Jiri Marsalek

Trace metal composition and speciation in street sediment: Sault Ste. Marie, Canada

Street sediment collected in Sault Ste. Marie, Ontario was examined for trace element composition (As, Cd, Cr, Cu, Fe, Pb, Hg, Ni and Zn) and the metal partitioning to various sediment properties was determined by sequential extraction. Total Ni, Cu, Zn and Pb concentrations exceeded the lowest effect levels specified in the Ontario Provincial Sediment Quality Guidelines for Metals (Environment Ontario, 1992) and derived from bioassay studies. According to these Guidelines, the disposal of such sediment has to be guided by environmental considerations. A significant fraction of these metals was extractable in 0.5 N HCl over a 12-hour period and considered as potentially bioavailable. The major accumulative phases of toxic metals in this sediment are exchangeable, carbonate, Fe/Mn oxides and organic matter but the relative importance of each phase varied for individual metals. Approximately 20% of the total extractable Cd is found in each of these four fractions. Pb, Zn and Mn are predominantly bound to carbonates, Fe/Mn oxides and organic matter. Cu shows a high affinity for organic matter and to a lesser extent for carbonates. Elevated levels of Cd, Pb, Cu, Zn, Mn and Cr in the exchangeable and/or soluble phase suggest that sediment associated metals, mobilised from streets in Sault Ste. Marie during runoff and snowmelt, would adversely impact water quality in the receiving waters. However, large fractions of the total metal load are associated with coarser particles which are unlikely to be transported through the drainage system into receiving waters.

Urban wet-weather flows: sources of fecal contamination impacting on recreational waters and threatening drinking-water sources.

Discharges of urban stormwater and combined sewer overflows (CSOs) contribute to fecal contamination of urban waters and need to be considered in planning the protection of recreational waters and sources of drinking water. Stormwater characterization indicates that Escherichia coli counts in stormwater typically range from 103 to 104 units per 100 ml. Higher counts (105 units/100 ml) suggest the presence of cross-connections with sanitary sewers, and such connections should be identified and corrected. Fecal contamination of stormwater may be attenuated prior to discharge into surface waters by stormwater management measures, which typically remove suspended solids and attached bacteria. Exceptionally, stormwater discharges in the vicinity of swimming beaches are disinfected. The levels of indicator bacteria in CSOs can be as high as 106 E. coli per 100 ml. Consequently, the abatement of fecal contamination of CSOs is now considered in the design of CSO control and treatment, as for example stipulated in the Ontario Procedure F-5-5. CSO abatement options comprise combin ations of storage and treatment, in which the CSO treatment generally includes disinfection by ultraviolet (UV) irradiation. Finally, indicator bacteria data from Sarnia (Ontario) were used to demonstrate some fecal contamination impacts of wet-weather flows. In wet weather, the microbiological quality of riverine water worsened as a result of CSO and stormwater discharges, and the recreational water guidelines for indicator organisms were exceeded most of the time. Local improvements in water quality were feasible by source controls and diversion of polluted water.

THERMAL ENHANCEMENT OF STORMWATER RUNOFF BY PAVED SURFACES

Abstract A methodology for predicting the thermal enhancement of stormwater runoff from paved surfaces is documented for a test facility in Kingston, Ontario, Canada. Prediction of runoff temperature is based on TRMPAVE, a mathematical model that was developed using a thermal energy balance approach and the one-dimensional heat equation to predict the surface temperature and temperature gradient in asphalt during dry-weather and wet-weather periods. Runoff temperature is then estimated as a function of rainwater temperature and surface temperature of the asphalt. In order to supplement wet-weather data, a number of simulated rainfall events were generated over a test plot to help develop, calibrate and verify the wet-weather model. Computer simulations for both dry and wet-weather periods compared well with measurements of temperature from the test plot. In addition, the average temperature of runoff contributed by the entire parking lot area was cooler than the average temperature of runoff from the test plot, but both values were higher than runoff from the upstream catchment. In light of the results obtained, TRMPAVE can be used to predict thermal loading from impervious areas.

Application of the log-normal and normal distributions to stormwater quality parameters

Abstract Concentrations of water quality constituents in urban stormwater are often expressed in probabilistic terms—using statistics such as the mean and standard deviation and selected quantiles. In many studies, the log-normal distribution has been assumed to apply. In this 3-year study, the distributions of concentrations of 14 constituents in five sources of run-off were studied—parking-lot run-off discharging into an on-stream pond, baseflow and event flow in a small suburban creek feeding the same on-stream pond, and the pond outflow under both baseflow and event flow conditions. Two probability distributions, log-normal and normal, were fitted and the goodness-of-fit was assessed using probability plots and the Cramer-von Mises test. Of the two, the log-normal was the better distribution in most of the cases tested. It was more suitable for parking-lot run-off and creek baseflow, and somewhat less suitable for creek event flow and pond baseflow. With a few exceptions, the log-normal distribution did not apply for soluble constituents (total dissolved solids, chlorides, sulphate, COD) and/or event outflow from the pond. In these cases the normal distribution was preferred. The composition of outflow from the pond was controlled by intense mixing of the incoming event run-off with the water stored in the pond. The assumption of an inappropriate probability distribution can result in substantial errors when estimating the mean concentration for censored data. This in turn can affect calculation of pollutant loads and extrapolation to estimate quantiles.

Adaptation of a Storm Drainage System to Accommodate Increased Rainfall Resulting from Climate Change

Extreme rainfalls in southern Ontario may increase significantly as a result of climate change. This study was designed to determine the impact of a 15% increase in design rainfall intensities on drainage of a typical urban catchment and to investigate adaptive measures. A calibrated model (PCSWMM 2000) was used to: (1) determine the system performance under current and climate-changed design rainfalls; and (2) calculate the magnitudes of various adaptive measures required to reduce the peak discharge to current levels. For this type of catchment, effective retrofit options that provide the required peak discharge reductions included downspout disconnection (50% of connected roofs), increased depression storage (by 45 m3/impervious hectare), and increased street detention storage (by 40m3/impervious hectare).

Toward the Sustainable Management of Urban Storm-Water

Despite the development of urban drainage systems over the past 5000 years, there are still many challenges to their effective use. There are growing demands with respect to runoff quantity and quality, visual amenity (landscape aesthetics), protection of ecology and beneficial water uses and interaction with the operation of existing municipal wastewater systems. Current solutions that rely mainly on pipe networks may not be sustainable, especially in developing countries. By considering the driving forces in action during the first years of the 21st century, different scenarios for the future use and development of urban drainage systems can be proposed; all of them rather pessimistic. The implementation of the sustainable management of urban water will require an integrated approach to all the related problems, including the better delivery of urban drainage services.

Calibration of the tipping-bucket raingage

Abstract Three models of the tipping-bucket raingage were calibrated in the laboratory by adjusting the volume required to tip the bucket and by correcting the raingage output readings. In the volumetric calibration, the effects of raingage installation, the wetting of buckets, and the surface tension of the liquid used were considered. To calibrate the raingage output, the recorded rainfall intensities (i.e. calculated from the raingage record) were compared to the actual intensities calculated from the rate of inflow to the raingage receiver. Recorded intensities wre typically smaller than actual ones, in extreme cases by as much as 10%. An explanation for this underestimation was found by considering the loss of water during the bucket rotation. Estimates of these losses were obtained by timing the bucket movement for various rainfall intensities. Finally, the sensitivity of the tipping-bucket raingage output to the variations in the basic desing parameters of the raingage was studied numerically using the analytical expression derived for the recorded intensity.

Toxicity testing for controlling urban wet-weather pollution: advantages and limitations

Abstract Toxicity of Combined Sewer Overflows (CSOs) and stormwater was studied at 15 sites in Southern Ontario, using a battery of seven bioassays. The highest frequencies of severe and moderate toxicity (19% and 24%, respectively) were found at highway runoff sites; frequencies of CSO toxicity were much lower (from 6.6% to 13%, for moderate and severe toxicity combined). Stormwater ponds contributed to toxicity reduction, with respect to both water and sediment downstream of ponds. Conventional toxicity testing was found useful for screening and assessing potential receiving water impacts, but was somewhat limited by the dynamic nature and large variety of wet-weather pollution sources.

Modelling of flocculation and transport of cohesive sediment from an on-stream stormwater detention pond

A new model to predict the transport characteristics of suspended sediment from an on-stream stormwater management pond is presented. It is based on Krishnappans model of flocculated settling in still water, which was extended to dynamic conditions and verified by experiments with stormwater pond sediment in a laboratory rotating flume. The model was derived from first principles, but some input parameters, such as floc properties, had to be obtained by calibration, and input parameters describing flow field properties were obtained from a kappa-epsilon turbulence model. Simulated suspended concentrations vs. time and the size distribution of the flocculated sediment, produced with the calibrated model, agreed well with flume measurements.

Evaluation of Pollution Loadings from Urban Nonpoint Sources: Methodology and Applications

In preparation of remedial action plans for the St. Clair, Detroit, and St. Marys rivers, a planning-level methodology for evaluation of pollutant loadings from urban nonpoint sources was developed and applied in three Canadian cities: Sarnia, Sault Ste. Marie, and Windsor. This methodology uses computed annual volumes of runoff and mean constituent concentrations, estimated from field sampling, to produce estimates of annual pollutant loadings. For the constituents studied, the total loadings were predominantly from point sources in about three quarters of all cases. For some of the less common substances, occurring at low levels, the nonpoint sources contributed loadings which were comparable to or even higher than those from point sources. Such findings will be useful in the development of remedial action plans which need to focus on control of pollutant sources.