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Transcript of 1 Using Historical Data to Assess Potential Fecal Coliform Contribution During Storms at Kensico...
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Using Historical Data to Assess Potential Fecal
Coliform Contribution During Storms at Kensico
Reservoir: A Case Study
Christian Pace, NYCDEP and Kerri Alderisio, NYCDEP
NYC Watershed/Tifft Science and Technical Symposium
Thayer Hotel West Point, NY September 19, 2013
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Presentation Outline
Kensico Reservoir
Effect of storms on concentration
Case Study: TS Irene / Lee
Historical FC data
Loading estimate from flow and concentration
Compare low flow + storm loads to other estimates
Summary
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Kensico Reservoir
New York City’s terminal source water reservoir
- 30.6 BG storage
Aqueduct Monitoring Sites
Influents – CATALUM
– DEL17
Effluent – CATLEFF
– DEL18
Kensico also has its own small watershed = 34.3 km2
-Mixed land use
-approx. <1% of annual flow
During storms… direct runoff pushes stream flow contribution from 0.1% at base flow up to 4% (or more in extreme cases)
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Kensico Reservoir Watershed
N5-1
E10
BG9
MB-1
N-12
WHIP
E11
E9
")
")
")
")
")
")
")
")
CATLEFF
N1 ")
DEL18
")
")
CATALUM
DEL17
")
")
Aqueducts provide most of the inflow
>1 BGD
Eight perennial streams
- Monitoring began:
MB-1 1987
Others 1991
- WQ samples taken monthly
- Each equipped for flow monitoring
Ungauged area = approx. 54%
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Kensico Reservoir Watershed
N5-1
E10
BG9
MB-1
N-12
WHIP
E11
E9
")
")
")
")
")
")
")
")
CATLEFF
N1 ")
DEL18
")
")
CATALUM
DEL17
")
")
Aqueducts provide most of the inflow
>1 BGD
Eight perennial streams
- Monitoring began:
MB-1 1987
Others 1991
- WQ samples taken monthly
- Each equipped for flow monitoring
Ungauged area = approx. 54%
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Base Flow Storm Flow
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Small stream flow increases 10X+ during moderate events and 100X+ during extreme events
Pathogens more concentrated in storm runoff
- Generally consistent for bacteria and protozoans
Storm Event Effects
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Flow and G/C composite sample results for stream N5-1MAIN Storm on 10/17/2006, Rainfall total = 0.82”
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Tropical Storm Irene Aug 27–28, 2011
Preceded by wet August (>7” rain) - 2.85” rain 3 weeks before - 3.14” rain 2 weeks before - almost 1” in 7 days prior
Intense rain (up to 0.92” in 10min)
Rainfall total = 6.60” – 7.06”
Sharp rise in fecal coliform at effluents (less than 24 hours)
Extreme Events : Case Study TS Irene/Lee
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TS Lee (+ Katia) Sept 6–8, 2011
8 days after TS Irene
Less intense (<1” per hour)
Rainfall total = 6.27” – 6.80”
Sharp rise in fecal coliform at effluents
Elevated FC counts at Kensico into October
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Methods created for Kensico protozoan budget (2009)
Vital to separate storm and base flow for loading estimates
Importance to factor in whole watershed (gauged and ungauged sub-basins)
Apply method to estimate fecal coliform loading
Prior DEP Work with Loading Estimates
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Fecal Coliform Data
Data Handling
Utilize only data for existing stream conditions (ex. post-BMP)
(BMP data from ~2000 and unmodified stream data from 1991)
Coliform data issues
Confluent growth – samples removed
Too Numerous To Count (TNTC) – samples removed
Greater than or equal, estimated – Used value given
Non-detects or “Less thans” (ex. <1, <10, etc.) - ???
< 14% of samples for any stream were non-detects
ExamplesNon-detect =
Detection Limit
Non-detect =
½ Detection Limit
Non-detect =
0
<1 1 0.5 0
<100 100 50 0
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MB-1 (All) Detection Limit ½ Detection Limit Zero
Mean 1617 1611 1605
Median 250 238 220
Handling of FC Non-Detects
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DL ½ Zero % ND
BG9 47 42 42 9.8
E10 100 100 100 1.3E11 100 100 100 13.7E9 100 100 100 3.5MB-1 250 238 220 6.0N12 50 50 46 5.2
N5-1 3500 3500 3500 2.9
WHIP 52 50 50 5.8
Medians
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Separation of Storm Influence
Rainfall Bin Classification System
Divide long-term routine and storm event dataset into bins
according to:
- Amount of precipitation
- Time interval since precipitation
Allows for use of data prior to flow measurement
Westchester County Airport and DEL18 met station data used
#1 (Light
Influence)
#2 (Moderate Influence)
#3 (Heavy
Influence)< 24 hours 0.20”+ 0.50”+ 2.00”+
24 – 48 hours 1.00”+ 1.50”+ 3.00”+
48 – 72 hours 2.00”+ 2.50”+ 4.00”+
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Separation of Storm Influence
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Sample N using historical data
BG9 E10 E11 E9 MB-1 N5-1 N12 WHIP
Low Flow
101 274 72 313 110 98 341 356
Bin #1 Light
18 57 7 59 23 23 64 90
Bin #2 Mod
12 42 39 47 64 136 52 90
Bin #3 Heavy
1 9 20 8 4 52 8 13
Between 132 and 549 samples from each site
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Separation of Storm Influence
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MB-1 FC ConcentrationsSignificant difference between low flow and storm flow
Mean and median increase with rainfall bin
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Separation of Storm Influence
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N5-1 FC ConcentrationsSignificant difference between low & storm flow,
but doesn’t increase for every rainfall bin
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Separation of Storm Influence
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Mean FC concentration using historical data
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Separation of Storm Influence
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Median FC concentration using historical data
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Following the same rainfall criteria used to create means/medians …
Apply the appropriate concentration to flow measurements (10-min)
Must consider cumulative amount of rainfall and time interval since accumulation
Historical mean represents high estimate (worst-case scenario)
Historical median represents lower estimate
Utilize samples taken on site during the time period
DEP assigned these measured values to a 6-hr timespan
Concentrations Used to Create Load Estimates
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Concentrations Used to Create Load Estimates
WHIP Flow (10-min)
Median Concentration
Sampled on site
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Concentrations Used to Create Load Estimates
WHIP Flow (10-min)
Median Concentration
Sampled on site
Mean Concentration
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FC Loading Estimate – Whippoorwill Brook
Flow
Loading estimate
Closely follows flow because mean is applied consistently (except when samples were
collected)
Historical means when missing values
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Kensico Perennial Stream Loading Estimate
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* Estimated flow – above rating curves
Aug 28 8 Streams =
10.6% Kensico Input Volume*
Volume (L / 10 min) and fecal coliform load (accumulating) for 8 streams Aug 23 – Sept 12, 2011
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Kensico Perennial Stream Loading Estimate
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Median Estimate 57.7 trillion
Arithmetic Mean Estimate 97.7 trillion
Cumulative loading estimate for 8 streams (Aug 23 – Sep 29, 2011)
N5-1
BG9
E9WHIP
E11MB-1
E10N12
(~46% by area)
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Kensico Input Loading Estimates
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Arithmetic Mean Estimate 249.0 trillion FC
Median Estimate 162.0 trillion FC
Ungauged Watershed (54% by area)
N5-1
N12 E10
MB-1 E11
WHIPCATALUM
E9BG9
DEL17
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Mean Loading Estimate
Total load = 249.0 trillion FC
Breakdown of Loading Estimates
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Median Loading Estimate Total load = 162.0 trillion FC
Estimated Watershed Load - 85.4% Estimated Watershed Load - 77.5%
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HDR/Gannett Fleming (JV) contracted to :
- Review events and DEP operational response
- Create fecal coliform loading estimate for these storms
- Assess function of BMPs during the storm
- Make recommendations on future response measures and program enhancements to protect WQ
Final Summary Report – May 2012
Tropical Storms Irene and Lee
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Tropical Storms Irene and Lee
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Tropical Storms Irene and Lee
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80,000
60,000
40,000
20,000
JV used 2 approaches to “fill in” daily concentration data for FC load estimates:
1. Interpolated concentrations between samples & geometric means for ungauged areas
2. Missing values set to the median concentration from historical data (Jul ‘99 – Nov ‘11)
MB-1 Hydrograph from Aug 26 – Sept 13, 2011
FC
Con
cent
ratio
ns (
FC
/ 10
0mL)
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Kensico Input Loading Estimates
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Arithmetic Mean Estimate 249.0 trillion FC
Median Estimate 162.0 trillion FC
JV Median Estimate61 trillion FC
JV Interpolated Estimate170 trillion FC
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Summary Many ways to do loading calculations for a complex
system such as Kensico Goal to estimate worst case scenario during timeframe Separating historical samples by storm size allowed us
to differentiate loading calculations by storm size Use of “0” for non-detect samples did not significantly
affect mean or median concentrations Worst case load estimate = 249.0 trillion FC Sample sizes:
DEP 132 - 549 samples from each siteJV 58 - 184 samples from each site
DEP estimates:High estimates are almost 1.5X JV highLow estimate is more than 2.6X JV low
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Acknowledgements
WWQO East of Hudson Field Staff
Kensico Laboratory Staff
Kurt Gabel and James Alair
Kelly Seelbach
Glenn Horton and Jim Machung
*2012. HDR Gannett Fleming. Kensico Reservoir Watershed Assessment, Fecal Coliform Occurrence, and Operation Response During and After Tropical Storms Irene and Lee – Final Summary Report. May 2012.
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THANK YOU!
Questions?