(A) General standards.
(1) All regulated activities shall meet or exceed the applicable minimum standards of federal, state, regional, or other local agencies having jurisdiction over the work governed by the permit.
(2) No regulated activity shall be allowed to alter the ground surface such that runoff will be diverted onto or detained on an adjacent property that the permittee does not have the right to use.
(3) No regulated activity shall be allowed to significantly alter existing drainage patterns or discharge concentrated stormwater runoff onto an adjacent property.
(4) All downspouts shall discharge onto the ground surface, except that downspouts in separate sewer areas may be directly connected to a storm sewer in order to prevent an adverse impact on an adjacent property. Where downspouts discharge onto the ground surface, the discharge shall be allowed to flow overland to a private storm drain that is connected to a village storm sewer or combined sewer, provided the overland flow distance is at least ten feet.
(5) Concentrated discharges to the ground surface, such as those from storm drains, downspouts, and sump pumps, shall discharge toward established flow paths in order to minimize the risk to adjacent properties of flooding, erosion, and other drainage hazards. No concentrated discharge created on or after November 1, 2016 shall be constructed within 25 feet of a village sidewalk or ten feet of an adjacent property line, except in cases where the owner of the subject property has an ownership interest in, or an easement on, the adjacent property.
(6) No pavement created on or after November 1, 2016 shall be constructed within two feet of a property line, except pavement necessary for authorized driveway access from the property to a public or private right-of-way, or in cases where the owner of the subject property has an ownership interest in, or an easement on, the adjacent property.
(7) Depressional storage areas that will be filled or drained by a regulated activity shall be replaced on the subject property as a new depressional storage area or as part of a stormwater detention system.
(8) Ground slopes shall be no steeper than 25%, unless permanent ground treatments that do not require mowing are used.
(B) Soil erosion and sediment control standards.
(1) Acceptable control measures include, but are not limited to: silt fence, ditch checks, erosion control blanket, stabilized construction entrances, and inlet protection. Control measures shall meet the minimum standards and specifications of the Illinois Urban Manual, unless otherwise modified by the code official pursuant to the applicable procedures of this code. If the minimum standards and specifications of the Illinois Urban Manual conflict with the other provisions of this code, the requirements that provide the greatest protection to the public, as determined by the code official, shall govern and control.
(2) Soil disturbance shall be conducted in such a manner as to minimize erosion. Areas that are not to be disturbed shall be protected from construction equipment or other disturbance until final stabilization is achieved.
(3) Soil stabilization measures shall consider the time of year, site conditions, and the use of temporary or permanent control measures.
(4) Adjacent properties shall be protected from erosion and sedimentation. Velocity dissipation devices shall be placed at concentrated discharge locations as necessary to prevent erosion.
(5) Sediment control measures shall be installed prior to the disturbance of upland areas.
(6) Stabilization of disturbed areas shall be initiated immediately whenever any clearing, grading, excavating or other earth disturbing activities have permanently ceased on the site, or temporarily ceased on the site for a period exceeding seven days.
(7) All temporary control measures shall be removed within seven days after final stabilization of the site is achieved, or after the temporary measures are no longer necessary, as determined by the code official. Trapped sediment shall be removed and disturbed areas shall be permanently stabilized.
(C) Stormwater detention standards.
(1) Stormwater detention shall be required on the subject property for the following regulated activities:
(a) Construction of any new residence, including construction of a new residence on an existing foundation;
(b) Construction of any new commercial building; and
(c) Construction of a “substantial alteration,” as this term is defined in Chapter 153 of this code, as amended.
(2) The required volume of stormwater detention shall be determined using the Metropolitan Water Reclamation District of Greater Chicago’s Modified Rational Method with the data and design conditions listed below:
(a) The rainfall intensity shall be based on the Illinois State Water Survey, Bulletin 70 Northeast Illinois sectional rainfall intensity, published in 1989.
(b) The allowable release rate for existing and proposed conditions shall be based on a runoff coefficient of 0.15 and the rainfall intensity for a three-year storm event.
(c) The composite runoff coefficient for the proposed conditions shall be based on the maximum impermeable lot coverage allowed by Chapter 153 of this code, as amended.
(d) The required volume of stormwater detention shall be the difference in the storage volume calculated for existing and proposed conditions for a 100-year storm event.
(3) Stormwater storage volume located within the void space of best management practices, such as a rain garden or the aggregate base of permeable pavement, may be credited toward the required stormwater detention volume according to the following standards:
(a) The maximum void space shall be 36% for gravel and 25% for engineered soil.
(b) No more than 25% of the required stormwater detention volume may be provided within the aggregate base of permeable pavement.
(c) No more than 25% of the required stormwater detention volume may be provided within a rain garden.
(4) The volume of depressional storage areas that will be filled or drained by a regulated activity may be replaced as part of a stormwater detention system.
(5) All runoff from the new impervious areas of the site shall be routed to the stormwater detention facility. The system shall convey the 100-year peak rate of runoff from the impervious areas to the facility, with a minimum of six inches of freeboard against overflowing off-site.
(D) Building elevation standards.
(1) The first floor elevation for any new single-family residential construction on a previously developed property shall not exceed the first floor elevation of the previous residence.
(2) The lowest floor elevation for any new building construction which includes a basement, cellar or crawlspace on a previously developed property shall not be lower than at least 18 inches above the seasonal high groundwater elevation. The seasonal high groundwater elevation for the subject property shall be determined by a qualified professional.
(Ord. 1178, passed 10-17-2016)