§ 784.20 - Subsidence control plan.

§ 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.

(iv) Peak-flow magnitude and frequency for perennial and intermittent streams within the proposed permit and adjacent areas.

(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.

(vii) The biology of perennial and intermittent streams within the proposed permit and adjacent areas, except as provided in § 784.19(g) of this part.

(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.

(iv) The predicted impact of the mine pool on the hydrologic balance of the proposed permit and adjacent areas after the mine pool reaches equilibrium.

(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.

(1) The regulatory authority must review each application for a permit revision to determine whether a new or updated PHC determination is needed.

(2) The regulatory authority must require that you prepare a new or updated PHC determination if the review under paragraph (c)(1) of this section finds that one is needed.

Subsidence control plan.

(a) Pre-subsidence survey. Each application must include:

(1) A map of the permit and adjacent areas at a scale of 1:12,000, or larger if determined necessary by the regulatory authority, showing the location and type of structures and renewable resource lands that subsidence may materially damage or for which the value or reasonably foreseeable use may be diminished by subsidence, and showing the location and type of drinking, domestic, and residential water supplies that could be contaminated, diminished, or interrupted by subsidence.

(2) A narrative indicating whether subsidence, if it occurred, could cause material damage to or diminish the value or reasonably foreseeable use of such structures or renewable resource lands or could contaminate, diminish, or interrupt drinking, domestic, or residential water supplies.

(3) A survey of the condition of all non-commercial buildings or occupied residential dwellings and structures related thereto, that may be materially damaged or for which the reasonably foreseeable use may be diminished by subsidence, within the area encompassed by the applicable angle of draw; as well as a survey of the quantity and quality of all drinking, domestic, and residential water supplies within the permit area and adjacent area that could be contaminated, diminished, or interrupted by subsidence. If the applicant cannot make this survey because the owner will not allow access to the site, the applicant will notify the owner, in writing, of the effect that denial of access will have as described in § 817.121(c)(4) of this chapter. The applicant must pay for any technical assessment or engineering evaluation used to determine the pre-mining condition or value of such non-commercial buildings or occupied residential dwellings and structures related thereto and the quantity and quality of drinking, domestic, or residential water supplies. The applicant must provide copies of the survey and any technical assessment or engineering evaluation to the property owner and regulatory authority. However, the requirements to perform a survey of the condition of all noncommercial buildings or occupied residential dwellings and structures related thereto, that may be materially damaged or for which the reasonably foreseeable use may be diminished by subsidence, within the areas encompassed by the applicable angle of draw is suspended per court order.

(b) Subsidence control plan. If the survey conducted under paragraph (a) of this section shows that no structures, or drinking, domestic, or residential water supplies, or renewable resource lands exist, or that no material damage or diminution in value or reasonably foreseeable use of such structures or lands, and no contamination, diminution, or interruption of such water supplies would occur as a result of mine subsidence, and if the regulatory authority agrees with this conclusion, no further information need be provided under this section. If the survey shows that structures, renewable resource lands, or water supplies exist and that subsidence could cause material damage or diminution in value or reasonably foreseeable use, or contamination, diminution, or interruption of protected water supplies, or if the regulatory authority determines that damage, diminution in value or foreseeable use, or contamination, diminution, or interruption could occur, the application must include a subsidence control plan that contains the following information:

(1) A description of the method of coal removal, such as longwall mining, room-and-pillar removal or hydraulic mining, including the size, sequence and timing of the development of underground workings;

(2) A map of the underground workings that describes the location and extent of the areas in which planned-subsidence mining methods will be used and that identifies all areas where the measures described in paragraphs (b)(4), (b)(5), and (b)(7) of this section will be taken to prevent or minimize subsidence and subsidence-related damage; and, when applicable, to correct subsidence-related material damage;

(3) A description of the physical conditions, such as depth of cover, seam thickness and lithology of overlaying strata, that affect the likelihood or extent of subsidence and subsidence-related damage;

(4) A description of the monitoring, if any, needed to determine the commencement and degree of subsidence so that, when appropriate, other measures can be taken to prevent, reduce or correct material damage in accordance with § 817.121(c) of this chapter;

(5) Except for those areas where planned subsidence is projected to be used, a detailed description of the subsidence control measures that will be taken to prevent or minimize subsidence and subsidence-related damage, such as, but not limited to:

(i) Backstowing or backfilling of voids;

(ii) Leaving support pillars of coal;

(iii) Leaving areas in which no coal is removed, including a description of the overlying area to be protected by leaving coal in place; and

(iv) Taking measures on the surface to prevent or minimize material damage or diminution in value of the surface;

(6) A description of the anticipated effects of planned subsidence, if any;

(7) For those areas where planned subsidence is projected to be used, a description of methods to be employed to minimize damage from planned subsidence to non-commercial buildings and occupied residential dwellings and structures related thereto; or the written consent of the owner of the structure or facility that minimization measures not be taken; or, unless the anticipated damage would constitute a threat to health or safety, a demonstration that the costs of minimizing damage exceed the anticipated costs of repair;

(8) A description of the measures to be taken in accordance with §§ 817.41(j) and 817.121(c) of this chapter to replace adversely affected protected water supplies or to mitigate or remedy any subsidence-related material damage to the land and protected structures; and

(9) Other information specified by the regulatory authority as necessary to demonstrate that the operation will be conducted in accordance with § 817.121 of this chapter.

[60 FR 16748, Mar. 31, 1995, as amended at 64 FR 71653, Dec. 17, 1999; 81 FR 93355, Dec. 20, 2016; 82 FR 54958, Nov. 17, 2017]