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Streams and Longwall Coal Mining Subsidence: A Pennsylvania Perspective Anthony T. Iannacchione, engineer (mining) Stephen J. Tonsor, biologist (ecology)

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Presentation on theme: "Streams and Longwall Coal Mining Subsidence: A Pennsylvania Perspective Anthony T. Iannacchione, engineer (mining) Stephen J. Tonsor, biologist (ecology)"— Presentation transcript:

1 Streams and Longwall Coal Mining Subsidence: A Pennsylvania Perspective Anthony T. Iannacchione, engineer (mining) Stephen J. Tonsor, biologist (ecology) Associate Professors, University of Pittsburgh

2 The Question Can We Conduct Underground Coal Mining and Protect PA Streams? Full extraction mining impacts water sources, perhaps most importantly surface streams Can we subject streams and associated systems (springs, wetlands, ponds, etc.) to subsidence and not diminish their value to society? Pavilion b)a) Stream control Stream pooling

3 The University of Pittsburgh Conducted the 3 rd ACT 54 Report Released in January of 2011

4 3 rd Assessment Report (on the PA DEP website) Topics o Stream and Wetlands o Water Supplies (Thursday presentation) o Structures (Thursday presentation) o Land o I79 (presented at last years conference)

5 Many opinions exist, some are extreme and polarizing Prepared for: Citizens Coal Council 605 Taylor Way Bridgeville, PA The Increasing Damage from Underground Coal Mining in Pennsylvania A Review and Analysis of the PADEPs Third Act 54 Report Kitty Werthmann equated the modern environmental movement to Communism, declaring that green is the new red.

6 Story Background LW mining can contaminate and diminish stream waters and impair the biological character of plant and animal communities living in the streams PA regulations require action by mining companies to repair impacts The engineering solutions to comply with these standards are fundamentally affected by topics covered in the conference, e.g. geologic discontinuities, in-situ stress conditions, mining process, etc. Geologists, biologists, and engineers are all playing a pivotal role in developing prevention controls and recovery measures necessary to protect streams and sustain underground coal mining

7 Pennsylvanias Subsidence Standards PA has the most far-reaching subsidence regulations and standards in the U.S. (maybe the world) The Bituminous Mine Subsidence and Land Conservation Act (BMSLCA) of 1966

8 Run-up to ACT the Deep Mine Mediation Project brought together the underground bituminous coal industry, agricultural, and Non- Governmental Organizations (NGOs) for the purpose of attaining a consensus position on the BMSLCA. Three years later, consensus was achieved to address: – Impaired water supplies must be replaced – Mine discharges must be treated – Incentives for re-mining previously mined areas – Relaxation of regulatory obstacles to full extraction, i.e. longwall and pillar recovery mining

9 Essence of ACT 54 ACT 54 signed into law in 1994 Initially provisions focused on repairing structural damage: – Repair or compensate for subsidence damage to public building, dwellings used for human habitation, permanently affixed pertinent structures, and certain agricultural structures – Entitled the structure owner or occupant to payments for temporary relocation and other incidental expenses – Pre-mining surveys by mine operators were allowed – Voluntary agreements between mining operators and land owners – Permitted underground mining beneath any structure as long as the consequential damages are not irreparable and are mitigated. There were exceptions… – Stipulated that irreparable damage can only occur with the consent of the owner

10 Enhancements to ACT 54 Surface land Water sources, both wells and springs Streams, wetlands, and ponds Utilities Public infrastructure

11 The 2005 Technical Guidance Document for Stream and Wetlands Implemented in 2005 Outlines how to measure potential impairments to streams and wetlands Biological integrity => total biological score (100-m stream segments) Impairment of streams is now measured by water diminution and contamination and biologic diversity

12 High Quality Stream Incident The Pa Environmental Hearing Board decided that the tributary streams over the mines 4E, 5E and 6E panels were a valuable resource and deserved protection Restrict longwall mining beneath the 6E tributary in 2005 PennFuture and the UMWA intervened 6E panel 6E unnamed stream

13 What factors are important in the High Quality case Very low overburden Considerable damage to stream over 4E and 5E panel Companies reliance on using city water to augment flow

14 The University of Pittsburgh Reported 55 Stream Investigations conducted by the PA DEP from 2003 to 2008 Resolution StatusNumber Final: Resolved18 Final: Not Due to Underground Mining2 Interim: Not Yet Resolved35 Total55 Pitt Biologist => over 20 streams TBS using TDG protocols

15 Pitt biologists conducting field work to determine the Total Biological Scores (TBS) of undermined streams Approximately 8 hours of laboratory work to identify species / genius of life forms is needed for every 1 hour of field work b) a) c) Observational surveys exam flow conditions Kick test captures benthic macro-invertebrate species

16 Threats to Streams 1) Tension cracks - disrupting aquifers and streams Tension cracks are ubiquitous in the strata over longwall panels Most common above the longwall panel mining horizon Lessen as overburden increases Formed as the longwall face passes underneath Typically develop in a non-violent fashion On rare occasions can form in as rapid release of energy Most are relatively small in scale (a few meters in length) The largest are typically curvilinear and can extend for tens of meters Some remain open after the longwall panel has been mined Can intercept perched aquifers Can cause loss of flow within a stream

17 Examples of tension cracks d) a) b)c) Crack extending 30 m Dry stream bed Flow entering crack Cracks in flowing stream

18 Geologic controls Fractures are less damaging when the stream bed stratum is comprised of cohesive soils or clay-shale rock layers Clayey soil and rock at the stream bed level can enter and fill the fractures

19 Engineering Controls – stream grouting to prevent water loss in streams with tension fractures b) a) Boreholes are drilled and clay or grout pumped into fractures Stream flow must be collected and diverted around the area where grouting will occur, and then Substances injected include: clay, cement-based mixtures, epoxies or urethanes

20 Engineering Controls - Geo-fabric to prevent water loss in streams with tension fractures b) a) d)c) Stream bed preparation Geo-fabric anchoring system Habitat controls Covering the geo-fabric

21 Springs in Headwater Stream Areas Headwaters = first order stream (water flow is ephemeral and the channels are dry during parts of the year) Contain springs, wetlands, ponds or lakes that may flow for portions of the year when precipitation or snowmelt is high Disruption of water flow from any of the headwater springs can create periodic dry segments and affect the stream ecology In PA, impairment of macro-invertebrate communities can violate permit requirements

22 Perched aquifers and loss of headwater springs Lower aquifers often produce springs further down the streams gradient and away from the headwater area. Recharge Area Discharge Area Spring Headwater Area Decrease flow from upper spring Increase flow from low spring

23 Engineering Controls - stream augmentation c) a) b) Water wells are drilled near the affected stream Water is pumped from the well to the stream during dry periods Large capacity storage facilities are used to distribute water to distant points of need Occasionally water from municipal sources has been used to augment flow

24 Subsidence Basins Alter Stream Gradients Little stream subsidence over gate entries Significant stream subsidence (1.4 m) over the middle of the longwall panel Stream beds up-grade from the underlying gate entries are reduced in elevation relative to the gate portion, inducing water pooling Potentially to flood previously dry land Stream over the gate entries are more likely to develop dry sections Flow Direction Increased Ripple Structures Pooling Section Observation Points

25 Example of stream pooling Sedimentation observed south of a longwall panel during mitigation work to relieve pooling in the panel Pooling observed during a post-mining survey of stream 41246, Robinson Run

26 Engineering Controls – gate cutting Both Alpha and Consol are using gate cutting to re-establish pre-mining stream gradients Consist of reducing the elevation of the stream over the gate entries concordant with the areas of greatest subsidence in the adjacent panel

27 Engineering Control – Gate Cutting First – divert stream flow c) a) b) Large capacity pumps Large diameter flexible water conduits Discharge points protected with rip-rap

28 Next - Altering the stream gradient c) a) b) Clearing debris from the stream Ripping and breaking stream bedrock Re-grading the stream channel

29 Lastly – restore stream ecology and stabilizing stream banks c) a) b) Establishing habitats with in-stream structures Bank stabilization to reduce erosion Post-restoration stream restored to standards that will sustain future use

30 Stream Compression Ruptures and Horizontal Stress Cause water loss due to deep stream bed strata fractures Often propagate the entire length of dry sections Similar to cutter roof failure, buckled strata Northeast trending steep-sided stream valleys Weathering quickly Frequently in stiff rocks Can fail violently

31 Examples of compression ruptures Upside-down teepee structures Ruptures found along Polly Hollow, Greene County

32 Location of stream segments with compression ruptures (thick red lines) above the Bailey mine Water wells are drilled near the affected stream

33 Other stream compression ruptures orientations Bulldog Run (Blacksville No. 2 Mine) oriented north-northeast, Tributary to Rock Run (Enlow Fork Mine) oriented north- northwest, Tributary to Templeton Fork (Enlow Fork Mine) oriented north- northwest, Dutch Run over Panels 52 and 53 (Cumberland Mine) oriented north- northwest, Dyers Fork over Panels 52 and 53 (Cumberland Mine) oriented northwest.

34 Probable cause Stream valleys in western Pennsylvania contain elevated levels of horizontal stresses Is elevated by valley shape, stream orientation and stiff strata Pushed to failure when longwall mining temporarily concentrate stresses

35 Summary ACT 54 = robust requirement for protecting streams effected by mine subsidence In 2005 the PA DEP implemented enhanced standards to protect streams from diminution, contamination and biologic impairment The mining industry was given two years to implement these new standards (2007) Four significant threats: a) tension cracks, b) springs in headwater stream areas, c) stream gradients and subsidence basins, and d) stream compression ruptures and horizontal stress. PA DEP continues to refine its implementation of the TGD

36 Conclusions The mining industry has implemented numerous engineering controls Control measures = best scientific and engineering methods available PAs regulations are striving to make underground bituminous coal mining more sustainable To date, the results are mixed (35 of 55 stream investigations remain unresolved) Many are likely to eventually be resolved Many will require intervention for greater than 2-years post- undermining for resolution Some streams may never fully recover flow This has become a significant financial burden for the companies PAs mining laws and regulations, while improving, may not have yet achieved the required protection of the environment

37 Authors Opinion This review demonstrates the increasing level of effort by mining companies to protect PAs streams New intervention techniques are being introduced regularly The most challenging problems can be solved by a combination of increased accuracy in prediction of mining effects, continued engineering innovations and collaborative efforts of mining companies and regulators The standards for protecting PAs streams are indeed high, but if mining companies are able to attain a resolution to nearly all of these streams impacted by longwall mining, then clearly this industry will be viewed as one that can sustain the environment while complying with societal expectations This is no small feat and could help to ensure sustainable longwall mining in the future

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