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The remaining upper part of the annulus is grouted to below the frost line. The grout pre- vents movement of ground water and surface water within the annular space between the well casing and borehole wall. It also maintains the structural integrity and alignment of the well casing. Drill cuttings removed from the borehole sometimes are used as grout instead of bento- nite or cement, but the effectiveness of these materials as a sealant needs careful evaluation and is not to be used for NAWQA wells. For NAWQA, bentonite, cement, or mixtures of ben- tonite and cement probably are the most common grout materials that will be used. Generally bentonite is recommended for grout if the well is used for water-quality sampling. However, as in the case of the underlying seal, the choice of a material depends on the purpose of the well. Detailed discussions of characteristics of annular seals and methods of placement can be found in ASTM (1992) and Driscoll (1986). The surface seal prevents surface runoff down the annulus of the well and, in situations in which a protective casing around the well is needed, holds the protective casing in place. The depth of installation of a surface seal can range from several feet to several tens of feet below land surface. Local regulatory agencies might specify a minimum depth of installation. Because of likely desiccation of bentonite, a cement surface seal is recommended. A protective casing should be installed around the well to prevent unauthorized access to the well and to protect the well from damage. The protective casing is installed at the same time as the surface seal and should extend to below the frost line (ASTM, 1992). One design for protective casing is a steel casing with vented locking protective cover and weep hole, which permits condensation to drain out of the annular space between the protective casing and well casings (fig. 4). ASTM (1992, p. 132) also calls for coarse sand or pea gravel or both to be placed in the annular space between the protective casing and the well to prevent entry of insects. A second design is a steel casing with bolted or locked manhole cover enclosing a well that is flush with the land surface. Well Development Wells drilled for the NAWQA Program should be developed to enhance flow of water to the well, to remove sediments that are artifacts of well installation, and to provide water rep- resentative of the unit being sampled. Developing a well mitigates artifacts associated with drilling, such as changes in aquifer permeability, sediment distribution, and ground-water chemistry. Redevelopment of a well can be necessary because of sedimentation in the well casing, or clogging of the aquifer or well screen. Development of a well is to be documented as discussed in the section "Documentation." Documentation includes: (1) the method of development; (2) equipment being used; (3) the volume of water removed; (4) a measure of the clarity of water removed from the well over 39