Steven G. Buchberger

Fractionation of heavy metals in pavement runoff

Abstract The transport of anthropogenic constituents by runoff from urban roadways can adversely impact the quality of adjacent receiving waters and soils. Metal elements are the most persistent constituents found in pavement runoff. A section of urban highway pavement in Cincinnati, Ohio, USA with an average daily traffic count of 150 000 vehicles was instrumented to sample lateral sheet flow from the pavement. Field samples from two diverse rainfall runoff events were analyzed to determine metal element partitioning between dissolved and particulate-bound fractions. Results indicate that dissolved metal element washoff response is a function of the degree to which a metal element is in dissolved form. Irrespective of the degree to which a metal element is dissolved, the particulate bound metal element washoff response is mainly a function of rainfall intensity. Results indicate that for both events Cu, Cd, Zn and Ni are mainly in dissolved form while Al and Fe are mainly in particulate-bound form. Cr and Pb partitioning is intermediate to these two cases. These findings can assist in the development of effective control strategies to immobilize dissolved and particulate-bound metal elements in pavement runoff.

Relationships between levels of heterotrophic bacteria and water quality parameters in a drinking water distribution system

Conventional plating methods were used to quantify heterotrophic bacteria from a drinking water distribution system. Three media, plate count agar (PCA), R2A agar and sheep blood agar (TSA-SB) were used to determine heterotrophic plate count (HPC) levels. Grab samples were collected weekly during the summer and autumn of 1997 at four locations in a municipal water distribution system. The four sampling sites included the water treatment plant, a vertical standpipe, a booster pump station and a private residence along a dead-end mainline. The pump station and private residence were also instrumented with water quality probes and on-line bioreactors. Relationships between levels of HPC bacteria and standard physical and chemical parameters were examined. HPC levels from R2A agar were found to be uncorrelated with HPC levels on TSA-SB agar at all four locations. Orange and yellow pigmented bacteria were the dominant expressions in all bulk fluid and biofilm samples. The fraction of pigmented bacteria in bulk fluid samples was greatest at the standpipe. Pigmentation percentages were found to be uncorrelated with standard physical and chemical parameters of water quality in distribution systems.

Effects of vegetation on flow through free water surface wetlands

Abstract The one-dimensional Saint-Venant equations are modified to account for stem drag and volumetric displacement effects of dense emergent plants on free surface flow. The modified equations are solved with an implicit finite difference method to give velocities and depths for shallow flows through a vegetated wetland channel. Estimated flow profiles are used to investigate how vegetation density, downstream boundaries and aspect ratio affect detention time, an important parameter in determining nutrient and pollutant removal efficiencies of wetlands constructed to treat wastewater. Results show that free water surface wetlands may exhibit static, neutral or dynamic behavior. Under static conditions, the wetland behaves like a pond in which displacement effects caused by submerged plant mass invariably decrease detention times. Under dynamic conditions, stem drag induced by aquatic plants predominates and wetland detention times increase with vegetation density. These opposing responses are separated by a narrow neutral condition where the presence of vegetation has virtually no net effect on detention time. For a given flow rate and surface area, detention times and hence treatment efficiencies in vegetated free water surface wetlands can be managed to some degree by adjusting the downstream control or by changing the aspect ratio.

An approach toward rational design of constructed wetlands for wastewater treatment

Abstract A simulation-based design approach is used to find the optimal size a wetland constructed for wastewater treatment. The simulation scheme synthesizes submodels describing variable wastewater loadings, atmospheric moisture fluxes, contaminant fate and transport, and effluent release and recycle rules. The wetland is modeled as a lined densely vegetated prismatic open channel that behaves as a non-ideal plug flow reactor (PFR) with first-order temperature-dependent kinetics. The hydrodynamic equation for gradually varied unsteady free surface flow is linked with the one-dimensional advection diffusion decay equation for a nonconservative nonsorbing substance. The coupled equations are solved using an implicit finite difference method. The flexibility of the simulation approach is illustrated with four hypothetical examples which compare treatment performances among alternate wetland configurations and operating strategies. Results show that ambient temperature and the effluent release and recycle rule are much more important than precipitation and evaporation in determining the size of the wetland required to meet permit limits.

Characterization of Metals and Solids in Urban Highway Winter Snow and Spring Rainfall-Runoff

Urban highways are a nonpoint source of metal elements and solids. These constituents are generated from traffic activities, pavement degradation, roadway maintenance, and atmospheric deposition. Pavement degradation and abrasion generates solids ranging in size from submicron particles to gravel-size aggregates. These constituents accumulate on the highway until they are transported from the pavement by traffic-induced turbulence or precipitation-runoff processes. Total metal elements and solids concentration are higher in snow washoff from urban highways than rainfall runoff. One reason is the snow washoff volume is less than the volume generated during a rainfall-runoff event. Another reason is that the residence time of a highway snowbank can range from hours to months depending on weather conditions. In addition, porous snow banks act as repositories that trap metals and solids. Metal elements and solids in urban highway winter snow and spring runoff at one highway site located along I-75 in Cincinnati, Ohio, are described and compared. Both snow and rainfall-runoff samples were fractionated into particulate-bound and dissolved metals. Solids characterization included dissolved, inorganic, and organic fractions. Results from snow samples taken at daily intervals from late January through mid-February 1995 indicate a significant increase in metal elements and solids accumulation for several days after two snow events. Results from runoff events in April 1995 indicate that the particulate-bound metal element washoff response was a function of rainfall intensity. In contrast, the dissolved response exhibited a dependence on the solubility of the metal element. Metal elements in rainfall-runoff were predominately dissolved as compared with more particulate-bound metals in snowfall.

Calibration of Rainfall-Runoff Model in Urban Watersheds for Stormwater Management Assessment

AbstractPhysically based semidistributed rainfall-runoff models are an important tool for assessing decentralized green infrastructure alternatives in controlling combined sewer overflows (CSO). Few studies have analyzed reliable calibration methods of highly detailed rainfall-runoff models at the subcatchment level. This research presents calibration of the storm water management model version 5 (SWMM5) using high temporal resolution rainfall and flow data to perform a 10-month continuous simulation on a physically distributed urban catchment. Detailed analyses of parameters that physically represent the area in the SWMM5 model were done using remote sensing and geographical information systems techniques. Parallel computing and a multi-search driver were implemented along with a model-independent parameter estimation (PEST) method, to find global optima and accelerate the calibration process. PEST internal settings were tuned for the continuous SWMM5 estimation problem using one month of rainfall data. ...

COMPARISON OF WATER DEMAND MODELS: PRP AND SIMDEUM APPLIED TO MILFORD, OHIO, DATA

There is growing interest in modeling water demands on short time scales (as brief as one second) and small spatial scales (typically single homes). Buchberger et al. (1996, 2003) have developed the Poisson Rectangular Pulse (PRP) model for this purpose. Blokker et al. (in prep.) have developed an end-use model SIMDEUM (which stands for SIMulation of Demand, and End-Use Model) which is based on statistical information from end-uses and does not require any flow measurements. SIMDEUM was developed and validated for Dutch water use. In this paper the PRP model and SIMDEUM are compared with each other and with measured indoor water demands from 21 homes in Milford, Ohio. Both models compare well to the measurements; the PRP model works better in simulating the cumulative flows of a sum of 20, SIMDEUM works better in simulating the flows of a single home.

Evaluation of Climate Change Impact on Drinking Water Treatment Plant Operation

AbstractThis paper describes a technique for evaluating the impact of climate change on drinking water treatment operations and for applying engineering principles to minimize those impacts. The U.S. Environmental Protection Agency (USEPA) Water Treatment Plant model was modified, validated, and applied to a case study based on the Greater Cincinnati Water Works’ Richard Miller treatment plant to provide quantitative measures of these impacts. Multivariate Monte Carlo experiments were executed to simulate and track performance of the Miller plant subject to nine jointly distributed source water quality parameters under both current and potential future hydrologic conditions. Results from the case study indicate a risk that finished water may exceed critical total organic carbon (TOC) levels, leading to potential violations of disinfection by-product regulations under plausible future scenarios. The future risk, however, can be managed with operational adjustments at the water treatment plant, such as incr...

Sizes for Self-Cleaning Pipes in Municipal Water Supply Systems

Historically, the minimum diameter of a pipe in a municipal water distribution system has been governed by fire flow requirements. In most cases across North America, the minimum allowable pipe size is six inches (150 mm), even on branching stubs that feed 100 or fewer homes. These peripheral regions of the pipe network often experience low velocities, long residence times, poor water quality and accumulation of settled deposits. As a consequence, many water utilities routinely flush these lines in an effort to cleanse them. In recent years, several water utilities (most notably in the Netherlands) have introduced the concept of a “self-cleaning” network where, for several minutes each day, a critical pipe velocity occurs and resuspends particles that settled during the low flow periods. Self-cleaning networks are a radical departure from the typical looped distribution system. Self-cleaning networks have a branch-type arrangement with downstream declining diameters and unidirectional velocities that reach at least 0.4 m/s for several minutes each day. Peak flows in the self-cleaning network are estimated using an empirical “ qN ” method, where q is the tapping unit demand usually taken as 0.083 litre per second per unit and N is the number of tapping units in the neighborhood. The problem of estimating the peak flow and, hence, the required pipe diameter can also be investigated using basic principles from the Poisson Rectangular Pulse (PRP) model for residential water demands. The objective of this paper is to apply theoretical results from the PRP model to generate reliability based estimates of the peak flow and the corresponding pipe size needed to assure a critical self-cleaning velocity as a function of neighborhood size. Results from the PRP model are compared against the conventional but conservative qN method.

CROSS CORRELATION ANALYSIS OF RESIDENTIAL DEMAND IN THE CITY OF MILFORD, OHIO

Estimating future demands with a high degree of accuracy in water distribution network design remains an elusive goal. The desired outcome is to match the design demands to the demands that are eventually “realized” in the built system. To this end, this paper explores the cross correlation between demands in an existing system in order to gain a better picture of the representative spatial and temporal patterns of design demands. The aim of the paper is to analyze the cross correlation in the residential demand data collected in the city of Milford, Ohio. More specifically, the paper begins to answer five important questions concerning the cross correlation of the Milford demand data: how strongly cross correlated are indoor, residential demands? How strongly correlated is the deterministic, diurnal component of residential demand? How strongly correlated is the random noise component of residential demand? To what extent does the choice of time step influence the strength of correlation between these 3 demand components? Does the correlation between these 3 demand components differ significantly between weekdays and weekends? To answer these questions, a periodic regression model was used to isolate the deterministic and the random noise components from the residential demand data collected in Milford. Correlation indices were formulated to measure the cross correlation of residential demand, its deterministic, diurnal component, and its random noise component. The Milford results pointed to a number of preliminary findings: (1) both residential demand and its deterministic, diurnal component had a positive and moderate to high correlation, while the random noise component of demand had a low level of correlation for the cases investigated; (2) increasing the time step length (from 600 s to 3,600 s) did increase the strength of the correlation in residential demand and its deterministic, diurnal component. This suggests that a longer time step increases both the coherence in diurnal demand patterns and their synchronicity. It is unclear whether time step length had any influence on the correlation of the random noise component of demand; (3) both residential demand and its deterministic, diurnal component were more strongly correlated during weekend periods than during weekday periods. This finding suggests that weekend periods may be characterized by less erratic water use patterns between customers leading to more coherent and synchronous diurnal patterns. It is unclear whether the random noise component was influenced by day-of-week effects. The implications of these preliminary results are discussed in the context of extended period simulation (EPS) and water quality modeling as they pertain to cost-effective design.