Historical baseline data

Every month MyRWA has sampled at 10 sites around the watershed for 20 years in our baseline monitoring program. Specific conductance data over time at each site is depicted in this figure. Trends at all sites seem to be positive, in all seasons, suggesting increasing chloride concentrations in freshwater lakes, streams, and even groundwater over time.

Conductivity sensor deployment, Jan 28 - Feb 12, 2022

Aberjona River, Alewife Brook, Mill Brook, and Mystic River

Air temperature

Precipitation

Total Daily Precip

Flow

Location

The data loggers are located on Alewife Brook in Somerville (ALB), Aberjona River in Winchester (ABR), Mill Brook in Arlington (MIB), and Mystic River in Medford (MYR).

Data sources

Specific conductance measurements (every 15 min) gathered by an Onset HOBO data logger in Alewife Brook in Arlington, MA. Chloride concentrations calculated using a regression developed by Mass DEP describing the relationship between specific conductance and chloride concentrations, published in Massachusetts Consolidated Assessment and Listing Methodology (CALM) Guidance Manual for the 2018 Reporting Cycle (MassDEP, 2018). https://www.mass.gov/files/documents/2018/05/07/2018calm.pdf

Chronic and acute toxicity thresholds taken from Ambient Aquatic Life Water Quality Criteria for Chloride (EPA, 1988). https://www.epa.gov/sites/production/files/2018-08/documents/chloride-aquatic-life-criteria-1988.pdf Guidelines specify that 4-day average Cl concentration should not exceed 230 mg/L more than once every three years on the average and the one-hour average concentration does not exceed 860 mg/L more than once every three years on the average.

Temperature and precipitation data downloaded from USGS gage at Fresh Pond, Cambridge, MA. https://waterdata.usgs.gov/usa/nwis/uv?422302071083801

Flow data downloaded from USGS gage at Alewife Brook, Arlington, MA. https://waterdata.usgs.gov/nwis/uv?site_no=01103025