Anyone who has been paying attention to the proposed rezoning of Route 28 near Lake Wentworth has likely been aware of concerns that commercial development allowed by the new district would threaten water quality in nearby streams and, eventually, in the lake itself. The issue has centered around stormwater runoff — the damaging flow of water caused by rain and snowmelt running off hard surfaces such as roofs and parking areas.

Confronted with those concerns, the Planning Board has drafted a set of stormwater management rules that it proposes to add to its site plan review regulations. Those regs are used to evaluate new subdivision and commercial developments.

As a first step in implementing that approach, the board’s Route 28 rezoning proposal relies exclusively on the stormwater regulations to control runoff from from future development in the areas that would be rezoned. Those areas include the business complex around the West Lake restaurant, as well as commercial properties near the intersection of Routes 28 and 109 (the Trites car dealership, Seven-11, Parsons Furniture).

For that reason, it will be important for members of the community to understand the proposed new rules and to express their views at the formal Planning Board hearing on Tuesday, Nov. 5. The meeting will take place at the Wolfeboro Public Library at 7 p.m.

Because the stormwater rules are being proposed as additions to the site review regulations, they require a public hearing, but there is no public vote. After the hearing, the Planning Board is free to adopt the rules as it chooses.

The most recent version of the stormwater regulations can be found here.

Among the requirements that would be imposed on new subdivisions and commercial developments by the proposed regulations are:

• The need for a formal stormwater management plan detailing how runoff would be controlled, both during and after construction
• Standards and strategies for minimizing the effects of stormwater runoff
• Requirements for ongoing operation and maintenance of stormwater mitigation structures

Impervious and porous surfaces

Many of the provisions of the new regulations rely on some complex – even confusing – definitions. Foremost among these are definitions for various types of impervious surfaces and materials.

“Impervious” implies that a surface sheds water rather than absorbing it, and it can apply to roofs, concrete walkways, standard asphalt parking lots, and similar surfaces. On a developed site, most of the runoff from rain and snowmelt is created by the flow of water across impervious surfaces.

Unfortunately, the stormwater regulations offer separate definitions for “impervious cover” and “impervious surface.” In the end, both definitions appear to refer to the same thing, and the regulations would be improved by the use of one or the other.

The same can be said for another set of related definitions. The regulations refer to both “porous cover” and “porous media.” In each case, the reference is to material that can absorb water rather than shedding it. Included would be some special types of asphalt as well as paving stones that allow water to infiltrate rather than run off.

Again, selecting one definition or the other would greatly simplify interpretation of the  proposed rules.

When impervious is irrelevant

The regulations provide additional definitions that make it clear that not all impervious surfaces are created equal. For example, the rules say that hard surfaces that are made of porous materials or that are “disconnected” (capture and infiltrate runoff rather than simply shedding it) do not count in any calculations of a site’s actual impervious cover. When the absorbent or disconnected surfaces are removed from consideration, the sum of the remaining hard, non-absorbent surfaces is referred to as “effective impervious area” (EIA).

What’s the import of these distinctions? For one thing, in the town’s zoning regulations, the extent to which a site can be covered with hard surfaces such as roofs, parking areas, walkways, and the like is calculated using only effective impervious area. In other words, a development could contain vast expanses of parking lot as long as a developer either used pervious asphalt or directed runoff to an infiltration area. Such pervious or disconnected cover does not count when determining any limits on impervious surfaces for a lot.

Why should we care? For starters, the town of Wolfeboro has no long-standing experience with the use of materials that are claimed to be pervious. Relying on representations about the ability of such materials to prevent stormwater runoff is risky business around lakes and streams that are at the heart of the town’s economy.

Secondly, when managing development, there are – or should be – considerations beyond the ability of building materials to handle stormwater runoff. Just because it’s theoretically feasible to cover a site with hardscape from setback to setback doesn’t mean that it’s a good idea. Does the town really want outlying developments in areas such as Route 28 north to look like our downtown, with vast expanses of building structure and parking lot?

As noted above, the extent of impervious cover permitted on a site is governed by the town’s zoning regulations. (Each zoning district has its own stated limit on permitted coverage.) However, those limits rely on a definition in the zoning regulations that exempts materials that are claimed to be pervious – that is, that claim to let water run into the ground.

The stormwater regulations, on the other hand, provide a more sophisticated set of definitions and provide a way of distinguishing among pervious materials, hard surfaces that are disconnected from a site’s stormwater flow, and surfaces that are truly impervious and so contribute to runoff.

Unfortunately, those regulations make almost no attempt to manage the extent of impervious coverage on a site. The one provision of the stormwater rules that makes explicit reference to EIA (section X 1) is badly written to the point of being undecipherable. (While intended to limit EIA – a desirable goal – it inadvertently sets a minimum level on it.)

Unlike the state’s model stormwater management ordinance, the town’s separation of its regulations between zoning and site plan review means that the most sophisticated tools for management of impervious cover are relegated to the rules least designed to implement that control.

In the end, the discussion going forward needs to focus on effective impervious area (EIA) if we want any meaningful control on the amount of hard surface permitted in a site. Doing that, however, will mean pushing for the inclusion of the most comprehensive definitions of impervious surfaces when we turn our attention to the proposed rezoning ordinance for Route 28. (That discussion takes place at the Planning Board’s Nov. 19 meeting.)

A question of standards

The regulations lay out “performance standards” for new developments. Among these are stated preferences for the use of low-impact development (LID) techniques, which attempt to deal with runoff with small facilities throughout a site rather than a few centrally located large facilities. The rules also set standards for the amount and rate of runoff from development sites.

Unlike the state model ordinance, however, the proposed Wolfeboro regulations do not include requirements for recharge of groundwater and pre-treatment of runoff before it either leaves a property or is allowed to return to the soil. Recharge is important because impervious surfaces can simply cause rain and snowmelt to run off into surface waters, affecting the amount of water left in the ground for wells and other uses. Pre-treatment, for its part, prevents pollutants such as petroleum products from automobiles from getting into groundwater.

Lastly, the rules stipulate that stormwater runoff from a site should not degrade the water quality of any streams and lakes that receive that runoff. The problem with that approach, however, is that, given the size of a lake like Wentworth, it would be almost impossible to detect pollution coming from a single site. A better standard would be to check the quality of runoff as it leaves the site, not at its ultimate destination.

Operation and maintenance requirements

An element originally missing from the regulations is the requirement for an operation and maintenance (O&M) plan spelling out how and when the owners of developments must take care of stormwater mitigation and treatment facilities. Without such a requirement, rain gardens, pervious asphalt parking areas, and similar structures intended to reduce and filter stormwater runoff could be expected to deteriorate and eventually become ineffective.

The proposed rules now require an O&M plan, and the Planning Board has distributed two checklists that are apparently intended to provide property owners a means of reporting the checks and maintenance that they perform on their facilities. The frequency of the required checks and reports would need to be stipulated in a site’s stormwater management plan.

It’s not clear that the Planning Board has settled on a checklist to be used in complying with the operation and maintenance plan.