Wenlin Chen, Peter Hertl, Paul Hendley

Syngenta Crop Protection, Inc., Greensboro, NC

Preliminary Probabilistic evaluation osampling “peak” atrazine residues usdaily monitoring data from Midwesterdrinking water streams and rivers
2

Objective

 Test three alternatives to daily sampling 

evaluating the probability of finding high percentile atrazine residue concentrationdrinking water monitoring data sets from Midwestern streams and rivers with daily samples during the high use/runoff seaso

 Compare findings to USGS study in Perr

KS
3

Data Sets

 Data from flowing water bodies are NOT 

CWS intakes

 Stagnant water data and analysis are cite

USGS Perry Lake Study in KS
4

Data Set 1

 Syngenta Atrazine Ecological Monitoring 

Program (AEMP) 2009 data, including 1in IN, MO, and NE.

o Daily samples between May1 – July 3

grabs in April, August, September

o High runoff vulnerability, high atrazine 

intensity, and Headwater Watersheds between 8 and 388 square miles

o Typically not representative for drinkin

production
5

Data Set 2

 Ohio Heidelberg College (OHC) Water Qua

Monitoring Program 2000-2004, including HCreek, Rock Creek, Sandusky, and Maume

o Mostly 1 sample/day (up to 3 samples/da

during high runoff season (Apr.15–Aug. frequent samples for the rest of the calen(~2 samples/month) (Richards and Bake

o Watershed size (square miles): Rock: 34

149; Sandusky:1251; and Maumee: 633

o Predominant agriculture land use (67–83

crop)
6

Method

 Developed annual daily chemo-graphs from 

atrazine runoff season daily data; low atraziseason daily residue values were estimated interpolation from measured values

 Random Monte Carlo sampling technique - 

to sample annual daily chemo-graphs based alternative sampling scenarios.

 Comparison of the bootstrap-sampled annua

maximum to the 95% confidence limit (CL) omeasured data at 95th, 99th, and 99.9th uppe

percentiles per site per year 
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Daily monitoring data 

per site year

Annual daily chemograph per site year 

1000 iteratper site yea

Three alternative 

scenarios

Determine if Simulated Max is equal to or greater than the 95% CL of measured upper percentiles (95th, 99th, & 99.9th)

Procedures
8

Sampling scenarios tested

Month Scenario A (summer weekly window=AMP) Scenario B (summer 4 day window) Scenario C 

2 day wi

Jan 3 3 3

Feb 2 2 2Mar 2 2 2

Apr 4 8 15

May 5 8 16

Jun 4 7 15

Jul 5 8 15

Aug 2 2 2

Sep 2 2 2

Oct 2 2 2

Nov 2 2 2Dec 2 2 2

Total annual 

samples 35 48 78
9

Data range and upper percentiles of measured d

95th%=6.2 ppbLCL=5.8 ppbUCL=6.9 ppb

99.9th%=62.1 ppbLCL=53.3 ppbUCL=71.6 ppb

Max=155 

99th%=18.2 ppbLCL=16.5 ppbUCL=21.1 ppb

Non-parametric estimates by S+ (v.8.1)© and EnvironmentalStats©. Referencand Neerchal, Environmental Statistics with S-Plus. CRC Press LLC. 2001. 
10

Preliminary Resul

 Summary statistics of the river/stream-measure

sets

 Probability of bootstrap-simulated daily maxima 

concentrations to meet or exceed the lower 95% confidence limit (LCL) of the measured data poi

99th, and 99.9th percentiles

 A comparison to the statistical analysis available 

USGS for Perry Lake, Kansas (1993-1994)
11

Preliminary statistics (AEMP 2009 data)

Site_Year Watershed size (mi2) No. of Samples Max

99.9th 

%centile 

(1-sided 

LCL)*

99th 

%centile (1-

sided LCL)*

95th 

%centile 

(1-sided 

LCL)*

Min Mean Medi

IN-11 9 106 21.07 19 (15.5) 8.7 (8.5 ) 3.7 (2.2 ) 0.080 0.76 0.2

MO-01 12 108 72.00 71.9 (71.6 ) 63.1 (29.5 ) 6.6 (2.2 ) 0.025 1.90 0.0MO-02 28 114 155.20 122.7 (66.0 ) 48.7 (30.6 ) 11.2 (7.4 ) 0.025 2.60 0.1

MO-04A 8 110 52.14 44.2 (30.2 ) 14.2 (10.4 ) 6.0 (4.7 ) 0.025 1.09 0.1

MO-04B 388 106 23.92 22.4 (19.8 ) 12.9 (10.7 ) 6.1 (4.8 ) 0.025 1.06 0.1MO-05B 182 114 67.60 65.8 (62.6 ) 44.3 (32.8 ) 11.7 (9.1 ) 0.025 2.50 0.0

MO-05 25 110 42.60 42.2 (41.6 ) 24.1 (20.1 ) 11.2 (4.8 ) 0.025 1.62 0.3

NE-05 49 107 55.10 46.3 (31.0 ) 25.8 (17.9 ) 8.8 (5.8 ) 0.025 1.41 0.0NE-07 9 94 19.69 16.2 (10.1 ) 9.2 (7.8 ) 3.1 (2.4 ) 0.025 0.57 0.0

NE-08B 188 93 38.78 31.6 (19.0 ) 13.4 (10.1 ) 6.6 (5.1 ) 0.025 1.11 0.1

Atrazine Concentration Unit: ppb

NE04 not included in analysis since site was dry until May 2
12

Preliminary statistics (OHC 2000-04 data)

Site_Year Watershed size (mi2) No. of Samples Max 99.9th centile (1-side LCL)* 99th centile (1-side LCL)* 95th centile (1 side-LCL)* Min Mean 

HONEY - 2000 149 129 17.25 16.8 (16.1 ) 14.2 (13.0 ) 6.0 (3.8 ) 0.00 0.94 HONEY - 2001 149 102 16.32 15.8 (14.8 ) 9.7 (7.9 ) 3.7 (3.2 ) 0.00 0.90 HONEY - 2002 149 101 130.42 108.7 (70.7 ) 31.0 (26.1 ) 7.4 (4.6 ) 0.00 2.10 HONEY - 2003 149 135 13.05 13.0 (12.8 ) 8.8 (6.6 ) 3.6 (2.9 ) 0.04 0.74 HONEY - 2004 149 149 46.29 38.0 (23.7 ) 15.4 (11.0 ) 6.4 (4.3 ) 0.00 1.14 MAUMEE - 2000 6330 118 11.68 11.0 (9.9 ) 8.5 (7.9 ) 5.9 (4.5 ) 0.00 0.83 MAUMEE - 2001 6330 99 26.45 23.9 (19.4 ) 16.2 (14.6 ) 6.6 (5.5 ) 0.00 1.32 MAUMEE - 2002 6330 81 16.56 16.5 (16.3 ) 13.8 (11.4 ) 9.3 (8.7 ) 0.11 2.00 MAUMEE - 2003 6330 120 11.86 11.8 (11.7 ) 9.4 (8.2 ) 2.9 (2.5 ) 0.00 0.73 MAUMEE - 2004 6330 93 9.29 9.1 (8.8 ) 8.1 (7.1 ) 5.8 (5.0 ) 0.00 0.89 ROCK - 2000 34 93 23.43 21.5 (18.2 ) 12.4 (9.3 ) 2.7 (1.8 ) 0.00 0.60 ROCK - 2001 34 86 17.89 16.5 (14.0 ) 10.7 (8.0 ) 3.3 (1.5 ) 0.00 0.62 ROCK - 2002 34 116 99.58 82.9 (53.7 ) 38.5 (27.1 ) 7.0 (4.1 ) 0.00 2.07 ROCK - 2003 34 107 16.37 16.1 (15.6 ) 9.8 (7.2 ) 3.8 (2.8 ) 0.00 0.70 ROCK - 2004 34 137 46.31 39.6 (27.8 ) 19.3 (14.3 ) 5.1 (3.6 ) 0.00 1.09 SANDUSKY - 2000 1251 134 13.94 13.8 (13.5 ) 11.2 (10.4 ) 5.1 (3.7 ) 0.00 0.80 SANDUSKY - 2002 1251 118 28.38 27.8 (26.8 ) 20.5 (16.7 ) 9.6 (7.3 ) 0.09 1.73 SANDUSKY - 2003 1251 133 11.86 11.8 (11.6 ) 8.6 (7.2 ) 3.8 (2.6 ) 0.00 0.73 SANDUSKY - 2004 1251 134 24.70 22.5 (18.6 ) 17.2 (12.2 ) 7.4 (6.0 ) 0.00 1.24 

Atrazine Concentration Unit: ppb
13

Reported summary statistics in the USGCWS data (ppb)*

* Blomquist et al. Pesticides Pesticides in Selected Water-Supply Reservoirs and Finished DrinkinSummary of Results from a Pilot Monitoring Program. U.S. Geological Survey (USGS), Open-File 

USGS CWS site Maximum 99th 95th Median (50th) 

Perry Lake, Kansas, 

1993-94 3.790 3.640 3.475 1.720 

 Drainage basin size 1,117 mile2 Less spiky Relatively lower magnitude
14

Preliminary Bootstrap simulation results: 2009 data

Probability of bootstrap-simulated daily maxima (1000 rep/site year) exceeding the 95% lower confidence limit (LCL) of the measured da95th, 99th, and 99.9th upper percentiles

Site_Year

Scenario A (growing season weekly 

window =AMP)

Scenario B (growing season 4 day 

window)

Scenario C (g

w

95th 

percentile

99th 

percentile

99.9th 

percentile

95th 

percentile

99th 

percentile

99.9th 

percentile

95th 

percentile

IN 11 - 2009 100% 66% 14% 100% 89% 26% 100% 

MO 01 - 2009 100% 87% 15% 100% 96% 26% 100% 

MO 02 - 2009 100% 75% 28% 100% 94% 45% 100% 

MO 04A - 2009 100% 76% 26% 100% 92% 44% 100% 

MO 04B - 2009 100% 70% 15% 100% 90% 25% 100% 

MO 05B - 2009 100% 78% 16% 100% 100% 24% 100% 

MO 05 - 2009 100% 78% 26% 100% 100% 47% 100% 

NE 05 - 2009 100% 73% 25% 100% 95% 43% 100% 

NE 07 - 2009 100% 69% 27% 100% 88% 44% 100% 

NE 08B - 2009 100% 70% 29% 100% 93% 50% 100% 

Average 100% 74% 22% 100% 94% 37% 100% 
15

Preliminary Bootstrap simulation results: 2000-04 data

Probability of bootstrap-simulated daily maxima (1000 rep/site year) mexceeding the 95% lower confidence limit (LCL) of the measured data 

99th, and 99.9th upper percentiles

Site_Year

Scenario A (growing season 

weekly window =AMP)

Scenario B (growing season 4 

day window)

Scenario C (growing 

window

95th 

percentile

99th 

percentile

99.9th 

percentile

95th 

percentile

99th 

percentile

99.9th 

percentile

99th 

percentile

99th 

percentile

HONEY - 2000 100% 80% 13% 100% 92% 24% 100% 100% 

HONEY - 2001 100% 71% 27% 100% 93% 53% 100% 100% 

HONEY - 2002 100% 73% 13% 100% 92% 27% 100% 100% 

HONEY - 2003 100% 78% 30% 100% 95% 44% 100% 100% 

HONEY - 2004 100% 71% 27% 100% 94% 51% 100% 100% 

MAUMEE - 2000 100% 85% 28% 100% 97% 50% 100% 100% 

MAUMEE - 2001 100% 76% 30% 100% 94% 50% 100% 100% 

MAUMEE - 2002 100% 83% 24% 100% 100% 46% 100% 100% 

MAUMEE - 2003 100% 87% 14% 100% 95% 25% 100% 100% 

MAUMEE - 2004 100% 100% 30% 100% 100% 49% 100% 100% 

ROCK - 2000 100% 89% 26% 100% 100% 43% 100% 100% 

ROCK - 2001 100% 81% 14% 100% 100% 25% 100% 100% 

ROCK - 2002 100% 77% 30% 100% 95% 47% 100% 100% 

ROCK - 2003 100% 78% 15% 100% 94% 25% 100% 100% 

ROCK - 2004 100% 82% 14% 100% 95% 22% 100% 100% 

SANDUSKY - 2000 100% 89% 15% 100% 97% 24% 100% 100% 

SANDUSKY - 2002 100% 78% 15% 100% 94% 24% 100% 100% 

SANDUSKY - 2003 100% 89% 13% 100% 96% 27% 100% 100% 

SANDUSKY - 2004 100% 76% 25% 100% 92% 44% 100% 100% 

Average 100% 81% 21% 100% 95% 37% 100% 100% 
16

Summary results of USGS Perry Lake sampling frequanalysis (Blomquist et al., USGS Open File Report 01

“Estimmaxim95th pshoweon sustandreasoof the could using samp
17

Preliminary Conclusions

 Atrazine Summary Statistics

o Chemographs from rivers/streams are spikier, with max

~ 53-2018

o Static Water Bodies such as Perry Lake have lower con

changes as evident from much lower max/median ratio 

o Magnitude of the peaks in the river systems are higher 

reservoirs. 

o Chemographs in rivers draining larger watersheds tend 

spiky than in smaller ones

o The stream data used in these analyses are from envir

monitoring programs not CWS intakes
18

 The current 35 samples/year as implemented in AMP will prov

o Potential single maximum exposure values at or above the 

confidence limit for the 95th percentile 100% of the time

o Potential single maximum exposure values at or above th

confidence limit for the 99th percentile level most of the tim

 The 4-day grab program used for the Eco-Monitoring sites pro

o Potential single maximum exposure values at or above the 

confidence limit for the 99th percentile 94-95% of the time 

o Given the transient nature of peaks in the ecological monit

it is to be expected that high end percentiles in flowing watlarger watersheds were determined with even greater certa

 Given reservoirs less temporal variability in concentration, the 

program is able to sufficiently determine peak exposures equathan the 95th percentile values.

Preliminary Conclusions
19

Additional Data Recently Submitted by Sy● Long-term (1994-2006) Trend in Atrazine Occurrence in Ra

the U.S. Midwestern and Southern Community Water Systeet. al, April 16, 2008, Syngenta Crop Protection, Inc.)

● Atrazine Evaluation of Sampling Frequency Alternatives for 

Monitoring Program of Raw Water Sources at U.S. CommuSystems (W. Chen et. Al., October 13, 2009, Syngenta Crop Inc.)
20

Next Steps● Protocol development in Progress with RTI for a feasibility a

use the historic DW monitoring data to determine - The probability for a high percentile concentration within 

space domain of historic drinking water monitoring data - An estimate a high quantile concentration in finished drinand its confidence intervals - The probability for this high quantile concentration not to predefined threshold concentration

● Protocol will be provided to EPA● Preliminary Results expected end of January 2010