Improving stormwater infrastructure O&M: BMP design, monitoring and workforce development

The growing need for better operations and maintenance (O&M) practices for stormwater assets, best management practices (BMPs), green infrastructure improvements, and innovative approaches to stormwater management are being developed around the country.

After years of stormwater characterization studies, feasibility assessments, and municipal planning document development, stormwater treatment controls are cropping up in commmunities not commonly seen as centers for stormwater progress. In Los Angeles County alone there are hundreds of stormwater capture and treatment projects in the design and construction phase, and completed ones are being operated and maintained. Each stormwater BMP has a unique O&M Plan — the document that identifies the inspection, operation and maintenance frequency and cleaning methods. The resounding report from most municipalities is that compliance with these plans and the O&M of these assets is an ongoing challenge and requires more frequent cleanings than originally planned. Private landowners, industrial facilities and commercial developments (think big box stores) are also challenged with maintaining their stormwater infrastructure. Most commercial developments constructed after 2010 have stormwater treatment infrastructure in accordance with NPDES MS4 compliance, and there is a growing need for trained and qualified staff to maintain this infrastructure. Three ways to begin overcoming these challenges are to design with O&M in mind, to monitor the BMPs’ condition and performance and to develop a qualified workforce.

Types of BMPs

Beginning with design, a typical stormwater treatment project will consider operations and maintenance as a cost consideration. Controls on system configuration for above ground and below ground BMPs are usually governed by hydraulics, existing utilities and available land area, such as medians, parks and open spaces. Long term O&M efforts are more difficult to predict.

Above ground treatment controls

The forward-facing BMPs are generally composed of bioswales, biofiltration or vegetated infiltration systems, and formally known as green infrastructure (GI). With GI maintenance, most maintenance activity includes trash removal, vegetation management, identification and removal of invasive species, and cleaning of stormwater conveyance and underdrains.

Below ground treatment infrastructure

Most large scale BMPs use a stormwater diversion located in the storm drainpipe or channel to direct flows into the treatment system. Flows can be controlled with a slide gate and a subsequent trash rack collects larger debris. There are many different types of pretreatment and screening devices such as hydrodynamic separators, debris separating baffle boxes, and pretreatment chambers to remove most trash and some sediment. From there, flows are directed into cisterns to infiltrate or reuse the stormwater or are directed into drywells designed to recharge groundwater. Each one of these components requires regular inspections and maintenance.

Designing with O&M in mind

To ensure BMPs function as designed, frequent maintenance is necessary, and access to perform this maintenance makes the process much simpler. Too often, the manhole for inspections and cleanings are located in the intersection, requiring lane closures and traffic controls for every maintenance event. Some examples are underground pretreatment devices with access doors located in parking spots, limited space to park a vacuum truck and access manholes that are too small for a person to enter. These are all potential challenges for maintenance crews. At the predesign stage, it is important for engineers to seek input from the maintenance staff within the agency department. Simple changes to design, like placing the most frequently maintained assets, such as the diversion and pretreatment devices, outside the public roadway.

If the system is fitted with flowmeters or monitoring equipment, placing those devices in dedicated conduits prevents damage during maintenance. Many pretreatment devices require a confined space entry. Special attention should be considered when designing and locating these devices to either minimize confined space entry or eliminate it altogether. The level of effort to perform a confined space entry and cleaning in a busy intersection can cost much more. Another example of designing with O&M in mind is to locate the access in a parking lane with a “No Parking” sign on designated days. This way the truck and crews can set up, clean the device, and leave without costly lane closures and traffic disruptions. By designing with future O&M in mind, the result is to increase safety, minimize O&M burden and reduce hours spent.

Optimizing BMP performance

Many of the newer stormwater treatment systems as described above are fitted with water level loggers, flow meters and rain gauges telemetry for data acquisition. The concept is that continued monitoring of these parameters can help assess the BMP effectiveness over time.

When coupled with maintenance data, monitoring the system can inform when maintenance is needed. This is known as predictive maintenance or “just in time” maintenance, which means the inspection reports should include quantity removed, material type, liquids and organics amounts. Storm predictive data and historical rainfall amounts can help correlate slide gate opening to anticipated rainfall and/or dry well water levels. This helps to optimize drywell performance.

In addition, when influent and post BMP effluent water quality samples are collected, the performance of the BMP can be directly measured. Future designs can be better constructed when based on actual data, which ultimately reduces O&M effort.

Developing a qualified workforce

As more BMPs are constructed, cities will need to continue hiring staff to maintain these assets. Municipalities will need to establish a framework for training staff on O&M of stormwater infrastructure, particularly treatment control measures including GI.

A common challenge is maintenance crews being able to recognize invasive species from the vegetation originally designed and planted. Invasive weeds are undesirable plants from other regions that grow and spread quickly. Removing the wrong vegetation can significantly reduce the BMP’s effectiveness. The best way to avoid improper maintenance is to implement a training program consisting of classroom, field and on-the-job training.

Maintaining underground stormwater assets requires OSHA certified technicians with confined space training and equipment operation experience. The staff may be required to operate hoists and lifts, vactor trucks, hydrojetting equipment and slide gate controls. It is essential that a robust training program is in place and that safe working practices are implemented. With GI maintenance, some important detailed learning points include vegetation management, identification of invasive species, understanding of stormwater conveyance and underdrains.

Several national GI training programs currently exist, including the National Green Infrastructure Certification Program (NGICP) through Envirocert International Inc., and the Green Infrastructure Training Program (GRIT) and more local to Southern California, such as the Los Angeles Conservation Corps (LACC).

Effective training consists of classroom or virtual training content, field training and regular assessments of said training. The most effective training programs work in conjunction with municipal stormwater programs already in place: community outreach, educational signage, storm drain markings and public-facing information related to green infrastructure and stormwater treatment projects.

Summary

Most municipalities are reporting that full compliance with the O&M plans for their stormwater treatment assets are an ongoing challenge, as well as maintaining a qualified workforce. It is clear the way to begin overcoming these challenges is to design with O&M in mind, monitor BMP condition and performance, and develop a qualified workforce.