# Environmental Modeling Public Meeting April 28, 2015 Gabe Rothman, Meridith Fry, Dirk Young, Chuck Peck, Jim Lin, Faruque Khan, James Hetrick, Mah Shamim

# Background  

# V olatilization algorithm evaluated: last of remaining PRZM routines needing formal evaluation  

# Calculates daily loss of pesticide due to volatilization flux from treated field to the atmosphere  

# Scope of review: only evaluated soil component of algorithm at this time (bare soil applications only, foliar applications not evaluated)  

# Provides potential for refinement of aquatic EECs for soil fumigants and semi -volatiles  

# Intended use to address quantity of pesticide available for runoff to water bodies  

# Not intended for use with terrestrial air exposure assessments 2

# Evaluation and Final Products  

# QA/QC Tasks  

# Phase I: Evaluation of PRZM Code  

# Phase II: Case Study (Ground Truth) Comparison 

#  

# Final Products  

# QA/QC Report: Documentation of Phase I and Phase II Findings  

# Input parameter guidance document specific for volatilization algorithm and soil application methods  

# Updated version of SWCC containing critical inputs for the volatilization algorithm 3

# Phase I Evaluation of PRZM Code, Step 1 Overview  

### First Step: Reviewed critical routines for volatilization production from literature and inspected calculation process for accurate soil concentration and volatilization flux **Routine Key**  **Parameters Process**  Dynamic Soil Temperature Routine (Hanks et al., 1971) • Air temperature, solar radiation, & albedo • Soil lower boundary temperature • Initial HLC input (at 25 degrees Celsius) • Heat of Henry (e.g., Enthalpy of Vaporization) • %Sand, %Clay Adjusted HLC and resulting vapor-phase concentration in soil
Diffusion in Soil Adjustment ( Millington and Quirk, 1961) • Diffusion in Air Coefficient • Field Capacity • Wilting Point Adjusted diffusion coefficient in soil accounting for soil porosity and tortuosity Volatilization Flux Boundary Condition (Jury et al., 1983) • HLC • Diffusion in Air Coefficient • Stagnant BL Height • Vapor phase soil concentration in top soil compartment Soil volatilization flux to the atmosphere from top soil layer through stagnant boundary layer Citations: Dynamic Soil Temperature Routine : Hanks , R. J., D. D. Austin, and W. T. Ondrechen . 1971. Soil temperature estimation by a numerical method. Soil Science Society of America Proceedings 35:665 - 667 . Millington - Quirk Expression: Millington and Quirk, 1961. Permeability of porous solids. Trans . Faraday Soc., 57, 1200 -1207, doi : 10.1039/TF9615701200 . Jury Equation : Jury, W. A., W. F. Spencer, and W. J. Farmer, 1983. Use of models for assessing relative volatility, mobility, and persistence of pesticides and other trace organics in soil systems. Pages 1-43 in J. Saxena, editor. Hazard Assessment of Chemicals. Academic Press, New York, New York, USA. 

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# Phase I Evaluation of PRZM Code, Step 1 Results  

## Bug Found and Corrected: Index to incorrect soil compartment with HLC in solution for “C term” of advection- dispersion equation for top soil compartment

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## Only impacted volatilization algorithm function C(1)= - (DISP(K,2)*THETN(2) + new_henry (K,2) *DGAIR(2) )*DELT/(DELX(1)* 0.5*(DELX(1)+DELX(2)))



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# Phase I Evaluation of PRZM Code, Step 2 Overview  

# Second Step: Functionality tests for volatilization algorithm - mass balance and sensible volatilization calculation criteria for success:  

# Mass balance completely accounted for in soil  

# Flux the same for applied non-partitioning gas under both dry and saturated moisture conditions  

# Flux higher for highly volatile chemical versus semi - volatile chemical  

# Flux higher for same chemical under high soil heating (low albedo, high temperature) than low soil heating (high albedo, low temperature) 6

# Additions to SWCC Output Options for Mass Balance in Soil

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# Phase I Evaluation of PRZM Code, Step 2 Results

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## Dry vs. Moist Conditions

• Soil Moisture (Dry = 0.00 cm water input, Moist = 20.o0 cm water input) • Field capacity and wilting point the same in dry and moist scenarios • Gas, Non- Partitioning Chemical (HLC = 10 4) • No degradation or sorption • Chemical Incorporated Uniformly to 46 cm depth 

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# Phase I Evaluation of PRZM Code, Step 2 Results  

## Highly Volatile vs. Semi -Volatile

• Chemical State Inputs (Highly Volatile HLC = 104, Semi -Volatile HLC = 0.1) • Dry Conditions(Water Input= 0.00 cm) • No degradation or sorption • Chemical Incorporated Uniformly to 46 cm depth 

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# Phase I Evaluation of PRZM Code, Step 2 Results  

## High vs. Low Soil Heating: Dynamic Soil Temperature Routine Functionality

• High Soil Heating Parameters (Air Temperature = 35 ° C, Albedo =0.14) • Low Soil Heating Parameters ( Air Temperature = 5° C, Albedo =0.60) • Dry Conditions(Water Input= 0.00 cm ) • No degradation or sorption • Chemical Incorporated Uniformly to 46 cm depth 

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# Phase 2 Case Study Comparison, Overview  

# Compared modeled volatile flux to measured volatile flux in the field  

# Considered bare soil broadcast applications only (no tarps)  

# Evaluated case studies with a mix of shallow and deep incorporation applications  

# Case studies encompassed three field volatility studies done with three soil fumigants 11

# Phase 2 Case Study Comparison, SWCC Application Method Inputs Case Study Modeled Application Method SWCC Demo Chemical A Washington State Multi- Nozzle Shank Injection Uniform Incorporation to 14 inches Chemical B Florida Shank Injection Incorporate Entirely to 5 inches Chemical C Arizona Shank Injection Incorporate Entirely to 13 inches 

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# Phase 2 Case Study Comparison, Preliminary Results

Magnitude Underpredictions : 2.9 1.6 1.8 1.3 963.4 136.1 

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# Addressing Incorporation Depth Issue  

# Underprediction in volatilization with preliminary analysis appears to occur with deep incorporation depths  

# Preliminary analysis modeled entire chemical incorporated “@ depth” for shank injection applications  

# Literature on actual chemical distributions with shank injection applications with fumigants

Figure citation: Guo , M. et al.,2004. Distribution and Leaching of Methyl Iodide in Soil Following Emulated Shank and Drip Application. J. Enviro . Qual. 33: p. 2151 Also referenced: Ajwa . et al., 2002. Application of Alternative Fumigants Through Drip Irrigation Systems. American Phytopathological Society 92: 1349 -1355 Injected Chemical


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# Examining Soil Chemical Distribution, SWCC Inputs
Case Study Modeled Application Method SWCC Demo Chemical B Florida Shank Injection Linearly Increasing to 5 inch Injection Depth Chemical C Arizona Shank Injection Linearly Increasing to 14 inch Injection Depth Atmospheredepth Δ Option for App. Method Injection Depth Soil Chemical Distribution 

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# Examining Soil Chemical Distribution, Results
**Before: @ Depth** 

**After: Δ**  1.8 1.3 963.4 136.1

1.4 1.5 4.8 4.7 Magnitude Underpredictions :

Magnitude Underpredictions : Trace



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# Impact on Aquatic EECs

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### For shank injection cases ran with **Δ** , EECs without volatilization greater than EECs with volatilization for study sites ran with historical weather

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### Reduction in EECs associated with underpredicted volatile loss from soil for these cases produce reasonably conservative EECs **Chemical Case Study**  **SWCC One -** **in -** **Ten Year Surface Water Peak Concentrations**  **(ppb) No**  **Volatilization Volatilization**  Chemical B with Tampa, FL Historical Weather 27.2 14.6 Chemical C with Phoenix, AZ Historical Weather 3.4 x 10 -3 1.1 x 10 -3



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# QA Findings and Conclusions
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# Volatilization algorithm functions sensibly after bug fix  

# Underpredictions in flux occur within 3X of measured values with shallow shank injections and uniformally incorporated applications  

# Large underprediction of flux rates with deep injections of soil fumigant applications when modeled with “@ depth” option
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# Guidance for Soil Applications with Volatilization Algorithm in SWCC
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## Shank injection applications: Recommend “**Δ”** option

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## Consistent with empirical soil chemical distributions from research with deeply- applied soil fumigants

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## Improves agreement in measured flux rates with deeper incorporation depths more common with soil fumigants

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## Impact of initial chemical distribution SWCC input minimal with shallower incorporation depths (< 5 inches), occurring with both soil fumigants and soil - applied conventional chemicals  

## Surface applications: Recommend “Below Crop” default option  

## Recommend use of volatilization algorithm for both soil fumigants and soil - applied conventional chemicals

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## Expected model sensitivity of flux with HLC verified during Phase I of evaluation

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## Modeled flux calculations within acceptable range of measured values in case study comparisons following SWCC guidance above

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## Not recommended for chemicals with HLC< 10 - 6 

## atm•m3 

## / mol 

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# Future Work

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# Corrected version of volatilization algorithm to be released in next version of SWCC  

# Also will be incorporated into PRZM - GW

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# Questions ?

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