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Topic:  Design of Sub-Slab Active Vapor Mitigation Systems

Speaker:  Bob Roth, P.E., Terracon Consultants Inc.

Time: Tuesday, March 12, 11:30am-1pm

CEMS has received one (1) CLE for this presentation  

Sub-slab vapor mitigation systems (VMS) are installed when there is a risk of vapors migrating through a building floor slab (via cracks, construction joints, footings, or other pathways) into the occupied space of buildings which could cause risk to human health, creation of odor nuisances, and in some cases, explosive conditions.  The contaminated vapors can be from contaminants in the soil or vapors off gassing from contaminated groundwater. Contaminants can include volatile organic compounds (VOCs) or semi-volatile volatile organic compounds (SVOCs) from petroleum hydrocarbons (gasoline, diesel, other fuels), chlorinated VOCs (most often tetrachloroethylene and trichloroethylene, and associated breakdown products), or landfill gas.

VMSs can be passive or active. Passive systems include soil gas collectors (slotted or perforated pipe in gravel beneath the slab), vapor retarder membrane above the gravel layer, and vertical exhaust piping that conveys the collected vapors to the roof for discharge. Active systems use similar components as well as a vacuum blower/fan to create a vacuum in the sub-slab soil gas collectors which in turn extracts the vapors from beneath the slab and conveys the vapors to the exterior of the building.

When it is recommended by a regulatory agency or environmental consultant, or requested by the building owner to install an active VMS, the VMS designer must consider numerous variables that influence the effectiveness of the VMS. These include layout of soil gas collectors, size of vacuum blowers, as well as meeting regulatory requirements for operation. While many VMS designs use commercially available slotted or perforated piping for sub-slab soil gas collectors, empirical data show that these materials do not equally distribute the vacuum along the axis of the pipes which in turn do not equally distribute the inflow of sub-slab vapors along the axes of soil-gas collectors (i.e., skewed vacuum/flow leaving some areas with no vapor extraction). During the design of an active VMS, the designer must select a vapor extraction flow rate to select a vacuum blower that is both technically effective as well as cost effective (with respect to energy use during operation). Flow rate is dependent upon may variables such as sub-slab area to be vented, foundation type, sub-slab structures (footings, footing walls, grade beams, thickened slabs, changes in slab elevation, etc.), sub-slab vapor flow pathways, pneumatic permeability of gravel used beneath the slab, and soil type beneath the building.

After selecting a flow rate, the VMS designer must then select the vacuum needed at the inlet of the blower which is dependent upon friction loss of the vapors through the soil gas collectors, soil gas headers (solid piping), header fittings (ells, tees, contractions or enlargements), blower inlet filter, as well as loss from pressure drop through blower exhaust piping.

This presentation will present the above concepts and issues, and methods that can be used to address these during the design of an active VMS.

Mr. Roth has been a civil/environmental engineer for 34+ years specializing in soil and groundwater remediation, wastewater treatment, landfill remediation, and vapor mitigation system design. He has managed the design, construction, and operations of 40+ soil and groundwater remediation projects for industrial and commercial clients with costs ranging from $25K to $12M. EPA innovative technologies he has implemented include SVE, air sparging, dual phase extraction, multi-phase extraction, groundwater pump and treat, ISCO, bioventing, biosparging, methane mitigation, and vapor intrusion mitigation. Mr. Roth has a BS in civil engineering, and MS and PhD in environmental science, all from Rutgers University.

CEMS March 2019 Presentation Notes

LOCATION: The EPA Conference Center located on the 2nd floor of the EPA Region 8 Headquarters building at 1595 Wynkoop St.  When entering the building, visitors will be asked by the building security guards to display valid photo identification, pass through airport type security machines, and wear a temporary EPA visitor badge.

The EPA building has changed since the last time you were here: To get to the EPA Security check in room, simply go up the Atrium stairs or catch the elevator (the room is on the 2nd floor, directly across from the big stairs, entrance door on the left. Since the Security area is smaller than it was before, and the EPA only has one (very sensitive) metal detector, it will take a while so I recommend giving yourself plenty of time.  Then please proceed to the Bison Bitterroot Room (where we regularly meet) to register with the CEMS representative. 

MEETING FORMAT: Members may either bring their own lunch and attend the meeting for no charge, or they may request that CEMS order a box lunch for them. The cost of the box lunch for members is $16.00; for non-members, $19.00.

RESERVATIONS: PLEASE give your name, company name and phone number via email to admin@coems.org. PLEASE INDICATE IF YOU ARE RESERVING A BOX LUNCH OR BRINGING YOUR OWN. Reservations must be received BEFORE Friday, March 8, 2019 at 5:00PM. No reservations will be taken after this date! Payment of $16.00 for members, $19.00 for non-members will be accepted at the door with prior reservation. Please cancel your reservation by Friday, March 8, 2019 if you are unable to attend. It is the policy of the Society to bill for meals reserved but unclaimed. You may also pay with credit card via PAYPAL below:


Box Lunch
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NOTICE: CEMS would like to thank EPA for the use of meeting space and would like to emphasize that the use of EPA space does not constitute endorsement of CEMS, sponsors of CEMS functions, or the content of CEMS workshops or meetings.