30 CFR § 817.57 - Hydrologic balance: Stream buffer zones.
(a) No land within 100 feet of a perennial stream or an intermittent stream shall be disturbed by underground mining activities, unless the regulatory authority specifically authorizes underground mining activities closer to, or through, such a stream. The regulatory authority may authorize such activities only upon finding that—
(1) Underground mining activities will not cause or contribute to the violation of applicable State or Federal water quality standards and will not adversely affect the water quantity and quality or other environmental resources of the stream; and
(2) If there will be a temporary or permanent stream-channel diversion, it will comply with § 817.43.
(b) The area not to be disturbed shall be designated as a buffer zone, and the operator shall mark it as specified in § 817.11.