Civil & Environmental Engineering
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Item The Spatial Distribution of Imperviousness in Watershed Hydrology(2009) Mejia, Alfonso Ignacio; Moglen, Glenn E.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urbanization affects the hydrology of watersheds often leading to increases in runoff volumes and peak flows. These impacts are mainly attributed to the presence of imperviousness on the landscape which inhibits the soil infiltration process. Normally, these impacts are studied at the hillslope scale and under lumped watershed conditions. The impacts at the watershed scale under more spatially distributed conditions have been studied less. Advancements in spatial observations and techniques, distributed hydrologic modeling, and greater understanding of the importance of scale in hydrology have increased the feasibility and need for including spatial data sets and methods into hydrologic investigations. This dissertation focuses on understanding the role and importance of the spatial distribution of imperviousness in watershed hydrology. The spatial distribution of imperviousness is investigated by incorporating various spatial datasets, techniques, and modeling approaches that are used routinely for the hydrology of natural watersheds but less frequently for urbanized conditions. The distribution of imperviousness is investigated based on three approaches. The first approach uses optimization concepts to study where imperviousness can be placed in the watershed to reduce negative impacts on flooding. The second approach develops, implements, and tests a hydrologic event-based model to study the influence of the spatial distribution of imperviousness on the hydrologic response. The last approach relates analytically the space-time variability of rainfall, runoff, and the routing process to the imperviousness pattern, and synthesizes the complex space-time variations into a simpler framework. From the first approach distinct patterns of imperviousness were obtained that embodied water resources objectives. For example, the clustering of imperviousness along the main channel was found to globally reduce peak flows along the stream network. The second approach indicated that the overall imperviousness pattern can have a considerable impact on the hydrologic response. The last approach showed that the spatial patterns of rainfall and imperviousness can interact to increase or decrease the average amount of rainfall excess. The main contribution from this research is a larger understanding of the role of the spatial distribution of imperviousness in watershed hydrology. It also demonstrates the usefulness of applying hydrologic knowledge of natural watersheds to anthropogenically-altered watersheds.Item Environmental Performance and Sustainability of Bioretention Cells(2009) Jones, Philip Sumner; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention cells use vegetation and soil media for source control of urban stormwater runoff, alleviating waterway impairment. Environmental performance of two cells was investigated. First, a cell capturing road runoff was monitored for one year. At a second cell, media were sampled to measure lifetime metal accumulation and evaluate the environmental, health, and maintenance implications of metal sequestration. Monitoring found high metal and suspended solids removal, generally poor nutrient performance, and chloride export. Runoff volume and peak flow rate reduction occurred for small storm events. For larger events, outflow volume consistently exceeded inflow because of unique site conditions. Lead, copper, and zinc media concentrations in the second cell were elevated but well below cleanup thresholds. Metals were strongly bound to bioretention media and largely immobile; lead bioavailability was comparable to generic soil estimates. Most metal accumulation was near the inflow point in the top 3 to 12 cm of media.Item THE KINETICS OF TWO HETEROTROPHIC TETRACHLOROETHENE-RESPIRING POPULATIONS AND THEIR EFFECTS ON THE SUBSTRATE INTERACTIONS WITH DEHALOCOCCOIDES STRAINS(2009) Huang, Deyang; Jennifer, Jennifer G; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study focused on evaluating how interactions between the hydrogenotroph Dehalococcoides ethenogenes strain 195, which is able to completely dechlorinate tetrachloroethene (PCE) to ethene, and the two heterotrophs Desulfuromonas michiganensis strain BB1 and Desulfitobacterium sp. strain PCE1, which dechlorinate PCE to either cis-dichloroethene (cis-DCE) or trichloroethene (TCE), on the fate of PCE under common in situ bioremediation scenarios. Meaningful kinetic parameter estimates were obtained for the heterotrophic dehalorespirers under a wide range of conditions. Batch culture assays and numerical experiments were conducted with Desulfuromonas michiganensis to evaluate the effect of the initial conditions including the ratio of the initial substrate concentration (S0) to the initial biomass concentration (X0) and the ratio of S0 to the half-saturation constant (KS) on parameter correlation. Most importantly, S0/KS, but not S0/X0, strongly influenced parameter correlation. Correlation between the Monod kinetic parameters could be minimized by maximizing S0/KS. In the present study, dechlorination of high PCE concentrations by Desulfuromonas michiganensis and Desulfitobacterium sp. strain PCE1 was monitored. The maximum level of PCE that could be dechlorinated by each strain was not constant, and varied with X0. This phenomenon could not be described using conventional Monod kinetics; therefore, a new model that incorporated an inactivation term into the biomass growth equation was developed to describe dechlorination at high PCE concentrations. The interactions among Dehalococcoides ethenogenes and heterotrophic dehalorespirer in continuous-flow stirred tank reactors (CSTRs) were performed under two conditions that reflect either a natural attenuation or engineered bioremediation treatment scenario. Extant kinetic estimates accurately predicted the steady-state chlorinated ethene concentrations in the CSTRs. However, intrinsic kinetic parameter estimates better described the CSTR start-up phase. The modeling and experimental results suggested that the ability of Dehalococcoides ethenogenes to utilize PCE and TCE is limited by the presence of a PCE-to-TCE/cis-DCE dehalorespirer, which forces Dehalococcoides ethenogenes to function primarily as a cis-DCE-respiring population. This study provides insight into how the activities of different dehalorespiring cultures are interrelated and will aid in the design of engineered bioremediation approaches that optimize the potential benefits associated with different dehalorespiring populations to achieve efficient and effective clean-up of PCE- and TCE-contaminated sites.Item FIELD EVALUATION OF HYDROLOGIC AND WATER QUALITY BENEFITS OF GRASS SWALES WITH CHECK DAMS FOR MANAGING HIGHWAY RUNOFF(2009) Jamil, Nor Eliea Eluziea; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Thesis: FIELD EVALUATION OF HYDROLOGIC AND WATER QUALITY BENEFITS OF GRASS SWALES WITH CHECK DAMS FOR MANAGING HIGHWAY RUNOFF Nor Eliea Eluziea Jamil, Master of Science, 2009 Thesis Directed By: Professor Allen P. Davis Departrment of Civil and Environmental Engineering Managing highway runoff is a complex storm water management problem. This research is an input/output field study that specifically examines the hydrologic and water quality benefits of having grass swales with an additional pre-treatment area and incorporation of check dams for managing highway runoff at a Maryland highway. These swales manage the hydrology of the stormwater by increasing the lag time (2-3 hours), reducing the overall average peak (32-44%) and reducing the total runoff volume (4-46%). The overall mass pollutant loads are reduced for TSS (38-62%), nitrate (92-95%), nitrite (54-71%), lead (78-82%), copper (56-70%) and zinc (67-79%). On the other hand, TKN (-120 to 44%), TP (-5 to 40%) and chloride (-61 to -4%) show mass increase. Compared to previous study, swales with check dams do not show any significant improvement over swales without check dams. However, a check dam swale with a pretreatment area has higher reduction of the overall mass pollutants removal for all pollutants except for TSS.Item ENVIRONMENTAL FATE OF POLYBROMINATED DIPHENYL ETHERS IN AGRICULTURAL SOILS WHICH HAVE RECEIVED BIOSOLIDS APPLICATION(2008) Andrade, Natasha Almeida; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polybrominated diphenyl ethers (PBDEs) are used as additives in consumer products for their fire-retardant properties. While scientists observe PBDEs in various environmental media, little is known of their fate in soils. This study examines the potential fate of PBDEs in soils treated with biosolids. Surface soil samples were collected from commercial farms in the Mid-Atlantic region. Biosolids samples from the source wastewater treatment plant were collected to evaluate PBDE levels and trends. Results show that mean concentration of PBDEs in biosolids from this plant is 1496±158µg/kgd.w., mean concentration in soil from fields that had not received biosolids was 6.8µg/kgd.w., fields with a single application had a mean of 18µg/kgd.w., and fields with multiple applications had a mean of 52µg/kgd.w. Statistical analysis revealed that concentrations in the multiple application group were significantly higher than those in the single application group. This work suggests that PBDEs are relatively persistent in agricultural soils.Item ANALYSIS OF LIDAR DATA FOR FLUVIAL GEOMORPHIC CHANGE DETECTION AT A SMALL MARYLAND STREAM(2008) Gardina, Vincent Joseph; Brubaker, Kaye L.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Numerous detailed topographic measurements, which must be periodically repeated, are required to characterize stream bank and channel geometry. Light Detection and Ranging (LiDAR) is becoming more widely used, but its accuracy for change detection in and around small streams is not well quantified. Two LiDAR and one ground-surveyed elevation data sets are compared for a thickly vegetated riparian area in the Maryland Piedmont. Interpolated surfaces (prediction maps) and estimates of their uncertainty (standard error maps) are created from the point data using kriging. The LiDAR 2006 elevations are compared to ground-survey to evaluate accuracy. LiDAR 2002 and 2006 elevations are compared to evaluate the potential for change detection. When the estimated LiDAR system error is included in hypothesis testing, no statistically significant elevation differences are found between 2002 and 2006. Conclusions about geomorphic change based on LiDAR scenes should account for error and uncertainty in the data collection and processing.Item Thermal impact study of an underground stormwater management system(2008-12-08) Natarajan, Poornima; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increase in stream temperature by heated stormwater runoff from impervious surfaces is a serious environmental problem. An underground storage/slow release facility is a versatile stormwater best management practice (BMP) for buffering high flows. Temperature reductions in underground storage BMPs, however, have not been quantified. A field study on an underground storage facility was undertaken to characterize its effect on stormwater runoff temperatures. In colder months, when the runoff temperature ranged from 5 and 15○C, small or no temperature change was observed. Runoff produced during summer storm events, with event mean temperatures over 20○C, exhibited mean temperature reductions of 1.6○C through the BMP. While statistically significant, the reductions were not sufficient to cool the summer runoff discharges below the Maryland Class III temperature standard (20○C) 100% of the time. The results indicate that underground facilities can moderate high runoff temperatures, but that a more efficient design is needed.Item Transport and Catpture of Bacteria from Urban Stormwater Runoff Using Bioretention(2008-11-14) Zhang, Lan; Davis, Allen P; Seagren, Eric A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention, a nature-based treatment practice, has significant potential for reducing the threat of microbial pollutants from urban stormwater runoff to receiving water bodies. The overall goal of this research was to evaluate the removal efficiency for bacteria from urban stormwater runoff in bioretention systems and the potential of an engineered media (iron oxide-coated sand (IOCS)) for enhancing bacterial removal. This investigation was accomplished through laboratory column studies coupled with field tests. Column studies on the transport and destruction of Escherichia coli O157:H7 strain B6914 (a surrogate of pathogenic E. coli) in conventional bioretention media (CBM) and IOCS demonstrated that the bacteria were well removed in CBM (a mean 70% efficiency), but IOCS significantly enhanced the capture of strain B6914 (a mean 99.4% efficiency) due to the greater positive charge and surface roughness. However, the decay of trapped strain B6914 cells was much faster in CBM compared to the IOCS. More than 99.98% of B6914 cells attached to CBM died off within one week, while approximately 48% of trapped cells still survived in the IOCS after one week. Predation by indigenous protozoa in the CBM appears to play a dominant role in the faster decline of the number of trapped B6914 cells in CBM. Additionally, long-term (18 months) column experiments indicated that during the periodic application of simulated rainfall, the removal efficiency for strain B6914 improved over time, achieving 97% or higher efficiency after six months. Consistent with the laboratory studies, two years of field studies showed that bioretention systems reduced the concentration of indicator bacteria in the outflow during most storm events and increased the probability of meeting specific water quality criteria. The concentration of indicator bacteria in the input flow generally increased with higher daily temperature. No clear trend for the bacterial removal efficiency with respect to temperature was found in laboratory and field studies. However, the bacterial decay coefficients in CBM increased exponentially with elevated temperature. Based on these results, it is concluded that CBM not only achieves good removal for bacteria, but also has the potential to render the process sustainable.Item Remediation of Petroleum Contaminated Soils and Groundwater Using High Carbon Content Fly ash(2008-03-31) Demirkan, Mehmet Melih; Aydilek, Ahmet; Seagren, Eric; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Class F fly ash, a by-product of coal-burning power plants, is generated in large quantities and occasionally contains significant amounts of unburned carbon (i.e., high loss on ignition) as a result of equipping the power plants with the low nitrogen oxide burners. The overall goal of this research was to assess the feasibility of using high carbon content fly ash (HCCFA) as a stabilizing agent for petroleum contaminated soils (PCSs) and as a reactive medium in permeable sorptive barriers (PSBs) for remediation of petroleum hydrocarbon contaminated groundwater. A battery of laboratory tests was conducted to evaluate the geotechnical and environmental suitability of stabilized PCSs. The test program included batch adsorption, compaction, long-term column leaching, column sorption-desorption, and column biodegradation tests. Naphthalene and o-xylene sorption onto seven different fly ashes and powder activated carbon (PAC) was studied in a series of batch adsorption tests. A tertiary model non-aqueous phase liquid was used as the pollutant in column leaching tests conducted on PCS-fly ash mixtures. Retardation performance of HCCFA or PAC mixed with sand was investigated through column sorption-desorption and column biodegradation experiments to study the mass transfer behavior of the medium in a PRB application. Batch sorption tests demonstrated a nonlinear sorption behavior for naphthalene and o-xylene onto HCCFA. Sorption was strongly correlated with carbon content of the ashes. Compaction test results indicated that the maximum unit weights and optimum liquid contents of the stabilized soils satisfy the limits set for highway embankment construction. Column leaching test results indicated that the naphthalene and o-xylene concentrations in the effluents collected from the stabilized PCS columns were lower than those collected from the control (soil only) columns. Column sorption-desorption tests revealed a retardation capacity of 48 to 78% for naphthalene and 15 to 48% for o-xylene. The biodegradation tests showed that high levels of biodegradation occurred when fly ash was employed as reactive medium. The study indicated that HCCFA can be effective in remediation of PCSs, and has good hydraulic and adsorption properties which may justify its potential use as a PSB material in remediation of groundwater contaminated with petroleum residues.Item Release of inorganic and organic contaminants from fly ash amended permeable reactive barriers(2008-01-25) Morar, Doina Lorena; Aydilek, Ahmet H.; Seagren, Eric A.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Large quantities of fly ash are generated in the United States via coal combustion, most of which is disposed of in lagoons or landfills. The overall goal of this research was to assess the feasibility of using high carbon content (HCC) fly ashes as a reactive medium in permeable reactive barriers (PRBs) for remediation of petroleum hydrocarbon contaminated groundwater. A series of column and batch tests were performed to evaluate the leaching of selected metals from the fly ash, and adsorption/desorption of two target hydrocarbons (naphthalene and o-xylene) onto/from this PRB medium. Leaching of metals in the column experiments exhibited a first-flush, followed by a tailing slope elution pattern for all fly ashes. The naphthalene and o-xylene adsorption/desorption on/from the fly ashes were directly correlated with the organic carbon of the fly ash as measured by loss in ignition. Adsorption/desorption hysteresis was obvious in column and batch tests, suggesting that the adsorption/desorption was not completely reversible during the testing.