Before any load test is made, the proposed apparatus and structure to be used in making the load test shall be satisfactory to the commissioner. The test shall be made under the responsible engineer's surveillance. A complete record of such tests shall be filed with the commissioner. Areas of the foundation site within which the subsurface soil conditions are substantially similar in character shall be established by the engineer. For piles installed by impact hammer, one load test shall be conducted in each area of substantially similar conditions, but not less than one typical pile for the entire foundation installation of the building or group of buildings on the site occupying a total area of 5,000 square feet(465 m2) or less; and not less than two load tests for a site having a footprint between 5,000(465 m2) and 30,000(2787 m2) square feet and one additional load test for each 20,000 (1860 m2) square feet of added footprint area.