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samples and related data (Koterba and others, in press), the NAWQA Program design (Gilliom and others, 1995; Alley and Cohen, 1991), the conceptual framework of the NAWQA Program (Leahy and Wilber, 1991 a and b; Hirsch and others, 1988; Cohen and others, 1988), an imple- mentation plan for the NAWQA Program (Leahy and others, 1990), and a description of a quality-assurance plan for the NAWQA Pilot Program (Mattraw and others, 1989). For the purposes of this report, a protocol identifies a course of action that is mandatory under most circumstances as a consequence of USGS and NAWQA policies. For example, decontaminating equipment according to prescribed methods between uses to avoid cross- contamination of the aquifer is a protocol. A recommended procedure is one that generally is preferred over other procedures that are available or commonly used. A recommended procedure generally conforms to rules for good field practices and is expected to result in reproducible data of desired and defined quality. Recommended procedures are not protocols because they either are too restrictive or possibly inappropriate in some situations. For example, one recommended procedure is to measure the water level in the well before sampling. This is not possible for many water-supply wells. Although modifications to methods are likely as new technologies evolve, the described protocols and recommended procedures reflect methods of data collection and documentation generally considered capable of reproducing data of known quality that are suitable for assess- ment, yet feasible to employ given limitations of time and funds. Their use also promotes consis- tency and comparability of ground-water data among Study Units in the NAWQA Program. Overview of National Water-Ouality Assessment Program The USGS began full-scale implementation of the NAWQA Program in 1991. The goals of the NAWQA Program are to: (1) provide a nationally consistent description of current water- quality conditions for a large part of the Nation's water resources; (2) define long-term trends in water quality; and (3) identify, describe, and explain, as possible, the major factors that affect observed water-quality conditions and trends (Hirsch and others, 1988). The design concepts of the NAWQA Program are based in part on a pilot program that be- gan in 1986. The NAWQA Pilot Program consisted of water-quality assessment in seven study areas. These study areas were distributed geographically throughout the continental United States and represented diverse hydrologic environments and water-quality conditions. Four of the pilot assessments focused on surface water and three focused on ground water. The ground- water pilot study areas were the Carson River Basin in Nevada and California (Welch and Plume, 1987); the Central Oklahoma Aquifer in Oklahoma (Christenson and Parkhurst, 1987); and the Delmarva Peninsula in Delaware, Maryland, and Virginia (Bachman and others, 1987). The NAWQA Program design that has evolved from the pilot program consists of two ma- jor components: (1) Study-Unit Investigations of both surface and ground water and (2) National Synthesis activities. The design provides information on water quality for policy makers and managers at local, State, regional, and national scales. Investigations of 60 Study Units, which range in area from 1,200 to more than 60,000 square miles, are ongoing or planned. The 60 Study Units include parts of most of the major river 2