CBOT sampling protocols

Best Practices in Wood Waste Recycling

Product Sampling and Quality Control Testing

Material: Wood Waste

Issue: Wood-waste processors and their customers often use inadequate sampling techniques, perhaps using only one or two grab samples from an exposed pile. These procedures could cause inaccurate, misleading results, confusing the supplier and end-user. Inadequately or not sampling has allowed bad loads of processed wood waste into manufacturing processes and subsequently ruined finished product, and has damaged manufacturing equipment. Such disastrous circumstances are expensive and significantly reduce interest and demand for recovered wood by manufacturers.

Best Practice: This Best Practice recommends that processing facilities design and implement a sampling and monitoring plan designed to detect problems, and accurately and objectively characterize the processed material. Manufacturing plants and other end-users should also implement a sampling plan to ensure that specific loads and suppliers are providing material that meets their specifications. This Best Practice only discusses sampling and sample preparation methods and does not go into detail about test methods for two reasons. First, the type of appropriate tests vary depending on the parameters of concern to specific markets. Second, specific test methods have already published in other sources (see References), and would be too lengthy to duplicate here.

Implementation: A proper sampling and quality control testing program includes:

· sample procurement

· sample storage/handling

· testing

· feedback/corrective measures

Sample procurement. It is easy to take a sample incorrectly. Most importantly, combat sampling uncertainties by developing a standard method based on sound principles, consistently using standard methods, and documenting any adjustments caused by atypical conditions at the time of sampling.

Tailor standard sampling methods to each facility or situation, preferably taking advantage of occasions when material is being mixed or moved. The ideal sampling situation is to pull periodic samples from a conveyor belt or similar configuration, and to combine these samples. The goal is to create a final sample that is representative of the entire load or batch, rather than filling a scoop or bucket at one moment or place in a pile. Taking a single grab sample is inadequate, although taking several such grab samples and mixing them together (to form a composite sample) is an excellent sampling method.

Obtain those samples coming from a pile, rather than a moving conveyor, from several points within the pile. When sampling from piles, avoid the surface and instead dig into the pile from several directions to vary and combine samples. Least ideal is sampling from trucks (or rail cars, barges, etc.), especially if sampling is conducted after the material has been transported. Vibrations, air movement and other

impacts of transportation could settle the material by size and added or sorted contaminants from the exposed surfaces. Even without these problems, procuring representative samples of the full volume of contained material is difficult because of its limited access.

A defensible sampling methodology employs strategies that avoid biases and that spread a number of smaller samples over the course of a day or over the full volume of a pile. Pre-determination of a sampling frequency or sampling locations helps avoid biases. For instance, to generate a composite sample consisting from 20 to 30 gallons of material, when the sampling tools have a capacity of about 2 gallons, requires from 10 to 15 grab samples. Evenly spread these 10 to 15 samples during a day’s operation or evenly over a pile using a grid system. Use of a grid system involves visualizing a pile separated into a minimum of 6 sections. Generally, divide the pile in half along its long axis (i.e., visualizing a left and a right side). Then divide its length into 3 parts to create 6 sections. Conduct sampling by digging from 1 to 2 feet into the pile at the center of each section and then removing the sample.

For proper sampling technique, avoid taking samples from the following:

· Areas of a pile or conveyor belt where unusual materials are present, unless they are common.

· The very start or end of an operation, which may not be typical of the material being processed or its operating parameters. That is, the final material on a conveyor or pile may come from either the bottom of the stockpile, clean-up around processing equipment, or scraping the processed stockpile area. So, it may contain atypical particle sizes or contaminant levels.

· Situations where gravity or crosswinds may cause size grading.

Design the sampling process to produce significantly more material than is required for testing. The total volume of sample must then be mixed and reduced to quantities appropriate for testing, including possibly creating several sub-samples, which are allocated to different tests or shipped to different laboratories for testing. The process of dividing the sample must be done carefully to ensure that sub-samples are uniform and representative.

Conduct sample division using standard coning and quartering methods. To do this, all grab samples are placed on a plastic sheet and thoroughly mixed. After mixing, the corners of the sheet are lifted simultaneously, thus causing the sample to mound in the center of the sheet. The sample is divided into quarters, and two opposing quarters are removed and discarded. This process is repeated until the sample is approximately twice as large as needed. At that point, the last two quarters removed should be set aside for storage (see below) instead of being discarded. The remaining sample, which will be used for testing purposes, should be securely packaged and clearly labeled. Other sample division techniques, such as using a fabricated diverter box, can also be used.

Sample storage and handling. This Best Practice recommends that an extra sample be retained for six months in case questions arise as to a particular batch of material. Safe storage generally means storage in plastic bags or buckets, clearly labeled, and placed in a cool, dark spot. The sample may have to be dried before storage to prevent deterioration. Verify that the volume of stored sample is adequate for the full range of tests if additional testing is needed, for example, to settle a material quality dispute.

Testing. Specific test methods will vary depending on the market for a processed material. The required tests for material specifications and acceptable test methods should be confirmed with customers.

Feedback and corrective measures. A good sampling and testing program will document problems, provide quick and accurate feedback to the facility’s operators, allow testing of duplicate samples (if necessary), and prearrange resolution guidelines (i.e., price discounts and warning procedures).

Benefits: A comprehensive sampling and quality-control testing program helps a wood-waste processor to resolve problems with customers, while also demonstrating to their customers that they are serious about the quality of their product. Not only will this help win over new customers, but the type of problems that can be avoided by this approach will help retain existing customers.

Application Site: This Best Practice applies to wood-waste processing facilities and manufacturing sites.

Contact: For more information about this Best Practice, contact CWC (206) 443‑7746, e-mail info@cwc.org.

References:

1. ASTM D 4687-95, Standard Guide for General Planning of Waste Sampling.

2. ASTM D 5658-95, Standard Practice for Sampling Unconsolidated Waste from Trucks.

3. E&A Environmental Consultants. “Urban Wood Debris Characterization Study.” Clean Washington Center. Seattle, WA. 1997

4. Hlavka, Rick. Green Solutions, South Prairie, WA.

5. Smith, David C. CE/Western Engineering, Inc., Albany, OR.

6. Yeasting, John. ReSourcing Associates, Seattle, WA.

Issue Date / Update: March 1997