Upper Blackstone Clean Water
2021 River Quality Monitoring Program
The Blackstone River originates at the confluence of the Middle River and Mill Brook in Worcester, Massachusetts. It flows southeast for 48 miles into Rhode Island where it discharges into the Seekonk River and then Narragansett Bay. The mainstem of the Blackstone River is joined by six major tributaries: Quinsigamond River, Mumford River, West River, Mill River, Peters River, and Branch River, as well as many smaller tributaries.
Significant development has occurred within the Blackstone River watershed. There are nine wastewater treatment facilities (WWTF) that discharge into the Blackstone River watershed; the largest facility is the Upper Blackstone Clean Water (Upper Blackstone) WWTF, and other facilities include Grafton, Northbridge, Burrillville, Uxbridge, Hopedale, Douglas, and Upton. In addition to development near the river, many dams and canals were constructed to power mills during the Industrial Revolution. Over the years, the development has contributed to water quality degradation, including excess concentrations of nutrients and algal growth in downstream receiving waters.
UMass Amherst Staff Sampling at UBWPAD2 in 2022
Upper Blackstone is committed to protecting the water quality of the Blackstone River. To help achieve this goal, Upper Blackstone conducts a comprehensive water quality monitoring program in the Blackstone River to assess the river’s response to wastewater treatment facility upgrades. The river monitoring program was initiated in 2010 and expanded in 2012, with consistent year-to-year monitoring to build a multi-year data record. The Upper Blackstone water quality monitoring program collects data under an approved Quality Assurance Project Plan (QAPP), and data collected are shared annually with MassDEP's Watershed Planning Program
Upper Blackstone continued its monitoring program in 2021, collecting and analyzing water quality samples from 9 sites located in Massachusetts and Rhode Island. The 2021 monitoring season represented a restart of the full monthly monitoring after an abbreviated sampling seasion in 2020 due to the impacts of COVID-19. Monitoring consisted of monthly grab samples at all 9 sites plus continous temperature and dissolved oxygen metering at four locations in the vicinity of the Upper Blackstone effluent discharge location. Grab samples were collected April through November, and the continous monitoring July through November.
This StoryMap provides a summary of the 2021 monitoring program and results. The full report, written by the University of Massachusetts Water Resources Research Center, is available on the WRRC website .
The map on the right shows each of the monitoring locations along with the Blackstone River watershed sampled during the 2021 monitoring program. Click on each monitoring location to see a site description and a photo. Several of these locations were monitoring stations surveyed by MassDEP during their previous sampling programs.
In 2009, in response to an Administrative Order of Consent signed by Upper Blackstone and the Environmental Protection Agency, Upper Blackstone completed a $180 million capital improvement program to meet more stringent effluent limits that target nutrient-related water quality degradation in the Blackstone River. These upgrades included significant reductions in phosphorus and nitrogen loads to the river. As a result, river phosphorous and nitrogen concentrations are much lower than in the past, and there is less algal growth in many segments of the river.
The nutrient loads to the river from Upper Blackstone's effluent have decreased significantly since 2009, due to constructed plant upgrades and other measures that were implemented in 2012 and 2017 to optimize the plant's Biological Nutrient Removal (BNR) process. During 2021, the average TP and TN loads to the river were 92 and 64 percent lower than pre-upgrade (2006 through 2008) loads.
Aerial photo of the Upper Blackstone Wastewater Treatment Facility
Historically, the Blackstone River has been listed as impaired for aquatic life use, which was indicated by high total phosphorus and algae concentrations and low dissolved oxygen concentrations. Reductions in total phosphorus, such as those implemented by Upper Blackstone in the nutrient upgrade completed in 2009, have resulted in improvements in downstream water quality, measured by lower total phosphorous concentrations, lower algae and higher dissolved oxygen concentrations.
The seasonal average TP concentrations have declined significantly relative to historical conditions. This map shows the trend in TP at all sites during the 2012 through 2021 monitoring period. Click on each sampling location to view the average TP concentrations for each period and a graph of TP concentrations from 2012 to 2021.
The gray shaded circles indicate the 2021 average concentration, the green circles indicate the 2016 through 2020 average concentration, and the red circles indicate the 2012 through 2015 average concentration. Massachusetts uses a TP threshold of 100 µg/L as one of the indications that a water body may be impaired due to excessive nutrients ( 2018 MassDEP Consolidated Assessment and Listing Methodology (CALM) guidance manual ).
In 2021, TP concentrations in the Blackstone River were below the MassDEP 2018 CALM screening threshold of 100 ppb 87% of the time June through September, compared to 35% in 2020. Exceedance of the CALM screening threshold occurred mostly at UBWPAD2 (April, August, October, and november) and once at W1779, in June.
Reductions in the TP and TN load leaving the Upper Blackstone facility are reflected in lower river TP and TN concentrations and loads. The figure on the right shows the average April through November TP and TN concentrations by river mile for the historical data (pre-upgrade, red line) and from Upper Blackstone’s annual monitoring program.
The shaded area represents the range in average concentrations observed between 2012 and 2021. The black line is the average concentration during the 2021 monitoring period (April through November). These graphs indicate that the river nutrient concentrations downstream of the Upper Blackstone discharge have decreased significantly from pre-upgrade conditions. At all sites, the mean TP concentration was the lowest since Upper Blackstone's monitoring program started in 2021. Similarly, the mean TN concentrations were the lowest since 2012 except at UBWPAD2, where the mean concentrations were still much lower than the majority of years monitored by Upper Blackstone.
The historical data shown in these graphs reflect data from multiple studies and sampling locations conducted by MassDEP, the United States Army Corps of Engineers, the United States Geological Survey, the University of Rhode Island, and the Narragansett Bay Commission between 1996 and 2011. The temporal and spatial distribution of the historical data vary. This accounts for some of the variation seen in the red line.
Nutrients in the river from both point and nonpoint sources can contribute to increased algal growth, measured with chlorophyll-a. Point sources include WWTFs and nonpoint sources include pollutant loads in stormwater. Upper Blackstone monitors chlorophyll-a concentrations to evaluate the river's response to the decreased WWTF loads. MassDEP's CALM guidance manual indicates that a river is at risk of impairment if the mean summer (May through September) chlorophyll-a concentration exceeds 16 µg/L.
In this map, the pink shaded circles indicate the 2021 average concentration, the green circles indicate the 2016 through 2020 average concentration, and the red circles indicate the 2012 through 2015 average concentration. Lower river nutrient concentrations due to improvements at the Upper Blackstone WWTF have resulted in lower chlorophyll-a concentrations, particularly in Rhode Island where most of the large impoundments exist.
Click on each sampling location to view the average chlorophyll-a concentrations for each period and a graph of chlorophyll-a concentrations from 2012 to 2021. Chlorophyll-a concentrations in 2021 were generally lower than historical observations at most locations, and were always below the MassDEP 16 µg/L CALM guidance value.
Dissolved Oxygen/Temperature Monitoring
Data collected during the regular monthly sampling program provide important information on the Blackstone River’s health. However, these data do not provide any information about water quality between sampling events. To help fill this gap, Upper Blackstone has monitored continuous temperature and dissolved oxygen in the river since 2019. Upper Blackstone’s implementation of this program builds on a previous cooperative monitoring program implemented with MassDEP. DO is essential for fish and other aquatic life, and low levels put these sensitive organisms at risk. As temperature increases, the amount of DO that the river can hold decreases. Therefore, measuring temperature along with DO helps evaluate whether DO levels are healthy relative to the temperature of the river.
Onset HOBO dissolved oxygen meter attached to the cinder block metering enclosure used to securely deploy the meters at each of the four monitoring locations. The DO meter is placed inside the PVC meter housing and attached securely to the cinder block.
Massachusetts water quality standards require a minimum DO concentration of 5 mg/L in the Blackstone River. In addition, the CALM has a guidance value for diel (daily) DO variations, where a diel change in DO greater than 3 mg/L is a potential indicator of nutrient enrichment. The continuous DO data were assessed against the Massachusetts surface water quality standards and the CALM guidance values.
In 2021, Upper Blackstone deployed the continous DO and T meters at four locations: one in the Upper Blackstone Outfall Channel, one location upstream of the Upper Blackstone discharge location, and two downstream of the Upper Blackstone effluent discharge location (see map above). Two of these meters (the Outfall Channel and the upstream location, Route 20) were relocated based on results from deployments in previous years. The new meter placement was designed to obtain improved data on oxygen levels in the vicinity of Upper Blackstone's discharge:
- In previous years (2017, 2019 – 2020), the upstream meter in the sampling program was located at station W0680. At this location, high stream flow regularly dislocated or overturned the meter. A new upstream location was identified closer to where the Outfall Channel discharges to the Blackstone River.
- The second relocated meter was placed in the Outfall Channel downstream of the discharge but prior to the discharge to the river. This location is a concrete channel and is not a receiving water (water quality criteria do not apply), so the data from this site were used to understand the potential for treatment plant operations to impact downstream water quality.
- The remaining two meters (UBWPAD2 and Central Cemetary) remained in the same locations used for previous continous monitoring programs.
2021 DO and T Monitoring Results
The figure on the left presents the corrected, continuous DO metering data for all four sites during the 2021 monitoring period. This figure is interactive; click on the figure to zoom in to a certain time period or to view the data. The data are corrected to compensate for meter drift from fouling and calibration shifts between maintenance visits.
Overall, a consistent pattern in DO was observed during 2021 in the Blackstone River. Precipitation during the months of May, June, July, and September was above average, leading to higher streamflow throughout the summer, which was always above the 7Q10 flow (37.2 cfs at the USGS Millbury gage). Higher than average flows, possibly resulting in higher velocity and greater reaeration during dry weather conditions, contributed to river conditions where DO concentrations more consistently met Massachusetts DO criteria and guidance than in previous, drier years.
The comparison between the 2021 DO measurements and Massachusetts criteria is summarized in the table below. Data from each of the meters in the Blackstone River showed that compliance with the Massachusetts minimum DO criterion of 5 mg/L ranged from 90% to 100% during the monitoring period. DO at the Route 20 Overpass and UBWPAD2 stations was consistently at levels that support Aquatic Life Use based on guidance in MassDEP’s 2018 CALM. DO at the most downstream station (W1258), had two periods with less than 5 mg/L DO concentration. The Outfall Channel location is not a recieving water, so compliance statistics were not calculated for this location.
Future Monitoring Activities
Upper Blackstone is continuing water quality monitoring in the Blackstone River in 2021. The Blackstone River water quality data collected as part of the Upper Blackstone’s monitoring program are publicly available for download. Data collected between 2012 and 2018 are available from the Consortium of Universities for the Advancement of Hydrologic Science (CUAHSI) at http://data.cuahsi.org/ . The 2019 through 2021 data will be maintained on the National Water Quality Monitoring Council's Water Quality Portal at www.waterqualitydata.us .
The Blackstone River upstream of the UBWPAD2 Sampling Location
