30 Tex. Admin. Code § 37.151
An owner or operator may request that the executive director approve a decrease in the current cost estimate. The revised current cost estimate must be approved by the executive director. Whenever the revised current cost estimate decreases to an amount less than the amount being provided in the financial assurance mechanism(s), the owner or operator may submit a written request for a reduction in the amount of the financial assurance to the executive director. Following written approval by the executive director, the amount of the financial assurance may be reduced to the amount of the revised current cost estimate. An owner or operator may simultaneously request the executive director's approval of both a revised current cost estimate and a reduction in the amount of the financial assurance.
30 Tex. Admin. Code § 37.151