On April 18, 2012, Fairfax County held an informational session to provide conceptual guidance for how to implement the Tysons Corner stormwater management vision, as presentated in the Tysons Corner Comprehensive Plan, adopted June 27, 2010. In addition, the County introduced a few tools to help developers meet the stormwater goals for Tysons Corner. As specified in the aforementioned goals, the first 1" of rainfall should be retained and infiltrated on-site. If the rain can't be infiltrated then it must be reused. A determination as to how long the collected rainwater can be stored before it must be reused has not yet been made.

These goals only apply to rezonings in Tysons, not to maintenance or retrofits of existing stormwater management facilities. In addition to meeting the Tysons Stormwater goals, developers must still meet the PFM stormwater requirements and the forthcoming state stormwater regulations. The thought is that that by retaining, infiltrating and/or reusing the first 1" of rainfall, a developer will exceed or come very close to meeting any other quantity or quality requirements.

To aid engineers in designing a site that conforms with the guidelines, Fairfax County has developed the following tools:

• A compliance flow chart that steps the developer through the design   process: http://www.fairfaxcounty.gov/tysons/stormwater/download/
  tysonsprocessflowchart.pdf

• A conformance checklist: http://www.fairfaxcounty.gov/tysons/
  stormwater/download/tysonschecklist2012_0418_draft.pdf

• A conformance spreadsheet (.xls 7MB): Similar to DCR's spreadsheet, this   document has been established to help an engineer calculate if their site   meets the criteria. DPZ will also use this spreadsheet to determine if a   developer has met the stormwater criteria (or at least have met it to the   maximum extent practicable). Currently, the spreadsheet is in a beta form   and the County will make revisions, if necessary, based on any comments   they receive as engineers begin using the spreadsheet. In the future, the   spreadsheet may be required as an electronic submission as part of   rezoning applications.

For a complete overview of the stormwater goals for Tysons and urban best management practices that can be used to implement the Tysons Corner Comprehensive Plan vision for stormwater reuse, infiltration, and runoff reduction, visit: http://www.fairfaxcounty.gov/tysons/stormwater.

For more information on WSSI's Low Impact Development (LID) and green infrastructure services that can assist in meeting these stormwater goals, contact Scott Petrey, Bethany Bezak or Janice Cessna.