Delineated water shed drainage area issue

srinivasiitr[CodePlex]
While I was cross checking the delineated water shed drainage area for some of the EPA STORET sites with the same latitude and longitude as of USGS sites the drainage area is not the same.

For example
EPA STORET

site name: Sny Magill Creek Site #1 (SN01)
Org and site id : 21IOWA_WQX, 15220004
HUC Id: 07060003
The delineated drainage area obtained : 3.0107 Sq Km / 1.1624 Sq Miles

USGS SITE with same latitude and longitude

USGS Site id : 05411400
Drainage Area from USGS NWIS web site: 27.6 Sq miles

I have encountered few more sites with drainage areas different.

Start by comparing the EPA STORET and USGS NWIS records for Sny Magill Creek Site #1 (SN01), using the identifiers and coordinates in the issue. Trace how HydroDesktop obtains and displays each drainage area, then document the cause and verify that the two sources are handled or explained consistently.

Written by the indexing model from the issue text.