Site S-7 Representative Model and Application for the Vadose Zone Monitoring System (VZMS) McClellan AFB - 1998 Semi-Annual Report

Vadose zone data collection and enhanced data analysis are continuing for the Vadose Zone Monitoring System (VZMS) installed at site S-7 in IC 34 at McClellan MB. Data from core samples from boreholes drilled in 1998 and from VZMS continuous monitoring are evaluated and compared to previously collected data and analyses. The suite of data collected to date is used to develop and constrain a spatially averaged, one-dimensional site S-7 representative model that is implemented into T2VOC. Testing of the conceptual model under conditions of recharge of 100 mm/yr produces plausible moisture contents relative to data from several sources. Further scoping calculations involving gas-phase TCE transport in the representative model were undertaken. We investigate the role of recharge on TCE transport as well as the role of ion- and gas-phase flow driven by density and barometric pumping effects. This report provides the first example of the application of the site S-7 representative model in th e investigation of subsurface VOC movement