Erosion, sediment, and stormwater runoff have an unquestionably critical impact on the quality of our environment. The EPA’s implementation of stormwater protection plans for any land disturbance of 1 acre or greater stresses the tremendous responsibility for environmental protection. This mandate affects virtually every construction effort that disturbs soil. Furthermore, revisions to related effluent guidelines are scheduled to be implemented soon, and these revisions will intensify the need for construction-site erosion and sediment controls. The EPA estimates that these new rules will cost more than $900 million annually to keep pace with site control needs.
Commonly, the erosion and sediment controls that are selected are referred to as best management practices, or BMPs. BMPs are cited ubiquitously in project specifications and product literature. But what puts the “B” in BMP?
BMP is an extremely broad term, extending well beyond any particular type of product or activity. In erosion control, it can refer to hydraulically applied products, rolled products, materials with natural or synthetic components, and others. BMP can refer to products or systems, both traditional and alternative. BMP can even refer to how a product or system is installed or monitored.
For the ever-expanding erosion and sediment control products industry, this broad use of the term has presented a problem to product and system specifiers. Historically, there has been a lack of generally accepted methods to define performance of these products, making it difficult to demonstrate definitively why a particular BMP might actually be the “best” in comparison to alternative management practices. Thus, users have lacked an objective means to specify performance. This is not in line with how other construction products are vetted, approved, and purchased.
The good news is that this problem may be going away. The implementation of standardized, repeatable large-scale performance tests for erosion and sediment control products is now well under way. These tests provide a long-needed means to perform “apples-to-apples” comparisons of the various technologies in different applications, and they offer data to show how the unique characteristics of these products translate into actual field performance.
Important to this development in the field is the work of the independent and influential National Transportation Product Evaluation Program (NTPEP), which has now incorporated large-scale testing performance data into its system. The objective process offered by NTPEP is a key factor in making the selection of BMPs more of a science and providing the quantitative evidence needed to determine which product or practice truly is “best” for a given application. The initial focus of NTPEP has been on rolled erosion control products (RECPs). More recently, NTPEP has been developing plans to include hydraulically applied erosion control products (HECPs). And, NTPEP hopes, in the not too distant future, to be able to incorporate sediment retention devices (SRDs).
Getting Here
Since the early 1990s, the Erosion Control Technology Council (ECTC), an association of manufacturers, has played a key role in improving the state of practice in erosion and sediment control. ECTC has strongly supported the development of standard test methods as it has worked to encourage a free but fair marketplace for its members. As a testament to ECTC efforts, standardized test results and performance information have rightfully become expected by the users of erosion and sediment control materials. Test data are a valuable tool that helps to ensure fair competition by improving product understanding, selection, installation, and, most importantly, success. ECTC has been vital to bringing test data to light.
In the 1990s, the council’s work included providing the essential funding to independently establish appropriate index and bench-scale tests. Those tests have since provided the main source of erosion and sediment control product comparative data. Index tests are relatively simple tests that manufacturers use routinely to control product quality. They also give users, such as land developers and government agencies, a way to verify product conformance to project specifications. Relevant index material properties include thickness, water absorption, and mass per unit area. Bench-scale performance tests offer a low-cost, quick way for companies or independent laboratories to test product bench-scale performance under “indexed” standard conditions. While not equal to large-scale field performance testing, these tests essentially give manufacturers an estimate of expected product behavior, particularly in relation, for example, to how a variation in a product’s components or construction might affect expected field performance under certain installation conditions, against certain flows, on a particular slope angle, and so on.
NTPEP, meanwhile, set about minimizing the duplication of product prequalification efforts by state departments of transportation (DOTs). The organization created a single database of material test results-a move that has made product specification more efficient, clearer, and ultimately more economical for NTPEP’s members. Materials submitted to NTPEP undergo a standardized suite of tests performed by an independent third-party NTPEP laboratory, the results of which are available online as public record at http://data.ntpep.org/. DOTs can, as a result, use those data (in full or in part) for the creation of their own approved product lists (APLs) and specifications for work performed in their states.
The NTPEP program
- relieves states of the economic burden relating to the construction, staffing, and maintenance of a facility specifically to test and approve products;
- provides consistent testing practices across a wide range of materials; and
- provides a single submission process for the manufacturer, thereby reducing the cost of doing business in each state while improving competition in each marketplace.
NTPEP’s work has involved and continues to involve a large array of traffic safety, construction, and maintenance issues and products, from crack sealants to flashing arrow panels to geotextiles and geogrids. The NTPEP focus is on the development and delivery of meaningful product evaluation data.
For erosion and sediment control, ECTC’s and NTPEP’s independent efforts jointly nudged the industry toward greater reliance on objective quantitative measurements and generic material specifications.
Still, index and bench-scale performance tests have not been sufficient, especially in this rapidly expanding field of engineered products and manufacturers of various levels of sophistication. These tests provide essential details on material and manufacturing quality and basic characteristics regarding performance, but they offer only an impression of actual full-scale performance. Thus, specifications, cost/benefit analyses, APLs, and other attempts at product comparisons are incomplete if based only on index and bench-scale testing. This is where standardized large-scale performance testing becomes important.
The Future of the Practice
“Standardized testing is essential for proper comparison of products,” says Tracy Gore, a construction technology leader with the Alabama Department of Transportation (ALDOT) Construction Bureau. She recognizes, though, that the vast differences in soil types, precipitation levels, and climates throughout the United States have complicated standardization efforts. Gore has served on NTPEP’s Erosion Control Products Testing Program Committee since 2009.
“These variations make it difficult to write a national standard specification,” she says.
The differing types of products, and their disparate performance within these varied environments, also complicate matters.
“There are installation limitations for both rolled and hydraulic erosion control products,” Gore says. “For example, rolled erosion control products cannot be easily installed to contact the soil surface on hard soils or on irregular surfaces. Hydraulic erosion control products cannot be used in channel flow applications or in areas subject to frequent flooding. However, both rolled and hydraulic erosion control products have comparable abilities to protect against rainfall impact erosion.”
The recognition of both rolled and hydraulic products is essential. In many instances, they can be used in the same way. But not every product within each class is applicable. In that lies the heart of the argument: how to identify the best BMPs.
Objective, quantitative “proof” then becomes more important, especially as product options and manufacturer numbers increase. Manufacturing quality controls via in-house index testing labs, independent manufacturing quality assurance via independent third-party agencies (such as NTPEP), and relevant, comparable performance evaluations via accredited independent testing labs together provide a “systematic” path to defining BMPs.
It has become imperative to utilize standardized, comparative, quantitative information throughout the product evaluation process. This has already been discussed concerning the use of index and bench-scale tests for quality control and quality assurance. Still, it is equally important to the effort to understand the real-world implications and expectations of one product or product type versus another, and this can be clearly quantified in large-scale performance testing. Large-scale testing is the only way to assess the effect of the recommended installation practice(s), such as anchorage type and frequency or coverage rate and minimum cure time, on performance.
“I believe that the lack of performance testing standards for erosion control products has inhibited their recognition as “˜engineered’ products by many in the design community,” says Tim Lancaster, director of technology-erosion control and marine with North American Green. He has been closely involved in developing programs with ECTC to provide clearer data for end users.
“The leading product manufacturers have in the past developed their own large-scale testing protocols in order to establish design values and guidelines for their products, but many engineers are hesitant to accept performance data from “˜non-standardized’ tests,” he says.
Additionally, various universities and agencies have performed versions of large-scale tests. With each organization using different protocols, it has meant that the performance information available until recently has been unique to each laboratory, thus making it impossible to compare results produced at different labs.
These efforts, while not universally beneficial, have certainly not been wasted. They’ve been central to the path the field now finds itself on. “Many of the elements of manufacturer-designed test protocols have now been rolled into ASTM testing standards,” says Lancaster. “[These] certainly help legitimize erosion and sediment control products and their functionality.”
And they do.
ASTM has listened and has steadily progressed with the standardization of large-scale protocols. Beginning in 1999, the ASTM consensus standards have provided the public with full details of how to run relevant large-scale tests, including the specific size, boundary conditions, reporting requirements, and all other testing details. Thus far, at least two laboratories have implemented test procedures in accordance with these standards.
One of those labs, in Anderson, SC, is the world’s first accredited laboratory for the full-scale testing of erosion and sediment control products.
“Accreditation is a way of assuring that a lab is running “˜letter of the law’ standardized large-scale tests,” says independent laboratory TRI/Environmental Inc.’s Joel Sprague. He runs the 4-acre site in Anderson: the Denver Down Research Facility (DDRF). It has been accredited by the Geosynthetic Accreditation Institute’s Laboratory Accreditation Program (GAI-LAP), and NTPEP has contracted with TRI to have it conduct the critical erosion control product testing for NTPEP’s member-distributed reports. TRI is also the same company that was engaged by ECTC in the 1990s to develop standardized index and bench-scale tests for erosion and sediment control products.
As with index and bench-scale testing, the use of ASTM’s consensus standards is important for large-scale testing. It is NTPEP’s openly declared preference to use agreed-upon, established standards in its process.
“The standards available to us,” Sprague says, “provide an impartial guide as to how these tests must be conducted so that they are repeatable, dependable, and fair. They are readily accessible to both users and manufacturers and provide dependable basic performance information.”
Key ASTM full-scale performance tests of note at DDRF include the following:
- ASTM D 6459-Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall-Induced Erosion
- ASTM D 6460-Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Earthen Channels from Stormwater-Induced Erosion
- ASTM D 7208-Determination of Temporary Ditch Check Performance in Protecting Earthen Channels from Stormwater-Induced Erosion
- ASTM D 7351-Determination of Sediment Retention Device Effectiveness in Sheet Flow Applications
(Note: While these four tests are all full-scale performance tests, D 6459 and D 6460 are the only large-scale tests available at the moment for NTPEP reports.)
The transparency of the process and the repeatability of the procedures lead to results that can confidently be used to compare alternatives.
“No matter what the product is, or how it is installed, slope dimensions are identical,” Sprague says. “Channel hydraulics are commonly interpreted. Rainfall intensities are repeated. Soil veneers are compacted to the same thickness. And the installation details are clearly recorded.”
John Ravert, technical director for East Coast Erosion Control, also believes that large-scale performance tests can provide more accurate and useful data in some instances than conventional bench-scale testing. For example, there is a dramatic difference when testing a product for shear stress.
“On the bench scale,” Ravert says, “they put it in a round pot, really like a kettle. And then they just apply the water to that, and that’s it. You go into a large-scale test, you’re looking at a 40-foot-long slope and you get a much better sense of soil loss. It gives you a real-world application.”
He considers large-scale testing to be the most valid way to determine the efficacy of a product.
“If you have a large-scale performance [test],” he says, “you’re running down three slopes, and you’re increasing the flows, and you have replicates and you’ve got a baseline to compare…you’re definitely getting a better analysis of what a product should do.”
Given the range of product classes and the variations within each class, that ensured consistency is central to validating not only the per-product data but, ultimately, the entire industry’s breadth of quality. For example, a double-net erosion control blanket with straw installed with two staples per square yard may be the presumed choice for a particular application. RECPs of this nature have been regularly included in NTPEP reports since 2003, but they do not represent the limit of real options. It may be that more recently incorporated products, such as hydraulically applied erosion control products applied at a coverage rate of 3,500 pounds per acre and cured for 48 hours, are just as effective. For the user making the purchasing decision, the latter choice may turn out to be more readily available or economical without sacrificing any site effectiveness. Or a site-specific combination of these technologies may be the best approach.
“Standardized testing is essential for proper comparison of products,” says Gore. “Testing data shows that there is not a direct correlation between the type or makeup of a product and the performance of a product. It is very important to review large-scale testing data to determine the anticipated field performance when approving products
for use.”
One solution may seem like apples and the other like oranges, but objective data collected on how they actually perform in like situations highlights exactly why these are apples-to-apples comparisons-how these BMPs may both be best, in which case economics can be the deciding factor.
Large-scale testing is currently optional to the manufacturers participating in the NTPEP program. Some states, including Alabama, are requiring large-scale testing from AASHTO NTPEP.
Gore reports that the NTPEP erosion control products testing program will publish a guidance document to help states understand and utilize the testing data. The document is expected by the end of 2011 and will be updated as needed.
Additional Advantages
Inclusion in the NTPEP program requires that products be subject to independent quality assurance testing via index and bench-scale testing every three years. Large-scale performance testing is currently optional. Yet, the impact of NTPEP’s offer to incorporate full-scale performance data lets the manufacturer go beyond proving product quality to proving product performance using its recommended installation practices.
“A key component of product performance,” Gore says, “is following the manufacturer installation recommendations such as staple patterns or frequency and application rates.”
In addition to submitting products for testing, participating manufacturers must also have in place strong quality control programs that routinely test both raw materials and finished goods in-house. These manufacturer-directed control programs must produce data using standardized tests and at frequencies that provide a clear view of process controls. These data must be readily available.
NTPEP also requires signed certificates of product quality and reserves the right to conduct random, independent sampling of materials from manufacturers for quality assurance purposes.
Quality control and quality assurance checks are becoming common in the erosion and sediment control products industry; but joining them with an outside, independent process and relevant, standardized performance characterization tests is what makes the overall NTPEP process so valuable here, as well as valuable beyond the DOT members who immediately benefit from the product reports.
Full-scale testing is certainly not the last step in this dynamic field’s evolution, but it seems to be the final step in the industry’s maturation. The process officially began with the development of those first, key standardized tests in the 1990s, and it has now led to a process that gives erosion and sediment control products and producers the full vetting and quality recognition that makes them consistent with other common (and necessary) construction products.
“The broad reach of NTPEP, the considerable product-purchasing investments made by its members, and the influence this synergy can have on product industries represents a tremendous opportunity for erosion and sediment control,” Sprague concludes. “NTPEP’s process supports and protects designers and end-users and facilitates free and fair markets. It’s a process, and just a process; but it is a process that has been missing and one that is welcomed.”