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By M. Sanchez

In the last decades, the Chilean copper mining and metallurgical industry have had to modify their technological processes to meet the environmental regulations implemented by the Chilean government, and also to support the pressure of the public opinion. Thus, air quality standards for sulfur dioxide and particulate matter (primary and secondary), plans for reducing emission of arsenic by the Chilean copper smelters, effluents discharge limits, among others regulations were applied by the environmental agency. Additionally, agreements on cleaner production were carried out by mining sector and government. Now, a draft law on mine closure, and another on environmental mining wastes (abandoned mines) are being discussed by the authorities and the mining sector. In the context, production and environmental impacts in different ways to produce copper in the Chilean mining industry are reviewed and regulatory tendencies as well as abatement technologies today used are exposed and discussed in this presentation. Pyro, hydro and electrometallurgical processes employed and their current effluent and contaminants are presented showing various alternatives of treatment in the copper industry. An update of regulations established in Chile vis a vis copper production, with an especial attention to mine closure are also presented.

Jan 1, 2007

By C M. Evans, D Thomas

Solid EnergyÆs Wangaloa open cast coal mine was operated between 1945 - 1989, and remained closed and disused until 2001 when SENZ initiated a mine rehabilitation programme. It is nearing the final stages of physical and environmental rehabilitation, aimed at creating an aesthetically pleasing and useful landscape. The final goals of these efforts are to produce an area, which has recreational and educational value. SENZÆs holistic approach to rehabilitation has been undertaken, treating the entire historical mine footprint instead of focusing only on those disturbed areas and the minimum range of issues just to meet with legal compliance. Rehabilitation at the site has included overburden modification with an emphasis on stability, removal and replacement of unhealthy and invasive plant species, and an AgLime amendment to alter soil pH conditions, which would support native plant species. To date, most ongoing activities relate to final planting and plant upkeep, and maintenance of the landform including ongoing erosion control, pest control, environmental monitoring, and research. Environmental quality concerns at the site may be treated by using a combination of methods, including regrading and capping of acid-generating pyrites, soil treatment with AgLime, and passive wetland treatment within existing water courses. Following major works, the mine site area may be opened to the public for recreational activities, interpretive displays on historical mining activities, and observation and appreciation for otherwise unseen geological features. SENZÆs holistic approach to reclamation, rather than treating minor issues, will result in the former mine site being transformed into an asset and the environmental and financial liability associated with the closed mine being discharged. Former mine sites can be turned from environmental liabilities with no recreational or public value (and potentially dangerous to life) into sites that can be safely used by the public for recreational and educational purposes.

Jan 1, 2006

By F Carrick, W A. Ellis, D R. Mulligan, S I. FitzGibbon

"One of the major environmental impacts of mining is the destruction of habitat. The koala (Phascolarctos cinereus) is an iconic Australian marsupial that has been severely affected by land clearing and its decline is continuing. This has placed pressure upon mining companies and government agencies to ensure koalas are managed throughout the life-of-mines - from land clearing through to rehabilitation of post-mining landscapes. This paper reports on the æKoala VentureÆ research partnership between The University of Queensland and Rio Tinto. As part of the Koala Venture program we examined koala use of two types of restored environments: rehabilitated mined land (20 sites) natural regrowth forests (six sites), at Blair Athol Coal Mine in Central Queensland, Australia. Searches for koala scats revealed evidence of koalas in ten per cent of rehabilitated sites (2/20) and 33 per cent of natural regrowth sites (2/6). Two factors were identified as being of greatest importance in facilitating koala recolonisation of restored habitats. Firstly, all recolonised sites were located close to native forest occupied by koalas (mean 135 m ¦ 52). Proximity to source animals is considered crucial to recolonisation of suitably restored habitats. Secondly, three of the four recolonised sites were dominated by koala food trees, most of which were large enough to be utilised by koalas. Availability of suitably abundant food resources is, therefore, also considered crucial. The requirement for these two factors, in combination, is highlighted by the absence of koalas at several sites that contained abundant food trees, but that were distal to areas with source animals, and vice-versa.Our research demonstrates the enormous potential for restoration of wildlife habitat on post-mining lands, even for species with specific requirements such as the koala. Consideration of the ecological requirements of wildlife during rehabilitation planning is critical to enhancing the likelihood of recolonisation.CITATION:FitzGibbon, S I, Ellis, W A, Mulligan, D R and Carrick, F, 2012. Rehabilitating post-mining landscapes for wildlife - A case study from the Koala Venture research program in Central Queensland, in Proceedings Life-of-Mine 2012, pp 319-324 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 10, 2012

It was once considered sufficient to revegetate old mine sites using grass or trees. At the commencement of the Stawell JV (SJV) operation in 1981, management determined that pre-existing vegetation would be replaced. This policy was somewhat 'ahead of its time'. The cost of rehabilitation at SJV averages $8000 per hectare. Rehabilitation of this calibre requires a practical understanding of local ecosystems.

Jan 1, 1992

Coal mining ceased at Strongman Mine this year after 70 years of production. Underground mining finished in 2003 and opencast methods began in 1998. During the life of the mine, 8 million tonnes of coal was extracted from two underground mines and 1.2 million tonnes removed through opencast methods. Strongman Mine is within the Grey Coal Fields; various seams have been extracted from the Rewanui Coal Measures. Coal extracted was predominantly of thermal or semi-soft specifications and characterised by low sulphur and low ash.   The area has steep topography, high rainfall (>3000 mm/yr) and is particularly exposed to westerly quarter winds. Strongman 1 and 2 underground mines are located in the steep, narrow valley which leads to the Strongman Opencast at the top of the valley. Subsidence from underground mining combined with spontaneous combustion, has resulted in an underground fire which has had substantial surface effects. Opencast mining in the steep topography resulted in several landslides at the perimeters of the site. These factors, along with water management, topsoil management and erosion control have added to the complexity of rehabilitating the site.   Rehabilitation of the site is well underway, including infrastructure removal, final landform creation and revegetation of the Strongman Opencast footprint (~45 hectares). Some innovative methods of rehabilitation have been trialled. Successful trials such as helicopter-seeding and moss hydro-seeding on highwalls are now routinely used along with traditional revegetation practices. 18 hectares disturbed land has been replanted with 88 000 seedlings, and another 200 000 seedlings are scheduled for planting over the three years. Fire management is an ongoing challenge; however thermal photography shows a steady decrease in hot areas which have been contained by grout curtains.   Mine closure is some time away and will occur after all standards set by Solid Energy and regulatory bodies are achieved.

Jan 1, 2006

Gold mineralisation at the Macraes Gold Project is hosted in the Hyde-Macraes shear zone and can be traced for ~30km along strike, although economic resources are confined to a 7 km section in the vicinity of the Macraes township. The shear zone, which typically dips at a low angle (~20 o ) to the NE, is bounded by an upper hanging wall shear and a lower footwall fault. Mineralisation occurs along the hangingwall of the shear zone as well as in low angle concordant shears and stockworks. Ore types include graphitic cataclasites with variable amounts of quartz veining, ælode schistsÆ and quartz-vein stockworks. Rehabilitation at the mine has focused on creating an environmentally benign site dominated by pasture to allow continuation of the traditional pre-mine farming economy. Changing regional economics, continued urbanisation and a reduction in traditional employment opportunities has seen a rethink in the long-term rehabilitation outcomes. The community has recognised that the rehabilitated site will provide the basis of a viable tourism venture and the creation of a Heritage and Art Park (working title æGolden Point ParkÆ) is the culmination of that process.

Jan 1, 2002

By M Pizey, C Ross

Rehabilitation approaches, methods and outcomes have changed markedly over the last 100 years, and especially over the last 20 years. Alluvial gold dredges have moved from creating a legacy of boulder fields and ponds to radiata pine plantations and highly productive dairy pastures. The rehabilitated farmland has reduced flood risk, improved drainage and efficient paddock design. The next challenge is to include areas of environmental diversity in these projects, for example, shelter belts, patches of native trees, and wetlands that were part of the original landscape.   West Coast coal mines have also come from a legacy of leaving it to nature to rehabilitate damage by mining to establishing native ecosystems or plantation forests. Developments in techniques at Stockton Mine are used to illustrate the changes in approach to rehabilitation of native forest and tussock heathland ecosystems. The proposed Cypress Mine will adopt a full range of avoidance, remediation through rehabilitation, and off-site mitigation techniques in a æthree-prongedÆ approach.   We propose a coordinated extractive industry approach to mitigate for the impacts of mining on native ecosystems and achieve nationally important conservation benefits that individual projects cannot afford. This approach is particularly beneficial in New Zealand, as our native ecosystems must be actively managed to conserve native plants and animals. Currently, some important species and ecosystems are not being actively managed for conservation.

Jan 1, 2004

By Daniel A. Thome, Robert C. Janke

"Installation of permanent soil nails through distressed mechanically stabilized earth retaining walls is a cost effective and aesthetically pleasing solution when using the appropriate equipment and drilling methods for installation. A forensic investigation was performed on an existing mechanically stabilized earth retaining wall to determine the possible causes for the excessive horizontal displacements and visual structural flaws found along a portion of the wall. Reports concluded that the visual shifting was due to a number of factors including improper drainage in the vicinity of the wall and unsuitable compaction of the backfill material. Conceptual designs were proposed to the owner and the installation of permanent soil nails through the existing precast panels was determined to be the most practical solution. A total of ninety-three permanent soil nails were installed to lengths of up to 40 feet (12 m) through sand backfill and silty day fill using a hydraulic rotary percussion drill attached to a tract mounted excavator.IntroductionThe Illinois State Toll Highway Authority awarded Contract RR-03-5144 in the summer of 2004. Construction work for the project consisted of the rehabilitation of two existing concrete culverts and approximately 100 linear feet (31 m) of mechanically stabilized earth (MSE) retaining wall. The retaining wall is located below the southbound lanes of the Tri-State Tollway near the intersection of Federal Highway 41 in Wadsworth, Illinois as shown in Figure 1.Reports were prepared by Applied Technologies in cooperation with Giles Engineering Associates to determine the condition of the MSE wall and recommended conceptual designs to extend the service life of the wall.Nicholson Construction Company (Nicholson) wasselected as the design-build geotechnical subcontractor to install the recommended permanent soil nails through the existing precast concrete panels of the MSE wall. Rehabilitation of the wall involved the installation of ninety-three permanent soil nails through the existing wall, along with soil nail verification tests and proof tests on production nails."

Jan 1, 2005

By Eoin Murphy, Stephen Beauchamp, Steven Cowell

"INTRODUCTION Electrification of the heavily trafficked Manchester to Preston route by Network Rail required the rehabilitation of the Victorian era Farnworth Tunnels to accommodate 21st century high speed trains. Network Rail, J. Murphy and Sons Ltd (JMS) and OTB Engineering Ltd (OTB) collaborated closely to complete these works in close proximity to heritage infrastructure whilst maintaining a rail service on the route. This significant challenge has been mastered by a combination of detailed investigation, complex modelling, robust design, extensive monitoring, ground treatment, secant piling, sprayed concrete, steel arches and segmental lining techniques. Investigation of the “Down” Tunnel found deformation and cracking of the lining and this was reconstructed during 11 weekend possessions. The “Up” Tunnel was filled with low strength concrete and a 9m diameter open face shield was used to construct an 8m diameter segmental lined tunnel during a 23 week blockade whilst traffic was maintained in the “Down” Tunnel. ELECTRIFICATION OF THE RAILWAY The Farnworth Tunnel project is part of the UK wide £1bn Railway Upgrade Plan to provide improvements throughout the rail network which includes the Manchester to Preston route. The project also supports the UK Government commitment to build a “Northern Powerhouse” by improving links that bind northern England together and which will help it release its full potential with a more balanced, healthier economy. The majority of the current UK rail network infrastructure resulted from the rapid growth of the railways in the mid to late 19th century which means that most of the existing tunnels are over 120 years old. Over the centuries the introduction of larger rolling stock has reduced the original clearances provided in tunnels. The electrification of a route requires that any over-line structures provide clearance for Overhead Line Equipment (OLE), new rolling stock and to meet modern standards. As part of Network Rail’s current electrification programme a further 36 tunnels have been identified on routes requiring electrification. Not of all these Victorian structures will require alterations to provide OLE clearance but the condition of the existing tunnels and modern fire / waterproofing requirements may ultimately dictate the need for rehabilitation."

Jan 1, 2016

By D. Berberick

Hecla?s Lucky Friday Mine is a deep, underground producer of silver, lead and zinc in the Coeur d?Alene mining district of northern Idaho. Main access into, and production from, the mine is via the Silver Shaft, a 5.5-m (18-ft) diameter, concrete lined shaft sunk by J.S. Redpath to an original depth of 1,890 m (6,200 ft) in the early 1980s. The shaft is divided into four compartments (Fig. 1), with sets made of 225 mm x 175 mm (9 in. x 7 in.) hollow structural section (HSS) steel buntons and 150-mm x 150-mm (6-in. x 6-in.) HSS dividers spaced every 4.5 m (15 ft) down the length of the shaft. Two skip compartments on the east side of the shaft are equipped with 125-mm x 150-mm (5-in. x 6-in.) HSS steel guides and 9-t (10-st) skips with three deck trailer cages for men and materials. The west side of the shaft is divided into a manway, and a fourth compartment that was originally designed for a service cage. Shaft services consist of a 250-mm (10-in.) a compressed air line and 150-mm (6-in.) sandfill line along the south side of the shaft, and 250-mm (10-in.) discharge (gray) water and 150 mm (6 in.) fresh water lines on the north wall. The mine?s primary 13.8 kV power lines, as well as communication lines are located on the west wall of the shaft. The production hoist is a 3.7-m (12-ft) diameter, double drum, double clutch, 2,238 kW (3,000 hp), direct current unit equipped, at the time, with thyristor drives. The 30-year-old drives would prove to be problematic during the rehabilitation project, leading to an upgrade to modern ABB drives later in the project, after the shaft rehabilitation was complete. The shaft had been subjected to the typical wear and tear of 30 years of operation, including intermittent sandfill and muck spills, and, in the lower areas, some corrosion. During those 30 years, the west compartment, originally designed for the service cage, could only be accessed from a work deck on top of the skips or from the manway.

By D. Berberick

On January 5, 2012, the Mine Safety and Health Administration ordered the closure of the Silver Shaft, the primary underground access to Hecla?s Lucky Friday Mine, for removal of built up backfill material that accumulated over time on the shaft walls and furnishings. Lucky Friday and Cementation USA personnel worked quickly to identify the most effective means to get the mine back into production. The team developed a fast-track procurement and refurbishment plan utilizing shaft sinking winches, headframe modifications, a partial shaft sinking Galloway, and modified cages to not only complete clean-off of buildup, but also replace pipe brackets, shaft steel, and power and communications cables as needed in the 1,860 m (6,100 ft) deep shaft within 14 months.

Feb 23, 2014

By N TassT, J Cyr

At the East Sullivan site, wood wastes covering the abandoned mine tailings impoundment prevent sulfide oxidation by creating an anoxic environment. The addition of coarse ligneous wastes and their high permeability favour infiltration, resulting in a water table rise that maintains most tailings under water saturation and thus provides an additional protection against sulfide oxidation. Moreover, high infiltration allows a more rapid flushing of acid prone groundwater generated prior to the cover placement, which could cause acid mine drainage over a long period of time. Finally, the pore-waters under the cover are characterised by a strong reducing potential, high alkalinity, and near neutral pHs. These conditions favour sulfate reduction and base metal precipitation as sulfides and as carbonates. Pore-water composition monitored from 1992 to 1998 showed a significant Fe2+ decrease, following cover placement. Thereafter, the restoration strategy capitalised on the alkaline and reductive properties of the waters underlying the wood-waste cover. An original treatment of acid effluents, based on the recirculation of water discharging around the impoundment through the organic cover, was implemented. In 2002, the recirculated water from May to October had a mean pumping rate of 240 m3/h, for a total volume of 800 000 m3. Data gathered near the dispersal zone from 2000 to 2002 show that despite the recirculation of acid water (pH ÿ3), the pH decreases by only one unit from 7 to 6, during the recirculation period, ie from May to November. However, alkalinity decreases from 800 to 100 mg/L-CaCO3. Despite this decrease, the alkalinity is back up to 800 mg/L-CaCO3 the following May, thanks to sulfate reduction. From 2000 to 2002, Fe2+ concentration in the pore waters near the dispersal zone is maintained below 2 mg/L. Evolution of surface water quality suggests that the contaminated groundwater flush is completed in the north and north-west area of the impoundment; the east sector is under recovery, while the south sector remains the most problematic. A wood-waste cover, besides limiting sulfide oxidation, can fill the role of alkaline reducing barrier for the treatment of these acidogenic waters, until a balance between acidity and alkalinity in the effluent is reached.

Jan 1, 2003

This paper describes the planning mechanism and implementation of a progressive rehabilitation programme at Hunter Valley Mine in the Upper Hunter Valley of New South Wales. Hunter Valley Mine is a large open cut coal mine which produces approximately 7.0 million tonnes of coal (run of mine) annually for export. This production level involves the movement of some 60 million tonnes of waste and coal each year.The rehabilitation programme at Hunter Valley Mine has been developed to provide a combination of pasture, based on improved pasture species and timber belts to enhance the visual characteristics of the rehabilitated landform, whilst creating amenity in the form of shade for livestock.The operational philosophy for the rehabilitation programme is that of progressive rehabilitation. The best time to undertake rehabilitation is now.' As a result, planning for the rehabilitation programme is continuous, so that all site works are completed in time for vegetation establishment during the critical periods each year.

Jan 1, 1992

Plant growth is likely to prove the most suitable and satisfactory material to stabilise and cover quarry faces and worked-out surface mining sites. The careful selection of plant species is of paramount importance to the success of any attempts to re- vegetate these sites. Various tech- niques are recommended and attention is drawn to different factors,which will adversely affect plant growth.

Jan 1, 1976

By J Burgess, G Scanlan

In 1993 after over 110 years of mining operations, production ceased at the Broken Hill North Mine. Following the cessation of operations a rehabilitation program was developed to satisfy the requirements of the various government departments. This program has been implemented progressively since mine closure. The paper will discuss: primary aims and objectives of the rehabilitation program, implementation of the program, rationale behind rehabilitation objectives, and problems encountered in implementation of the program. To-date the primary rehabilitation of the mine has involved the capping of redundant tailing dams with inert waste rock to prevent the contamination of the receiving environment. A Water Management Plan has been developed to contain all run-off from the mine area in an extreme storm event. A cultural heritage assessment of the leases has been undertaken to ensure the rehabilitation is consistent with the historical significance of the site and community expectations. All redundant material from the mine has been sold in a æno reserveÆ auction and the workshop area has been relocated to the Southern operations. At present the only active areas on the mine are a maintenance area for equipment for the Potosi open pit, and a primary crusher for Potosi ore which is railed to the Southern operations for further processing. Upon completion of the rehabilitation program, Pasminco Broken Hill Mine intends to relinquish the mining leases to the Department of Mineral Resources.

Jan 1, 1998

By A. J. Vivyurka

"This is a talk about the experiences that Rio Algom Mines Ltd. has had in the Elliot Lake uranium area trying to make the tailings more compatible with the surrounding environment. To get a better idea of the problem that we are associated with we have to go back to the location. The Elliot Lake uranium area is situated about half way between Sault Ste Marie and Sudbury and is about 20 miles north of Lake Huron. In 1950, uranium was discovered along the north shore of Lake Huron and by 1961 we had up to 9 mines operating in the area. Then the United States Atomic Energy Connnission withdrew their contracts so that at present there are only 2 mines operating. From all the mines that we had operating, we ended up with 7 tailings areas. From these 7 tailings areas we have 5 sites where we have active treatment or rehabilitation. There is the Pronto site where we are treating uranium tailings and copper tailings. There is the Lacnor-Nordic site which is located just out of Ellio Lake. The Milliken-Stanleigh site is in the Crotch Lake area. The Panel tailings is off the north end of Quirke Lake and finally there is the operating property of Rio Algom Mines at Quirke Lake.To understand fully the problem with this rehabilitation we have to look at the constituents of the ore. The ore body is a quartz conglomerate with uraninite and brannerite as the uranium bearing minerals in a fine ground mass of quartz, sericite and pyrite which separates the larger quartz pebbles. The approximate composition of the ore is: 80% quartz, 13% chlorite, 7% pyrite and 0.2% uranium minerals. The processing method also adds a few constituents to the final tailings."

Jan 1, 1975

By Z. Kowalski

In the defunct Gorka quarry, there are situated both a waste disposal site of an area of 6.7 ha and containing approximately 1 million ton of high aluminium wastes and a pond of an area of roughly 3 ha, up to 15 m deep, with about 400000 m3 of polluted water. The reservoir is fed with the filtrates arriving from the disposal site mentioned, at a rate ~130 m3/day. An alarming phenomenon is the subsidence of the pond bottom and the infiltration of solutions into the Triassic and Jurassic water resources, assessed at ~40 m3/ day. The basic problem related to the effluents in the Gorka pond is their high alkalinity (pH 12-13.4) and variable pollutants whose level increases appreciably with the pond?s depth. The solution offered provides pumping out and treatment of about 500000m3 of effluents retained in the Gorka reservoir in an about yearly time. Effluents would be treated in a reverse osmosis plant, according to a process so far verified on a quarter-commercial scale. The treatment process by-product would be discharged into the Ropa stream. The brine solution (containing about 25% NaCl), whose amount may reach up to100000m3, might be supplied to the Debiensko Mine which produces technological salt from salt-bearing mine waters. Similarly, there would be provided an intake of underflows of infiltrates (by means of deep wells, and possibly girdling ditches) arriving from the high aluminum site, and such effluents would be subject to ongoing dilution in water courses. It would be possible to test the system of underflows reaching the Gorka reservoir by means of geochemical identification, previously performed. The next stage following the pumping, would be the utilization of approx. 50 000m3 of bottom slurry. Highly alkaline slurries would be utilized in the production of self-solidifying mixtures. Slurries would be pumped out and temporarily dumped on drying beds, located nearby the Gorka reservoir, and later on used successively for making self-solidifying mixtures in a plant similar to a concrete making seat. Those mixtures would be applied for sealing the bottom of the Gorka reservoir and the necessary part of the edges of the defunct quarry. An alternative solution is the utilization of slurries in the facilities of the Trzebionka Mining Works and the application of self-solidifying mixtures, made in the Trzebionka Works, for sealing the reservoir bottom.

Jan 1, 2006

By Frank Haehnig, Kurt Kogler

"With a height of 200 m, a crown width of 626 m and a concrete volume of 1.6 million m³, the Kölnbrein Dam in the upper Malta valley in Carinthia / Austria is the largest concrete dam in Austria. Boasting a storage capacity of 200 million m³ with a received water load of 54 MN, this is one of the strongest arch dams in the world.During its construction from 1974 to 1977, the dam was equipped with a comprehensive monitoring system capable of comparing developing deformations and stresses with the design values.With a planned reservoir level of 1,900 m a.s.l. the dam saw the reservoir level of 1,860 m a.s.l. breached in the year 1978. This led to extremely high seepage losses of up to 200 ltr/sec and a rise in the foundation water pressure up to 100% of the dam’s height. These observations were caused by the development of horizontal cracks in the area of the middle dam blocks, between the lowest inspection walkway and the waterside.As a consequence, power plant operations had to significantly be reduced and a number of additional measures were carried out – though these did not lead to the desired sealings.The developer subsequently decided that the dam should undergo a general rehabilitation from 1998 to 1994 in accordance with a concept developed by Professor Lombardi. This concept involved erecting a 50 m high support structure with a concrete volume of 500,000 m³ on the airside of the dam, along with the addition of neoprene bearings to transfer 1.2 million tons of the horizontal load. These measures were able to reduce the deformations in the dam enough so that mostly load-bearing injections into the cracks in the dam’s concrete could successfully be carried out by way of targeted grouting measures using injection resin (RODUR) specifically developed for this purpose.In the years 1998 - 1994, a total of 130,000 m of grouting, monitoring and control drillings were executed, and around 200,000 kg of synthetic resin was injected into the cracks in the dam’s concrete.These measures have ensured the dam‘s uninterrupted operation since 1994. A number of small re- injections were again carried out on the contact surface in the years 2011 and 2012."

Jan 1, 2016

By Ryan Marsters, Adam Pring

The Rawah Ditch is a mountainous water supply diversion which supplies Larimer County, Colorado with water since 1903. The ditch includes two historic tunnels excavated by drill and blast through a gneissic rock buttress. Both rock tunnels were failing with annual convergence. After a snowshoe-accessed eld investigation, nite element modeling, and an alternatives analysis, a diameter DE pipe was inserted within each tunnel and the annulus lled. The proect was implemented in an Alternative Delivery contract lasting ve months from eld investigation through procurement and construction.

Jun 23, 2024

By Teena Redhorse, David Tsztoo, Anthony Yu

"Since ancient times, storing and conveying water via underground water systems and tunnels has been touted for its strategic advantages. Underground cisterns and tunnels assured protection of essential fresh water supplies from man made contamination and especially from enemies who would gain an advantage by disrupting an adversary’s water supply in a siege. Modern day engineers do not usually specify tunnels for reasons of avoiding deliberate contamination or siege — however, they are just as enamored with the idea of building tunnels for water conveyances.Such was the case for the San Francisco Public Utilities Commission (SFPUC). The SFPUC provides drinking water to 2.6 million residential, commercial and industrial customers in the San Francisco Bay Area. The SFPUC’s water system includes 257 km (160 miles) of transmission pipelines and tunnels from the SFPUC’s largest reservoir, the Hetch Hetchy Reservoir inside Yosemite National Park, to San Francisco. About 129 km (80 miles) of the system consist of tunnels. A 30-km (19-mile) section of the tunnel network, called the Mountain Tunnel, was thought to be at risk of a catastrophic failure in its concrete-lined section of 18 km (11 miles). For much of the project planning process, a new replacement tunnel was presumed to be required according to the tunnel planners.Originally constructed between 1917 and 1925, the Mountain Tunnel has been in continuous service since 1925. The 30-km (19-mile) tunnel is located downstream of the Hetch Hetchy Reservoir water source in Yosemite National Park, between the Early Intake and Priest Reservoir (Fig. 1). Approximately 18 km (11 miles) of the tunnel is lined with unreinforced concrete. Though the condition of the tunnel was being monitored through water sampling and periodic inspections, there was growing concern that the tunnel lining was at risk of a partial collapse that could interrupt water delivery for up to nine months. The SFPUC was faced with a decision to construct a new bypass tunnel to replace the lined section of the Mountain Tunnel or to rehabilitate the existing tunnel."

Jan 6, 2018