(1) Vibrating wire piezometers shall be sealed using materials as allowed in WAC 173-160-450; or sealing materials as designed and recommended by the manufacturer provided that the material, when placed, provides a permeability of 1 x 10-7 cm/sec or less. The licensed driller or engineer shall provide documentation from the manufacturer demonstrating that the sealing material meets the permeability requirements of this section.

(2) The use of bentonite products intended for use as drilling fluids, low solids content bentonite mixtures, fly ash, and hydrated lime are prohibited as additives or sealants.