A combined field and laboratory study was conducted to compare purge and trap gas chromatography/mass spectrometry (PT‐GC/MS) and purgeable organic chloride (POC1) analysis for measuring volatile chlorinated hydro‐carbons (VCH) in ground water. Distilled‐water spike and recovery experiments using 10 VCH indicate that at concentrations greater than 1 /ig/1 recovery is more than 80 percent for both methods with relative standard deviations of about 10 percent. Ground‐water samples were collected from a site on Cape Cod, Massachusetts, where a shallow unconfined aquifer has been contaminated by VCH, and were analyzed by both methods. Results for PT‐GC/MS and POC1 analysis of the ground‐water samples were not significantly different (alpha = 0.05, paired t‐test analysis) and indicated little bias between the two methods. Similar conclusions about concentrations and distributions of VCH in the ground‐water contamination plume were drawn from the two data sets. However, only PT‐GC/MS analysis identified the individual compounds present and determined their concentrations, which was necessary for toxicological and biogeochemical evaluation of the contaminated ground water. POC1 analysis was a complimentary method for use with PT‐GC/MS analysis for identifying samples with VCH concentrations below the detection limit or with high VCH concentrations that require dilution. Use of POC1 as a complimentary monitoring method for PT‐GC/MS can result in more efficient use of analytical resources.
