Streams and Longwall Coal Mining Subsidence: A Pennsylvania

Perspective

Anthony T. Iannacchione, engineer (mining)Stephen J. Tonsor, biologist (ecology)

Associate Professors, University of Pittsburgh

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 controlStream pooling

The University of Pittsburgh Conducted the 3rd ACT 54 Report

Released in January of

2011

3rd Assessment Report (on the PA DEP website)

• Topicso Stream and Wetlandso Water Supplies (Thursday presentation)o Structures (Thursday presentation)o Lando I79 (presented at last year’s conference)

Many opinions exist, some are extreme and polarizing

Prepared for:Citizens Coal Council

605 Taylor WayBridgeville, PA 15017

412-257-2223www.citizenscoalcouncil.org

The Increasing Damagefrom

Underground Coal Miningin Pennsylvania

A Review and Analysis ofthe PADEP’s Third

Act 54 Report

Kitty Werthmann equated the modern environmental movement to Communism, declaring that “green is the new red.”

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

Pennsylvania’s 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

Run-up to ACT 54

• 1986 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

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

Enhancements to ACT 54

• Surface land• Water sources, both wells and springs• Streams, wetlands, and ponds• Utilities• Public infrastructure

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

High Quality Stream Incident• The Pa Environmental Hearing Board decided that the tributary

streams over the mine’s 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

600

500

400

20

0

4 East

5 East

3 East

2 East¹

0 0.2 0.40.1 Miles6E panel

6E unnamed stream

What factors are important in the High Quality case

100

600

10

0

50040

0

400

40

020

0

Tri

b 3

98

15

To

Ma

ple

Cre

ek

4 East

5 East

3 East

2 East¹

0 0.2 0.40.1 Miles

• Very low overburden

• Considerable damage to stream over 4E and 5E panel

• Companies reliance on using ‘city water’ to augment flow

The University of Pittsburgh Reported 55 Stream Investigations conducted by the PA DEP from 2003 to

2008

Resolution Status Number

Final: Resolved 18

Final: Not Due to Underground Mining 2

Interim: Not Yet Resolved 35

Total 55

Pitt Biologist => over 20 streams TBS using TDG protocols

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 conditionsKick test captures benthic

macro-invertebrate species

Threats to Streams1) 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

Examples of tension cracks

d)a) b) c)

Crack extending

30 m

Dry stream

bed

Flow entering crack

Cracks in flowing stream

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

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

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

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

Perched aquifers and loss of headwater springs

Lower aquifers often produce springs further down the stream’s gradient and away from the headwater area.

Ridge Line

Recharge Area

Discharge Area

Spring

Headwater Area

Aquifer

Flow

Flow

Decrease flow from

upper spring

Increase flow from low spring

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

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

Longwall Panel

Longwall Panel

Gate Entries

Increased Ripple Structures

PoolingSection

Observation Points

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

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

Engineering Control – Gate Cutting

First – divert stream flowc)a) b)

Large capacity pumps

Large diameter flexible water

conduits

Discharge points protected with

rip-rap

Next - Altering the stream gradient

c)a) b)

Clearing debris from the stream

Ripping and breaking stream bedrock

Re-grading the stream channel

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

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

Examples of compression ruptures

Upside-down teepee structures

Ruptures found along Polly Hollow, Greene County

Location of stream segments with compression ruptures (thick red lines) above the Bailey mine

Water wells are drilled near the affected stream

Other stream compression ruptures orientations

• Bulldog Run (Blacksville No. 2 Mine) oriented north-northeast,• Tributary 32721 to Rock Run (Enlow Fork Mine) oriented north-

northwest,• Tributary 32740 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.

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

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

Conclusions• The mining industry has implemented numerous engineering controls • Control measures = best scientific and engineering methods available• PA’s 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• PA’s mining laws and regulations, while improving, may not have yet

achieved the required protection of the environment

Author’s Opinion• This review demonstrates the increasing level of effort by mining

companies to protect PA’s 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 PA’s 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