Air testing flows smoothly with advance planning

Environmental NEWS - Spring 2009

Volatile chemicals from contaminated groundwater or buried wastes can emit vapors that may migrate through soil and into the air of buildings situated above. Although the concentrations of the contaminants are typically low, there are extreme cases where vapors may accumulate in buildings to levels that pose health hazards. Known as vapor intrusion, this problem has prompted USEPA and many states to develop guidance documents for assessing indoor air quality. Planning and communication with the laboratory are key to the success of any indoor air or soil vapor monitoring projects. Sample size and interval, choice of test method, quality control sample collection, parameter list and reporting format are among the variables to consider so that the test results generated will meet regulatory needs.

The preferred sampling technique for whole air samples employs a summa canister, which is a specially cleaned and passivated metal container. The canisters are available in various sizes, and Lancaster Laboratories maintains a large stock of the one and six liter sizes. Ambient or indoor air sampling usually requires a six liter canister to meet the stringent sampling limits. Because summa canisters are reusable, they must be cleaned after each use. To ensure that no trace of the previous sample remains, Lancaster Laboratories certifies that their canisters are clean down to the method detection limit of the analysis. After cleaning, the canister is evacuated and sent into the field with appropriate sample collection equipment, including vacuum gauges to monitor the sampling process and flow controllers fitted with filters to prevent interference from particulates. Each flow controller is individually set based on the sampling event parameters, such as the volume of the canister, the sampling time interval and the location of the sampling equipment. Consistent vacuum throughout the sampling event is achieved by setting the flow control valve to collect about five liters of sample in a six liter canister. Pressure checks are performed on canisters returned to Lancaster Laboratories to confirm a detectable vacuum, indicating a valid sample.

The list of compounds of concern for possible soil vapor intrusion, usually identified through earlier remediation assessments, must be communicated to the laboratory, along with the required analytical method and detection limits. Volatile organic compounds are typically determined by USEPA Method TO-15. In order to generate defensible data, quality control samples are needed to prove that the sampling process was not compromised in any way. Lancaster Laboratories supplies appropriately prepared canisters for use as field blanks and trip blanks to detect sources of sample contamination. Lancaster Laboratories also provides the hardware necessary to collect field duplicates, which may be required to demonstrate the reproducibility of the sampling process. Some sampling plans also incorporate the use of a tracer gas to demonstrate that the sampling system is free of leaks at the probe level. Selection of a tracer gas is based on the sampling situation and the compounds of concern. The tracer gas must not interfere in the chromatography of the target compounds, but it must also be readily detected using the chosen analytical method. Therefore, discussion of the tracer gas with the laboratory is critical. All QC samples are processed using the same procedures and analytical methods as the field samples.

The analytical method should be chosen prior to sampling to ensure that all of the project requirements can be met by the laboratory. Lancaster Laboratories offers a number of methods appropriate for air analysis and has specialized equipment to meet the low limits often specified for indoor air analysis. Most of these tests employ a GC/MS, and Lancaster Laboratories has instruments that are capable of operation in the selected ion mode (SIM), which provides even greater sensitivity and the lowest detection limits. Typical method detection limits for TO-15 are in the range of 0.2 ppbv. The reporting units needed are also part of the information to be communicated to the laboratory since the conversion factors for air testing are more complex than for other matrices. Lancaster Laboratories has years of experience analyzing air samples and holds certifications for air analysis in eight states.

With air analysis comes many details to be worked out between the client, the sampling team and the laboratory. Advance planning and communication are key to successful, efficient completion of each project. Lancaster Laboratories has knowledgeable client service representatives who are trained to assist clients with questions on sampling equipment, method selection and reporting requirements. For more information on air analysis, call Environmental Client Services at 717-656-2300.