June Monitoring Results

The monitoring results for June 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 0.9 mg/l and Cherry St. in Bridgewater 0.8 mg/l). This suggests that the Brockton WWTP plant has not attained full operation of its nitrogen removal facilities yet. Total phosphorus levels are showing an increase with decreasing river flow (Cherry St below Brockton WWTP 0.103 mg/l, and Haywood St below Bridgewater WWTP 0.136 mg/l. These levels of phosphorus are high enough to stimulate algae and weed growth in the fresh waters in these areas.

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 however 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). For the 11 days prior to our sampling river flow steadily decreased from 1080 to 350 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 10 days prior to our sampling date kept the magnitude of bacteria violations measured in June down.

As our sampling moves through the season we will be watching how river water temperature (20 to 22 degrees C last summer) and stormwater runoff affect bacteria 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.

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