This Additional Site Characterization Work Plan presents a strategy for collecting site characterization information at the closed Maricopa County Cave Creek Landfill to support ongoing remedial action planning for trichloroethene-impacted groundwater underlying the site. The Work Plan supplements previous remedial investigation work plans prepared to characterize the nature and extent of site contamination.

To evaluate whether VOCs are migrating out of the landfills into the vadose zone, a soil vapor survey of the soil beneath the landfill bases was performed. Permanent vapor monitoring probes were installed and then sampled twice for VOCs. Groundwater beneath the landfills has been impactd by VOCs, namely TCE, DCE, and toluene.

This study involved the review of 417 ADEQ LUST site files and compilation of relevant data from 323 of these sites into an electronic database. It also involved the collection and analysis of over 700 supplemental groundwater samples, the assessment of aquifer flow properties from 32 wells at 11 sites, and more detailed characterization at six LUST sites representative of a range of conditions at AZ LUST facilities. In addition, over 300 groundwater level measurements were performed and 175 monitoring wells were re-surveyed in order to assess errors in standard practice and their impact on groundwater flow direction determination. An empirical analysis of groundwater impacts at AZ LUST sites was conducted using these data sets, with emphasis on identifying relationships between site conditions (e.g., geology, depth-to-groundwater, etc.) and groundwater impacts. Finally, a combined theoretical-spatial (GIS) analysis was performed to identify LUST scenarios posing the greatest threats to use of groundwater resources.