1. Environmental Economics
How does the combined sewer system contribute to water pollution in NYC area?
Tsz Ying Liu
Environmental Economics
ECON 2505
Prof. Sean P. MacDonald
5/24/17

2. Combined Sewer System Built in mid-19th century
Transfers rain water and untreated sewage waste to a wastewater treatment plants
It overflows during heavy rainfall which causes Combined Sewer Overflow (CSO)

4. Combined Sewer Overflows
Causes serious health issues
The waste breaks down the dissolved oxygen that marine creatures need in order to survive
Contains fecal bacteria that can make people sick and fish unhealthy to eat
E. coli, Salmonella and Campylobacter

5. CSO

6. CSO

7. Stormwater Runoff
Stormwater is rain water is runoff that channels into waterways
It flows through many different locations and pick up many materials along the way, sometimes pollutants
Problem: It end up in the sewer system and goes to the ocean along with pollutants

8. Bioswales Project
A project that NYC works on to reduce stormwater runoffs
Smart green infrastructure
It collects data to inform city planning efforts
Slow down the flow of stormwater; reduce the stress on sewer system

11. The Billion Oyster Project
An operation to restore oysters and reefs to NYC harbor
Started at NY harbor school by NY Harbor Foundation 
Oysters filters 40 – 50 gallons per day
Recycled 300,000 pounds of shell and restored million oysters

13. Works Cited
HWU Water Utility. (n.d.). Combined Sewer System. Retrieved May 23, 2017, from
NYC Department of Environment Protection. (n.d.). Types of Sewer Drainage Areas in New York City. Retrieved May 23, 2017, from
Murphy, J. (2015, June 19). New York Confronts Polluted Past in its Waterways. Retrieved April 10, 2017, from
NY Department of Environmental Conservation. (n.d.). Stormwater. Retrieved April 10, 2017, from
Chan, G. (2016, December 30). Stormwater in the City: How NYC is Addressing Urban Pollution Through Data.Retrieved April 10, 2017, from
NYC Department of Environment Protection. (n.d.). Bioswales and Stormwater Greenstreets . Retrieved May 23, 2017, from
Schiff, Y. (2016, July 28). How a Billion Oysters Are Set to Change New York’s Harbor. Retrieved April 25, 2017, from