APPENDIX L: FYFE REPORT ON QCLNG PROJECT SOIL SUBSIDENCE MONITORING SURVEY

Transcription

1 Surat North Water Monitoring & Management Plan QGC APPENDIX L: FYFE REPORT ON QCLNG PROJECT SOIL SUBSIDENCE MONITORING SURVEY Page 199 of 199

2 QCLNG PROJECT SOIL SUBSIDENCE MONITORING SURVEY PREPARED BY Fyfe Pty Ltd ABN ADDRESS 84B Hypatia Street, Chinchilla Qld 4413 CONTACT Craig Scutchings, Survey Manager TELEPHONE office DATE 18/08/

3 Fyfe Pty Ltd, Proprietary Information Statement The information contained in this document produced by Fyfe Pty Ltd is solely for the use of the Client identified on the cover sheet for the purpose for which it has been prepared and Fyfe Pty Ltd undertakes no duty to or accepts any responsibility to any third party who may rely upon this document. All rights reserved. No section or element of this document may be removed from this document, reproduced, electronically stored or transmitted in any form without the written permission of Fyfe Pty Ltd. Document Information Prepared by: MARK SINDERBERRY SITE SUPERVISOR, Fyfe Pty Ltd Date: 17 ust, Approved by: CRAIG SCUTCHINGS SURVEY MANAGER, Fyfe Pty Ltd Date: 18 ust, Revision History Revision Revision Status Date Prepared Reviewed Approved A 18/8/ MDS CAS

4 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT CONTENTS Page EXECUTIVE SUMMARY ii 1. SCOPE OF WORK 1 2. METHODOLOGY Preparations Field Work Collate Data 4 3. RESULTS Results Table Result Analysis 6 4. CONCLUSION 7 APPENDICES Appendix A MONITORING STATION AHD Charts Appendix B Ground Monitoring Maps (ober to ) Appendix C Ground Monitoring Maps (ober to ust ) 18/08/ PAGE I

5 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT EXECUTIVE SUMMARY Coal Seam Gas (CSG) mining, undertakes a process whereby it removes associated waters from beneath the surface, reducing the pressures in the soil formations, which leads to the premise that there may be a degree of subsidence at the surface. The Queensland Gas Company (QGC) has a legal obligation to detect any subsidence, and has instigated an ongoing Soil Subsidence Monitoring Plan, to measure this potential ground movement. Presented in the following pages, is a report in relation to how this ground monitoring is being measured and results to date. During the course of background research for this project it was found that a baseline study has already been conducted over four years (from uary 2007 to uary 2011), utilising Synthetic Aperture Radar (InSAR), to give a historic data account of the ground movement, but this data is not shown in and does not represent any part of this report. 18/08/ PAGE II

6 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 1. SCOPE OF WORK Fyfe have been tasked to conduct geodetic surveys on a quarterly basis in order to monitor key permanent marks in the QGC area of operations, predominately in the Surat Basin. The observations are to be recorded and presented in a suitable manner to show any trending in the rise or subsidence of the ground surface over a period of time. 18/08/ PAGE 1

7 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 2. METHODOLOGY Approximately 30 previously coordinated permanent survey marks (PSMs) were supplied to Fyfe as a base to utilise for observations. The selected marks were chosen to give a good geometry over the area of interest. These marks were checked for stability, access and repeatability. Prior to the first round of observations Fyfe suggested the installation of concrete monitoring pillars for use as the stations for the project. The advantage of having well constructed, deep stable permanent marks like pillars as the stations is the elimination of seasonal ground heave and swell, elimination of equipment setup errors and the added ability to site each mark in the best possible location to satisfy the project needs. In the end, the cost and time associated with the installation of pillars made them uneconomical and existing PSMs were reverted to as originally planned. 2.1 Preparations Prior to performing the field work a field reconnaissance was undertaken in order to verify the survey marks to be used. All equipment was check and calibrated and software updated to suit. A network design was carried out in order to utilise the resources in the best possible method, and a spreadsheet for results was established Field Reconnaissance The PSMs supplied to Fyfe for use in the subsidence survey were examined to ensure they were suitable as high precision monitoring stations. A field reconnaissance was required to check that the marks were suitable to use. The criterion for suitability was based upon the type of permanent mark and construction (for stability), having a clear unobstructed line of sight to satellites (sky plot) and good access to the sites whilst adhering to the QGC Land Access policy. If any of the marks did not adhere to this, alternative marks were selected in the vicinity, in order to maintain good geometry Equipment Preparation A full review of all equipment was undertaken which included the calibration of tribrachs, bubble centering and checks for centering errors. A comparison of measuring tapes was completed for consistency of setup measurements across all sets of equipment. All GPS units were updated with the latest software and survey styles adjusted to acquire like readings. Units were also checked against a baseline (known survey marks) for accuracy and performance for geodetic quality measurements Network Design and field procedure A Global Navigation Satellite System (GNSS) network was designed to ensure sufficient static observations were planned, that gave satisfactory redundancies, to facilitate a network adjustment to be made if required. This network design exercise helped plan and prepare for the utilisation of resources, time, costs and data reporting. It allowed for resources to be minimised and timeframes maximised in order to achieve the results 18/08/ PAGE 2

8 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT as required by Survey Practise (SP1) standards. As a result of the network design, crew scheduling and equipment utilisation was organised and a procedure developed to maintain consistency of measurements and reporting of results. This design led to the expectation that 3 crews were to be utilised (unless more became available), using 6 Dual frequency GNSS receivers on each day of observations. The observation sessions were to be a minimum of 4 hrs each, with up to three sessions per day per crew Office Calculations Observations were recorded in a raw format and then converted to RINEX, to be reduced through the online GeoScience Australia AUSPOS GPS processing service. This enables a consistent approach to the reduction of observations and ensures that results would be calculated from precise monitoring stations which were independent to the area of interest, continually monitored and maintained by the Geosciences Australia governing body. The results obtained for horizontal, vertical and Positional Uncertainty (PU) measurements would be recorded against each survey mark for each independent observation. Both the ellipsoidal height and orthometric height would also be recorded in order to ensure that geoid spheroid separation values (N) would not distort the results. A spreadsheet showing the Easting, Northing, Elevation, PU values and the deltas, corresponding to these measurements, has been created and will be updated on a quarterly basis following each monitoring session. Individual data sets processed through AUSPOS increase with accuracy over time and therefore will have an initial calculation using the Ultra Rapid or Rapid method using a predicted ephemeris, and then reprocessed against the precise ephemeris to achieve the best result. It is envisaged that the results using the above techniques would have a PU of mm in Easting and Northern, and mm in Elevation. 2.2 Field Work A field procedure was written to standardise the equipment setup, observation methodology and recording rate. A Static GPS Observation sheet was also created to record field equipment measurements and other significant details i.e. crew names, dates, equipment, antennas and file names. The field work utilised one crew in each of the Northern, Central and Southern areas. They observed up to 4 stations per day for 3 consecutive days. Each session was observed for a minimum of 4 hrs on a standard 30 second epoch rate. To date there have been three surveys conducted in the field, these being ober, and ust. The frequency of these surveys is scheduled quarterly, however the uary survey was not completed due to a delay in the approval to proceed. The next survey is due to be completed in ember. 18/08/ PAGE 3

9 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 2.3 Collate Data Once the data was captured, it was transferred to the office for processing where field observation sheets were checked against the files, the files were converted to RINEX format, then individually submitted online using the AUSPOS facility. Resultant reports have been filed and entered into an excel spread sheet. This spreadsheet has been established to contain all relevant data, and incorporates multiple checks to ensure that data entry errors were highlighted and removed. The spreadsheet records the coordinated results from each station, PU values and compares them to past results in order to determine if there have been any changes. The differential changes in elevation have been tabulated to allow for the creation of monitoring station charts (Appendix A), which show the vertical movement at each point. These will be updated as more observations are surveyed and give a better representation of what is occurring over time. There are also 3 maps (Northern, Central and Southern Areas) showing the locations of each station and their corresponding elevation change from the initial ober observations. Each set of maps defines the elevation change, and is displayed in Green if the change is contained within the PU value and Red if the change is outside the PU value, for the latest monitoring observation. These can be found in Appendix B & C. 18/08/ PAGE 4

10 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 3. RESULTS Below is a tabulated set of results showing the difference in elevation observations since ober. 3.1 Results Table Station Name ober to ober to ust Northern (mm) (mm) MK51_K new New Central BM New Southern new CGL /08/ PAGE 5

11 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 3.2 Result Analysis The initial sets of observations taken in ober have been used as the bench mark from which all future observations will be compared against. It was initially suggested to use the Department of Natural Resources and Mines (DNRM) published Form 6 Station elevations as a starting bench mark, as it may have helped provide historic data. This would be true, however, it was noted that not all monitoring stations were Permanent Survey ks (PSM) having a Form 6 submitted. It was also observed that the Class and Order (which is now referred to as Positional Uncertainty) were different between some of the marks, making them unviable to use as part of the monitoring survey due to their unknown relative accuracy. Unfortunately some of the marks initially used in the ober sessions were either destroyed or had become inaccessible, requiring other monitoring stations in the near vicinity to be found as replacements for the sessions. The Results Table (3.1), displays the word new in those rows where these replacement marks were utilised. These stations will use the results as their bench mark. All 29 marks shown in the table (3.1) will be utilised for future observation unless some unforseen damage occurs to them. The results of the horizontal observations showed that each set of Easting and Northing coordinates did not vary greatly between quarterly sessions, and were contained within the PU of each monitoring station. This seems to indicate that there is not a lot of horizontal movement at these locations. The elevation observations also indicate minimal change between sessions, but as there are only a small number of sessions, it is too early to make any solid predictions about their movements. The range of change (mostly between 0 30mm) is expected given the PU values obtained from the AUSPOS processing. There are only a few results just outside these values and could be possibly contributed to a number of factors including natural periodic ground movement. Rainfall causes potential swelling of the ground whereas periods of dry weather may affect the shrinkage. Wetting and drying of the ground are expected to occur, due to seasonal change, therefore constant monitoring over long periods of time is required in order to quantify and eliminate them from the elevation changes. At this stage of monitoring, there is not enough evidence to conclude there is any movement of the ground outside of the expected survey accuracies. For a true analysis of the data to show potential ground movement, consistent measuring and computations need to be made. These data results prove that a solid method of measuring has been established and that with continual surveys, the evidence of any ground movement would be displayed. 18/08/ PAGE 6

12 SOIL SUBSIDENCE MONITORING SURVEY QCLNG PROJECT 4. CONCLUSION The ground monitoring of specific locations within the QGC tenement area has been conducted in order to satisfy the federal conditions for potential subsidence due to the mining of coal seam gas. A consistent process of survey observations has been adopted and the computational results recorded have proven that a solid procedure has been established. The results of the surveys conducted to date on 29 ground monitoring stations, within the QGC tenement, have given consistent results and do not highlight any trend in the movement of the ground during the period ober through to ust. The surveys would need to continue in order to provide enough data for analysis in order to eliminate seasonal effects, and to provide evidence of potential subsurface movement. 18/08/ PAGE 7

13 APPENDIX A MONITORING STATION AHD CHARTS

14 Northern Area Monitoring Station AHD Charts PSM AHD PSM AHD PSM AHD PSM AHD WORK IN PROGRESS PSM AHD MK51_K AHD WORK IN PROGRESS PSM AHD PSM AHD PSM AHD PSM AHD

15 Central Area Monitoring Station AHD Charts PSM AHD PSM AHD BM 1221 AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD

16 Southern Area Monitoring Station AHD Charts PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD PSM AHD CGL1000 AHD

17 APPENDIX B GROUND MONITORING MAPS (OCTOBER TO MAY )

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21 APPENDIX C GROUND MONITORING MAPS (OCTOBER TO AUGUST )

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