Q&A: Land Science Technologies’ Grant Says New Barrier Aid to Brownfield Redevopment
- Oct 06, 2008
Covering over brownfields to pave the way for redevelopment is always tough. But now there is a new vapor barrier that may ease the challenges. Land Science Technologies, a division of San-Clemente, Calif-based Regenesis, has developed Geo-Seal, a vapor barrier technology that combines the strong chemical resistance of two bonded, high-density polyethylene layers to cap polluted sites. It can, according to its developers, also be installed easily and effectively, in a fashion similar to the basic spray-applied asphalt/latex products now used.CPN recently interviewed Peter Grant, division manager at Land Science Technologies, the division of Regenesis that developed the science behind these vapor barrier products.CPN: What is the GEO-SEAL, how is it made, what is it made of — and how will it be applied?Grant: Geo-Seal is a composite membrane, installed under the building foundation to protect against pollutant vapors from entering the finished building. The Geo-Seal composite membrane system is comprised of 3 distinct layers, and we call these layers, Geo-Seal BASE, Geo-Seal CORE and Geo-Seal BOND. The Geo-Seal BASE and Geo-Seal BOND layers are comprised of a geotextile fabric and high density polyethylene sheet. The Geo-Seal CORE layer is a 60 mil spray applied asphaltic emulsion that is applied between the two sheets layers. An applicator certified by Land Science Technologies will install these three components in the field. The installation of the Geo-Seal system is typically done just before the building slab in poured. CPN: What brought about this creation or development? Was it found as a solution to what problem? Grant: Geo-Seal was created to allow for the safe development of properties impacted with aggressive chemicals commonly found on brownfields. The most common of these chemicals are tetrachloroethylene (PCE), trichloroethylene (TCE), and benzene. CPN: What has been traditionally used to deal with this problem?Grant: In the past, the primary concern associated with unwanted vapor entering a structure came from methane and radon gases. Methane is an inert gas that will not aggressively attack gas vapor barriers in the same manner as PCE, TCE and benzene. If the building foundation is sealed properly and the methane is given an avenue to exit from under the building–such as a passive or active sub-slab venting system–there is little risk associated with methane gas entering the structure. Moreover, methane is only considered a threat when it collects at levels around 50,000 parts per million (PPM) and can be easily monitored in buildings. Radon is another gas that has presented concern and it is commonly mitigated in existing structures by actively removing the vapor from under the slab. PCE, TCE and benzene on the other hand present a much more acute risk to all parties involved in brownfield development, i.e. building occupants, developers, regulators, consultants, lenders, etc. The increased risk is due the potential health hazard caused by exposure to these chemicals at low concentrations over a period of time, low parts per billion (PPB). Since the allowable exposure levels are so slow, it is crucial that the barrier selected is both easily constructible and chemically resistant the chemicals in question. Currently two different barrier materials are being used to prevent vapor intrusion under buildings, 60 mil HDPE and 60 mil spray applied asphalt. Each of these products lies on different ends of the desired spectrum of chemical resistance and constructability. 60 mil HDPE has high chemical resistance to aggressive chemicals, but is very difficult to install properly under building foundations; 60 mil spray applied asphalt barriers are easy to properly install, but provide questionable chemical resistance to PCE, TCE and benzene. Geo-Seal blends together the best of both these products, the chemical resistance of HDPE and the ease of constructability of spray applied asphalt liners, to provide a system that has high chemical resistance and which can be easily installed. CPN: Can you explain and describe — if there was any ahah moment in the discovery—or tell how the new approach/solution was come upon?Grant: Feedback from the industry really fueled the idea. Engineers and regulators have openly questioned the long-term effectiveness and testing data of spray applied asphalt latex membranes in relation to PCE, TCE and benzene, because inherently these chemicals can easily breakdown asphalt and latex. The “ah ha” moment came when we realized that we could achieve the desired chemical resistance and maintain the ease of construction by combining the materials in a unique composite which essentially encapsulates the spray-applied latex asphalt within HDPE material. CPN: In conclusion, then, how is GEO-SEAL better? Grant: There are several advantages to Geo-Seal. Geo-Seal is 18-times more chemical resistant than simple spray-applied asphalt barriers. That drastically decreases the ability for toxic vapors to move through the barrier into the building. Improved construction methods make the installation of Geo-Seal quicker and more cost effective to apply than 60 mil HDPE and spray applied asphalt. In addition, the Geo-Seal membrane provides triple layers of protection, compared to an HDPE liner or simple spray-applied asphalt liners which only provide one layer of protection.