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!

kalderisio@dep.nyc.gov

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