(a) In areas of carbonate geology, a geologist shall certify to the following:
(1) No stormwater management facility will be placed in, over, or immediately adjacent to the following features:
A. Closer than 100 feet from sinkholes
B. Closer than 100 feet from closed depressions
C. Closer than 100 feet from caverns, intermittent lakes, or ephemeral streams
D. Closer than 50 feet from lineaments in carbonate areas
E. Closer than 50 feet from fracture traces
F. Closer than 25 feet from bedrock pinnacles (surface or subsurface)
(2) Stormwater resulting from regulated activities shall not be discharged into sinkholes.
(3) If the developer can prove through analysis that the project site is an area underlain by carbonate geology, and such geologic conditions may result in sinkhole formations, then the project site is exempt from recharge requirements as described in Section 937.04, Volume Control. However, the project site shall still be required to meet all other standards found in this Ordinance.
(4) It shall be the developer's responsibility to verify if the project site is underlain by carbonate geology. The following note shall be attached to all stormwater management plans and signed and sealed by the developer's geologist: "I, ______________, certify that the proposed stormwater management facility (circle one) is / is not underlain by carbonate geology."
(5) Whenever a stormwater management facility will be located in an area underlain by carbonate geology, a geological evaluation of the proposed location by a geologist shall be conducted to determine susceptibility to sinkhole formation. The evaluation may include the use of impermeable liners to reduce or eliminate the separation distances listed in the BMP Manual. Additionally, the evaluation shall at a minimum, address soil permeability, depth to bedrock, seasonally high groundwater table, susceptibility for sinkhole formation, suitability of stormwater management facilities, subgrade stability and maximum infiltration capacity in depth of water per unit area.
(6) A detailed soils evaluation of the project site shall be performed to determine the suitability of recharge facilities. The evaluation shall be performed by a qualified professional, and at a minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. The general process for designing the infiltration BMP shall be:
A. Site evaluation to determine general areas of suitability for infiltration practices.
B. Provide field test throughout the area proposed for development to determine appropriate percolation rate and/or hydraulic conductivity. At least one (1) infiltration test must be included in each soil group and at least one (1) infiltration test must be conducted for each five (5) lots proposed for development. Infiltration tests must be taken at the location and depth of all proposed infiltration structures.
C. Design infiltration structure for required storm volume based on all available data.
(7) Extreme caution shall be exercised where infiltration is proposed in geologically susceptible areas such as strip mine or limestone areas. It is also extremely important that the design professional evaluate the possibility of groundwater contamination from the proposed infiltration/recharge facility and recommend a hydrogeologic justification study be performed if necessary. Whenever a basin will be located in an area underlain by limestone, a geological evaluation of the proposed location shall be conducted to determine susceptibility to sinkhole formations. The design of all facilities over carbonate formations shall include measures to prevent ground water contamination and, where necessary, sinkhole formation. The infiltration requirement in the High Quality/Exceptional Waters shall be subject to the Department's Chapter 93 and Anti-degradation Regulations. A detailed hydrogeologic investigation may be required by the Municipality and where appropriate, the Municipality may require the installation of an impermeable liner in detention basins.
(Ord. 32-2011. Passed 10-4-11.)