75th Air Base Wing. Comparison of CALPUFF and OBODM for Open Burn/Open Detonation Modeling. 22 May Mark Bennett, Ph.D.

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1 75th Air Base Wing Comparison of CALPUFF and OBODM for Open Burn/Open Detonation Modeling 22 May 2007 Mark Bennett, Ph.D. CH2M Hill, Inc Joint Services Environmental Management Conference and Exposition Columbus, Ohio 1

2 Co-authors Glenn Palmer Hill Air Force Base, UT Mitchell Lindsay CH2M Hill, Inc Andrea White CH2M Hill, Inc Chris Merrill CH2M Hill, Inc Sara Van Klooster CH2M Hill, Inc 2

3 Outline Background Goal and Objective Methods Results Conclusion 3

4 Background Hazardous waste combustors require a RCRA permit (40 CFR Part 264) Guidance provided in Final Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities (HHRAP), EPA, September 2005 HHRAP Chapter3: Air Dispersion and Deposition Modeling Written primarily with application to incinerators Recommends use of ISCST3 Not appropriate for Open Burn/Open Detonation events (lacks buoyant area or volume source capabilities) Typically the Open Burn/Open Detonation Dispersion Model (OBODM) is used (an alternative EPA model) 4

5 Background OBODM OBODM is intended for use in evaluating the potential air quality impacts of the open-air burning and detonation (OB/OD) of obsolete munitions and solid propellants. OBODM uses cloud/plume rise, dispersion, and deposition algorithms taken from existing models (e.g., REEDM and the original ISC) for instantaneous and quasi-continuous sources to predict the downwind transport and dispersion of pollutants released by OB/OD operations. The model can be used to calculate peak concentration, time-mean concentration, dosage (time-integrated concentration), and particulate gravitational deposition for emissions from multiple OB/OD sources for either a single event or up to a year of sequential hourly source and meteorological inputs. 5

6 Background OBODM While OBODM has algorithms for OB and OD events, it does have some limitations: Complex terrain option cannot be used when calculating concentration with gravitational deposition occurring or gravitational deposition for particulates with appreciable settling velocities older, gravitational settling method used for dry deposition cannot calculate wet deposition limited number of gridded receptors discrete receptors must be entered by hand, thus greater opportunity for error cont. 6

7 Background CALPUFF CALPUFF is EPA preferred model for long-range transport (>50 km) and case-by-case for complex wind fields Non-steady state Puff Model (CALPUFF) causality stagnation flows Standard use with Diagnostic Meteorological Model (CALMET) However, can be used with augmented ISC met file or AERMOD met file Includes special option for time varying buoyant area sources (designed for forest fires) both wet and dry deposition 7

8 Background OBODM and CALPUFF Lite used to evaluate the air concentration and deposition values from the detonation of representative Trident C4 motors at the UTTR. Two phases of analysis Phase I: Use CALPUFF in screening mode and OBODM to model the Open Detonation (OD) of C4 with varying Net Explosive Weights (NEW) Phase II: Use CALPUFF in screening mode and OBODM to model OD events with varying particle size distributions 8

9 Goal The goal of the present study was to evaluate CALPUFF as an alternative to OBODM for the air dispersion modeling for Open Burn/Open Detonation events. 9

10 Objectives Use OBODM and CALPUFF to model the impacts of the emissions from open detonation events with parameters representative of the Thermal Treatment Unit (TTU) at Utah Test and Training Range (UTTR). 10

11 Methods Meteorological Data Same met file will be used in both OBODM and CALPUFF Lite 2004 meteorological data from the onsite TTU surface station most complete set of data available at this time Since most interested in a comparison between the two models - filled in the missing onsite wind direction, wind speed, temperature, stability class, and mixing height data with Salt Lake City data The EPA PCRAMMET processor used to combine with upper air data from Salt Lake City Extended records for use in CALPUFF 11

12 Methods Meteorological Data ISCMET.DAT (CALPUFF) Hourly values (standard records) wind speed, flow direction temperature, stability class mixing height for rural/urban Hourly values (extended record) surface friction velocity Monin-Obukhov length surface roughness precipitation code and rate others not used 12

13 Methods Receptor Grid 20km by 20km with a 500 meter spacing All of the vapor phase impacts will be evaluated using terrain-adjusted receptors for both models OBODM cannot model particle phase impacts with complex terrain or elevated terrain, therefore, for OBODM, all particle phase impacts will be evaluated in flat terrain CALPUFF Lite results for terrain adjusted receptors for both vapor and particle phase 13

14 Methods Source Terms FOR BOTH OBODM & CALPUFF LITE Detonation events can only occur between 10am and 4pm Particle phase pollutant will be modeled as Aluminum Oxide Vapor phase pollutant will be modeled as Carbon Monoxide Heat released during detonation of C4 motors calculated from POLU4WN CO and Al 2 O 3 emission rates calculated from POLU4WN Detonation time of 2.5 seconds (default value for OBODM for detonation) CO emission rate: 1.4E-06 lbs of CO per lb of NEW Al 2 O 3 emission rate: 0.4 lbs of Al 2 O 3 per lb of NEW 14

15 Methods OBODM Source Terms OBODM Source Terms (entered directly) NEWs (lbs): 3,000; 17,000; 39,000; 81,000 Heat content: 2448 cal/g from POLU Locations (NAD 1927): UTMX , UTMY Source Elevation: 1431 meters Dimensions: 8 ft by 10 ft (only for burn) Events cannot occur when wind speeds are less than 1.3 m/s 15

16 Methods CALPUFF Source Terms CALPUFF Buoyant Area Source Emission File (BAEMARB.DAT) Area of the source Based off of the observed initial plume radius Horizontal radius of plume Experimental data indicates that an 81,000 lb NEW detonation results in an initial horizontal radius of approx 150 meters. Assuming that the initial puff is a hemisphere, the corresponding volume was calculated. The plume volumes were scaled linearly by total mass and the effective radius was calculated for each NEW. Initial Vertical Spread Vertical radius of the puff is approximately half the horizontal radius Detonation Duration For consistency, OBODM default of 2.5 seconds used Initial Release Height Midpoint of the initial vertical spread 16

17 Methods CALPUFF Source Terms CALPUFF Buoyant Area Source Emission File (BAEMARB.DAT) - continued Initial Vertical Velocity Initial puff vertical velocity was calculated using the plume buoyancy flux equation and the heat flux equation Emission Rate Data from POLU4WN Puff Temperature Final temperature of the puff calculated using heat balance between the puff before and after the entrainment of ambient air. Initial specific volume and temperature of the puff based on POLU4WN. Initial mass assumed stoichiometric combustion of the total NEW. The final volume was from observational data. The difference in the initial mass and the final mass was assumed to be from entrainment of ambient air. 17

18 Methods Phase II Five log-normal particle size distributions were chosen to span range of expected particle sizes Minimum Diameter (μm) Maximum Diameter (μm) Average Diameter (μm) Geometric Standard Deviation (μm) Geometric Mass Diameter (μm)

19 Results - General Both sets of concentration contours consistent with windroses; however, show differences consistent with plume model vs puff model Location of maximums generally do not agree Generally, OBODM maximums greater than CALPUFF Lite maximums CALPUFF Lite wet deposition approx twice CALPUFF Lite dry deposition 19

20 Results Phase I Ratio of OBODM / CALPUFF concentrations Timeweighted average Vapor Phase Particle Phase 17,000 lb 81,000 lb 17,000 lb 81,000 lb 1 hour 24 hour Annual

21 Results Phase I: Vapor Phase 21

22 Results Phase I: Particle Phase 22

23 Results Phase I Comparison of Maximums for Dry and Wet Deposition Timeweighted average OBODM Dry / CALPUFF Dry CALPUFF Wet / CALPUFF Dry 17,000 lb 81,000 lb 17,000 lb 81,000 lb 1 hour 24 hour Annual

24 Results Phase I: Dry Deposition 24

25 Results Phase I: Wet vs Dry Deposition 25

26 Results Phase II Ratio of Max Particulate Concentrations: OBODM / CALPUFF 17,000 NEW Timeweighted average hour hour Annual

27 Results Phase II Ratio of Max Particulate Concentrations: OBODM / CALPUFF 81,000 NEW Timeweighted average hour hour Annual

28 Results Phase II Ratio of Max Dy Deposition: OBODM / CALPUFF 17,000 NEW Timeweighted average hour hour Annual

29 Results Phase II Ratio of Max Dy Deposition: OBODM / CALPUFF 81,000 NEW Timeweighted average hour hour Annual

30 Results Phase II Ratio of Max Wet Deposition to Dry Deposition (CALPUFF Lite) 17,000 NEW Timeweighted average hour hour Annual

31 Results Phase II Ratio of Max Wet Deposition to Dry Deposition (CALPUFF Lite) 81,000 NEW Timeweighted average hour hour Annual

32 Results Phase II: OBODM 32

33 Results Phase II CALPUFF Lite 33

34 Results Phase II: Wet vs Dry 34

35 Conclusions Even for small grid, refinement of puff model over plume model significant Refinement that allows terrain effects for particle phase also significant Refinement that allows wet deposition significant even for relatively dry climate More realistic results likely justify slight increase in level of effort 35

36 Conclusions - continued Variations in concentrations small as a function of particle sizes However, large variations in both wet and dry deposition Impacts of further refinement to full CALPUFF worth examining 36

37 Questions? 37