Document ID: EPA-HQ-OPP-2007-0934-0014
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2008-01-07T05:00Z

Assessment of the Missouri Major Land Resource Area (MLRA) 113 that
contain monitored sites MO-01, MO-02, MO-04 and MO-05: Charge question
#11 asks the Panel to comment on the approaches to determine whether the
watersheds that exceeded the LOC in multiple years are randomly
distributed within the 1,172 vulnerable watersheds or represent a unique
subset of conditions.  Two documents that will be provided to the Panel
at the meeting on December 4 (these documents are electronically too
large to e-mail) contain the results of in-depth assessments of the
Missouri MLRA 113 and MO-01 and MO-02 watersheds, detailing the unique
hydrogeology and agronomics of this region and these subwatersheds. 
This assessment shows that the Missouri MLRA 113 is uniquely vulnerable
to runoff due to the unusual combination of the a high percentage of
vulnerable soils, the presence of an unusually continuous and shallow
claypan layer, plus the occurrence of steeper slopes than are generally
present in other areas of the Midwest corn/sorghum growing region. These
documents provide evidence that the monitoring results from
subwatersheds MO-01 and MO-02 (as well as MO-04 and MO-05 that were
monitored in 2007) should be considered as representative of a unique
subset of conditions during the analysis to identify watershed beyond
the 40 where higher atrazine exposures potentially occur.