Since it appears to be happening during business hours, this might help. It is a script that shows what SQL statements are being consumed by the tempdb. You can run it periodically during the day or put it in a job and write the results to a table. I received this from someone else on the forum, but I cannot remember who or I would give credit.

SELECT t1.session_id, t1.request_id, t1.task_alloc,

t1.task_dealloc, t2.sql_handle, t2.statement_start_offset,

t2.statement_end_offset, t2.plan_handle

FROM (Select session_id, request_id,

SUM(internal_objects_alloc_page_count) AS task_alloc,

SUM (internal_objects_dealloc_page_count) AS task_dealloc

FROM sys.dm_db_task_space_usage

GROUP BY session_id, request_id) AS t1,

sys.dm_exec_requests AS t2

WHERE t1.session_id = t2.session_id

AND (t1.request_id = t2.request_id)

ORDER BY t1.task_alloc DESC

Also, the tempdb is growing because it is not checkpointing properly. We had this problem earlier and traced it to a open transaction in the tempdb. You might DBCC OPENTRAN on tempdb every once and a while.