Sample calculations are provided in EPA document No. EPA/625/3-89/016, March 1989, incorporated by reference in s.
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Reference: Adapted from NATO/CCMS, 1988a.
1Interim Procedures for Estimating Risks Associated with Exposures to Mixtures of Chlorinated Dibenzo-p-Dioxins and Dibenzofurans (CDDs and CDFs) 1989 Update EPA/625/3-89/016, March 1989, incorporated by reference in s.
NR 660.11.
Section 5.0 Hazardous Waste Combustion Air Quality Screening Procedure
The HWCAQSP is a combined calculation/reference table approach for conservatively estimating short-term and annual average facility impacts for stack emissions. The procedure is based on extensive short-term modeling of 11 generic source types and on a set of adjustment factors for estimating annual average concentrations from short-term concentrations. Facility impacts may be determined based on the selected worst-case stack or on multiple stacks, in which the impacts from each stack are estimated separately and then added to produce the total facility impact.
This procedure is most useful for facilities with multiple stacks, large source-to-property boundary distances, and complex terrain between one and 5 km from the facility. To ensure a sufficient degree of conservatism, the HWCAQSP may not be used if any of the 5 screening procedure limitations listed below are true:
• The facility is located in a narrow valley less than 1 km wide;
• The facility has a stack taller than 20 m and is located such that the terrain rises to the stack height within 1 km of the facility;
• The facility has a stack taller than 20 m and is located within 5 km of the shoreline of a large body of water;
• The facility property line is within 200 m of the stack and the physical stack height is less than 10 m; or
• On-site receptors are of concern, and stack height is less than 10 m.
If any of these criteria are met or the department determines that this procedure is not appropriate, then detailed site-specific modeling or modeling using the “Screening Procedures for Estimating the Air Quality Impact of Stationary Sources," EPA -450/4-88-010, Office of Air Quality Planning and Standards, August 1988, incorporated by reference in s.
NR 660.11, is required. Detailed site-specific dispersion modeling shall conform to the EPA “Guidance on Air Quality Models (Revised)", EPA 450/2-78-027R, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina, July 1986, incorporated by reference in s.
NR 660.11. This document provides guidance on both the proper selection and regulatory application of air quality models.
Introduction
The Hazardous Waste Combustion Air Quality Screening Procedure (HWCAQSP) (also referred to hereafter as “the screening procedure" or “the procedure") provides a quick, easy method for estimating maximum (hourly) and annual average ambient air impacts associated with the combustion of hazardous waste. The methodology is conservative in nature and estimates dispersion coefficients2 based on facility-specific information.
Note: 2 The term dispersion coefficient refers to the change in ambient air concentration (mg/m 3) resulting from a source with an emission rate of 1 g/sec.
The screening procedure can be used to determine emissions limits at sites where the nearest meteorological (STAR) station is not representative of the meteorology at the site. If the screen shows that emissions from the site are adequately protective, then the need to collect site-specific meteorological data can be eliminated.
The screening procedure is generally most helpful for facilities meeting one or more of the following conditions:
• Multiple stacks with substantially different release specifications (e.g., stack heights differ by >50%, exit temperatures differ by >50 °K, or the exit flow rates differ by more than a factor of 2),
• Terrain located between 1 km and 5 km from the site increases in elevation by more than the physical height of the shortest stack (i.e., the facility is located in complex terrain), or
• Significant distance between the facility's stacks and the site boundary [guidance on determining whether a distance is “significant" is provided in Step 6(B) of the procedure].
Steps 1 through 9 of the screening procedure present a simplified method for determining emissions based on the use of the “worst-case" stack. If the simplified method shows that desired feed rates result in emissions that exceed allowable limits for one or more pollutants, a refined analysis to examine the emissions from each stack can be conducted. This multiple-stack method is presented in Step 10.
The steps involved in screening methodology are as follows:
Step 1. Define Source Characteristics
Step 2. Determine the Applicability of the Screening Procedure
Step 3. Select the Worst-Case Stack
Step 4. Verify Good Engineering Practice (GEP) Criteria
Step 5. Determine the Effective Stack Height and Terrain-Adjusted Effective Stack Height
Step 6. Classify the Site as Urban or Rural
Step 7. Determine Maximum Dispersion Coefficients
Step 8. Estimate Maximum Ambient Air Concentrations
Step 9. Determine Compliance With Regulatory Limits
Step 10. Multiple Stack Method
Step 1: Define Source Characteristics
Note:
3 Worksheet space is provided for three stacks. If the facility has additional stacks, copy the form and revise stack identification numbers for 4, 5, etc.
Nearby Building Dimensions
Consider all buildings within 5 building heights or 5 maximum projected widths of the stack(s). For the building with the greatest height, fill in the spaces below. Building Height (m) _____ Maximum projected building width (m) _____
Nearby Terrain Data
Determine maximum terrain rise for the following 3 distance ranges from the facility (not required if the highest stack is less than 10 m in height):
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Distance from facility to nearest shoreline (km) _____
Valley width (km) _____
Step 2: Determine the Applicability
of the Screening Procedure
If the answer is “no" to all the preceding questions, then the HWCAQSP is acceptable. If the answer to any question is “yes", the procedure is not acceptable.
Step 3: Select the Worst-Case Stack
If the facility has several stacks, a worst-case stack shall be chosen to conservatively represent release conditions at the facility. Follow the steps below to identify the worst-case stack.
Apply the following equation to each stack:
K = HVT
where:
K=an arbitrary parameter accounting for the relative influence of the stack height and plume rise.
H=Physical stack height (m)
V=Flow rate (m 3/sec)
T=Exhaust temperature (°K)
Complete the following table to compute
the “K" value for each stack:
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Select the stack with the lowest “K" value. This is the worst-case stack that will be used for Steps 4 through 9.
Worst-Case Stack is identified as Stack No. ___
Step 4: Verify Good Engineering
Practice (GEP) Criteria
Confirm that the selected worst-case stack meets Good Engineering Practice (GEP) criteria. The stack height to be used in the subsequent steps of this procedure may not be greater than the maximum GEP. Maximum and minimum GEP stack heights are defined as follows:
CEP (minimum)=H+(1.5×L)
GEP (maximum)=greater of 65 m or H+(1.5×L)
where:
H=height of the building selected in Step 1 measured from ground level elevation at the base of the stack
L=the lesser dimension of the height or projected width of the building selected in Step 1
Record the following data for the worst-case stack:
Stack height (m) =_____
H(m) =_____
L(m) =_____
Then compute the following:
GEP (minimum) (m)=_____
GEP (maximum) (m)=_____
• If the physical height of the worst-case stack exceeds the maximum GEP, then use the maximum GEP stack height for the subsequent steps of this analysis;
• If the physical height of the worst-case stack is less than the minimum GEP, then use generic source number 11 as the selected source for further analysis and proceed directly to Step 6;
• If the physical height of the worst-case stack is between the minimum and maximum GEP, then use the actual physical stack height for the subsequent steps of this analysis.
Step 5: Determine the Effective Stack Height and the Terrain-Adjusted Effective Stack Height (TAESH)
The effective stack height is an important factor in dispersion modeling. The effective stack height is the physical height of the stack plus plume rise. As specified in Step 4, the stack height used to estimate the effective stack height may not exceed GEP requirements. Plume rise is a function of the stack exit gas temperature and flow rate.
In this analysis, the effective stack height is used to select the generic source that represents the dispersion characteristics of the facility. For facilities located in flat terrain and for all facilities with worst-case stacks less than or equal to 10 meters in height, generic source numbers are selected strictly on the basis of effective stack height. In all other cases, the effective stack height is further adjusted to take into account the terrain rise near the facility. This “terrain-adjusted effective stack height" (TAESH) is then used to select the generic source number that represents the dispersion characteristics of the facility. Follow the steps below to identify the effective stack height, the TAESH (where applicable), and the corresponding generic source number.
(A) Go to Table 5.0-1 and find the plume rise value corresponding to the stack temperature and exit flow rate for the worst-case stack determined in Step 3.
Plume rise =____(m)
(B) Add the plume rise to the GEP stack height of the worst-case stack determined in Steps 3 and 4.
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(C) Go to the first column of Table 5.0-2 and identify the range of effective stack heights that includes the effective stack height estimated in Step 5(B). Record the generic source number that corresponds to this range.
Generic source number = _____
(D) If the source is located in flat terrain4, or if the generic source number identified in Step 5(C) above is 1 or 11 (regardless of terrain classification), use the generic source number determined in Step 5(C) and proceed directly to Step 6. Otherwise, continue to Step 5(E).
Note: 4 The terrain is considered flat and terrain adjustment factors are not used if the maximum terrain rise within 5 km of the facility (see Step 1) is less than 10 % of the physical stack height of the worst-case stack.
(E) For those situations where the conditions in Step 5(D) do not apply, the effective stack height shall be adjusted for terrain. The TAESH for each distance range is computed by subtracting the terrain rise within the distance range from the effective stack height.5
Note: 5 Refer to Step 1 for terrain adjustment data. Note that the distance from the source to the outer radii of each range is used. For example, for the range >0.5-2.5 km, the maximum terrain rise in the range 0.0-2.5 km is used.
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1EPA, Guideline on Air Quality Models (Revised), EPA-450/2-78-027R, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina, July, 1986, incorporated by reference in s.
NR 660.11.
2Auer, August H. Jr., ``Correlation of Land Use and Cover with meteorological Anomalies,'' Journal of Applied Meteorology, pp. 636-643, 1978.
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If the terrain rise for any of the distance ranges is greater than the effective stack height, set the TAESH equal to 0 and use generic source number one for that distance range.
Record the generic source numbers from Table 5.0-2 based on each of the TAESH values.
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