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 city to construct the lowest floor of a residential building below the BFE in the flood fringe. The City Administrator or his designee shall not issue such a permit unless the applicant has complied with all the criteria set forth in the this section.
(A) Compensatory storage shall be provided per § 159.27(B).
(B) The elevation of the lowest opening in the basement wall (i.e., window wells, access ways) 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 beyond the outside face of the structure.
(D) The grade around the perimeter of the structure, measured at a distance of 20 feet from the structure, shall be above the BFE.
(E) The ground around the building shall be compacted fill that meets all requirements of this section and is at least five feet thick under the basement floor slab. Nothing in this section shall be interpreted to require the removal or replacement of fill that was placed as part of a 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.
(G) All fill material and compaction shall be designed, certified and inspected by an Illinois licensed professional engineer, as warranted by the site conditions.
(H) The basement floor shall be at an elevation that is no more than five below the BFE.
(I) There shall be a granular drainage layer beneath the floor slab, and minimum of one-quarter horsepower sump pump with a backup power supply shall be provided to remove seepage flow. The pump shall be rated at four 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.
(J) The drainage system shall be equipped with a positive means of preventing backflow.
(K) All foundation elements shall be designed to withstand hydrostatic pressure in accordance with accepted engineering practices.
(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 18 inches, 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.
(M) The builder and design engineer must certify that the design for the development is reasonably safe from flooding in accordance with FEMA's Technical Bulletin 10-01, and in accordance with accepted professional practices.
(Ord. 2008-08-0196O, passed 8-12-2008; Am. Ord. 2019-10-0759O, passed 10-22-2019) Penalty, see § 159.99