Stormwater Management – Notices to Industry

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Periodically, the County’s stormwater management staff provide updates and information about how to meet the requirements of the stormwater management ordinance. These notices are intended for all architects, builders, contractors, developers, engineers, surveyors, and property owners, and are supplemental to the Stormwater Management Guidance Manual.

Frequently Asked Questions

General

If I remove impervious cover from my site before I get the LDA permit, can I count that impervious surface under the existing conditions? 

I was told that 

I need to complete a Stormwater Facility Maintenance and Monitoring Agreement before my permits can be released. Where can I get this agreement, and where do I get the information to complete it?

Can I pay a fee-in-lieu for stormwater treatment at my site? 

  • No, the County does not offer a fee-in-lieu program.

Can I purchase offsite stormwater credits? 

  • No, the County does not offer the purchase of offsite stormwater credits.

Can a sump discharge connect to an infiltration trench (BMP) if there is no storm system in the near vicinity? 

  • No, sump pump water must be day lighted at least 10 feet away from the property boundary.

Do the new stormwater management regulations consider pools as pervious or impervious area? 

  • Pool is considered to be impervious area.

Are roof drains from a single family house allowed to tie into the public storm sewer directly, assuming the stormwater management requirements for the site are met? 

  • Yes, the roof drain can be connected to the public storm sewer. If the connection is to the pipe instead of a structure, the builder or engineer should add a note on the plan indicating the location of the core drilled connection to the existing storm pipe, with prior coordination with the DES inspector.

Per Section 48-55.A. Placement of Buildings and Structures, it states: “All new construction of and substantial improvements to residential structures shall be set back fifteen (15) feet horizontally from the location of the base flood elevation boundary.” Does that mean that a driveway is NOT required to be set back 15’ horizontally since it is not part of the structure, and can abut the floodplain limits? 

  • Yes, driveway is not a structure, it can be inside the 15 feet zone.

How long does the review of the As-built certification documentation usually take? 

After plugging in all of a project’s data into the runoff reduction spreadsheet (v. 3.0) the results state “No further TP load reduction required (Required – Achieved < 0.0005 lb/yr)”, does this mean that the project meets the TP load reduction requirement? 

  • No, the required TP load reduction has always been 0, including any decimal places (it was not previously rounded down to 0.00), therefore it continues to be 0, including any decimal places. 

Stormwater Planters

Can a large/long planter have more than one downspout draining into it? Or is there a one downspout per planter rule? 

  • Yes, there can be more than one downspout draining to the planter. An appropriate design for this type of planter would have the downspouts at opposite ends with the overflow pipe centered between them.

Cisterns

Can cisterns be used for stormwater management credit? 

  • Cisterns are required to have year round drawdown to qualify for stormwater credit, so the house/building would need to be plumbed for graywater use in order to receive stormwater credit.


Bioretention

What plants can I install in my bioretention? 

  • The Virginia Department of Environmental Quality (VDEQ) provides a list of popular native plants for use in bioretention facilities (see Table 9.4 of the VDEQ Stormwater Design Specification No.9 on page 28). Also for reference, Fairfax County has published a Recommended Plant List for Bioretention Facilities and plants found on this list are also acceptable. Note that the planting requirements are 1 quart-sized perennial installed per 1-2 square feet and/or 3 gallon shrub installed per 7.5 square feet throughout the entire ponding area.

Who is an approved vendor that can supply the new required bioretention soil media that meets the testing requirements? Approved filter media vendors for VDEQ Bioretention Soil Media (Version 2.0) in Arlington County: 

Pervious Surfaces

What are the requirements to become an ICPI certified installer for permeable pavers? 

  • Information on how to become an ICPI certified installer is available on the ICPI website.

How can I find a certified ICPI installer that is required for installation of permeable pavers? 

What are the requirements to become an NRMCA certified installer for pervious concrete? 

  • Information on how to become an NRMCA certified installer, along with a list of certified installers, can be found on their website.

I heard there are new updated details for permeable pavers and urban bioretention (planter boxes). Where can I find these new details? 

  • The new[LM1]  County stormwater details for permeable pavers, including details for stepped driveway installations, along with details for urban bioretention (planter boxes) are posted on the County’s Stormwater Management Ordinance webpage under the Stormwater management Ordinance Guidance Manual section.

During installation of permeable pavers and pervious concrete, what type of geotextile fabric is required on the bottom subgrade? 

  • Per the State specifications, permeable pavements must be installed using non-woven geotextiles that have a minimum flow rate greater than 125 gpm/sq ft and an AOS equivalent to a US #70 or #80 sieve. Please note that most woven geotextiles have flow rates of 4 to 5 gpm, and therefore they do not meet the specifications.

Does Arlington County accept Flexi-Pave as a form of porous pavement? 

  • Yes, Flexi-Pave is considered porous, but it is not suitable for driveways as it is not strong enough for vehicle use.

Does the County accept GrassPave as permeable pavers as long as we provide the proper section underneath? 

  • The County does not accept GrassPave as a form of pervious paving system. It could be classified as managed turf if the grass can be maintained.