Despite some tempting advantages, LID techniques have a downside for inspection and long-term maintenance.

By Gordon England

One of the hot topics in stormwater these days is the use of low-impact development (LID) techniques to provide stormwater-quality and -quantity benefits. LID practices have been heralded by many as the panacea for the challenges of National Pollutant Discharge Elimination System (NPDES) and total maximum daily load (TMDL) requirements. Although LID techniques certainly have many positive attributes, the full, long-term implications of their use must be recognized by the regulatory agencies and entities responsible for best management practice (BMP) maintenance. I'm going to play devil's advocate on a couple of issues that have ended up haunting me over the years.

With the growing awareness of the need for control of water pollution, Prince George's County, MD, developed a program of BMPs in the mid-1990s. The underlying philosophy of the program was the use of many small treatment areas and methods scattered throughout the watershed rather than regionalization of just a few larger treatment facilities. The typical scenario for this philosophy was the use of individual microretention areas on each lot of a subdivision, with the intent of reducing the size of, or totally eliminating the need for, larger stormwater ponds. While the principal issue discussed here is stormwater treatment, these BMPs also serve the function of providing stormwater-quality benefits. A prime advantage of this type of design was that the smaller pond sizes led to an increase in the number of buildable lots. Another advantage cited was the transfer of maintenance responsibility for a pond from a homeowners association to the individual homeowners for their small treatment systems on their own lots. Thus, this type of BMP philosophy became appropriately known as low-impact development.

Naturally, the development community embraced LID concepts because it was rewarded with more lots and fewer maintenance headaches. This in turn led to less resistance from the communities and their politicians as they struggled to implement NPDES requirements for the development of new stormwater regulations.

Of course, stakeholder involvement is one of the key principles to the NPDES process. Has LID improved the situation for all stakeholders? Maybe, maybe not. Let's take a look at LID concepts a little more closely.

To begin with, it must be recognized that there are two distinct types of stormwater treatment systems. The first type, which is easily apparent to all parties involved, is the treatment system put in for new development. With new development, there is the advantage of vacant land on which to design larger systems, leaving it up to the creativity of the design engineer to minimize the pond size and maximize the number of lots. Regulations and permitting processes are routinely established for new development to follow desired design standards to accomplish desired pollution treatment and flood protection goals.

The second type of stormwater treatment system, which is not so commonly recognized, is the kind used for stormwater retrofitting. Retrofitting is the difficult task of going into the older, developed areas of a community and installing BMPs into the existing storm drain systems to clean the stormwater, which historically has flowed straight to the streams, rivers, and lakes.

In the retrofitting world, there is rarely adequate land available to construct treatment ponds, and LID practices are often-used tools in an engineer's toolbox. Every piece of available land and road right of way is often used to construct filter strips, vegetated swales, bioretention areas, dry retention ponds, exfiltration trenches, and so on. Since the communities are installing these systems, they also take on the maintenance responsibility of these systems. All BMPs require maintenance to remain effective long term, and herein lies the rub.

It is easy to see the developer's and engineer's perspectives in maintenance issues. The developer would prefer to turn over maintenance to the city, the individual homeowners, or–if necessary–to a homeowners association. The engineer's main emphasis is on design; rarely is maintenance on the engineer's radar screen.

It is the perspective of the city or county that often gets ignored in the maintenance picture; yet the driving force behind NPDES and TMDLs is the community's responsibility for meeting stormwater cleanup goals. This means the communities must have active inspection and enforcement programs for the construction and long-term maintenance of all facilities installed by the development industry. Many communities new to the stormwater world probably do not recognize the magnitude of the bookkeeping and maintenance effort to perpetually track newly built systems.

In Florida there have been development requirements for stormwater treatment systems for more than 20 years. In Brevard County, which is principally lightly developed residential property, the stormwater utility tracks hundreds of stormwater systems built for new development, and the number increases year after year. These systems, which are typically one or two ponds per subdivision, are inspected biannually for proper maintenance in order to provide maintenance credits against the subdivision's stormwater utility assessment. The staff time to accomplish these inspections is substantial. Now consider the magnitude of the county's inspection effort if every lot of every subdivision had individual ponds to track. It would be totally unmanageable.

The nature of these low-impact swales, ponds, buffer strips, and so on is that they do their jobs well and will fill up in a few short years with sediment and yard debris. Everyone has seen how grass grows thicker with time. Will the homeowners be expected to take out their grass, excavate their yards, and regrass every three to five years? Many of these shallow systems last no longer than that. This could lead to a scenario in which inspectors would be constantly trying to convince thousands of homeowners to regrade and regrass their yards. Some homeowners would cooperate, but many would not, and politically it would not be practical to levy fines for enforcement.

Therefore, these permitted stormwater systems would lose their water-quality and -quantity benefits in a few short years. A perhaps-unrecognized consequence would be that the street gutter and stormwater piping systems would receive significantly more runoff than they were designed for and then start flooding. Once the streets routinely flooded, the residents would start calling the politicians for relief, and the communities would have to either put in bigger pipes or dig up everyone's yard!

With regard to construction inspection, site inspectors are already overloaded with inspecting roads, pipes, ponds, and so on, with little time and attention left for thousands of lot swales or rain gardens. The additional burden upon limited city budgets would be significant.

Another aspect to consider is the permitting perspective. Typically in Florida, the subdivision developer pulls permits to install stormwater treatment facilities. The developer posts bonds for the work and, as permittee, is responsible for completion of the work. Transferring construction responsibility to numerous homeowners presents all kinds of legal enforcement challenges. Once again, the workload for city staff would seem to increase unnecessarily.

Also, consider the TMDL perspective. To properly model pollutant loadings and BMP removal credits, every one of the lot systems would need to be modeled. A super-computer would be needed in areas with high growth rates. Remember, the other side of the fairness coin is the implementation complexity.

Some proponents of LID say that regional ponds are maintenance problems despised by homeowners. In Florida we treat ponds as multiuse facilities integrated into a community's design. Benefits, such as hiking trails, parks, fishing areas, and wildlife habitat, actually increase the value of the lots around the ponds. Sure, there is long-term maintenance associated with cleaning ponds. You have to mow them, clean out cattails, and once every 15-30 years dig them out. This is really a very minor expense. I live on one of these wet ponds in a condominium, and after more than 20 years, it is nowhere near needing excavation. The residents love the ponds full of fish and wildlife and the open space. We put in pumps to create fountains to keep the dissolved oxygen up and the stratification down. Twice we have bought carp for a few hundred dollars and used them to control algae and weeds. The pond adds to our property values, and the fountains are beautiful. Developers in Florida recognize they can charge more for waterfront property than for other lots.

In Florida we allowed individual lot ponds in the early days. These days they are highly discouraged or not permitted in most areas because of long-term maintenance and enforcement issues. It is much easier to take enforcement action against a homeowners association for one pond than against many individual property owners for their separate ponds.

Communities considering LID for new subdivisions need to look at the whole picture and consider the long-standing implications for staff, budget, enforcement, maintenance requirements, and TMDL credits for properly functioning systems. In some communities these issues might not be significant. But in other communities, LID might be just the beginning of a long-term headache.

Gordon England, P.E., is a project manager with Creech Engineers Inc. in Melbourne, FL, and a member of Stormwater's Editorial Advisory Board.

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