The document discusses key aspects of developing and implementing a Quality Assurance Project Plan (QAPP) for environmental sampling. It notes that a QAPP is required by the EPA to define the quality assurance program, and must be prepared and approved every four years. The QAPP is used to communicate, summarize, document, and audit the sampling process. Proper sample collection, handling, preservation, custody documentation and approved analytical methods are essential elements of quality assurance, along with standard operating procedures, certification programs, proficiency testing, data validation, and audits.