May 29, 2002

Stormwater Retrofitting to Protect Drinking Water Reservoirs from the Impacts of Urban Runoff - Part 1

To meet federal Surface Water Treatment Rule requirements & U.S. Environmental Protection Filtration Avoidance mandates, the NYC Environmental Protection Dept developed a proactive program

The prime components of the program are stormwater and
waterfowl management, sewer system inspection and repair, an in-reservoir
turbidity curtain, reservoir dredging and hazardous spill containment.
Protecting water quality in the Kensico Reservoir is particularly important
because it is the final impoundment for more than one billion gallons (90
percent) of New York City’s unfiltered water supply before it enters the
distribution system.

This paper summarizes the stormwater management element of
the program and its control of the two key pollutants regulated by the SWTR:
fecal coliform bacteria and turbidity that are conveyed to the reservoir by

The first phase of the project, watershed assessment, site
selection and stormwater management facility screening and design, is complete.
Facility construction began in the spring of 1999 and was completed in 2001.

DEP also developed a protocol to assess the effectiveness of
the program, collected baseline and storm event water quality data prior to
facility construction, and will collect data from representative stormwater
facilities once they are operational to assess the effectiveness of the nearly
$15 million program.

New York City (the City) has placed great emphasis on
protecting and improving the quality of its drinking water supply through
watershed protection and management programs. One such program was developed
and implemented by DEP’s Bureau of Water Supply.

The City’s drinking water supply system is one of the
largest in the world, supplying approximately 1.33 billion gallons of potable
water each day to some 9 million City and upstate residents. The entire
watershed covers 1,969 square miles on both sides of the Hudson River and is
composed of 19 reservoirs, three controlled lakes and numerous wetlands,
watercourses and intermittent streams. Land use, topography, hydrology and
political climates in the system’s three watersheds (i.e., the Delaware,
the Catskill and the Croton [Figure 1]) vary dramatically. One reservoir, the
Kensico, is integral in managing unfiltered systems because it serves as the
final impoundment for water from the Catskill and Delaware watersheds before it
enters the City’s distribution system through Kensico’s two
effluent chambers. On average, approximately 1.3 billion gallons flow through
the Kensico Reservoir each day, accounting for 90 percent of the system’s
daily demand. For this reason, it is critical to protect water quality in the
Kensico. Controlling stormwater entering the reservoir is an important part of
the City’s Kensico Water Quality Protection Program.

The United States Environmental Protection Agency (EPA)
recognizes the importance of the Kensico Reservoir and has required that the
DEP implement an aggressive watershed management and protection plan that
reduces fecal coliform bacteria and turbidity inputs into the Kensico
Reservoir. Elements of DEP’s plan include aggressive stormwater and
waterfowl management programs, sewer and septic system inspection and repair,
an in-reservoir turbidity curtain, hazardous spill containment and a variety of
other regulatory and nonregulatory nonpoint source pollution control programs.
Other components of DEP’s Kensico Program include the following.


Sewer Inspection and Repair

The sewer system within the watershed, including type and
size of pipe and manhole locations, was mapped by the City. Of the 95,000 feet
of sewer line in the watershed, 55,000 feet were installed before 1970 and are
more prone to defects. The older sections of sewer line were inspected using a
video camera to locate potential sources of exfiltration. The inspection
program found 39 segments and three manholes in need of repair. The Town of
Mount Pleasant and Westchester County completed the repairs under
intermunicipal agreements with City funding.


Stormwater Infrastructure Inspection/ Sewer System Disconnection

To comply with the FAD requirement to track down discharges
of wastewater into storm sewers, DEP is digitally mapping the storm sewer
system in the Kensico watershed. When the mapping is completed, DEP will video inspect
the storm sewer system in areas of the Kensico watershed served by sanitary
sewers and locate any illicit wastewater connections that discharge into the
storm sewer system. The results of the inspection will be referred to DEP and
County enforcement officials for appropriate enforcement and remediation


Waterfowl Management

The gull and waterfowl management program is designed to
reduce the number of geese and gulls roosting and defecating in or near the
surface water. Through hazing, shoreline meadow management, egg addling,
physical barriers and Canada geese egg depredation, the City has dramatically
reduced the amount of bird waste that enters the reservoir. The program,
implemented August 1 through March 31 each year, also includes research into
new methods of bird control and ongoing assessments of program effectiveness.
Although labor intensive, the waterfowl management program has been an
overwhelming success in eliminating the greatest source of fecal coliform
bacteria to the Kensico Reservoir.


Turbidity Curtain

A turbidity curtain installed at the mouth of Malcolm Brook
in the southwest section of the Kensico Reservoir successfully directs
turbidity and fecal coliform bacteria conveyed to the reservoir by two
watercourses away from the Catskill Upper Effluent Chamber. Maintaining high
quality water in the effluent chamber is critical as water is conveyed directly
to the distribution system from the chamber. Water entering the chamber is
constantly monitored to determine compliance with the SWTR. Due to the
curtain’s effectiveness, the City will maintain it indefinitely.


Reservoir Dredging

The channels leading to the reservoir’s two effluent
chambers were dredged in 1999 to eliminate the potential for accumulated
sediments to be resuspended during storms and impact the quality of water
entering the effluent chambers. Some 1,777 cubic yards of sediment were
excavated, dewatered and removed from the Kensico Reservoir, significantly
reducing the potential for elevated turbidity in the reservoir.


Failing Septic System Detection and Remediation

DEP is conducting a house-to-house survey to identify any
watershed residences with septic systems to determine if any systems are
failing. DEP conducted a similar survey in 1991 and is applying a May 1998
“Methodology for Prioritizing Routine Inspections to Detect Septic System
Failures” to stream and reservoir water quality monitoring data to
identify potential septic failures. DEP also routinely patrols the watershed
for potential water quality threats, including failing septic systems.
Potential septic failures are thoroughly investigated and promptly remediated.


Part 2 will detail the three main phases of stormwater
management at the Kensico Reservoir and also will focus on the inspection and
maintenance of facilities.

About the author

James D. Benson, AICP, CPESC, is a supervisor for the NYC Department of Environmental Protection, 465 Columbus Avenue, Valhalla, N.Y. 10595, phone: 914-742-2034, e-mail: [email protected].
Melissa Beristain, CPESC, works with Benson in the New York City Department of Environmental Protection’s Bureau of Water Supplies.