Formerly WEF/ABC Certification Study Guide for Wastewater Treatment Personnel, this newly revised and expanded version of the best-selling WEF/ABC publication is designed to help operators prepare more effectively for certification exams. Includes 240 questions based on validated need-to-know criteria for four skill levels (Operator Level I - IV). For each of the seven need-to-know criteria, the Guide provides: Need-to-know matrix, suggested topics for study, sample questions referenced to specific technical sources, practice with math problems in both metric and English units and feedback including detailed solutions for math problems.