Over the past few years, several cases have resulted in Daubert challenge rulings that are affecting the standards of practice and gradually providing guidance on what is required for the bases of opinions of testifying geoscience experts. Our initial paper on this subject was presented at the NGWA’s Chicago Conference, 2004. This paper is an extension of this subject and will provide a summary of the types of opinions testifying experts are presenting and current rulings, some published and some not, that have limited the scope of the opinions that are being offered. These rulings can be used to develop some guidelines that if followed will generally allow a testifying expert to withstand many Daubert challenges and provide more credible opinions when needed

Daubert affects the scoping process for developing opinions, the language applied in opinion statements, and, most importantly, the bases required to support the opinions offered. Examples of the areas about which geoscience experts may be qualified to provide expert testimony include: ground-water supply studies, water well and monitoring well designs and adequacy of completions, aquifer characteristics and prediction of likely yields and usability of ground water, scope of site investigations and historical practice regarding site investigation practices and typical flaws associated with site investigation procedures and interpretation of site analytical data, choice of remedial measures, and a host of other areas. We will also present examples of what is expected to be required for a geoscientist to offer opinions in any area based on examples of Daubert challenges and rulings.