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Assessment of Protozoa in New York City’s Hillview Reservoir
Kerri A. AlderisioSteve S. DiLonardoPathogen Research, Science and Research Division
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
NYC DEP
WSTC September 15, 2009
Outline
Background Objective Project Design Data analysis Results Conclusion
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
LT2 – Long Term Enhanced Surface Water Treatment Rule 2 Promulgated January 5, 2006
Purpose: ”…To improve public health protection through the control of microbial contaminants by focusing on systems with elevated Cryptosporidium risk…”
Systems with an uncovered finished water storage facility must cover or treat
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Sample Year
99 00 01 02 03 04 05 06 07 08
Cry
pto
sp
ori
diu
m o
ocys
ts. 5
0L
-1
0
2
4
6ICR DEP 1623 HV DEP
CATLEFF Crypto Results 1999 - 2008
CATLEFF LT2 valuesand additional treatment threshold
Are we a system with an elevated Cryptosporidium risk?
Cryptosporidium
oo
cy
sts
L-1
0.000
0.005
0.010
0.015Croton Catskill Delaware
LT2ESWTR Treatment Threshold
About Hillview
SA 90 acres 900 MG 450 MGD input Avg. residence
2d Balancing
reservoir 90 yrs
continuous Elevated berm
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Basic Schematic of Hillview Reservoir Operations
Study Objective
To determine if there is a significant increase in protozoa between Hillview Site 1 (Catskill Uptake) and Hillview Site 3 (Catskill Downtake)
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Project Design
Catskill and Delaware aqueducts above and below Hillview Reservoir for Giardia and Cryptosporidium.
Delaware bypassed the reservoir throughout the study (aside from minimal influence during high and low flows)
Data evaluation – 2 parts
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Part I: Initial Samples US EPA Method 1623 HV
– 50L filtered through HVF at 2L/ min.
– IMS, IFA and DIC microscopy
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Description
Site Sample Matrix spike
MS dupe
DEL above Site 2 1/ wk 1/ 2wk 1/ 2mth
DEL below Site 58 1/ wk 1/ 2wk 1/ 2mth
CAT in Site 1 1/ wk 1/ 2wk 1/ 2mth
CAT out Site 3 1/ wk 1/ 2wk 1/ 2mth
Part I:Initial Results Sampled Sept. 2006 – Sept. 2007 49-51 Paired Samples 12-14 MS per site 2-3 MSD per site
Preliminary data analysis suggested there may be more Crypto at Site 3 (CAT OUT); however, more QC, and other statistical approaches, needed to be considered
DEL system showed no differences, or a reduction
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Part II QC Enhancement DEL sites dropped Collection and
analysis methods remained the same
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Description Site Sample Sample dupe
MS
DEL above Site 2 NA NA NA
DEL below Site 58 NA NA NA
CAT in Site 1 2/ wk 2/ wk 2/ wk
CAT out Site 3 2/ wk 2/ wk 2/ wk
NEW
Sample Yield per Type
Part I Part II Total
Paired Samples
49-51 49 98
MS 12-14 45 58
MSD 2-3 0 2-3
Sample Duplicates
0 46 46
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Result Summary – Delaware(n=51, per 50L)
Site 2 Crypto
Site 58 Crypto
Site 2 Giardia
Site 58 Giardia
Detects Freq.
7/5113.7%
3/515.9%
19/5137.3%
21/5141.2%
Mean 0.2 0.06 0.84 0.98
Median 0 0 0 0
Std dev 0.53 0.24 1.36 1.45
Min 0 0 0 0
Max 2 1 5 5
Result Summary – Catskill(n=98, per 50L) Parts I &II
Site 1 Crypto
Site 3 Crypto
Site 1 Giardia
Site 3 Giardia
Detects Freq.
7/987.1%
14/10014.0%
44/9844.9%
37/10037.0%
Mean 0.07 0.15 0.94 0.68
Median 0 0 0 0
Std dev 0.26 0.39 1.41 1.08
Min 0 0 0 0
Max 1 2 6 4
Data Analysis
Three Main Questions:– Is Site 3 Crypto > Site 1?– Is there a relationship with environmental
variables?– Do the duplicates and MS recoveries affect
the data interpretation?
Statistics:– Parametric and non-parametric tests
explored– Statistician – Dr. Dennis Helsel– Modified sign test, Fong et al., 2003
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Data Analysisissue
Traditional statistical tests were built assuming no, or limited, ties in the data
Traditional tests for paired data exclude the ties from the data analysis and only include non-tied data.
Most of the Crypto data here are ties (82%) and
it is inappropriate to exclude them
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Cryptosporidium Detection Distribution
Cryptosporidium oocysts 50L-1
0 1 2
Det
ectio
n Fr
eque
ncy
0
20
40
60
80
100BX-1 BX-3
82% = Tied data
Tied data(In = Out)
Modified sign test
Diff.data
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Tied data(In = Out)
Diff. Data
Traditional tests
Data Analysis…Choices
Modified sign test considers all data (blue +green)
Tied data(In = Out)
Diff. Traditional tests only
consider data that
showed a change
82%
18%
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
(Fong et al., 2003)
Sign Test equivalent to Chi-square test
Sign Ranked Test or Wilcoxon’s
TraditionalExcluding ties
With many ties, these tests over-inflate the chance of Type I error
Diff.data
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Cryptosporidium
Giardia
Modified SignIncluding All Data
Therefore, Site 3 is not sig. greater than Site 1
Alldata
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Is there a relationship between environmental variables and Cryptosporidium and Giardia?
Variables
• Temperature
• Chlorine Residual
• Turbidity
• pH
• Final Filter Pressure
• 24 hr. precipitation
Analysis
• Logistic regression:
Model to predict probability of occurrence by fitting data to a logistic curve
• Used to determine if variables were related to Crypto and Giardia occurrence
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Significance of Environmental variables
Site 1 C Site 1 G
Site 3 C Site 3 G
Temp NS ( - ) ( - ) ( - )
Chlorine
NS ( - ) w NS NS
Turb NS (+) w (+) w NS
pH NS NS NS NS
Pressure
NS NS NS NS
Precip. NS NS NS NSW = weak significanceNS = not significant
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Does intra-site variability affect inter-site variability?
0
1
2
3
4
5
6
7
8
9
Site 1 & dup Site 1 & Site 3 Site 3 & dupSites compared
Perc
en
t d
iffere
nce
8.7%
6.5%
4.3%
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
BootstrappingTechnique
46 sample duplicates per site Assessed by a statistical random re-
sampling technique– 1000 iterations each for Crypto and Giardia – no significant difference between sites for
either organism Intra-sample variability does not
significantly affect inter-sample variability
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Mat
rix S
pike
Rec
over
y (%
)
0
20
40
60
80
100
Site 1 Site 3
Cryptosporidium oocysts
95th Percentile
5th Percentile
Median
25th Percentile
75th Percentile
Mat
rix S
pike
Rec
over
y (%
)
0
20
40
60
80
100
Site 1 Site 3
Giardia cysts
.
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Do the Matrix Spike recoveries affect Data interpretation?
Cryptosporidium
No significant difference in recovery between Site 1 and Site 3 (p=0.115)
Recovery had no significant influence on oocyst conclusion
MS Recovery Data Test: Mann-Whitney U (nonparametric independent analysis)
Giardia
Site 3 recovery > Site 1 (p=0.007)
Yet, results found no evidence Site 3 > Site 1; This further strengthens Site 3 is not > Site 1
Biologically insignificant
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Conclusions
Modified sign test - appropriate choice
When all data are considered, Site 3 is not significantly higher than Site 1 for either Crypto or Giardia
Temperature and Giardia had the most significant relationship
Duplicates and MS data support conclusion
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Thank you!
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
Assessment of Protozoa in New York City’s Hillview Reservoir
Kerri A. AlderisioSteve S. DiLonardoPathogen Research, Science and Research Division
New York City Department of Environmental ProtectionBureau of Water Supply
Water Quality
NYC DEP
WSTC September 15, 2009