The monitoring results for July have been added to our 2024 sampling season spreadsheet. The results may be accessed from the Water Quality Monitoring Tab at the top of the TRWA website home page and clicking on either the sample bottle picture or link to the data under the Documents heading.
The results show high levels of nitrate downstream of the Brockton WWTP (Matfield River 1.66 mg/l and Taunton River at Cherry St. in Bridgewater 1.32 mg/l, almost double last month)! This suggests that the Brockton WWTP plant may not have attained full operation of its nitrogen removal facilities. It also reflects lower available stream dilution (351 cubic feet per second (cfs) in June vs only 165 cfs in July). The Town River below the Bridgewater WWTP had a similarly high nitrate level of 1.48 mg/l potentially indicating a combination of reduced removal efficiency and certainly lower effluent dilution.
Total phosphorus (TP) levels are elevated in some locations like last month due to lower dilution, however, the instream levels benefited from low rainfall which contributed less TP containing stormwater to the rivers. TP measured at in the Town River at Haywood St below Bridgewater WWTP was high again at 0.149 mg/l because Bridgewater negotiated a 10 year schedule until 5/01/2027 for installation of TP removal facilities. Fortunately the Bridgewater Clean Water Act permit schedule for total nitrogen was only for 5 years (completion required 5/01/2022). These levels of phosphorus are high enough to stimulate algae and weed growth in fresh waters.
The number of bacteria water quality criteria violations increased from last month due to warmer waters and lower river flow. This follows a similar pattern from last year’s results. It is almost certain that the bacteria violations would have been worse except for the fact that the last significant rain storms prior to our sampling were at the end of May when river flow at the Bridgewater USGS gauge was 1080 cubic feet per second (cfs) except for a small storm on 6/27 (river flow 400 cfs). In July for the 11 days prior to our sampling river flow steadily decreased from 400 cfs to 165 cfs. Last year we saw that stormwater discharges associated with significant summer rain storms deliver high levels of bacteria to our rivers. The absence of stormwater discharges in the 11 days prior to our sampling date kept the magnitude of bacteria violations measured in July down.
As our sampling moves through the season we will be watching how river water temperature currently 21 to 24 degrees C and stormwater runoff affect bacteria (and TP) levels. Our data last year indicated that municipalities, commercial properties, state and EPA need to do a better job of stormwater management to keep bacteria levels in our rivers safe. More intense rainfall rates associated with climate change make addressing this problem critical.
TRWA wants to thank our 29 dedicated water quality sampling volunteers for their great work! We couldn’t understand what is happening in our rivers or advocate effectively for the changes needed to protect our waters without their support!