EDUCATION CENTER – WASHINGTON D.C.
Approximately 19,000 square feet
- Geo-Seal® FILM 5 protective layer 5 mil thickness
- Geo-Seal® CORE 30 mil spray layer and Geo-Seal CORE Detail
- Geo-Seal® FILM 11 base layer 11 mil thickness
A national chain of early childhood education centers chose the location of its Washington D.C. project on property known to have soil and groundwater contamination left behind from its former uses. The building designers were cognizant of the potential for vapor intrusion risk which might present itself to a sensitive population and researched design options.
Their choice was to employ a vapor intrusion mitigation system, which included a combination of two elements: an active pump sub-slab depressurization system (SSDS) component, and a spray-applied asphaltic vapor barrier (AVB). The SSDS consists of two square subterranean concrete vault “pits” with slotted openings at the top, and piping running from the pits to risers penetrating the sub-floor. The risers are connected to a pump service which pumps soil gas accumulated below the buildings sub-slab, out and away from the building above the roof.
Both vapor pits were installed as part of the General Contractor’s (GC) pre-vapor intrusion mitigation installation commitment to provide for large scale construction items prior to the finishing of the SSDS and AVB by vapor intrusion mitigation installation specialists.
The GC accomplished pre-installation work which included construction of the vapor pits, all plumbing and electrical penetrating uprights, concrete collars around clustered penetrating uprights, smooth-grinding of rough surfaces for attachment of AVB to the foundation, and constructed and compacted the sub-slab gravel bed.
Vapor Mitigation Strategies’ team completed the piping from the vapor pits to the risers for the SSDS, installed the AVB, and installed four vapor monitoring wells. These allow for regular monitoring of the vapor under the buildings slab for contaminants in the soil vapor.
The AVB was installed using a three-layer approach. First, by applying a polypropylene tarp which was rolled out tailored to fit around the vertical uprights and sealed to the foundation or uprights with Geo-Seal.
After the tarp was completely rolled out and all uprights and edges were addressed and sealed, the core layer of Geo-Seal was sprayed over the entire tarped area.
Then, a final layer of tarp was installed to provide protection to the vapor barrier itself since metal rebar and concrete were layered on top.
The installation was observed and inspected by a Land Science Technologies trained and certified inspector. The inspection included a coupon thickness test to verify the specified thickness of the vapor barrier, and a smoke test to ensure the integrity of the finished vapor mitigation system. Vapor Mitigation Strategies documented these tests and provided the materials to the manufacturer, Land Science Technologies, to enforce the warranty accompanied by these products.
The project required approximately 19,000 square feet of vapor barrier to be installed. From start to finish, the process took approximately five days to complete.