A person who has obtained a letter of map revision based on fill that removes a site in the flood fringe from the floodplain due to the use of fill to elevate the site above the BFE may apply for a permit from the village to construct the lowest floor of a residential building below the BFE in the flood fringe. The building inspector shall not issue such a permit unless the applicant has complied with all the following criteria:
A. Compensatory storage shall be provided per subsection 12-2-3B of this chapter.
B. The elevation of the lowest opening in the basement wall (i.e., window wells, accessways) shall be at or above the flood protection elevation (FPE).
C. The lowest adjacent grade to the foundation shall be at or above the FPE, for a minimum distance of ten feet (10') beyond the outside face of the structure. However, if site conditions are such that this requirement cannot be met, the building inspector may waive the ten foot (10') minimum setback if an Illinois licensed professional engineer certifies that an alternative method to protect the building from damage due to hydrostatic pressures has been met. The certifications shall be in the form of a detailed soils and structural design analysis, which shall be submitted to the building inspector for review. The building inspector may require such additional documentation as necessary to prove that the proposed shorter setback distance will keep the structure reasonably safe. In no case shall the setback distance be less than four feet (4').
D. The grade around the perimeter of the structure, measured at a distance of twenty feet (20') from the structure, shall be above the BFE. However, if site conditions are such that this requirement cannot be obtained, the building inspector may waive the twenty foot (20') minimum setback distance if an Illinois licensed professional engineer certifies that an alternative method to protect the building from damages due to hydrostatic pressures has been met. A detailed soils analysis and structural design proving that a shorter setback distance will keep the structure reasonably safe from flooding shall be submitted to the village for review. In no case shall the setback distance be less than four feet (4').
E. The ground around the building shall be compacted fill that meets all requirements of this subsection and is at least five feet (5') thick under the basement floor slab. Nothing in this subsection shall be interpreted to require the removal or replacement of fill that was placed as part of an LOMR-F, if such fill consists of material, including soils of similar classification and degree permeability, such as those classified as CH, CL, SC or ML according to ASTM standard D-2487, "Classification Of Soils For Engineering Purposes".
F. The fill material must be homogeneous and isotropic. That is, the soil must be all of one material, and the engineering priorities must be in the same direction. (Ord. 08-07, 6-9-2008)
G. All fill material and compaction shall be designed, certified and inspected by an Illinois licensed professional engineer, as warranted by the site conditions. The basement floor shall be at an elevation that is no more than five feet (5') below the BFE. (Ord. 08-07, 6-9-2008; amd. 2016 Code)
H. There shall be a granular drainage layer beneath the floor slab, and minimum of one-fourth (1/4) horsepower sump pump with a backup power supply shall be provided to remove seepage flow. The pump shall be rated at four (4) times the estimated seepage rate and shall discharge above the BFE and away from the building in order to prevent flooding of the basement or uplift of the floor under the effect of the seepage pressure.
I. The drainage system shall be equipped with a positive means of preventing backflow.
J. All foundation elements shall be designed to withstand hydrostatic pressure in accordance with accepted engineering practices.
K. If the applicant is unable to meet all of the requirements set forth in this section, the building inspector may allow the construction of a basement below the BFE only if the applicant demonstrates that the proposed fill and structure meet the guidelines and requirements set forth in FEMA technical bulletin 10-01 and are reasonably safe from flooding. In order to demonstrate that the proposed structure is reasonably safe from flooding, the applicant shall submit a detailed engineering analysis of the proposed fill and foundation wall. The engineered basement study shall be completed in accordance with the latest edition of FEMA technical bulletin 10-01, with the analysis of the fill being prepared by an Illinois licensed professional engineer.
L. In order to provide the required compensatory storage on site, in no case shall the depth of excavation in the front and side yards of the lot exceed eighteen inches (18"), as measured from the previously existing natural grade. The rear yard shall be permitted to have a greater depth of excavation, if necessary. All such excavation shall be constructed to drain freely and openly to the watercourse or storm sewer system. The use of mechanical means to drain the compensatory storage area will not be permitted. (Ord. 08-07, 6-9-2008)