Siormwater and Sediment 



Mean annual oil volume entering receiving waters of the Nairagansett Bay watershed was 

 1 1,900 gallons, or 40 tons per year (Latimer, 1984). 



Heavy Metals 



Metals are also derived fipom various sources in the Bay watershed. Urban runoff is the 

 primary source of lead, presumably due to use of leaded fuel in automotive vehicles. Lead 

 derived from this source is an exhaust component, and is a component of highway oil 

 drips. Lead concentration in runoff has decreased over time due to greater use of unleaded 

 fuel. Bay copper is primarily industrial in origin; over 50 percent comes from the 

 Providence wastewater treatment plant Zinc is derived from treated sewage and urban 

 runoff (Hoffman et al., 1984) 



Suspended Solids 



As outlined in previous sections, the importance of settieable solids in determining the 

 fate of urban runoff constituents should be carefully considered in developing management 

 strategies. Hoffman et al. (1984), in studies of the Pawttaxet River, found that a number of 

 pollutants, such as petroleum hydrocarbons, PAHs, and lead were primarily associated 

 with particles. Using sediment accumulation results from outer Boston Harbor adjusted to 

 an area the size of Narragansett Bay, the same authors estimate that the Bay removal rate 

 for higher molecular weight PAH should approximate 400 kg per year. Again, noting tiie 

 similarity in chemical distribution of the higher molecular weight PAHs between urban 

 runoff and Bay sediments, and the similarity in estimated inputs and sedimentary 

 accumulation rates, the authors point to circumstantial evidence that urban runoff PAHs 

 strongly influence the composition of coastal marine sediments, especially close to cities. 



In the highway runoff characterization study, Hofftnan et al. (1984) found that flow 

 weighted mean concentrations of total suspended solids and settieable solids were 332 mg/1 

 and 199 mg/1 respectively in mnoff from an interstate highway sampling station; i.e., 62 

 percent of the soUds were settieable. Total suspended solids loadings factors for all land 

 uses (in kg/ sq km of land use per year) were 4400 for single family residential use; 32,400 

 for commercial shopping mall; 548,000 for heavy industry; and 424,000 for 8 lane 

 highway. Nationwide Urban Runoff Program factors for the residential and commercial 

 shopping mall uses were 12,200 and 54,300 respectively (EPA, 1983). 



Pathogens 



Stormwater discharges are increasingly recognized as a major factor in pathogen-related 

 closure of Bay areas to shellfish harvesting. Bacteriological monitoring conducted during 

 the NURP investigations, in the Rhode Island salt ponds, and in Buttermilk Bay, 

 Massachusetts indicate that stormwater is a source of very significant loadings. These 

 results may be applicable to many areas of the Narragansett Bay watershed where similar 

 soils, drainage patterns, hydrogeoiogical conditions, and settiement patterns exist 



Recent research in Buttermilk Bay, sponsored by the Buzzards Bay Project, suggests 

 strongly that stormwater inputs are the most important factor causing recent shellfish area 

 closures, and that coliform levels are positively correlated with extent of residential 

 development Warm weather also contributes to increased density, while frequency of rain 

 events is associated with lowered density at discharge points. Dry weather surveys of each 

 surface drainage area in the Buttermilk Bay watershed show that the source of the fecal 



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