A dry cleaning establishment in a residential neighborhood has been accidentally

Question

A dry cleaning establishment in a residential neighborhood has been accidentally leaking tetrachloroethylene (also known as perchloroethene or PCE) into the ground for several years Free-product (liquid) PCE has permeated through the subsurface and has leaked into the basement of a nearby house. The basement has an area of 1180 ft2 = 110 m2 and a height of 7' 7" = 24m As is typical for houses with basements, the warm, buoyant air of the upper floors pulls air up from die colder basement causing a natural and continuous ventilation of the basement However this air then enters the living area above In this house the ventilation rate of the basement averages one basement volume every 3 days (Complete change of basement air every 3 days all of which enters the first floor.) The first floor of the house has the same arenas the basement but a higher ceiling of 2 5 in The first floor has better ventilation and averages one volume every 12 hr. Note that the first-floor ventilation rate is the sum of the air entering from the basement plus additional outside air that contains no PCE. For the questions below, assume for simplicity that everything is at 25 degrees C, ever though there are small differences from the basement to the first floor. If the PCE liquid seeping into the basement achieves equilibrium with the slow -moving basement air. What is the expected mass flux of PCE into the first floor in units of g h? b. What is the expected steady state concentration of PCE vapor in the air of the first floor in units of mg/L?

Explanation / Answer

J = (-D) (dC/dZ) x A

= D(C/ z)

= 8.2 x 10-2 cm2/sec x (2.494 cm^3/sec/2.5 m) X 110 m2

= 8.99 gh-1

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