Document 6waydRb68eqGwzQ7B85mg8oeR
AR226-2616
4
Draft: Prepared at the Request of Council
AR226-2616
Screening level modeling report which was superceded by ISC modeling report Data and Modeling Procedures
Dispersion modeling was performed using the U.S. EPA's Screens model. This model is a screening tool which gives predictions of ambient ground level concentrations for a single stack. Due to the assumptions made in the model, particularly those regarding meteorological conditions, these predictions will always be more conservative than predictions made by the ISC3 model.
Although there are several different sources of C8 emissions in the Telomers area at the Washington Works site, these emission points are all headered together into a common stack. The following parameters for this stack were used in the model:
Stack Height: 85 feet Diameter: 1.5 feet Temperature: 68F Velocity: 47 ft/s C8 Emission Rate: 0.16 Ib/yr (1.83x10"5 Ib/hr)
The C8 emission rate is based on the maximum production rate for the Telomers area. The basis for the emission calculations is shown in the attached document titled "Calculation of Emissions from the Telomers Process."
To determine the impacts of building downwash on dispersion from the stack, the Screen3 model uses only the dominant downwash structure as an input to the model. The dominant downwash structurecan be found by first locating all buildings which have an area of influence encompassing the stack. The area of influence is defined by EPA as a distance of five times the lesser of the height or the maximum projected width of the building. Once all of the potential downwash structures are located, the dominant downwash structure is determined by calculating the GEP (Good Engineering Practice) stack height for each building. The building with the greatest GEP stack height is the building that should be included in the Screen3 model. The GEP stack height is calculated according to the following formula:
H = h + 1.5L
where H = GEP stack height
h = building height L = lesser of the building height or maximum projected width
The following table shows the buildings that were included in the downwash analysis and their respective GEP's:
Building
Height (ft)
Length (ft)
Width (ft)
Max Projected
Width (ft)
GEP (ft)
164
44
90
90
125
180
64
70
.25
75
184*
96
195
120
230
"This building has the highest GEP and was used in the model.
110 160 240
Modeling Results
Using the above data the Screen3 model predicted a maximum off-site ground level concentration of
0.0023 u.g/m3 at a distance of 289 feet from the source. This concentration is based on a 1-hour averaging time. To convert a Screen3 model result to an annual average, EPA guidance directs the user to multiply
Draft: Prepared at the Request of Council
the predicted Screen3 concentration by a value of 0.05. This gives an annual average concentration of 1.15x10'4 ng/m3. This concentration is four orders of magnitude below the recommended ambient air concentration level in the community. A copy of the Screen3 model output is attached.
Draft: Prepared at the Request of Council
08/01/03
*** SCREENSr MODEL RUN *** *** VERSION DATED 96043 ***
13:17:07
WASHINGTON WORKS TELOMERS EMISSIONS ** 0
SIMPLE TERRAIN INPUTS:
SOURCE TYPE
EMISSION RATE (G/S) STACK HEIGHT (M) STK INSIDE DIAM (M) STK EXIT VELOCITY (M/S)= STK GAS EXIT TEMP (K) AMBIENT AIR TEMP (K) RECEPTOR HEIGHT (M) URBAN/RURAL OPTION BUILDING HEIGHT (M) MIN HORIZ BLDG DIM (M) = MAX HORIZ BLDG DIM (M) =
POINT
.230576E-05 25.9080
.4572 14.3256 293.1500 293.0000
.0000
RURAL
29.2608 36.5760 59.4360
THE REGULATORY (DEFAULT) MIXING HEIGHT OPTION WAS SELECTED. THE REGULATORY (DEFAULT) ANEMOMETER HEIGHT OF 10.0 METERS WAS ENTERED.
BUOY. FLUX =
.004 M**4/S**3; MOM. FLUX = 10.719 M**4/S**2.
*** PULL METEOROLOGY ***
**********************************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF ***
0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES
DIST
(M)
CONC
(UG/M**3)
STAB
U10M (M/S)
USTK
(M/S)
MIX HT
(M)
PLUME HT (M)
SH3MA Y (M)
SK3MA Z (M)
DWASH
10. .0000
0
100. -2091E-02
6
200. 1291E-02
6
300. .8797E-03
6
400. -6730E-03
6
500. 5466E-03
6
600. 4609E-03
6
700. -3988E-03
6
800. 3517E-03
6
900. -3147E-03
6
1000. .2848E-03
6
1100. .2601E-03
6
1200. .2394E-03
6
1300. .2217E-03
6
1400. .2065E-03
6
1500. .1932E-03
6
1600. 1815E-03
6
1700. .1711E-03
6
.0
.0
.0
.00
.00
.00
NA
1.0
1.7 10000.0 26 .21
4 .07 18 .28
SS
1.0
1.7 10000.0 26 .21
7 .73 24 .04
SS
1.0
1.7 10000.0 26 .21 11 .23 30 .17
SS
1.0
1.7 10000.0 26 .21 14 .64 30 .53
SS
1.0
1.7 10000.0 26 .21 17 .97 30 .89
SS
1.0
1.7 10000.0 26 .21 21 .24 31 .25
SS
1.0
1.7 10000.0 26 .21 24 .46 31 .60
SS
1.0
1.7 .10000.0 26 .21 27 .63 31 .95
SS
1.0
1.7 10000.0 26 .21 30 .78 32 .29
SS
1.0
1.7 10000.0 26 .21 33 .88 32 .63
SS
1.0
1.7 10000.0 26 .21 36 .96 32 .96
SS
1.0
1.7 10000.0 26 .21 40 .01 33 .29
SS
1.0
1.7 10000.0 26 .21 43 .04 33 .62
SS
1.0
1.7 10000.0 26 .21 46 .05 33 .94
SS
1.0
1.7 10000.0 26 .21 49 .03 34 .26
SS
1.0
1.7 10000.0 26 .21 51 .99 34 .57
SS
1.0
1.7 10000.0 26 .21 54 .94 34 .89
SS
Draft: Prepared at the Request of Council
1800. 1900. 2000.
.1618E-03 .1534E-03 .1459E-03
1.0
1.7 10000.0 26.21 57.87 35.20
SS
1.0
1.7 10000.0 26.21 60.78 35.50
SS
1.0
1.7 10000.0 26.21 63.68 35.80
SS
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND
10. M:
88. .2254E-02
6
1.0
1.7 10000.0 26.21
3.65 17.65
SS
DWASH= DWASH=NO DWASH=HS DWASH=SS DWASH=NA
MEANS MEANS MEANS MEANS MEANS
NO CALC MADE (CONC = 0.0)
NO BUILDING DOWNWASH USED HUBER-SNYDER DOWNWASH USED
SCHULMAN-SCIRE DOWNWASH USED
DOWNWASH NOT APPLICABLE, X<3*LB
****************************************
*** REGULATORY (Default) ***
PERFORMING CAVITY CALCULATIONS
WITH ORIGINAL SCREEN CAVITY MODEL
(BRODE, 1988)
****************************************
*** CAVITY CALCULATION -
CONC (UG/M**3)
=
CRIT WS @10M (M/S) =
CRIT WS @ HS (M/S) =
DILUTION WS (M/S) =
CAVITY HT (M)
=
CAVITY LENGTH (M) =
ALONGWIND DIM (M) =
1 ***
.8839E-03
1.27 1.54 1.00 38.48 67.12 36.58
"** CAVITY CALCULATION -
CONC (UG/M**3)
=
CRIT WS @10M (M/S) =
CRIT WS @ HS (M/S) =
DILUTION WS (M/S) =
CAVITY HT (M)
=
CAVITY LENGTH (M) =
ALONGWIND DIM (M) =
2 ***
.1001E-02 2.37 2.87 1.44 32.60 48.77 59.44
**************************************** END OF CAVITY CALCULATIONS
****************************************
***************************************
*** SUMMARY OP SCREEN MODEL RESULTS ***
***************************************
CALCULATION PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TER]y^IN
HT (M)
SIMPLE TERRAIN
.2254E-02
88.
0.
BLDG. CAVITY-1
.8839E-03
67.
-- (DIST = CAVITY LENGTH)
BLDG. CAVITY-2
.1001E-02
49.
--
(DIST = CAVITY LENGTH)
********************<
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Note: The off-site concentration referenced in the report is the concentration shown for simple terrain. This concentration is valid for receptor locations near the fenceline since this area is relatively flat. Although the model predicted a building cavity concentration which is higher than the predicted value for simple terrain, this concentration will occur on site and is not applicable for this analysis.