(a) A stormwater management plan (plan) shall be submitted to the county Department of Environmental and Development Services for review and approval concurrent with the submission of applications of site plans, subdivision plans or land disturbing activity permits. Land disturbing activity permits shall not be issued for the activity until the plan, as required by this chapter, detailing how run-off and associated water quality impacts resulting from the activity will be con-trolled and managed is approved.

(b)  The standards contained within the Virginia Stormwater Management Law and Regulations and the Handbook are to be used by the applicant when making a submittal under the provisions of this ordinance and in the preparation of stormwater management plans. The plan-approving authority, in considering the adequacy of a submitted plan, shall be guided by these same standards, regulations and guidelines. When the standards vary between the publications, the Virginia Stormwater Management Regulations shall take precedence.

(c)  It is the responsibility of an applicant to include in the plan sufficient information for the plan-approving authority to evaluate the environmental characteristics of the affected areas, the potential and predicted impacts of the development and the effectiveness and acceptability of the proposed measures detailed in the plan.

(d)  All stormwater management plans shall be appropriately sealed and signed by a professional engineer licensed to practice in Virginia certifying that the plan meets all submittal requirements outlined in this ordinance and is consistent with good engineering practice.

(e)  Stormwater management plans shall be approved or disapproved according to the following:

     (1) A maximum of 60 calendar days from the day a complete stormwater management plan is accepted for review will be allowed for the review of the plan. During the 60-day review period, the plan approving authority shall either approve or disapprove the plan and communicate its decision to the applicant in writing. Approval or denial shall be based on the plan’s compliance with the requirements of this chapter.

      (2) A disapproval of a plan shall contain the reasons for disapproval.

(f) An approved plan may be changed by the plan approving authority when:

      (1) An inspection reveals that the plan is inadequate to satisfy applicable requirements; or

     (2) The person responsible for carrying out the plan finds that because of changed circumstances or for other reasons the approved plan cannot be effectively carried out, and proposed amendments to the plan, consistent with the requirements of this ordinance are agreed to by the plan approving authority and the person responsible for carrying out the plans.

(g) In addition to the above standards, the following requirements shall be met for plan submissions:

     (1) The size, number, format, etc. of the plan shall meet the applicable requirements for site plan submission in accordance with chapter 24.1 of this code or for subdivision plan submission in accordance with Chapter 20.5, depending upon whether the stormwater management plan is being submitted as part of a site plan or subdivision plan application.

     (2) Plans shall be prepared to an appropriate engineer’s scale and the scale shall be shown on the plan.

   (3) The location and extent of any transitional buffers, infiltration yards, Chesapeake Bay preservation areas, floodplain management areas, wetlands, historic resources management areas, tourist corridor management areas and/or watershed management and protection areas that may be required by the application of chapters 24.1 (zoning ordinance), 23.2 (Chesapeake Bay preservation areas) or 23.1 (wetlands) of this code shall be shown on the plan.

    (4) The location, type, extent, owner’s name and recordation information of any existing or proposed landscape, conservation, preservation, drainage, impoundment, utility, ingress/egress or similar easements on the subject property or adjoining the property shall be shown on the plan.

     (5) Hydrologic and hydraulic design calculations for the pre-development and post-development conditions shall be prepared and submitted along with the plan. Such calculations shall include (i) description of the design storm frequency, intensity and duration, (ii) time of concentration, (iii) soil curve numbers or runoff coefficients, (iv) peak runoff rates and total runoff volumes for each watershed area, (v) stormwater routing, (vi) infiltration rates, where applicable, (vii) culvert capacities, (viii) flow velocities, (ix) data on the increase in rate and volume of runoff for the specified design storms, (x) hydraulic grade lines, (xi) inlet sizing, (xii) and documentation of sources for all computation methods and field test results.

     (6) Pre-development and post-development drainage area maps with topography (minimum scale to be one inch equals 200 feet) which extends a minimum of 500 feet beyond the limits of the proposed development detailing (i) the various drainage basins, (ii) the direction and flow rate of runoff, and (iii) the flow routing for the controlling time of concentration shall be prepared and submitted along with the plan.

     (7) A topographic base plan (minimum scale to be one inch equals 50 feet) demonstrating positive drainage from each lot or structure shall be prepared and submitted along with the plan. Such plan shall include (i) direction of flow arrows, (ii) elevations of lot corners, center, high points, low points, finished floor, curbing, and other drainage features (iii) locations where proposed grades meet existing grades, (iv) sizing, slope and elevation of culverts and pipes, (v) depth, size, shape and slope of ditches (vi) size, inverts and elevations of receiving channels or systems, and (vii) lo-cation, access to, and details of any BMPs. The one-hundred year flood boundary as depicted on the Flood Insurance Rate Map shall be shown on the plan and all proposed development within the floodplain shall meet the requirements of the Floodplain Management Area Overlay District section of chapter 24.1 of this code.

    (8) BMPs for subdivisions shall be sized based upon total impervious cover which is the summation of the actual impervious cover of the streets and other improvements being proposed as part of the subdivision and the expected average percent impervious cover per lot. The expected average percent impervious cover per lot shall be determined by the applicant based upon such factors as: the size and style of homes; length, width and configuration of the driveways; number and size of decks, pools, sheds and other accessory structures; and other development that can reasonably be expected to occur on the lots. In no case shall the expected average impervious cover per lot be less than is defined by the curve containing the following data points in the form of (average lot size in square feet: minimum expected percent impervious cover): (87120:12), (43560:20), (21780:25), (14505:30), (10890:38) and (5445:65).

     (9) Retention or detention facilities shall be shown on the plan with the following details where applicable (i) a minimum of two cross-sectional views at 90 degrees to each other (one through the outfall) for each basin showing: adequate freeboard, ground water elevation, bottom elevation, normal water surface elevation, water surface elevations for two, ten and 100-year storm, side slopes and top of bank elevations (ii) spillway, (iii) emergency spillway, (iv) outfall structure, (v) forebay, (vi) plantings (vii) impoundment easement, (viii) access for maintenance, and (ix) stock pile areas for future dredging spoils. All details should be drawn to scale and slopes shown as horizontal distance in feet required for one foot change in vertical distance (H:V).

    (10) Geotechnical properties for the hydrologic and structural properties of soils for all stormwater retention and detention facilities shall be described in a soils report and submitted as part of the plan. The submitted report shall follow the criteria in the Handbook and shall include (i) boring depth, (ii) ground water elevation, (iii) sampling frequency, (iv) sample type, and (v) associated laboratory testing with results and conclusions. Soil properties for infiltration facilities shall also conform to the guidance and specification outlined in the Handbook.

    (11) The maintenance requirements for all BMPs proposed on the plans shall be identified on the plans in the form of a maintenance plan. The purpose of the maintenance plan is to ensure the BMPs will continue to function as designed. The maintenance requirements are to be classified as routine or long term. The required frequency of the maintenance is to be given along with any details necessary to explain each requirement, how it is to be performed, expected cost, level of expertise required to perform, etc. The maintenance plan shall identify the owner of the BMPs and the responsible party for carrying out the maintenance plan. For each facility requiring the removal of accumulated sediments, the point at which the removal of sediment must be performed shall be identified in a quantifiable manner. Access for inspections and maintenance activities must be ensured and permanent easements provided as necessary.

     (12) The following standards shall apply to the design and construction of stormwater systems and shall be incorporated into the plans:

            a. The maximum depth of open channels should not exceed three feet measured from the invert of the ditch to the adjacent proposed ground elevation.

           b. The minimum longitudinal slope for open channels shall be 0.0050 foot per foot for channels with unpaved bottoms and 0.0025 foot per foot for channels with paved bottoms.

             c. The minimum longitudinal slope for curb and gutter shall be 0.0030 foot per foot.

           d. Stormwater systems that utilize a pump or pumps shall not be approved unless the pumping system will be owned and operated by the county.

            e. Permanent drainage easements are required where the stormwater system is located on private property owned by other than the owner of the stormwater system.

            f. Permanent impoundment easements are to be provided where the stormwater system is expected to impound waters during a 100-year storm on private property owned by other than the owner of the stormwater system.

           g. All stormwater runoff shall be conveyed to a stormwater system and shall not be permitted to sheet flow offsite unless otherwise approved.

          h. Existing drainage patterns must be preserved to the maximum extent practicable. Requests to alter drainage patterns must be made in writing and submitted for approval as part of the drainage plan.

             i. Wet ponds shall have a minimum depth of water of six feet.

(h)  Each plan approved shall be subject to the following conditions:

     (1) The applicant shall comply with all applicable requirements of the approved plan, and shall certify that all land clearing, construction, land development and drainage will be done according to the approved plan.

    (2) The land development project shall be conducted only within the area specified in the approved plan.

     (3) The county administrator shall be allowed, after giving notice to the owner, occupier, or operator of the land development project to conduct periodic inspections of the project.

     (4) The person responsible for implementing the approved plan shall conduct monitoring and submit reports as the county may require to ensure compliance with the approved plan to determine whether the plan provides effective stormwater management.

     (5) No changes may be made to an approved plan without review and written approval of the county.
 
(Ord. No. 06-17, 7/18/06)