Example Problem:  Calculate Air Pollutant Concentrations Downwind

                                     of Air Stripper of Contaminated Groundwater

 

Given:  Air Toxic Emission Rates for Air Stripper of Groundwater proposed for

            construction in Kent-Auburn area (South King County, Washington State).

 

Pollutant

  CAS

  Q (grams/sec)

Type

ASIL (micrograms/m3)

Vinyl Chloride

  75-01-4

   0.05

   A

   0.012

 

The above ASIL for vinyl chloride was obtained from a Puget Sound Clean Air Agency web site:

    http://www.pscleanair.org/regulated/businesses/regulations.aspx

    http://www.pscleanair.org/regulated/reg3/asil.pdf

 

Washington State type A air toxics are carcinogens.  ASIL = "acceptable source impact level" concentration of air pollutant in the atmospheric air.  Most other states use "AAL" or "acceptable ambient air".  The averaging time for type A ASILs is the annual arithmetic mean (or annual average).

            Stack Height                          20 ft                6.096 meters

            Stack Inside Diameter           2 ft                  0.6096 meters

            Stack gas exit velocity           10 ft/sec          3.08 m/sec

            Stack gas temperature          68oF                20oC=293.33oK

            Ambient air temperature      68oF                20oC=293.33oK

            Receptor Height                    4.92 ft             1.5 meters

            Land is flat terrain in Kent-Auburn Area (use Rural option)

            Building Height                     12 ft                3.658 m

            Building Width                        8 ft                2.438 m

            Building Length                    16 ft                4.877 m

            Distance between stack base and fence       2 m

 

Find:   Use SCREEN3 or TSCREEN to find the downwind air pollutant concentrations.  Note that the stack is not at the "Good Engineering Practice" height so there will be plume downwash.

_-______________________________________________________________________________________________________________________________________________________________

 

 ***  SCREEN3 MODEL RUN  ***  *** VERSION DATED 95250 *** 10/07/07  

                                                                               

 Vinyl Chloride GroundWater Air Stripper       10/7/07 

                                                                                

 SIMPLE TERRAIN INPUTS:                                       

    SOURCE TYPE            =        POINT                     

    EMISSION RATE (G/S)    =      .500000E-01                  

    STACK HEIGHT (M)       =       6.0960                       

    STK INSIDE DIAM (M)    =        .6096                        

    STK EXIT VELOCITY (M/S)=       3.0800                    

    STK GAS EXIT TEMP (K)  =     293.3300                    

    AMBIENT AIR TEMP (K)   =     293.3300                      

    RECEPTOR HEIGHT (M)    =       1.5000                    

    URBAN/RURAL OPTION     =        RURAL                         

    BUILDING HEIGHT (M)    =       3.6580                     

    MIN HORIZ BLDG DIM (M) =       2.4380                        

    MAX HORIZ BLDG DIM (M) =       4.8770                     

 

 

 

 

 

 

      ***************************************                                  

      *** SUMMARY OF SCREEN MODEL RESULTS ***                                  

                                                                                

  CALCULATION      MAX CONC   DIST TO   TERRAIN                        

   PROCEDURE      (UG/M**3)   MAX (M)   HT (M)                       

 --------------  -----------  -------  -------                       

 SIMPLE TERRAIN    291.4          11.       0.                       

                                                                     

 BLDG. CAVITY-1    987.8           9.     --  (DIST = CAVITY LENGTH)

 BLDG. CAVITY-2    527.4           3.     --  (DIST = CAVITY LENGTH)

                                                                               

                                                                               

 BUOY. FLUX =     .000 M**4/S**3;  MOM. FLUX =     .881 M**4/S**2.             

                                                                               

 *** FULL METEOROLOGY ***                                                      

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 *** SCREEN AUTOMATED DISTANCES ***                                            

 **********************************                                            

                                                                                

 *** TERRAIN HEIGHT OF    0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***

                                                                               

  DIST     CONC          U10M   USTK  MIX HT  PLUME    SIGMA  SIGMA       

   (M)  (UG/M**3  STAB   (M/S)  (M/S)  (M)    HT (M)   Y (M)  Z (M)  DWASH 

    2.   .0000     1     1.0    1.0   320.0   11.73    1.02     .74   NO 

  100.   99.18     6     2.5    2.5 10000.0    8.02    4.12    5.40  Yes  HS

  200.   72.68     6     1.5    1.5 10000.0    9.85    7.80    6.88  Yes  HS

  300.   56.21     6     1.5    1.5 10000.0    9.85   11.28    8.23  Yes  HS

  400.   52.64     6     1.0    1.0 10000.0   10.53   14.69    7.16   NO 

  500.   48.66     6     1.0    1.0 10000.0   10.53   18.01    8.49   NO 

  600.   42.93     6     1.0    1.0 10000.0   10.53   21.27    9.77   NO 

  700.   37.35     6     1.0    1.0 10000.0   10.53   24.49   11.00   NO 

  800.   32.54     6     1.0    1.0 10000.0   10.53   27.66   12.04   NO 

  900.   28.54     6     1.0    1.0 10000.0   10.53   30.80   13.04   NO 

                                                                               

 MAXIMUM 1-HR CONCENTRATION AT OR BEYOND     2. M:                        

  11.   291.4      6     4.0    4.0 10000.0   6.11    .62    2.64   Yes HS 

                                                                               

                                                                               

  *** CAVITY CALCULATION - 1 ***       *** CAVITY CALCULATION - 2 ***          

   CONC (UG/M**3)     =    987.8        CONC (UG/M**3)     =    527.4          

   CRIT WS @10M (M/S) =     3.78        CRIT WS @10M (M/S) =    14.17          

   CRIT WS @ HS (M/S) =     3.78        CRIT WS @ HS (M/S) =    14.17          

   DILUTION WS (M/S)  =     1.89        DILUTION WS (M/S)  =     7.09          

   CAVITY HT (M)      =     6.12        CAVITY HT (M)      =     4.69          

   CAVITY LENGTH (M)  =     8.62        CAVITY LENGTH (M)  =     3.06          

   ALONGWIND DIM (M)  =     2.44        ALONGWIND DIM (M)  =     4.88          

 

 Note that the concentrations in cavity exceed those at 11 m downwind.

*** USER SPECIFIED AVERAGING TIMES ***

    ESTIMATED MAXIMUM CONCENTRATION FOR 24 HR AVERAGING TIME:

     116.56 (+/- 58.28) UG/M**3

  Where is this 24 hr maximum concentration located? 

   At x = 11 m or in the building cavity?

   1 hr max conc = (116.56 ug/m3)/0.4 = 291.4 ug/m3 = conc at x = ll m

 

    ESTIMATED MAXIMUM CONCENTRATION FOR ANNUAL AVERAGING TIME:

      23.312 (+/- 5.828) UG/M**3

 

   Note ASIL = 0.012 for ug/m3 vinyl chloride annual average

 

 

 

  DIST    = DISTANCE FROM THE SOURCE                                           

  CONC    = MAXIMUM GROUND LEVEL CONCENTRATION                                  

  STAB    = ATMOSPHERIC STABILITY CLASS (1=A, 2=B, 3=C, 4=D, 5=E, 6=F)         

  U10M    = WIND SPEED AT THE 10-M LEVEL                                       

  USTK    = WIND SPEED AT STACK HEIGHT                                          

  MIX HT  = MIXING HEIGHT                                                      

  PLUME HT= PLUME CENTERLINE HEIGHT                                            

  SIGMA Y = LATERAL DISPERSION PARAMETER                                       

  SIGMA Z = VERTICAL DISPERSION PARAMETER                                      

  DWASH   = BUILDING DOWNWASH:                                                 

            DWASH=   MEANS NO CALC MADE (CONC = 0.0)                           

            DWASH=NO MEANS NO BUILDING DOWNWASH USED                           

            DWASH=HS MEANS HUBER-SNYDER DOWNWASH USED                          

            DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED                        

            DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB                     

 

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*** END OF SCREEN MODEL OUTPUT ***

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