new abutments and improved stormwater management. Scour protection is proposed at the mouth of the culverts in Bound Brook. Stormwater runoff also will be discharged into Bound Brook from the proposed North Scituate Station. Under present development conditions (commercial buildings, parking and public open space), the stormwater is not detained and received little or no water quality treatment. Under the proposed conditions (the North Scituate Railroad Station), MBTA will use best management practices including street sweeping, deep-sump hooded catch basins and Downstream Defenders treatment units (MassDEP 2004b). They will also be utilizing an underground detention system and were required to develop a Stormwater Pollution Prevention Plan (SWPPP).
2.2 Impervious Surface Impacts
Table 1-3. Percent of Impervious Surface for each Gulf and Scituate Harbor Watershed
Subwatershed Aaron River
% Impervious 5.16% 5.10%
Aaron Reservoir Bound Brook
Gulf Estuary Little Harbor, and
, Scituate Harbor
This table, based on 1999 MassGIS data, is useful in determining where to focus stormwater best management practices improvements. Please, also refer to map1-3 for the area’s impervious surface
vulnerability. According to the Center for
Watershed Protection, an area with less than 8% impervious surfaces is considered
"sensitive"; 12-20% is considered "threatened"; and more than 20% is considered "non-supporting" or urbanized. This data is useful for communities to take steps to prevent stormwater impacts in sensitive areas. The Lily Pond Limnology and Water’s Edge Study (Aaron River Watershed) recommends watershed management controls to reduce non point pollution sources such as reviewing development plans, developing lawn fertilization packages, evaluating settling basin discharge management, and implementing stormwater retrofits (ENSR, 2003).
Given the concentration of impervious coverage on the eastern side of the watershed, it helps to weigh the environmental impacts on a even a smaller scale Land area just south of the Gulf estuary, for example, has surfaces with 20 percent impervious coverage, and should be considered as impacted. Land around Musquashcut Pond is also heavily built with 20 to 50 percent impervious coverage, classifying it as degraded. (GRE Inventory, 2003)
2.3 NPDES Permits Impacts
Cohasset Cove The Town of Cohasset is authorized (October 2000) to discharge from the Cohasset Wastewater Treatment Plant (WWTP) a flow of 0.3 MGD (average monthly) of treated municipal wastewater via outfall #001 to Cohasset Cove. The facility was upgraded in 2000 to an advanced secondary wastewater treatment plant. Upgrades include improved denitrification, a membrane filtration system that does not allow passage of bacteria and an ultraviolet disinfection chamber, an anoxic tank that improves the denitrification of waste water and a back-up generator. The permit requires effluent limits for BOD5, TSS, pH and fecal coliform bacteria and requires reporting of ammonia-nitrogen and total nitrogen concentrations. Toxicity testing for this facility is required four times a year. No acute toxicity was detected by either M. bahia or M. beryllina (LC50>100% effluent in all valid tests, DEP, 2006).
South Coastal Watershed Action Plan 9/12/2006 Watershed Action Alliance