FAQs
- Establishes water quality and CSO discharge requirements.
- A plan to meet water quality and CSO discharge requirements.
- Evaluates how well proposed improvements perform under typical (average) rainfall conditions.
- A 2050 planning horizon, which is bounded by 30 years from 2040-2069.
- Future rainfall and temperature projections based on the RCP 8.5 greenhouse gas emissions scenario, which is a more conservative scenario that assumes “business as usual” levels of greenhouse gas emissions, compared to the more optimistic and moderate greenhouse gas emissions scenario RCP 4.5.
- An evaluation of an ensemble of 11 global climate models that were downscaled to best represent local climate conditions in the study area.
- The most recent climate change projections that have been integrated into the Climate Resilience Design Standards & Guidance that have been adopted by the State of Massachusetts.
What is a Combined Sewer Overflow (CSO)?
Combined sewers are sewer pipes designed to collect both wastewater and stormwater runoff in the same pipe. A combined sewer overflow (CSO) occurs when a large rainstorm overwhelms the combined sewage system causing stormwater to mix with wastewater (or sewage) and discharge to a nearby river or lake. This relief measure prevents sewage backups into homes, businesses, and streets.
How do CSOs impact you?
During large storms, CSOs discharge to the Alewife Brook, the Charles and Mystic River. CSOs are mostly stormwater but do contain wastewater, and discharge bacteria, harmful nutrients, and other pollutants into waterways. CSOs can be harmful to public health and impact recreational uses during and immediately following those heavy rain events. CSOs do not cause flooding but do contribute additional pollutants to waterways.
How do stormwater discharges impact you?
Stormwater runoff can carry harmful nutrients, like fertilizers, pesticides, and dog waste, to local waterways, affecting public health and recreational uses.
Stormwater from separate systems impacts water quality and can cause flooding. When stormwater is separated from a combined sewer system, additional analysis is needed to ensure that the stormwater discharge does not worsen current flooding.
What is a CSO Control Plan?
The CSO Control Plan:
What is a typical year, why is it used, and how is it used?
A typical year of rainfall is a full year of rain that is most characteristic of rainfall conditions in the region over a selected period of time. A typical year is established to measure how alternatives for decreasing or eliminating CSOs would perform under a series of rainfall events. The Environmental Protection Agency has a Combined Sewer Overflow Control Policy that has various requirements for CSO communities to achieve Clean Water Act goals. Those requirements include developing a typical year to assess progress related to CSO control options. The typical year is used in two ways: first, during the development phase, where CSO mitigation options are being developed and evaluated; and second, during the implementation phase, where CSO mitigation projects have been implemented to assess and measure their effectiveness in reducing CSOs.
Does the typical year consider climate chage?
Usually, the typical year is developed based upon historic rain events. The typical year to be used for the updated CSO Control Plans will use a forward-looking typical year, which will consider the following: