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Statistical Evaluation of Attenuation Factors at Lowry Air Force Base, CO
Helen E. Dawson, PHDRegional Superfund Hydrogeologist
US EPA Region VIIIDenver, CO
AEHS VI Workshop October 2004
LAFB TCE PlumeOff-Site TCE Plume
MW0B21
MW0B04
CP-56
Figure 1
DateTCE
(ug/L)Aug-98 140Apr-00 160 JJun-00 170 JSep-00 150 JNov-00 124Dec-00 75Feb-00 140
N
N”
N
N”
Study Area
LAFB Cross-Section
Depth to groundwater: 6 m
Vadose zone: fining upwards sequence; sand and gravels to sandy
silts.
Saturated zone: sands and gravels
Residential AreaBase
LAFB Soil Gas
Study Area
LAFBIndoor Air & Foundation Vapor
0.01
0.1
110
100
1000
Ne
w P
rov
isio
na
lT
ox
icit
y V
alu
es
Old
Pro
vis
ion
al
To
xic
ity
Va
lue
s
CD
PH
E T
CE
Po
licy
Ca
l EP
A N
SR
L-C
hro
nic
RE
L
De
nv
er
Ho
me
s
AT
SD
R 2
00
2
UA
03
UA
22
UA
04
UA
18
UA
21
UA
23
UA
24
UA
19
TC
E C
on
ce
ntr
ati
on
(u
g/m
3)
TCE ConcentrationsRegulatory Levels Backgroun
dLowry Air Force Residences
Full Basemen
t
½ Basement½ Crawlspace Slab
Sampling Methods Indoor and ambient air:
24-hour Summa; TO15S
Subslab: Summa after 2 L purge; TO15S
Groundwater: Bailer; 8260S
Chemicals 11DCA 1,1-Dichloroethane 12DCA 1,2-Dichloroethane 11DCE 1,1-Dichloroethene C12DCE cis-1,2-Dichloroethene T12DCE trans-1,2-
Dichloroethene PCE Tetrachloroethene 111TCA 1,1,1-Trichloroethane 112TCA 1,1,2-Trichloroethane TCE Trichloroethene VC Vinyl Chloride
Attenuation Factors Calculated
Groundwater to indoor air (GW-IA)
Groundwater to subslab (GW-SS)
Subslab to indoor air (SS-IA)
Data Quality Filters Data excluded if:
GW, SS, or IA value < detection limit IA conc. > subslab conc. IA conc. < OA conc. (IA – OA)/IA < 20%
Chemicals filtered out: 12DCA, T12DCE, 112TCA
Groundwater to Subslab Attenuation Factors
LAFB: UA21
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
SS
Alp
ha
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA18
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
SS
Alp
ha
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA23
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
SS
Alp
ha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA24
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
SS
Alp
ha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
Groundwater to Subslab Attenuation Factors
Groundwater-to-Subslab Alphas
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
UA03 UA22 UA04 UA18 UA21 UA23 UA24 UA19
Full Basement Half Basement, Half Crawlspace
Slab onGrade
Subslab to Indoor Air Attenuation Factors
LAFB: UA21
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
SS IA
Alp
ha
TCE
PCE
111TCA
LAFB: UA18
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
SS IA
Alp
ha
TCE
PCE
111TCA
LAFB: UA23
1.0E-061.0E-051.0E-041.0E-031.0E-021.0E-011.0E+001.0E+011.0E+02
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
SS IA
Alp
ha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA24
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
IA A
lpha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
Subslab to Indoor Air Attenuation Factors
Subslab-to-Indoor Air Alphas
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
UA03 UA22 UA04 UA18 UA21 UA23 UA24 UA19
Full Basement Half Basement, Half CrawlspaceSlab onGrade
Groundwater to Indoor AirAttenuation Factors
LAFB: UA23
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
IA A
lpha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA24
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
IA A
lpha
11DCE
TCE
PCE
c12DCE
11DCA
111TCA
LAFB: UA21
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
IA A
lpha
TCE
PCE
111TCA
LAFB: UA18
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
Mar-00 J un-00 Sep-00 Dec-00 Mar-01
Sample Date
GW
IA A
lpha
TCE
PCE
111TCA
Groundwater to Indoor AirAttenuation Factors
Groundwater-to-Indoor Air Alphas
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
UA03 UA22 UA04 UA18 UA21 UA23 UA24 UA19
Full Basement Half Basement, Half CrawlspaceSlab onGrade
Q4 Generic AlphaQ5 Alpha
Comparison with Figure 3(b)of EPA’s VI Guidance
Figure 3b- DRAFTVapor Attenuation Ratios -
Ground Water to Indoor Air Pathway Basement Foundations
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
0 5 10 15 20 25 30
Depth to Contamination from Foundation (m)
Vapor A
ttenuatio
n F
acto
r
SandLoamy SandSandy LoamLoam
