Water Treatment for NYC

Croton Schematic

NYC Filtration Plant for Delaware and Catskill Systems

Filtration avoidance criteria Alternatives to Filtration Where should the plant(s) be located?

Multiple plants or one plant?Treatment steps at different locations?

Design flow Treatment scheme Backwash water

Safe Drinking Water Act Turbidity Loophole

At no time can turbidity (cloudiness of water) go above 5 nephelolometric turbidity units (NTU)

Systems that filter must ensure that the turbidity never exceed 1 NTU, and must not exceed 0.3 NTU in 95% of daily samples in any month

NYC DEP Data Interpretation

As of 2001 NYC only reports monthly average turbidity

“The MCL for turbidity is the monthly average rounded off to the nearest whole number”

“Data presented are range and averages of monthly averages”

Average turbidity (NTU)

Croton Delaware Catskill

2001 1.4 1.1

2002 1.1 1

141.71 Criteria for Avoiding filtration

The turbidity level cannot exceed 5 NTU (measured as specified in § 141.74 (a)(4) and (b)(2)) in representative samples of the source water immediately prior to the first or only point of disinfectant application unless: (i) the State determines that any such event was caused by circumstances that were unusual and unpredictable; and (ii) as a result of any such event, there have not been more than two events in the past 12 months the system served water to the public, or more than five events in the past 120 months the system served water to the public, in which the turbidity level exceeded 5 NTU. An ‘‘event’’ is a series of consecutive days during which at least one turbidity measurement each day exceeds 5 NTU.

Limited Alternative To Filtration

States may allow unfiltered water systems with surface water sources to use treatment other than filtration

In order to qualify for alternative treatment, a water system must have an __________, ____________ watershed in consolidated ownership and have control over access to and activities in the watershed

The alternative treatment must ensure _________ removal or inactivation efficiencies of pathogenic organisms than would be achieved by the combination of filtration and chlorine disinfection required by section 1412 (b)(7)(C). [1412(b)(7)(C)] Sec. 106

uninhabited undeveloped

greater

§ 141.71 Criteria for Avoiding Filtration

The public water system must demonstrate through ownership and/or written agreements with landowners within the watershed that it can control all human activities which may have an adverse impact on the micro-biological quality of the source water. The public water system must submit an annual report to the State that identifies any special concerns about the watershed and how they are being handled; describes activities in the watershed that affect water quality; and projects what adverse activities are expected to occur in the future and describes how the public water system expects to address them.

Should NYC have to Filter?

Pro Con

Croton Plant

The construction costs of the water filtration plant, with a design capacity of 290 million gallons per day (mgd), and the related facilities, is estimated at $660 million.

Annual operations and maintenance costs are projected to be $11 million.

The plant will use state-of-the-art disinfection and filtration processes including dissolved air flotation for the removal of solids, ozonation for primary disinfection, and biologically active carbon filtration.

3 3

33

$660,000,000 $5212.7

$5283 4.3 !

millionm s m s

millionm s billion

m s

=

× =To treat Delaware Catskill water

Croton Treatment Scheme

Croton Plant

Where Should Plant(s) Be Located for Catskill/Delaware?

______________________________________________________________________

_________________________________________________________________________________________________________

Between last watershed reservoir (Kensico) anddistribution reservoir (Hillview)

Near tunnel

On hydraulic grade line! (No pumps)

Commercial/Industrial area (not residential)

Design Flow for Water Treatment Plant

Max day ever was 94 m3/s in 1975Future growth?Conservation?

Croton system is separateProposed filtration plant for 12.7 m3/sAbility to shut down Croton system?

Catskill/Delaware designed for 83 m3/s

Maximum Daily Flow

0.010.020.030.040.050.060.070.080.090.0

1978

1980

1982

1984

1986

1988

1990

1992

1994

year

Max

imum

dai

ly d

eman

d (m

3 /s)

Catskill/Delaware

Croton

Treatment Plant Options for NYC

NYC’s water is high quality (<2 NTU)Low particle concentration means that

___________ ______ aren’t necessaryThree options for WTP with high quality

surface watersDirect FiltrationContact FiltrationUltraviolet disinfection (selected by NYC)

sedimentation basins

Direct Filtration

Screening

Rapid Mix

Flocculation

Filtration

Disinfection

Storage

Distribution

Raw water

AlumPolymers

Cl2

sludge sludge

Contact Filtration

Screening

Rapid Mix

Filtration

Disinfection

Storage

Distribution

Raw water

AlumPolymers

Cl2

sludge sludge

UV Disinfection

Kills pathogensDoes not reduce turbidityMay be approved as an alternative to

filtration for NYC Catskill/Delaware water supply

Costs much less than a filtration plant

Size of Major Unit Processes

Unit Process Parameter Range

Flocculation 10-30 min

Sedimentation Q/As 0.67 m/hr

Filtration Va 2.5 - 37 m/hr

Los Angeles - _______

37 m/hr

Backwash Requirements

U FB B

TTotal filter bed areaotal filter bed area

Useable production (or area)

Production used for backwash

Filter beds off line to be backwashed

AT = AU + AFB + AB

Area of Filter Beds in Useable Production (U)

Plant Design Flow83 m3/s

Area required without backwash (Va = 25 m/hr)

Backwash requirements?10 minutes at 50 m/hr once every 12 hours assume 30 minute downtime for backwashThe useable filter bed area must be increased by 5 – 10%

to meet backwash requirements

23

U m 11,952

s 3600hr

hrm 25

/sm 83

VQ

A 36.4 ha siteha=10,000 m2

Backwash Water Disposal Options

Backwash water productionApproximately 3% of useable production!Often not recycled because of potential concentration

of pathogensWill be recycled at the Croton filtration plant

Solids productionparticles present in raw water (0.1-10 mg/L) coagulant (5 - 50 mg/L)

Disposal options

Area of Flocculation Tanks

Hydraulic retention time of 10-30 minutesLos Angeles uses 8 minutes

Typical depth of 5 metersArea required for flocculation will be

similar to that required for filtrationContact filtration would eliminate the need

for flocculation tanks

Summary

NYC is designing an ultraviolet disinfection plant (with 2009 target for operation)

The WTP will be constructed somewhere between Kensico and Hillview Reservoirs

The WTP will be designed to handle recent peak daily flows

Supply Aqueducts and Tunnels

Catskill Aqueduct

Delaware Aqueduct

East Delaware tunnel

West Delaware tunnel

Shandaken Tunnel

Neversink Tunnel

Kensico to Hillview

CatskillAqueduct

DelawareAqueduct

Possible Water Treatment Plant Site

Kensico

1 km

90 acre site36.4 haha=10,000 m2

Close to Catskill and Delaware Aqueducts

Possible Water Treatment Plant Site