The water quality monitoring results for May are available. Click the link here or visit our 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.
In May, as show on the Bridgewater USGS River Flow Gage the month started with a relatively low river flow of only 274 cubic feet per second (cfs) on Friday 5/9, this was followed by a large storm Saturday 5/10 which by Sunday 5/11 brought river flow up to 947 cfs. We sampled on Tuesday 5/13 as river low was dropping to 578 cfs. By 5/22 river flow had dropped back to 278 cfs however later that day and through much of the next day we had a large rainstorm which has brought the river up to over 2000 cfs . Rainstorm timing and river flow are important elements to interpreting our results.
The results for May look generally good, except for five 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. The river had ample flow at almost 600 cfs to dilute the wastewater treatment plant effluents. The more pressing concern today is pollution in urban stormwater runoff. When we sampled in May we were 2 days after the storm which greatly 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, June 10th. We will be watching how quickly river flow decreases from the high flow we saw after the 5/23 rainstorm and if there is significant rain a short time prior to our sampling day, which generates a pulse of stormwater pollution.