AbstractSEAMISTTMis an innovative technology that facilitates measurements of contaminants in both vertical and horizontal boreholes. The essence of SEAMISTTMis an airtight membrane liner pneumatically emplaced inside the borehole and maintained with positive pressure. Sampling ports, absorbent collectors, and various in‐situ measuring devices can be fabricated into the liner. Small instruments and cameras can be guided through the borehole to obtain real‐time data.This article reports on the cost and performance effectiveness of this new technology. In this report, SEAMISTTMis evaluated as a tool for obtaining data on volatile organic compounds, semivolatile organic compounds, other water‐borne contaminants, and radionuclides. SEAMISTTMis also compared to traditional borehole casing, to conventional soil vapor probes, and to conventional pore‐fluid collecting lysimeters. The most cost‐ and performance‐effective applications of SEAMISTTMare shown to be those applications for which multiple characterization requirements can be combined into one SEAMISTTMmemb