This document evaluates the feasibility of in-situ detection of technetium-99 in Hanford Site vadose zone soils (the soils between the surface and groundwater) using laboratory tests.The detector system performs adequately for high technetium concentration, but more development and laboratory testing is needed before field demonstration is performed.TRADEMARK DISCLAIMER. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The detector system performs adequately for high technetium concentration, but more development and laboratory testing is needed before field demonstration is performed.The detector system clearly detects a 100.8 nanoCurie surface-deposited source of 99 Tc. The display system monitoring the tests shows that the detection system and the associated electronics can detect