Why don't you run a profiler trace on the stored procedures that the web app is executing , maybe you will find something there . Also look at your stored proc's if they have the with recompile option enables - if so ...disable it , let sql use the buffer manager to read execution plans .

Did you run dbcc checktable statement to look at the consistancy of the table ???

Also maybe create a nonclustered index on the column . What data type are you using for the column ? Hope I gave you an idea ...