aid in our ability to predict mobilization.

Residual gasoline saturation in unsaturated soil with and without organic matter

Abstract The goal of this study was to investigate the influence of one variable, natural organic matter, on residual gasoline saturation in sandy soils. Capillary pressure-saturation ( P c − S ) relationships (air-gasoline) were determined for three physically-similar sandy soils, with different organic carbon contents (0.086%, 0.89% and 1.65%) and residual gasoline saturations were compared. Two initial moisture conditions, residual water saturation and air-dry, were evaluated. One soil type was packed to two different bulk densities. Visualization of the soils using cryo-scanning electron microscopy was performed to aid in better understanding the role of the organic matter in the soil. The results showed that soils with higher organic contents had higher residual gasoline saturations when starting with an initially air-dry soil. Increasing the bulk density of the same air-dried soil resulted in an increase in residual gasoline saturation. In the presence of a residual water saturation, however, residual gasoline saturations were virtually identical for the three soils and independent of bulk density; approximately 5–10 times lower than in soil that was initially air-dry. The presence of the residual water effectively coated the surface of the soil thereby reducing or eliminating gasoline/soil interactions. Some residual water may also be occupying very small pore spaces, making these locations inaccessible to the gasoline.

Service-Learning in Engineering Education and Heritage Preservation

Many communities and nonprofit organizations in the United States grapple with the reuse of publicly owned buildings and infrastructure from the 19th and early 20th centuries that have become landmarks in their communities. Often these communities or organizations do not have adequate resources (technical expertise, funding) for even preliminary engineering services. Engineering programs at universities can assist these communities by providing engineering expertise through service-learning (SL) projects, at the same time providing engineering students exposure to the field of heritage preservation and to important preservation engineering issues. This article presents SL case studies at the University of Vermont (UVM) as examples of this type of collaboration. Benefits, challenges, and SL assessment results are included. For the past 4 years, as part of a National Science Foundation Department Level Reform (NSF DLR) grant, civil and environmental engineering students at UVM have worked on multiple SL projects with local communities throughout their 4-year program. In many cases, these SL projects have involved historic structures. Although not an original emphasis of the DLR grant, heritage preservation is becoming a component of the UVM reform efforts, such that in 2010 this topic began to be formally included in both the first-year introductory engineering course and senior capstone design course. The SL approach was found to be effective in meeting education goals of the civil and environmental engineering programs and their accreditation requirements as well as providing meaningful service to the local communities caring for historic structures and sites. Both students and faculty gained exposure to and understanding of preservation engineering topics, as well as networking with the heritage preservation community in Vermont and elsewhere. Incorporating heritage preservation issues into engineering programs through SL projects may prove beneficial at other institutions.

Prediction of leachate concentrations in petroleum‐contaminated soils

Abstract The efficacy of cleanup methods in reducing gasoline contamination at spill sites is typically determined by measuring benzene, toluene, xylene (BTX), and total petroleum hydrocarbon (TPH) concentrations in soil samples. Although these values may provide a direct measurement of soil contamination, they may not be indicative of what is transferred to percolating water. This study addresses this issue by measuring TPH, toluene, m‐ and p‐xylene, and naphthalene levels in gasoline‐contaminated soil columns before and after forced‐air venting and relating these values to the aqueous‐phase concentrations measured when water is percolated through the same columns. Sandy soils with and without organic matter were packed into glass columns. The soils were brought to residual water and residual gasoline saturations by applying a vacuum to a ceramic pressure plate at the column bottom. Venting was performed by passing clean, moist air through the columns. The columns were subsequently leached under unsatura...

Commonly Used Porous Building Materials: Geomorphic Pore Structure and Fluid Transport

Knowledge of microscopic geomorphic structures is critical to understanding transport processes in porous building materials. X-ray scans were obtained of a variety of commonly used porous building materials to both qualitatively and quantitatively evaluate their pore structures. The specimens included natural materials (two sandstones and a limestone) and engineered materials (three types of concretes and a brick). Scanned images were processed to reconstruct the geomorphic structures of these materials. Random walk analyses were performed on the reconstructed pore structures to estimate macroscopic transport properties (including tortuosity, specific surface, and permeability). The effective porosity and permeability of these materials were also experimentally determined and compared to computed values. Calibration of the threshold pixel value used in the postprocessing of X-ray images against measured effective porosity appears to be a more appropriate method of selecting this value than the typical approach, which employs selection based solely on observed histograms. The resulting permeabilities computed by using a calibrated threshold pixel value compare better with the measured permeabilities. This study also demonstrates that the relatively homogeneous and heterogeneous pore structures associated with the natural and engineered building materials under investigation can be captured by X-ray tomography.

Service-Learning Design Projects to Enhance Geotechnical Engineering Education

Service learning (SL) is an educational approach that couples service to a community partner with academic learning for students. Often SL goals include those related to academic or technical enhancement, civic engagement, and personal and interpersonal skills. The civic engagement aspect of this approach meshes well with the service-oriented nature of the civil engineering profession. This paper presents pedagogical aspects of SL, its benefits, and ideas on how it can be implemented within undergraduate engineering courses, specifically geotechnical engineering courses. Some examples of SL projects undertaken in a foundation engineering course and the civil and environmental senior capstone course at the University of Vermont are also presented.

Research-Based and Service-Learning Modules for Undergraduate Geotechnical Engineering Courses

Four hands-on educational modules were designed for undergraduate geotechnical engineering courses at the University of Vermont; introduction to geotechnical engineering (Geotechnical Principles) and foundation engineering (Geotechnical Design). These modules were designed to incorporate inquiry-based learning and expose students to a systems approach to engineering education, which are the two major thrusts of an NSF funded curricular reform within the civil and environmental engineering programs. All modules were conducted within a group setting and required students to write technical papers in ASCE conference format or prepare a technical report and a presentation, with an additional underlying objective of the development of students’ interpersonal skills. Some statistical analysis and analytical and numerical modeling were required in some of the modules to expose students to information technology and understand the importance of coupling numerical and experimental methods. The educational modules included: (1) Atterberg limits using Casagrande and fall cone devices; (2) physical, analytical and numerical modeling of steady-state seepage; (3) validation of undrained slope stability, bearing capacity of shallow foundation and active and passive lateral earth pressure solutions using centrifuge modeling; and (4) service-learning projects related to foundations, retaining structures or slope stability for rehabilitation of historic structures. Integrated reflection and assessment activities were conducted. Student assessment results indicate that many of the curricular reform objectives are being successfully implemented. INTRODUCTION The civil and environmental engineering programs at the University of Vermont are undergoing NSF funded curriculum reform with a vision of creating an inquiry-based, environmentally-conscious undergraduate learning experience that prepares students in the following areas: (1) capable of adopting a systems approach to define and solve complex engineering problems, (2) skillful in information

Transferable Skills Development in Engineering Students: Analysis of Service-Learning Impact

The practice of engineering, especially the design process, involves many aspects beyond just the technical and includes such critical components as engineering ethics, sustainability and transferable skills such as communication, leadership and mentoring. Engineering educators often struggle with how to best incorporate these nontechnical aspects within their curricula. Service learning offers an opportunity to do this. The disconnect is that students often view engineering as only the technical number crunching and these other nontechnical components as less important. We report on the assessment of student written reflections across two very different service-learning engineering design projects for the purpose of evaluating student attitudes about these service-learning experiences and to assess their awareness and appreciation of transferable-skills development. In the spirit of service-learning pedagogy, we divided the contents of the written reflections into three categories – academic enhancement, civic engagement and personal growth skills. The commonality across both courses centered on academic enhancements and the value of transferable skills (i.e., leadership, teamwork, negotiation skills, mentoring, scheduling, verbal and written communication skills). Assessments show our current service-learning pedagogy improves students’ understanding of the importance of written and oral presentation skills. However, as of yet, many students do not consider leadership, negotiation skills, design setbacks, scheduling and mentoring skills to be part of “real” engineering.