Except as otherwise provided in subsection (b) of § 22a-439, if federal funds for contract plans and specifications for the construction of a pollution abatement facility are not available to the municipality at the time of its scheduled planning, the commissioner shall advance to such municipality a sum equal to seven per cent of the estimated construction cost, said amount to be used by the municipality for the purpose of preparing contract plans and specifications; provided any remaining balance of the seven per cent advanced under this section shall be applied to the cost of construction of the facility. The funds advanced to the municipality under this section shall be considered a part of the total amount of the state grant provided for in § 22a-439. Such facility shall be constructed in accordance with a schedule of the commissioner and shall be in conformance with an engineering report approved by the commissioner. Before approving the engineering report required in this section and in § 22a-428, and as may be required under § 22a-431, the commissioner shall, among other factors, give due regard to whether such report is in conformance with his applicable guidelines, whether such report makes adequate recommendations concerning all existing and anticipated community discharges, whether such report conforms with existing planning studies and whether satisfactory considerations have been given to all regional problems outlined to the engineer in a prereport conference with the commissioner.