Rain Garden Plan Raises Questions

Rain Garden Plan Raises Questions

Expert to meet with Planning Commission on Monday.

At a Planning Commission public hearing earlier this month, many citizens and commission members voiced concerns about a proposed storm water management plan for the pending Elkins Heights subdivision off Madison Street.

The proposal, submitted by applicant Edgemoore Land LLC and developer Paciulli Simmons & Associates, suggests using rain gardens for the planned 15-lot subdivision to meet state storm water management requirements.

Henry Bibber, director of community development for the town, said this concept of a landscaped bioretention area to filter storm water run-off in residential areas, although appealing to the town, raises further questions.

"Rain gardens seem to work as well as ponds as far as cleaning the storm water from residential sites in general," said Bibber. "The hope is to incorporate it into sites in a manner that is more successful than open storm water ponds — it's a more attractive alternative."

A town staff report defines the proposed rain gardens as "an area within a yard that collects rainwater. The soils of the rain garden are amended to enhance the retention and filtering properties of the soil. Suitable plants are planted on top of the rain garden so that it blends with the landscape, unlike the standard bioretention trench, which is usually covered with loose gravel or stone."

ALTHOUGH BIBBER said the rain gardens meet state requirements, former Town Council member and environmentalist John De Noyer said the plan only meets the minimum for a low impact development, or LID.

"Legally, they do meet the state's requirements, that they don't increase the amount of run-off," said De Noyer. "But, from an environmental and practical approach, they should exceed the state's requirements and they can do that with a low impact development."

De Noyer explained there are state law requirements when increasing the land use of an area and other requirements that designate an LID.

In order for the subdivision to be approved, the developers have to make sure the storm water run-off from the development does not exceed the current run-off.

To be considered an LID, the site has to mimic a natural watershed in its management of storm water run-off, which means the developers have to take this into account in the initial planning.

The current proposal seeks approval of a preliminary subdivision plan for the zoned R-10, residential area, to turn three lots on the 400 block of Madison Street into 15 lots, with one lot to remain undeveloped until further notice.

This would mean the removal of two of the three houses, with the third house remaining on a smaller lot, and five lots facing Madison Street. The other lots would be accessible through an added cul-de-sac off of Madison Street.

Brian McCormick, Paciulli Simmons & Associates project engineer for the Elkins Heights subdivision, said the R-10 residential zoning issues strict guidelines to follow when planning the designation of the subdivision as an LID.

McCormick said there are "a lot of tools in the low impact development tool box," but to meet the state's requirements, rain gardens were the best choice.

"From a water quality sense," said McCormick, "rain gardens do better in terms of treatment."

Because rain gardens are new to Herndon, evidence is linked to a more than 10-year survey of rain gardens in Prince George's County, Md.

DE NOYER'S CONCERN with this comparison is the differences in soil. He said Prince George's has sandy soil, allowing for fast absorption, whereas Fairfax County has piedmont soil with bedrock and clay, limiting absorption.

"Regardless if it's Prince George's County, Fairfax County or Loudoun County," said McCormick, "the soil media inside the rain garden is going to be similar, it's always a mix that is placed at the site."

Bibber explained that because of the high possibility of hitting bedrock and clay, events that would halt absorption, the developer's plan is to add outfall pipes which would feed into the Runnymede Manner storm sewer site.

"Even though the site is not being developed like a low impact development," said Bibber, adding in order to be an LID it should be developed with a conscious effort to reduce storm water run-off, "that doesn't mean it doesn't utilize the rain gardens to satisfy the pollution and run-off [requirements]."

De Noyer suggested other relevant LID techniques that could be used include narrower streets, the designation of one side of the street having a sidewalk and no curb or gutters.

"From a storm water point of view, in these types of developments, ordinances require these things," said McCormick in response to the suggestion, saying those alternatives will not happen.

THE PLANNING COMMISSION deferred the Elkins Heights request for approval until the September meeting, saying they needed to discuss maintenance responsibilities.

Bibber said the commission and town staff will hear on Monday, Aug. 30, from a Virginia Department of Forestry rain garden expert who will provide more information and answer any questions.

De Noyer said he thinks rain gardens are a step in the right direction, but his main concern is that the Town Council will approve the plan without the developers presenting the final water management plan.

"The problem I see is they won't do the calculations until the final site plan that the Town Council and the Planning Commission won't see," said De Noyer, adding that would mean no public hearing.

Bibber said the town staff is waiting to judge the proposal, to make sure the developers follow state storm water management requirements, as well as change rain garden maintenance responsibilities from the town to home owners.

"Our intentions and our hope is that we can successfully put that maintenance responsibility onto the home owner of the land," said Bibber, emphasizing maintenance would be less frequent than mowing the lawn on a regular basis.

"Maintenance of rain gardens is very much like gardening," said McCormick, adding that short term they have seen rain gardens last up to 20 to 30 years before the soils and filter media need to be replaced.

As for the increase in rain gardens in the future, there is a general consensus that these storm water management practices, if developed properly, will increase in popularity among developers.

"I foresee a number of additional single-family home subdivisions that might be developed in town that would utilize the rain garden concept," said Bibber.