Page 31 - Materials Chemistry, Second Edition

14 Practical Design Calculations for Groundwater and Soil Remediation

(c) Vapor concentration in ppmV:
MW of methylene chloride [CH Cl ] = (12) + (1)(2) + (35.5)(2)
2
2
= 85 g/mole
At T = 20°C and P = 1 atm,
1 ppmV of methylene chloride = (85/24.05) mg/m 3
= 3.53 mg/m 3

Vapor concentration in vol/vol = 7,417 mg/m ÷ [3.53 (mg/m )/
3
3
ppmV] = 2,100 ppmV
∴ It would exceed the PEL and the STEL.
Discussion:
1. Specific gravity is the ratio of the density of a substance to the
density of a reference substance, most commonly water at 4°C (=
1 g/cm = 9.807 kN/m ).
3
3
2. STEL is based on a sampling period of 15 min.
3. This calculation illustrates that a relatively small amount of COC
emission could yield unhealthy air quality.
Example 2.5: Mass and Concentration Relationship

A boy went into a site and played with dirt impacted with ethyl benzene
(C H C H ). During his stay at the site, he inhaled 2 m of air containing 10
3
6
5
5
2
ppbV of ethyl benzene and ingested a mouthful (≈1 cm ) of soil containing 5
3
ppmethyl benzene. Which system (ingestion or inhalation) is exposed to more

ethyl benzene? Assume the total bulk density of soil is equal to 1.8 g/cm .
3
Solution:
(a) Ethyl benzene inhaled
MW of ethyl benzene (C H C H ) = (12)(8) + (1)(10) = 106 g/mole
6
5
2
5
At T = 20°C and P = 1 atm,
10 ppbV of ethyl benzene = (10 × 10 )(106/24.05) mg/m 3
−3
= 0.0441 mg/m 3
Mass of ethyl benzene inhaled
= (air volume)(vapor concentration)
= (2 m )(0.0441 mg/m ) = 0.0882 mg

3
3
(b) Ethyl benzene ingested
= [(soil volume)(total bulk density)](COC concentration in soil)
= [(1 cm )(1.8 g/cm )(1 kg/1,000 g)](5 mg/kg)
3
3
= (1.8 × 10 )(5) = 0.0090 mg
−3
∴ The inhalation system is exposed to more ethyl benzene.