ATTACHMENT B8 Incident History

Transcription

1 Appendix B GIS/Imagery Outputs ATTACHMENT B8 Incident History

2 Appendix B - GIS/Imagery Outputs Appendix B: Attachment B8 Incident History TABLE OF CONTENTS B.B8-1 INTRODUCTION... 1 B.B8-2 FACT SHEETS... 3 B.B8-3 EVOLUTION OF THE LEFT ABUTMENT ROCKFILL TRENCH List of Tables Table B.B8-1 Summary of incidents at Fundão... 1 List of Figures Figure B.B8-1 Incidents at Fundão shown in plan... 2 Page B.B8-i

3 B.B8-1 INTRODUCTION The list of incidents documented over the life of the Fundão facility are given below in Table B.B8-1 and shown in plan on Figure B.B8-1. Section B.B8-2 includes the fact sheets for each incident. Section B.B8-3 includes documentation on the evolution of the left abutment open channel. Table B.B8-1 Summary of incidents at Fundão Abutment Date Elevation Incident Type - April 13, Piping Right July 9, Main Gallery settlement Left June 26, m Seepage Left November 25, Secondary Gallery sinkhole Left March, m Saturation of slope and ponding of water Left June, m Seepage Left November 15, m Seepage, cracks on slope Left December 26, m Upwelling at El. 860 m, cracks on crest Right July 18, m Seepage Left August 26, Slope movements, saturation Right January 30, m Seepage Left April 16, m Saturation of slope Left May 18, m Saturation of slope Left July 9, m Saturation of slope Page B.B8-1

4 Figure B.B8-1 Incidents at Fundão shown in plan Page B.B8-2

5 B.B8-2 FACT SHEETS April 13, 2009 Piping Incident A leak on the downstream face of Dike 1 above the Principal Foundation Drain developed. A berm was placed immediately on top of the leak, but this did not stop the flow. Tailings deposition was diverted from Fundão, the Dike 1 reservoir drained, and the Principal and Auxiliary Foundation Drains excavated on the upstream and downstream side of Dike 1 for inspection. Both drains were noted to have defects such as erosion of the filter layers and clogging of drain material with fines. Both drains were decommissioned by plugging on the upstream side of Dike 1. The downstream remnants were extended past the Reinforcement Berm placed on the downstream slope of Dike 1. The base drains were replaced with one blanket drain at El. 826 m with 27 Kananet pipes. Old Dike 1A was constructed to allow continued deposition of tailings in Fundão while the El. 826 m blanket drain was constructed. April 13, 2009 site inspection photo [23] showing piping on the downstream face of Dike 1. The Principal Foundation Drain can be seen to the right of the spring. ITRB and Andrew Robertson engineering audit reports and [24]. October, 2010 construction photo showing plugging of the Auxiliary Foundation Drain to the left with the excavated Principal Foundation Drain to the right. None Page B.B8-3

6 July 9, 2010 Main Gallery Settlement The module between Joint 26 and 27 experienced settlement which manifested as a vortex at the surface of the tailings. Tailings deposition in this area was suspended and an inspection showed tailings entering the Gallery through a large crack. New Dike 1A was built to shield this area from tailings deposition while jet grouting was completed on the foundation of the Gallery. July, 2010 site inspection photo [25] showing the vortex that formed at the surface of the tailings above the settlement. Samarco 2010 presentation [27], Samarco 2010 presentation [28], GMAIA 2010 inspection [26] July, 2010 inspection photo from GMAIA [26] showing the inflow of tailings to the Gallery. Joint references differ between sources, the second most common being the leak having occurred between Joints 22 and 23 instead of 26 and 27. This is due to different stationing having been used on drawings over time. Page B.B8-4

7 June 26, 2012 Left Abutment Seepage at El. 845 m Seepage was noted at El. 845 m on the non-setback part of the dike crest at the left abutment. VOGBR attributed this to the damming of water in the Grota da Vale which was upstream of the seepage location. The saturated upstream raise material was excavated and a drain installed. The drain consisted of a geotextile, granular material and coarse rockfill. No formal drain exit was installed until around May, 2015 in the form of a concrete channel that discharged into a buried pipe crossing the left abutment access road to the left abutment concrete channel. Flow records for this drain were not available. Marked up September 2, 2012 Samarco aerial image shown. Photo from VOGBR 2013 report [29]. Samarco weekly reports, VOGBR 2013 report [29] None Page B.B8-5

8 November 25, 2012 Secondary Gallery Sinkhole Sinkhole discovered on the El. 855 m bench at the setback portion of Dike 1 at the left abutment. This sinkhole was located above the Secondary Gallery at Joint 18. An inspection revealed slug discharge of tailings and water from the tailings side of the Secondary Gallery. Joint 18 was grouted internally. November 25, 2012 inspection photo [30] showing the sinkhole. Samarco 2012 inspection [30] December 14, 2012 inspection photo [30] showing evolution of the sinkhole since November 25. None Page B.B8-6

9 March 2013 Seepage at Left Abutment at El. 855 m and Ponding of Surface Water The weekly report from the week of March 25, 2013 notes a saturated region at the left abutment. After a review of aerial images, part of the reason for saturation and ponding could be lack of surface drainage control on the left abutment roads above the dam. Topography shows this area to be ~El. 855 m. A buried drain (Drain 1) was put in, leading to a geotextile-wrapped rockfill trench (Drain 2) on the left setback. The buried drain was an inverted trapezoid, geotextile-wrapped rockfill drain. The geotextile-wrapped rockfill trench (Drain 2) eventually became a large open channel on the setback platform as the dam was raised around it. Details on the evolution of this drain are given on the last fact sheet of this section. Weekly report from week of March 25, March 2, 2013 Samarco aerial image showing the Secondary Gallery sinkhole to the left and a region of saturation and ponding to the right at the dam s contact with the left abutment. Weekly reports None Page B.B8-7

10 June 2013 Seepage at Left Abutment at El. 855 m There are a number of conflicting records on the elevation and date of this seepage incident: Source Date of Incident Elevation of Incident ITRB June, m Samarco [31] June, m August, m VOGBR [13] August, m There is no mention of seepage events in the June or August, 2013 weekly reports, but drain construction activities were mentioned in the June reports. This drain (likely Drain 1 from March, 2013) was connected to the open channel wrapped in geotextile running down the left abutment (likely Drain 2). No signs of this activity can be seen in the August, 2013 aerial image. It is possible that the incident took place during end of buried drain (Drain 1) construction in June. The drains that were already going to be executed as part of the March, 2013 saturation event were used to address this new seepage event. No clear description or photos of this drain are available except from weekly reports that seem to show: 1 m layer of sand being placed upstream of the buried drain (Drain 1); construction was started in April, The sand being connected to the rockfill trench (Drain 2). Construction photo from June 17-23, 2013 weekly report showing the geotextile and sand placement, with the beginnings of the rockfill trench to the left. Construction photo from June 17-23, 2013 weekly report showing the beginnings of the rockfill trench. Page B.B8-8

11 June 2013 Seepage at Left Abutment at El. 855 m Document from Samarco [31] showing details of the November 2013 seepage event and mention of the June 2013 incident. Document from Samarco [31] showing details of the drains constructed at the left abutment to address the November and August, 2013 incident. The August, 2013 incident was referred to in a previous slide as the June, 2013 incident. ITRB, weekly reports, Samarco 2013 document [31], VOGBR document [13] Dates and elevation as listed in the section. Page B.B8-9

12 June 2013 Seepage at Left Abutment at El. 855 m November 15, 2013 Left Abutment Seepage and Cracks at El. 860 m There are a number of conflicting records on the elevation and date of this seepage incident: Source Date of Incident Elevation of Incident ITRB November, m Samarco [31] Between November 15 and 17, m VOGBR [13] November, m The slope face was saturated and localized slumping was noted. Longitudinal cracks appeared. Cracks at higher elevations were dry. An inverted drain (Drain 3) was placed and connected to the one placed at El. 855 m (Drain 1) which was connected to the rockfill trench (Drain 2). Document from Samarco [31] showing details of the November 2013 seepage event and mention of the June, 2013 incident. Samarco 2013 document [31], VOGBR 2013 inspection [13] Document from Samarco [31] showing details of the saturated and slumped slope in November, Dates and elevation as listed in the section. Page B.B8-10

13 December 26, 2013 Left Abutment Upwelling at El. 860 m and Cracks on Crest Upwelling incident noted in December 23-30, 2013 Samarco weekly report and confirmed to be observed on December 26, 2013 in December 2013 Samarco monthly geotechnical inspection report. Cracks noted in December 30, 2013 to January 5, 2014 Samarco weekly report and confirmed to be observed on December 26, 2013 in December 2013 Samarco monthly geotechnical inspection report. Upwelling elevation inconsistencies between sources: Weekly report states El. 855 m. Aerial image taken by drone on December 27, 2013 shows sand placement at ~El. 858 m. For consistency with naming convention for other seepage incidents, this will be referred to as the El. 860 m upwelling since it is on the downstream face of the El. 860 m bench. 1 m of sand was placed on the slope face to retain fines. Setback was raised following the sand placement. Cracks were noted to be approximately 10 mm wide and 60 m long along the crest. Photo from December 23-29, 2013 weekly report showing placement of sand over area of upwelling. Photo from December 23-29, 2013 weekly report showing placement of sand over area of upwelling. Page B.B8-11

14 December 26, 2013 Left Abutment Upwelling at El. 860 m and Cracks on Crest December 30, 2013 to January 1, 2014 weekly report describing temporary cessation of operation at the left abutment due to cracks. Weekly reports, geotechnical inspection report December 26, 2013 inspection photo from Samarco geotechnical inspection report showing a crack on the crest. None Page B.B8-12

15 July 18, 2014 Right Abutment Seepage at El. 855 m There are a number of conflicting records on the elevation and date of this seepage incident: Source Date of Incident Elevation of Incident ITRB Not stated 855 m Samarco [14] July 18, m VOGBR [13] Late m The incident was discussed in detail by Samarco [14] which concluded: The interface between the soil backfill and sand tailings as part of the Auxiliary Spillway construction works has become a preferred seepage path. The closest piezometer to the seepage incident is approximately 50 m away on Section AA. This piezometer (16LI011) showed the water level to be below the point of seepage. The saturated slope was excavated and replaced with a sand and gravel drain which can be seen in the drone aerial image taken on August 4, During a site visit in April 2015, VOGBR noted saturation of the bench downstream of the drain and recommended replacing the drain with one of VOGBR s design. This was done in May, Flow from this drain was regularly monitored and reported in instrumentation and weekly reports. July, 2014 inspection photo showing seepage outbreak on the downstream face of Dike 1. Location plan showing the seepage outbreak in relation to the earthworks extent for the Auxiliary Spillway. Page B.B8-13

16 July 18, 2014 Right Abutment Seepage at El. 855 m Sand tailings Backfill July, 2014 inspection photo showing the sand and gravel drain placed. Samarco 2014 inspection [14], VOGBR [13] Marked up photo from the Auxiliary Spillway construction period showing the interface between the backfill and sand tailings. Dates and elevation as listed in the section. Page B.B8-14

17 August 26, 2014 Left Abutment Setback Slope Movement At 6:00 AM on August 27, 2014, cracks were observed on the upstream beach, dam crest and downstream slope of the setback. The cracks showed differential thicknesses, some on crest ~6 cm, reaching up to 3x as thick on the upstream bench. Uplift at the toe of the El. 865 m bench was noted by the ITRB. Water was not observed on the upstream beach and crest, only normal saturation of sand tailings. At the toe of the El. 865 m bench, saturation was noted. Samarco designed and implemented a Reinforcement Berm. Piezometers and survey monuments were also installed. September 2014 inspection photo showing saturation of material at the toe of the El 865 m bench. Location plan showing the mapped cracks. Samarco 2014 inspection [32], Samarco surveys [33, 34] None Page B.B8-15

18 January 30, 2015 Right Abutment Seepage at El. 860 m There are a number of conflicting records on the elevation and date of this seepage incident: Source Date of Incident Elevation of Incident ITRB Not stated 855 m Samarco [35] January 30, m VOGBR [13] January 30, m According to topography, this incident occurred on the downstream face of the El. 860 m bench at El 858 m. This is one bench above the incident that occurred in July, Incident discussed in detail by Samarco [35] which concluded: The interface between the soil backfill and sand tailings as part of the Auxiliary Spillway construction works has become a preferred seepage path. The closest piezometer to the seepage incident is approximately 50 m away on Section AA. This piezometer (16LI010) showed the water level to be below the point of seepage. The saturated slope was excavated and replaced with a sand and gravel drain. During a site visit in April, 2015, VOGBR recommended replacing the drain with one of VOGBR s design. This was done in May, Flow from this drain was regularly monitored and reported in instrumentation and weekly reports. Location plan showing the seepage outbreak in relation to the earthworks extent for the Auxiliary Spillway. Samarco 2015 [35], VOGBR 2015 inspection [13], ITRB report January, 2015 construction photo showing the beginning of stripping for placement of drain material on the slope [35]. Dates and elevations as noted in Section. Page B.B8-16

19 April 16, 2015 Saturation at Left Abutment, El. 867 m Saturation above and below the El. 860 m blanket drain was noted by Samarco in the monthly geotechnical report. A photograph shows saturation at El. 867 m just above the on-going construction of the El. 860 m blanket drain. Drone aerial images from February 27, 2015 to April 24, 2015 show saturation at the location of the monthly report photograph. Photo from monthly geotechnical report showing saturation at the toe of the slope above the El. 860 m blanket drain. February 27, 2015 aerial image. March 20, 2015 aerial image. Samarco 2015 inspection [36] April 24, 2015 aerial image. None Page B.B8-17

20 May 18, 2015 Saturation at Left Abutment, El. 820 m Saturation of slope was noted by Samarco in the monthly geotechnical inspection report. Marked up May, 2015 inspection photo from the Samarco geotechnical inspection report showing saturation of the slope left of the concrete channel. Samarco 2015 inspection [36] None Page B.B8-18

21 July 9, 2015 Saturation at Left Abutment, El. 820 m Saturation of the slope was noted by VOGBR during the July, 2015 site visit as part of Regular Safety Inspections. This appears to be the same saturation that was noted by Samarco in May, July, 2015 inspection photo from VOGBR showing saturated slope between El. 830 m and El. 820 m bench. VOGBR 2015 inspection [13] None Page B.B8-19

22 B.B8-3 EVOLUTION OF THE LEFT ABUTMENT ROCKFILL TRENCH Evolution of the Left Abutment Rockfill Trench (Drain 2) The rockfill trench (Drain 2) was initially put in as part of June, 2013 seepage incident and receives water from the El. 855 m buried drain (Drain 1) and the El. 860 m drain (Drain 3 installed in November, 2013). Water from this drain was permitted to sheet flow across the setback plateau and access road to Grota da Vale. As the setback was raised around this trench, it became a large open channel lined with geotextile. This can be seen in the drone aerial image taken on December 27, By January 29, 2015, the aerial image shows the open channel having been buried with a light grey material. It is unclear whether this is drain rock or dry tailings sand. During a May interview with a Samarco employee, the buried open channel was recounted to have an outlet in the form of a buried pipe. The alignment of this pipe is unknown to the Panel, but based on site photographs and aerial images, it is likely at the exposed toe of the El. 860 m blanket drain. Ponded water is consistently noted at this location. VOGBR completed a drain design in May, 2014 to convey water from the buried El. 855 m drain (Drain 1) to the left abutment concrete channel. No records were found of this design having been implemented. However, as part of the design process, VOGBR conducted a site visit and took photographs of the open channel as it existed in March, Open channel lined with geotextile Marked up drone aerial image taken December 27, Marked up drone aerial image taken January 29, Page B.B8-20

23 Evolution of the Left Abutment Rockfill Trench (Drain 2) Marked up drone aerial image taken May 27, Marked up drone aerial image taken June 22, March 27, 2014 site visit photo from VOGBR showing the open channel looking down the slope of the dam toward the plateau of the left setback. March 27, 2014 site visit photo from VOGBR showing the open channel looking upslope towards the dam crest. The erosion on the setback plateau can be seen to the right of the photo. Page B.B8-21

24 Evolution of the Left Abutment Rockfill Trench (Drain 2) July 10, 2014 site visit photo from VOGBR showing a pipe conveying water from the open channel through the access road berm. The water then sheet flows across the access road to Grota da Vale which is to the right of the photo. VOGBR 2014 [11] January 16, 2015 construction photo showing the buried open channel with light grey material. None Page B.B8-22