No Slide Title

							 Empirical Attenuation Factors
 Predictions & Observational Data

Helen Dawson, Ph.D.   Ian Hers, Ph.D.         Robert Truesdale
US EPA Region VIII    Golder Associates       RTI International
Denver, CO            Vancouver, BC, Canada   RTP, North Carolina




                                                                    1
Empirical Attenuation Factors

   2001-2002 Evaluations (Helen Dawson)

   2004 Evaluations (Ian Hers)

   Future Evaluations (Robert Truesdale)


                                            2
Measured Attenuation Factors
2001-2002 Database Summary
   15 sites, 15 VOCs, 274 total residence/chemical
    combinations

   35 BTEX; 239 CHC residence/chemical combinations

   99 sites with IA > 10-6 IA RBC
    (84 CHC, 14 BTEX)

   68 sites with IA > 10-5 IA RBC


                                                      3
2001 – 2002 Empirical Attenuation Factors
Groundwater-to-Indoor Air
              All residences and chemicals with concentrations above MDLs

                              Measured Groundwater-Indoor
                                 Air Attenuation Factors
              45                                                                                            120%
              40
                                                                                                            100%
              35
  Frequency




              30                                                                                            80%
              25
                                                                                                            60%
              20
              15                                                                                            40%
              10
                                                                                                            20%
               5
               0                                                                                            0%
                   1.00E-07


                               1.00E-06


                                          1.00E-05


                                                     1.00E-04


                                                                1.00E-03


                                                                           1.00E-02


                                                                                      1.00E-01


                                                                                                 1.00E+00
                                                                                                                   4
Factors evaluated (2001 – 2002)
   Chemical type

   Foundation type

   Soil type

   Depth to source
                              5
2001 – 2002 Empirical Attenuation Factors
Chlorinated Hydrocarbons vs. BTEX
                                          Measured Attenuation Factors
                                           Groundwater to Indoor Air

                              1

                             0.1
  Attenuation Factor




                            0.01
                                                                          IA BTEX > 10-6
                           0.001

                          0.0001                                          IA CHC > 10-6

                         0.00001

                        0.000001

                       0.0000001
                                   0%   20%   40%     60%    80%   100%
                                              Cumulative %


                                                                                           6
2001 – 2002 Empirical Attenuation Factors
Influence of Foundation Structure?
                                                    Database
                                                 Groundwater
                            10000000
 Groundwater Source Vapor




                             1000000
                                                                           Basement
                              100000
                                                                           Crawlspace
         (ug/m3)




                               10000                                       Slab on Grade
                                1000                                       1:1
                                 100

                                  10

                                   1
                                    0.01   0.1     1    10    100   1000
                                             Indoor Air (ug/m3)


                                                                                           7
2001 – 2002 Empirical Attenuation Factors
Influence of Foundation Structure?
                                       Lowry Air Force Base
                                     Foundation Vapor vs Indoor Air
                         10000
 Subslab or Crawlspace




                          1000

                           100
                                                                        Basement
        (ug/m3)




                            10                                          Crawlspace
                                                                        1:1
                             1

                           0.1

                          0.01
                              0.01    0.1        1        10      100
                                         Indoor Air (ug/m3)


                                                                                     8
2001 – 2002 Empirical Attenuation Factors
Influence of Soil Type?
                                                    Database
                           10000000
Groundwater Source Vapor




                           1000000

                            100000                                               Silts & Clays
        (ug/m3)




                             10000                                               Sands
                                                                                 1:1
                              1000

                               100

                                10

                                 1
                                  0.01   0.1        1     10        100   1000

                                               Indoor Air (ug/m3)

                                                                                                 9
2001 – 2002 Empirical Attenuation Factors
Depth to Groundwater?
                                   Groundwater Indoor Air Attenuation Factor
                                           Versus Depth to Water
                            10000000
   1 / Attenuation Factor




                             1000000

                              100000

                               10000
                                                                                      Sands
                                                                                      Silts & Clays
                                1000

                                 100

                                  10

                                   1
                                       0.0   2.0    4.0   6.0   8.0     10.0   12.0
                                                   Depth to Water (m)

                                                                                                      10
2001 – 2002 Empirical Attenuation Factors
Conclusions
   Measured attenuation factors range from 10-2
    to 10-7 with median values around 10-4.

   Influence of foundation type, soil type, and
    depth to water on the empirical attenuation
    factors is unclear.

   Higher ranges of attenuation factors are
    observed for BTEX compounds; median value
    is around 10-5.
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