Standard Specifications for Improvements
Section V. Grading
Every engineering plan shall include a topographic survey of the existing project site and shall be signed and sealed by a registered Illinois Professional Land Surveyor or a registered Illinois Professional Engineer. All topographic data shall be collected a minimum of fifty feet (50'). beyond the project site. All plans shall indicate the existing contours in one-foot (1'’) intervals. The five-foot (5') contour line shall be a solid line and all other contours shall be dashed. The existing contours and spot elevations must be indicated on the plans in a lighter line style or shade to provide distinction between the existing and proposed conditions.
The minimum grading shall be two percent (2.0%) for any grass area such as but not limited to residential lot, dry bottom detention facility, parkway, commercial site and park areas. Park areas such as but not limited to ball fields, track and field facilities, etc. can be exempt from the minimum grading slope if an under drain system is proposed. The maximum transition grading shall be 4:1.
Minimum slopes for parking areas shall be 0.50% and the maximum slopes shall be 3.0%. All parking areas that are adjacent to, and slope toward, storm water detention facilities shall be constructed with guardrails or sufficient structural parking stops to preclude the possibility for vehicles to roll into the detention facility. All roadways shall conform to the standards set forth in the Street section of these standards.
All developments shall be designed in compliance with the “Illinois Accessibility Code” latest revision. Specifically Subpart C: Public Facilities – New Construction section 400.310. At least one accessible route shall connect accessible buildings, facilities, elements and spaces that are on the same site. An accessible route with a running slope greater than 1:20 (5%) is a ramp and shall comply with Section 400.310 (e) of the Illinois Accessibility Code. Nowhere shall the cross slope of an access route exceed 1:50 (2%).
All grading plans shall indicate proposed spot elevation in bold lettering at a minimum of every fifty feet (50'). The calculated slope shall be shown with an arrow in the direction of the downward slope.
Overland flood routes shall be shown with large arrows to depict the route. Overland flood routes located in side yards is discouraged. However, when it is unavoidable and a flood route is located in the side yard of a structure with a basement, there shall be no basement windows on the side of the house where the flood route is located. Top of foundation/ lowest opening elevations shall be one foot (1') above the 100 year BFE and shall be two feet (2') above the 100-year BFE for the flood route if the tributary area is greater than 20 acres.
Rim elevations for all storm sewer structures shall be shown on the grading plans at a minimum.
Should a site require a retaining wall, a detail shall be indicated on the plans to indicate the type and style of wall to be used. A retaining wall that is greater than three feet (3') in height shall be designed and sealed by a registered Illinois Structural Engineer. The design criteria can be provided during the final engineering submittal.
Retaining walls around detention basins may not be continuous. There must be a sloped opening to allow for maintenance. Also, walls greater than three feet (3') in height are not permitted. If a height of greater than three feet (3') must be attained, the wall must be constructed in a terrace fashion, three feet (3') maximum high wall to a minimum three feet (3') wide terrace, then another three feet (3') maximum wall to another minimum three feet (3') wide terrace, etc.
The under drain outlet shall be shown on the plans. The ends of the retaining wall shall transition so that the grading shall not exceed the maximum transition grading of 4:1.