Protocol for the Derivation of Environmental and Human ... - CCME

Appendix G
Table G.1 Continued
? p = pressure difference (kPa)
b c = thickness of cracks (mm)
t c = thickness of slab (m)
A = floor area (m 2 )
µ = viscosity of air (Pa⋅s)
m′ D1 = D s (C sg - C sgs )/L s Eq.(5)
m′ D2 = D c (C sgs - C ba )/L c
where:
m′ D1 = diffusive mass flow rate through soil (mg/m 2 ⋅h)
m′ D2 = diffusive mass flow rate through slab (mg/m 2 ⋅h)
D s = soil diffusivity (m 2 /h)
C sgs = concentration in soil gas below slab (mg/m 3 )
L s = diffusive path length in soil (m)
D c = concrete diffusivity (m 2 /h)
C ba = concentration in building air (mg/m 3 )
L c = diffusive path length in concrete = t c (m)
D s = D a (S a ) 10/3 2
/S p
D c = D a (C a ) 10/3 2
/C p
Eq.(6a)
Eq.(6b)
where:
D a = air diffusivity (m 2 /h)
S a , C a = air content of soil, concrete (unitless)
S p , C p = porosity of soil, concrete (unitless)
m 1 p = m 1 D1 - m′ D2 = C sgs × Q sg Eq.(7)
where:
m 1 p = pressure driven mass flow rate through slab (mg/m 2 ⋅h)
C ba = (m′ D2 + m′ p )/(Q sg + Q f ) Eq.(8)
where:
Q f = flow rate of fresh air through building (m 3 /m 2 ⋅h)
3.3 Derivation of Dilution Factors
Previous experience has indicated that variations in soil conditions (principally porosity, moisture
content, and organic carbon fraction) and depth to contamination have a significant influence on the
relationship between soil vapour concentration and indoor air concentration. It was therefore decided
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