What is a Combined Sewer Overflow?

The majority of New York City’s sewer system is combined, which means it is used to convey both sanitary and storm flows. Sometimes, during heavy rain and snow storms, combined sewers receive higher than normal flows. Treatment plants are unable to handle flows that are more than twice their design capacity and when this occurs, a mix of excess stormwater and untreated wastewater discharges directly into the city’s waterways at certain outfalls to prevent upstream flooding. This is called a combined sewer overflow (CSO). CSOs are a concern because of their effect on water quality and recreational uses in local waterways.

Combined Sewer System

Roof Drain Sanitary Flow to the Hood to prevent Sewer treatment plant floatables from entering the sewer system

During wet weather , Catch combined sewage Overf Basin Tide gate to keep tidal inflow low may over flow through Combined Sewer Outfall out of the sewer system the combined sewer outfall (Normally flowing only during wet weather)

Wet weather flow Combined Sewer

Dr y weather flow channel Dry weather flow Combined Sewer Overflows in New York City

Combined Sewer Overflow (CSO) Volumes Tier 1 = 50% of Total CSO Volume Tier 2 = 20% of Total CSO Volume Tier 3 = 10% of Total CSO Volume Bronx

Signs are placed near every CSO outfall location Manhattan

Queens

Brooklyn

Staten Island Various Ongoing & Completed CSO Projects

Paerdegat Basin CSO Retention Facility Gowanus Canal Pump Station & Flushing Tunnel

Flushing Bay CSO Retention Facility English Kills In-Stream Aeration Current Water Quality Standards

New York State Saline Surface Water Quality Standards

Bacteria (when disinfection is practiced) Class Dissolved Oxygen Total Coliform Fecal Coliform Enterococci

Median __ Geometric mean > 4.8 mg/l (daily avg) SA _< 70 MPN/10 mL <_ 35/100 mL _> 3.0 mg/l

SB Monthly median Monthly geometric mean Geometric mean > 4.8 mg/l (daily avg) _< 2,400/100 mL _< 200/100 mL <_ 35/100 mL >_ 3.0 mg/l 80% _< 5,000/100 mL

Monthly median Monthly geometric mean Geometric mean > 4.8 mg/l (daily avg) SC _< 2,400/100 mL _< 200/100 mL <_ 35/100 mL >_ 3.0 mg/l 80% _< 5,000/100 mL

I Monthly geometric mean Monthly geometric mean __ >_ 4.0 mg/l _< 10,000/100 mL _< 2,000/100 mL

SD ______>_ 3.0 mg/l Nine Elements of a Long Term Control Plan*

N .Y.C . S E W E R

Characterization, monitoring, Public participation Consideration of Evaluation of and modeling of the combined sensitive areas alternatives to meet sewer system CWA requirements

$

Cost/performance Operational Plan Maximizing treatment at Implementation Post-construction considerations the existing wastewater schedule compliance treatment plant monitoring program

* As defined by EPA CSO Control Policy NYC's Combined Sewer Areas and LTCP Waterbodies

Combined Sewer Watersheds Other (Separate Sewers, Direct Drainage, Unsewered Areas)

Hutchinson River

Westchester Creek

Bronx River

East River and Open Waters Alley Flushing Creek Flushing Creek Bay

Newtown Creek

Gowanus Canal Jamaica Bay and Tributaries

Coney Island Creek