1 

### The Ecological Significance of Atra zine Effects on Primary Producers

in Surface Water Streams in the Co rn and Sorghum Growing Region of the United States (Part II)

Addendum to Section VI: Additional Analysis of the 40 AEEMP Sampling Sites to Identify Additi onal Areas That May Exceed the LOC

Submitted to the FIFRA Scientific Advisory Panel

For Review and Comment

May 12 – 15, 2009

Office of Prevention, Pestic ides and Toxic Substances Office of Pesticide Programs

Environmental Fate and Effects Division Washington, DC

May 1, 20092 

### Addendum to Section VI: Additional Analysis of the 40 AEEMP Sampling Sites to Identify Additi onal Areas That May Exceed the LOC

This addendum to Section VI (Identifying Wa ters That Exceed Effects-Based Atrazine Thresholds Beyond the 40 Sampling Sites) de scribes additional analyses conducted by

the US EPA to evaluate watershed charac teristics of the 40 Atrazine Ecological Exposure Monitoring Program (AEEMP) sites in order to identify additional watersheds

with characteristics similar to the sites that exceed the atrazine LOC in multiple years.



### A. Further Evaluation of Watersh ed Factors Driving Atrazine Exposures in the AEEMP Study

US EPA evaluated a number of pestici de use, soil, hydrologic, weather, and

watershed characteristics for the 40 AEEMP watersheds. The goal of this assessment was to identify those factors, singly or in combination, that best distinguish the 3 sites that exceeded the atrazine LOC in multiple years (MO-01, MO-02, NE-04) from those si tes that did not exceed the LO C. For the time-being, the Agency grouped the 6 sites that exceeded t he LOC in one year only (IN-05, IN-11, MO-03, NE-02, NE-05, NE-07) as a separate population.

In the 2009 SAP Review Document (dat ed April 15, 2009), the US EPA noted a minimum atrazine use intensity of approximat ely 0.1 lb ai/watershed acre for the

sites that exceeded the LOC in one or mo re years (Figure 1); above that level, differences in soil-related factors largely characterized the differences between the

sites that exceeded the LOC and those t hat did not. The upstream catchment area

of the nine sites that exceeded atrazine in one or more years gene rally had a higher percentage of runoff prone soils, as indica ted by a high or very high USDA runoff class or by the presence of hydrologic group C or D soils. The three sites that exceeded the LOC in multiple years had a higher fraction of soils with a shallow restrictive layer, as indicated by t he presence of a subsurface layer with a moderately low or low saturated hydraulic conductivity (Ksat) within 50 cm of the

surface.

Because the proposed use intensity thre shold is based on a limited number of samples (as shown in Figure 1, only three sites are near or below the 0.1 lb ai/A level), the US EPA looked at an alter native approach that weighted the soil parameters by the use intensity.

US EPA calculated soil parameter-use intens ity indices by multiplying the fraction of high/very high runoff soils, hydrologic group C or D soils, or soils with a shallow depth to a restrictive layer in the upstr eam catchment area by the atrazine use intensity for the catchment.3 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDAtrazine Use Intensity, lb ai/ac



## *

* *

o

o o o

o

o * Sites exceeded LOC in multiple years o Sites exceeded LOC in 1 year

Figure 1 Atrazine use intensity, lb ai/ catchment acre, for the 40 AEEMP monitoring sites



### The USDA soil runoff classes rank soils acco rding to their potential for loss of water

due to surface runoff based on a combinatio n of saturated hydraulic conductivity (Ksat) of the surface horizon and slope. So ils with either a high or very high runoff potential made up 50% or more of the upstream catchment s at sites that exceeded the LOC in multiple years (indicated by a red asterisk in Figure 2) and more than

40% at sites that exceeded the LOC at least once (indicated by a red circle in Figure 2). Except for NE-01, similar high-runoff soils comprised less than 46% of upstream

catchments for sites that never exceeded the LOC.

Weighting the fraction of watersheds with hi gh runoff soils by use intensity provides

a clearer distinction between sites that exceed the LOC and t hose that do not exceed the LOC (Figure 3). The sites that exceed the LOC in multiple years had a use intensity-high runoff index greater than 0.20 while site s that did not exceed the

LOC had an index of less than 0.17. Sites that exceeded the LOC in one year overlapped both groups, with a use intensit y-high runoff index r anging from 0.05 to

0.35.4 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed High Runoff Potential

Very High Runoff Potential 

## *

*

* o

o o

o

o o * Sites exceeded LOC in multiple years

o Sites exceeded LOC in 1 year

Figure 2 Fraction of AEEMP watersheds containing soils with high or very high runoff potential

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed x Use Intensity High Runoff Potential

Very High Runoff Potential



### * *

*

o o o

o o o * Sites exceeded LOC in multiple years

o Sites exceeded LOC in 1 year

Figure 3 Use intensity-adjusted fraction of AEEMP watersheds containing soils with high or very high runoff potential (use intensity – high runoff index)5 

### The hydrologic soil group classification is used in curve number method commonly used in water quality models. Higher portions of rainfall are expected to runoff from soils in hydrologic group C or D than soils in group A or B. The classifications are based on surface hydraulic conductivity and the water storage capacity of the soil.

While the two MO sites that exceeded the LO C in multiple years had a high fraction of hydrologic group D soils in the upstream catchment (shown as blue bars in Figure 4), NE-04, which also ex ceeded the LOC in multiple years, had a much lower fraction, less than that of 3 other sites (Figure 4). While the upstream catchments of

all three sites that exceeded the LOC in multiple years had greater than 85% hydrologic group C and D soils, two sites t hat did not exceed the LOC (IN-03 and OH-01) also had similarly high fractions of C and D soils.

When the fraction of the watershed in C or D soils was weighted based on atrazine use intensity, the resulti ng use intensity-group C&D soils index for the sites that exceeded the LOC in multiple years was great er than 0.3. (Figure 5). However, two

sites that did not exceed t he LOC (IN-03 and IN-09) and one site that exceeded once (IN-05) also had a similarly high use intensity-group C&D soils index.

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed HSG C soils

HSG D soils 

## * *

*

o o

o

o o o * Sites exceeded LOC in multiple years

o Sites exceeded LOC in 1 year

Figure 4 Fraction of AEEMP watersheds containing hydrologic group C and D soils6 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed x Use Intensity HSG C soils

HSG D soils 

## *

* *

o

o o

o o o * Sites exceeded LOC in multiple years

o Sites exceeded LOC in 1 year

Figure 5 Use intensity adjusted Fraction of AEEMP watersheds containing hydrologic group C and D soils (use intensity-group C&D soil index)



### US EPA defined the depth to drainage restrict ive layers based on the depth to which subsurface soil layer with Ksat value of <1 μm/s occurs. Greater than 67% of the

catchments for the three site s that exceeded the LOC in multiple years contained soils that had a Ksat value of less than 1 μm /s within 50 cm of t he surface while, for the sites that did not exceed the LOC, less than 41% of the catchment areas had similar soils (Figure 6). Two additional NE sites that exceeded the LOC once (NE-05 and NE-07) had fractions of soils with shallow, low-Ksat soils similar to the sites that exceeded in multiple years.

However, when the proportion of soils with a shallow drainage-restrictive layer was weighted by use intensity, t he three sites that exceeded the LOC in multiple years were clearly separated from the remainin g sites (Figure 7). The resulting use intensity-low Ksat index was greater than 0.25 for the sites that exceeded the LOC in multiple years and less than 0. 17 for the remaining sites (l ess than 0.15 for the sites that did not exceed the LOC).7 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed Ksat<1 um/s, 25-50cm

Ksat<1 um/s, <25cm

o o

o o o

o 

## * * * * Sites exceeded LOC in multiple years o Sites exceeded LOC in 1 year

Figure 6 Fraction of AEEMP watersheds with Ksat <1 μm/s within 50 cm of the surface

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50IA-01IA-02IL-01IL-02IL-03IL-04IL-05IL-06IL-07IL-08IL-09IN-01IN-02IN-03IN-04IN-05IN-06IN-07IN-08IN-09IN-10IN-11KY-01KY-02MN-01MO-01MO-02MO-03NE-01NE-02NE-03NE-04NE-05NE-06NE-07OH-01OH-02OH-03OH-04TN-01

Site IDFraction of watershed Ksat<1 um/s, 25-50cm

Ksat<1 um/s, <25cm



## *

* *

o

o o
o o

o * Sites exceeded LOC in multiple years o Sites exceeded LOC in 1 year

Figure 7 Use intensity-adjusted fraction of AEEMP watersheds with Ksat <1 μm/s within 50 cm of the surface (use intensity-low ksat index)8 

### Preliminary multivariate approaches have confirmed the impor tance of both the use-weighted Ksat index as well as depth to low Ksat values, High-to-Very High runoff potential, and soil type (D soils) factor s in combination. Further evaluation

of these factors with a lar ger set of data is key to developing more definitive models beyond the current working hypotheses.



### B. Update on Approaches for Identifying Watersheds with

Characteristics Similar to Those That Exceed the Atrazine LOC

The 2009 SAP Review Document describes the parameters US EPA used to identify

other watersheds within the atrazine use ar ea that are similar to the sites that

exceeded the atrazine LOC in multiple years:

1) Define the extent of potential vu lnerable watersheds based on a minimum atrazine use intensity (0.1 lb ai/A) and ra infall (average annual precipitation of at least 23 inches). 2) Identify runoff-prone watersheds that have at least 40% soils with a high or very high runoff potential or at least 60 % hydrologic group C or D soils. 3) Identify watersheds that have at least 45% soils with a subsurface layer that has

a Ksat value of < 1 μm/s within 50 cm of the surface.

Figure 8 shows the extent of NHDPlus wate rsheds in a 10-state region (OH, KY, TN, IN, IL, MN, IA, MO, NE, KS) that meet thos e criteria. The dark green areas meet the precipitation, soils, and use ct iteria; the light green areas meet the prec ipitation and soil criteria, but have a lower atrazine use intensity; the gray areas meet the soil

criteria but have no no corn or so rghum in the watershed. The dark orange background shows the extent of vulnerab le watersheds identified by WARP that were represented by the 40 AEEMP monito ring sites. The light orange shows the

extent of the next lower ti er of vulnerable watersheds.

Table 1 provides a breakdown of the ar ea percentages of the NHDPlus catchments that met either the precipit ation and soil criteria alone or the precipitation, soil and atrazine use intensity criteria for the ten state area. Roughl y 22% of the area in both the upper 20th percentile and t he 60-80th percentile tiers of vulnerable watersheds as identified using WARP (see the ba ckground documents for the 2007 and 2009 SAP meetings for details) consisted of NHDPlus watersheds that meet both the precipitation (average annual rain fall >23 inches) and the soil (> 60% hydrologic group C or D soils and > 45% soils with a low Ksat w/in 50 cm of the surface) criteria. This fraction may represent the maximum potential extent of areas where atrazine concentrations in flowing streams might exceed the LOC. Because of varying use

intensities over time and expected crop rotations, the atrazine use intensity is not expected to be this great for the entire area.

NHDPlus watersheds that meet the precipitation, soils, and use criteria cover 15% of the area in the upper 20th percentile of vul nerable watersheds and half that much in9 

### the next lower (60-80th percent ile) tier. Very few areas outside of these tiers meet

the criteria.

Figure 8 Map Showing Distribution of Watersheds That May Exceed the Atrazine LOC Based on Atrazine Use, Precipitation, and Soil Criteria.

Table 1 Percentage of area with watersheds with characteristics similar to the AEEMP sites that exceed the LOC based on separate precipitation, atrazine use intensity, and

soil criteria



### Percent of area AEEMP sites exceeding 2 or more years (for the entire upper 20 th 

### %ile WARP watersheds) 12% (0-25%, 95% CI)

NHDPlus catchments in the 10-state region (see Figure 8) that meet: Precipitation +

soil criteria Precipitation +

soil + use

criteria Upper 20 th 

### %ile of vulnerable wate rsheds (WARP) 22.6% 15.3%

60-80 th 

### %ile tier of vulnerable watersheds (WARP) 22.8% 7.6% Remaining area 11.6% 0.4%10 

### US EPA used the use intensity- low Ksat index to identify watersheds that are similar

to the sites that exceeded the atrazine LOC in multiple years. For each NHDPlus watershed in the 10-state region, US EPA multiplied the fraction of the watershed

with soil that hav e a Ksat of < 1 μm/s within 50 cm of the su rface by the atrazine use intensity and mapped the resu lting use intensity-low Ks at index (Figure 9). The

watersheds that meet the us e intensity-low Ksat index criteria cover a similar pattern, though a smaller area, than the watersheds that m eet the precipitation-use intensity-soil criteria (c ompare Figures 8 and 9 and Tabl es 1 and 2). However, the percent of area in the upper 20 th 

### percentile of vulnerable watersheds is in line with the population estimate based on the AEEMP results (Table 2).

Figure 9 Map Showing Distribution of Watersheds That May Exceed the Atrazine LOC Based on the Use Intensity-Low Ksat Index11 Table 2 Percentage of area with watersheds with characteristics similar to the AEEMP sites that exceed the LOC based on the use intensity-low Ksat index



### Percent of area AEEMP sites exceeding 2 or more years (for the entire upper 20 th 

### %ile WARP watersheds) 12% (0-25% 95% CI)

NHDPlus catchments in the 10-state region (see Figure 8) with a: Use-ksat

index >0.15 Use-ksat index

>0.20 Upper 20 th 

### %ile of vulnerable watersheds (WARP) 12% 8%

60-80 th 

### %ile tier of vulnerable watersheds (WARP) 3% 1.5% Remaining area 2% 0.1%



### C. Update on Evaluating Vulnerab le Watershed Criteria with Monitoring Data Not in the AEEMP

In the 2009 SAP Review Document (dated Ap ril 15, 2009), the US EPA identified a number of monitoring data sour ces it plans to use to evaluate the results of the watershed analysis. To provide a comparable data set for analysis, US EPA selected those sites that sampled 1 st 

### to 5 th 

### order streams (based on Strahler’s stream order) during the 2004- 2008 time frame. That r epresented comparable water bodies and a comparable time frame for bot h atrazine use and weather. Where the sample frequency is sufficient (bi-weekly to monthly during the growing season), USEPA evaluated the chemographs using the PATI LOC MEI 

### . US EPA identified 330 monitoring stations from NAWQA (U SGS, 2009), Nebraska Department of Environmental Quality (NDEQ) ambient st ream and Blue River Basin Water Quality Source Assessment programs (NDEQ, 2008), Kansas Department of Health and Environment (KDHE, 2008), Iowa Departm ent of Agriculture (IADA, 2009), Minnesota Department of Agriculture (Mn DA, 2008), and the USDA ARS in MO (Lerch et al, 2008) that met the criteria fo r stream order and time frame (Table 3).

Table 3 Summary of Monitoring Data Used to Evaluate the AEEMP Watershed Criteria

Total number of sites

Source No.

Sites Max Detect >10 μg/L Max Detect >20 μg/L Max detect <1 μg/L Exceed

LOC NAWQA (10 states) 44 9 7 13 6 NE Dept. of Envir. Qual. 101 33 25 37 26 KS Dept. of Health & Envir. 121 15 8 58 IA Dept. of Agric. 54 3 0 8 2 MN Dept. of Agric. 9 2 0 0 0 USDA ARS, MO 1 1 1 0 1

Total 330 63 41 116 354



### The first step US EPA is taking in evaluati ng the watershed criteria is to overlay the locations of the monitoring sites summarized in Table 3 onto the NHDPlus watersheds in the 10-state region that encompasses the 40 AEEMP monitoring sites. The Agency will dete rmine how effectively the propos ed criteria for identifying vulnerable watersheds (precipitation-use-so il combination or t he use intensity-low12 

### Ksat index) separate sites that either exceed the LOC or have maximum detects greater than 10 or 20 μg/L fr om sites that did not have atrazine detections greater than 1 μg/L.

As a second step, US EPA plans to furt her evaluate the proposed criteria for identifying vulnerable watersheds and refi ne, if needed, by comparing the watershed

characteristics of the additional non-AEEM P monitoring sites that exceeded the LOC

to the AEEMP sites.

To date, US EPA has completed the first step of evaluati on for the precipitation-usesoil criteria combination. Approximately 15% of the 330 monitoring sites occur in

NHDPlus catchments that meet the precipitation-use-soil combination criteria used to identify watersheds similar to those t hat exceeded the LOC in multiple years (Table 4). Over half of the sites in t hese vulnerable areas had maximum detections >10 μg/L, compared to 20% of all sites. Conversely, while more than a third of the total monitoring sites did not have atrazine det ections >1 μg/L, only 8% of the sites in the vulnerable areas never had detections >1 μg/L.

Nearly half of sites in the vulnerable ar eas exceed the PATI LOC, compared to 16% for all sites (Table 4). While the sites with pr ecipitation-use-soil criteria similar to the AEEMP sites that exceed the LOC in multiple years capture more than half (19 out of 35) of the total monitoring stations that exceed the LOC, some sites that exceed

the LOC occur in areas that did not meet the combined precipitat ion-use-soil criteria

similar to the AEEMP sites that ex ceed the LOC in multiple years.

Table 0-4 Preliminary Evaluation of Sites Not in the AEEMP That Exceeded the PATI

LOC MEI Number of Sites Monitoring Data

Set Location Total

Sites Max

Detect >10 μg/L Max

Detect >20 μg/L Max

detect <1 μg/L Exceed

LOC

All sites 44 9 (20%) 7 (16%) 13 (30%) 6 (14%) NAWQA 10

states Vulnerable area 1 7 5 (71%) 4 (57%) 1 (14%) 3 (43%) All sites 101 33 (33%) 25 (25%) 37 (37%) 26 (26%) Nebraska DEQ

Vulnerable area 1 24 17 (71%) 12 (50%) 0 (0%) 13 (54%) All sites 121 15 (12%) 8 (7%) 58 (48%) Kansas DHE

Vulnerable area 1 8 3 (38%) 0 (0%) 3 (38%) All sites 54 3 (6%) 0 (0%) 0 (0%) 2 (4%) Iowa DA

Vulnerable area 1 8 2 (25%) 0 (0%) 0 (0%) 2 (25%) All sites 9 2 (22%) 1 (11%) 0 (0%) 0 (0%) Minnesota DA

Vulnerable area 1 0 0 0 0 0

All sites 1 1 1 0 1 Missouri USDA

ARS Vulnerable area 1 1 1 1 0 1 All sites 330 63 (19%) 41 (12%) 116 (35%) 35 (16%) 2 All Sites

Vulnerable area 1 48 26 (54%) 17 (35%) 4 (8%) 19 (48) 2

1 Catchments meet the vulnerable watershed criteria of annual average precipitation >23 inches, atrazine use intensity > 0.1 lb ai per catchment acre, and runoff-prone soils (> 60 percent13 of the upstream catchment area consisted of hydrologic group C or D soils with > 45 percent of the soils having a subsurface layer with a Ksat of <1 um/s within 50 cm of the surface)..

2 Total percentages for sites that exceed the LOC are based on 209 total sites and 40 sites in the vulnerable watersheds, excluding the KS sites which did not have a sufficient sample frequency to evaluate with the PATI LOC.



### The Agency plans additional analyses of all of these monitoring sites, including an evaluation of the upstream catchment characte ristics of selected monitoring sites. In addition, US EPA plans to conduct a similar evaluation for the use intensity-low Ksat index method for identifying watersheds wit h characteristics similar to the AEEMP

sites that exceeded the LOC in multiple years.

To date, the watershed analysis has focus ed on the 10 states that encompass the 40 sites in the AEEMP. US EPA plans to expand the watershed analysis to encompass the extent of the area identified is the upper 20 th 

### percentile of vulnerable watersheds based on WARP (Figure 10).

Figure 10 Geographic extent of watersheds in the upper per centiles of vulnerability

based on WARP.