The Color-Tec method was developed during 1997 by Perry Kelso with Ecology and Environment, Inc. while assessing some of the earliest sites addressed under the Florida Department of Environmental Protection’s (FDEP) Drycleaning Solvent Cleanup Program. Since its early development, the method has been used extensively at EPA, DOD, and State regulatory agency sites to provide real-time, decision quality data at thousands of chlorinated solvent sites.  

Color-Tec is a field-based analytical method which combines the use of colorimetric gas detector tubes (originally designed for occupational breathing-zone monitoring) with sample purging to detect very low concentrations of total chlorinated volatile organic halocarbons (CVOHs) in liquid and solid samples. Samples are analysed by purging the volatile compounds from a groundwater or soil sample through the colourimetric tube, which is designed to produce a distinct colour change when exposed to chlorinated compounds. Estimated sample concentrations are obtained by comparing the tube readings to a conversion table based on comparing Color-Tec and GC/MS split sample data.

Each colorimetric tube contains an oxidizer (PbO2) and a catalyst (H2SO4) which decomposes and converts the chlorinated compounds to hydrogen chloride, which discolours a reagent (4-phenylazodiphenylamine) in the tube from yellow to purple.

2 sample preparation methods can be used depending on the soil type and detection limits needed. For clay or similar soils, it is recommended that a methanol extraction is used to dissolve the chlorinated solvent from the clay matrix. This will still allow a detection limit of 0.25 ppm to be achieved. For sandy soils or soils that are unlikely to absorb the solvents, direct partition into water can be used and a detection limit of 0.003 ppm achieved.

Water samples can be analysed directly to achieve a 0.003 ppm detection limit.

The detection limits do depend on the type of chlorinated solvent present. The quoted limits are for Tetra Chloro Ethylene under ideal conditions.

The ColorTec method is a semi-quantitative method, but if the type of chlorinated solvent present is known, it can give sufficiently reliable data to identify action levels. If the solvent type is unknown, the method is best used as an absence/presence indicator to identify samples requiring laboratory analysis. The method is very robust and with minimal training can be used to analyse at least 50 samples per day.

Chlorinated Solvents by ColorTec

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