A. 
The Director of Public Works shall be responsible for review and assessment of a proposed project with regard to the adequacy of stormdrain discharge in accordance with all local laws, ordinances, resolutions, regulations, policies and procedures.
B. 
Determining adequacy. The proposed project shall be served by an adequate storm drainage system. A storm drainage system shall be considered adequate if:
(1) 
The on-site stormwater drainage system installed by the developer will be capable of conveying through and from the property the design flow of stormwater runoff originating in the development during a two-, ten-, and 100-year flood as determined in accordance with criteria specified in the Calvert County Road and Site Development and Stormwater Management Ordinance, in addition to flows from undeveloped land upstream in the natural watershed of the proposed project, flows from existing upstream developments, and designs flows from developments for which plats and plans have been approved, without resulting in erosion, sedimentation or flooding of the receiving channel and downstream properties; and
(2) 
The off-site downstream public drainage systems are capable of conveying to an acceptable outfall the design flow of stormwater runoff originating in the development, as determined in accordance with criteria specified in the Calvert County Road and Site Development and Stormwater Management Ordinance, in addition to flows from undeveloped land upstream in the natural watershed of the proposed project, flows from existing upstream developments, and design flows from developments for which plats have been recorded, without resulting in erosion, sedimentation, or flooding of the receiving channel and downstream properties.
C. 
Off-site downstream public drainage system improvements. A public storm drainage system shall be considered adequate if there is compliance with § 3-12B(1) and the County has awarded a contract for the construction or improvement of off-site downstream drainage systems necessary, in combination with existing systems, to comply with the standard specified in § 3-12B(2) and if the construction or improvement of the off-site downstream drainage system is expected to be completed before the issuance of the first building permit for the development or the developer agrees to undertake the construction or improvement of the off-site downstream drainage systems.
D. 
Calculating runoff. In determining the adequacy of a storm drainage system, stormwater runoff flows from land for which a plat has not been recorded shall be calculated as if the land was developed according to its existing zoning classification and as if stormwater management techniques, as may be required by the Stormwater Management Ordinance, have been utilized. Stormwater runoff flows from other lands shall be calculated on the basis of whether or not stormwater management techniques have been utilized.
Stormwater management and storm drainage systems found not to be adequate may be mitigated in accordance with the following:
A. 
A proposal that is subject to denial or delay under this article shall be given an opportunity to provide infrastructure funds, to improve facilities directly, or to donate necessary facilities in order to allow for approval of the application under this article for a certificate of adequate public facilities.
B. 
The forms and levels of mitigation required shall be proportionate to the projected impact of the proposed project upon the facility or facilities and shall be determined by the Planning Commission Administrator in consultation with the Director of Public Works.