Displaying items by tag: Residential

SP w carson river 027 10 10 2010 1In 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.

How Vapor Intrusion Mitigation (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.

What is Passive Vapor Intrusion Mitigation?

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.

Three Top Passive Vapor Intrusion Mitigation Methods

1) Sealing

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

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

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.

IMG00158 20100419 1622Passive 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.

How do Passive Vapor Intrusion Mitigation (VIM) Methods Compare

Existing Building Versus New Construction

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.

Sealing, Vapor Barrier, or Passive Venting

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.

Other Passive VIM Methods

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:

  • A notice that there is contamination that may cause vapor intrusion risk.
  • Prohibitions against specific uses of the property, interference with VIM systems, or activities that would disturb site conditions defined at the time the LUC is executed.
  • Property access agreements for the oversight institution and other relevant stakeholders.
  • Inspection and reporting requirements for the property owner.

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.

Long-Term Responsibilities for Active Vapor Intrusion Mitigation Methods

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.

Passive Vapor Intrusion Mitigation Methods: An Overview and How We Can Help

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.

How Much Will a Phase II Assessment Cost?

drilling in townA close friend called. She told me she was working on a development project, and just got the results of a Phase I Environmental Assessment. The assessment pointed to a potential obstacle to the project - a Recognized Environmental Condition (REC). The project site used to be a dry cleaner that closed up shop a few years back, and the assessment noted there could have been a release of tetrachloroethylene, or perchloroethylene (PCE) into the soil and groundwater. My friend was really upset. It was already difficult enough with stakeholders, banks, city and county regulators taking chunks of her time and money - now this. She was stressed. “Can you help?” she said, “Now they want a Phase II Assessment to investigate the REC (Recognized Environmental Condition). All I want to know is, how much is this going to cost?”

I paused for a moment thinking, “It depends…”, but quickly remembered the stress she was under. “How about we meet for coffee in a couple of hours and in the meantime, I will work up a cost for a Phase II Assessment for you?” That’s what she wanted to hear.

Why a Phase II Assessment is Often Recommended

A Phase II Assessment is often recommended to verify a REC (Recognized Environmental Condition). In the case of my friend, a Phase II was recommended to determine whether there was a release of PCE. Typically, a Phase II assessment entails collecting soil and/or groundwater samples and analyzing the samples for particular chemicals. Often, a Phase II Assessment means the same thing as a soil and groundwater investigation.

My friend described the site as a small empty retail unit at a shopping mall, so it seemed to me that we could find out if there had been a chemical leak by drilling three small-diameter holes into the ground to collect soil and groundwater samples. One at the former location of the dry-cleaning machine, one at the floor drain, and one along the sewer leaving the unit. At least two soil samples and one groundwater sample would be collected from each hole, and samples would be analyzed at a state-certified laboratory. A soil and groundwater investigation report would be prepared that would include methods, results, conclusions, and recommendations. All the work would be overseen by a professional geologist or engineer whose signature would appear on the final report.

Breaking Up the Phase II Assessment Into Tasks

puzzleOne way to estimate the cost of work is to break it up into tasks, and then estimate the cost of each task. A Phase II soil and groundwater investigation can be broken into three main tasks:

  • preparation of a work plan,
  • fieldwork, and
  • reporting.

Estimate the Cost

With the tasks identified, we can estimate the cost. My knowledge and experience are important here, but a reference carries weight. The California Underground Storage Tank Cleanup Fund, a state program for underground storage tank owners and operators that funds investigation and cleanup, publishes cost recommendations (Guidelines). While these recommendations are associated with work on sites contaminated with gasoline and the like, they can be applied to assessment work for other compounds, such as the dry-cleaning chemicals my friend was worried about.

Work Plan

The work plan:

  • identifies known property conditions,
  • the potential contaminants and
  • suggests how best to take samples.

The Guidelines estimate the 2018 cost of a Phase II soil and groundwater investigation work plan at $3,380.

Adjusting for inflation, about 8.6% according to California Consumer Price Index (CPI) Inflation calculator, we have estimated the cost of a Phase II soil and groundwater work plan at $3,671. (Note – you can also adjust estimated costs to a particular area of California or to a national average.)

Field Work

For field work, we will consider the cost of drilling three holes to 30 feet as suggested in the Guidelines. In the description of work, the Guidelines include scheduling, coordination, field preparation, permitting and field work in the estimated cost for three holes. The Guidelines also include costs for equipment rental and supplies, a drilling contractor, chemical analyses, and subcontractor mark-up. Here the number of samples and methods of sampling that the Guidelines recommend differing slightly from the proposed work for my friend’s site. To address the differences, we will simply adjust the Guidelines cost by subtracting unnecessary costs.

sampleAs presented in the Guidelines, the total cost to drill three holes to 30 feet is $11,244, but after adjusting for the difference in the number of samples to be analyzed (9 for my friend versus 15 in the guidelines) and the number of analyses to be conducted (one for my friend versus two in the guidelines), the total cost for drilling three holes to 30 feet comes down to $8,308.

Field work also includes health and safety coordination and waste disposal. The Guidelines estimate the cost of a Community Health and Safety Plan at $1,392 and waste disposal at $145 per 55-gallon drum of soil waste. It is likely only one drum of waste will be generated during field work on my friend’s project.

Reporting

Regarding an assessment report, the Guidelines provide the cost for a report where six holes are drilled and three of the holes are converted to groundwater monitoring wells. It’s clear the scope of work linked to the Guidelines estimate is greater than for my friend; however, in my experience, the difference in terms of report preparation is small, in this case, less than $500. The Guidelines quote $6,944 for an investigation report – let’s say $6,500 for our report.

Something Left Out

Finally, is there anything we left out? For example, it’s likely the floor of the unit is concrete, and we will need a concrete driller to actually get underground. Additionally, now that we have holes in the floor, we will need to restore the floor by backfilling the holes and patching the surface. The Guidelines are not much help here, but in my experience, a concrete-cutting contractor is going to cost about $500 and the backfill and patch is going to cost about $900.

Now, what else did we miss? Something. To address this something, we use a contingency factor, say 10 percent. This additional 10 percent is to account for things we did not address or for unforeseen circumstances – like the concrete floor being 15 inches thick instead of the typical 6-to-8-inch thickness.

Estimated Cost

Now we are ready to sum up the costs. Between the work plan, field work, and the report, the total estimated cost (adjusted for inflation) is $22,946. With a 10% contingency the total cost ranges from $22,946 to $25,241. Now I was ready for a cup of coffee with my friend.

I arrived on time to find my friend seated at a window table. She looked up and noticed me, “Hi, great to see you”, she said. We received our coffee and spent what seemed like forever adding cream and sugar in silence. I spouted up, “Ready for the news?” She slumped, “Okay.”

I started with my explanation of how I got the estimate, but when I looked over, her glazed eyes told me to get on with it. “Alright, I estimated the cost for a Phase II soil and groundwater investigation at your location to be $25,000.” The glaze turned intense, “That’s a heck of a lot of money - why does it cost so much?” I thought for a moment and said, “Let’s look at the factors that drive cost.”

Factors That Drive Cost Up in a Phase II Assessment (Why Does it Cost So Much?)

There are several factors that drive the cost of a soil and groundwater investigation, but for me, two factors top the list: the type of contamination and site location.

Type of Contamination

The type of contamination can be broken down into the composition (what’s in it), the magnitude (how much is there), and the extent (how far has it spread).

Site Location

Site location includes things like where the site is located, how big it is and whether improvements have been done, the location of groundwater, site geology, local regulations, site use (residential or commercial); and how hard it is to properly dispose of waste from drilling.

Let’s take a closer look at some of these factors.

Factor That Drives Up Cost

How and Why the Factor Drives Cost

Kind of Contamination Hazardous contaminants, such as those that are toxic, require specialized personnel, equipment, and disposal that drive up costs.
Contamination Level Higher levels of contamination drive up waste disposal fees and require specialized methods, personnel, and equipment that cost more.
Contamination Area and Depth Larger areas and depths of contamination need more time to investigate and bring on more waste to dispose of, more samples to analyze, and more data to report.
Soil and Rock Very hard or dense ground requires special equipment for drilling and longer drilling times that drive up costs. The same is true for drilling in sandy or loose soil.
Groundwater Dealing with groundwater drives up costs and the depth of groundwater below the ground drives costs because greater depths require more drilling, more well construction time, and more waste disposal.

 

"Well, that sounds complicated," she said. “So you’re saying that if the groundwater was deeper at my place, a soil and groundwater investigation would cost more?” “Yes”, I said, “for one thing, the field investigation might take longer than it would otherwise, increasing the cost.”

“So it could be worse…” she said flatly.

We sat in silence for a moment and then I asked if she had any more questions. She sat up straight and said, “Probably, but thank you. I need to let this soak in.” “No problem”, I replied, “let me know if you need any more help with your project.” I let her know our firm was a one-stop-shop that could provide all the environmental-related services she would need to complete her project. I also told her we are very sensitive to the hardships, both financial and emotional, that environmental issues bring.

Understanding the Cost of a Phase II Environmental Assessment: Factors That Influence the Price

We covered a lot of ground here. Using cost guidelines from California’s Underground Storage Tank Cleanup Fund as a reference, we broke down how much it costs to complete a Phase II soil and groundwater investigation, including the work plan, field work, report, and a 10% contingency. We also looked at the two primary factors that make a Phase II assessment so expensive - the type of contamination and site location. 

Are you staring down the barrel of a Phase II Assessment, and don’t understand why? Are you having trouble juggling the competing demands of regulators and other stakeholders?  Let us help. We’ve got 20 years of experience solving problems just like this. Schedule a consultation by clicking the button below, or just give us a call at 831-475-8141.

An Inroduction to Vapor Intusion

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.”

The Vapor

Understanding Chemical Evaporation: Why Some Liquids Evaporate Faster than Others

vaporintrusion.jpgI’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.

The Intrusion

The Risks of Vapor Intrusion: How Chemicals from Leaked Liquids Can Enter Buildings

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.

What is Vapor Intrusion?

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.”

What is the definition of vapor intrusion?

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.

Protecting Yourself from Vapor Intrusion: Tips and Solutions

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.

Protecting Your Well from Contamination: Essential Tips and Strategies

SP w carson river 098 10 10 2010

What to do if your well is near a site where contamination was recently discovered

“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.

well depthsAn 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.

Next Steps if Your Well is Contaminated

Here are Your Next Steps:

  1. Find your well information and review the design specifics.
  2. Prepare a list of questions - here are some suggestions:
    • Should we stop drinking our water until it can be tested?
    • How did you determine this contamination is a threat to our water source?
    • Who will pay for testing?
    • Who is the consultant hired to mitigate the contaminated property?
    • How can I get records and status updates on the cleanup?
  3. Call the person at the environmental health department who sent the letter for more information.
  4. Call an environmental cleanup agency or consultant for an independent assessment of the situation.

What if the site has been identified as a source of contamination

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.

Close

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.

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