1

Summary Report 

Pesticide Monitoring in the Walla Walla Basin 

2005-2007 Results

September 28, 2007 

Kevin Masterson 

Agency Toxics Coordinator 

Oregon Department of Environmental Quality, Laboratory Division 

I. INTRODUCTION 

The Walla Walla River sub-basin in northeastern Oregon is largely an agricultural area, with tree fruits 

such as apples and cherries comprising a significant proportion of the agricultural land in the watershed. 

The other major agricultural crops in the area include wheat, peas and winegrapes. A segment of the 

Walla Walla River is on the Department’s 303(d) list of impaired waters due to elevated temperatures 

during the summer months. Based on knowledge of the use of organophosphate insecticides for tree 

fruit crops and the adverse impacts of low levels of such chemicals on aquatic life, the Department, the 

Walla Walla Basin Watershed Council, Oregon State University (OSU) Extension Service and the Blue 

Mountain Horticultural Society initiated a Pesticide Stewardship Partnership (PSP) in the Walla Walla 

sub-basin in 2005. The objective of the PSP project is to conduct monitoring of streams within the area, 

and then use the results of the monitoring as a catalyst for collaborative efforts by local stakeholders to 

reduce pesticide concentrations in streams where detections have been identified. This is a report on the 

results of pesticide analysis of water samples collected in the Walla Walla sub-basin from 2005 to 2007 

II. MONITORING METHODS AND LOCATIONS 

Water samples were collected from March through the first half of June, when the majority of 

insecticide applications occur. The timing and frequency of sampling each year was based on 

information about when specific types of insecticide applications were occurring in the Walla Walla 

Valley. For instance, applications of chlorpyrifos (the “dormant” spray) in fruit orchards typically occur 

during the last three weeks of March, while azinphos-methyl applications (for post-bloom codling moth 

control) usually occur at the end of May and beginning of June. However, the exact timing of pesticide 

applications is dependent on several variables, including the insect growth cycle, crop phenology and 

prevaling weather conditions. 

When monitoring began in 2005, two smaller Little Walla Walla River tributary sites were included 

along with several main stem Walla Walla River sites. These tributaries are also known as 

“distributaries” because the flow is controlled at a diversion point in Milton-Freewater. In response to 

the pesticide detections observed at these tributary sites in 2005, two additional Little Walla Walla 

tributary locations were added to the sampling program in 2006 to better assess the extent and 

magnitude of pesticide detection in these smaller streams. 

Water samples were collected from Walla Walla basin streams at the locations described below in Table 

1 and depicted visually in Fig. 1. Water samples were analyzed for organophosphate insecticides and 

triazine herbicides according to US EPA Method 8141B (Table 2). 
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 Table 1. Sampling locations. 

Station Upstream Land Use 

South Fork Wall Walla River at Harris County 

Park 

National Forest (reference site) 

Walla Walla River at Day Road South Agriculture – fruit orchards & berries 

Walla Walla River at Gove School Bridge Mixed urban and agriculture 

Walla Walla River at Pepper Bridge Agriculture – mixed crops 

Little Walla Walla River Main Stem at The Frog Urban 

East Little Walla Walla River, North of 

Stateline Road 

Agriculture – fruit orchards 

West Prong Little Walla Walla River, North of 

Stateline Road 

Agriculture – fruit orchards 

Little Walla Walla River, West 

Branch/Crockett1

Agriculture – fruit orchards 

Little Walla Walla River, Midwest Prong1 Agriculture – fruit orchards 

 Table 2. Pesticide analysis using USEPA Method 8141B. 

 Insecticides Herbicides Insecticide Metabolites

 Azinphos-methyl Atrazine Azinphos-methyl oxon 

 Chlorpyrifos Simazine Chlorpyrifos oxon 

 Diazinon Imidan oxon 

 Dimethoate Malathion oxon 

 Fenvalerate-Esfenvalerate 

 Imidan 

 Malathion 

 Methyl parathion 

 Pyriproxyfen 

 

1

 Sampling locations added in 2006 
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Figure 1. Map of Pesticide Monitoring Sites in the Walla Walla Watershed near Milton-Freewater 

[ELECTRONIC MAP GOES HERE]
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SUMMARY OF RESULTS 

Watershed-Wide Results

Between 2005 and 2007, pesticide residues were detected at five of the nine sampling sites included in 

the monitoring project. However, since inception of the project, no pesticide detections have been 

observed (at or above the 0.025 μg/l method detection limit) at any of the Walla Walla River main stem 

sampling locations. In addition, only one pesticide detection was found at the Little Walla Walla River 

main stem site (“The Frog”) within the City of Milton-Freewater. Nearly all of the pesticide detections 

over the three years of monitoring were found in the tributaries of the Little Walla Walla River. 

Multiple detections were found in all four of the tributary sampling locations, but none were found in 

2007 at the East Little Walla Walla River, North of Stateline Road site. 

Chlorpyrifos, diazinon, and azinphosmethyl were detected in all three years, and most of the detections 

of chlorpyrifos and azinphosmethyl exceeded state water quality standards. Dimethoate, another 

organophosphate insecticide, was detected less frequently, while the herbicide simazine was detected 

once. However, in 2007, detections occurred at only three of the nine sites. 

The median concentrations of all pesticide detections throughout the watershed are presented in Figure 2 

and the maximum concentrations are in Figure 3 below. Limited conclusions can be drawn from a 

comparison between the 2005 results for all sites in the watershed with those from 2006 and 2007 

because of the two new tributary sites that were added in 2006. These sites were chosen because of the 

high likelihood of detecting pesticides. However, the figures do illustrate significant reductions in both 

the median and maximum concentrations of chlorpyrifos between 2006 and 2007. The median 

concentration in the watershed decreased by 67% between 2006 and 2007, while the maximum 

concentration dropped by 94%. In addition, the maximum diazinon detection decreased by 97% 

between 2006 and 2007. The 2007 median concentration for diazinon depicted in Figure 2 represents 

only one data point, as there was only one diazinon detection in 2007 compared with ten in 2006. 

Dimethoate was also not detected in 2007 at any of the sites. 

All detections of azinphos-methyl exceed the state water quality standard, as the method detection limit 

for this pesticide is above the water quality standard. The watershed-wide median and maximum 

azinphos-methyl concentrations observed in 2007 were less than the corollary concentrations in both the 

2006 and 2005. However, the number of sampling events conducted during the late May and early June 

time frame (the application period for azinphosmethyl) in 2007 were about one-half the number of 

sampling events during the same period in the previous two years. A larger set of samples may make 

for a more useful comparison. 

Figure 4 shows the detection frequency for pesticides in the watershed. Detection frequency is 

expressed as a ratio of the number of detections to the total number of samples collected. Detection 

frequencies for most pesticides dropped between 2006 and 2007. The chlorpyrifos detection frequency 

is slightly higher in 2007 than in 2006. However, this is attributable to the larger number of sampling 

events in 2006 during the latter part of spring when chlorpyrifos detections have not been observed. A 

review of detections found in March of both years (the month when nearly all chlorpyrifos detections 

have been found) reveals that there were 5 fewer chlorpyrifos detections in March 2007 than in March 

2006. The number of March sampling events in 2006 and 2007 were the same. 
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Figure 2. Median Pesticide Concentrations of all Detections for Walla Walla Sub-basin 2005-2007 

Walla Walla Subbasin: 2005-07 Median Pesticide Concentrations

0.00

0.10

0.20

0.30

0.40

0.50

Azinphosmethyl

Chlorpyrifos

Diazinon

Dimethoate

Simazine

Median (ug/L)

2005 median

2006 median

2007 median

WQS Azinphosmethyl (0.01 ug/l)

Chronic WQS Chlorpyrifos (0.041 ug/l)

Acute WQS Chlorpyrifos (0.083 ug/l)

Figure 3. Maximum Pesticide Concentrations for All Walla Walla Sites 2005-2007 

Walla Walla Subbasin: Maximum Pesticide Concentrations

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

Azinphosmethyl

Chlorpyrifos

Diazinon

Dimethoate

Simazine

Maximum (ug/L)

2005 maximum

2006 maximum

2007 maximum
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Figure 4 – Pesticide Detection Frequencies in the Walla Walla Subbasin 

Walla Walla Subbasin: 2005-2007 Pesticide Detection Frequencies

0

0.05

0.1

0.15

0.2

Azinphosmethyl Chlorpyrifos Diazinon Dimethoate

2005 Detection Frequency

2006 Detection Frequency

2007 Detection Frequency

Site-Specific Results

A more detailed analysis of two tributary sites where pesticides have been consistently detected provides 

some useful insights. One of the sites (West Prong Little Walla Walla River, North of Stateline Road) 

has been sampled each of the past three years, while the other (Little Walla Walla River, West 

Branch/Crockett) was added in 2006. Tables 3 and 4 provide a chlorpyrifos and diazinon data 

comparison between the monitoring years for both of these sites. [Note: The other site where multiple 

detections have been found, the Midwest Prong site, is not included in this analysis because insufficient 

flow resulted in sporadic sample collections in 2006 and 2007] 

Table 3. Chlorpyrifos and Diazinon Concentrations and Detections: West Prong Little Walla Walla 

River, North of Stateline Road 

Number of Detections Median 

Concentrations 

Maximum 

Concentrations 

2005 2006 2007 2005 2006 2007 2005 2006 2007 

Chlorpyrifos 6 6 3 0.112 0.245 0.067 0.49 0.54 0.091 

Diazinon 2 3 0 0.073 0.092 ND 0.122 0.15 ND 
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Table 4 Chloryrifos and Diazinon Concentrations and Detections: Little Walla Walla River, West 

Branch/Crockett 

Number of Detections Median 

Concentrations 

Maximum 

Concentrations 

2006 2007 2006 2007 2006 2007 

Chlorpyrifos 5 4 1.100 0.245 7.4 0.46 

Diazinon 5 0 0.390 ND 6.2 ND 

The most noteworthy findings from this data are the significant reductions in median and maximum 

concentrations between 2006 and 2007, and the drop in the number of diazinon detections. The median 

and maximum concentrations at the Stateline Road site decreased by 73% and 83% respectively between 

2006 and 2007, and there was a 78% reduction in median concentrations and a 94% reduction at the 

West Branch/Crockett site. The 2007 median concentration at the Stateline Road site was also 40% 

lower than the 2005 median. In addition, diazinon was detected eight times at the two sites in 2006, yet 

no detections were found in 2007. 

Figures 5 and 6 below provide a graphic illustration of the median concentrations of all pesticide 

detections observed at the Stateline Road and West Branch/Crockett sites. The water quality standards 

for chlorpyrifos and azinphosmethyl are also depicted. The median concentration for detections at the 

Stateline Road site fell below the acute water quality standard for chlorpyrifos in 2007, but it remains 

above the chronic water quality standard. The median concentrations of detections found at the West 

Branch/Crockett site exceeded the state water quality standards for azinphosmethyl and chlorpyrifos 

during all three years of monitoring. However, the significant decrease in chlorpyrifos concentrations 

observed in 2007 resulted in a much less substantial exceedance of the standards than occurred in 2006. 

There were no azinphosmethyl detections at the Stateline Road site in 2007, compared with five 

detections in 2006. However, the aforementioned caveat regarding the relatively small number of late 

season sampling events should be considered when assessing these results. There was little difference 

between the 2006 and 2007 median concentration of azinphos-methyl at the West Branch/Crockett site. 
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Figure 5 Median pesticide concentrations of detections observed at West Prong Little Walla Walla 

River, North of Stateline Road, 2005-2007 

Median Pesticide Concentrations:

West Prong Little WW River, N. Stateline Rd.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Azinphosmethyl

Chlorpyrifos

Diazinon

Dimethoate

Simazine

Median (ug/L)

2005 median

2006 median

2007 median

WQS Azinphosmethyl (0.01 ug/l)

Chronic WQS Chlorpyrifos (0.041 

Acute WQS Chlorpyrifos (0.083 ug/l)

Figure 6 Median Pesticide concentrations of detections observed at Little Walla Walla River, West 

Branch/Crockett, 2006-2007 

Median Pesticide Concentrations: 

Little WW River, West Branch/Crockett

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Azinphosmethyl

Chlorpyrifos

Diazinon

Dimethoate

Simazine

Median (ug/L)

2006 median

2007 median

WQS Azinphosmethyl (0.01 ug/l)

Chronic WQS Chlorpyrifos (0.041 ug/l)

Acute WQS Chlorpyrifos (0.083 ug/l)
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IV. CONCLUSIONS 

The pesticide monitoring from 2007 produced a number of encouraging results related to improved 

water quality in the Walla Walla Sub-basin. Reductions in median and maximum chlorpyrifos 

concentrations and the decrease in the number of diazinon detections were substantial. Dimethoate and 

simazine were detected multiple times in 2006 (and dimethoate was detected in 2005), but neither were 

detected at any site in 2007. In addition, no detections of azinphosmethyl were detected at any of the 

sampling locations in 2007, where consistent pesticide detections had been observed since monitoring 

began in 2005. Also, no detections of any pesticides were found at one tributary location (East Little 

Walla Walla River, North of Stateline Road) where they had been detected in both 2005 and 2006 

The Department and the Walla Walla Basin Watershed Council met with growers from the Blue 

Mountain Horticultural Society and OSU Extension Service in July 2007 to learn about what – if any – 

changes in application practices occurred earlier in the year. A significant level of applicator education 

was provided, including a spray calibration workshop in February as well as individualized training. 

Some of the growers also completely discontinued the use of organophosphate insecticides, and 

switched to less toxic pesticides and mineral oil. Furthermore, buffer zones between orchards and 

waterways were also were also created on properties, which had open ditches. OSU Extension Service 

will be developing a report documenting these best management practices and other pest management 

practices in the area. Funds are available to continue pesticide monitoring in 2008, and all of the 

stakeholders are optimistic about the potential for further improvements in stream quality. 

Acknowledgements 

This project was funded by a 319 grant from the Environmental Protection Agency. 
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APPENDIX A – SAMPLE COLLECTION DATES 

 2005

March 10 April 4 May 31 

March 14 May 2 June 1 

March 16 May 13 June 3 

March 17 May 17 

March 21 May 20 

March 28 May 23 

March 30 May 24 

March 31 May 26 

 

 2006

March 22 (1) May 18 June 6 

March 22 (2) May 23 June 8 

March 28 May 25 (1) 

March 29 May 25 (2) 

March 30 May 31 

April 11 June 1 

April 12 June 5 

 2007

March 19 May 15 June14 

March 21 May 23 

March 22 May 24 

March 26 

March 29 
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 APPENDIX B – PESTICIDE DETECTION DATA 

Walla Walla Pesticide Stewardship Partnership 2005 and 2006 Pesticide Detections 

Case Sample date Year 

Bottle 

No. Site Analyte 

20050240 3/10/2005 2005 2675 West Prong Little WW River, North of Stateline Rd. Diazinon 20050240 3/10/2005 2005 2675 West Prong Little WW River, North of Stateline Rd. Dimethoate 20050244 3/14/2005 2005 2626 East Little WW River, North of Stateline Rd. Chlorpyrifos 20050244 3/14/2005 2005 2627 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050260 3/16/2005 2005 2629 East Little WW River, North of Stateline Rd. Chlorpyrifos 20050260 3/16/2005 2005 2663 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050264 3/17/2005 2005 2657 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050279 3/21/2005 2005 2632 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050310 3/28/2005 2005 2624 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050310 3/28/2005 2005 2624 West Prong Little WW River, North of Stateline Rd. Diazinon 20050218 3/30/2005 2005 2687 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20050542 5/26/2005 2005 4156 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060224 3/22/2006 2006 5023 Little WW River, West Branch/Crockett Chlorpyrifos 20060225 3/22/2006 2006 5028 Little WW River, West Branch/Crockett Chlorpyrifos 20060224 3/22/2006 2006 5022 Little WW River, Midwest Prong Chlorpyrifos 20060225 3/22/2006 2006 5029 Little WW River, Midwest Prong Chlorpyrifos 20060224 3/22/2006 2006 5024 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060225 3/22/2006 2006 5030 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060224 3/22/2006 2006 5023 Little WW River, West Branch/Crockett Diazinon 20060225 3/22/2006 2006 5028 Little WW River, West Branch/Crockett Diazinon 20060224 3/22/2006 2006 5022 Little WW River, Midwest Prong Diazinon 20060225 3/22/2006 2006 5029 Little WW River, Midwest Prong Diazinon 20060225 3/22/2006 2006 5030 West Prong Little WW River, North of Stateline Rd. Diazinon 

20060235 3/28/2006 2006 5037 Little WW River, West Branch/Crockett Chlorpyrifos 

20060235 3/28/2006 2006 5041 Little WW River at the Frog Chlorpyrifos 20060235 3/28/2006 2006 5038 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060235 3/28/2006 2006 5037 Little WW River, West Branch/Crockett Diazinon 20060237 3/29/2006 2006 5044 Little WW River, West Branch/Crockett Chlorpyrifos 20060237 3/29/2006 2006 5045 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060237 3/29/2006 2006 5044 Little WW River, West Branch/Crockett Diazinon 20060237 3/29/2006 2006 5045 West Prong Little WW River, North of Stateline Rd. Diazinon 
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20060237 3/29/2006 2006 5044 Little WW River, West Branch/Crockett Dimethoate 

20060237 3/29/2006 2006 5045 West Prong Little WW River, North of Stateline Rd. Dimethoate 

20060242 3/30/2006 2006 5052 Little WW River, West Branch/Crockett Chlorpyrifos 20060242 3/30/2006 2006 5053 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060242 3/30/2006 2006 5052 Little WW River, West Branch/Crockett Diazinon 20060242 3/30/2006 2006 5053 West Prong Little WW River, North of Stateline Rd. Diazinon 

20060242 3/30/2006 2006 5052 Little WW River, West Branch/Crockett Dimethoate 

20060279 4/11/2006 2006 5092 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 

20060421 5/18/2006 2006 5144 Little WW River, Midwest Prong Simazine 20060421 5/18/2006 2006 5146 West Prong Little WW River, North of Stateline Rd. Simazine 20060450 5/25/2006 2006 5165 Little WW River, West Branch/Crockett Azinphosmethyl 20060445 5/25/2006 2006 5142 Little WW River, West Branch/Crockett Azinphosmethyl 20060450 5/25/2006 2006 5167 Little WW River, Midwest Prong Azinphosmethyl 20060450 5/25/2006 2006 5153 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060445 5/25/2006 2006 5149 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060459 5/31/2006 2006 6107 Little WW River, West Branch/Crockett Azinphosmethyl 20060459 5/31/2006 2006 6108 Little WW River, Midwest Prong Azinphosmethyl 20060459 5/31/2006 2006 6109 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060463 6/1/2006 2006 6116 Little WW River, West Branch/Crockett Azinphosmethyl 20060463 6/1/2006 2006 6117 Little WW River, Midwest Prong Azinphosmethyl 20060463 6/1/2006 2006 6118 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060463 6/1/2006 2006 6116 Little WW River, West Branch/Crockett Simazine 20060479 6/5/2006 2006 6228 West Prong Little WW River, North of Stateline Rd. Azinphosmethyl 

20060479 6/5/2006 2006 6222 Little WW River, Midwest Prong Azinphosmethyl 20060479 6/5/2006 2006 6227 Little WW River, West Branch/Crockett Azinphosmethyl 

20070236 3/21/2007 2007 6342 Little WW River, West Branch/Crockett Chlorpyrifos 20070245 3/22/2007 2007 7010 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20070245 3/22/2007 2007 6338 Little WW River, West Branch/Crockett Chlorpyrifos 20070253 3/26/2007 2007 7013 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20070253 3/26/2007 2007 7012 Little WW River, West Branch/Crockett Chlorpyrifos 20070263 3/29/2007 2007 7024 West Prong Little WW River, North of Stateline Rd. Chlorpyrifos 20070263 3/29/2007 2007 7022 Little WW River, West Branch/Crockett Chlorpyrifos 20070263 3/29/2007 2007 7021 Little WW River, Midwest Prong Chlorpyrifos 20070263 3/29/2007 2007 7021 Little WW River, Midwest Prong Diazinon 20070486 5/23/2007 2007 7037 Little WW River, West Branch/Crockett Azinphosmethyl 20070493 5/24/2007 2007 7046 Little WW River, West Branch/Crockett Azinphosmethyl 20070493 5/24/2007 2007 7045 Little WW River, Midwest Prong Azinphosmethyl