New composite yields efficient and cost-effective alternatives.
Fiber rolls (or wattles), silt fence, and fiber blankets traditionally used for sediment control on residential, commercial, or linear construction sites may leave builders desiring better alternatives. In a recent survey, several builders cited a desire for products that do the following: withstand subcontractor traffic and abuse; endure the entire construction cycle and can be reused; have a lower total cost; are simple to transport, install, maintain, and store; and offer better sediment control performance to reduce site sweeping. Traditional solutions civil engineers, developers, and cities specify and approve do not always protect water quality, nor keep jobsites clean in the most efficient and cost-effective way.
During home building projects, traditional solutions can be destroyed by foot and vehicular traffic. They can become ineffective by damming and allowing undercutting. As straw in fiber rolls decays and slumps, stormwater overtopping becomes common. Within months, silt fence deteriorates from wind and ultraviolet radiation (UV) exposure, necessitating regular maintenance and replacements. Furthermore, these traditional Best Management Practices (BMPs) usually cannot be reused and often are costly to remove and dispose.
Problems abound on commercial construction projects as well. They often last 18 months or more, and it is common that a large percentage of wattles or silt fence must be maintained or replaced during these projects.
While builders have become accustomed to multiple installations and continuous maintenance, they desire alternatives. Polymer Composite Flow-Through Technology (PCFTT), a product platform developed and manufactured by ERTEC Environmental Systems, is offering such opportunities on many sites. In addition to being lightweight, tough, easy to install and maintain, reusable, and recyclable, products made from this type of high-performance polymer and fabric composite allow water to flow off the site, while retaining a high percentage of sediment. According to research conducted at San Diego State Universitys Soil Erosion Research Laboratory in 2002, PCFTT technology was shown to retain up to 80 percent of soil that would otherwise leave a site. Whats more, sediment control products made from PCFTT, on average, allow users to slash costs by 50 percent.
A new alternative for sediment control
A new type of perimeter sediment control system made from PCFTT offers the land development industry alternatives to traditional solutions. ERTECs Perimeter Guard is a recyclable and UV-stable, high-density polyethylene (HDPE) netting that houses an internal, clog-resistant HDPE filter (Figure 1).
Figure 1: PCFTT perimeter sediment control system
The barrier is "L" shaped with a 7.5- to 8-inch vertical height. The system is designed to allow water to flow through while filtering a high percentage of sediment. Additionally, Perimeter Guard is flexible so that it bends back and forth in vehicular traffic. When deformed or flattened after significant abuse, it can be reshaped to near-original form. Additionally, sediment drops out upstream, thereby preventing undercutting.
A PCFTT perimeter sediment control system is installed similarly to other sediment control devices. It must be trenched 1 or 2 inches. The 7-foot-long sections need to be inserted into each other, taking care to butt the pieces together to prevent the joints from popping apart during vehicular traffic. The upstream flap should be anchored with 6-inch nails and then backfilled to prevent undercutting. Also, the flap must be covered with soil to force water to flow through the filter. It can be installed about 20 percent to 30 percent faster than silt fence and at about the same speed as wattles. Additionally, the product packs around six times more densely than wattles and is light, reducing transportation and storage costs.
Once the product is installed properly, maintenance is minimal. Sediment must be removed when the system reaches 50 percent of capacity, and the product must be reshaped after vehicles run over it.
While it has excellent economic advantages and strong sediment control performance, Perimeter Guard has limitations. Since the system is less than 8 inches tall, it has a limited sediment capture zone. This system should not be used where there is heavy concentrated flow. For protection of large sloped areas, this perimeter protection system should be used in combination with other source control or erosion control measures such as track walking, mulches, or soil amendments.
ERTEC worked with Shea Trilogy at its Rio Vista residential development in Northern California and with commercial builder Jackson Properties of Elk Grove, Calif., to determine whether a new alternative that meets the criteria desired by builders also could provide better risk management and an economic advantage.
A perimeter sediment control system—totaling 7,000 feet—was installed in September 2005 at the Shea Trilogy home sites. It was monitored closely for the next 12 months, and, according to site management, many promised benefits were achieved. Solids in rainwater runoff to the street, and eventually to the storm drain, were reduced significantly. Additionally, funds spent to replace and maintain the barriers were reduced by more than 50 percent. In fact, a single installation stood up to typical abuse with normal maintenance and then was reused as such that an average of two houses were built with each set of perimeter control sections. Normal maintenance required about six minutes per house per week for houses under construction (about two to three hours per week for the subdivision). Idle lots required little maintenance, if any. Because the builder was able to reuse the product, the savings continued to grow.
"We usually go through three to five sets of wattles (two to four complete replacements) during the course of home construction. This system stayed in place, from land development to landscaping, and then was reused for one more cycle. If this system gets banged up, it can be reformed and reinstalled," said Wayne Collins, field manager for Shea Trilogy.
Kirk Williamson, who is also a field manager at the Shea Trilogy subdivision, said, "When there is a damaged piece, we dont have to replace 25 feet. We can usually repair it and put it back into service. This system is easy for all the trades to work around."
Jackson Properties tested the product on commercial developments, finding that it could reuse the perimeter sediment control system at least two times (two removals and reinstallations). In March 2005, 4,000 feet of Perimeter Guard was installed around the perimeter of a 20-acre retail center. After 14 months, the product was removed while the site perimeter was landscaped, and 95 percent of it was able to be reinstalled at another site. Since then, some of the product was removed and reinstalled on a third project. Sediment control costs on the projects were reduced significantly as compared with traditional methods.
"I liked that when the product gets hit or run over by equipment, it can be easily reformed. Before we installed a fence around the project, long sections were run over by cars, several times. [With Perimeter Guard], each time we could reshape the product to vertical in minutes," said Dan Jessee, general superintendent of Jackson Properties.
He added, "It is very difficult to compare sediment control performance between BMPs in the field, but overall, it seemed that sediment reaching the street was less, which is consistent with the lab data."
Jessee also noted the economic benefits of this sediment control option. He said, "The material from our Elk Grove project was in excellent condition after removal by the landscapers. Our savings were nearly 50 percent after the first two projects. Then, we expect our savings to grow even further as we use the same material again on subsequent projects."
David Korfas, the city of Elk Groves lead stormwater compliance inspector, recognized the advantages for builders using a PCFTT perimeter sediment control system. He said, "A particular benefit for builders is the products durability and long-term sustained performance. Contractors and their subs should not drive over BMPs except for stabilized rock entrances and exits. This is difficult for superintendents to control, especially on residential projects, and so the ability for this system to be reformed after contractors drive over it provides the developer a big cost advantage."
Other uses for PCFTT
On construction sites, storm drain inlet protection is required to intercept flow at curb gutter openings and to prevent debris, sediment, and associated pollutants from entering the stormwater system. For inlet protection systems installed in front of drain openings, it is difficult to balance the trade-off between allowing water to flow off streets for safety reasons with removing sediment. The PCFTT platform enables the development of products that optimize this trade-off, while offering other desirable characteristics such as being easy to monitor and clean.
ERTECs Curb Inlet Guard and Combo Guard are such examples. Each system reduces water velocity, which causes heavier soil particles to be deposited upstream. While allowing flow through the module, the systems filter debris and certain smaller-sized particles from suspension and prevent them from flowing through the device and into the stormwater system. Excessive flows bypass over the top of the filter.
Similar to the advantages of PCFTT perimeter control systems, these inlet protection products are effective, durable, reusable, and easily installed and cleaned. Curb Inlet Guards have the added advantage that one-size-fits-all. For long curb openings, the sections can be overlapped as necessary. Combo Guards, which protect curb and grate combination openings, are sized for various grate sizes.
These systems are recommended for use during construction at curb openings where drainage areas are less than 1/3 acre; the total for inlets in series should be 1 acre or less with slopes flatter than 5 percent in the contributing drainage area. These systems can be particularly advantageous for linear construction and utility maintenance activities where the need for multiple installations, removals, and compact transportation are important.
The systems should be installed with the horizontal sections facing upstream toward the street. Small gravel bags containing clean, pea-sized graded gravel must be placed on each end of the flap with the bags butting against the curb to keep water in the gutter from flowing behind the filter.
Users are finding that the products meet their needs. "Until now, we typically spent hundreds of dollars per season for each inlet for installation and maintenance of curb inlet protection BMPs. Curb Inlet Guard, because it is so easy to install and maintain, was able to reduce costs drastically," said Don Moore, division environmental manager for Lennar Homes, a national homebuilder.
Lyn Hudgens, safety representative for the general construction-gas division of PG&E, commented on this technologys performance on utility projects. "Combo Guard worked great for us on a 6-mile pipeline project. The units were so easy to install, maintain, and reuse, and we never had to lift heavy grates. We used Combo Guard in several cities, and the inspectors liked the product. The savings were substantial," she said.
Construction-related erosion and sedimentation can cause problems for down-slope property owners, create nuisances on adjacent streets, clog streams and storm drains, result in turbidity plumes in downstream water bodies, and can cover sensitive habitat areas with sediment. The cumulative toll on the environment can be devastating. Uncontrolled erosion and sedimentation is costly; violates state and federal pollution laws; exposes developers, contractors, and landowners to legal liabilities; and provides ammunition to those who argue that the land development process is out of control.
The erosion and sediment control market is 30 years old, yet it is still in its infancy. Tremendous opportunities for products, ideas, and people lie ahead. It is important for civil engineers, contractors, developers, and municipalities to keep their eyes on the horizon. New ways of controlling erosion and sediment are providing opportunities to cut costs and improve performance.
Steve Stonehouse is an independent technical writer located in San Francisco. He can be reached via e-mail at firstname.lastname@example.org.
Sidebar: Inspiration from unexpected places
John McGinn was on a beach in Australia in 1997 when a novel idea struck. He was trying to solve a problem common with ocean racing yachts such as those that compete in the Americas Cup. Wind flowing around the large masts in these yachts causes unwanted turbulence, reducing the beneficial forces on the sail.
In an attempt to reduce this effect, McGinn developed several "flow-through" model masts from carbon fiber material. One day during testing, while a few of the models lay on the beach, McGinn noticed that they surprisingly captured sand at a remarkable rate. The flow dynamics caused particles to enter, then fall-out within the structures. In less than one hour the models were covered with sand. Perhaps, he reasoned, this technology could also be used to reduce the force of waves hitting and eroding beaches.
It was this discovery and McGinns understanding of the worldwide need for erosion and sediment control products that led to the establishment of ERTEC Environmental Systems. He raised the required capital and began working to develop the technology platform called Polymer Composite Flow-Through Technology that, when formed into various shapes and sizes, led to a series of products. Today, McGinn is vice president of product development at ERTEC.