COLLEGE OF ENGINEERING Chemical, Biological & Environmental Engineering

PROJECT OVERVIEW

MASS FLUX CHAMBER EXPERIMENTAL SETUP

Flux Chamber

Design

Acquire FluxChamberMaterials

Completed

In Progress

Upcoming

Assemble Flux

Chamber

Conduct Pressure &

PID Test

Analyze Results

Conduct Blank Test

Reevaluate Flux Chamber

Assembly

GC/MSAnalysis

DevelopSampling

Device

Figure 2.The work flow diagram illustrates the sequence of

tasks performed to accomplish objectives.

Objectives(1) Utilize existing test system (mass flux chamber) to

characterize vapor intrusion

(2) Prepare concrete samples to assemble with new flux

chamber components

(3) Conduct experiments to determine VOC flux through

concrete

OpportunityVolatile organic compounds (VOCs) in groundwater diffuse

through soil and concrete foundations to contaminate

indoor air. Measuring VOC concentration is the first step to

mitigating exposure risks to people. The ultimate goal is to

develop a passive sampling device for VOC vapor intrusion.

Figure 1. A typical site contaminated with a VOC such as

trichloroethylene (TCE) is shown with the contaminant diffusing into the

indoor air of a building, causing significant hazards to human health.

Figure 4. Experimental setup for PID testing. A) pump air inlet

B) Peristaltic pump C) Tedlar® bag (impermeable to VOC) D)

Mass flux chamber E) Top chamber air inlet

Figure 5. Tools used in experimentation. F) 5 and 100

mL gas-tight syringes G) Tedlar® bag H) PID.

How It Works

(1) VOC is loaded into the bottom chamber through the septum with a 5 mL

liquid syringe.

(2) VOC volatizes into a gas and diffuses through the concrete which is sealed

by heat shrink tubing to prevent gas from circumventing the sample.

(3) A constant flowrate of air is pumped through the top chamber inlet to

clear the heptane gas, providing a constant mass transfer driving force.

(4) Outlet gas is collected in a Tedlar® bag and VOC concentration is tested

using a Photoionization detector (PID). VOC concentration in the bottom

chamber is tested using gas-tight syringes through the septum.

Volatile Organic Compounds

Trichloroethylene (TCE)

Primary Uses

• Industrial Solvent

• Degreaser

• Found in adhesives, paint removers,

carpet cleaner

Regulations

• OSHA Standard is 100 ppm for 8-hour

exposure

Heptane (Experimental Substitute)

• Non-toxic VOC

• Similar molecular weight and vapor

pressure to TCE

• Easily detected using PID and GC/MS

Decane (Experimental Substitute)

• Non-toxic VOC

• Low Vapor Pressure Low

Concentration

• Easily detected using PID and GC/MS

Concrete

Figure 7. Different modes of diffusion in

concrete.

Project Work Flow

Figure 6. Concrete and aluminum blank that

are 1.5”–3.0” tall with a 2.75” diameter.

Table 1. Physical property comparison of VOC.

Acknowledgements• Mike Niemet, Ben Thompson, Mike Novak, Jake

Donally, Katie Rabe, Blake Wimer, CH2M Sponsors

• Columbia Concrete Sawing Co. - Concrete samples

• King Machine - Fabricated metal components

• Dr. Pommerenck - COMSOL Model support

• Dr. Semprini– Concrete diffusion and adsorption

• Dr. Gibson – Mathematical model

• Dr. Harding - Project guidance and support

References[1] Musielak, M. “Indoor Air Pollution: Study of

Trichloroethylene Transport through Soil and Basement.”

Université de Toulouse. 2010.

[2] Welty, JR. et al. “Fundamentals of Momentum, Heat,

and Mass Transfer.” Wiley and Sons, Inc. 5th ed. 2008.

[3] Green, Bradley A., Shea, D., and Ashton, A . "Use of

VOC Mass Flux to Estimate Vapor Intrusion Impacts."

Sanborn. Web. 2012.

Future Work• Develop passive sampling device for vapor intrusion

• Test flux chamber using different VOC’s and concrete

subslabs

• Field test of passive sampling device

Experimental Results• Pressurizing the chamber verified that a sufficient

seal was provided and no air could circumvent the

concrete.

• Replacing the concrete with an impermeable

aluminum cylinder during PID testing confirmed that

vapor was not circumventing the subslab.

• Steady state conditions for the heptane chamber

were observed in the system after 450 hours at a

value of 37 (±3) g/m2/day illustrated in Figure 9.

• The decane chamber data confirms the time to

reach steady state is longer and the steady state

flux value will be lower than heptane as a result of

lower vapor pressure also seen in Figure 9.

• PID reading accuracy of ±5% was verified using

GC/MS.

Figure 9. Steady state was observed at 450 hours for heptane

with a value of 37 g/m2/day. Steady state has not been

achieved with the decane chamber, but the value is expected

to be much less than the Heptane steady state value .

Mass Transfer Influenced by:

• Water/Cement Ratio

• Aggregate Size

• Cracking: Micro/Macro

“vapor Intrusion.” Navaf. <www.navfac.navy.mil>

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0 200 400 600 800 1000

Mass

Flu

x (

g/m

²/day)

Mass

Flu

x (

g/m

²/day)

Time (Hours)

Mass Flux of Heptane and Decane

Heptane Flux

Decane Flux

Vapor Intrusion Assessments for Concrete SubslabsJacob Lum, John Collin Hall, Amro Al-Habsi

Figure 3. Experimental setup for PID testing. A) Air flow inlet B) Air flow outlet C) Heat

shrink tubing D) Concrete subslab E) Syringe septums

COMSOL Multiphysics

Welty. Fundamentals of Momentum, Heat, and Mass Transfer.

Figure 9. A steady-state COMSOL concentration

simulation developed at 20ºC using a laminar flow

and species transport in porous media package.

• Porosity

• Diffusivity

VOC Contamination

Mass Flux Model:

𝑁𝐴 =𝐷𝐴,𝐵𝐶𝐴,𝑠𝐿−2𝐷𝐴,𝐵𝜋

𝑛=1

∞𝐶𝐴,𝑠𝜋

𝐿𝑐𝑜𝑠𝑛𝜋𝑧

𝐿𝑒𝑥𝑝(−𝐷𝐴,𝐵𝑛

2𝜋2𝐿−2𝑡)

Mathematical Model

Fick’s 2nd Law: 𝜕𝐶𝐴

𝜕𝑡= 𝐷𝐴,𝐵

𝜕2𝐶𝐴

𝜕𝑧2

IC : CA(x,0) = 0 for all x

BC(s): CA(0,t) = CAs for t > 0

CA(L,t) = 0 for t > 0

Heptane Flux

ChamberDecane Flux

Chamber

0.38

VOC Flux

2.0𝑥10−4

0.05

0.18

0.09

1.9

0.9

0.3

(𝒊𝒏𝒄𝒉𝒆𝒔)

(𝒊𝒏𝒄𝒉𝒆𝒔)

(𝒎𝒐𝒍/𝒎𝟑)