Section 61.252 - Standard(a) Each owner or operator of a conventional impoundment shall comply with the following requirements: (1) Radon-222 emissions to the ambient air from an existing conventional impoundment shall not exceed 20 pCi/(m2-sec) (1.9 pCi/(ft2-sec)) of radon-222 and all owners or operators shall comply with the provisions of 40 CFR 192.32(a)(1) in the operation of the impoundment notwithstanding the exemption for existing impoundments in 40 CFR 192.32(a)(1) .(2) After December 15, 1989, no new conventional impoundment may be built unless it is designed, constructed and operated to meet one of the two following management practices: (i) Phased disposal in lined impoundments that are no more than 40 acres in area and comply with the requirements of 40 CFR 192.32(a)(1) . The owner or operator shall have no more than two conventional impoundments, including existing conventional impoundments, in operation at any one time.(ii) Continuous disposal such that uranium byproduct material or tailings are dewatered and immediately disposed with no more than 10 acres uncovered at any time and shall comply with the requirements of 40 CFR 192.32(a)(1) .(b) Each owner or operator of a non-conventional impoundment shall comply with the following requirements: Non-conventional impoundments shall meet the requirements of 40 CFR 192.32(a)(1) . During operation and until final closure begins, the liquid level in the impoundment shall be maintained so that solid materials in the impoundment are not visible above the liquid surface, verified by daily inspections documented through notations and by digital photographic evidence collected at least weekly. Should inspection reveal that solid materials in the impoundment are visible above the liquid surface, the owner or operator must correct the situation within seven days, or other such time as specified by the Administrator.(c) Each owner or operator of a heap leach pile shall comply with the following requirements: Heap leach piles that have completed their operating life but have not yet entered final closure shall be managed in compliance with the phased disposal management practice in paragraph (a)(2)(i) of this section. Heap leach piles shall be constructed in lined impoundments that are no more than 40 acres in area and shall comply with the requirements of 40 CFR 192.32(a)(1) . The owner or operator shall have no more than two heap leach piles, including existing heap leach piles, subject to this subpart at any one time. 82 FR 5179 , Jan. 17, 2017