Contractor shall promptly, and before such conditions are disturbed, notify NIA in writing of (a) sub-surface or latent physical conditions at the Site differing materially from those indicated in this Contract (b) unknown physical conditions at the Site, or an unusual nature, differing materially from those ordinarily encountered and generally recognized as inherent in work of the character provided for in the Contract. NIA shall investigate the conditions and if NIA finds that such conditions do so materially differ, the Contractor shall perform such measure as required by NIA. If such measures result in any extra cost to Contractor or entitle him to an extension of time he shall submit a claim in accordance with the requirements of the Contract.

The Contractor shall be furnished with all available information on the site conditions including data for boreholes, test pits and any other investigations.