On each project existing prior to December 5, 1924, where, in the opinion of the Secretary, it appears that on account of lack of fertility in the soil, an inadequate water supply, or other physical causes, settlers are unable to pay construction costs, or whenever it appears that the cost of any reclamation project by reason of error or mistake or for any cause has been apportioned or charged upon a smaller area of land than the total area of land under said project, the Secretary is authorized to undertake a comprehensive and detailed survey to ascertain all pertinent facts, and report in each case the result of such survey to the Congress, with his recommendations: Provided, That the cost and expense of each such survey shall be charged to the appropriation for the project on account of which the same is made, but shall not be charged as a part of the construction or operation and maintenance cost payable by the water users under the project.