Pollutant Mass Flushing Characterization of Highway Stormwater Runoff from an Ultra-Urban Area

Water quality of highway stormwater runoff from an ultra-urban area was characterized by determining the event mean concentration (EMC) for several pollutants and by evaluating pollutant flushing. Thirty-two storm events were monitored between June 2002 and October 2003. Mean EMCs in mg/L were 0.035, 0.11, 0.22, 1.18, 420, 3.4, 0.14, 1.0, and 0.56 for Cd, Cu, Pb, Zn, total suspended solids (TSS), total Kjeldahl nitrogen (TKN), NO2–N, NO3–N, and TP. First flush as defined by flushing of 50% of the total pollutant mass load in the first 25% of the event runoff volume occurred in 33% of the storm events for NO2?, 27% for TP, 22% for NO3? and TKN, 21% for Cu, 17% for TSS, 14% for Zn, and 13% for Pb. Median values for the mass flushed in the first 25% of runoff volume were greater than the mass flushed in any 25% portion beyond the first for all pollutants. The mass in later 25% volume portions were greater than in the first 25% volume in at least 17% of the events for all pollutants, indicating that a significant amount of the pollutant load can be contained in later portions of the runoff volume. Nonetheless, management of the first 1.3?mm (1/2?in.) of runoff was able to capture 81–86% of the total pollutant mass.     

Phosphorus Treatment Capability of Marshland Upwelling System under High Background Salinity Conditions

The marshland upwelling system (MUS) is an alternative onsite wastewater treatment system developed for coastal communities. The phosphorus treatment efficiency of the MUS operated under high background salinity conditions ( ～ 32?ppt) was examined over the course of a one-year field study. Five individual studies were investigated by intermittently injecting wastewater at a depth of 3.8?m using flow rates/injection frequency regimes of 1.9?L/min (30?min/3?h), 5.5?L/min (30?min/3?h), 2.8?L/min (30?min/3?h), and 2.8?L/min (15?min/h). There were two studies conducted within the 2.8?L/min (30?min/3?h) flow regime: (1) with normal influent and (2) with high strength synthetic wastewater. Over the course of the study, no signs of phosphorus saturation were observed. The overall system efficiency for the entire study was estimated to be >98%. Removal rate coefficients ranged from 0.73–1.25?m?1 and 0.66–1.08?m?1 for total phosphorus and orthophosphate, respectively. Upon completion of the final 2.8?L/min (15?min/h) study, it was determined that a travel distance of only 9.4?m would be needed to reduce influent concentrations below 0.1?mg?P/L.     

Modeling and Control of Vinyl Chloride in Drinking Water Distribution Systems

In water distribution systems containing PVC pipe manufactured in the “early era” (prior to 1977), vinyl chloride can leach into drinking water resulting in vinyl chloride concentrations exceeding the 2 μg?L?1 maximum contaminant level. Field testing of dead-end segments of water distribution systems consisting of early-era PVC pipe was conducted to examine their initial intrapipe vinyl chloride monomer (VCM) concentrations based on a Fickian-diffusion-based leaching model. The experiments showed a wide range of VCM concentrations within early-era PVC pipe ranging from less than 50 to more than 600 mg?kg?1. Based on the diffusion modeling approach, a protocol was designed that provides a means for utility managers to calibrate the model for specific dead-end lines. The paper delineates procedures to determine which dead ends require flushing to control vinyl chloride, examines the effects of system parameters such as temperature on vinyl chloride leaching, and provides a method to devise flush schedules and volumes. Through a properly designed, tested, and maintained flush protocol such as that developed in this research, public water systems with dead-end lines consisting of early-era PVC pipe can control vinyl chloride concentrations using either manual or automatic flush valves.     

Attenuation of Roadway-Derived Heavy Metals by Wood Chips

Wood chips were evaluated for their ability to attenuate heavy metals in roadway runoff. Column experiments with controlled synthetic runoff composition and flow rate were used to assess effects of flow rate (intercepted sheetflow from a 3-m wide roadway section), runoff salt concentration, wood exposure to alternating wetting and drying cycles, wood aging, competition among dissolved heavy metals, and removal of particle-associated heavy metals. Overall, wood chips damped the “pulse” of copper in the synthetic runoff such that the effluent was characterized by lower concentrations (3–25% of input) over longer periods of time, but with little retention of the total copper mass. The most effective treatment was wood chips aged up to 9 months. Increased aging and chip water content reduced effluent concentrations, relative to no treatment. Flow rate had no effect on effluent concentrations. The presence of salt (>2?mS/cm) or dissolved lead (500?μg/L) in the runoff caused greater copper effluent concentrations than the no treatment case. Removal of suspended particles (and associated contaminants) was greater than 85% with an estimated capacity of 0.16?g/gwood. Field evaluation with concentrated flow to a gutter containing a wood chip treatment showed little effect on total or dissolved copper and zinc runoff concentrations and indicated that wood chips may be a source of contaminants in subsequent storm events. Applications of wood chips to treat roadway runoff would not provide a significant decrease in total maximum daily load contributions (e.g., kg/d); however, there may be some scenarios for which wood chip treatments to decrease peak storm water concentrations of dissolved heavy metals in sheetflow runoff is desirable.     

Field Studies of Discoloration in Water Distribution Systems: Model Verification and Practical Implications

Discoloration in water distribution systems has been studied in partnership with a number of U.K. water companies by measuring the turbidity response to changes in hydraulic conditions induced by systematic flushing. The resulting data was used to verify a predictive empirical model and hence the underlying assumptions made in its development. Model simulations, made using previously established parameters defined solely by pipe diameter and pipe material, are presented alongside measured data to demonstrate this verification. The primary cause of discoloration observed is the mobilization of material from cohesive layers bonded to pipe walls. These layers demonstrate a profile of increasing shear strength with increasing degree of discoloration. Differences are demonstrated in the layer and ultimate shear strength characteristics of the discoloration layers formed in iron and plastic pipes, with a modeled shear stress of 1.2?N/m2 shown to exhaust material layers in plastic pipes. Based on the observed data it is theorized that accumulation of material to the pipe walls is primarily dependent on two mechanisms; ubiquitous background concentrations in the bulk water, and if present corrosion by-products from iron pipes and fittings. A consequence of this is that all pipes within a water distribution system are susceptible to the development of material layers. In the formulation of operation and maintenance strategies it is suggested that iron and plastic pipes should be treated differently to obtain optimum operational effectiveness and minimize discoloration risk.     

Development and Evaluation of Soil Moisture-Based Seepage Irrigation Management for Water Use and Quality

A 2-year study was conducted at a seepage-irrigated vegetable farm in south Florida to develop and evaluate an improved, soil moisture-based irrigation management practice that could potentially reduce irrigation water use, prevent water quality impairment, and maintain or improve crop yield. The improved practice reduced irrigation water use by 36% compared to the conventional irrigation management. Moreover, the improved practice also increased rainfall retention and decreased runoff events by lowering the water table 13?cm compared to the conventional practice. Total dissolved phosphorus (P) concentrations in groundwater were higher (p<0.01) for the improved practice compared with the conventional practice in two of the three fields where ground water quality was monitored. Higher P concentrations for the improved practice were likely due to the dilution effect. Statistically, no differences (p>0.05) were observed in groundwater nitrogen (N) (NOx–N, NH4–N, and total dissolved N) concentrations between the improved and the conventional practices. Similarly, no statistical difference was observed in crop yield between the improved and the conventional practices, although the average total yield was higher for the improved practice. The improved practice also reduced the incidence of plant disease compared to the conventional practice which resulted in crop failure in some fields. Thus, use of the improved practice reduced irrigation water use without impacting crop yield.     

Sorption Behavior and Mechanism of Pb(II) on Chinese Loess

Lead pollution is common in Western China and has caused serious public health problems recently. The treatment of wastewater containing Pb(II) is stringent for the sustainable development of local economics. The Chinese loess proved effective to remove Pb(II) from aqueous solution and applicable in the treatment of wastewater from lead–zinc ore mining sites. The adsorption capacity of Chinese loess about Pb(II) is determined as high as 270.26?mg?g?1 in this study. Factors affecting the adsorption of Pb(II) include slurry concentration, solution pH, temperature, and equilibrating duration. The optimum conditions for Pb(II) adsorption include sorbent dosage ≥ 0.05?g/50?mL, pHi ≥ pHzpc, temperature = 55°C, and equilibration duration ≥ 30?min. The isotherms and kinetic data are well fitted with Langmuir model and pseudo-first order kinetics, respectively. The thermodynamic behavior reveals the exothermic and spontaneous nature of the adsorption. The adsorption of Pb(II) on loess involves chemical reaction with calcite and surface complexation with clay minerals and hydrolysis of quartz; the former is considered as the dominant mechanism. X-ray diffraction and Fourier transform infrared patterns confirmed these speculations.     

Contaminant Diffusion, Solubility, and Material Property Differences between HDPE and PEX Potable Water Pipes

The objectives of this work were to identify differences between the composition, bulk properties, contaminant diffusivity and solubility for new high-density polyethylene (HDPE) pipe and crosslinked polyethylene (PEX) pipe, as well as determine which contaminant and polymer properties are useful for predicting contaminant fate in water pipe. Variations in PE pipe density (0.9371–0.9547?g/cm3), crystallinity (69–72%), crosslinking (60 and 76%), and oxidative induction time (33 to >295?min.) were detected. While numerically these differences seem minor, results show that slight material differences have a notable effect on contaminant diffusivity and solubility. Nonpolar contaminant diffusivity and solubility were best predicted by bulk density. Polar contaminants were more soluble and diffused faster through PEX than HDPE pipes because PEX pipes contained a greater amount of oxygen. For all materials, dipole moment and Log Kow were good predictors of contaminant fate and molecular volume was only useful for predicting diffusivity and solubility values for haloalkane and nonpolar aromatic contaminants.     

Removal of Metal Ions from Storm-Water Runoff by Low-Cost Sorbents: Batch and Column Studies

The possibility of using the sorption technology to reduce the levels of metal ions present in urban storm-water runoff was investigated in this study. Seven sorbent materials including Amberlite XAD7, chitosan, crab shell, peat, Sargassum, sawdust, and sugarcane bagasse were initially examined for removal of 11 metal ions (Na, K, Ca, Mg, Mn, Co, Ni, Cu, Zn, Cd, and Pb) from simulated storm-water runoff at different concentrations. Among these sorbents, crab shell performed well with removal efficiencies exceeding 93% for all heavy metal ions examined and thus selected for further studies. Based on scanning electron microscopy/energy-dispersive x-ray analysis, microprecipitation of metal carbonates followed by adsorption onto the surface of crab shell was identified as the major mechanism responsible for removal of heavy metal ions by crab shell. Crab shell exhibited rapid removal of meal ions with attainment of biosorption equilibrium within 20 min. A crab-shell-packed column was used to study the continuous metal retention process. The column performed very well in the removal of heavy metal ions and was able to operate up to 192 h at a flow rate of 10 mL/min before outlet concentrations of Mn and Co reached 0.3 times of their respective inlet concentrations. Other metal ions such as Pb, Zn, Ni, Cd, and Cu were only in trace levels in the final effluent until 192 h. These findings would form the basis for the future development of crab-shell-based biofilters for removal of dissolved heavy metal ions from storm-water runoff.     

Effects of a Permeable Friction Course on Highway Runoff

This project documents the impact of a porous asphalt overlay on the quality and quantity of highway storm-water runoff. A permeable friction course, also known as open graded friction course, is a layer of porous asphalt approximately 50?mm thick, which is often applied on top of conventional asphalt or concrete highways to enhance safety and reduce noise. Storm-water runoff from a four-lane divided highway in the Austin, Texas area was monitored at two sites before and after the installation of a PFC. Observed concentrations of total suspended solids and pollutants associated with particulate material were much lower in the runoff from the PFC than that derived from the conventional asphalt surface. Concentration reductions were observed for total suspended solids, total lead, total copper, and total zinc at both monitoring locations. In addition to the above-mentioned constituents, concentrations of chemical oxygen demand and total Kjeldahl nitrogen were also lower in the runoff from the PFC at a site collecting paired samples from both pavement types. Concentrations of dissolved constituents were not significantly different and concentrations of polycyclic aromatic hydrocarbons were below the detection limit for both pavement types. The runoff coefficient for the PFC appears to be higher than for conventional pavements.     

Dioxin in Storm-Water Runoff in Houston, Texas

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in runoff were measured at 10 small flood control drainage channels in the Houston area. Total toxicity equivalent concentrations in runoff ranged from 0.01?to?0.11?pg/L for the dissolved phase and from 0.02?to?0.88?pg/L for the suspended phase. The dissolved concentrations were lower than their respective suspended concentrations, with average suspended/dissolved ratios between 5 and 152 for individual congeners. Average observed logs of organic-carbon (OC)-normalized suspended sediment-dissolved partitioning coefficients (log?KOC) varied between 5.47 and 7.83?L/kg OC. Dioxin concentrations in runoff were generally at the same level or lower than those measured in the receiving water body. Principal component analyses indicated that the signatures for dissolved runoff match those observed in dissolved ambient water in the channel, while the suspended-sediment runoff signatures are similar to those observed in dry air deposition in the Houston area.     

Air–Water Mass Transfer on a Stepped Waterway

Stepped waterways are commonly used as river training, debris dam structures, storm water systems, and aeration cascades. The present study was focused on analysis of basic air–water flow properties on a low gradient stepped chute, combined with dissolved oxygen measurements. The oxygen aeration efficiency was found to be about 30% for 12 steps with a total drop in invert elevation of 1.4?m, nearly independently of the inflow conditions. Detailed air–water flow measurements, including void fraction, velocity, bubble count rate, and interface area, were used to integrate the mass transfer equation and to estimate the aeration potential of the waterway. Direct comparisons with dissolved oxygen measurements showed good agreement between the two methods.     

Water Quality Improvement through Reductions of Pollutant Loads Using Bioretention

As an increasingly adopted storm-water best management practice (BMP) to remedy hydrology and water quality impairment from urban development, bioretention facilities need rigorous investigation to quantify performance benefits and to allow design improvements. This study examines water quality improvements [total arsenic, total cadmium, chloride, total chromium, total and dissolved copper, E. coli, fecal coliform, lead, mercury, nitrogen species, oil and grease, phosphorus, total organic carbon (TOC), total suspended solids, and total zinc] via monitoring for a 15-month period at two bioretention cells in Maryland. Both bioretention cells effectively removed suspended solids, lead, and zinc from runoff through concentration reduction. Runoff volume reduction promotes pollutant mass removal and links BMP water quality benefits with hydrologic performance. From a load perspective (kg/ha?year), all but TOC at one cell showed pollutant reduction. Bioretention effluents exhibited good water quality for all significant pollutants except for nitrate, copper, and phosphorus in one cell, the latter two of which may be attributed to media organic matter dissolution. Copper dissolved/particulate analyses showed that significant changes in copper speciation behavior result from transport through the bioretention media.     

Heavy Metals Removal from Acidic and Saline Soil Leachate Using Either Electrochemical Coagulation or Chemical Precipitation

This study compares electrocoagulation and chemical precipitation for heavy metals removal from acidic soil saline leachate (SSL) at the laboratory pilot scale. The electrocoagulation process was evaluated via an electrolytic cell [12 cm (width)×12 cm (length)×19 cm (depth)] using mild steel electrodes (10 cm width×11 cm high), whereas chemical precipitation was evaluated using either calcium hydroxide [Ca(OH)2] or sodium hydroxide (NaOH). By comparison with chemical precipitation at a pH varying between 7 and 8, electrocoagulation was more effective in removing metals from SSL having a relatively low contamination level (124?mg?Pb/L and 38?mg?Zn/L). For SSL enriched with different heavy metals (each concentration of metals was initially adjusted to 100 mg/L) and treated at a pH lower than 8.5, with the exception of Cd, the residual metal concentrations at the end of the experiments were below the acceptable level recommended for effluent discharge in urban sewage works (less than 4 mg/L of each residual metal concentration was recorded) using electrocoagulation, contrary to chemical precipitation using NaOH (more than 15 mg/L of each residual metal concentration was recorded). By comparison, chemical precipitation using Ca(OH)2 was effective in reducing Cr, Cu, Ni, and Zn under the permissive level, but not for Cd and Pb. However, both chemical precipitation processes needed to be operated at higher pH values (around 10.0) to be more effective in reducing metals from SSL and, therefore, required a pH adjustment of the effluent before discharge, whereas electrochemical treatment had a practical advantage of producing an effluent having a pH close to the neutral value and suitable for stream discharge in the receiving water. On the other hand, electrocoagulation was also found to be very efficient for removing Pb from very contaminated solutions (250–2,000 mg?Pb/L). At least 94% of Pb was removed regardless of the initial Pb concentration in the SSL. Electrochemical coagulation involves a total cost varying from 8.67 to 13.00 $/tds, whereas 0.84 to 16.73 $/tds is recorded using chemical precipitation. The cost included only energy consumption, chemicals consumption, and metallic sludge disposal.     

Lead Removal from Acidic Solutions by Sorption on Cocoa Shells: Effect of Some Parameters

The objectives of this work were to evaluate the effects of different parameters (Pb concentration, solution pH, Ca/Mg/Na/K salt concentrations) on Pb uptake by cocoa shells and to study the mechanisms of Pb removal in very acidic conditions. Sorption tests were conducted in shaken flasks with synthetic Pb solutions and 15 g/L cocoa shells. A lead uptake value of 161 mmol/kg was measured during the assay with [Pb]i = 3.66?mmol/L in solution at pHi = 2.0 and T = 22°C. Results show that Pb uptake is very similar (14.5–16.0 mmol/kg) for an initial pH between 2.0 and 4.0, but a moderate decrease (10.8 mmol/kg) occurred when the initial pH=1.5 and the [Pb]i = 0.25?mmol/L. High Ca and Mg concentrations (2.35 mol/L) in solution induced a significant decrease in Pb removal by cocoa shells, whereas high K and Na concentrations did not affect Pb uptake by this sorbent. This suggests that Pb uptake by cocoa shells is controlled by ion-exchange reactions with Ca/Mg ions and protons. Finally, chemical tests have shown that carboxyl and amine functional groups play a dominant role in Pb uptake by cocoa shells.     

乙酸根配位浸出硫酸铅的热力学分析

采用热力学平衡计算和验证性实验的方法, 研究乙酸根配位浸出硫酸铅的热力学问题。首先, 通过Pb(OH)₂-H₂O体系的热力学计算评价了Pb(OH)₆4-形成常数的合理性。结果表明, 考虑Pb(OH)₆4-存在时所得计算结果明显不符合Pb(OH)₂两性化合物的性质, 因而不建议采用。然后, 计算并绘制了乙酸根配位浸出硫酸铅的热力学平衡图。结果表明, 在不同总乙酸根浓度下, pH值在6~9的范围对乙酸根浸出硫酸铅更有利, Pb(Ac)₄2-是该pH值区域中铅的主要物种; 并且, 总乙酸根浓度越高, 浸出液中, Pb(Ac)₄2-与游离Ac-的浓度比越高, 表明浸出硫酸铅的乙酸根利用率随之增大。此外, 根据电中性原则、质量守恒原则和同时平衡原理, 计算并绘制了不同HAc和NaAc比例的初始液浸出硫酸铅平衡后各溶解物种的lgc-[Na]/[Ac]_T图, 表明总乙酸根一定时浸出液铅浓度随着初始液乙酸钠比例增加而增加, 验证性实验结果与热力学计算结果趋势上一致。      

Concentration–Duration–Frequency Curves for pH in a Stream in the Great Smoky Mountains

Multiparameter monitors (sondes) were installed at four sites in a stream in the Great Smoky Mountains National Park. These sondes recorded pH, turbidity, and other parameters every 15?min. The data were analyzed to determine the time-connected duration of excursions below various pH levels (pH 4.5, 5.0, 5.5, 6.0, and 6.5). The durations for excursions below each pH level were assigned probability quantiles and plotted. This created a concentration–duration–frequency curve similar to precipitation intensity–duration–frequency curves. The pH excursion events appear to follow a Poisson arrival process and were fitted to a corresponding exponential distribution. The mean event duration for each pH level is the fitting parameter, μ, for the exponential distribution, and μ followed an exponential trend with pH. The characteristics of the concentration–duration–frequency family of curves capture the information contained in the original data and potentially allow comparisons with toxicity data as well as a temporal and spatial comparison.     

Model for Predicting Effects of Land-Use Changes on the Canal-Mediated Discharge of Total Suspended Solids into Tidal Creeks and Estuaries

The Land Use Input Canal Output Model (LUICOM) was created for the purpose of predicting canal-mediated, total suspended solids (TSS) loading in receiving estuaries. Tidal flushing (related to the tidal prism) within a subject estuary (i.e., Yellow Bluff Creek) was also evaluated. Estimates of flushing times were based on those estimated for Georgia and South Carolina creeks that have better coverage of hypsometric data. Two rain events were sampled for this effort, and TSS concentrations predicted by LUICOM compared favorably with observed values. With subsidence of each rain event, TSS concentrations gradually decreased to baseline concentration in the receiving estuary. Moreover, LUICOM provided a reasonable estimate of the time of peak TSS. The results of this study suggest that TSS measured in the subject canal and creek increase as the result of significant rain events (>1.0 in. in 3?h). The correlation between model-derived and measured TSS values suggest LUICOM could be used to evaluate changes in a basin’s land use as it relates to predicting subsequent increases in TSS discharges. The simplicity of the model makes it an ideal tool for resource managers concerned with changes in land use within coastal areas.     

Effect of ClO2 Pretreatment on Subsequent Water Treatment Processes

The effect of chlorine dioxide (ClO2) pretreatment on subsequent treatment processes (coagulation, flocculation, sedimentation, filtration, and ozonation) was studied at pilot-scale at the Upper San Leandro Water Treatment Plant near Oakland, Calif. Potential impacts of ClO2 on the distribution system were also studied at bench scale using simulated distribution system (SDS) tests. Pilot trials were conducted with one train operating without ClO2 pretreatment (Train 1) and the other with a ClO2 dose of between 0.6 and 1.0?mg/L (Train 2). Comparison between Trains 1 and 2 showed that ClO2 pretreatment resulted in a 0.1–0.2 NTU decrease in settled water turbidity when compared to no pretreatment. ClO2 pretreatment also resulted in a small (0.01?cm?1) decrease in ultraviolet absorbance at 254?nm. Following sedimentation, about 60% of the applied ClO2 formed chlorite (ClO2?), with 10–20% forming chlorate (ClO3?). Ozonation immediately converted all residual ClO2 and ClO2? to ClO3?. There was no significant difference in the performance of the filters between the two trains in terms of headloss, particle count, and turbidity. Bench-scale SDS tests indicated that chlorine dioxide preoxidation did not affect subsequent chloramine stability or concentrations of trihalomethanes, haloacetic acids, or adsorbable organic halides in the distribution system.     

Effect of Calcium on Lead in Soft-Water Distribution Systems

Meeting the lead rule action level for drinking water can be difficult for soft-water systems. One concern in these systems is the formation of particulate or colloidal lead that is difficult to remove from the aqueous phase. In this preliminary study, batch and pipe-loop systems are used to assess the effect of calcium addition on lowering the concentration of particulate or colloidal lead. The addition of calcium at levels as low as 5 mg∕L reduced zeta potential of lead-bound colloids and in some cases resulted in a reduction of total Pb concentration.