Vapor Intrusion Assessments: Improving Data Quality Using Today’s Best Practices for Sample Collection

This blogpost is a summary based on a webinar hosted by TestAmerica, presented by Taryn McKnight on January 24, 2017 entitled, Vapor Intrusion Assessments Part One: Improving Data Quality Using Today’s Best Practices for Sample Collection.

Vapor Intrusion is the term given to the migration of hazardous materials (especially Volatile Organic Compounds, VOCs) from the subsurface into overlying buildings. Other possible vapor intrusion materials may include certain semi-volatile organic compounds and inorganic chemicals, such as elemental mercury, naturally occurring radon and hydrogen sulfide. Sources from the subsurface may include contaminated groundwater or impacted soils. Varying hazards may occur from the vapor intrusion of differing chemicals such as a safety hazard (potentially related to flammable vapors intruding a building or enclosed area) or a health hazard both acute (headaches, nausea, etc) and chronic (carcinogenic, etc).

Vapor intrusion science has progressed from the Johnson and Ettinger model in 1991 to the EPA establishing the OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air in 2015.

Variability (factors) in vapor intrusion studies include but are not limited to, barometric pressure, surface cover, preferential pathways, soil moisture & permeability, building depressurization, biodegradation, background air, etc…

Pros of indoor air sampling include, actual indoor air concentration, no modeling, no attenuation factors, relatively quick with no drilling or heavy equipment, and less spatial variability than soil gas. Cons associated with indoor air sampling include, planning time with the home/property-owner to perform sampling events, the removal of potential interior or lifestyle sources and contribution from unknown indoor sources and ambient air. The collection of outdoor air in conjunction with indoor air is a way to check the contribution of ambient air to the indoor air sample. It is important to conduct a building survey prior to the collection of an indoor sample. The building should include the deduction of potential background contamination sources such as common household products, building materials, etc… Sub-slab sampling can help resolve the issue of background contamination by bypassing the contamination potential from the room and sampling closest to the source of vapor intrusion.

Pros of soil gas sampling include, near source data and may provide an estimate of source vapor concentration. Additionally, it can be performed without entering the structure as to eliminate the need for coordination with the buildings occupants. Cons of soil gas sampling include, significant lateral and vertical variability and may not be representative of vapor concentrations under the buildings. The EPA suggests several rounds of sampling are generally recommended. Soil gas sampling protocols include, purging the tube using a syringe, bag or canister, dialing in a flow rate for purging/ collecting using a flow controller, measure the vacuum being applied on the subsurface using a vacuum gauge, rotometer or syringe, measure for biodegradation at sites containing petroleum by testing for CH4, O2, and CO2 and application of a tracer gas such as helium, Freon or isopropyl alcohol (IPA) using a shroud and a field detector.

A leak check using a tracer gas is to be performed to ensure no leaks from ambient air into the sample collection system is found. The shroud is placed over the sample probe with a hydrated bentonite seal where an inert tracer gas is added to the shrouded environment. A test sample is then drawn from the sampling probe and if detection of the inert gas is observed, then ambient air is capable of reaching the subsurface and contamination of the sample collected is likely. Refer to the figure below to view a basic “in field” leak test.

A second leak test referred to as the shut-in test is to be performed on the sample collection system. This test is to ensure there is an air tight seal between the sample probe/tube and sample collection system such as a Summa canister. The figure below highlights the steps to perform an air tight seal.

Finally, canisters have no preservation required and can be shipped via air with few caveats. The hold time on canisters is specified in TO-15 as 30 days so it is generally dependent on the consultant’s necessary turn-around-time. The quality of data collected is dependent on the entire process of data collection from beginning to end. A careful process is necessary for thorough, accurate and precise data.

 

Leaching Analysis Procedures

Leaching is a process by which soluble constituents are dissolved form a solid material (solid or waste) into a contact water phase.  The extent to LEAFwhich they are dissolved depends on the site, material specific conditions (chemical, physical and biological) and the length of time involved.  The process of leaching includes the partitioning of contaminants between a solid and liquid phase and the mass transport of aqueous or dissolved constituents.  When fill material comes in contact with a liquid like rainwater, groundwater, or surface water constituents in the solid dissolve forming a leachate.  This leachate can then have an impact on local water quality.

Several laboratory methods are utilized to evaluate the leaching potential of a soil sample including the following:

EPA Method 1311 – toxicity characteristic leaching procedure (TCLP) was first used by the USEPA in 1990 to replace EPTOX as the regulatory method for classifying wastes as hazardous based on toxicity. This method was essentially a pass or fail where if the TCLP extract contained one of the TC constituents equal to or exceeding the concentrations specified then the material would be considered hazardous. This method was later criticized for being too broad. In 1999 the USEPA SAB recommended developing multiple leaching testes that could be more flexible, cases specific and have tier testing or a suit of related tests incorporation the most important parameters affecting leaching.

No one leaching test can provide accurate assessment for all potential soil impacts, so many different methods are used.  New leaching tests take into account the following aspects of leachability:

  • broad range of conditions;
  • Influence of pH on equilibrium; and
  • Influence of L/S on equilibrium and influence of mass transfer rates.

Some of these new methods are as follows:

EPA Method 1311 – Toxicity Characteristic Leaching Procedure (TCLP): Designed to simulate leaching a waste will undergo if co-disposed with municipal solid waste.  Used for hazardous waste determination.

EPA Method 1312 – Synthetic Precipitation Leaching Procedure (SPLP): Designed to assess the leaching potential of soils and waste disposed in a monofill when exposed to rainfall.  There are no federal regulatory requirements for the use of SPLP.

EPA 1313 – Liquid/solid partitioning as a function of extract pH using parallel batch extraction procedure. This method had nine parallel extractions and the contact time was determined by particle size.

EPA 1314 – Liquid/solid partitioning as a function of liquid solid ratio for constituents in solid materials using an up-flow percolation column procedure.  This tried to minimize the air entrapment and flow channeling so the entire effluent volume is collected.

EPA 1316 – Liquid/solid partitioning as a function of liquid/solid ratio for constituents in solid materials using a parallel batch extraction procedure. This method had five parallel extractions where the contact time was determined by the particle size.LEAF-2

EPA 1315 – Mass transfer rates of constituents in monolith or compacted granular material using a semi-dynamic tank leaching procedure.  This was a flux based leaching method for monolith/compacted material where the sample is immersed in reagent water at specific liquid/solid surface area providing the mass transfer rate of COPC under diffusion control leaching conditions as a function of leaching time. This method states that it is for non-volatile organics only.  There is a modified 1315 method for PAHs and VOAs.

ANSI/ANS – 16.1 – 2003 – The measurement of the leachability of solidified low-level radioactive wastes by a short-term test procedure. This method was developed for low-level radioactive waste and can be used to measure the leach resistance of any waste solidified into a well-defined geometric shape.

Tiered Testing was developed so each tier can provide leaching data which is more specific to the material being tested and leaching conditions.

Thank you to Test America for the original presentation on this material.

Laboratory Analysis for Petroleum Hydrocarbons

EPA method 8015 is one of the most commonly used analytical methods in determining the extent of total petroleum hydrocarbons (TPH) impacts on soil and groundwater, specifically diesel range organics (DROs) and gasoline range organics (GROs). This method is often employed for leaking underground storage tank (LUST) sites or other characterization sites and is used to determine the concentration of semi volatile organic compounds and various non halogenated volatile organic compounds by gas chromatography using flame ionization detection. Diesel range organics correspond to the range of alkanes with carbon chains from C10-C28 and cover a boiling point range of approximately 170 degrees C to 430 degrees C. Gasoline range organics correspond to the lighter alkanes with carbon chains from C6- C10 with a boiling point range of approximately 60 degrees C to 170 degrees C.

tph
Graphic from Brewer et al. (Risk-Based Evaluation of Total Petroleum Hydrocarbons in Vapor Intrusion Studies. International Journal of Environmental Research and Public Health. June 13, 2013.

EPA method 8015M is a known modification of Method 8015B which provides an analysis of motor oil range organics.  Motor oil range organics correspond to the range of alkanes with carbon chains from C28-C35.  Silica gel cleanup is sometimes included in Method 8015. Scientific investigation has shown that the analytical signature of water-soluble petroleum hydrocarbons should be composed of discrete peaks and should not have an unresolved complex mixture or “hump” in the chromatogram. These humps can be resolved by doing a silica gel filtration of the sample. Our testing is done reliably and expeditiously at Performance Analytical Laboratories Inc. located in Signal Hill (pali-labs.com). For more information on this procedure, please see the EPA science inventory webpage on TPH.

Total Petroleum Hydrocarbon (TPH) Analysis

One very common analysis run on soil and / or groundwater samples collected during a site characterization project is Total Petroleum Hydrocarbon (TPH).  Many times, we focus this analysis on gasoline range (TPHg), diesel range (TPHd), motor oil range (TPHo), or the full carbon chain (TPHcc) depending on the historic site use or the findings of previous site investigations.

There several ways of analyzing TPH in soil and groundwater, but the general theory is to attempt to identify the portions of the carbon chain and length of the carbon chain present in the sample.  This stems from the fact that these compounds originate from long-chain crude oil that is refined into shorter carbon chain segments.  The, “Lighter-end” hydrocarbon chain with 5-12 carbons generally represent the gasoline range (TPHg).  The carbon chains ranging between 10-28 are generally considered diesel (TPHd), with compounds such as kerosene and jet fuels somewhere in between.  The actual number of carbons in the chain varies based on the specific type of petroleum product, it’s purity, and age (extent of degradation).  The, “Heavier-end” of the carbon chain up to around 40 carbons is considered the motor oil range (TPHo) and in this range, we generally request that the laboratory perform a silica gel clean up on the sample to remove naturally-occurring lipids that would create a false-positive.  One example of a naturally occurring compound that would be removed by the silica gel cleanup method would be eucalyptus oil.  The only drawback of the silica gel cleanup process is a small amount of dilution and subsequently slightly higher detection limits.  For this reason, we really only perform the silica gel cleanup process when performing a site investigation or characterization and avoid it in more long-term groundwater monitoring or remediation projects.

In our next post, we will talk further about the various analysis methods for TPH.

AeroJet Sacramento Facility

one of the major west coast sites that it seems everyone in the environmental remediation business gets to work on at one point is the AeroJet Sacramento Facility. Even though I am based in Southern California, I did a soil gas investigation out there in the summer of 2002 or 2003. It seems that the site continues to require attention and has received additional federal funding. The EPA issued the following press release last week:

SAN FRANCISCO — The U.S. Environmental Protection is ordering a $60 million clean-up of rocket fuel-polluted groundwater at the Aerojet Superfund Site in Sacramento County, Calif., the latest phase of a long-term decontamination project at the site. The extent of toxic pollution at the site makes it one of the largest and most comprehensive Superfund groundwater cleanups in California.
A 27-square mile swath of groundwater underneath and around the former aerospace facility is polluted with several compounds, including very high levels of perchlorate — a main component of rocket fuel — and a known developmental toxin. Aerojet, under the direction of the EPA, will contain the underground plume to prevent it from spreading into nearby rivers and streams. Future plans will also treat groundwater within the site’s boundaries.

This site is one of many former aerospace facilities that requires site investigation, cleanup, and various other compliance-related focus.

Form more information, see the EPA website: www.epa.gov/region09/Aerojet

New Maximum Contaminant Levels Adopted

The California Department of Public Health adopted a new and updated Maximum Contaminant Level (MCL) list in November of 2010. As you look through it, you may notice that there are quite a few compounds on the list that did not previously have MCLs. We commonly substituted the San Francisco Regional Water Quality Control Board (RWQCB) Environmental Screening Levels (ESLs) for those compounds, if necessary. You may also notice that many compounds have lower MCLs than what was listed previously by the California Department of Public Health.

Perhaps most interestingly, 1,4-dioxane, 1,2,3-TCP, NDMA, and Nitrosamines now have notification limits, but do not have MCLs. These notification limits really only pertain to potable water suppliers, but the same values are likely to be the MCLs in the upcoming years.

This is worth keeping an eye on.