The water quality monitoring results for June are available on the website. Click the Monitoring Tab at the top of the TRWA home page and click on either the sample bottles picture or the link further down the page under Documents to see the results.
In June as show on the Bridgewater USGS River Flow Gage, the month started with a relatively high river flow of 650 cubic feet per second (cfs) but the flow fell steadily until a storm on June 7 and 8th brought flow back up to 606 cfs. When we sampled two days later on June 10th flow was 529 cfs. Since that time, river flow has decreased steadily. On June 23rd, flow was only 187 cfs. As mentioned last month, rainstorm timing and river flow are important elements to interpreting our results.
The results for June look generally good, except for six bacteria violations (greater than 80 CFU/100 ml) downstream of urban areas. We used to be concerned about the wastewater treatment plant discharges during summer low flow, however now that the five upriver plants have been upgraded this should be a smaller concern. We haven’t sampled on a low enough river flow day to see if this is true.
The more pressing concern today is pollution in urban stormwater runoff. When we sampled in June, we were again sampling 2 days after a storm which significantly raised river flow. As a consequence, we missed the most polluted first flush of stormwater runoff. Nevertheless, we measured bacteria water quality criteria violations downstream of urban areas.
Our next sampling day is Tuesday, July 8th. We will be watching to see if river flow continues to decrease to typical summer low flow conditions. If there is a brief rainstorm just prior to our sampling, whether it delivers a measurable load of stormwater pollution.