CHAPTER 5

Summary of Findings

5.1 Introduction

The objective of this synthesis is to identify and document the current use of plastics in ESC practices across state DOTs and state DOT policies and plans to reduce or eliminate the use of plastics in ESC. Findings from the literature review, state DOT survey, and case examples are summarized in this chapter and highlighted in the following sections. Additionally, ideas for future research are presented based on knowledge gaps and barriers identified within the key findings.

5.2 Literature Review Findings

The literature review provided a background for ESCs, regulations, common practices, environmental concerns, and ongoing efforts to address the use of synthetics in ESCs. This review also included ongoing state DOT efforts to reduce, reuse, or remove synthetics from ESC practices across the United States. The following is a summary of findings from the literature review:

• Among ESC measures, RECPs have the greatest potential to cause wildlife entanglement.
• Erosion control practices are likely to introduce higher concentrations of microplastics into the environment due to their application on slopes, concentrated flow areas, and so forth. Microplastics are generated from practice cracking, embrittlement, and flaking due to solar radiation, mechanical abrasion (e.g., vehicles), or runoff. Additional research on microplastics in ESC is needed.
• Hydromulching often contains malachite green, a dye that is toxic to aquatic species and may have a greater potential to release polymers used in the creation of hydromulch slurry.
• Plastic manufacturing emits greenhouse gases, and plastic in the environment continues to release these gases.
• The USFWS has created fact sheets, literature reviews, and product lists for wildlife-friendly erosion control, which have been adopted by several state DOTs.
• Wildlife-friendly erosion control recommendations include using net-free or natural-fiber, loose-weave blankets and anchoring them with wooden stakes or burying the edges.
• A 2020 DOT peer exchange, initiated by Minnesota DOT and Vermont Agency of Transportation, revealed various initiatives and practices by state DOTs to move away from plastic-based ESC plans.
• Slash mulch berms, an alternative to silt fence, are up to 98% effective at retaining sediment.
• Large-scale testing has indicated that net-free and natural-fiber ECBs have up to 99% sediment-capturing efficiency and 97% runoff-trapping efficiency.
• Performance-based research and innovation for natural ESC practice alternatives are needed to move away from plastic-based ESC.

5.3 Survey Findings

• Of the 42 responding state DOTs, 33 possess an APL/QPL for erosion or sediment control products used on their projects.
• Of the responding state DOTs that utilize an APL/QPL, 82% (27 of 33) have an evaluation process for both ESC products.
• A wide range of methods is used to evaluate products for inclusion in an APL/QPL, including independent third-party testing, reviews of product specifications, evaluations of product and materials, and in-field demonstrations.
• The three most used ESC measures that contain plastic are temporary floating turbidity barriers, sediment barriers, and dewatering bags.
• The three most used ESC measures that do not contain plastic are temporary hydraulically-applied erosion control products, permanent hydraulically-applied erosion control products, and permanent ditch checks.
• The top alternatives to plastic-based ESC measures utilized by state DOTs include seeding, hydroseeding, mulch, and alternative netting materials.
• Nine of the 41 responding state DOTs provide guidelines, initiatives, policies, or specifications to facilitate the reduction of plastic-containing ESC materials.
• Evaluation of materials and products is one of the most challenging aspects associated with the use of sustainable materials in ESC measures.
• Wildlife concerns and entanglements were the top motivational factors for reducing plastic-based materials and products, followed by concerns about water quality.
• Aesthetics was the least motivating factor for reducing plastic-based materials and products, followed by reducing carbon footprint.

5.4 Case Example Findings

• All DOTs interviewed perceived ECBs as having the most negative impact on the environment or wildlife due to entanglement and entrapments. All DOTs that have shifted away from plastics started with ECBs.
• Many different natural-based and netting-free alternatives have been used and adopted by state DOTs to replace plastic-based RECPs.
• DOTs interviewed indicated that silt fence is also one of the most problematic practices; however, a viable alternative does not exist.
• DOTs did not report a decrease in functional performance of non-plastic alternatives and, in some cases, reported higher performance when compared to plastic-based measures.
• There are concerns about coconut-based alternatives due to reliance on imports, fear of transporting invasive species, and potentially unfair labor practices used during manufacturing.
• Cotton, wood excelsior, and hemp-based products are the most used domestically-sourced alternatives to plastic-based products.
• Several state DOTs have experimented with using wood and bio-based anchors for RECPs; however, all DOTS reported the inadequacy of the alternatives and continue to rely on metal staples.
• Two state DOTs indicated issues with sourcing and cost of stone and are relying on alternatives.
• DOTs reported that plastic-free ESC products are installed in the same way as are traditional plastic-based products and that additional installation oversight, inspection, and maintenance are not required.
• Two of the interviewed state DOTs reported perceived cost savings associated with inspection and maintenance due to higher-performing natural-based alternatives. State DOTs also reported less damage to equipment from entanglements and cost savings when removal of practices from the jobsite is unnecessary. State DOTs have reported concerns about the

• increased cost of plastic-free alternatives; however, those with widespread adoption of alternatives have reported cost decreases as supply has caught up to demand.
• State DOTs indicated that one practice in which the use of plastic products has increased is track-out control devices. Plastic-based products have helped reduce dependency on rock used in traditional track-out control practices. In some regions, rock has become difficult and expensive to source. Plastic-based track-out control products can be reused from project to project.

5.5 Future Research

In addition to the strategies highlighted in this study for implementing sustainable materials in ESC measures, two major topics emerged as areas for more exploration. Each of the topics identified can aid state DOTs in their development of sustainable ESC measures.

5.5.1 Alternative Sediment Barrier Fabrics

Sediment barriers are ESC measures commonly installed along the perimeter of construction sites to intercept and treat sediment-laden sheet flow. The most common type of sediment barrier specified by state DOTs is the silt fence. These sediment barriers are assembled on-site using support post, geotextile fabric, and, often, reinforcing support. Case example interview discussions suggest a need exists for the development of alternatives to geotextile-based silt fence installations. While silt fence support posts (i.e., steel t-post) and reinforcing (i.e., woven wire) can often be recycled or reused, geotextile fabric has a one-time use and can be a source of microplastics as it deteriorates. Future research efforts could focus on identifying and evaluating natural-based alternatives to geotextile fabrics. Potential alternatives may include cotton fabric, hemp fabric, or coir fabric. The evaluation of these natural-based alternatives would be of considerable value to state DOTs transitioning away from plastic-based materials.

5.5.2 All-Natural RECP Reference Guide

RECPs reduce soil erosion and promote vegetation establishment on slopes and disturbed areas. These products are manufactured using natural and synthetic fill materials held together with a wide array of netting materials. Case example interviews suggest that there are several all-natural options available within the marketplace and that RECPs are the all-natural alternative ESC materials easiest to transition to. Nonetheless, some state DOTs have found it challenging to source these products within their geographic regions. Future research efforts could focus on (1) identifying RECPs manufactured with all-natural materials within the United States; (2) developing a reference guide that illustrates products that can be locally sourced based on manufacture location; (3) providing performance evaluations that classify all-natural RECPs based on specific project site parameters (e.g., soil type, slope gradient, vegetation type); and (4) creating an online clearinghouse for dissemination of information. These guidelines would be of considerable value to state DOTs promoting the use of sustainable ESC products that are locally sourced.

5.5.3 Microplastics and Biodegradability

Plastic-based ESCs are an emerging environmental concern within industry, since they can contribute to pollution in the form of microplastics as the materials break down due to UV light exposure, weathering, and mechanical wear. Issues posed by microplastics in the environment are multifaceted, ranging from bio-accumulation within aquatic and terrestrial organisms to bio-magnification in humans. Future research efforts could focus on (1) identifying naturally occurring fibers and bio-based alternatives to conventional plastics, (2) developing new ESC practices utilizing the alternative materials identified, and (3) evaluating the effectiveness of

new ESC practices in comparison to traditional plastic-based ESC practices. This performance-based approach would facilitate the adoption of environmentally friendly materials in ESC applications, reduce the ecological footprint of construction activities, and protect ecosystems and human health from the adverse effects of microplastic pollution.

5.5.4 Hydromulch Dye

The green dye used in hydromulch, although generally designed to be safe and environmentally friendly, can pose certain environmental concerns. Potential issues associated with these dyes include toxicity to specific ecosystems and sensitive species, especially if high concentrations are introduced; water quality impacts due to runoff of freshly applied hydromulch; and dye degradability into compounds that can impact soil and water chemistry. Future research efforts could focus on developing and testing safer, more biodegradable dye formulations; assessing long-term environmental impacts of dye degradation products; and creating improved application techniques to minimize runoff and ensure dye remains within the target area. Additionally, studies could evaluate the ecological effects on soil microbiota and aquatic life to better understand and mitigate potential risks associated with hydromulch dyes.

5.5.5 Cost Analysis

To enhance decision-making and policy development within state DOTs, it is essential to incorporate actual cost savings associated with implementing BMPs that utilize natural-based alternatives. This research could focus on detailed cost implications, including formulas and calculations, that can be directly linked to various BMP practices and materials. By quantifying the economic benefits of these sustainable alternatives, state DOTs can more effectively evaluate the financial impact of adopting environmentally friendly practices, thereby supporting more informed and cost-efficient decisions. This data-driven approach could lead to broader adoption of sustainable methods that align economic and other objectives within transportation infrastructure projects.