Chapter 13.10 COMPREHENSIVE DRAINAGE PLAN

Chapter 13.10
COMPREHENSIVE DRAINAGE PLAN

Sections:

13.10.010 Comprehensive drainage plan permit procedures and requirements.

13.10.020 Exceptions to on-site stormwater management requirements – Exceptions for providing stormwater management.

13.10.030 General and technical criteria for stormwater management.

13.10.040 General and technical criteria for erosion and sediment control.

13.10.050 Construction inspection provisions.

13.10.060 Maintenance and repair of stormwater facilities.

13.10.010 Comprehensive drainage plan permit procedures and requirements.

(1) For the purposes of this section, when land-disturbing activity will be required of a contractor performing work pursuant to a construction contract, the preparation, submission and approval of an erosion and sediment control plan shall be the responsibility of the owner of the land upon which activity takes place.

(2) Except as provided in Sections 10.1-564 and 10.1-603.5 of the Code of Virginia, as amended (state agency projects), no person may engage in any land-disturbing activity (except as provided under SCC 13.05.040) until submitting to the administrator a comprehensive drainage plan for the land-disturbing activity and such plan having been approved by the administrator and a permit issued therefor.

(3) Where the land-disturbing activity results from the construction of a single-family residence with less than 10,000 square feet of disturbance, a performance bond must be provided in lieu of an erosion and sediment control plan.

(4) Permit Requirements. No land owner shall receive any of the building, grading or other land development permits required for land-disturbance activities without first meeting the requirements of Division I of this title prior to commencing the proposed activity.

Other city agencies authorized under any other law to issue grading, building or other permits for activities involving land-disturbing activities may not issue any such permit unless the applicant submits with the application an approved comprehensive drainage plan and certification that the plan will be followed.

Should a land-disturbing activity associated with an approved plan in accordance with this section not begin within 180 days following approval or cease for more than 180 days, the administrator may evaluate the approved comprehensive drainage plan to determine whether the plan still satisfies the requirements of Division I of this title and to verify that all design factors are still valid. If the administrator finds the previously filed plan to be inadequate, a modified plan must be submitted and approved prior to the resumption of land-disturbing activities.

(5) Permit Application Requirements. Unless specifically excluded or exempted by Division I of this title, any landowner desiring a permit for a land-disturbance activity shall submit to the administrator a permit application on a form provided by the city and have such form accompanied by the following in order that the permit application be considered:

(a) Stormwater management plan in accordance with this section;

(b) Erosion and sediment control plan in accordance with this section and SCC 13.10.040;

(d) Performance bond in accordance with SCC 13.05.060; and

(e) Plan review fee and permit application in accordance with SCC 13.05.050 and 13.05.055.

No application for land development, land use conversion, land disturbance, or redevelopment will be approved unless it includes a comprehensive drainage plan, as required by Division I of this title, detailing how runoff and associated water quality and quantity impacts resulting from the activity will be controlled or managed.

No building, grading, or sediment control permit shall be issued until a satisfactory final stormwater management plan and/or erosion and sediment control plan, or a waiver thereof, has undergone a review and is approved by the administrator after determining that the plan or waiver is consistent with the requirements of Division I of this title.

(6) Stormwater Management Plan Required. For newly developed projects which are being or will be developed in more than one phase, including all major subdivisions, a stormwater management plan shall consist of a concept plan for all phases of development and a final plan for the phase(s) submitted for permitting to ensure adequate planning for the management of stormwater runoff. All developments, except those exempted by Division I of this title, shall provide a final stormwater management plan. Both plans shall be in accordance with the criteria established in this section.

(a) Stormwater Management Concept Plan. A stormwater management concept plan shall include all information as required by this chapter in order to evaluate the environmental characteristics of the planning area, the potential impacts of all proposed development of the site, both present and future, on the water resources, and the effectiveness and acceptability of the measures proposed for managing stormwater generated at the project site.

(i) The concept plan should be prepared at the time of the preliminary plan of subdivision or other early step in the development process to identify the type of stormwater management measures necessary for the proposed project. The intent of this conceptual planning process is to ensure adequate planning for management of stormwater runoff from future development. To accomplish this goal, the following information shall be included in the concept plan:

(A) A map (or maps) indicating the location of existing and proposed buildings, roads, parking areas, utilities, riparian buffers, integrated management practices, structural stormwater management; and existing two-foot contours. The map(s) will also clearly show proposed land use; drainage patterns and boundaries; and the limits of clearing and grading. The map(s) shall be at a minimum scale of one inch equals 100 feet.

(B) A written description of the site plan and justification of proposed changes in natural conditions.

(C) A preliminary (conceptual) engineering analysis to show that the proposed stormwater management measures are capable of controlling runoff from the site in compliance with Division I of this title and the specifications of the Virginia Stormwater Management Manual.

(D) A written or graphic inventory of the natural resources at the site and surrounding area as it exists prior to the commencement of the project and a description of the watershed and its relation to the project site. This description shall include a discussion of soil conditions, presence or extent of karst geology, forest cover, topography, wetlands, other native vegetative areas on the site, and the presence of rare, threatened or endangered species downstream. Particular attention should be paid to environmentally sensitive features that provide particular opportunities or constraints for development.

(E) Existing Conditions – Plans and Narrative. The applicant must present detailed plan(s) and narrative to including the following:

(I) Existing Tree and Vegetation Plan. The plan shall include the following for the entire project area:

(a) The location of all existing trees of three inches or larger (freestanding) and 18 inches or larger (in forested areas) in diameter measured four and one-half feet above the ground within the project property and within a line 25 feet beyond the project property.

(b) The outline of existing masses of other vegetation that may include trees less than three inches in diameter and shrubs.

(II) Description of Existing Conditions. A narrative shall describe the quality of the existing vegetation and the impacts of the development on the vegetation.

(III) Description of Preservation Strategies. A narrative shall be provided to describe strategies for preservation and protection of existing vegetation to remain.

(F) A written description of the required maintenance burden for any proposed stormwater management facility.

(ii) The city requires a concept plan to consider the maximum development potential of a site under existing zoning, regardless of whether the applicant presently intends to develop the site to its maximum potential.

(iii) The applicant may be required to include within the stormwater concept plan measures for controlling existing stormwater runoff discharges from development or redevelopment occurring on a previously developed site in accordance with the standards of Division I of this title to the maximum extent practicable.

(b) Final Stormwater Management Plan. After review of the stormwater management concept plan, and modifications to that plan as deemed necessary by the administrator, as required by Division I of this title, a final stormwater management plan must be submitted for approval.

(i) All stormwater management plans shall be appropriately sealed and signed by a professional engineer in adherence to all minimum standards and requirements pertaining to the practice of that profession including Chapter 4 (Section 54.1-400 et seq.) of Title 54.1 of the Code of Virginia and attendant regulations certifying that the plan meets all submittal requirements outlined in Division I of this title and is consistent with good engineering practice.

(ii) The final stormwater management plan, in addition to the information from the concept plan, shall include all of the information required by Division I of this title, which includes, but is not limited to, the following:

(A) Contact Information. The name, address, and telephone number of all persons having a legal interest in the property and the tax reference number, zoning, use and parcel number of the project property, adjacent properties and other properties affected by the project, including reference to any immediately prior source deed for title to the property.

(B) Topographic Base Map. A minimum scale of one inch equals 100 feet topographic base map of the site which extends a minimum of 100 feet beyond the limits of the proposed development and indicates existing surface water drainage including streams, ponds, culverts, ditches, and wetlands; current land use including all existing structures; locations of utilities, roads, and easements; and significant natural and manmade features not otherwise shown.

(C) Final Stormwater Management Plan. The map(s) shall be drawn at a minimum scale of one inch equals 100 feet and include the following additional information:

(I) The final location of proposed buildings, roads, parking areas, utilities, riparian buffers, integrated management practices, structural stormwater management, and sediment control facilities.

(II) Existing and proposed two-foot contours with spot elevations at critical locations, including corners of pavement edges.

(III) Watershed and drainage boundaries and area data.

(IV) Limits of clearing and grading.

(V) A table summarizing the calculations for each structural stormwater management and erosion control facility.

(D) Calculations. Hydrologic and hydraulic design calculations for the pre-development and post-development conditions for the design storms specified in Division I of this title. Such calculations shall include the following:

(I) Description of the design storm frequency, including intensity and duration;

(II) Time of concentration path shown on pre- and post-development drainage maps, to a common design point and labeled with type of flow, length and slope;

(III) Soil curve numbers or runoff co-efficients;

(IV) Pre- and post-development peak runoff rates and total runoff volumes for each drainage area;

(V) Infiltration rates, where applicable;

(VI) Culvert capacities;

(VII) Flow velocities;

(VIII) Data on the increase in rate and volume of runoff for the specified design storms; and

(IX) Documentation of sources for all computation methods and field test results.

A summary table showing the pre- and post-development drainage areas, peak runoff rates, and velocities for all required storm frequencies at each discharge point shall be provided on the final stormwater management plan.

(iii) Soils Information. Geotechnical properties for the hydrologic and structural properties of soils, especially for dam embankments, shall be described in a soils report. The submitted report shall include boring depth, sampling frequency and types and associated laboratory testing with results and conclusions and follow the criteria in the Virginia Stormwater Management Manual. Soil properties for infiltration facilities shall also conform to the guidance and specifications outlined in the Virginia Stormwater Management Manual.

(c) Stormwater Planting Plan. The landscape plans shall be prepared and stamped by a registered professional engineer or landscape architect licensed in the commonwealth of Virginia.

(i) This plan must be prepared by a qualified individual familiar with the selection of emergent and upland vegetation appropriate for the selected BMP.

(ii) The city encourages the use of a vegetation strategy that can produce an aesthetically pleasing, compatible with its surroundings, facility while simultaneously augmenting pollutant removal capabilities and wildlife habitat. The Virginia Stormwater Management Manual Section 3.05 provides guidance in the plant selection and planting zone location for both within and surrounding the stormwater management facility.

(d) Other Environmental Permits. The applicant shall assure that all other applicable environmental permits have been applied for prior to issuance of the site construction permit.

(7) Erosion and Sediment Control Plan Required. All erosion and sediment control plans and reports shall be appropriately sealed and signed by a professional engineer licensed in Virginia, in adherence to all minimum standards and requirements pertaining to the practice of that profession in accordance with Virginia Erosion and Sediment Control Regulations, certifying that the plan meets all submittal requirements outlined in Division I of this title and is consistent with good engineering practice.

(a) The erosion and sediment control plan(s) and narrative shall include all of the information required in the Checklist for Erosion and Sediment Control Plans, Narrative and Minimum Standards Checklist.

(b) The documentation shall follow the format and conform to the approved standards and specifications for control techniques as set forth in the Virginia Erosion and Sediment Control Handbook, which by reference is adopted as a part of Division I of this title. The plan shall be consistent with the criteria, techniques and methods as set forth in the Minimum Standards (Section 4 VAC 50-30-40) of the Virginia Erosion and Sediment Control Regulations adopted by the board.

(8) Stormwater Management Inspection and Maintenance Agreements. Prior to the issuance of any permit that has a stormwater management facility as one of the requirements of the permit, the applicant or owner of the site must execute and record in the land records of the city of Staunton a stormwater management inspection and maintenance agreement which shall be a covenant to the city binding on all subsequent owners of properties upon which stormwater management facilities are situated or served.

The inspection and maintenance agreement shall be prepared, executed and submitted to the city in the form currently provided by the city engineering department, as revised from time to time. (Ord. 2009-09; Ord. 2007-30; Ord. 2007-20. Code 1985, § 11-20).

13.10.020 Exceptions to on-site stormwater management requirements – Exceptions for providing stormwater management.

(1) An applicant may file a written request for a waiver. Requests to waive the stormwater management plan requirements shall be submitted in writing to the administrator for approval. An exception from the stormwater management regulations may be granted; provided, that:

(a) Exceptions to the criteria are the minimum necessary to afford relief; and

(b) Reasonable and appropriate conditions shall be imposed as necessary upon any exception granted so that the intent of the law and Division I of this title are preserved.

(2) The minimum requirements for stormwater management may be waived, in whole or in part, upon written request of the applicant; provided, that at least one of the following conditions applies:

(a) It can be demonstrated that the proposed development is not likely to impair attainment of the objectives of Division I of this title;

(b) Alternative minimum requirements for on-site management of stormwater discharges are established in a stormwater management plan that was previously approved by the administrator;

(c) Provisions are made to manage stormwater by an off-site facility. The off-site facility is required to be designed and adequately sized to provide a level of stormwater control that is equal to or greater than that which would be afforded by on-site practices and to be constructed prior to the on-site land development activity. The owner shall designate a legally obligated entity responsible for long-term operation and maintenance of the stormwater practice; or

(d) The administrator finds that meeting the minimum on-site management requirements is not feasible due to the natural or existing physical characteristics of a site.

(e) Economic hardship is not sufficient reason to grant an exception from the requirements of Division I of this title.

(3) The administrator grants a waiver from strict compliance with stormwater management provisions that are not achievable, only if acceptable mitigation measures are provided. However, to be eligible for a waiver, the applicant must demonstrate to the satisfaction of the administrator that the immediately downstream waterways will not be subject to:

(a) Deterioration of existing culverts, bridges, dams, and other structures;

(b) Deterioration of biological functions or habitat;

(d) Increased threat of flood damage to public health, life and property.

(4) If the waiver request meets all of the above conditions and is acceptable to the administrator, the administrator shall approve the waiver.

(5) Off-Site Stormwater Management Facilities. In lieu of providing on-site stormwater management, an applicant may obtain a waiver of the required stormwater management by entering into an agreement with the city for the granting of an easement or the dedication of land by the applicant to be used for the construction of an off-site stormwater management facility. The applicant must provide calculations to the administrator showing that an adequate channel is/will be provided to convey the stormwater runoff from the development to an off-site facility. The agreement shall be entered into by the applicant and the city prior to the recording of plats or, if no record plat is required, prior to the issuance of the building permit. (Ord. 2009-09; Ord. 2007-20. Code 1985, § 11-21).

13.10.030 General and technical criteria for stormwater management.

The following general and technical criteria shall apply to land development and land-disturbance activities:

(1) Regional Stormwater Management Plans. Applicants shall contact the administrator prior to submitting an application for stormwater management plan approval to determine if a regional stormwater management plan was developed for the applicable watershed. If such a plan is in existence, the applicant must provide stormwater management water quality treatment on site in accordance with the provisions of the regional plan and other management provisions as specified by the administrator.

(2) General.

(a) Proposed residential, commercial, or industrial subdivisions shall apply the stormwater management criteria provided in this section to the land development as a whole, including submission, review and approval of a stormwater management concept plan reflecting all proposed lots in the ultimate developed condition.

(b) Use of nonstructural stormwater practices (low-impact development) as part of the site layout and design for all developments and redevelopments is required in order to reduce the amount of stormwater runoff that must be managed. This will help to minimize the reliance on structural practices which require ongoing maintenance in order to be effective.

(c) On-site stormwater conveyance systems shall be designed for the 10-year storm event utilizing the rational method to determine the flow rate. Closed storm sewer systems shall be designed such that the hydraulic grade line for the 10-year storm event is a maximum elevation of one foot below the throat of the inlet. Closed systems shall be checked such that the hydraulic grade line for the 100-year storm event causes a maximum ponding depth at the inlet of six inches.

(d) Determination of flooding and channel erosion impacts to receiving streams due to land development projects shall be measured at each point of discharge from the development project and such determination shall include any runoff from the balance of the watershed that also contributes to that point of discharge.

(e) For stormwater detention design, design storms shall be defined as one-, two-, 10- and 100-year, 24-hour storms using rainfall distributions as recommended by the U.S. Soil Conservation Service, TR-55 and TR-20 methodologies. For other BMP design, the modified rational (critical storm duration) method may be used, per guidance provided in the Virginia Stormwater Management Handbook, if the contributing drainage area is less than 20 acres.

(f) The rainfall rates for all calculations shall be as provided in the U.S. National Oceanic and Atmospheric Administration (NOAA) publication “Atlas 14: Rainfall Precipitation Frequency Data,” latest edition.

(g) For purposes of computing runoff, all pervious lands in the site shall be assumed prior to development to be in good condition (if the lands are pastures, lawns, or parks), with good cover (if the lands are woods), or with conservation treatment (if the lands are cultivated); regardless of conditions existing at the time of computation. Cultivated lands must be in a cultivated state for five years prior to application for the purposes of claiming cultivated pre-developed runoff rates.

(h) Pre-development and post-development runoff rates shall be verified by calculations that are consistent with good engineering practices and performed with methods approved and illustrated in the Virginia Stormwater Management Manual.

(i) Stormwater management facilities and best management practices shall be designed and sited to capture, to the maximum extent practicable, the runoff from the entire land development project area and, in particular, areas of impervious cover within the development project area. If the entire land development cannot be captured by the stormwater management facilities, the facilities shall be sized so that the addition of the peak release rate from the facility(ies) individually and the undetained areas within the same watershed do not exceed the requirements of Division I of this title.

(j) The number, type, and siting of stormwater management facilities shall be designed so as to preserve natural channel characteristics, existing vegetation, and natural groundwater recharge on a site to the extent practical.

(k) Outflows from a stormwater management facility shall be discharged to an adequate channel (exceptions may be granted in accordance with subsection (6)(h) of this section), and velocity dissipaters shall be placed at the outfall of all stormwater management facilities and along the length of any outfall channel as necessary to provide a non-erosive velocity of flow from the basin to a channel. A karst feature, whether on site or downstream and off site, may only be considered an adequate receiving channel if design criteria are in compliance with the criteria in subsections (2)(n) and (o) of this section.

(l) Construction of stormwater management facilities or modifications to channels shall comply with all applicable laws and regulations. Evidence of approval of all necessary permits, such as US Army Corps of Engineers and VA DEQ Wetland Permits, VA DEQ VPDES Permits, etc., shall be provided prior to beginning construction.

(m) Land development projects shall comply with the Virginia Erosion and Sediment Control Law and SCC 13.10.040.

(n) Construction of stormwater management impoundment structures or facilities may occur in karst areas only after a geological study of the area is conducted supporting the compatibility of such structures. A karst feature may only be filled or “improved” in accordance with proper geotechnical design (see VDOT IIM-228).

(o) No adverse environmental impacts shall occur to any identified karst features. Discharge of stormwater into a karst feature shall not occur unless the pretreatment and water quality criteria are met. Increased volumes of stormwater runoff to a karst feature shall not occur.

(p) Impounding structures that are not covered by the Virginia Impounding Structures Regulations (Dam Safety) shall be designed and checked for structural integrity and for floodplain impacts for a minimum of the 100-year storm event.

(q) Construction of stormwater management impoundment structures within a Federal Emergency Management Agency (FEMA) designated 100-year floodplain shall be avoided to the extent possible. When this is unavoidable, all stormwater management facility construction shall be in compliance with all applicable regulations under the National Flood Insurance Program, 44 CFR Part 59, and Chapter 18.170 SCC, Floodplain Districts and Regulations, and the Staunton City Code. These SWM facilities shall be designed and located, to the extent practical, to: (i) provide an unrestricted release up to at least the 10-year flood elevation of the receiving state water; and (ii) maintain their water quantity and/or water quality control value during the 100-year flood condition.

(3) Stormwater Management Facilities.

(a) Minimum Control Requirements.

(i) All stormwater management practices shall be designed so that the specific storm frequency storage volumes as identified in Division I of this title and the current Virginia Stormwater Management Handbook, whichever is more stringent, are met, unless the administrator grants the applicant a waiver or the applicant is exempt from such requirements.

(ii) In addition, if hydrologic or topographic conditions warrant greater control than that provided by the minimum control requirements, the administrator reserves the right to impose any and all additional requirements deemed necessary to protect downstream properties and aquatic resources from damage due to increased volume, frequency, velocity, and rate of stormwater runoff.

(b) Site Design Feasibility.

(i) Stormwater management practices for a site shall be chosen based on the physical conditions of the site. Among the factors that should be considered are as follows:

(A) Topography.

(B) Existing vegetation.

(D) Depth to water table.

(E) Soils.

(F) Slopes.

(G) Terrain.

(H) Hydraulic head.

(I) Location in relation to environmentally sensitive features.

(J) Intended or proposed land use.

(K) Karst features.

(L) Depth to rock.

(ii) Applicants shall consult the Virginia Stormwater Management Handbook for guidance on the factors that determine site design feasibility when selecting a stormwater management practice.

(i) All stormwater management practices shall be designed to convey stormwater to allow for the maximum removal of pollutants and reduction in flow velocities. This shall include, but not be limited to:

(A) Maximizing of flowpaths from inflow points to outflow points;

(B) Protecting of inlet and outfall structures;

(D) Providing of under-drain systems, where applicable and appropriate;

(E) Incorporating appropriate BMPs in consideration of site-specific conditions.

(ii) The Virginia Stormwater Management Manual provides detailed references on the requirements for conveyance for each of the approved stormwater management practices.

(d) Pretreatment Requirements. Every stormwater treatment practice shall have an acceptable form of water quality pretreatment, in accordance with the pretreatment requirements found in the current Virginia Stormwater Management Handbook. Stormwater infiltration practices or practices having an infiltration component, as specified in the Virginia Stormwater Management Handbook, are prohibited, even with pretreatment, in the following circumstances:

(i) Where stormwater is generated from highly contaminated source areas known as “hotspots”;

(ii) Where stormwater is carried in a conveyance system that also carries contaminated, nonstormwater discharges;

(iii) Where stormwater is being managed in a designated groundwater recharge area; or

(iv) Under certain geologic conditions (e.g., karst) that prohibit the proper pretreatment of stormwater.

(e) Treatment/Geometry Conditions.

(i) All stormwater management practices shall be designed to capture and treat stormwater runoff according to the specifications outlined in the Virginia Stormwater Management Handbook. These specifications will designate the water quality treatment and water quantity criteria that apply to an approved stormwater management practice as required by Division I of this title.

(ii) Stormwater management facilities shall be designed to conform to the natural topography where practical.

(iii) Any detention facilities that are designed to have a permanent pool of water constructed in or adjacent to residential and commercial zoning areas shall be constructed with an aquatic bench or have a minimum of a six-foot fence installed around the perimeter of the facility.

(4) Nonstructural Stormwater Quantity and Quality Control (Low-Impact Development – LID).

(a) The use of LID site planning and integrated management practices is required by the city for all developments and redevelopments to control stormwater runoff at the source and more closely approximate pre-development runoff conditions.

(b) LID stormwater management design plans developed consistent with the requirements of this subsection shall satisfy the water quality and quantity performance criteria of Division I of this title.

(c) The design criteria, hydrologic analysis and computational procedures for LID stormwater management design plans shall be those of the low-impact development design manuals.

(d) LID stormwater management design plans shall not conflict with existing federal, state or local laws, ordinances, regulations or policies.

(e) Stormwater facility maintenance easement agreement documentation, as provided by SCC 13.10.010(8), shall be recorded to identify the locations of integrated management practices on lots or parcels. The owner shall not remove or structurally alter integrated management practices without prior written approval from the city.

(f) Developments shall, to the extent practicable, incorporate LID practices in accordance with the low-impact development design manuals into the site layout and design to minimize increases in runoff rates, volumes, and pollutant loads.

(g) In addition, the following LID practices are required to be incorporated into each project:

(i) Disconnect Impervious Areas/Downspout Disconnection. All runoff from rooftops and parking lots shall be directed onto vegetated swales or filter strips prior to entering a closed storm sewer system.

(ii) Disconnected impervious areas shall be treated as close as practical to their source, and not at the low point of the site just prior to entering the public drainage system, unless that is the only possible location for treatment.

(iii) Site Minimization/Impervious Areas Reduction.

(A) Minimal ground disturbance shall be achieved by identifying the smallest possible land area that can practically be impacted during site development.

(B) Development should be placed away from environmentally sensitive areas, future open space, tree preservation areas, future restoration areas, and temporary and permanent buffer zones, as required in Chapter 13.12 SCC. Existing vegetated or open space may be preserved instead of clearing a portion of the site in order to create lawn areas. Impervious surface area shall be limited by site designs that minimize the area of streets, parking lots, and rooftops and/or utilize permeable paving material. For residential areas, cluster development shall be provided where appropriate.

(iv) Other best management practices such as individual rain gardens, infiltration basins and trenches (where permeable soils are present) and filtration basins and sand filters (on highly impervious or industrial developments) shall be utilized where appropriate.

(5) Stormwater Water Quality Control. Unless determined by the administrator for a project to be exempt, the following criteria shall be addressed for stormwater management at all sites:

(a) All stormwater runoff generated from land development and land use conversion activities shall not discharge stormwater runoff directly into a wetland or local water body without adequate treatment. Where such discharges are proposed, the impact of the proposal on wetland functions shall be assessed using a method acceptable to the administrator. In no case shall the impact on functions be any more than allowed by the Army Corps of Engineers (ACE) or the Department of Environmental Quality.

(b) Land development projects shall comply with the water quality criteria in accordance with Title 10.1, Chapter 6, Article 1.1 of the Code of Virginia and the Virginia Stormwater Management Handbook, latest edition.

(c) Stormwater discharges to critical areas with sensitive resources (i.e., cold water fisheries, impaired streams and tributaries, recreational waters, recharge areas, karst features, water supply reservoirs) may be subject to additional criteria, or may need to utilize or restrict certain stormwater management practices at the discretion of the administrator.

(d) Industrial sites which are listed under the Standard Industrial Code are required to prepare and implement a stormwater pollution prevention plan, and shall file a notice of intent (NOI) under the provisions of the National Pollutant Discharge Elimination System (NPDES) general permit. The stormwater pollution prevention plan requirement applies to both existing and new industrial sites.

(e) Stormwater discharges from land uses or activities with higher potential pollutant loadings, known as “hotspots,” may require the use of specific structural BMPs and pollution prevention practices.

(6) Stormwater Quantity and Velocity Control (Stream Channel Erosion and Flooding).

(a) Calculations for determining peak flows and specific channel protection criteria shall be provided as prescribed in the Virginia Stormwater Management Handbook and Virginia Sediment and Erosion Control Regulations.

(b) Properties and receiving waterways downstream of any land development project shall be protected from erosion and localized flood damage due to increases in volume, velocity and frequency of peak flow rate of stormwater runoff in accordance with the minimum design standards set out in this section.

(c) The administrator shall require compliance with subdivision 19 of 4 VAC 50-30-40 of the erosion and sediment control regulations, promulgated pursuant to Article 4 (Section 10.1-560 et seq.) of Chapter 5 of Title 10.1 of the Code of Virginia and as modified below (whichever is more stringent).

(d) Concentrated stormwater runoff leaving a detention facility shall be discharged directly into an adequate natural or manmade receiving channel, pipe or storm sewer system. The adequacy of channels and pipes shall not be verified by demonstrating that the total drainage area to the point of analysis within the channel is 100 times greater than the contributing drainage area of the project in question.

(e) A “level spreader” design shall not be used to exempt a detention facility from subsection (6)(b) of this section.

(f) The 10-year post-developed peak rate of runoff from the development site shall not exceed the two-year pre-developed peak rate of runoff.

(g) The two-year post-development peak rate and velocity of runoff from the land development shall not exceed the one-year pre-development peak rate and velocity of runoff.

(h) All detention facilities proposed for new developments shall provide 24-hour extended detention of the runoff generated by the post-development one-year, 24-hour duration storm.

(i) If existing natural receiving channels or previously constructed manmade channels or pipes are not adequate, the applicant shall:

(i) Improve the channel to a condition where a 10-year storm will not overtop the banks and a two-year storm will not cause erosion to the channel bed or banks; or

(ii) Improve the pipe or pipe system to a condition where the 10-year storm is contained within the appurtenances; or

(iii) Provide a combination of channel improvement, stormwater detention or other measures that is satisfactory to the administrator to prevent downstream erosion. (Ord. 2009-09; Ord. 2007-30; Ord. 2007-20. Code 1964, § 9A-2; Ord. 2-25-82; Code 1985, § 11-22; Ord. 6-25-92).

13.10.040 General and technical criteria for erosion and sediment control.

The following general and technical criteria shall be applied on all single-family residential construction, applicable land development, and land conversion activities:

(1) Soil Stabilization. Permanent or temporary soil stabilization shall be applied to denuded areas within seven days after final grade is reached on any portion of the site.

(a) Temporary soil stabilization shall be applied within seven days to denuded areas that may not be at final grade but will remain dormant for longer than 30 days, but less than one year.

(b) Permanent stabilization shall be applied to areas that are to be left dormant for more than one year.

(2) Soil Stockpile Stabilization. During construction, soil stockpiles and borrow areas shall be stabilized as noted in subsection (1) of this section or protected with sediment trapping measures. Temporary protection and permanent stabilization shall be applied to all soil stockpiles on site and borrow areas or soil intentionally transferred off site.

(3) Permanent Stabilization. Permanent vegetative cover shall be established on denuded areas not otherwise permanently stabilized. Permanent vegetation shall not be considered established until a ground cover is achieved that is uniform, mature enough to survive, and will inhibit erosion.

(4) Sediment Basins and Traps. Sediment basins, sediment traps, perimeter dikes, sediment barriers, and other measures intended to trap sediment shall be constructed as a first step in any land-disturbing activity and shall be made functional before upslope land disturbance takes place.

(5) Stabilization of Earthen Structures. Stabilization measures shall be applied to earthen structures such as dams, dikes, and diversions immediately after installation.

(6) Sediment Traps and Sediment Basins. Sediment traps and basins shall be designed and constructed based upon the total drainage area to be served by the trap or basin as follows:

(a) Sediment Traps.

(i) Only control drainage areas less than three acres.

(ii) Minimum storage capacity of 134 cubic yards per acre of drainage area.

(b) Sediment Basins.

(i) Control drainage areas greater than or equal to three acres.

(ii) Minimum storage capacity of 134 cubic yards per acre of drainage area.

(iii) The outfall system shall, at a minimum, maintain the structural integrity of the basin during a 25-year, 24-hour storm.

(7) Cut and Fill Slopes Design and Construction. Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. Slopes found to be eroding excessively within one year of permanent stabilization shall be provided with additional slope stabilizing measures until the problem is corrected.

(8) Concentrated Runoff Down Slopes. Concentrated runoff shall not flow down cut or fill slopes unless contained within an adequate temporary or permanent channel, flume, or slope drain structure.

(9) Slope Maintenance. Whenever water seeps from a slope face, adequate drainage or other protection shall be provided.

(10) Storm Sewer Inlet Protection. All storm sewer inlets made operable during construction shall be protected so that sediment-laden water cannot enter the stormwater conveyance system without first being filtered/treated to remove sediment.

(11) Stormwater Conveyance Protection. Before newly constructed stormwater conveyance channels or pipes are made operational, adequate outlet protection and any required temporary or permanent channel lining shall be installed in both the conveyance channel and the receiving channel.

(12) Work in Live Watercourse. When work in a live watercourse is performed:

(a) Precautions shall be taken to minimize encroachment, control sediment transport, and stabilize the work area to the greatest extent possible during construction.

(b) Nonerodible material shall be used for the construction of causeways and cofferdams.

(13) Crossing Live Watercourse. When a live watercourse must be crossed by construction vehicles more than twice in any six-month period, a temporary vehicular stream crossing constructed of nonerodible material shall be provided.

(14) Regulation of Watercourse Crossing. All applicable federal, state and local regulations pertaining to working in or crossing live watercourses shall be met.

(15) Stabilization of Watercourse. The bed and banks of a watercourse shall be stabilized immediately after work in the watercourse is completed.

(16) Underground Utility Line Installation. Underground utility lines shall be installed in accordance with the following standards in addition to other applicable criteria:

(a) No more than 500 linear feet of trench may be opened at one time.

(b) Excavated material shall be placed on the uphill side of trenches.

(c) Effluent from dewatering operations shall be filtered or passed through an approved sediment trapping device, or both, and discharged in a manner that does not adversely affect flowing streams or off-site property.

(d) Material used for backfilling trenches shall be properly compacted in order to minimize erosion and promote stabilization.

(e) Restabilization shall be accomplished in accordance with these regulations.

(f) Comply with applicable safety regulations.

(17) Vehicular Sediment Tracking. Where construction vehicle access routes intersect paved or public roads:

(a) Provisions shall be made to minimize the transport of sediment by vehicular tracking onto the paved surface.

(b) Where sediment is transported onto a paved or public road surface, the road surface shall be cleaned thoroughly at the end of each day.

(c) Sediment shall be removed from the roads by shoveling or sweeping and transported to a sediment control disposal area. Street washing shall be allowed only after sediment is removed in this manner.

(18) Removal of Temporary Measures. All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization or after the temporary measures are no longer needed, unless otherwise authorized by the administrator. Trapped sediment and the disturbed soil areas resulting from the disposition of temporary measures shall be permanently stabilized to prevent further erosion and sedimentation.

(19) Stormwater Management. Refer to SCC 13.10.030. (Ord. 2007-20).

13.10.050 Construction inspection provisions.

(1) Stormwater management and erosion and sediment control construction inspection shall utilize the final approved plans and specifications for compliance. In addition, the inspection shall comply with the latest version of the Virginia Stormwater Management Law and Regulations Erosion and Sediment Control Regulations, promulgated pursuant to Article 4 (Section 10.1-566) of Chapter 5 of Title 10.1 of the Code of Virginia.

(a) Preconstruction Meeting. Prior to any land-disturbing activity and upon receipt of the land-disturbing permit from the administrator, the owner shall schedule a preconstruction meeting. The owner shall provide a minimum of 48 hours’ notice to the administrator for this meeting.

(b) Notice of Construction Commencement. The applicant must notify the administrator in advance before the commencement of construction. In addition, the applicant must notify the administrator in advance of construction of critical components of the SWM facility(ies) and erosion and sediment control measures.

(c) Periodic inspections of the stormwater management system and erosion and sediment control construction shall be conducted by the administrator or their designee, a DCR-certified inspector. Upon completion, the applicant and owner are responsible for certifying that the completed project is in accordance with the approved plans and specifications and shall provide regular inspections sufficient to adequately document compliance. The inspector shall be a DCR-certified inspector. All inspections shall be documented and written reports prepared that contain the following information:

(i) The date and location of the inspection;

(ii) Whether construction is in compliance with the approved stormwater management plan;

(iii) Variations from the approved construction specifications; and

(iv) Any violations that exist.

(d) If any violations are found, the property owner shall be notified in writing of the nature of the violation and the required corrective actions. No additional work shall proceed until any violations are corrected and all work previously completed has received approval by the administrator.

(e) In addition, the person responsible for carrying out the plan may be required to provide inspection monitoring and reports to ensure compliance with the approved plan and to determine whether the measures required in the plan provide effective stormwater management.

(f) If the administrator determines that there is a failure to comply with the plan, notice shall be served upon the permittee or person responsible for carrying out the plan in accordance with SCC 13.10.060.

(2) Post-Construction Final Inspection and As-Built Plans.

(a) All applicants are required to submit actual “as-built” plans for any stormwater management practices located on site after final construction is completed, in accordance with the latest Department of Conservation and Recreation requirements. The plan must show the final design specifications for all stormwater management facilities and must be certified by a professional engineer.

(b) A final inspection by the administrator is required before the release of any performance securities can occur. A certified inspection of all aspects of the BMP construction is required, including surface as-built surveys, and geotechnical inspections during subsurface or backfilling, riser and principal spillway installation, bioretention soil placement and compaction activities. (Ord. 2007-30; Ord. 2007-20).

13.10.060 Maintenance and repair of stormwater facilities.

(1) Maintenance Inspection of Stormwater Facilities.

(a) All stormwater management facilities must undergo inspections to document maintenance and repair needs and ensure compliance with the requirements of Division I of this title and accomplishment of its purposes. These needs may include removal of silt, litter and other debris from all catch basins, inlets and drainage pipes; grass cutting and vegetation removal; and necessary replacement of landscape vegetation and any repair or replacement of structural features.

(b) In compliance with the maintenance covenant included in the approved comprehensive drainage plan, the owner, or any successor owner, unless such responsibility is lawfully transferred to the city, shall inspect, maintain and repair all structural and nonstructural stormwater management measures required by the plan.

(2) Records of Maintenance and Repair Activities. Parties responsible for the operation and maintenance of a stormwater management facility shall make records of the installation and of all maintenance and repairs, and shall retain the records for at least three years. These records shall be made available to the administrator during inspection of the facility and at other reasonable times upon request. (Ord. 2007-20).