## Presented by 

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# Modeling pesticide fate and transport through flowing water bodies for endangered species assessment in the California Central Valley
Lauren Padilla, Stone Environmental Inc. Michael Winchell, Stone Environmental Inc. Natalia Peranginangin , Syngenta Crop Protection, LLC JiSu Bang, Syngenta Crop Protection, LLC

Katie Budreski, Stone Environmental Inc. March 24, 2014

# Introduction

 SWAT model application to agriculturally intensive Central Valley region in California for endangered species assessment 

#  Area of interest is CA Bay - Delta

− E stuary habitat

− Flowing water bodies are important species habitat

− Source of drinking water for many Californians

Critical Habitat Area

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# Overview

 G oal to estimate herbicide concentrations in Delta flowing water bodies 

#  Requires simulation of transport of pesticide residues from application sites upstream 

#  Model must address several key components

− Hydrology

− Spray drift modeling

− Spatial and temporal distribution of applications 

#  Presentation of modeling approach to these components, then comparison of modeled and observed concentrations Critical Habitat Area

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# Hydrology – Watershed Delineation

 A large, diverse watershed drains through Delta 

#  Included only model area below mountain reservoirs, upstream of use sites

− 24 freshwater reservoir outflows

− Drain 26,300 square miles or 40% of watershed area

− 30 year daily time - series of USGS inflows

− Some missing data linearly interpolated 

#  Excluded Tulare and Kings River basins

− Only hydrologically connected during flood times

− Assume flood flows originate upstream of pesticide use

− Model flood flows as water inputs without pesticide residues using USGS data Critical Habitat

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# Hydrology – Landscape Characterization

 Watershed area assessed:

− 344 subbasins with average area 140km 2 ranging from 0.01 - 1000 km 2

− 37,041 Hydrologic R esponse U nits (HRUs) 

#  This delineation was accomplished using high - resolution input data sets:

− Topography : 30 - m NHDPlus V2 Hydrologically Conditioned DEM (2012) (complies with HUC12 boundaries)

− Soils Data: Soil Survey Geographic database, 1:24,000 scale (2012)

− Land Use Data: Cropland Data Layer (CDL), 30 - m, multiple crop classes, classified into crop groups, dominant crop group taken based on 5 - year composite (2007 - 2011) 

### Land use **Soils DEM** 

**HRUs**

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# Hydrology – Weather Data

 Need to capture heterogeneity of climate across large modeled watershed area 

#  Historic temperature and precipitation data from nearest weather station supplied to each subbasin

− 30 years of daily data between 1981 - 2010

− Data sources: Global Historical Climatology Network, Integrated Surface Database, California Irrigation Management Information System

− 51 temperature stations and 48 precipitation stations with most complete records

− Missing data filled in by nearest secondary stations Critical Habitat Area

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# Hydrology – Complex Flow Diversions

 Complex network of surface water control structures in and around Delta

− Time - varying flow

− High flow rates

− Lack temporal patterns

− Diverted to destinations hundreds of miles away 

#  Modified SWAT code to improve transport of water, chemical, and other dissolved and suspended masses

− Previously SWAT did not allow transport of water and mass according to historic time series

− Our modification allows specification of daily - or monthly - average time - series

− Modification made possible modeling the many complex flow diversions

− R esulted in greatly improved accuracy of flows and chemical concentrations 

#  Examples:

− Flood control structures

− Irrigation canals

− Withdrawals by pumping plants



### Tisdale Weir

CVP Jones Pumping Plant 7

# Modeled Diversions – Daily time - step

 Modeled Weirs and Channels:

− Moulton, C olusa, Tisdale Weir transfers to Sutter Bypass

− Fremont, Sacramento Weirs to Yolo Bypass

− Delta Cross Channel connection to Mokelumne River

− Little Potato Slough connection to San Joaquin River

− All returned to watershed 

#  Modeled Pumping Plant Withdrawals:

− Central Valley Project Jones Pumping Plant to Delta - Mendota Canal

− State Water Project Banks Pumping Plant to CA Aqueduct

− Contra - Costa Canal

− All exported out of watershed 

#  Daily Datasets

− US Geological Survey, DAYFLOW Sources: Exports and Flood Control, USGS and CA DWR 8

# Modeled Diversions – Monthly time - step

 Modeled 33 i rrigation d iversions 

#  Can capture yearly variation with modified transfer scheme 

#  Monthly datasets

− CA Department of Water Resources

One line per year 1981 - 2010 Sources: Full Watershed, USGS; Inlet locations, USGS; Diversion Locations, CA DWR 9

# Modeled diversions – I mproved Flow Rates

 Better magnitude and timing of flows 

#  Avoid compensating flow errors with calibration 

#  More accurate prediction of pesticide concentrations

Observed Flow Modeled Flow Without transfers With transfers Subbasin 97, Sacramento below Wilkins NSE: 0.91 RSR: 0.29 PBIAS: - 2.44%

10NSE: 0.94 RSR: 0.24 PBIAS: 17.37% NSE: 0.99 RSR: 0.12 PBIAS: - 10.0% 

# Modeled diversions – I mproved Flow Rates

Observed Flow Modeled Flow Subbasin 219, San Joaquin near Vernalis Subbasin 183+190, Total Delta Outflow
Calibration period

Validation period

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# Pesticide Application Modeling - Spatial Distribution

 Annual application mass targets for each subbasin

− CA Pesticide Use Reporting (PUR) Database

− Highest use year between 2006 - 2010

− Max application rate with minimum interval according to label for each applicable land use 

#  Targets met by randomly choosing eligible HRUs within each subbasin

− Many different combinations of HRUs could meet annual subbasin target

− 100% of selected HRU area gets application at label rate

− If this would exceed the target, dynamically decrease applied area fraction of HRU to meet target Critical Habitat

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# Pesticide Application Modeling – Temporal Distribution

 Probability distributions of applications occurring in each month for every subbasin and applicable land use

− PUR data between 2006 - 2010

− Application month drawn according to distribution

− Application day drawn with uniform probability 

#  For crops with applications made close to planting date, shift planting date after application date determined 

#  Ground and aerial application methods selected according to PUR probability 13

# Spray Drift Modeling

 Potential water body areas

− 1:24,000 scale high - resolution NHD area features (USGS, 2012)

− Bay Inlet, Canal/Ditch, Foreshore, Sea/Ocean, Stream/River 

#  Ground spray drift fractions from AgDrift

− 50 in boom height

− Fine to medium/coarse droplet size 

#  Aerial spray drift fractions from AgDisp

− 10 - 20ft boom height

− 10mph windspeed

− Fine/medium droplet size Critical Habitat Area

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# Spray Drift Modeling

 Conducted proximity analysis of water body area within 400 m of each HRU 

#  Average drift fraction as a function of distance from HRU edge in ranges: 0 - 20 m, 20 - 40m, 40 - 60 m, 60 - 120 m, 120 - 200m, 200 - 400m 

#  Drift mass input directly into flowing water bodies according to,

Critical Habitat Area Sources: Full Watershed, USGS; Water bodies, ( 1:24,000) CA NHD area; Critical Habitat, USFWS 15

# Monte Carlo Simulations

 64 simulations sampling range of application timing and locations

− Accounts for variation in management practices among growers

− Application scenarios remain constant for each simulation year



#  30 - year simulations sampling range of weather conditions



#  Substantial computational requirements

− Over 3 hours per run

− Developed software to automatically generate application scenarios and distribute runs among several processors

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# Simulated vs. Observed Concentrations
 Observed maximum concentrations were compared with modeled 90 th 

## percentile concentrations. 

#  M odeled concentrations were same order of magnitude as monitoring data. 

#  Modeled EECs for variety of water body types: major rivers to small sloughs 

#  Data sources: CEDEN, NAWQA, NWIS, EPA STORET, CILRP Critical Habitat Area 17

# Simulated vs. Observed Concentrations

 Comparison for the four reaches with the most detections

− San Joaquin near Vernalis (219), Patterson (235)

− Sacramento near Freeport (148)

− Tuolumne near Shiloh (227) 

#  77% - 98% of observations below level of quantification. Minimum quantification (min LOQ): 0.001 ug /L
Reach 148 Reach 219 Reach 227 Reach 235 Observed Max Conc. (ppb) 0.011 0.015 0.006 0.015 Modeled Max Conc. (ppb) 0.216 0.574 0.725 0.664 Modeled 99 th % - ile Conc. (ppb) 0.020 0.008 0.006 0.014 Modeled 95 th % - ile Conc. (ppb) 0.003 0.002 0.001 0.003 Observation days below LOC (%) 98 92 84 77 Modeled days below LOC (%) 91 92 96 91
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# Summary

 Comprehensive SWAT model for the CA Bay - Delta watershed capturing upstream pesticide use area 

#  Hydrology accounting for freshwater reservoir outflows, diversion of surface water and associated residues due to flood control, irrigation, and pumping 

#  Use of best available land use, soils, topography, weather, and pesticide use data 

#  Characterized pesticide applications according to ‘worst case’ historic use 

#  Realistic drift modeling based on actual water bodies 

#  Model concentrations compared well to monitoring data

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