[Ord. No. 2601, 2-28-2017]
A. 
Intent And Purpose. The evaluation of a Concept Stormwater Management Plan is intended to ensure the adequate review and consideration of potential stormwater management impacts of proposed site alterations upon the surrounding uses, activities, properties, the existing stormwater infrastructure, and the watershed, and that the site alterations adhere to the principles and acceptable practices outlined in Section 422.060.
1. 
The Concept Stormwater Management Plan shall illustrate how the proposed site alternations will:
a. 
Preserve and/or protect existing natural resources areas that facilitate pollutant removal and reduce runoff.
b. 
Limit disturbance and preserve existing pervious surface areas and sensitive areas such as flood plains and stream buffers.
c. 
Reduce the amount of impervious surface area. (i.e., rooftops, parking lots, sidewalks, roads, etc.)
d. 
Disconnect the stormwater flow generated from impervious surface areas from the MSD built stormwater infrastructure system and utilize overland flow to vegetated buffers and other "green" infrastructure techniques that promote infiltration.
e. 
Use pervious surface materials, such as permeable paver blocks, porous asphalt, porous concrete and green roofs.
f. 
Install engineered systems that treat stormwater runoff and/or reduce peak stormwater runoff rates using techniques that employ vegetation and infiltration.
B. 
Submission Requirements. Submission requirements for the Concept Stormwater Management Plan shall be in accordance with the standards identified in Section 400.1080.
1. 
The Concept Stormwater Management Plan may be incorporated into other documents identified in Section 400.1080, if in the opinion of the Director of Public Services, there will be sufficient detail provided.
C. 
Review Procedure. Applications shall be reviewed in accordance with the review procedures identified in Section 400.1090.
[Ord. No. 2601, 2-28-2017; Ord. No. 2686, 11-26-2019; Ord. No. 2728, 7-27-2021]
A. 
Applications for detached single-family residential shall provide for the following on-site detention:
1. 
Construction Of New Detached Single-Family Home. Volume designed to accommodate the entire roof area based on a 15-year, 20-minute rain event.
2. 
Lot Coverage. Residential addition, reconstruction, or improvement in which the combined lot coverage is increased as follows:
a. 
One thousand two hundred (1,200) square feet or more. Volume designed to accommodate the proposed impervious area based on a 15-year, 20-minute rain event.
b. 
Four hundred (400) square feet or more, but less than one thousand two hundred (1,200) square feet. Incorporate BMPs as noted under Section 422.060 to minimize the stormwater impact generated by the proposed improvement.
3. 
Residential addition, reconstruction, or improvement in which the residential combined floor area is increased as follows:
a. 
Four Hundred (400) Square Feet Or More. Incorporate BMPs as noted under Section 422.060 to minimize the stormwater impact generated by the proposed improvement.
B. 
Exceptions. The following exceptions may be authorized through site plan review:
1. 
The volume design requirement may be exempted for the initial construction of a new single-family home when on-site detention is provided for the subdivision as a whole, subject to the following conditions:
a. 
The final subdivision plat shall include:
(1) 
A minimum 10-foot-wide easement for all ground surface swales and underground pipes that direct stormwater from lot to lot and onto the subdivision detention system.
(2) 
The square foot area of the average house footprint utilized in calculating the size of the stormwater detention system.
b. 
Subdivision indentures shall include language regarding the preservation and maintenance of the stormwater easement.
c. 
In the event a new home exceeds the average size house footprint identified in Subsection (B)(1)(a) above, stormwater detention for the excess square footage on said lot shall be provided.
[Ord. No. 2601, 2-28-2017]
Before an application for a building permit is submitted for a site alteration, except single-family site alterations, the application for site alterations, including the site plan documents and Concept Stormwater Management Plan approved by the Commission, must be reviewed and approved by the MSD.