Christina Y. S. Siu

Peristaltic pump autosamplers for solids measurement in stormwater runoff.

Regulatory agencies approve automatic samplers containing peristaltic pumps as a sample collection method for stormwater characterization and for treatment-device evaluation. Autosampler performance, as discussed in the limited available literature, can vary across the entire particle size range typically found in stormwater from different source areas and outfalls-reasonably consistent performance for particle sizes < 250 microm, but much less consistency for particles > 250 microm. Therefore, a series of experiments was undertaken to quantify the upper range of consistent particle capture that may occur with sampling stormwater suspended sediment and particulate-bound pollutants. These experiments, based on triplicate sampling at each experimental condition, found that peristaltic pump autosamplers commonly used in stormwater monitoring could not repeatedly and effectively capture particles > 250 microm from a simulated stormwater whose particles have a specific gravity of 2.65. It was expected that the effective size for autosamplers would be correspondingly larger for particles having smaller specific gravities. The height of the sampler had no influence on particle recovery up to a height of 2.5 m, with slightly decreasing recoveries of large particles occurring at greater heights, as a result of reduced sampler intake velocity. Therefore, to characterize the solids across the entire size range and specific gravities that may occur in stormwater runoff, autosamplers should be deployed in conjunction with bedload and floatables sampling.

Roof Runoff Water Quality—A Comparison of Traditional Roofing Materials

Increasing urbanization and rapidly growing populations are beginning to place a strain on the worlds potable water supply. The use of harvested rainwater is one approach for freeing up potable water for more essential applications such as drinking water. Roofs are a readily available surface area that can easily be adapted for rainwater collection; however, some surface materials are not benign and may be more likely to leach contaminants than others. For this study, several commonly available roofing materials (uncoated galvanized, coated galvanized, cedar shakes, asphalt shingles, treated woods, and a green roof) were evaluated for runoff water quality for approximately a year and a half. The runoff samples were analyzed for zinc, copper, pH, total phosphorus, total nitrogen, and conductivity. In addition, a plexiglass roof panel was evaluated as a control in order to subtract background atmospheric contributions from the runoff concentrations. Data from this study showed that traditional roofing materials such as uncoated galvanized metal and treated woods are more likely to leach heavy metals, nitrates, and ammonia than other materials such as green roofs and coated metal roofs. Currently, the water quality data is being compared to recorded storm data and inter-event times to determine what factors affect the quality of the runoff.

Codorus Creek Restoration — A Case Study for the Chesapeake Bay

Healthy streams have the physical characteristics and chemical water quality to support healthy and diverse populations of organisms. The Codorus Creek, a tributary to the Susquehanna River, which eventually drains to the Chesapeake Bay, is being restored in several locations. Penn State University (York and Harrisburg campuses) is evaluating the effectiveness of the state-funded restoration activities. We examine the current pollutant loadings of two branches of this stream in conjunction with land use practices, particularly agriculture and wastewater treatment plants. Fish, macroinvertebrates, and periphyton are routinely sampled. Streamwater sampling for water chemistry analyses occurs during both baseflow and storm event conditions. Restored sites are being compared to both impaired and control sites to determine whether restoration has any significant reduction in a pollutants load. Preliminary results indicate that the southern branch has greater impairment than the eastern branch. The southern branch impaired site showed greater annual mean loads of total nitrogen and total phosphorus, a macroinvertebrate community dominated by pollution tolerant organisms, and a greater number of fish with parasitic diseases. All sources contributing to the total nitrogen load to Codorus Creek have not been identified. Although restoration activities may decrease pollutant loads, such as as suspended solids, restoration is not believed to be effective in decreasing nitrogen loads. Nitrogen is found more readily in the aqueous phase (streamwater) rather than adsorbed to sediment particles. Therefore, more effective ways to remove nitrogen in water is to decrease or eliminate the source or to treat the streamwater directly. Further monitoring and comparison of restored sites to control and impaired sites are needed. In addition, future work on the toxicity of the legacy sediments has been proposed.

Inclined Plate Settlers to Treat Stormwater Solids

It has been well-documented that, in stormwater runoff, many of the problem pollutants are associated with the particulate fraction. Past characterization of urban runoff and source contributions has shown the following: (a) soil disturbance increased the TSS and turbidity in the runoff; and (b) correlations were observed between TSS and particulate runoff concentrations of chromium, copper, and zinc, indicating that solids removal may reduce total metals concentrations. The first concern when investigating innovative treatment methods is determining the needed level of stormwater control. Specific treatment goals usually specify about 80% reductions in suspended solids concentrations. In most stormwater, this would require the removal of most, if not all, particulates greater than about 10 μm in diameter, which is about 1% of the 1-mm size that must be removed to prevent sewerage deposition problems. The ability of inclined cells (inclined plates/tube settlers) to provide excellent treatment of stormwater for a variety of pollutants was demonstrated by Pitt et al. (1999) in the report on the multi-chambered treatment train (MCTT) at the University of Alabama at Birmingham. This project is adding to that body of knowledge by investigating the potential of inclined plate settlers to treat stormwater runoff both in the field (at the City of Harrisburg Public Works Yard) and through a full-scale “laboratory” demonstration. Inclined plate settlers can be designed in one of two ways – through the use of Stokes’ Law and through the use of the Hjulstrom diagram, which accounts for scour and re-suspension. The test device in this research was sized using the Hjulstrom diagram. The results showed that the Hjulstrom diagram may be a very effective tool to predict the performance of inclined plate sedimentation devices based on the particle size for which 100% control is desired. Once the runoff’s particle size distribution is known, estimating the average percent removal for the system would be trivial, and could be done using Stokes’ Law. A sieve analysis of the influent and effluent, using a 250-μm sieve, demonstrated that the inclined plates were capable of removing particles in >250-μm size range, even when these particles were a substantial part of the mass load to the system. An analysis of the TSS and SSC