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A total of 42 storm-water overland-flow samples were collected from four sampling sites (a highway off-ramp, a gas station, and a low- and high-traffic-volume parking lot). For each sample, the suspended-sediment and water phases were separated and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs). The gas station site produced the highest total PAH loading (2.24 g/yr/m2), followed by the high-traffic-volume parking lot (5.56 X 10-2 g/yr/m2), the highway off-ramp (5.20 × 10-2 g/yr/m2), and the low-traffic-volume parking lot (3.23 × 10-2 g/yr/m2). In several samples, one or more PAHs were detected in the aqueous phase at concentrations above its aqueous solubility. This result suggests the presence of colloidal-size particles capable of sorbing PAHs to an appreciable extent, or the presence of an oil-and-grease microemulsion. Based on rainfall and PAH data from seven discrete storm events, PAH concentrations were usually highest during the “first flush” of storm-water runoff and tapered off rapidly as time progressed. It is apparent from these analyses that storm-water runoff from parking lots, highways, and gas stations is a significant source of PAHs to the environment. Because some of the PAHs are carcinogens or suspected carcinogens, best management practices such as oil/grit separators should be implemented at “hot spots” in urban areas to mitigate potential PAH pollution.

This paper presents an integrated methodology that allows determining the probability of noncompliance for a given wastewater treatment plant. The methodology applies fault-tree analysis, which uses failure probabilities of individual components, to predict the overall system failure probability. The methodology can be divided into two parts : risk identification and risk quantification. In risk identification, the key components in the system are determined by analyzing the contribution of individual component failures toward system failure (i.e., noncompliance). In risk quantification, a fault-tree model is constructed for the particular system, component failure probabilities are estimated, and the fault-tree model is evaluated to determine the probability of occurrence of the top event (i.e., noncompliance). A list can be developed that ranks critical events on the basis of their contributions to the probability of noncompliance. Such a ranking should assist managers to determine which components require most attention for a better performance of the entire system. A wastewater treatment plant for treating metal-bearing rinse water from an electroplating industry is used as an example to demonstrate the application of this methodology.

A vertically averaged two-dimensional hydrodynamic model was developed to simulate water movements in a small shallow unstratified impoundment. The hydrodynamic model was then coupled with a two-dimensional pollutant transport model to calculate the mass fluxes of pollutant. The differential equations were numerically solved on a space staggered grid using a two-level time ADI integration scheme. The model was used to simulate the flow and pollutant transport and to assess the pollutant removal performance of an urban detention pond located in Charlottesville, VA. Results of the simulation were compared to field data taken at the site. The model was successfully utilized in simulating pollutant transport and trapping, making it useful in analyzing wet detention pond modification for urban pollution control.