In landfills suspected of threatening groundwater, risk assessments must be conducted. They are crucial in determining whether remediation is necessary. The risk assessment also serves as the basis for the groundwater monitoring plan, which is established for the long-term monitoring of contaminated sites. Years of practical work in risk assessment, evidence preservation, and remediation-related investigations have shown that the methods of classical hydrogeology, developed for groundwater exploration studies, are insufficient for groundwater protection. This book therefore presents methods for the exploration, evaluation, and assessment of hydrogeological techniques that have been developed in the context of work on contaminated sites and landfills.