Vapor Intrusion Emerges as a Major Cleanup Driver

When I started work as an environmental professional in 1986, I do not recall thinking about or even being aware of the risks posed by vapor intrusion. Vapor intrusion (sometimes referred to as “VI”) occurs when a volatile solvent or the volatile portion of a petroleum hydrocarbon from a release under or adjacent to a building migrates into the air inside a building.  Once in the indoor air, these volatile constituents can be readily inhaled by the building occupants, which is important because the lungs are the most efficient mechanisms by which chemicals enter the body.

How the VI Pathway Works

Volatile compounds are generally considered to include those that have boiling points less than that of water or vapor pressures greater than that of water, such as benzene from gasoline, industrial degreasers such as trichloroethylene (TCE), or perchloroethylene (PCE) dry-cleaning solvent.  These volatile compounds are the ones most likely to cause VI problems.   Following a release, these compounds are present in the ground partially in a liquid or solid phase, but they are also present partially in the vapor or gaseous phase.  As a gas or vapor, they can move readily through the soil to nearby buildings.

This mechanism is often intensified during winter heating conditions, when buildings are closed up, and heating systems vent to the outside, creating negative relative pressures inside buildings, sometimes called the ‘chimney effect.’  Even a relatively small relative negative pressure in a building significantly enhances the rate at which vapor intrusion occurs.

Comparing Exposures from VI to those from Soil and Groundwater

In the early days of waste site cleanup, we were focused on exposures and risks arising from soil and groundwater contamination.  While we are still concerned with the potential exposures to these media, limiting them is usually relatively simple (i.e. don’t eat or play in the soil and don’t drink the groundwater). In contrast, limiting exposures to indoor air containing volatile compounds is more problematic because everybody has to breathe continuously.  With experience has come the awareness that for volatile chemicals, VI is probably the most important exposure pathway to control for reducing risk when it is present.

Developing the Right Measurement Tools

While the Massachusetts Department of Environmental Protection became aware of VI issues in the late 1980’s, it wasn’t until they issued a  guidance document in 2002 that we had some state level agency guidance on how to proceed.  The guidance called for an initial field screening to evaluate whether soil gas was beneath a building which might result in vapor intrusion. With hindsight, has come the realization that the field screening methods of the day were not nearly sensitive enough to rule out vapor intrusion.

Vapor intrusion studies now usually rely on collection of soil gas samples in the field that are subsequently analyzed in a laboratory setting with highly sensitive instrumentation.  Alternately, portable gas chromatograph/mass spectrometers (GC/MS) can also be used.  In 2016, the Massachusetts Department of Environmental Protection issued final guidance, which describes the  state of the practice for “investigating, assessing, understanding, and mitigating vapor intrusion” in Massachusetts.

Remediating VI Conditions

The preferred remedial method for VI sites has become the installation of sub slab depressurization system or SSDS.  Borrowing from the radon remediation industry, regulators and environmental consultants realized that the mechanism by which radon gas enters buildings is almost identical to VI, and thus has a nearly identical solution. By capturing the vapor within the soil beneath a building, and venting it to the outside air before it can migrate into a building, we can almost eliminate the inhalation exposure that would otherwise occur in the building. This diagram presents a generalized depiction of an SSDS.


BHN blog figure

In designing an SSDS, environmental practitioners need to consider a number of site-specific factors such as how large an area the SSDS needs to cover, the permeability of the soil below a building, and the characteristics of the vacuum fan required.  A building underlain by a coarse sand or gravel might need only one vapor extraction point to cover the entire footprint, while a building underlain by finer grained soils might need more extraction points or horizontally laid slotted pipe to get the desired coverage.

At OTO, we typically perform an initial evaluation to help design an SSDS with an appropriately sized fan and geometry (i.e., a single extraction point or horizontal pipe). A small system for a residential fuel oil release under a portion of the basement might need a single extraction point with a small fan.  A system like this uses about the same amount of electricity as a standard light bulb.  In contrast, a large industrial property may need a larger system with multiple zones and stronger fans, and will result in a significantly higher electrical bill.

My first experience installing and operating an SSDS came in 2005, as a response to a relatively small residential fuel oil release. Since then, I have had a number of projects including SSDS’s ranging from relatively small and simple to quite complex.  To me, no other innovation in our industry has had a greater impact on our ability to reach acceptable endpoints for vapor intrusion than sub-slab depressurization systems.

As an environmental professional, many of the problems I have worked on have been difficult to solve. However, because of their relatively low cost, ease of installation and ability to improve conditions rapidly, solving vapor intrusion through installation of an SSDS has been a genuine bright spot in my career.




Coal Tar – Yesterday’s Nuisance, Today’s Problem
OTO’s work includes a lot of remediation Massachusetts and Connecticut. One of the things we run into on occasion is coal tar, a viscous, black, smelly product of our industrial heritage. Coal tar is not one of the more common challenges encountered at MCP sites in Massachusetts, with gasoline, fuel oil, chlorinated VOCs and metals all coming up more often. It is, however, a complex and challenging mixture of contaminants. Thanks in part to the unfortunate experience with the Worcester Regional Transit Authority’s redevelopment project on Quinsigamond Avenue in Worcester, or the recent proposal to cap tar-contaminated sediments in the Connecticut River in Springfield, coal tar is back in the news after a period of relative obscurity.


Don’t worry– this isn’t in Massachusetts.

Coal tar is a challenge for three main reasons.

First, it can be a widespread problem. Most coal tar encountered in the environment is a legacy of the coal gasification plants that supplied Massachusetts’s cities and towns with heating and lighting gas before natural gas became available via pipeline in the 1950s. Virtually any city or substantial town before 1900 had a gasworks, and some towns had several. Gasworks were often historically built on the ‘wrong side of the tracks’ due to their historically noisome character—their smell and constant racket beggared description. Where such “city gas” plants were not available, mill or factory complexes like the Otis Mills Company in Ware often had their own private gas plants, some of which also sold surplus gas to local residents for gas lights and stoves, and in some cases essentially became the town’s gas company.

As byproducts of making gas out of coal, these plants produced coal tar, cyanide-laden spent purification media, and much else of a dangerous nature. Some coal tar could be refined into waterproofing pitch, paving materials, industrial solvents, and even the red, foul-tasting carbolic soap that nobody who has ever seen “A Christmas Story” will ever forget. Massachusetts was also home to several plants that reprocessed tar into these plants, some of which later became all too well known, like the Baird & McGuire site in Holbrook, MA or the Barrett plant in Everett and Chelsea.

In addition to historically releasing wastes to the environment at the gasworks, gas companies also historically created off-plant dumps for their wastes, creating hazardous waste sites that might be located miles from the gasworks, or even in a different town.
EPA historically kept a sharp eye out for coal gasification plants, and during the 1980s listed over a dozen coal tar sites in Massachusetts on CERCLIS. Many of the sites that most alarmed MassDEP in the ‘80s were also related to MGPs—for example, Costa’s Dump in Lowell or the former Commercial Point gasworks in Boston. In recent years, however, regulatory attention has taken on an increasingly narrow focus towards other concerns, most notably vapor intrusion from chlorinated VOCs.

The second important consideration about coal tar is that it is pretty dangerous stuff, and poses both cancer and noncancer risks. Coal tar is typically a heterogeneous mixture of something like 10,000 distinct identifiable compounds, ranging from low molecular weight, highly volatile compounds like benzene and styrene to massive “2-methyl chickenwire” asphaltene compounds. From an environmental and toxicological perspective, coal tar is most conspicuous for its high concentrations of polycyclic aromatic hydrocarbons (PAHs), as much as 10% PAHs by weight, which make it significantly more toxic than petroleum. Two of the coal tar’s signature PAHs are benzo [a] pyrene and naphthalene; some coal tar can be up to 3% naphthalene alone, which accounts for the distinct, penetrating ‘mothball’ odor at MGP remediation sites.

Coal tar was associated with occupational diseases ranging from skin lesions to scrotal cancer even during the mid-19th Century, and was the first substance to be conclusively shown to be a carcinogen (by the Japanese scientist Katsusaburo Yamagiwa in 1915). The British scientist E.L. Kennaway subsequently proved that benzo [a] pyrene was itself a carcinogen in 1933, the first individual compound to be so categorized. Coal tar also contains concentrations of lesser-known PAHs, some of which may have significantly greater carcinogenic potential than benzo [a] pyrene. Coal tar is also a powerful irritant; remediation workers and others exposed to it can expect hazards including painful irritation of the skin, and respiratory or vapor intrusion hazards including high levels of benzene and coal tar pitch volatiles.

The third consideration is that coal tar is very persistent in the environment; tars and other gasworks wastes are highly resistant to geochemical weathering (and also to many remediation technologies, such as in-situ chemical oxidation), and do not break down in the environment like gasoline and most fuel oils do, so that tar contamination can still create problems over a century after the material was released.

So, coal tar is still with us, and will be for a long time. On the bright side though, with effort and careful planning, these challenges can be overcome. Many of the “wrong side of the tracks” locations of former gasworks are now prime downtown real estate, and a number of Massachusetts gasworks have been redeveloped as shopping plazas, transportation hubs, and biotech research facilities. As land prices, urban real estate availability, and government incentives continue to drive brownfield redevelopment, hopefully most of the Commonwealth’s former gasworks will see a new life.

From a professional perspective, PCBs entered my life in 1978 while I was post-grad research associate at the U of Hawaii College of Tropical Agriculture.  The mission of our lab was to develop data in support of EPA pesticide registrations for tropical crops.  Pesticide registration is normally conducted by the pesticide manufacturers, but tropical crops are such a small niche market, that it isn’t worth their trouble in most cases.

One day the lab director brought a box with ten 8-ounce jars into my work area and put them down on my lab bench (tangential comment – this is the work area from which I had a view of three waterfalls, sigh).  He told me each of the jars contained a different Aroclor PCB mixture and that the Hawaiian electric company wanted us to develop an analytical method to measure the amount of PCBs in transformer mineral oil.  For the next couple of months, while working up the analytical method, these jars were front and center on my lab bench.  These were not laboratory prepared analytical standards; these were jars containing pure (“neat” to you chemists) Aroclors.

As a young chemist the opportunity to work on an environmentally relevant project was a real thrill.  As you likely know, the percent of chlorine in an Aroclor is indicated by the last 2 digits in the model number; so Aroclor 1221 contains 21% chlorine by mass and Aroclor 1268 contains 68% chlorine (Note: this numbering does not apply to Aroclor 1016 which is a modified version of Aroclor 1242 and thus contains 42% chlorine).  The lighter Aroclors like 1221 and 1232 were as thin as machine oil.  The mid weight Aroclors (1248 and 1254) were as viscous as motor oil.  Aroclor 1268 was pretty much a solid at room temperature.  Also, the lighter Aroclors were clear and the heavier ones had a darker quality to them.

On the chemistry side, there are 209 different PCB molecules (called “congeners”), and each of the Aroclors is a mixture of 50 or more of these congeners.  Chemists sometimes organize the different congeners into groups based on the number of chlorine atoms they have and these groupings are called “homologs”.  So for instance, all the different congeners that have three chlorines belong to the tri-chloro homolog group, all the congeners with four chlorines belong to the tetra-chloro homolog group, and so on.

There is an interesting difference among the Aroclors (interesting to me at least) that even many chemists are not aware of; each Aroclor PCB mixture is dominated by a different homolog group.  So for instance, Aroclor 1221 is made up of 60% mono-chloro congeners (one chlorine), Aroclor 1248 is 56% tetra-chloro congeners (four chlorines), and Aroclor 1262 is 47% hepta-chloro congeners (seven chlorines).  This formulation was not created by design; it was just an accident of the manufacturing process.

Meanwhile back at my lab at the U of H, and many, many gas chromatographic runs later, I did finally come up with a reliable method for measuring PCBs in transformer oil.  Remember this was before there was an SW-846 (EPA’s compendium of analytical methods) or a Method 8082 (EPA’s PCB analytical method).  The method I developed for measuring PCBs in transformer oils was actually published in the Journal of Chromatography (JOC) and the article can still be obtained on-line (the link is for the curious, but purchase is not recommended since this method has been superseded by better USEPA analytical procedures).

When I looked up the link to the JOC article to include with this post I was disappointed to see that the U of H College of Tropical Agriculture now has a trendier name, the “Department of Agricultural Biochemistry”.  On the other hand, I was very pleased that when I clicked my name on the author list my address came up as “University of Hawaii, 1800 East-West Road, Honolulu, Hawaii”;  on a cold windy late winter day it’s nice to still have an address in Hawaii.

In closing, let me acknowledge Dr. James Ogata who directed my work at the U of H lab and who prepared the manuscript for publication.

For help with PCB chemistry questions, please contact me at

What are USEPA’s New PCE Toxicity Values About?

It has been a year since the USEPA issued its new toxicological profile for tetrachloroethylene (PCE).  The new profile resulted in the revision of PCE’s toxicity values in EPA’s Integrated Risk Information System (IRIS).  Despite their obscurity, IRIS toxicity values carry great importance because they are at the heart of the risk assessment process and thus play a central role in determining the extent of waste site cleanups.

What was unusual about the PCE toxicity value change is that the new values indicate PCE is less toxic than previously thought; this is a rare occurrence because most IRIS values changes have gone the other way.  EPA did not come up with the idea of lowering its estimate of PCE toxicity by itself; it received “encouragement” from a National Research Council (NRC) expert advisory committee.  To EPA’s credit, they solicited the input from NRC, even if not all at the agency were happy with the recommendations they received.  It turned out that NRC placed greater emphasis on higher quality scientific studies (those with more controls and less ambiguous toxicity endpoints) and urged EPA to discount studies of lesser scientific quality.  The higher quality studies indicated that PCE was in fact less toxic than previously thought

Very Interesting, but why is this Important?

EPA’s old PCE toxicity values suggested that PCE was so toxic that even concentrations in air that were too low to measure could pose a serious health risk.  As a result, PCE became a significant driver of cleanup actions at many waste sites where vapor intrusion was a pathway of concern.

As you likely know, vapor intrusion is an exposure pathway whose significance many environmental scientists and regulators consider to have been underestimated in the past. Remedial actions to address vapor intrusion have thus become more common, even in situations previously thought to have been satisfactorily closed-out.  In many of these vapor intrusion situations it has been the presence of PCE in air that drives remedial actions.  With PCE now recognized as being less toxic, some of these remedial actions may not be necessary.

Have State Agencies Adopted the New PCE Toxicity Values?

Much of the waste site cleanup work in the US takes place at the direction of state governments.  Most states and political bodies with waste site cleanup laws specifically cite EPA’s IRIS database as the first choice for all risk assessment toxicity values.  However, some states take an à la carte approach with IRIS; reserving their right to use their own toxicity values when they see fit.  Massachusetts is just such a state and its PCE toxicity values date back to the early 1980s (and have evolved since then), a time when there were no federal standards for PCE in drinking water.  MassDEP (then DEQE for the nostalgic) was responding to a big PCE problem in drinking water pipes and in the absence of federal criteria, it took a commendable DIY approach.

What about New Jersey?

But, this post is not about Massachusetts, it’s about New Jersey and its January, 2013 adoption of EPA’s new toxicity values for PCE. Like Connecticut, New Jersey tried to adopt a semi-privatized waste site cleanup law (modeled on the Massachusetts Contingency Plan), but neither state had the much success with their program..  Some place the blame for this lack of success on the inflexibility of NJ DEP and CT DEEP; I am not quite close enough to either situation to comment.

Now the New Jersey DEP seems intent on getting its privatized waste site cleanup program back on track.  It is breathing new life into its LRSP program and in January of this year it issued final guidance to address vapor intrusion sites.   As part of its vapor intrusion guidance, NJDEP has adopted the new EPA IRIS toxicity values for PCE.  By adopting the EPA values, New Jersey raises the threshold at which remedial action is required at sites with PCE.

Among the states, New Jersey is generally perceived to err on the side of environmental cautiousness and its adoption of the new EPA PCE toxicity factors can only add to the momentum in favor of  nation-wide adoption.   New Jersey is off to a good fresh start with its privatized cleanup program.

Impacts to indoor air quality from volatile organic compounds (VOCs) have been receiving greater attention recently due to a growing awareness of vapor intrusion (VI) from underground oil and chemicals.   VI occurs when chemicals spilled on the ground migrate under structures and then volatilize up into indoor air.  After a recent residential basement oil spill I was called in to provide a second opinion on why high indoor air VOC concentrations persisted in the home after the cleanup had been completed.  Some of the results were very surprising.

Locating VOCs in the Basement

Following the release, a well qualified response contractor had conducted a thorough cleanup.  The remediation included removing portions of the floor slab, wall board, wood framing and most other building materials that had been contacted by the oil.  Despite the cleanup, indoor air concentrations in the basement and first floor of the house exceeded the Massachusetts Department of Environmental Protection criteria.

The contractor suspected the problem was the first course of concrete chimney blocks, which had likely absorbed oil in the aftermath of the spill.  The oil in the blocks was now likely volatilizing into the air.  Removing and replacing the contaminated  blocks presented an obvious structural challenge so initially an epoxy sealant was applied to the entire chimney to prevent further oil volatilization.  However, indoor air testing conducted after the epoxy had cured showed that indoor air concentrations remained stubbornly high.

To assess the cause of the indoor air levels, I visited the subject home with a ppbRAE to see if it would help me locate the source of the organic vapors.  Once in the basement, it did not take long to discover that the epoxy sealant was not preventing VOC migration out of the concrete chimney blocks; the blocks were still off-gassing VOCs to the basement air.  While there were also a few pieces of previously unidentified wood framing off-gassing VOCs, the concrete blocks looked to be the main culprit.

But What’s Going on Upstairs?

With the basement VOC source identified, I went upstairs to check on first floor; what I found there was completely unexpected.  While ambient basement air VOC readings had been just above zero (at some distance from the chimney), ambient levels on the first and second floors were about 200 ppb!  How could this be?  I walked through the house with the home owner trying to identifying potential VOC sources.  After an hour of looking I hadn’t been able to identify a source and almost everywhere in the occupied space I was measuring 200 +/- 40 ppb of VOCs in the breathing zone air; there were no odors.  Big mystery!

Finally, on a high book shelf in the living room I noticed two glass hurricane lamps; each containing several ounces of clear liquid lamp oil.  When I held the tip of the ppbRAE probe over the glass lamp chimneys the instrument’s numerical readout shot up; the mystery of the upstairs VOC source was seemingly solved!  And the source was completely unrelated to the basement oil spill.

What is in lamp oil that causes such a strong response on the ppbRAE?  From my limited on-line research, there does not appear to be a commonly accepted formula for lamp oil.  At one time kerosene was used, but this now seems less common except in outdoor settings.  Whale oil was also once used, a practice now thankfully in the past.  The oil in these lamps had no odor, but beyond that I do not have any information on what it was.  I did not collect a sample for lab testing, so I do not know specifically what the ppbRAE was responding to.

Lessons Learned

This experience was a good reminder of just how sensitive today’s air monitoring equipment has become.  Even very small contributions from sources that do not seem particularly volatile can have a dramatic impact on indoor air testing measurements.  It is important to keep a watchful eye out for unanticipated VOC sources when conducting indoor air testing.

Paul Locke, MassDEP’s acting head of the Bureau of Waste Site Cleanup, was the lead speaker at the September 13th Licensed Site Professional Association (LSPA) membership meeting.  In his remarks, Locke repeatedly advised LSPs to be “on the lookout” for upcoming changes in the Department’s programs and structure.  However, he provided scant details about the changes and was very cagey about “not wanting to spill the beans” in advance of the commissioner’s announcement of the changes, expected sometime in October.

One change he was specific about was the elimination of the previous requirement that any site with Activity and Use Limitation (AUL) would be subjected to a MassDEP compliance audit.  This announcement was the first many in the audience had heard of this change.  Locke said the change was welcomed at the Department because it gave MassDEP greater flexibility to target audits in this time of decreasing resources.

The elimination of the “guaranteed audit” may remove one of the  disincentives for using AULs as a site closure tool.  While an audit is still a real possibility at any MCP site, there may be a shift in the perception of “audit risk” with this policy change.   It makes sense that if the use of AULs is perceived to be less risky, then their use will be given greater consideration in more situations.

If more AULs are used, this may result in a higher percentage of permanent site closures; an outcome that MassDEP and the regulated community would smile upon.

If you heat your home with oil, as so many of us in New England do, you should be aware of a new Massachusetts law regarding home heating oil tanks.  The law requires certain upgrades that make leaks from your tank less likely.  This may include either a safety valve or an oil supply line with a protective sleeve.  If these features are already part of your system, and if they were installed after 1990, you may not need to take any additional steps now.  But if you don’t have one or both of these important features, we urge you to have them installed.  It’s well worth the estimated $150 to $350 the upgrade will cost, and it’s the law.

Not maintaining your oil tank can have disastrous consequences.  When it comes to oil spills, we’ve seen it all.  Oil storage tanks in people’s basements that fail catastrophically at the seams, spraying oil all over the contents of the basement.  Floodwater in basements floating oil tanks upward until the feed line breaks.  Vent lines plugged by animal nests or leaves, causing the tank to overpressurize and burst during filling.  Imagine the heartbreak of tossing the entire oil-soaked contents of your basement into a dumpster, not to mention the cost of the clean-up!

To make matters even worse, a sudden release of more than ten gallons of oil to your basement may be reportable to the Massachusetts Department of Environmental Protection (MassDEP), and you, as the homeowner, become liable for the cleanup.  Released oil often migrates quickly through cracks in basement floors to the soil below the house.  Cleaning up soil and groundwater impacts after an oil spill can be very costly.  MassDEP estimates typical residential oil releases cost $20,000 to $50,000 to clean up, while some sites run over $200,000.  That’s a pretty big unexpected expense to try to squeeze into your household budget.

Fortunately, the new regulations have a second part: an obligation for homeowner insurance companies to offer coverage for home heating oil spills.  Many homeowners are shocked to learn (sometimes too late) that their insurance doesn’t cover spills from their heating system.  The new coverage won’t be automatically added to your policy; you’ll need to ask for it, and pay a bit extra for the coverage.  In our opinion, it’s well worth it to avoid the nightmare scenario of a large oil spill in your basement that you end up liable for on your own nickel.  So contact your oil burner service company to see if you need an upgrade, and contact your insurance company to inquire about oil spill coverage.


As we all know, one of the hottest topics in the environmental industry right now is vapor intrusion.  In Massachusetts, vapor intrusion considerations have been around for more than 20 years, since the beginning of the Massachusetts Contingency Plan (MCP) program.  This is no surprise, as Massachusetts has been a technical and regulatory leader in the environmental field since the early days.  However, Massachusetts has reached a critical crossroads in the regulation of the vapor intrusion pathway, and stakeholders, especially those who are involved in brownfields redevelopment projects, are hoping that they choose a wise pathway moving forward.

As a rookie regulator at the start of my professional career in 1992, I first became aware of vapor intrusion as an exposure pathway when a colleague of mine was working on a project in Needham.  Apparently, an industrial facility was discharging wastewater containing chlorinated solvents into corroded subsurface drain lines, resulting in groundwater contamination.  The impacted groundwater migrated downgradient to a school and a residential subdivision.  An indoor air testing program detected the solvents in indoor air.  From that event, vapor intrusion considerations were propelled forward, and the concept of MassDEP’s GW-2 standards based on the Johnson & Ettinger Model was born.

MassDEP’s GW-2 standards were based on an early version of this model that had been around since the early 1990s.  However, not long after implementation in late 1993, MassDEP technical staff began questioning whether the model was portraying an accurate picture of what was being observed in the real world.  In the late 1990s, MassDEP began to see a growing body of data collected at sites that indicated the Johnson & Ettinger Model was not providing a consistent prediction of what was being observed.  MassDEP lowered GW-2 standards for many common chlorinated volatile organic compounds and continued its evaluation of the data collected during site assessment and clean-ups.

Fast-forward to where we are today:  MassDEP has issued updated Vapor Intrusion Guidance, currently in draft form dated December, 2010.  While MassDEP’s updated guidance may be the state of the science available at this time, it is a substantial departure from how vapor intrusion has been regulated in Commonwealth over the past 20 years.  As it is currently issued by MassDEP, the updated guidance appears to bring a substantial amount of additional uncertainty to the redevelopment of brownfields sites.  Many brownfields projects are undertaken due to the availability of transferrable tax credits which make these projects economically feasible.  Without the availability of these credits, many projects would fail to receive financing.  However, the availability (and the amount) of the tax credits is dependent on these brownfields projects reaching some type of Permanent Solution.  The updated guidance, as currently proposed, reduces the likelihood of Permanent Solutions at vapor intrusion sites.

While all of us who work on vapor intrusion sites appreciate the hard work that MassDEP has put into the updated guidance, we also hope that the final version will not make it more difficult to achieve Permanent Solutions, especially at brownfields projects.  While we can not predict what the final guidance will include, there are actions that can be done now to reduce the likelihood of regulatory risk on projects now in the pipeline.  These actions include designing projects to include vapor intrusion barriers and properly engineered subslab depressurization system piping in new construction and rehab work.  First and foremost, consideration of potential vapor intrusion issues, and appropriate early due diligence and evaluation, should be at the top of every brownfields project to-do list.