Journal of Environmental Engineering

Although street sweeping is commonly regarded as a cost-effective storm-water best management practice, there is little quantitative evidence that street sweeping directly improves runoff water quality. In this paper, several previous street sweeping studies were reevaluated using statistical power analysis. Two-group, independent-sample one-sided $t$ -test power analyses were performed using log-transformed event mean concentrations (EMCs) of total suspended solids, suspended sediment concentration or chemical oxygen demand. The effect size between the two groups was estimated using the sweepers’ pickup efficiency, which showed that the failure to detect the difference between mean EMCs of the two sample groups (i.e., unswept and swept groups) is likely due to limited sample numbers. Too few samples, which also resulted in a high coefficient of variation, were analyzed to detect the likely difference between swept and unswept observations. In addition, the temporal gap between street sweeping and subsequent storm events was not controlled to improve statistical power.

Sediment fingerprinting has been developed by researchers over the past three decades for watershed sediment transport research. Sediment fingerprinting is a method to allocate sediment nonpoint source pollutants in a watershed through the use of natural tracer technology with a combination of field data collection, laboratory analyses of sediments, and statistical modeling techniques. The method offers a valuable tool for total maximum daily load assessment to aid in developing efficient remediation strategies for pollution in watersheds. We review the methodological steps of sediment fingerprinting including classification of sediment sources in a watershed, identification of unique tracers for each sediment source, representation of sediment sources and sinks using field sampling, accounting for sediment and tracer fate during transport from source to sink, and utilization of an unmixing model to allocate sediment sources. This review places additional emphasis upon tracers used to discriminate sediment sources during past studies performed on different continents and across different physiogeographic regions. Review and analysis of tracer dependence upon watershed variables provides an additional resource for tracer selection to the community. Finally, future improvements needed for sediment fingerprinting are discussed in order to practically apply the technology for sediment nonpoint source pollution allocation within the context of total maximum daily load assessments.

Heavy metals deposited on road surfaces and transferred to roadside environments by rainfall and snowmelt runoff can have serious impacts on receiving ecosystems. Infiltration is an effective best management practice for controlling metal contamination in runoff, although metals retention within infiltration facilities depends on a number of factors, including metal species, soil characteristics, and influent water quality concentrations. In cold climates, deicing compounds have been shown to mobilize heavy metals putting receiving waters at risk. This study ascertains the effects of two widely used road salts (NaCl and $\mathrm{Mg}{\mathrm{Cl}}_2$ ) on heavy metal mobility in two eastern Washington soils. Infiltration experiments were conducted using a basic soil, exhibiting a soil pH of 8.3, taken from a highway infiltration pond site in Spokane Washington and an acidic soil, exhibiting a soil pH of 5.9, taken from an infiltration pond site in Richland Washington. Three concentrations of each salt were percolated through both soils using continuous flow soil columns. Leachate samples were collected and analyzed for dissolved metals, organic matter, and pH. Experiments were also performed without salt and used as controls. Results indicate that metal mobilization can occur by a number of mechanisms including cation exchange, chloride complex formation, and colloid dispersion (release of organic matter and/or clay that can complex metal species). Sodium chloride resulted in the largest release of copper and lead via indirect mobilization of organic matter. The magnesium salt had less of an effect on lead and copper but had a much greater effect on the mobilization of cadmium. Releases of metals during or immediately following salt application produced concentrations that ranged from 50% to 1000% greater than the concentrations released from the control experiments.

A proprietary storm-water treatment system (Baysaver $1∕2\mathrm{K}$ ) was monitored as part of a low impact development project to assess pollutant removal efficiency and to model removal as a function of flow rate, season, and dry time. Twenty six storm events were sampled over a $12\text{-}\text{month}$ period and analyzed for total suspended solids, turbidity, conductivity, ammonia/ammonium, nitrate/nitrite, total phosphorus, total Zn, total Pb, and total Cu. The data were analyzed to determine which parameters showed significant removal by the device and whether or not the removal efficiencies were influenced by peak flow rate, season of the year, and/or dry time. Results indicated that the removal of each pollutant analyzed was statistically significant with the exception of conductivity, which showed higher outflow levels resulting in significant release of ions. Regression analyses revealed that all pollutants except for conductivity and total phosphorus showed significant negative relationships to peak flow rate and that conductivity and total Cu reductions were significantly related to the season of the year.

Trapping efficiency (TE) is defined as the percent of particles that are retained within an impoundment. TE can vary from $⩽0\%$ indicating no sediment is retained or is lost, to 100% where all the sediment is retained. In this paper a high quality, long-term data set $\left(32\text{years}\right)$ was used to demonstrate that annual sediment trap efficiencies for a run of the river impoundment are variable. For water years 1973–2005, annual trap efficiencies for Coralville Reservoir ranged from 5.6 to 95.8%, with a mean of 74.7% and a median of 79.9%. Overall trap efficiency for the entire period was determined to be 80.3% and a detention time of $12.4\text{days}$ . A comparison of the observed long-term TE was done against different empirical TE equations that are commonly used (Brown, Brune, Churchill, Dendy, Heinemann, & USDA/Summit Co., Water District). The Churchill equation provided the best fit of the empirical trap efficiency equations $({\mathrm{TE}}_C=79.1\%)$ ; all other empirical TE relationships underestimated the observed trap efficiency with errors ranging from 13.7 to 33.1%. Bathymetric data show that since 1958 the reservoir has lost 11% of its flood storage capacity, and over 62% of its normal pool capacity. For the time studied (1973–2005) the loss of storage is estimated to correspond to $16.9\times {10}^9\mathrm{kg}$ of sediment deposited in the reservoir, resulting in an annual sedimentation rate of $5.3\times {10}^8\mathrm{kg}{\text{year}}^{-1}$ .

The resuspension and transport of particulate mercury $\left({\mathrm{Hg}}_P\right)$ from a nearshore industrial waste deposit to the pelagic zone of Onondaga Lake, N.Y., was investigated using an array of sediment traps radiating from the deposit, and quantified through application of a steady-state mass balance model. Time-averaged downward fluxes of suspended solids and ${\mathrm{Hg}}_P$ decreased in the offshore direction, indicating a nearshore source. Strong temporal variations in resuspension were documented and were linked to the dynamics of wind-driven wave action, as quantified by a validated surface wave model. A simple steady-state model of offshore transport from the resuspension zone, which assumes a balance between offshore transport and settling, was used to analyze sediment trap data. The resulting larger, and likely more accurate, estimate of ${\mathrm{Hg}}_P$ resuspension $(\sim 60\mathrm{g}{\text{day}}^{-1})$ represents the dominant contemporary source to the water column. This result supports the planned remediation of this source as a part of a Superfund cleanup project.

The destruction of trichloroethylene (TCE) and perchloroethylene (PCE) dense nonaqueous phase liquids (DNAPLs) using catalyzed ${\mathrm{H}}_2{\mathrm{O}}_2$ propagations (CHP), an in situ chemical oxidation process based on Fenton’s reagent, was investigated in batch, bench scale reactors. TCE and PCE masses were quantified over time in DNAPLs, aqueous phases, and off gasses, and the rate of DNAPL destruction was compared to the corresponding rate of gas purge dissolution. TCE and PCE DNAPLs were rapidly destroyed by CHP at 1.7 and 4.4 times the rate of gas purge dissolution, respectively. Use of reactions in which a single reactive oxygen species was generated demonstrated that both hydroxyl radical and superoxide were involved in TCE and PCE DNAPL destruction, with superoxide having the major role in the destruction of the DNAPLs. These results show that DNAPLs composed of contaminants highly reactive with hydroxyl radical, such as TCE and PCE, are destroyed primarily through reaction with superoxide.

In this project the use of natural media filtration (NMF) was evaluated for its ability to remove colloidal particles from the aqueous phase as a function of ionic strength and filter media type by determining first-order kinetic deposition rate coefficients. Mushroom compost (MC) and leaf compost (LC) were tested as natural filter media and the results were compared to those obtained using sand and granular activated carbon (GAC). The highest deposition rate coefficients were observed for GAC, followed by LC and MC, and the lowest deposition rate coefficients were found for sand. As predicted by the Derjaguin–Landau–Verwey–Overbeek theory, higher deposition rates were obtained at higher solution ionic strengths. Overall the experiments suggest that the NMF process can efficiently remove colloidal particles from surface waters.

A computational fluid dynamics (CFD) model is presented and applied in the design of the secondary settling tanks of Psyttalia Wastewater Treatment Plant in Athens, Europe’s largest sewage treatment facility. The tanks are of the Gould Type II consisting of the following regions: an inlet-flocculation chamber with an inlet baffle, two zones of settling separated by an intermediate baffle, an outlet region, and a sludge collection region. The number of tanks and their dimensions were determined with an empirical design procedure. Then, theoretical considerations, information from similar existing tanks, and preliminary CFD calculations were combined to determine the dimensions of the main regions and the positions of the baffles. Finally, detailed CFD calculations were performed to examine the performance of the tanks for various design conditions. Computations showed that the flow in the inlet-flocculation region was completely mixed; while in the settling regions a “three-layer” structure with relatively constant layer heights was observed. CFD results were processed to determine parameters of practical interest, including the heights of the sludge blankets and the effluent suspended solids concentrations; these parameters were correlated satisfactorily with the Hazen number, which is used as a scaling parameter in primary settling tanks.

Aeration performance of a $500\mathrm{mm}$ diameter double-hub paddle wheel aerator was tested in a brick masonry tank of $5.9\times 2.9\times 1.6{\mathrm{m}}^3$ . The prime objective of the present study is to evaluate the aeration performance of double-hub paddle wheels at different dynamic conditions. The results showed that the oxygen transfer simulation curve for double hub almost matched that of a single-hub paddle wheel. However, the power consumption simulation curve for double hub distinctly deviated from that of a single-hub paddle wheel due to the fact that if geometric and process conditions remain the same, a double-hub paddle wheel consumes more power than a single hub. Hence, a separate power consumption simulation equation was developed for a double-hub paddle wheel. The optimum dynamic condition producing maximum standard aeration efficiency is also presented along with a sample calculation.