Service Tax on Construction Work

This query is for a construction plumbing contractor.

1- Service tax collected on Rs.1000000.00, apart of his total turnover Rs.3000000.00 

my question is, what would the service tax  liabilities for the Assessess. (A.Y.2011-12)will he liable to pay the service tax on total turnover or only the amount on which he collected the tax. 

2- What is the service tax exemption limit for civil construction (plumbing work) (Residential)

Thanks