“What is a Soil Gas Sample?”
It’s a good question. It’s part of a string of questions most of us are familiar with - the what, why, who, when, where, and how of something. Let’s check the list.
A soil gas sample is what you get when you remove a small portion of gas inside soil and hold it in a container for testing. Underground soil is like a sponge in that it has empty spaces. Between the surface of the ground and underground water (groundwater), these soil spaces are filled with gas and water. The gas is mostly air, but it can also have gaseous contamination from underground spills of chemicals such as gasoline and cleaning solvents (tetrachloroethylene or PCE). The soil gas may also have by-products of chemical spills like the vinyl chloride that comes from the breakdown of PCE.
Soil gas is sampled to see if there are any harmful gasses that are either naturally occurring or the result of a spill. The samples are usually analyzed at a State-certified lab to find out what chemicals are in the soil gas sample and what the levels are. There are several reasons to collect a soil gas sample.
One reason is to find out if there is a risk to human health and the environment. To check for risk, chemical levels detected at the lab are typically compared to levels judged to be safe by the regulatory community. These levels, sometimes called environmental screening levels (ESLs), are considered safe when they do not pose a potential risk to public health and the environment.
Another reason to collect soil gas samples is to find out where contamination is and where chemical levels are highest. A map showing where chemicals are found and at what levels they are found can provide a good idea of the area of contamination and highlight areas with higher levels. This can help to steer property development plans and keep people away from potentially harmful areas. This information can also significantly lower investigation costs by showing where soil and groundwater sampling should be targeted.
In the case of known underground contamination, soil gas samples may be collected over a period of time to monitor the change in chemical levels. A change that shows a decrease in chemical levels is necessary for environmental case closure.
Sometimes the reason for soil gas sampling is to just find out whether there is underground contamination. For example, a property owner may have soil gas samples collected along a property boundary shared with a dry cleaning business to find out if contamination from the dry cleaner moved beyond the dry cleaner’s property line.
Usually, an environmental consultant or environmental oversight agency proposes collection of soil gas samples. As mentioned above, the reasons are to find out what chemicals are in the soil gas, what the levels are, and where the chemicals are located.
In most cases, personnel trained in soil gas sampling collect soil gas samples. Sampling goals and how the sampling will be done are typically spelled out in a work plan that is approved by a regulatory agency prior to samping.
Soil gas samples are collected in areas of known or suspected underground contamination. Once the soil gas samples are collected, they are taken to a laboratory for chemical testing. In some cases, an on-site field laboratory is used to analyze samples.
In the field, soil gas sample containers are labeled with the sampling location, time the sample was collected, and a sample identification number. After labeling, samples are placed in a sealed container and transported to a state-certified laboratory for analyses.
A chain of custody is prepared at the point of sample collection and it travels with the samples to the laboratory. The chain of custody contains contact information, a list of the samples collected, and other important information. It is a clear line of responsibility from the sample location to the laboratory.
Soil gas samples can be collected at any time, but it is suggested that samples not be collected within 5 days of a good rainfall. Policy makers suggest that after you know where the soil gas contamination is, you should take samples twice per year to show levels during rainy and dry seasons. Once at the lab, it usually takes about two weeks to get the results. Of course, if you are willing to pay more, sample testing can be “rushed”.
Soil gas samples are collected from wells installed to at least 5 feet underground or from sample points that allow access to soil just underneath a concrete floor. In most cases samples are collected using a stainless steel canister that is supplied by a laboratory. The canister is delivered sealed and under a vacuum. During sampling, the canister is attached to a manifold that connects the canister to the well or sample point. The manifold is also equipped with pressure gauges, a filter, and a flow limiter that controls the flow of soil gas into the sample container to maintain sample quality. Sample collection stops when the canister pressure gauge shows the canister is nearly filled.
We answered the five Ws and a H for a soil gas sample. There are plenty of questions to ask about soil gas, contamination, and exposure at our homes and workplaces. We are here to help answer those questions and provide related services such as soil gas sampling and vapor intrusion mitigation system design, installation, and monitoring.
If you have any other questions about soil gas, or need help with another environmental question, please call us or click the button below for a free consultation. We’ve been helping folks for 35 years and we know what we are doing.
An attorney we work with asked me to look at a phase I environmental site assessment (ESA) for his client. His client was really interested in the property, which already had a solid lease.
The ESA disclosed a historically recognized environmental concern (HREC) and a recognized environmental concern (REC). Both had to do with a release of gasoline from a former underground storage tank (UST) at the property. The property had environmental case closure with very low levels of gasoline contamination left in place.
The question posed by the attorney’s client boiled down to the Phase I recommendation - “Complete a Vapor Intrusion Assessment and Prepare a Soil Management Plan”.
“Is this necessary?” the client asked.
I told them that the recommendation was very conservative based on the information provided by the ESA. I let them know that if they planned to redevelop the property, the county would probably look to them to voluntarily investigate for vapor intrusion and prepare a soil management plan as part of the redevelopment.
I advised that the recommendation was overly conservative given their intention to hold the property as is. I also told them that it was unlikely a vapor intrusion assessment would disclose a vapor intrusion problem.
As we were wrapping up, a question came up, “What is a vapor intrusion assessment?”
I started my answer with an explanation of vapor intrusion.
As a liquid chemical evaporates, it turns from a liquid into a vapor or gas. All liquids evaporate to some extent, and the extent to which a liquid evaporates shows its volatility. The more volatile a liquid is, the more quickly it turns into vapor.
When a liquid chemical leaks into the ground, it enters the soil and groundwater. Once in groundwater, the chemical moves along with the groundwater. As this process unfolds, and depending on its volatility, some of the released chemicals turn into a vapor and enter the space of dry soil above the groundwater. The vapor can leak up through the ground and enter a building causing a buildup of chemical vapors in the building. This process is vapor intrusion.
As time goes on, groundwater carries the dissolved chemical downstream from the chemical release. At the same time, a vapor plume (just like the billowing smoke that forms above a smokestack) forms in the soil above the affected groundwater. The area of the vapor plume mirrors the area of chemically-affected soil and groundwater.
A vapor intrusion assessment uses the link between the vapor plume and affected soil and groundwater to confirm whether there is contaminated soil and/or groundwater in an area and to determine whether any detected contamination poses a human health risk due to vapor intrusion.
In practice, a vapor intrusion assessment involves collecting soil vapor samples from small wells spread across the area you are investigating, and testing the soil vapor samples for suspected contaminants.
Typically, detected contamination levels in soil vapor are used to estimate how much area is contaminated, identify areas of high contamination or “hot-spots”, and gauge potential human health risks by comparing detected levels with published environmental screening levels (ESLs).
A vapor intrusion assessment has some real advantages over the more traditional phase II soil and groundwater assessment for figuring out where soil and groundwater contamination is, where the highest levels of contamination are, and whether soil vapor intrusion poses a human health risk.
Number one, a soil vapor assessment costs much less than a soil and groundwater assessment, generates less waste, is less intrusive, and provides information that can be used to target a groundwater and soil investigation, and possible cleanup. Additionally, a soil vapor assessment can be used to examine vapor intrusion health risks.
Of course, a soil vapor assessment does not provide all the information a soil and groundwater investigation can, but it gets you well down the road and allows more efficient and cost-effective phases of investigation and cleanup.
Our recommendation: Before drilling for soil and groundwater samples, use a soil vapor assessment to get a valuable overview.
In this article, we took a look at soil vapor intrusion, explained what a soil vapor assessment is, and described some of the advantages a soil vapor assessment has over a traditional phase II soil and groundwater investigation.
If you have a Phase I ESA that recommends verifying an HREC or REC, go ahead and get a second opinion, and if necessary, consider using a soil vapor assessment to confirm the ESA recommendation. With over 30 years of experience in conducting soil vapor assessments and reaping their advantages, we can help. Please call us at 831-475-8141 or click below to schedule a free consultation.
Groundwater monitoring is a crucial aspect of environmental management, helping to detect and manage potential groundwater contamination. However, the frequency and duration of monitoring can vary depending on site conditions and regulatory requirements. This page from Remediation Risk Management provides valuable insights into determining the necessary amount of groundwater monitoring, factors that affect monitoring requirements, and how to determine the appropriate frequency and duration of monitoring.
Everything has a beginning, middle, and end - even groundwater monitoring.
The Beginning. After contamination is identified in groundwater at a property, it’s common practice for the local environmental oversight agency to require groundwater monitoring. In California, the response to groundwater contamination is prescribed in State Water Resources Control Board Resolution 92-49 (SWRCB 92-49). This usually comes in the form of a regulatory directive - a letter arrives in the mailbox.
The Middle. The directive usually requires investigation, cleanup, and reduction of contamination by completing the following phases under their oversight:
1. Initial site assessment
2. Soil and groundwater investigation
3. Cleanup and reduction
4. Verification monitoring
The thing is, groundwater monitoring usually begins with initial site assessment and ends with long-term verification monitoring - which may take up to 10 years to complete.
What is groundwater monitoring? In essence, it’s measuring how deep groundwater is below the ground and collecting samples of groundwater for various tests. Groundwater is reached through wells that can be temporary or permanent. The wells are built in holes drilled through the soil into the groundwater. Sometimes, no well is used and groundwater is monitored using a bare hole.
During the initial site assessment phase, groundwater monitoring is used to identify the type and general location of contamination. During investigation and cleanup, groundwater monitoring is used to observe changes in contaminated groundwater and the effects of cleanup and contamination reduction. Long-term verification monitoring is used to build confidence that contamination left in place will not cause future problems. It's easy to see how groundwater monitoring seems to go on and on.
Groundwater monitoring is done to answer the following questions:
The answers to these questions provide much of the information used to complete investigation, cleanup and reduction of contamination - and receive environmental case closure.
As more information about the groundwater contamination becomes available, groundwater monitoring becomes more focused. As a result, it might be possible to reduce monitoring costs by reducing the monitoring frequency, the number of wells monitoring, or the number of tests performed.
The End. Groundwater monitoring ends when contamination levels no longer need watching. All the questions about groundwater contamination have been answered.
Early on - the what, where and how of contaminated groundwater are answered in the preliminary and investigation phases. Contaminant cleanup and reduction continue, and after a few years the seasonal patterns of groundwater flow and contaminant levels are generally understood. Over this period, the decrease in groundwater contamination over time is well established. There comes a point where the groundwater monitoring information shows that even with groundwater contamination safely left in place, cleanup goals will be reached in a reasonable time.
Finally verification monitoring is done to record final site conditions for environmental case closure. Groundwater monitoring usually stops at this point because in most cases verification monitoring supports case closure.
Groundwater monitoring begins with a regulatory directive and ends with a regulatory directive; No Further Action - Case Closure.
We answered the question about how much groundwater monitoring it takes. We described the beginning, middle and end of groundwater monitoring, and how it follows the phases of contamination investigation, cleanup, reduction and case closure. If you’re somewhere around the beginning, middle, or end of your own groundwater monitoring experience, and need some help or a second opinion, give us a call or click the button below for a free consultation. We have over 30 years of experience in completing environmental investigation, cleanup and reduction - including groundwater monitoring.
You’re reading this because you are looking for an honest and reliable environmental consultant who will save you money, give you the answers you need, and provide reassurance. When confronted with an environmental issue, one of the most important questions you’ll have is, who are the best consultants in my area?
RRM wants to help prospective clients find the best company to meet their needs. We’ve been in business since 1992 providing cost-effective solutions to environmental challenges, and we understand the necessity for exploring other options. We compiled a list of local companies to help you narrow your search.
Located in Watsonville, WHA has been providing environmental and geotechnical services since 1988. They have extensive experience providing services to the agricultural industry, including guidance on stormwater conveyance and detention, and waste discharge for composting operations.
This company operates from Monterey and offers a wide range of environmental testing and inspection services in areas such as industrial hygiene, building science, and specialty construction. Their industrial hygienist provides consulting in indoor air quality testing, indoor environmental services, and environmental analysis.
Established in 2005, Trinity is located in downtown Santa Cruz. They offer a broad range of environmental consulting, management, and construction services with a turnkey approach to environmental challenges. This includes providing drilling services in addition to environmental services.
Based in Los Gatos, RHE offers a full range of professional and technical services for the investigation, remediation, and management of difficult environmental conditions. They are great at helping people understand tricky compliance situations.
While cost is always one of the first topics you might discuss, you might also want to hear about their experience in dealing with your particular problem, about their relationship with the relevant county and state agencies involved, project timing, and what potential contract arrangements look like.
We hope this post has provided you with information that helps you make the best choice. No matter which consultant you choose, we are here to answer any questions. Click the button below to schedule a free consultation or call us today at (831) 475-8141.
I got a call from an exacerbated client who was rightly concerned about a letter from the county. “The county letter said my neighbor has finished cleanup at their dry cleaner and they were implementing active vapor intrusion mitigation, “ she told me. We were helping this client navigate the issues, concerns and requirements regarding investigation and cleanup at a property adjacent to her own. “What is active vapor intrusion mitigation and what does it mean for our property?” she asked.
“Good question,” I told her. “I know we’ve already talked about vapor intrusion as it relates to your property, but let's go over it briefly, then we can talk about active vapor intrusion mitigation."
“When we first spoke about investigation and cleanup at the dry cleaner next door, I told you there was a possibility that groundwater contaminated with tetrachloroethylene (PCE) traveled from beneath your neighbor's property to below your property,” I recalled. “I told you that PCE in the groundwater could contaminate soil vapor and contaminated soil vapor could enter the building on your property. Contaminated soil vapor traveling from an underground source into a building or building basement is vapor intrusion.”
“At the time, I let you know that soil vapor samples collected on your property showed there was no risk of vapor intrusion,” I said. “If we had found there was even a potential risk of PCE-contaminated vapor entering your building, we would have recommended active vapor intrusion mitigation (VIM) to keep vapors from entering into your building and to protect occupants from exposure.”
“While cleanup has occurred next door,” I continued, “it wasn’t enough to eliminate the vapor intrusion threat posed by the remaining contamination. So, to allow safe occupancy of the building, your neighbor decided to use active VIM until cleanup goals are reached.”
“Okay, sounds reasonable,” my client said. “So what is active VIM?”
Simply put, active VIM methods create a pressure difference between air on the inside of a building and the soil vapor under a building in a way that keeps vapors out of the building. Active VIM methods tend to be more effective than passive methods, but more expensive. These methods can be used on new and existing buildings, they have a successful track record of performance, they can be applied to a wide variety of site conditions, and simple pressure gauges show they work.
VIM methods require periodic maintenance and they have long-term energy and maintenance costs. Let’s consider three active VIM methods: sub-slab depressurization, sub-membrane depressurization, and building overpressurization.
Sub-slab depressurization systems are designed to provide continuous pressure reduction beneath a building’s floor and foundation. This method is for new or existing slab-on-grade foundations. Sumps, drain tiles and block wall foundations can also be depressurized. Depressurization refers to using a fan or blower to bring the air pressure in the sub-slab venting layer down below the air pressure in the building. In this method, a blower or fan pulls contaminated vapor from the venting layer and discharges it above the roof line into the atmosphere. An air discharge permit may be necessary to allow discharge to the atmosphere.
For new construction, a vent layer made from sand or pea gravel is placed below the slab foundation. Soil vapor collection piping and a common header are installed in the vent layer to direct contaminated soil vapor to a discharge stack that ends above the roofline. The blower/fan connects the common header with the discharge stack. Regulatory guidelines suggest using a sub-slab liner above the vent layer to provide added protection if the fan fails.
For an existing slab-on-grade building, installation of a sub-slab depressurization system entails cutting holes or trenches in the building slab, removing soil and building venting pits or trenches in the space left behind. The vent pits or trenches are arranged to provide depressurization coverage over the entire building footprint. Collection pipes are installed in the pits or trenches after which they are filled with sand or pea gravel and covered with slab material. A common header connects the collection pipes with a blower or fan. Extracted soil vapor is routed to a discharge stack.
Sub-membrane depressurization operates like the sub-slab variety but refers to creating a venting layer beneath a membrane that is installed in crawl spaces over bare earth. It can be used in new and existing buildings with crawl spaces. The membrane covers the exposed dirt surface of a crawl space, creating a venting layer between the membrane and the dirt floor. The rest of the system is similar to a sub-slab depressurization system.
The edges of the foundation and any pass-through piping need to be well sealed and the membrane should be loose enough to prevent tearing. Routine inspection of the membrane is necessary to check for the seals and membrane for damage. An air discharge permit may be necessary to allow discharge to the atmosphere.
Building overpressure involves using a building’s heating, venting, and air conditioning (HVAC) systems or a new system to maintain positive pressure in a building relative to the pressure beneath the building floor. This method is typically used for commercial buildings and can be inexpensive for buildings where the HVAC system maintains a positive pressure.
We wrapped up our conversation about active vapor intrusion mitigation (VIM) methods and turned to the question of how VIM might impact her property. I told my client that VIM at the neighbor’s property means her property won’t be exposed to soil vapor contamination from her neighbor’s property. I let her know that as long as VIM is underway, the state and local environmental health agencies will oversee the operation and that VIM will operate until cleanup goals for her neighbor’s property are reached. It was good news for my client.
We have over 35 years of experience providing solutions for environmental challenges including vapor intrusion mitigation. Can we help you? Please click the button below for a free consultation.
In many cases, vapor intrusion mitigation is needed after investigation and cleanup at sites with difficult contaminants like tetrachloroethylene (PCE). This is because active cleanup methods may not remove all the contamination or cleanup may not be possible. In these cases vapor intrusion health risk remains. As a result, folks responsible for investigation and cleanup at site sites with difficult contaminants may be faced with a decision regarding vapor intrusion mitigation (VIM). At some sites, building occupancy is critical to maintaining business, and VIM is the only solution.
Three top passive VIM methodsn methods can be separated into two groups: passive and active. Here we take a look at three top passive VIM methods, but first let’s look at how VIM works.
Volatile chemicals like PCE, when released into soil and groundwater, create a vapor that can enter a building through entry points like cracks or holes in slabs or basement floors and walls; openings around sump pumps and elevator shafts; or where pipes and electrical wires enter the building. It is also possible for vapors to pass through concrete, which is naturally porous. This movement of vapors from underground into a building is termed vapor intrusion. The purpose of VIM is to eliminate intrusion through building entry points.
Passive VIM methods prevent chemical vapors from entering a building or reduce contaminant levels beneath a building. They tend to be cheaper than active methods. Typically, multiple passive VIM methods, like a floor seal with a sub-barrier, are used at the same time to provide a backup in case one of the VIM methods loses efficiency or fails. Three top passive VIM methods are: sealing, vapor barriers, and passive venting.
Sealing entry points with a chemically resistant sealer is an important first step in VIM for existing buildings. Chemically resistant coatings can also be used to seal the floor, wall and entry points in an existing building and prevent vapor entry. Concrete can be poured on unfinished dirt floors to prevent entry.
Regulatory guidance suggests that in most cases sealing should be used with other VIM methods to provide a backup.
Vapor barriers (also called sub-slab liners or passive membranes) are materials or systems installed below a building floor to block the entry of vapors. Most barriers use sheets of “geomembrane” or heavy-duty plastic placed between the sub-base and building floor to prevent vapor entry. Vapor barriers are best installed during building construction, but can be installed in existing buildings that have a crawl space or basement.
In principle, vapor barriers cause soil vapor to move laterally beyond a building footprint instead of into a building. In practice, vapor barriers are not able to completely eliminate vapor intrusion due to the likelihood of punctures, perforations, tears, and incomplete seals. As a result, regulatory guidance suggests vapor barriers be used in combination with passive venting or sub-slab depressurization (active mitigation).
Passive venting involves installing a venting layer beneath a building to provide a pathway for soil vapor to move from below ground toward the sides of the building where it is vented outdoors. The system is designed to reduce or dilute subfloor contaminant levels. A venting layer can be included in new construction, but may be too expensive for an existing building. Passive venting is usually paired with a vapor barrier.
Passive venting systems typically consist of a layer of venting material (sand or pea gravel) emplaced below a floor slab to allow soil gas to move laterally under natural dilution or pressure difference. Soil vapor entering the venting layer is directed to the edge of the floor foundation by perforated pipes installed in the venting layer, either beneath the slab or at the periphery of the building foundation.
The vent piping usually comes together at a header pipe which runs vertically up the building wall and discharges above the roofline. Installation of a vertical inlet pipe that connects the vent layer with outside air and allows fresh air to enter the venting layer can help dilute chemical concentrations.
Regulatory guidance suggests constructing a passive venting system in a way that allows the system to become an active venting system with minimum effort if necessary (use of a fan or pump to move soil vapor from the venting layer to the header for discharge). Passive venting may not be appropriate in areas with a high groundwater table or surface water drainage problems because the venting layer will not work properly if saturated with water.
Finally, since the passive venting system discharges to air, it may need an air discharge permit to comply with applicable state or local air quality discharge regulations.
Sealing is appropriate for existing buildings and can be included into the design and construction of new buildings; however, in either case guidance suggests sealing be used with a barrier, passive venting, or sub-slab depressurization (as the name implies, used for slab-on-grade building construction). While sealing is applicable to new and existing buildings, it is not recommended as a stand alone VIM solution.
When it comes to a vapor barrier or passive venting, installation in an existing building without a crawl space could be difficult and would likely require the floor to be removed and replaced. Removing and replacing a building floor, even if possible, would be expensive. As a general rule, VIM for an existing slab-on-grade building is restricted to sub-slab depressurization, an active VIM method. Sealing, vapor barrier, or passive venting are appropriate for new construction and existing buildings with a crawl space, basement, or raised floor.
It is recommended that sealing or use of a vapor barrier include passive venting to counter the likelihood of leaks, punctures, perforations, tears, and incomplete seals. Sealing is already common practice in building construction and maintenance, so it is given that any existing or new construction is or should be sealed or re-sealed. This means in practice, most passive VIM systems will employ a vapor barrier and passive venting.
We took a look at three top passive VIM methods, but there are others. For example, in the case of new construction, installation of a building with a raised floor might be the best passive VIM method. A raised-floor design includes an open first floor or other well ventilated first floor design to interrupt vapor intrusion from entering the second story living/working space.
Another passive VIM method is termed “Institutional Control”. Institutional controls typically use institutions (state, county or city government) to monitor and enforce property use controls through a land use covenant (LUC) or Covenant to Restrict Use of Property. The LUC may include multiple institutional controls with specific orders, prohibitions, restrictions and requirements to ensure property conditions under control remain unchanged and the risks, restrictions, and requirements to future buyers and occupants are disclosed.
An LUC may contain:
For a LUC with California’s Department of Toxic Substances Control (DTSC), the LUC must be approved by DTSC legal counsel and publicly recorded in the county recorder’s office.
All VIM methods mentioned require some sort of performance monitoring, so it is important to consider long-term responsibilities. For example, while passive venting avoids the long term cost to operate a fan or blower, it requires monitoring effectiveness by measuring chemical levels in sub-slab soil vapor or by measuring indoor levels. Similarly, use of sealing or a vapor barrier would require indoor air and sub-slab soil vapor sampling to monitor effectiveness.
To address the long-term nature of VIM, and the need to assure they work, regulatory oversight agencies typically expect VIM implementation to include a plan outlining operation and maintenance, monitoring, reporting, financial assurance, an implementation schedule, five-year review schedule, and identification of who is responsible for the work.
We took a look at three top passive vapor intrusion mitigation methods. We found that for most cases, passive venting is the top passive VIM method, and that passive venting is used with sealing or a vapor barrier to provide eSxtra protection from vapor intrusion. We noted that in most cases, passive VIM is only applicable for new building construction or buildings with a crawl space, basement, or raised floor. We also noted that implementation of VIM requires long-term operation, maintenance, and monitoring to show effectiveness over the life of VIM.
Due to the toughness of some contaminants like PCE, cleanup limitations, and site constraints, complete cleanup to regulatory-approved levels is not often possible. In many cases VIM is relied on to keep a building safe and occupied during the span between active cleanup and low-threat case closure.
If your site is facing VIM, we can help. We have over 30 years of experience in solving environmental problems including VIM. To get more information, call 831-475-8141 or click on the button for a free consultation.
We got a phone call from a concerned citizen. She was concerned because the county environmental health agency sent a letter stating vapor intrusion could be occurring at her property. “Before I talk to anybody at county health, I want to know what vapor intrusion is and what it means for my family,” she confessed.
“If you have a moment, I’ll explain,” I said. “Let’s start with the vapor.”
I’m sure you’ve seen gasoline evaporate off the pavement, or a bowl of water evaporate leaving salt rings behind. How about rubbing alcohol? You might have noticed how it quickly evaporates leaving your skin cold. When you think about it, you might have noticed how gasoline or rubbing alcohol evaporates much faster than water. What’s going on?
When a liquid chemical evaporates, it turns from a liquid into a vapor or gas. All liquid chemicals evaporate to some extent, and the extent to which a chemical liquid evaporates shows its volatility. The more volatile a chemical liquid is, the greater the tendency it has to generate vapor. Gasoline has a greater tendency to turn into vapor than water, that’s why gasoline evaporates off the driveway faster than water, and that’s why gasoline is more volatile than water.
When a liquid chemical leaks into the ground, it enters the soil and groundwater. Once in groundwater, the chemical has the potential to move along with the groundwater. As this process unfolds, and depending on its volatility, some of the released chemical turns into a vapor and enters the space of dry soil between the groundwater surface and the ground surface. At the ground surface, the vapor can enter buildings causing a buildup of chemical vapors.
Vapors primarily enter through openings in the building foundation or basement walls such as cracks in the concrete slab, gaps around utility lines, and sumps. It also is possible for vapors to pass through concrete, which is naturally porous. In their vapor form, contaminants like gasoline, tetrachloroethylene (PCE), and other volatile organic compounds (VOCs) can be inhaled, thereby posing immediate or long-term health risks.
After explaining what vapor is and what intrusion is all about, we got back to the subject of the county's letter. I explained, “The letter is warning you that a groundwater plume contaminated with PCE may have moved under your property and the PCE vapor from the plume may be causing a vapor intrusion health risk.”
“The letter goes on to request you contact the county office so they can arrange sampling soil vapor at your property and determine if there is a health risk,” I finished.
“So what if they find contaminated vapor beneath my property?” she asked.
I told her it depends on the level of contamination. At low levels, only monitoring may be necessary to show vapor intrusion is not a threat over time. At moderate to high levels, contaminant cleanup and/or mitigation might be required to eliminate a vapor intrusion health risk.
“I have one more question,” she said. “Who’s going to pay for all this? It wasn’t our fault the contaminated groundwater moved under our property.”
I sympathized and explained that there are various grant and funding programs in California for this situation. “I am sure that if the county finds contamination, they will look to those responsible for the contamination, and if they can’t find those responsible, they will use the appropriate funding mechanisms available from the state.”
Vapor intrusion refers to the migration of volatile chemicals from contaminated soil or groundwater into the indoor air of buildings. This can occur when chemicals such as volatile organic compounds (VOCs) or radon gas migrate through the soil and into buildings through cracks in foundations, basement floors, or walls.
We looked at what vapor intrusion is and how it could affect anyone near a contaminant release, even if the release didn’t happen on your property. The next question is how to protect yourself from vapor intrusion. Check this space for some answers.
We have over 30 years of experience dealing with problems like vapor intrusion, cleanup, and mitigation. If you have similar issues, we may be able to help. Click on the button below for a free consultation and learn more about what we can do to help.
“I just received an alarming letter from my county environmental health department that our property well is near a site where contamination was recently discovered. Our well is our primary source for drinking water. What do we do? Should we be worried?”
First, try not to panic. We realize this can be concerning news, especially when the letter does not provide helpful information, or the language is overly technical and hard to understand. In most cases, private, domestic wells that serve a residential property are often installed to depths much deeper than the source of contamination and draw from a different underground water source (aquifer). To better understand this concept, which can feel abstract since we can’t see underground, let’s look at the graphic below which illustrates what this scenario might look like.
An aquitard is a layer of bedrock or other impermeable material that separates different aquifer zones. In most cases, an aquitard will prevent mixing between shallow and deeper aquifers. If the contamination affects the shallow aquifer, and a nearby well is drawing from a deeper aquifer, it’s not likely the same contamination will be found in the deeper aquifer because it’s separated by the barrier of the aquitard.
This graphic is only a generalized view, but it can put into perspective what might be the case for your well. To understand the situation more fully and what it means for your water source, you’ll want to review the installation records for your well. Once you have that information, you can compare your well with the depth of the contamination that was discovered. If you don’t have information on your well and don’t know the depth, the Department of Water Resources (DWR) may have a record of your well in their database. It is state law that geologic logs and pertinent information on all wells drilled in California be provided to DWR.
Here are Your Next Steps:
When a site has been identified as a source of contamination, one of the first requirements from the oversight agency handling the case is to conduct a well survey, which is a tool to identify all the wells within a given radius from the source (usually ½ mile). The caseworker will analyze the survey and identify which wells could be affected by the contamination based on their construction and the distance from the source. The next step is usually obtaining permission from the well owners who could be affected to test the water from their well.
Right now we are consulting for a property owner who had a small farm in the family. Underground storage tanks (USTs) were used at the farm for fueling equipment and vehicles. Although the USTs were removed in the 1980s, they leaked, and fuel was released into the surrounding soil and groundwater. A neighbor who lives in a house next door draws water from a private well on their property and is within proximity to the source of contamination. Although their well is constructed to draw water from a deep zone at 300 feet, their well has a screen that extends through the shallower aquifer where contaminants have been discovered in groundwater samples. We’ve tested samples from the well at least twice per year since 2007, and none of those samples showed traces of contaminants. It is the responsibility of the land owner or responsible person of the contaminated site to provide for testing, and relay the results to the well owner.
It can be daunting to receive a letter with such alarming news, but arming yourself with information and asking the right questions will go a long way toward helping you feel safe about the integrity of your water. We have over 40 years of experience dealing with government agencies and cleaning up environmental messes - we can help you. Give us a call at (831) 475-8141 or click the link below for a free consultation.
For many of those managing investigation and cleanup of property contaminated with tetrachloroethylene (PCE) and other solvents in California, low-threat solvent case closure is the best but least understood option. This lack of clarity leads to frustration and mistrust. Let’s get familiar with low-threat solvent case closure and develop some general criteria beginning with the cleanup goal.
California State Water Resources Control Board (SWRCB) policy does not require that contamination is completely gone at the time of case closure; it specifies compliance with cleanup goals and objectives within a reasonable timeframe. This means that case closure can occur with contamination left in place as long as cleanup goals, such as relevant environmental screening levels (ESLs) or maximum contaminant levels (MCLs), are met in a reasonable timeframe. What defines a reasonable timeframe is ultimately decided by the regulatory oversight agency, but the decision considers the pace of natural cleanup mechanisms such as biodegradation. SWRCB closure orders for low-threat petroleum hydrocarbon sites state a reasonable time frame for plumes of a limited extent is multiple decades or longer, but expect more restrictions because PCE is less susceptible to natural cleanup mechanisms and has much lower ESLs. The general criteria for achieving cleanup goals are:
Criteria: Establish that natural mechanisms can reduce levels to cleanup goals and that contamination levels are at a point where natural mechanisms can reduce levels within a reasonable time frame.