Combined Sewer Overflows in the Mystic River and Alewife Brook in 2023
Andy Hrycyna
12-31-2023
CSO activations and volumes, Alewife Brook and Mystic River 2023
The following data is downloaded from the MA EEA Data Portal for CSOs. Data in the portal extends backwards to mid-2022. Precipitation data is acquired from USGS gage at Fresh Pond, near Alewife Brook.
The CSO discharges on Alewife Brook are untreated: raw sewage makes its way directly to the stream. The CSO discharges on the Mystic River, while larger, are treated or partially treated CSOs.
More than 25 million gallons of CSO discharge in Alewife Brook 2023
Alewife Brook is the scene of the largest untreated CSO discharges in the Mystic Watershed. 2023 was a year in which many high-intensity storm events, expected to increase with climate change, drove high frequency and volumes of Alewife CSOs. CSO discharges to Alewife Brook in 2023 totaled 27,811,000 gallons in 45 events.
| Month | Releases | Gallons | EventType |
|---|---|---|---|
| Jan | 1 | 90,000 | Untreated |
| Feb | 0 | 0 | Untreated |
| Mar | 2 | 42,000 | Untreated |
| Apr | 0 | 0 | Untreated |
| May | 6 | 3,081,000 | Untreated |
| June | 1 | 216,000 | Untreated |
| July | 13 | 8,669,000 | Untreated |
| Aug | 10 | 10,100,000 | Untreated |
| Sept | 6 | 1,050,000 | Untreated |
| Oct | 0 | 0 | Untreated |
| Nov | 0 | 0 | Untreated |
| Dec | 6 | 4,563,000 | Untreated |
Total CSOs in Mystic River Watershed 2023
These graphs show the total number of activations and volumes for Alewife Brook and Mystic River together in 2023. CSO discharges in the Mystic watershed as a whole in 2023 totaled 202,638,984 gallons in 101 separate events.
| Month | Releases | Gallons | EventType |
|---|---|---|---|
| Jan | 4 | 9,760,000 | Treated |
| Jan | 1 | 90,000 | Untreated |
| Feb | 0 | 0 | Untreated |
| Mar | 5 | 23,120,000 | Treated |
| Mar | 2 | 42,000 | Untreated |
| Apr | 3 | 4,640,000 | Treated |
| May | 2 | 12,430,000 | Treated |
| May | 6 | 3,081,000 | Untreated |
| June | 7 | 2,940,000 | Treated |
| June | 1 | 216,000 | Untreated |
| July | 9 | 47,310,000 | Treated |
| July | 18 | 9,085,984 | Untreated |
| Aug | 7 | 27,460,000 | Treated |
| Aug | 12 | 10,295,000 | Untreated |
| Sept | 3 | 11,220,000 | Treated |
| Sept | 6 | 1,050,000 | Untreated |
| Oct | 1 | 1,620,000 | Treated |
| Nov | 1 | 600,000 | Treated |
| Dec | 5 | 33,040,000 | Treated |
| Dec | 8 | 4,639,000 | Untreated |
2023 Total Volumes by Outfall
CAM401 is responsible for the majority of releases in Alewife Brook.
| OutfallId | WaterBody | 2023 |
|---|---|---|
| CAM001 | ALEWIFE BROOK | 10,000 |
| CAM401A | ALEWIFE BROOK | 18,472,000 |
| CAM401B | ALEWIFE BROOK | 1,010,000 |
| MWR003 | ALEWIFE BROOK | 1,300,000 |
| SOM001A | ALEWIFE BROOK | 7,019,000 |
| BOS019 | LITTLE MYSTIC CHANNEL | 1,163,000 |
| BOS017 | MYSTIC RIVER | 601,000 |
| CHE003 | MYSTIC RIVER | 28,000 |
| CHE004 | MYSTIC RIVER | 58,984 |
| MWR205 | MYSTIC RIVER | 130,580,000 |
| SOM007A/MWR205A | MYSTIC RIVER | 43,560,000 |
High rainfall rates are the best predictor of CSOs
Precipitation rate (right hand column of graphs) is a better predictor of CSO volumes on Alewife Brook than total daily precipitation (left).
Greater Boston CSOs: Mystic, Charles, Boston Harbor
