Improved Erosion Control BMPs for Road Construction Projects in the North Carolina Mountains Results To determine whether if practical, alternative Best Management Practices for roadway projects are able to reduce the turbidity of water runoff as compared to the standard NC DOT practices currently used. Curley Maple Rd Site: Turbidity (NTU)StandardFiber check dams+PAM Fiber check dams only Average4,198 a 30 b 187 c Median Value1, Table 1. Runoff turbidity results (NTU) for the three treatment type sections at the Steeltown Rd site. Funding provided by: The North Carolina Department of Transportation NC DOT Standard BMPs These BMPs primarily consisted of periodic rock check dams and sediment basins, though at Steeltown the entire ditch channel was also lined with erosion control matting. The results suggest there is a significant advantage in the use of the new BMP types, particularly those with PAM 705 added. At the first site the average turbidity values (in NTU) for the stormwater runoff for were 4,198 for the standard DOT BMPs, 30 for the fiber check dams with PAM 705, and 187 for the fiber check dams alone. The second site showed similar results with average turbidity values of 64 for the fiber check dams with PAM 705, as compared to 852 for the standard DOT BMPs. However, only the fiber check dams with PAM 705 had an average turbidity that came close to achieving the sensitive habitat runoff turbidity limit of 10 NTU, though they did meet that threshold for eight storms at Steeltown Rd and two storms at Curley Maple. Summary Materials and MethodsIntroduction Project Objective Erosion Control BMPs: Definition and Function Erosion control Best Management Practices (BMPs) for construction sites are designed to reduce the amount of sediment leaving the project in water runoff. For roadway projects in the mountains they typically include small sediment basins and rock check dams, both of which are designed to detain or slow water runoff, allowing suspended sediment more time to settle out. Why Study Erosion Control? Sediment is the most common pollutant affecting North Carolina’s waterways, impacting a range of aquatic organisms, reducing reservoir capacity, and hurting their aesthetic and economic value. Construction activity, including roadway projects, is a significant contributor of state-wide sediment loading. The NC DOT program of widening and paving rural roads in the mountain region provided an opportunity to evaluate new types of roadside erosion control BMPs. Current regulations have established maximum allowable discharge turbidities for sensitive waters (to include trout streams) at 10 NTU (Nephelometric Turbidity Unit). However, this low threshold has proven quite difficult to meet and new structures and practices are needed to achieve this requirement. What is PAM? PAM is an acronym for polyacrylamide, a water soluble, synthetic polymer commonly used in a variety of water treatment processes. PAM exists in a variety of neutral or charged forms but each is intended to increase the rate of flocculation, or particle binding, that occurs in water, significantly increasing the rate of sedimentation. The anionic PAM 705 was used in this study and has been approved for stormwater treatment by the NC Dept. of Water Quality. Figure 3. A 120° weir used at the Steeltown site to capture runoff samples and to determine overall runoff flow volume. Each experimental section had a separate weir located above a culvert to capture runoff from only that section. Turbidity (NTU)StandardFiber check dams+PAM Average852 a 64 b Median Value30540 Steeltown Rd Site: Table 2. Runoff turbidity results (NTU) for the two treatment type sections at the Curley Maple Rd site. Figure 2. An ISCO brand water sampler used to sample runoff from the project sites. Solar panel and battery are in the foreground. Fiber check dams – Coir Logs The larger and stiffer of the two experimental types, the coir logs are made of woven coir fibers made from coconut husks. The rolls used were 10’ long and 12” diameter, costing around $55 each. Approximately 5 of these logs were placed per experimental section. Fiber check dams – Straw Wattles The smaller, lighter, and more malleable of the two experimental types, the straw wattles simply consist of straw packed into a plastic mesh casing. The rolls used were 10’ long and 9” in diameter, costing around $20 each. Approximately 15 of these wattles were placed per experimental section. Project Description The study was conducted on two roadway paving projects located in the North Carolina mountains. The first, Steeltown Rd is located north of Lenoir, NC in Caldwell County, while the second, Curley Maple Rd is located just north of Boone, NC in Watauga County. The Steeltown site consisted of three separate treatment type sections: DOT standard BMPs – a 137 m long section at 5% slope Fiber check dams plus PAM 705 – a 203 m long section at 7% slope with approximately 9.1 m spacing between BMPs Fiber check dams alone – a 141 m long section at 6% slope with approximately 7.6 m spacing between BMPs The Curley Maple site consisted of two separate treatment types: DOT standard BMPs – a 154 m long section at 3% slope Fiber check dams plus PAM 705 – a 149 m long section at 3% slope with approximately 8.5 m spacing between BMPs. Sampling Methods Runoff was collected by Teledyne ISCO brand 6712 portable water samplers programmed to collect samples after a set water volume had passed. At Steeltown, they collected the samples from the front side of constructed weirs located at the entrance of a culvert. At Curley Maple, they collected samples from the interior of the culverts themselves. Figure 4. A photo of the comparative average runoff turbidity results (in NTU) for the three treatment type sections at the Steeltown Rd site. Figure 5. A photo of the comparative average runoff turbidity results (in NTU) for the two treatment type sections at the Curley Maple Rd site. Figure 1. Photos of the PAM 705 used in the study. Approximately 100 g of granulated PAM (as shown on left) was sprinkled on each wattle or log after each significant storm event, though PAM may come in many different solid and liquid forms (as shown on right). Sediment Loading (kg) StandardFiber check dams+PAM Fiber check dams only Overall Total9, Average per Storm428 a 0.8 b 2.1 b Sediment Loading (kg) StandardFiber check dams+PAM Overall Total657 Average per Storm3.4 a 0.8 b Table 3. Sediment loading rates (kg) for the three treatment type sections at the Steeltown Rd site. Table 4. Sediment loading rates (kg) for the two treatment type sections at the Curley Maple Rd site. S.E. King, R.A. McLaughlin, and M.B. Shaffer *p < 0.05 for statistical comparisons There were 32 total storm events captured for the Steeltown Rd site with rainfalls ranging from 4 to 54 mm, with an average of 25 mm. There were 19 total storm events captured for the Curley Maple Rd site, with rainfalls ranging from 6 to 78 mm, with an average of 21 mm.