Tremendous improvements in ground-water sampling methodologies and analytical technologies have made it possible to collect and analyze truly representative samples to detect increasingly lower levels of contaminants-now in the sub-parts-per-billion range. Though these new methods produce more accurate and precise data and are less expensive, many

Groundwater monitoring is a complex undertaking. Cost-effective monitoring relies on careful planning and critical reading of the scientific literature. These activities will ensure that the application of well placement, construction, sampling, and analytical procedures result in the collection of high-quality data. The information needs of each program must be recognized and all subsequent monitoring network design and operation decisions must be made in light of the available data. In this sense, monitoring is an evolutionary process which should be refined as the information base expands.