NCC-ACHMM Dinner Meeting Highlights

Speaker: Bart Simmons, Ph.D., California Department of Toxic Substances Control Hazardous Materials Laboratory

New Methods for Sampling Soils for Volatile Organic Analysis: Are You Ready?

Wednesday, July 15, 1998

Meeting Summary by John Wondolleck, CHMM

(The following is a slightly embellished rendition of the talk provided by Dr. Simmons. Although based on Dr. Simmons talk, the text provides additional details and a few editorial comments regarding volatiles soil sampling and the SW-846 revisions.)

New Methods for Sampling Soils for Volatile Organic Analysis

In the old days of sampling soil, one would drive a split spoon sampler to a designated sampling depth (which would heat up to 150 degrees F due to friction), open the spoon and sniff the core with a vapor monitor, subsample the core and place the same into a wide-mouth jar, and then ship the sample to a laboratory. Studies performed by the Army Corps of Engineers and others showed that this method of sampling could result in the loss of up to 100% of the volatiles originally in the soil sample. The studies also showed an order of magnitude volatiles loss in capped sleeved soil samples due to volatilization and microbial degradation of the samples. A significant volatiles loss was demonstrated even though the "accepted" holding time for the samples was up to 14 days. These findings lead to the development of field methanol preservation methods for reducing the volatiles soil losses to provide accurate and representative site characterization data.

The latest revision to SW-846 (USEPA's Test Methods for Solid Wastes, Physical/Chemical Methods; Update III) effective December 1997, introduced Method 5035 - Closed-System Purge-and-Trap and Extraction for Volatile Organics in Soil and Waste Samples. The SW-846 update essentially requires the preservation of soil volatile samples in the field. Three options are provided: methanol preservation, acid preservation (sodium bisulfate), and the use of an Encore-type sampler.

The benefits of the methanol and sodium bisulfate preservation methods is that the soil sample is immediately preserved in the field and placed in an air tight container complete with a magnetic mixing spoon for laboratory use. The detriments of these methods are the need to measure and handle methanol and sodium bisulfate in the field, the need to provide a known quantity of soil in the container, shipping requirements for the preservatives, and the elevated detection limits caused by the methanol. Currently the method requires a precision of 0.01 grams of soil for the field measurement of the mass of soil. In addition, sodium bisulfate cannot be used for calcareous soils due to effervescence. Other concerns are the purity of the preservative solutions related to compounds of concern. Due to elevated detection limits, methanol preservation cannot be used for samples at concentrations less than 200 ppb. The manner in which surrogate compounds are injected into the sample also needs to be addressed (e.g., added in the field or by the laboratory). 200 ppb of contaminant in soil is the cutoff point between low versus high concentrations for determining the type of chemical preservative.

To subsample a soil core for preservation, the suggested method is the use of a syringe with its top cut off to collect the subsample of a specific volume. The plunger of the syringe is used to push the sample into the sample container with the preservative and the container is then immediately sealed. Equal volumes of soil and preservative are recommended by EPA; a ratio of 1 part soil to two parts preservative is recommended by DTSC.

A third suggested method is the use of an Encore sampler. This is a hermetically sealed combined sampling tool/container used to collect and contain the sample for shipment to the laboratory. The sample container needs to be cooled to 4 degrees C and the sample extracted by the laboratory within 24 hours of collection. The Encore sampler eliminates the field responsibility to field crew to chemically preserve the samples. Encore samplers cost $7-10 each. Two samplers must be used for each sample collected, and if moisture content is needed to be known, and third sample must also be collected. Studies are underway on the freezing of the sample container by the laboratory which may extend the laboratory holding period prior to extraction.

All three field collection/preservative methods require that the laboratory have specialized equipment to perform the analyses. Laboratories are in the processing of purchasing and using the new equipment so USEPA and DTSC are allowing a transition period prior to enforcing the requirement that the Method 5035 be followed. DTSC will require implementation through its lab accreditation program. DTSC is considering a deadline for use of the Method 5035 in the future. At present it will be enforcing the requirements on a case by case basis. The Army Corps of Engineers is enforcing the requirement now. DTSC is not planning to reopen closed sites based on the new sampling method, even thought it is suspected that the soil VOC results are biased low. DTSC does not expect the courts to reopen any cases due to the new science.

On another note, Dr. Simmons stated that the National Laboratory Accreditation Conference will be establishing uniform national standards, replacing individual state programs. California is a participant in this organization, thus there is a chance that California's accreditation program will be changing.

Additional notes on SW-846 and Method 5035.

On August 7, 1998, USEPA issued a memorandum entitled "Clarification Regarding Use of SW-846 Methods". In this memo, USEPA states that "SW-846 contains the analytical and test methods that EPA has evaluated and found to be among those acceptable for testing under Subtitle C of RCRA. In most situations, SW-846 functions as a guidance document setting forth acceptable, although not-required, methods to be implemented by the user, as appropriate, . . ." In this statement, USEPA is recognizing that there are other means of measuring chemical and physical properties of environmental media. However, one should be cautioned that if they propose to use a method other than that presented in SW-846, Update III, the alternative method must be demonstrated to be either equal or superior to the method stated in SW-846 (if a comparable SW-846 method exists). One also must remember that USEPA has eliminated or replaced once commonly used SW-846 methods (such as 8010/8020 for VOCs) with newer and updated methods because of quality or procedural issues inherent to the older methods. This implies that the newer methods produce more accurate and therefore more defensible data than the older methods. Although USEPA and DTSC may still allow the use of the older methods during the transition period, one still using them runs the risk of data being produced by the older methods being rejected by either agency. Therefore the prudent person should use only those methods stated in the current update of SW-846.

Regarding Method 5035, USEPA provides the following clarification in its August 7, 1998 memorandum. "The Agency recommends that all soil samples collected for volatiles be preserved in some manner, whenever possible. For low concentration samples, generally those below 200 ppb of volatiles, preservation is essential. For samples with higher concentrations of volatiles (e.g., greater than 200 ppb), the Agency recommends that unpreserved samples be collected as a last resort, and that the rationale for not preserving the samples be clearly documented in a sampling and analysis plan that is reviewed and approved by the relevant regulatory authority." In the memorandum, USEPA requires that methanol be added to the vial by the laboratory before shipment of vials to the field. The vial then is reweighed in the field. If the difference between the two measurements is greater than 0.2 g, then the vial cannot be used. USEPA also states that if a 1:1 ratio of soil:solvent is used, the solvent must completely submerge the sample.