Quiz Solution1 ug/L benzene = ? ppbv

For gases, RT = 24 liters/mole at 20C

How to go from volume to mass?

Ug/L = mass/volume

ppbv = volume/volume

PV=nRT so V= nRT/P

n = 1/MW For benzene, MW=78

V = (1/MW)*RT = 24/78 = 0.325 ppmv *1000 =325 ppbv

Solution to Consultant’s Report

SG screening level (from table) = 36.2 ug/m3

0.005 ppmv = 5 ppbv * (78/24.0) = 16 ug/m3

SS screening level = 0.084/0.05 = 1.68 ug/m3

Lab report level (MDL):

Lab report level > SS screening level, hence consultant conclusion incorrect

SG screening level (from att factor) = 0.084/0.002 = 42 ug/m3

Solution - GW Data Exercise

TCE in soil gas ~= 50 µg/L x 0.5 = 25 ug/L = 25,000 ug/m3

TCE in indoor air ~= 25,000 ug/m3 x 0.001 = 25 ug/m3

Residential Setting, allowed Cindoor = 2.1 µg/m3

Does TCE exceed allowable value?

YES, by over 10xx

Is vapor intrusion likely occurring?

Possible.

Why? Predicted value likely overestimated but must test to be sure

Solution - Soil Gas Data Exercise

Benzene indoor air ~= 6 µg/L x 0.002 = 0.012 ug/L = 12 ug/m3

Commercial Receptor, allowed Cindoor= 15 µg/m3

Does the benzene value exceed allowable value?

No

Is vapor intrusion likely occurring?

Probably not

Why? Predicted value likely to be lower than 12 ug/m3 due to non-equilibrium & bioattenuation

Solution – Sub-Slab SG Exercise

PCE indoor air = 2 µg/L x 0.03 = 0.06 ug/L = 60 ug/m3

Dry cleaner, allowed Cindoor = 46 µg/m3

Does the PCE value exceed allowable value?

YES

What other data might you collect to see if VI is an issue?

Radon to determine slab att factor orBuilding ventilation rate