A person who has obtained a Letter of Map Revision Based on Fill that removes a site in 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 building below the BFE in the floodplain. The Administrative Department shall not issue such a permit unless the applicant has complied with all the criteria set forth in this section and maintain the documentation verifying such compliance.
(A) Compensatory storage shall be provided per § 152.018.
(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. However, if site conditions are such that this requirement cannot be met, the Administrative Department may waive the ten-foot minimum setback if an Illinois licensed P.E. 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 Administrative Department for review. The Administrative Department 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.
(D) The grade around the perimeter of the structure, measured at a distance of 20 feet from the structure, shall be above the BFE. However, if site conditions are such that this requirement cannot be obtained, the Administrative Department may waive the 20-foot minimum setback distance if an Illinois licensed P.E. certifies that an alternative method to protect the building from damages due to hydrostatic pressures have 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.
(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 division (E) 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 P.E., 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) If the applicant is unable to meet all of the requirements set forth in the preceding divisions of this section, the Administrative Department 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 P.E.
(M) 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.
(Ord. 3187, passed 1-22-19) Penalty, see § 152.999