North and South Rivers Riverwatch 2015 Water Quality Summary
The North & South Rivers Watershed Association has been sampling water quality at 10 sites along the North & South Rivers for 22 years to evaluate the health of the rivers. This volunteer-driven program monitors the rivers every other week from the beginning of June to the end of August. We monitor for both swimming and shellfishing standards, each of which have specific concentrations of fecal coliform bacteria that are considered safe for human consumption.
This summer, we found concentrations of fecal coliform bacteria exceeding the swimming standards on two sampling dates out of six. On August 6th, fecal coliform counts were above the standard of 400 cfu/100mL at Washington Street Bridge in Hanover, Norwell Canoe Launch and Willow Street in Marshfield, as well as at the Scituate wastewater treatment plant. The exceedance at the wastewater treatment plant was due to repairs being conducted on the ultra violet sterilization equipment at the time; the exceedance was reported to MassDEP and EPA. Within the 48 hours before sampling, we had received 0.57” of rain, which typically causes some of our samples to exceed standards. This usually happens at sites further upstream, due to stormwater runoff from residential and commercial areas. Historically, these sights have shown similar results after more than 0.5” of rain. In these instances, Washington Street Bridge has exceeded standards in 68% of samples and Willow Street exceeded standards in 74% of samples.
The more curious result from this summer occurred on August 20th when no rainfall had occurred in the previous 48 hours. On this date, the samples from Washington Street Bridge in Hanover and Cornhill Lane in Marshfield had much higher results than previous weeks and Willow Street in Marshfield exceeded standards, but just barely. Over the past decade with dry weather, Willow Street has exceeded standards in 51% of samples, and Washington Street in 24% of samples. However, Cornhill Lane has only exceeded standards in dry weather in 3% of samples over the past decade and just barely so (400 in July 1998 and 500 in August 2004). This day’s sampling result of 2100 cfu/100mL at Cornhill Lane is quite anomalous and could perhaps be explained by a localized source of feces like geese.
On the other 4 days of sampling, the river did not exceed swimming standards.
Two sampling sites in our Rivers are located within seasonally open shellfish beds. Currently the shellfish beds in the North and South Rivers are opened for recreational harvest between November 1st-May 31st. Among those two sites, North River Marine exceeded the shellfishing standard of 14 cfu/100mL fecal coliform on all six sampling days, and Damon’s Point exceeded the standard on four out of six sampling dates. Interestingly, Damon’s Point did not exceed fecal coliform levels on the day preceded by heavy rain.
Over the years bacteria counts have diminished in the rivers due to Title V septic improvements, implementation of town sewerage and improved treatment and minimization of stormwater runoff – all of which the NSRWA has advocated for using these data to make the case for reducing pollution sources.
Thank you to all of our dedicated volunteers who help with this important program. If you are interested in volunteering next year please contact Paula Christie at paula@nsrwa.org or (781) 659-8168.
Figure: This graph indicates the results from the 2015 RiverWatch sampling on the North and South Rivers. Black bars indicate that the sample was taken during dry weather (with less than .5” of rain within 48 hours prior to the sample) and gray bars indicate wet weather sampling (more than .5” of rain within 48 hours prior to the sample). The dashed horizontal line indicates the single sample swimming standard for fecal coliform concentrations.