30 CFR 784.20 - How must I prepare the determination of the probable hydrologic consequences of my proposed operation (PHC determination)?
(a)Content of PHC determination. Your permit application must contain a determination of the probable hydrologic consequences of the proposed operation upon the quality and quantity of surface water and groundwater and, except as provided in § 784.19(g) of this part, upon the biology of perennial and intermittent streams under seasonal flow conditions for the proposed permit and adjacent areas. You must base the PHC determination on an analysis of the baseline hydrologic, geologic, biological, and other information required under § 784.19 of this part. It must include findings on:
(1) Whether the operation may cause material damage to the hydrologic balance outside the permit area.
(2) Whether acid-forming or toxic-forming materials are present that could result in the contamination of surface water or groundwater, including, but not limited to, a discharge of toxic mine drainage after the completion of land reclamation.
(3) Whether underground mining activities conducted after October 24, 1992, may result in contamination, diminution or interruption of a well or spring within the permit or adjacent areas that was in existence when the permit application was submitted and that is used for domestic, drinking, or residential purposes.
(4) Whether the proposed operation will intercept aquifers in overburden strata or aquifers in underground mine voids (mine pools) or create aquifers in spoil placed in the backfilled area and, if so, what impacts the operation would have on those aquifers, both during mining and after reclamation, and the effect of those impacts on the hydrologic balance.
(5) What impact the proposed operation will have on:
(i) Sediment yield and transport from the area to be disturbed.
(ii) The quality of groundwater and surface water within the proposed permit and adjacent areas. At a minimum, unless otherwise specified, the finding must address the impacts of the operation on both groundwater and surface water in terms of the parameters listed in § 784.19(a)(2) of this part and any additional water quality parameters that the regulatory authority determines to be of local importance.
(iii) Flooding and precipitation runoff patterns and characteristics.
(v) Seasonal variations in streamflow.
(vi) The availability of groundwater and surface water, including the impact of any diversion of surface or subsurface flows to underground mine workings or any changes in watershed size as a result of the postmining surface configuration.
(viii) Other characteristics as required by the regulatory authority.
(6) What impact subsidence resulting from the proposed underground mining activities may have on perennial and intermittent streams.
(7) Whether the underground mine workings will flood after mine closure and, if so, a statement and explanation of -
(i) The highest potentiometric surface of the mine pool after closure.
(ii) Whether, where, and when the mine pool is likely to result in a surface discharge, either via gravity or as a result of hydrostatic pressure.
(iii) The predicted quality of any discharge from the mine pool.
(v) The potential for a mine pool blowout or other hydrologic disturbances.
(vi) The potential for the mine pool to destabilize surface features.
(vii) The potential impact of roof collapses on mine pool behavior and equilibrium.
(b)Supplemental information. You must provide any supplemental information that the regulatory authority determines is needed to fully evaluate the probable hydrologic consequences of the proposed operation and to plan remedial and reclamation activities. This information may include, but is not limited to, additional drilling, geochemical analyses of overburden materials, aquifer tests, hydrogeologic analyses of the water-bearing strata, analyses of flood flows, or analyses of other characteristics of water quality or quantity, including the stability of underground mine pools that might be affected by the proposed operation.
(c)Subsequent reviews of PHC determinations.
- 30 CFR 784.21 — What Requirements Apply to Preparation, Use, and Review of the Cumulative Hydrologic Impact Assessment (CHIA)?
- 30 CFR 784.19 — What Baseline Information on Hydrology, Geology, and Aquatic Biology Must I Provide?
- 30 CFR 784.23 — What Information Must I Include in Plans for the Monitoring of Groundwater, Surface Water, and the Biological Condition of Streams During and After Mining?
- 30 CFR 784.29 — What Information Must I Include in the Surface-Water Runoff Control Plan?
- 30 CFR 784.22 — What Information Must I Include in the Hydrologic Reclamation Plan and What Information Must I Provide on Alternative Water Sources?
- 30 CFR 783.26 — May I Submit Permit Application Information in Increments as Mining Progresses?