BMP Effectiveness Requires Regular Inspection and Maintenance

In February 2000 the Northern Virginia Planning District Commission issued a report to owners and operators of stormwater best management practices (BMPs), urging them to properly maintain their systems. According to the report, “Over half of BMPs fail in the first five years due to lack of proper maintenance.” For those who have just invested in constructing a BMP to manage stormwater, this statement alone should compel them to action. Whether a BMP is a natural (or “public domain”) system, such as a pond or a swale, or a proprietary structural solution, all pose a high risk of operative failure without proper maintenance. Maintenance of these BMPs should include regular inspections and, if necessary, removal of accumulated pollutants. The method of removal varies from system to system, but the end result should always be optimization of the system to function at or near its original specifications. Frequency of BMP maintenance is dictated by the rate at which pollutants are exported from the site to the BMP and the ability of the BMP to remove them. This can be determined for any type of system through regular inspections. Most factors that influence pollutant export rates are site-specific, such as erodibility of native soils and landscaping materials, land-use activities, housekeeping practices, and flow dynamics (such as sheet flow versus channelized flows, slope of pipes, and ground surface roughness). Other factors are less site-specific, such as winter sanding, fall leaf shedding, and activities on neighboring sites (especially construction). Different BMPs are designed to address different fractions of the pollutant load. Generally the greater a BMP’s ability to remove pollutants, the more frequently it will have to be maintained. Storage capacity is also a significant factor affecting maintenance frequency.Without proper maintenance, any system will fail. In keeping with the adage “an ounce of prevention is worth a pound of cure,” the costs of failure can be disproportionately high—both in terms of financial costs and environmental impact. Alan Lyscars, owner of Field Services Inc. in Portland, ME, says his firm was recently hired to clean out a pond-based system that had been neglected for 15 years. The system had lost 80% of its effectiveness. The catch basins were clogged and barely functioning. The company had to spend $80,000 to clean out the system and make it functional again. Cleaning out the pond alone cost $15,000. Another firm evaluated maintaining a 0.25-ac. pond for a municipal client and estimated that it would cost $40,000. The city chose not to maintain the pond because of the cost.

“People have a tendency to think of a catch basin like a sewer: It must be working if it’s not clogged,” observes Lyscars. “When it stops working they call a ‘plumber’ to fix it up.” But without regular maintenance, incremental loss of effectiveness occurs to any system—even one that is still functional. The Maintenance-Free MythHistorically, natural systems, such as ponds and swales, have been regarded as the easiest, least expensive way to manage stormwater. Wet and dry ponds, constructed wetlands, swales, vegetated filter strips, and detention basins generally function through a combination of filtration, infiltration, settling, absorption, and adsorption. Since the failure of many of these processes is not readily visible, ponds and other public domain systems are sometimes viewed as maintenance-free. The notion that once they are installed, Mother Nature will take over seems to be supported when vegetation appears to be thriving. In fact, invasion of non-native plants can itself be cause for maintenance. Ponds should be dredged and revegetated periodically, if necessary. Sand filters require that the sand be removed and replaced every so often. Swales require frequent removal of litter and trash, as well as periodic removal of the contaminated soil and replanting of the vegetation. While the maintenance of a natural system might be less frequent than for proprietary structural systems, the process for reclaiming a pond that has been filled—sometimes with toxic substances—can be catastrophic. Although little public data are available on pond clean-outs, in part because so few have been maintained regularly, information on similar water bodies is telling. Lake Merritt in Oakland, CA, a tidal lake and the first wildlife refuge in North America, was dredged from 1996 to 1997. Removal of 20,000 yd.³ of sediment cost $1.7 million. Annual costs to maintain the lake include $60,000 to harvest nuisance aquatic weeds and $50,000 to remove trash and debris by hand. This might be an extreme example, but it illustrates the need to maintain natural wetlands and the costs that can be incurred to do so. Failure to maintain natural systems can be especially problematic because any pollutants that have accumulated are not isolated from the rest of the environment. Some plants have been shown to uptake metals, nutrients, and other anthropogenic pollutants. But unless these plants are harvested and removed, these pollutants are not eliminated; they are simply concentrated in a natural environment. Some have expressed concern that ponds and constructed wetlands may become sinks for pollutants that can bioaccumulate and/or biomagnify as they progress through the food chain. Wildlife in ponds, including frogs, birds, and fish, adapt to the polluted environment and become vectors for pollutants, or cause other environmental problems. In California, stormwater ponds have become a habitat for bullfrogs, which eat red-legged frogs, a species protected under the Endangered Species Act. Pollutants may also migrate through ponds and swales, thereby contaminating groundwater. Perhaps more obvious than the biological issues associated with ponds are the health and safety issues. In addition to being holding areas for stormwater runoff, ponds and swales end up becoming repositories for a variety of waste, including trash, oil, and debris. To control biological development, ponds may also be treated with fertilizers, pesticides, and herbicides. The result is—at a minimum—unsightly, with visible trash and oil sheens and, in more egregious cases, a health hazard rife with toxins and pathogens. Institutional sites, such as schools and churches, discourage the use of ponds due to the liability of standing water at their locations.There are relatively few reported studies of the long-term performance and maintenance of public domain BMPs. King County Surface Water Management (October 1995) reported that 52% of wet ponds had significant defects. Seventy-five percent of the biofiltration swales surveyed were in either fair or poor condition due to a combination of design, construction, and inspection shortcomings and inadequate maintenance. In their 2000 report, Livingston, Baldwin, and Clevenger stated that less than 50% of the infiltration practices, including basins, trenches, dry wells, pervious pavement, and vegetated swales, were functional. The contributing factors included inaccurate estimates of infiltration rates, high water tables, excessive compaction and sediment loadings, and lack of maintenance.The California Department of Transportation (Caltrans), as part of a BMP retrofit program, is investigating the costs and operation and maintenance requirements of 39 BMPs using 12 different types of BMP technology. Caltrans reports that sand filters can require an average of 93 hours annually for such activities as vector control; dewatering; vegetation removal; repairs; sediment, trash, and debris removal; and inspections. Filter media will be required to be replaced on a longer-term basis. Caltrans also reports that public domain systems, such as extended detention basins, require 136 hours of annual maintenance, infiltration basins require 193 hours, biofiltration strips and swales require more than 200 hours, and wet basins require 570 hours—all of which exclude travel time to the sites.Proprietary, Structural BMPs As the biological and health risks of ponds, swales, and constructed wetlands become more widely understood, local regulators will look to proprietary, structural BMPs to help treat stormwater runoff or provide pretreatment for public domain BMPs, such as constructed wetlands. Proprietary BMPs for stormwater management include such structures as catch-basin inserts, filtration devices, and hydrodynamic separators. The costs of maintaining these structures vary widely, depending on the specifications of the system, the amount of rainfall, the cost of analyzing sediments, and the amount of debris that the site typically generates. Catch-basin inserts are generally cleaned manually by removing debris from the insert—usually inserts have a basket that is removed and dumped to remove solids. Any socks or pillows that might be used for oil removal are also replaced. Filtration devices typically require that the filter be replaced or recharged. Hydrodynamic separators and other vault-type BMPs conventionally require the use of a vactor-type truck to remove pollutants from the system.Most proprietary BMPs function by gravitational separation, vortex separation, filtration, or screening and retaining pollutants within the system in cases where secondary impact on wildlife is minimal. More frequent cleaning of these devices might be necessary to maintain adequate performance and, for some devices, to prevent release of pollutants. Installation of proprietary BMPs has largely occurred on private developments, and there is limited information on the maintenance of those systems. Surveys of catch-basin insert installations at nine sites in the San Francisco Bay Area over a two-year period found limited or no maintenance of those systems, resulting in a complete loss of functionality. A regular inspection program would have determined an appropriate maintenance regimen and prevented failure of those systems. Lyscars cautions owners to make sure that the maintenance company they contract with is properly equipped and knowledgeable about the system. Some maintenance contractors will “decant” a system by using a vactor truck to clean it out, then put the water back in without filtering it properly. This minimizes the ability of the clean-out to prevent pollution. Similarly, using a “clamshell” device to clean out catch basins might cause damage and remove as little as 30% of captured pollutants.“I think that we are on the cusp of seeing maintenance of these systems as important from both an infrastructure perspective as well as a way to control nonpoint-source pollution,” notes Lyscars. When properly maintained, proprietary BMPs, such as filtration systems and hydrodynamic separators, isolate pollutants from the environment. In some cases, the structures are designed to contain spills, such as oil and fuel, which can then be pumped out and disposed of properly. Regulation, Enforcement Key to Inspection and MaintenanceAs proprietary stormwater treatment systems are used more frequently to replace public domain systems, regulators will be challenged to figure out ways to ensure more regular inspection and maintenance of these systems. Property owners will obviously need to understand the requirements of each system and agree at the time of installation to keep the system maintained. Ideally, regulators will require inspection and maintenance plans for proprietary systems that meet the specifications dictated at the time of installation and provide for inspections to enforce implementation of those maintenance plans. Enforcement of any kind of maintenance agreements is complicated by such factors as sale of the site by the developer and transfer of maintenance contracts from vendor to vendor. Enforcement is also limited by a lack of money and personnel at the regulatory level. Increasingly, however, maintenance requirements are becoming part of the permitting process. There is a wide variation in regulatory oversight of the maintenance of stormwater BMPs in various parts of the United States. Some municipal stormwater programs have developed access and maintenance agreements to ensure access for inspections and provision for public agency maintenance of the BMP when owners fail to perform the required maintenance. The maintenance costs are reimbursed through property liens. Knoxville, TN, has been successful with this type of program. A weakness in these programs is that they are limited to proprietary systems and fail to cover the “public domain” systems.The City of Lacey, WA, reports that the State of Washington requires stormwater agencies to implement both private and public storm facility inspection and maintenance programs. The city found that it owned 17 storm facilities and there were approximately 300 private stormwater facilities. The clean-out of one small (28,000-ft.³) wet pond cost approximately $5,500. Municipalities faced with this level of oversight of private facilities and costs for maintenance will be challenged to carefully consider the type of facilities they implement and approve.ConclusionIn choosing a BMP to treat stormwater at a site, it is imperative that engineers, property owners, and regulators consider inspection and maintenance as part of the specification process. Parties responsible for BMPs should keep logs of inspections and maintenance to track system inspections, as well as routine maintenance, to be sure that the system doesn’t become a victim of “out of sight, out of mind” neglect. Proper maintenance is vital to the long-term viability of all BMPs, whether they are public domain or structural proprietary systems. Without regular maintenance, even the best designs become ineffectual and do not offer any protection for a community’s water resources.This article is the result of a collaboration of a number of companies in the stormwater industry.Contributors Include:AbTech Industries Inc.4110 N. Scottsdale Rd.
Scottsdale, AZ 85251
800/545-8999
www.abtechindustries.comBest Management Products Inc.53 Mt. Archer Rd.
Lyme, CT 06371
800/504-8008 www.stormwaterbmp.comStormwater Management Inc.12021-B Airport Way
Portland, OR 97220
800/548-4667www.stormwaterinc.comAquaShield Inc.2733 Kanasita Dr., Suite A
Chattanooga, TN 37343
423/870-8888www.aquashieldinc.comCDS Technologies Inc.
6360 S. Monterey Rd.,
Suite 250
Morgan Hill, CA 95037
888/535-7559
www.cdstech.comVortechnics Inc.41 Evergreen Dr.Portland, ME 04103207/878-3662www.vortechnics.comBaySaver Inc.1302 Rising Ridge Rd.,Unit 1Mount Airy, MD 21771800/229-7283www.BaySaver.comHydro International94 Hutchins Dr.Portland, ME 04102207/756-6200www.hydro-international.biz