Consider an environmental problem caused by a leak from an old tank at a local g
ID: 866978 • Letter: C
Question
Consider an environmental problem caused by a leak from an old tank at a local gas station. The gas has seeped under the houses in a nearby subdivision, and the measured concentration of gas vapor is 25 parts per million at a depth of 2.0 meters below the basement floors which have an area of 100 square meters. The basements are very well ventilated so that the concentration of gas vapor is very low. Data available in the literature states that the diffusion coefficient of gas vapor in such a situation is 0.01 cm2/sec. You estimate that the rate of gas vapor entering each basement per day is about:
Explanation / Answer
The volume/day V of air entered in the basement is surface area x rate x time.
V = 100 m2 x 0.0001 m/s x 24 x 60 x 60 s/day = 864 m3/day
Rate = V (m3/day)
If we consider that this is air from soil and this air has cgas = 25 ppm = 25x10-6 kg/L air = 25 x 10-3 Kg/m3 air:
Gas rate = c x V = 25 x 10-3 Kg/m3 soil x 864 m3 /day= 21.6 m3 /day.
Note:
The text is unclear.
The results depends on what the author understand by ppm, by the rate (of the contaminat or of the air).
Retain this result as a calculation model.