The Gulf is impaired by fecal coliform (category 5 on the Integrated List of Waters) and requires a TMDL. Fecal coliform counts were slightly elevated between July 1990 and July 1992 Measurements taken between Dec 1992 and May 1995 were below the 200 col/100ml threshold. In October 1996, elevated counts were measured at two stations near Gannet Rod (Cohasset High School Students, NR Inv. 34- 36) Students also measured the pH throughout the estuary and found values of pH below 5.5 in several areas in October 1996 and in December 1996 (Natural Resources Inventory, 2003).
Lily Pond and Aaron River Reservoir
Hydrologically, Lily Pond (1,603 acres) is somewhat unique due to the non-tidal, bi-directional flow in the outflow stream, Herring Brook. The Brook can function as a tributary when the water level control structure along Bound Brook is allowed to hold back water. This structure reverses the flow of Herring Brook allowing water from the Aaron River Reservoir to enter Lily Pond. According to a 2003 study (ENSR), 78% of the total lake surface area had vegetation coverage greater than 75%. In addition, over the past few years, sodium concentration in the pond has exceeded the state recommended guideline concentration partially due to the use of salt based deicing chemicals on roads where drainage systems are tributary to the surface water supply. Fecal coliform levels in the two tributaries to the Pond, Peppermint Brook and Bass Kettle Brook has exceeded water quality. standards. Data collected by USACE in1999 found counts of 290 (coliforms/100 ml). In 2000, Cohasset extended sewering to houses in the vicinity of Peppermint Brook.
Non-point source pollution is probably the single greatest immediate threat to the quality of these waters. An evaluation of existing surface water data conducted as part of the Surface Water Protection Plan (Norfolk Ram 2002) suggests both Lily Pond and the Aaron River Reservoir are eutrophic to hyper-eutrophic in terms of nutrient loading with the potential for uncontrolled plant growth. Watershed loading analysis suggests that a majority of the phosphorus potential draining to Lily Pond originates in the Brass Kettle Brook (57%). While Peppermint Brook contributes less than Brass Kettle Brook (29%), concentrations entering the pond are higher due in part to its smaller wetland system (less attenuation) and great percent of impervious surface in the Peppermint Brook Watershed (ENSR, 2003).
Turbidity: Recent observations along the entire segment of Bound Brook and between Beechwood Street in Cohasset to the outlet of Hunters Pond, found the water column highly turbid following a period of dry weather conditions (DeCesare 2005). Objectionable turbidity conditions were associated with both wet and dry weather conditions. Field survey crews observed dense growths of aquatic vegetation and algal mats were observed in the brook upstream of the flow control structure throughout the summer of 2001 as well as more recently in the Hunters Pond impoundment (MassDEP 2001 and DeCesare 2005).
According to the Wetland Protection Act Regulations Variance for the Greenbush Commuter Rail Restoration Project in Scituate, a bridge crossing of Bound Brook is being replaced with a box culvert,
South Coastal Watershed Action Plan 9/12/2006 Watershed Action Alliance