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shall not be installed by freefall unless the interval to be sealed is dry and no deeper than 30 feet below ground surface. 5. Ground Water Flow. Special care shall be used to restrict the flow of ground water into a well boring while placing material,where subsurface pressure causing the flow of water is significant. 6. Verification. It shall be verified that the volume of sealing material placed at least equals or exceeds the volume to be sealed. 7. Pressure. Pressure required for placement of sealing materials shall be maintained long enough for cement-based sealing materials to properly set." Section 10. Surface Construction Features. Subsection A, Item 5; Subsection B; and Subsection F (page 39 of Bulletin 74-81) have been changed. The remainder of Section 10 (page 36 of Bulletin 74-81) is unchanged. "A. Openings. 5. Bases. A concrete base or pad, sometimes called a pump block or pump pedestal, shall be constructed at ground surface around the top of the well casing and contact the annular seal, unless the top of the casing is below ground surface,as provided by Subsection B, page 23, below. The base shall be free of cracks, voids, or other significant defects likely to prevent water tightness. Contacts between the base and the annular seal,and the base and the well casing, must be water tight and must not cause the failure of the annular seal or well casing. Where cement-based annular sealing material is used, the concrete base shall be poured before the annular seal has set, unless otherwise approved by the enforcing agency. The upper surface of the base shall slope away from the well casing. The base shall extend at least two feet laterally in all directions from the outside of the well boring, unless otherwise approved by the enforcing agency. The base shall be a minimum of 4 inches thick. A minimum base thickness of 4 inches is normally acceptable for small diameter, single-user domestic wells. The base thickness should be increased for larger wells. Shape and design requirements for well pump bases vary with the size, weight, and type of pumping equipment to be installed,engineering properties of the soil on which the base is to be placed, and local environmental conditions. A large variety of base designs have been used. The Vertical Turbine Pump Association has developed a standard base design for large lineshaft turbine pumps. This design consists of a square,concrete pump base whose design is dependent on bearing weight and site soil characteristics. Where freezing conditions require the use of a pitless adapter,and the well casing and annular seal do not extend above ground surface or into a pit or vault,a concrete base or pad shall be constructed as a permanent location monument for the covered well. The base shall be 3 feet in length on each side and 4 inches in thickness, unless -22-