VOLATILE ORGANIC-COMPOUNDS - COMPARISON OF 2 SAMPLE COLLECTION AND PRESENTATION METHODS

Two soil sample collection and preservation methods for volatile organ ic compounds, used during site characterization activities, were evalu ated using standard U.S. Environmental Protection Agency analytical me thods. A conventional bulk method recommends completely filling a samp le container with soil; a less commonly used methanol method recommend s placing a soil aliquot into methanol. Analytical results showed larg e negative biases associated with the bulk samples as compared to the methanol samples for aromatic compounds. Order of magnitude difference s in concentrations measured between the methods were observed for ben zene and toluene. Lesser differences were noted for xylenes and ethylb enzene. Limited data for chlorinated compounds suggest behavior simila r to the aromatic species. A limited spike recovery study was conducte d using the methanol method on laboratory and field samples. Samples w ere analyzed 82 days after spike addition. Poorer spike recoveries wer e noted from spiked methanol vials transported to the field and used f or collection of soil samples. Differences between mean recovery value s for the laboratory and field samples appear to be the result of loss es during sample collection and transport. Despite the 82-day holding time, spike recoveries were within 70% of initial spike concentrations . These results demonstrate the stability of using methanol as a prese rvative for soil samples.