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Information about BinghamEtalWAFINAL

Published on December 4, 2007

Author: Maitane


INVESTIGATING EXTENT OF AN UNDERGROUND COAL MINE FIRE USING AIRBORNE INFRARED THERMOGRAPHY GEOREFERENCED TO LIDAR BASEMAP :  INVESTIGATING EXTENT OF AN UNDERGROUND COAL MINE FIRE USING AIRBORNE INFRARED THERMOGRAPHY GEOREFERENCED TO LIDAR BASEMAP John Bingham, P.E. - Hart Crowser Tim Ball, PhD - Fireball IT Ginger Kaldenbach - OSM Western Regional AML Project Manager Introduction:  Introduction Project Summary Local Geology/Mining Overview Project History Investigation Approach and Methods Lessons Learned Conclusions and Recommendations. Project Summary:  Problem: Venting steam from underground coal mine fire in county park Goal: Assist OSM in site investigation, subject to site constraints, and determine if remedial action was warranted Site Constraints/Concerns: Safety of park users & staff Potential for forest fire Maintain pristine nature of park Effective remedial measure(s) involve significant disturbance Unknown extent & severity underground mine fire Result: Monitor site to gather information until remedial measures appear warranted Project Summary Seattle Typical Steam Vents in Subsidence Pit :  Typical Steam Vents in Subsidence Pit Extent of Subsidence Steam Vent, Typ. Subsidence 40’ W x 20’ D Heavy vegetation Typical Geologic Cross Section (Looking West) :  Typical Geologic Cross Section (Looking West) Glacial soils 10’s ft. thick over coal bearing sandstone and shale Coal seam dips 35 to 40º to NNE 4 of 11 coal seams mined extensively Mined 1860’s to 1950’s Generalized Mine Cross Section A-A’ (Looking East):  Generalized Mine Cross Section A-A’ (Looking East) Typical mining used “Room & Pillar” methods No. 3 Seam ~10 ft. thick Bagley Seam ~15 ft. thick Poor mine map coverage in at site since different companies’ workings ended under site Project History:  Reported mine fires on the No. 3 and Bagley Seams 1890’s & 1950’s further south & west Band of fallen trees in areas with venting steam observed late 1990’s Mine workings ~50 to 100 years old below the areas of venting steam & expected to be mostly collapsed Project History Investigation Approach/Methods:  Investigation Approach/Methods Prepare Initial LiDAR Based Topography Map LiDAR basics LiDAR map Field Locate (GPS)/Inventory Features near and with Venting Steam Findings Prior to Infrared (IR) Survey Venting steam ~50 ft. NE of No. 3 Seam cropline (Dunrude) and coal seam ~40 ft. deep Elevated Ground Temperatures LiDAR and Steam Vents Map:  LiDAR and Steam Vents Map Mine Section A – A’ Temperature Profile T1-T2 LiDAR and Steam Vents Inset:  LiDAR and Steam Vents Inset Hillshade & elevation contours Steam vent and subsidence features Ground Temperature Profile T1 – T2 :  Ground Temperature Profile T1 – T2 Used 6 in. long soil thermometer probe Highest temperature at vent = 118º F Highest profile temperature ~76º F Ambient ground temperature ~50 º F Typical ignition temperatures for forest fuel ~300 º F Band of Fallen Trees Investigation Approach/Methods – Continued:  Investigation Approach/Methods – Continued IR Ground Surface Temperature Detection Methods IR Temperature Detection Basics Measurement of emitted heat energy in the infrared wavelength (~2 to 14 mm vs visible wavelength ~ 0.3 to 0.7 mm). Factors affecting IR detection: 1) heat source size, 2) distance from IR sensor to heat source, 3) if heat source is obscured from the IR sensor (i.e., vegetation, significant water vapor or dust in the air), and 4) emissivity. Fireball IT IR Temperature Detection System & Methods IR System: Helicopter with gimbal-mounted IR camera, DGPS, and INU to georeference IR data to LiDAR base map. IR System Calibration: In flight temperature targets, checked with GPS ground locations, and spot checked locations after the flight with hand-held IR camera. Steam Vents and Elevated Temperatures Map:  Steam Vents and Elevated Temperatures Map IR Survey Results: Temp. & locations generally similar to previously observations Elevated temp. coincide with No. 3 Seam outcrop Indicate new areas of elevated temp., but missed some small steam vents obscured by heavy vegetation See Inset Steam Vents and Elevated Temperatures Inset:  Steam Vents and Elevated Temperatures Inset Temp. Comparison: IR survey ground surface <80º F Handheld IR camera ground surface ~108º F Probe thermometer in ground ~118º F Near vent probe ground = 75º F & handheld IR camera surface = 67 º F Factors affecting IR detection yield ground surface temp. ~10º F < actual ground temp. (see lit.) IR survey is a baseline!! Lessons Learned:  Lessons Learned IR Investigation Lessons Learned It’s critical that the IR subconsultant achieve IR detection and mapping requirements. Several claimed to be able to georeference the IR data, but only Fireball IT could properly georeference the IR image. Fireball IT’s automatic (near real time) georeferencing system (~ < 10 ft. accuracy) malfunctioned the day of the flight. This required manual georeferencing IR imagery (accuracy ~ 10 to 30 feet) using the LiDAR base map. A preflight system check the day before the flight and a high altitude overview flight would improve accuracy, weather permitting. Lessons Learned – Continued:  Lessons Learned – Continued IR Detection and Typical OSM Coal-Mine Fire Reclamation Costs IR investigation costs: Fireball IT: Helicopter ~ $1,000/hr (in 2006) IR costs ~ $5,000/flight day (post processed). Typical coverage ~200 – 300 ac/hr, but ~10 – 30 ac/hr for multiple passes required due to terrain, vegetation, & weather. (~$14k this proj.) Hart Crowser costs depend on the project scope (~$27k this proj.) OSM coal mine fire reclamation costs (mostly eastern U.S.) from 2002 to 2004: Typical reclamation: earthwork to cut off air supply and/or excavation/quenching to eliminate fuel source and lower temperatures 0 to 10 acres of reclamation areas (not all mine fire) 150 to 30,000 cubic yards material involved $43,000/acre (average) up to $183,000/acre unit project cost Conclusions and Recommendations:  Conclusions and Recommendations Venting steam is an attractive nuisance & potential safety concerns include 1) falling into subsidence, 2) burns due to sudden ground collapse, 3) exposure to harmful gases, and 4) hazards not readily visible (see next slide). Potential risk for forest fire appears low based on current conditions including: Generally wet climate, Lack of highly flammable forest fuel, Ground temperatures < 120º F, and Ignition temperature for wood ~ 300 º F. However, sudden ground collapse resulting from the coal mine fire could lead to different conditions that could potentially start a forest fire. There is no certain way to predict risk of subsidence or ground collapse without significant disturbance required for exploration program. Hidden Hazards:  Hidden Hazards Typical park vegetation in area of steam vent. Same area as to left with a IR camera indicates the temperature extremes associated with this vent feature. Conclusions and Recommendations - Continued:  Conclusions and Recommendations - Continued Resolution: Monitor site to gain additional information until remedial measures appear warranted. The IR survey provides valuable baseline information for tracking how the underground mine fire may be changing. King County has performed some limited forest fuel cleanup around venting steam areas as a precautionary step. King County is monitoring visual, ground temperature, and ground stability changes to assess potential for subsidence or steam vents at critical areas. King County is also providing additional signage, public education of potential mine hazards, and educating emergency responders (e.g., fire department, etc.). Thank You Acknowledgements::  Acknowledgements: Tim Ball – Fireball IT | 775.848.4462 | Ginger Kaldenbach – OSM Mike Bailey – Hart Crowser My family for their patience while preparing this Contact information: John Bingham 206.324.9530

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