Stormwater and Sediment 



use. Among five Pawtuxet River watershed towns, for example, loadings of copper 

 attributable to urban runoff varied by more than a factor of ten (Hoffman et al., 1984). 



Non-urban "urbanizing" or "suburban" areas are also very significant sources of runoff, 

 contributing a range of nutrient and chemical contaminant loadings. Although the generic 

 term "urban runoff applies to runoff from these areas in addition to densely populated 

 land, the characteristic contributions of these areas merit distinct management attention. 

 Urbanization per se has the net effect of increasing pollutant export by at least an order of 

 magnitude over pre-development levels. (Issues of particular consequence in suburban 

 areas are identified within the following sections.) 



Several research methods have been employed to evaluate specific pollutant loadings, 

 and their sources, and to compare point and non-point source inputs. Hoffrnan designed a 

 research effort to examine hydrocarbons and PAHs in runoff as a function of land use in a 

 manner similar to the approach used for other components in the NURP studies. The 

 investigators found strong correlation between urban runoff pollutant loading and land use 

 (Hoffinan and Quinn, 1984). 



In a related investigation with the objective of producing urban runoff estimates for the 

 Bay as a whole, Hoffman (Hoffrnan et al., 1983) and her colleagues monitored storm 

 drains serving different land uses, and utilized land use data to estimate nmoff deliveries to 

 storm drains, a treatment facility, and combined sewer overflow discharge points. For 

 example, the authors calculated that, in Providence on an annual basis, 47 metric tons of 

 hydrocarbons were discharged by separate storm drains, 20 metric tons were discharged 

 via combined sewer overflows, 1(X) metric tons went to the treatment during rainy 

 conditions, and 222 metric tons were delivered to the treatment plant during dry conditions. 



Highway Runoff 



Highways are an iniportant source of several contaminants to the Bay watershed. In a 

 study of the chemical and physical characteristics of highway runoff, and implications for 

 treatment, Hoffman and Quinn (1984) found highways to be very significant sources of 

 high molecular weight PAHs, Fe, Mn, Cu, Pb, Cd, Zn, and suspended solids. Highways 

 contributing over 50 percent of the total input of suspended solids, PAHs, Pb, and Zn (77 

 percent) to the Pawtuxet River, despite the fact that they occupy only 8 percent of the 

 watershed area . 



In the same study, Hoffman also noted that the hydrocarbon concentration in the river 

 sediments downstream of the highway discharge had increased by 89 percent at a depth in 

 the core corresponding to 1970 to 1972 (after 1-95 and 1-295 opened in 1967) compared to 

 the 1965-1966 section of the core. Although the total increase in concentration cannot be 

 attributed to the interstate construction, highways clearly contribute an important part of the 

 pollutant load in urban areas. 



Results of a separate Bay study (Waterman and Hoffman, 1987) correlating land use 

 with traffic volume indicate that rapid suburbanization, population growth, and 

 construction of interstate highways have significandy affected highway runoff. Particularly 

 in southern coastal communities, increase in traffic volume and the development of open 

 space and wedands have resulted in increased runoff from the highway system into the 

 Bay. The study confirmed earlier results of Hoffman et al. (1983, 1984) which had 



122 



