In August, Stormwater Solutions and IECA hosted an erosion control webinar, “Valuing groundcover and vegetation as a tool from start to finish,” featuring Aaron Harper, roadside environmental field operations engineer with the North Carolina Department of Transporation (NCDOT), and Donald Pearson, assistant resident engineer with the Summit Design and Engineering Services, as the speakers.
Groundcover comes in a variety of options, some when combined with seeding, can significantly reduce erosion and enhance soil stability. The North Carolina Department of Transportation recognizes the importance of groundcover and phased vegetation establishment in managing erosion risks. Contract language, financial incentives, vegetation management plan guidance, seed species selection, and inspection emphasis are all combined to provide contractors the opportunity to be successful. This comprehensive strategy provides contractors with the tools they need to effectively manage soil erosion during construction.
In the webinar, Harper and Pearson shared four decades of experience highlighting the significance of groundcover and vegetation in linear construction, particularly from the Piedmont to the Coast of North Carolina. Their insights underscore the value of groundcover and vegetation as a practical BMP that can reduce erosion and create opportunities to improve stormwater runoff from active construction projects.
The webinar is now available to view on-demand here, and below, you will find responses to some of the questions posed by the audience in the Q&A session at the end of the live webinar.
Audience: Any advice for vegetation in solar farms?
Speakers: We do not have a lot of experience with solar farms but expect they create a challenging environment for establishment of vegetation because of the shading effect the panels generate as well as the way stormwater interacts with the areas under the panels and the need to address the splash energy generated where runoff flows off the edge of the panel. On highway construction projects, this is a little like the challenges created by bridges over wetlands, riparian buffer zones, and stream banks. The bridge's shadow prevents adequate sunlight for turf to establish in the floodplain. We have had minor success with some Fescues, specifically fine fescue, which has success developing in full shade. Another thought is to consider using ground/chipped clearing debris mulch as an alternative. We have used the shredded/ground clearing debris mulch generated from the initial clearing and grubbing of trees for new projects as groundcover and have been surprised at the groundcover longevity and ability to allow for natural growth to develop. Originally the thought was to allow it to function as a temporary solution, but the longer it remained the more volunteer plants moved in and eventually it became well stabilized. Of course, ABC stone or similar aggregate may also accomplish similar benefit. An out-of–the-box idea is to consider ornamental plants like Hostas or Ferns. These tend to be vegetative species that survive in shade and may be adaptable to the shaded areas under and around solar panels.
Audience: What are acceptable binding agents for mulching?
Speakers: NCDOT has been a long-time user of emulsified asphalt as a tackifier or binding agent for wheat straw mulch. However, this is changing with there being a market shift away from using the asphalt tack and more companies preferring hydraulic mulch. The current NCDOT specifications allow for both with emulsified asphalt tack at 484 gall/acre and any approved hydraulic mulch product to be used as tackifier at a rate of 1000 pounds/acre. However, if a hydraulic mulch to be used is marketed as a tackifier, then the manufacturer’s rate is required. The weight of the product on the wheat straw is the key, and success is truly based on the execution of the contractor in applying evenly over the mulch at the necessary rate.
Audience: How does this NCDOT program compare to a CESCL certification?
Speakers: NCDOT’s Level 1 and 2 Certifications were not developed with the intention of meeting a minimum national standard. Rather these certifications were developed specifically for NCDOT’s delegated program. The Level 1 Erosion and Sediment/Stormwater Control Certification for Installers is specifically for those employees working on an erosion and sediment control crew responsible for installing erosion and sediment/stormwater control measures. The Level 2 Erosion and Sediment/Stormwater Control Certification for Supervisors and Foreman is specifically for those in management roles on crews that generate land disturbing activities. The Level 2 Class equips those individuals with skills for observing risk and coordinating preventative and corrective actions. Having said that, there is a lot of information in these certification classes that addresses the basics of erosion and sedimentation, benefits of groundcover and vegetation, purpose and function of BMPs, approach to completing NPDES inspection and documentation on NCDOT projects, and other topics. Over the last couple decades, municipalities, private developers, and consultant firms have seen the value of the information provided and attend to help broaden the perspective of their employees. Currently NCDOT does not have a reciprocity agreement with national erosion control Certifications.
Audience: Out of all of the tools, specs, and contract tools you have, which one is the most important to your success?
Speakers: All the contract language and best management practice evolution experienced by NCDOT over the last several decades came from employees with a passion and commitment to being environmental stewards. There is so much value in the individual’s ability to observe, assess, think critically, educate, and communicate. The specs and standard drawings are ineffective if the boots on the ground are not aware of them, understand how to access them, and are intentional in using them. The certification programs become a box to check if the individuals pursuing certification are not empowered by their leadership to meet the responsibilities and expectations the certification entails. The incentives and contract language do not provide a benefit if they are not upheld and adhered to by the contract administration entities and contractors, respectively. It all boils down to the people, at all levels. Not only from the execution of the guidance and resources, but also in a commitment of setting a high level of expectation for achievement. Failure to achieve a high level of expectation is still better than failing to achieve at a low level of expectation.
Audience: How often do you look at the amount of organic matter that is on site or needs to be brought onto site?
Speakers: Topsoil is a scarce commodity on highway construction projects. If the project is a new location, then there is the potential for the initial land clearing and grading to identify some topsoil and reuse as needed on the project, but unfortunately this is not a common thing. NCDOT has contract provisions that are included in projects when the expected available soils on site are known to be extremely poor. A pay item is included for the contractor to bid on and receive compensation when used on the site. Unfortunately, not all projects include that contract language. In some cases, contractors have saved topsoil or organic material when working within streams and wetland areas when a box culvert or pipe is being placed. That wet heavy soil can dry and then be reused on fill slopes. NCDOT also has identified the value of compost on construction projects and includes contract language on projects where soil fertility is known to be poor. Using STA-certified Compost is necessary as there can be quite a variance in the quality of compost materials. As noted in the presentation, NCDOT does have standards that require a soil to include certain plasticity index and pH for construction of the embankment. The contractor must use soil that meets that, and if those are not available on the project limits, then the contractor must pursue other means to find soil that will. Pursuit of borrow sites may be the next step.
Audience: How often are you importing topsoil or compost on to a project for revegetation base?
Speakers: Unfortunately, importing topsoil is not common. Contractors rely heavily on the native soils being capable of supporting permanent desired vegetation with assistance of the soil amendment recommendations in the contract (limestone/fertilizer). However, local contractors familiar with the soil in this state are aware of fertility challenges and they may seek opportunities to find organic soils on the project that can be stripped and stockpiled for later use. Compost is an option but requires pre-construction planning by the erosion control plan designer. Several projects we have worked on included compost blanket/seeding which, though expensive, gave contractors a chance at success through use of a “perfect or ideal” media.
Audience: Do you have fertilizer limitations near or around wetlands or levees?
Speakers: NCDOT follows a standard fertilizer application rate of 500 pounds/acre in all areas of the project, including riparian and wetland areas. There is an emphasis by the Department of Environmental Quality that discourages the use of hydraulic seeders applying or washing out in and around streams and wetlands because of the concern over fertilizer in a liquid form being directly released into those surface waters.
In addition, there are some watersheds in the state that require online training for fertilizer applicators to raise awareness of over-applying or applying in sensitive locations. NCDOT includes this guidance within its contracts that those applicators obtain the training certificate if the project falls within that watershed.
Audience: In your experience, What method of education (from a regulator lens) do you find most useful/effective when explaining the importance of vegetation/ground cover to developers or consultants that only focus on sedimentation controls?
Speakers: It is hard to argue with the financial benefit of establishing vegetative cover or pursuing stabilization. I would lean in on the fact that groundcover alone provides an erosion reduction of 90%. 90% erosion reduction means less sediment migrating toward sedimentation control devices, which in turn equates to less maintenance, which in turn equates to more time to pursue production, which in turn equates to more efficient project delivery. And everyone knows, time equals money. Reduce erosion, reduce sediment transport, reduce maintenance of measures.
Proactive efforts always outweigh reactive efforts. NCDOT is trying to change an acceptance that some contractors have developed that “erosion happens and sediment can be cleaned up.” Contract language and specification manuals are only part of a solution to change some mindsets. As mentioned in a previous answer, the most valuable BMP is the individual. As more competent people become employed on the project, the better the efforts will become. Our recommendation is to engage the contractor community through the statewide Association of General Contractors and begin discussing a partnership or initiative that allows state regulatory groups and contract companies to openly discuss how erosion and sediment control is not an obstacle to overcome in order to build a project but rather that erosion and sediment control is part of the construction sequence that is needed to build a project. Get that conversation started and the 90% erosion reduction comment made earlier may take hold.
