Some of the most successful TRIAD case histories involve the use of X-ray Fluorescence (XRF) screening for metals. Prior to the advent of field-worthy XRF systems, site investigation and remediation for metal contaminants proceeded in a more classical manner of waiting for fixed laboratory results  or paying a premium for rush results.

In some cases, fixed laboratory methods were performed in a mobile laboratory setting with good results. This practice involved the use of concentrated acids and time consuming digestion steps and was useful for only a limited number of elements. This is no longer a problem with the availability of field portable and transportable Energy Dispersive X-ray Fluorescence Spectrometers (EDXRF).

Reporting limits are element, instrument, and sample matrix dependent. Each dependent variable contributes to the final achievable reporting limit. Once the suite of elements and instrument conditions are modeled, the only variable left is the sample matrix which can vary from site to site, or even within a particular site.

XRF techniques are not very useful for light elements (elements between atomic numbers 11-18). The remaining elements, those between atomic numbers 19 and 92, are candidates for this technique.

Reporting limits are also instrument dependent and can vary between manufacturers for a variety of reasons.

For radioisotope sources, the following factors impact the reporting limit: isotope used (Fe-55, Cd-109, Am-241, Cm-244); half life of the isotope; and the amount of isotope in millicuries. For X-ray tube sources, the energy level of tube and the current level of tube both impact the reporting limit. Both radioisotope and X-ray tube sources are affected by count time during analysis; detector type (gas filled, or Si(Li); grain size of sample; and moisture of sample.

Applications for EDXRF are varied and include lead investigations at battery recycling businesses, remedial investigations of military and public shooting ranges, munitions demolition areas, weapons manufacturing facilities, copper ore assay from mine tailing piles, and many industrial and household remedial actions for leaded paint removal.

As always, the benefit of a field analytical method is in providing near real time data so that time-critical decisions can be made in the field. This concept works best when the target analytes are limited to the main chemicals of concern for a particular site. The following application examples are from sites that had a limited list of target analytes so that the XRF method could be customized to maximize sample throughput and sensitivity.

Example 1. Lead Remediation at a Landfill Burn Site

This project had several time critical aspects: the rainy season was approaching, and there was a narrow window of time to complete all of the site work before a protected species of bird returned to the area. The project involved removal of 20,000 tons of lead-contaminated soil and ash from a burn pit operation at an abandoned land fill. The lead had contaminated the entire area surrounding the landfill, which bordered on an elementary school and a public lake. The required reporting limit for lead was 15 mg/kg, and the sample throughput was to be 40 samples per day. Confirmation samples were taken initially at a 10 percent frequency, and dropped to a five percent frequency once the correlation was determined.

A transportable XRF unit was set up on location in a mobile laboratory, complete with fume hood, generator power, and water. All samples were prepared by sieving, drying, and grinding prior to analysis. The calibration model used was Fundamental Parameters and results were provided at a rate of four samples per hour. The data correlated at R=0.988 (see North Chollas for data spanning nearly three orders of magnitude). The project was completed within the allotted time frame and budget.

The XRF approach was approved by city and state agencies, with the stipulation that a correlation be determined at the start of the project and confirmation samples be split throughout the project, initially at a 10 percent frequency, then decreasing to no less than five percent.

Example 2. Lead Remediation at an Active Battery Recycling Shop

This project was a State Superfund cleanup of lead-contaminated  soil from a battery recycling shop located in a residential area. The initial site study called for removal of 1,315 cubic yards of soil for transport and disposal at a Class I landfill at an approximate cost of $620,000. By using the EDXRF system, the volume of soil actually sent was reduced to 666 cubic yards, which saved $306,000. Other critical aspects of the project involved minimization of exposure risks to nearby residents and site workers. By using the rapid turnaround results from the EDXRF system, the site was cleaned up to an action level of 220 mg/kg with correlation to EPA method 6010 of R=0.989.

The State of California, under the State Superfund program, sanctioned this project. The XRF approach was initially approved with the stipulation that site-specific calibration be performed. The samples were quantified by using Fundamental Parameters software, and since the correlation was >0.900, the site-specific calibration was not needed.

Example 3.  Multiple Elements at Navy Dump Site

This project was a technology demonstration of both the EDXRF and a soil washing technique at a known contaminated site, Hunter’s Point. This site was adjacent to a densely populated area. It had been used by the Navy and private industry for a variety of activities, including transformer and battery storage and vehicle maintenance activities. The site was moderately contaminated with lead concentrations above non-residential clean up levels. Other elements of concern were mercury, antimony, copper, zinc, and chromium. During the two-week project, the EDXRF system was used to help optimize the soil washing system prior to the actual demonstration. The demonstration yielded 80 washed samples of which 23 were sent for confirmation.

The correlation for antimony was rather poor and was a function of the solubility of antimony in the acid digestion used in method 6010. Aside from antimony, all correlation coefficients were >0.990. Mercury was not detected in any of the samples, nor by the confirmation laboratory at a level >10 mg/kg. This demonstration helped confirm the findings from an earlier study published by the California Military Environmental Coordination Committee that a correlation coefficient of 0.9 or greater indicates that the field XRF data may be considered definitive (i.e. equivalent in data quality to CLP methods).

XRF techniques are rapidly gaining acceptance as a viable field solution to rapid metal analysis in a field setting. XRF is no longer considered an emerging technique and is in widespread use by state and federal agencies, as well as by environmental professionals throughout the country. Whether portable or transportable, the EDXRF technique is proving its worth as a rapid, accurate, and cost-effective tool for site investigation and remedial activities.

References

1. USEPA Field Analytic Technologies Encyclopedia (FATE), Online resource: http://fate.clu-in.org. Last updated, January, 2003.
2. USEPA TRIAD Report, Online resource: http://www.epa.gov/tio/triad. Last updated November, 2005.
3. TN Spectrace, Spectrace Instruments EDXRF Users School Manual, Spectrace Instruments, Fort Collins, Colorado.
4. Merck & Co., Inc., The Merck Index, Eleventh Edition, Table of Radioactive Isotopes, Merck & Co., Inc., Rahway, New Jersey, 1989.
5. Bertin, E.P., Introduction to X-Ray Spectrometric Analysis, Plenum Publishing, New York, 1978.
6. Panuscka, Barber, Smith, Mobile EDXRF Screening at Lead Contaminated Soil Removal Project, Conference Proceedings, Hazwaste World Superfund XVII, October, 1996, Washington D.C.
7. CMECC, Field Analytical Measurement Technologies, Applications, and Selection, April 1996.
8. Barber, M, Application Analysis Report, Onsite Environmental Laboratories, Bay Area Conversion Action Team (BADCAT).

Odor is a parameter which may be measured unto itself, following established ASTM and/or European Standards. This approach will quantify how odorous a sample is, ranking it on a relative scale with units of dilution to threshold (D/T).

Knowing the magnitude of an odor problem is useful, but often more detailed chemical information is necessary when odor control engineering solutions are being evaluated.  When a detailed chemical analysis of odorous compounds is needed, there are several analytical options:

1. Produced during the acidogenesis stage of anaerobic digestion, reduced sulfur compounds have a very characteristic odor of rotten eggs, rotten garlic/cabbage, skunk or natural gas. In fact, the human nose is sometimes more sensitive than the most current analytical instrumentation used to detect these compounds. An example of these compounds is methyl mercaptan, which has an extremely low odor threshold (this is why mercaptans are used as natural gas odorants). The most popular analytical option for reduced sulfur compounds is ASTM Method D5504. This method quantifies a list of 20 speciated reduced sulfur compounds (such as hydrogen sulfide, mercaptans, thiophenes) using gas chromatography with a sulfur chemiluminescence detector (GC/SCD).

2. With a characteristic fishy/fertilizer or putrid/sour/pungent odor, amines are the result of the biological breakdown of amino acids and are produced at various stages of anaerobic digestion. Columbia Analytical has developed a comprehensive amine sampling and analytical method that reports a list of 13 amine compounds with reporting limits at or below published odor threshold concentrations. A sample is collected on an in-house designed sorbent tube using a personal sampling pump. Due to their unique chemical characteristics, amines will not always be detected in any of the other tests described here (e.g. VOC test). Analysis of the samples is via a specially modified gas chromatography with nitrogen phosphorous detection (GC/NPD).

3. Ammonia, which is produced by microbial decomposition of animal waste, has a characteristic odor most people will recognize due to the compound’s use in window cleaners. At higher concentrations, ammonia can cause serious health damage, irritating and/or burning nasal passages and lungs. Collection of airborne ammonia may follow the OSHA ID-188 method, which uses sulfuric acid-coated Anasorb-747 (carbon bead) tubes and a personal sampling pump for collection. This means of sample collection is much easier and safer than the traditional collection technique of sulfuric acid solution impingers. Analysis may follow the OSHA-ID 164 analysis, which utilizes an ion-specific electrode (ISE) to detect ammonia.

4. Carboxylic (volatile fatty) acids are produced as a result of the biological anaerobic breakdown of proteins, with typical odor characteristics including a rancid, fecal, vomitous, or sweaty gym sock smell. Columbia Analytical has developed a comprehensive sampling and analytical method that reports a list of 15 carboxylic acid compounds with reporting limits at or below published odor threshold concentrations. The sample is collected on a sodium hydroxide-treated silica gel tube using a personal sampling pump; the subsequent sample is then analyzed via gas chromatography/mass spectrometry (GC/MS).

5. Several other analytical methods may be used to quantify levels of aldehydes and other miscellaneous volatile organic compounds (VOCs). EPA Method TO-11A (silica gel tubes coated with acidified 2,4-dinitrophenylhydrazine (DNPH) ) is an appropriate method for sampling of aldehydes (carbonyl compounds).  EPA Methods TO-15 (stainless steel canisters) and TO-17 (thermal desorption tubes) are appropriate methods for sampling of volatile organic compounds.  Polar volatile compounds such as alcohols, aldehydes, esters, ketones, ethers, phenols and cresols are often contributors to nuisance odors.

Due to their complex nature, there is no “one size fits all” approach for evaluating the chemical composition of odors. Odorous compounds may have additive, synergistic or antagonistic effects, all contributing to odor perception. Multiple analytical methods or evaluation approaches may be required to address a single source.

Depending on the disinfection procedure used, (chlorination, chloramines, bromine, ozone etc.), and the chemical composition of the water prior to disinfection; many different organic chemical disinfection byproducts can form in drinking water. Trihalomethanes, (THMs), are a byproduct of chlorine disinfection and to a lesser degree, disinfection using chloroamines. The THMs, (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) are formed when free chlorine combines with organic matter, like decaying vegetation commonly found in lakes and reservoirs. Total Trihalomethanes (TTHM) are regulated by the EPA at a maximum allowable annual average of 80 parts per billion. Some of the THMs are very volatile and will vaporize into air easily, so they may be inhaled while showering, however, the EPA has determined that this exposure is minimal compared to that from consumption. The Levels of THMs formed can vary widely on a number of factors including temperature, amount of chlorine used, season, and amount of plant material in the water, among others.

Some drinking water systems use chloroamines as a residual disinfection agent in place of chlorine. Chloroamine is not as reactive as chlorine and less THMs are formed. However, there are also drawbacks to chloroamine use. Chloroamine may cause nitrification and corrosion and may also increase exposure to other disinfection byproducts, such as N-nitrosodimethyl amine (NDMA).

EPA Method 524.2 is used to analyze samples for TTHMs. This method involves concentrating the THMs from a water sample using a technique known as purge and trap. This technique isolates the volatile organic compounds (VOCs) from the water. The VOCs are then desorbed into a gas chromatograph/mass spectrometer (GC/MS) where they are separated, their identity is confirmed, and their concentrations are determined. Standard reporting limits for individual TTH with this method are 0.5 µ/L

There is still controversy over PFOA’s toxicity, though the compound is persistent (doesn’t biodegrade, hydrolyse or photolyse), bioaccumulates in human and animal tissue (binds to proteins in the blood and liver), and biomagnifies up the food chain. In 2007, the Center for Disease Control and Prevention published the results of two studies on the levels of 11 different polyfluorochemicals in humans. In those studies PFOS, PFOA and Perfluorohexane Sulfonic Acid (PFHS) were found in 98% of those tested, confirming widespread exposure to these compounds. Exposure may occur through consumption of contaminated food or water or through the use of products containing these compounds, but not all sources are known or understood.

PFOA is a polymerization aid used in the manufacturing of fluoropolymers. The carbon fluorine part of the molecule is water resistant, which makes them valuable in producing fluoropolymer products that can repel water, grease and oil. These compounds are used in making non-stick surfaces for cookware, stain resistant clothing, carpets and other fabrics and in fire fighting foams. It is because of its unique polar anionic chemical properties that traditional models used to predict chemical behavior of non-polar organic chemicals, like PCBs or dioxins, in wildlife and humans, cannot be extrapolated from standard experimental data on mice and rats. In rodents PFOA has been shown to be carcinogen and immunotoxic, but whether this can be translated into information about its effect on humans is not clear. Studies continue. It should be noted, in February 2006, the EPA’s Science Advisory Board voted to approve a recommendation that PFOA should be considered a likely carcinogen.

The principal fluoropolymer producers committed to a minimum 50-percent reduction in total global emissions by 2006 (using 2000 as the baseline year), 95% reduction in emissions and product content by 2010 and elimination of its use altogether by 2015. However, because of the persistence of these compounds in the environment and the bioaccumulation and biomagnification in the food chain these compounds will continue to be in the environment long after manufacturing ceases.

Perfluorinated compounds are large molecules and are not amenable to common analytical techniques such as Gas Chromatography/Mass Spectroscopy (GC/MS).

References:

Recent studies have shown that many of these PPCP compounds at low concentrations can have negative effects on the endocrine systems of aquatic organisms. These compounds are collectively known as Endocrine Disrupting Compounds (EDCs). Other concerns regarding PPCPs include contamination of drinking water, estrogenic effects on humans and wildlife, and development of antibiotic resistant bacteria.

In 1999 and 2000, a study was performed by the USGS (Koplin, et al, 2000²) in which the concentrations of 95 of these compounds were measured in 139 streams in 30 states (mostly downstream from intense urbanization and livestock production). Eighty-two of the 95 compounds of interest were found and 80% of the streams tested contained one or more of these compounds. Multiple compounds were found in many samples. The average number was seven and the greatest number was 38. Concentrations were low, rarely exceeding health advisories or aquatic-life criteria. However, advisory limits are not available for many of these compounds. Little is known about the effects of long-term low exposure to these compounds, potential interactions with other compounds in the environment (synergistic or antagonistic), possible cumulative effects over time, or what effect any degradation products of these compounds may have.

These compounds enter the environment from a wide variety of sources including agriculture use of pesticides and antibiotics, industrial discharges, and household use of chemicals and pharmaceuticals. Most wastewater treatment and domestic septic systems are not designed to remove these compounds. In another USGS study (Stackelberg et al., 2004³), between 11 and 17 of these compounds were found in all finished drinking water samples at a conventional water treatment plant.

Analytical testing for these compounds requires the use of sophisticated instrumentation and experienced chemists. Due to their chemical nature, many of these compounds are not amenable to standard environmental gas chromatographic (GC) techniques. They are generally larger, less volatile, and more polar than other organic compounds that can be analyzed via GC and GC/MS techniques. Some of these compounds are also thermally labile, breaking down at elevated GC temperatures. Since PPCPs include many different classes of compounds with varying physical and chemical properties, Liquid Chromatography/Mass Spectroscopy/Mass Spectroscopy (LC/MS/MS) provides a convenient approach for determining a relatively wide range of chemicals of interest.⁴

GC/MS is an instrumental analytical technique comprised of a gas chromatograph and a mass spectrometer. In general, the GC is used to separate complex chemical mixtures into individual components. Once separated, the chemicals can be identified and quantified by the mass spectrometer.

Before analysis can occur a sample must be prepared, usually by extracting the analytes of interest into a liquid solvent phase. This extract is then injected into the GC where it is swept onto a separation column by an inert carrier gas such as hydrogen or helium. The analytes in the mixture are carried through the column by the carrier gas where they are separated from one another by their interaction between the coating (stationary phase) on the inside wall of the column and the carrier gas. Each analyte interacts with the stationary phase at different rates. Those that react very little move through the column quickly and will exit into the mass spectrometer before those analytes having longer interaction and retention times.

When the individual analytes exit the GC column they enter the ionization area (ion source) of the MS. Here they are bombarded with electrons which form ionized fragments of the analyte. These ionized fragments are then accelerated into the quadrapole via a series of lenses and separated based on their mass to charge ratio. This separation is accomplished by applying alternating RF frequency and DC voltage to diagonally opposite ends of the quadrapole, which in turn allows a specific mass fragment to pass through the quadrapole filter. From here the fragments enter the mass detector (electron multiplier) and are recorded. The MS computer graphs a mass spectrum scan showing the abundance of each ionized mass fragment.

A GC/MS system in Full Scan mode will monitor a range of masses know as mass to charge ratio (abbreviated m/z). A typical mass scan range will cover from 35-500 m/z four times per second and will detect compound fragments within that range over a set time period. Laboratories have extensive computer libraries containing mass-spectra of many different compounds to compare to the unknown analyte spectrum. The Full Scan mode is quite useful when identifying unknown compounds in a sample and providing confirmation of results from GC using other types of detectors.

Operation of a GC/MS in SIM mode allows for detection of specific analytes with increased sensitivity relative to full scan mode. In SIM mode the MS gathers data for masses of interest rather than looking for all masses over a wide range. Because the instrument is set to look for only masses of interest it can be specific for a particular analyte of interest. Typically two to four ions are monitored per compound and the ratios of those ions will be unique to the analyte of interest. In order to increase sensitivity, the mass scan rate and dwell times (the time spent looking at each mass) are adjusted.

When properly setup and calibrated, GC/MS-SIM can increase sensitivity by a factor of 10 to 100 times that of GC/MS-Full Scan. Because unwanted ions are being filtered, the selectivity is greatly enhanced providing an additional tool to eliminate difficult matrix interferences.

The ability of the mass spectrometer to identify unknowns in the full scan mode and quantitiate know target analytes in the SIM mode, makes it one of the most powerful tools available for trace level quantitative analysis in the lab today.

The goal of soil gas sampling is to collect a sample of the vapor that resides in the interstitial soil pores near a source of contamination and/or near a potential receptor structure. To sample soil gas, a temporary or permanent soil vapor probe is installed. If the well is installed incorrectly or is not sealed properly, leaks to the ambient air may occur. This can dilute or otherwise influence the concentrations seen, potentially leading to incorrect decision making.

Using a tracer gas can give quantitative proof that the sampling system was installed and sealed correctly. The tracer compound is placed around the soil gas probe at the ground surface, so that if the well is installed correctly and everything is sealed properly, no tracer compound will be seen in the sample. The soil gas sample is then collected. If the tracer compound is detected in the soil gas sample, it is an indicator that some amount of leaking has taken place and the sample may be deemed unrepresentative or even invalid.

Several state vapor intrusion guidance documents make recommendations about which soil gas tracers to use, but most states leave room for professional judgment by the environmental professional to use other compounds. Each potential tracer compound has its benefits and its drawbacks from a sampling and analytical viewpoint.

Many professionals have successfully used helium as a tracer compound for soil gas surveys. As opposed to other tracers, such as isopropyl alcohol, helium will not interfere with the TO-15 analysis even if there is a small leak. Another unique benefit is that helium may be monitored and evaluated onsite so leaks can be proactively fixed in the field prior to sampling.

In addition to choosing an appropriate tracer compound, when collecting a representative and defensible soil gas sample, it is also important to follow thorough quality control and quality assurance practices, and to have several lines of evidence to support your conceptual site model.

Measuring the levels of oxygen, carbon dioxide, and methane present in the soil gas (indicators of biological activity) can also prove useful. Measurement of these indicator compounds can be done onsite with a multigas meter and/or at the analytical laboratory via EPA Method 3C modified (GC/TCD). Interpretation of the fixed gas data can provide a secondary line of evidence to support the conceptual site model. For instance, if the oxygen profile is decreasing with depth and suddenly a deeper soil gas sample shows an increased concentration (or near ambient levels) of oxygen, it is possible that a leak occurred, letting in ambient air.

It is important to note that leak testing of the sampling train can also be done with the use of a vacuum pump and a magnahelic gauge. Evacuate the sampling line, close off the soil gas point and the canister with a gauge in line, and observe whether the gauge needle returns to zero. If the needle moves back to zero, a leak is present somewhere in the system.

The field of vapor intrusion is constantly evolving, and accepted sampling procedures may change. Always check for any applicable state or Federal regulatory guidance prior to conducting sampling.