The purpose of this project was to: 1) validate sample collection methods and procedures that minimize variability in groundwater monitoring results; and 2) validate improved methods to optimize monitoring frequency and assess long-term concentration trends that better account for short-term variability in groundwater monitoring results. All three objectives of the project were met. The demonstration results indicated that the sample method (except active no purge) has only a modest impact on monitoring variability and concentration, suggesting sampling methods should be selected based on factors such as cost, ease of implementation, and sample volume requirements rather than concerns regarding data quality. At both sites, low flow standard (purging to parameter stability) and low flow alternative (small volume) showed the lowest variability. The results were consistent between the two sites except for the active no purge (HydraSleeve) method, which was more variable at the California site than the Texas site. Low flow small volume purge and passive no-purge (SNAP sampler) were the two best sampling methods based on the combined goals of minimizing monitoring cost and minimizing variability in monitoring results.