43 CFR §3809.580

1. (a)If you modify a notice or an approved plan of operations under § 3809.331 or § 3809.431 respectively, and your estimated reclamation cost increases, you must increase the amount of the financial guarantee to cover any estimated additional cost of reclamation and long-term treatment in compliance with § 3809.552.
2. (b)If you modify a notice or an approved plan of operations under § 3809.331 or § 3809.431 respectively, and your estimated reclamation cost decreases, you may request BLM decrease the amount of the financial guarantee for your operations.