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Cement-based sealing material shall be placed between the outer walls of the vault and the excavation into which it is placed to form a proper,structurally sound foundation for the vault, • and to seal the space between the vault and excavation. Bentonite-based sealing material may be used between the vault and excavation at the approval of the enforcing agency. Sealing material surrounding a vault shall extend from the top of the annular seal to ground surface,unless precluded in areas of freezing. If cement-based sealing material is used for both the annular seal and the space between the excavation and vault,the sealing material shall be placed in a "continuous pour." In other words, cement-based sealing material shall be placed between the vault and excavation and contact the cement-based annular seal before the annular seal has set. The vault cover or lid shall be watertight but shall allow the venting of gases,unless otherwise approved by the enforcing agency. The lid shall be fitted with a security device to prevent unauthorized access. The lid shall be clearly and permanently marked "MONITORING WELL." The vault and its lid shall be strong enough to support vehicular traffic where such traffic might occur. The top of the vault shall be set at or above grade so drainage is away from the vault. The top of the well casing contained within the vault shall be covered in accordance with requirements under Subsections A and B, above, so that water, contaminants, or pollutants that may enter the vault will not enter the well casing. F. Protection From Vehicles. Protective steel posts, or the equivalent,shall be installed around a monitoring well casing where it is terminated above ground surface in areas of vehicular traffic. The posts shall be easily seen and shall protect the well from vehicular impact. Additional requirements for surface construction features are in Section 10 of the Water Well Standards. '' Section 11. Filter Pack Monitoring well filter pack material shall consist of nonreactive,smooth,rounded,spherical,granular material of highly uniform size and known composition. Filter pack material shall not degrade or consolidate after placement. The grain-size of the filter pack shall be matched to the slot size of the well screen so that any movement of filter pack material into the well will be limited to prevent significant voids in the filter pack that could ultimately destabilize the annular seal. Filter pack material shall be obtained from clean sources. Filter pack material should be washed and properly packaged for handling,delivery,and storage,if used in monitoring wells constructed for sensitive water quality determinations. Care should be exercised in the storage of filter pack materials at a drilling site to ensure the material does not come into contact with pollutants or contaminants. Care should also be exercised to prevent the introduction of foreign substances,such as clay or vegetative matter, that might interfere with the placement and function of the filter pack. Filter pack material shall be placed in the well boring by use of a tremie pipe or equivalent. The depth of the top of the filter pack shall be carefully checked and the volume of emplaced filter pack material verified to determine that filter pack materials have not bridged during installation. -46-