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D5495-21 – Standard Test Method Technical Guide
🎯 Purpose and Operation of the COLIWASA
The Composite Liquid Waste Sampler (COLIWASA) is a specialized tube-style device used to obtain a representative vertical column of liquid from waste containers. As established in ASTM D5495-21, this sampler is designed to penetrate stratified or unstratified liquids in tanks, barrels, and drums, providing an accurate cross-section of the material. The standard emphasizes that the device is operated by lowering a clean, open tube slowly into the liquid. Once the tube is filled, the bottom stopper mechanism is closed, securing the sample, and the device is retrieved for discharge into a sample container. This method is specifically intended for stagnant or containerized liquids only.
⚙️ Procedure Details and Critical Constraints
Proper execution of the sampling procedure is critical for data quality. The device must be lowered at a controlled rate to avoid disturbing the stratification of the liquid layers. Upon retrieval, the entire captured vertical column is transferred to the sample container. A fundamental geometric constraint of the COLIWASA is documented in Note 1 of the standard: the stopper mechanism generally prevents the collection of approximately the bottom 2.54 cm (1 in.) of the material. Users must therefore employ alternative sampling methods if analysis of this bottom layer is required. The standard strictly prohibits the use of the COLIWASA for sampling flowing or moving liquids. All observed and calculated values must conform to the significant digit guidelines established in Practice D6026.
⚠️ Important Constraint: The inherent design of the stopper mechanism creates a dead zone. Always factor in the inability to sample the bottom 2.54 cm (1 in.) of a container when using a standard COLIWASA.
🚫 Prohibited Use: ASTM D5495-21 Section 1.2 explicitly forbids using the COLIWASA for sampling flowing or moving liquids. Doing so will not only produce a non-representative sample but may also pose significant safety risks.
📊 Quality Framework and Referenced Standards
The reliability of the sampling event relies heavily on a comprehensive quality management system. D5495-21 integrates several key ASTM standards to ensure the sampling process is valid. The following tables summarize the core technical parameters and the supporting standards required for a compliant sampling operation.
| 🟦 Technical Parameter | 📐 Specification |
|---|---|
| Sample Type | Stratified or unstratified stagnant liquids |
| Target Containers | Tanks, barrels, drums, open pools |
| Bottom Sampling Gap | Approx. 2.54 cm (1 in.) due to stopper |
| Prohibited Application | Flowing or moving liquids |
| Unit Systems | SI units regarded as standard |
| 🎯 Standard Designation | ⚡ Relevance to COLIWASA Sampling |
|---|---|
| D4687 | General planning for waste sampling operations |
| D5088 | Decontamination of field equipment used at waste sites |
| D5283 | QA/QC planning for environmental data generation |
| D5743 | Sampling single or multilayered liquids in drums |
| D6232 | Selection of appropriate sampling equipment |
❓ Frequently Asked Questions
🔍 What is the primary purpose of a COLIWASA?
The COLIWASA is designed to obtain a representative vertical column of liquid from a container, providing an accurate cross-section of stratified or unstratified liquid wastes for analysis.
💡 What is the main limitation regarding the bottom of a sample container?
The stopper mechanism at the bottom of the COLIWASA tube typically prevents the collection of the bottom 2.54 cm (1 in.) of the liquid. This must be considered in the sampling plan.
⚡ Can a COLIWASA be used to sample a flowing river or a pipe?
No. Section 1.2 of D5495-21 strictly prohibits the use of the COLIWASA for sampling flowing or moving liquids. It is only valid for stagnant or containerized liquids.
📌 Which standard governs the reporting of significant digits for this practice?
Per Section 1.3 of D5495-21, all observed and calculated values must conform to the guidelines established in Practice D6026, Standard Practice for Using Significant Digits in Geotechnical Data.