DPWES Letters to Industry
Land Development Services
12055 Government Center Parkway
Fairfax, Virginia 22035-5503
703-324-1780, TTY 711
December 12, 2005
Information Required on Infill Lot Grading Plans to Assist in the Assessment of Adequate Drainage
Issue: Additional guidance on data to be provided on infill lot grading plans to facilitate review of the adequacy of storm drainage for compliance with Section 2-602 of the Zoning Ordinance and Section 6-0203 of the PFM.
Background: At the request of the Board of Supervisors, this agency created a committee to develop recommendations for enhancing the County’s erosion and sediment control program and review of adequate storm drainage to further minimize the potential for impacts on adjoining properties. The committee, comprised of both public and private sector representatives, recommended that additional guidance be provided to submitting professionals regarding the type of data about adjacent properties that must be provided with the submission of infill lot grading plans. This recommendation was referred to the Engineers and Surveyors Institute’s Fairfax Committee for implementation. The Fairfax Committee’s membership includes both public and private sector engineers. The guidance provided in this letter is the result of the efforts of that committee.
Procedures: Submitting professionals are reminded that infill lot grading plans must include sufficient information in accordance with Section 6-0203 of the PFM to verify the adequate drainage of surface waters as required by Section 2-602 of the Zoning Ordinance and the Minimum Standards and Specifications of the Virginia Erosion and Sediment Control Handbook. Many infill plans that are submitted for review do not contain sufficient information about adjoining properties to validate the adequacy of downstream systems. The information identified below is considered to be the minimum necessary to allow validation of adequate drainage and shall be included on all future submissions of infill lot grading plans. Information in addition to that identified below may be required during plan review as determined necessary to validate the adequacy of downstream systems both during and after construction.
- Five Hundred (500) scale topographical map of the site and adjoining properties with drainage divides depicted.
- Outfall narrative in accordance with the requirements of Section 6-0200 of the PFM that addresses both concentrated and sheet flow discharges from the site (see Letter to Industry 03-10 for additional guidance on the preparation of outfall narratives).
- Use and zoning district of properties contiguous to the proposed development.
- Sufficient topography for the proposed development site as well as sufficient topography and information about existing structures (e.g. houses, sheds, and swimming pools) on downstream contiguous lots to show on and off-site surface drainage to the point where an adequate outfall is reached. (Note: field run or aerial topography is required; however, alternative sources may be accepted as determined by the Director if it is shown that access to adjoining properties has been denied.)
- Inverts of all existing and proposed culverts on the subject lot and contiguous lots.
- Flow arrows showing the direction of flow.
- Appropriate runoff “c” factor for the design of erosion and sediment controls (e.g. use of a 0.6 factor pursuant to Section 6-0202.14 of the Public Facilities Manual).
If you have any questions or need additional information, please call Michelle Brickner at 703-324-1780, TTY 711.