How long does it take to collect soil and groundwater data for an AOI?

That largely depends on a number of factors.  Data has been collected at the site for years for various reasons, whether it was in response to a particular release or general characterization of an area.  Most AOI investigations begin with compiling all known past data and historical information such as the particular use of an area, then coming up with a work plan for collection of new information.  After the work plan activities are completed, often additional data needs to be collected to delineate an area of impact (further define the contamination horizontally and vertically).  Gathering historic information and generating work plans can take months.  The duration of a field data collection effort depends mostly on the number of borings/wells to be installed and the amount of sampling to be conducted.  Tasks such as clearing locations for utilities prior to drilling and developing wells after installation and prior to sampling also takes time.  Large scale sampling efforts can take months to years.