Why “all clear” may mean future danger: Surface-controlled reactions affecting hydrolysis of organic compounds in the environment can predominate over bulk solution hydrolysis, especially in soil environments. Unpredicted residual levels of chemical warfare agents (CWA) at threat levels in the field necessitated the development of new methods for investigating the fate of CWA delivered onto soil. Design and fabrication of Soil System Units now allows determination of the fate of CWA in soil, as well as investigation of the soil chemical and physical characteristics affecting the persistence of threat from continuing presence of CWA in soil, under conditions that represent those in the field. Initial results show that the Soil System Unit approach is highly effective for investigating the fate of CWA in the soil environment. Using the Soil System Unit approach we were able to replicate and investigate under controlled laboratory conditions residual levels of the nerve agent Soman (GD) in soil, such as those that might occur in the field from terrorist or wartime activities. Results of our initial experiments showed that persistence of GD in soil can be expected for days following contamination. Furthermore, we established that life threatening atmospheric levels of GD may be expected to successively reoccur in response to increasing moisture in soils contaminated with GD; this result had not been previously documented.