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By Letz H

An investigation of earthquake hazard in Papua New Guinea (PNG) by a yearly extreme magnitude method using the magnitude 7 earthquake record since 1900 shows that the Bougain-ville Island seismic zone is by far the most active, followed by the New Britain and northern mainland PNG regions. Return period for magnitude 7.0 earthquakes occurring in normalized 10,000km2 areas of the Bougainville Island, New Britain, Huon, West Bismarck, North Sepik and Ramu seismic zones is 37, 60, 81, 88, 125 and 125 years respectively. These areas are much more active than the California Seismic Zone 4 region including the San Andreas Fault, which has a normalized magnitude 7.0 return period of 299 years, calcul-ated here by the same method.Only southern PNG, including the Papuan Fold Belt and most of the Bismarck Sea, are less active than California Zone 4. The Papuan Fold Belt is only marginally less active than California Zone 4, but more active than the State of California taken as a whole.

Jan 1, 1994

By H. L. Cameron

Introduction Since the beginning of gold mining in Nova Scotia in the year 1860, the biggest problem o the mine operators has been to find and follow the ore zones in the narrow quartz veins. It was early recognized that all veins were not gold bearing and that, in those that were, the commercial ore was confined to limited zones. A large number of geologists and mining engineers have been interested enough to give time and thought to the problem, but, until the last four or five years preceding World War II, they were handicapped by lack of exact data from mining operations. The necessary data could only be obtained by daily checking of underground operations. Such daily checks were instituted at a number of mines during the period 1935-40 and, in every case, were successful in delimiting the ore zone or zones for the particular mine. The present paper deals with the results of this work as applied to practical ore finding. It is an attempt at extrapolation, from observations in the four districts with which the writer is personally familiar, co other districts in which similar conditions or structures are reported.

Jan 1, 1947

By G. G. Campbell

The Bureau of Mines initiated a field test of underground coal gasitication to investigate the technologic feasibility of gasifying a subbituminous coal. The test site is near the town of Hanna, Wyo., about 70 miles northwest of Laramie. Preliminary results of the experiment are described. The coal was ignited in the central well of a 16-well pattern. Both forward and reverse combustion techniques were attempted to prepare a path of sufficient permeability to permit the high air injection rat s necessary for gasification. Gasification between linked wellbores was sustained for periods as long as 3 months. Hydrogen-rich gas having a heating value of 100 to 150 Btu/scf was produced.

Jan 1, 1974

By M. Mirzazadeh

Air cooled crackable and conventional forged steel specimens were tested under reversed push-pull conditions to examine the effect of shot-peening on their high cycle fatigue behaviour (-106 cycles). The steels were tested in the normalized as well as shot-peened conditions. The results showed that shot-peening smooth specimens had little effect on the fatigue limit of the air cooled forged steels and the detrimental effect of the rougher peened surface was not apparent. Microhardness profiles indicated that the shot peening produced a gradient of compressive residual stresses that was greater than that of the loading stresses, suppressing the anticipated beneficial effect on fatigue life. Crack initiation was more likely to occur below the surface. The results indicate that the surface roughness was not a significant factor in controlling the fatigue lives, since they were essentially the same for the non shot-peened and shot-peened steels.

Jan 1, 2010

By J. M. Stuve

In this Bureau of Mines investigation, the low-temperature heat capacities of polycrystalline phases corresponding to the sulfide compounds CoSO?89' CoS1?33, and CoS2 were measured by adiabatic calorimetry within the nominal temperature range 5 to 300 K. The derived absolute entropies S298 were 10.36±O.02, 12.96±O.03, and 16.31±O.03 cal?mol-1?K-l, respectively, assuming third-law behavior. In addition, the standard enthalpy of formation 8Hf298 of CoSO?89 was determined by bromine solution calorimetry. The derived value of 8Hf298 was -50.63±2.1 kcal?mol-1, based on the 8Hf298 of Co0. This result is considerably more negative than previously published formation values based on high-temperature gas equilibrium studies.

Jan 1, 1985

By R Bearman

The importance of crushers in the mining industry declined with the introduction and resultant dominance of AG and SAG based circuits, but the recent move to consider more energy efficient circuits has caused the industry to re-consider the role of crushers.Different types of comminution equipment have different efficiency in the way the energy is applied in the size reduction process. Because of the general trend towards more sustainable production processes and emission of carbon dioxide, energy use has become more important. To fully understand how crushers can contribute to optimising the energy application in comminution circuits, detailed models of process performance are required. Such models need to take into account the mechanical design factors and how the crusher performance changes in response to feed conditions, the control strategy utilised and the wear of the crusher liners.It is also critical to analyse the total circuit, not just the individual crushers. To fully understand the performance of the entire circuit, dynamic simulation should be applied. Without the holistic understanding of the total circuit and the incorporation of transient effects, the full circuit performance cannot be adequately determined and the true energy picture will not be quantified.Based on detailed mechanistic modelling of crushers by the authors and the application of dynamic simulation, the opportunities to optimise the use of crushers for energy efficiency are examined.

Aug 8, 2011

By F. Figge, T. Hahn

In this article we present Sustainable Value, a valuation methodology to assess sustainable value creation of companies. Sustainable Development posits that decisions must not only take into account economic capital but also natural and social capital. Sustainable Value, the methodology presented in this paper, borrows the idea from financial economics that the return on capital has to cover the cost of the capital. Capital costs are determined as opportunity costs, i.e. the forgone return that would have been created by an alternative investment. By expanding the well established logic of the valuation of economic capital in financial markets to also cover natural and social capital we provide a methodology that allows an assessment of the most efficient allocation of economic, natural, and social capital for sustainable value creation in companies. We demonstrate the practicability of the methodology by the valuation of the sustainability performance of British Petroleum (BP).

Jan 1, 2005

By Jeffrey L. Zelms

There is no known, practical substitute for lead in the automobiles, communications systems, medical equipment and computers that Americans use every day. However, there are many who say lead should be stopped at its source -- banned. As America's largest lead producer, The Doe Run Company has ralized that it must do more than mine and reclaim lead efficiently and safely. It must also earn the public's consent to operate if it is to continue to be a viable business. LEAD - THE BRILLIANT PERFORMER: REFURBISHING AN IMAGE It's been an embarrassingly long time since I was a college student. However, I remember there was no course at the University of Missouri's School of Mines and Metallurgy that had anything to do with the public relations aspects of mining or, put another way, the politicization of mining. It's been an embarrassingly long time since I was a college student. However, I remember there was no course at the University of Missouri's School of Mines and Metallurgy that had anything to do with the public relations aspects of mining or, put another way, the politicization of mining. I haven’t perused the course catalog for Penn State’s College of Earth and Minerals Sciences. But I strongly suspect I wouldn’t find such a course there today, either. A statement by the chairman of one of the country’s largest chemical companies leads to the point I want to make. He described his business this way. He said, “We’re a public affairs company that just happens to produce and market chemicals.” Like chemicals, minerals and mining are politicized today. To the extent that we don’t understand that reality, we don’t understand that reality – and act on it – we’re less likely to survive in this business. Some of you may well be saying to yourselves, “This guy Zelms is an alarmist.” That’s fair enough. Because it is absolutely true that there’s n o known, practical substitute for lead today. And it’s also absolutely true that, knowingly or not, Americans use lead everyday. It’s in our automobile batteries. It’s an integral part of communications systems. High tech (and low tech) medical equipment contains lead. And lead is an essential component of computer and TV screens. But even with all these uses, lead has a negative image today. An image so negative that its very existence is threatened. If you doubt that, consider these two statements made in 1989. Statement one. “It is probably reasonable to argue that exposure is the single most important and critical environmental health problem in the U.S., and possibly also the world…” Statement number two. “Many of the uses of lead should be terminated. We need to go back to the ultimate source: that is, taking lead out of the ground and putting it into the product stream and we need to turn it off at the ultimate source. Not the approximate lead in gasoline, or lead in air, or lead in food. Go right back to the source and start cranking it down." (End quote.) Those are what I call strong statements. And they weren’t made by some celebrity spokesperson for the environment like Meryl Streep. Both these statements were made by Dr. Ellen Silbergeld, whose long list of professional and academic credentials includes: o Adjunct professor and research scientist at the University of Maryland Medical School and Johns Hopkins: o Chief toxic scientist and director of the Toxic Chemicals Program of the Environmental Defense fund; o and President of the Society for Occupational and Environmental Health. If Dr. Silbergeld were the only person making these kinds of statements, it would be one thing. But she’s not a voice in the wilderness, by any means. Also for those of you who say, well since there’s no known substitute for lead, how on earth could it be banned. I refer you to a number of bills before Congress that would permit the EPA to ban any product if it is determined that its

Jan 1, 1992

By D. L. Mckay

"Texasgulf's 25-foot-diameter Kidd Creek No. 2 Shaft is situated next to the company's No .1 Shaft, so that both shafts can share common surface and underground facilities. Shaft construction, covering a span of five years from collaring to commissioning , started by freezing the 50 feet of grey varved clay covering the bedrock. After first completing the concrete headframe, sinking to the 5/00-foot horizon utilized two different shaft construction methods. The top 2800 feet was excavated by slashing a 6-foot-diameter borehole and hoisting the broken material up the 3OO0-foot-deep No.1 Shaft; the remaining 2300 feet was excavated by conventional benching methods. Prior to installing the 5100 tons of galvanized shaft steel on the completion of the sinking operation, the sinker was able to install all thirteen armoured electrical cables in one pass with his modified galloway stage. All loading and lip pockets were installed along with the steel guides and bun tons during the equipping operation.IntroductionOn November 21,1978, Texasgulf completed the No.2 Shaft at Kidd Creek Mine. This shaft is the largest shaft (volumewise) in North America and is unique in many respects . The purpose of this paper is to outline some of the unique features of this shaft as well as to record how this facility was constructed.Soon after sinking No.1 Shaft, Texasgulf started a program of exploratory diamond drilling from the 2800 level in No. 1 Mine. The drilling outlined sufficient ore below that level to justify a second mine. Feasibility studies demonstrated that production could be increased by one-third exclusively from this deep ore . The study called for a 25-foot-diameter shaft to the 5100-foot horizon to service a mine producing 5,000 tons of ore per working day.The site chosen for No.2 Shaft and head frame is 350 feet southwest of No.1 Shaft. This, along with No.1 Shaft, will be away from the influence of ground subsidence when mining at depth. The collar and head frame foundations are located on a flat rock ledge some 70 feet below surface. This flat ledge was found by test holing through the overburden by diamond drilling. It is fortunate that this location best satisfied the surface layout and logistics for both surface and underground ore and waste handling."

Jan 1, 1981

By Dennis R. Rice

The Kettle River Joint Venture is 70 percent owned by Echo Bay Minerals Company, a wholly-owned subsidiary of Echo Bay Mines Limited, and 30 percent owned by Crown Resources. Initial announced ore reserves were 700,000 troy ounces of gold contained in three deposits located east and north of Republic, WA., U.S.A. Additional reserves are being proven. Processing of finely ground ore by preaeration-carbon in leach (CIL) circuit was selected followed by cyanide destruction by the INCO Air/SO2 process.

Jan 1, 1992

By J. W. Wilson, P. C. Graham

SUMMARY The Witwatersrand quartzites in which South African gold mining operations are moat exclusively conducted, are notoriously difficult and costly to drill. Despite this situation, however, with the high cost of developing new mines and extending existing mines, together with the rising cost of labour and mining problems resulting from the ever-increasing depths of workings, the demand for raise-boring in these formations is increasing rapidly. Not only is the demand for raises and shafts increasing, but also the length and size of these excavations. Raise-boring studies carried out in South African gold mines have indicated that increased penetration rates and possibly reduced costs could be obtained if higher thrusts were available at the reaming head. Until fairly recently there has been no raise-boring machine suitable for underground use that possessed the thrust and torque characteristics necessary to achieve high penetration rates in hard abrasive quartzite formations and the cutters available were not really developed for high loading. In response to these requirements a raise-borer, the Robbins 83R was designed and built in Seattle, U.S.A. for the Anglo American Corporation. This machine is operating in South African gold mines and is currently being used at a depth of 12 000 ft below surface in one of the. Group's mines. The initial raises bored have substantiated that increased penetration is attainable at high thrust and it is now apparent that the machine is sufficiently versatile to drill raises of up to 12 ft in diameter in quartzite formation over a length of 2 000 ft.

Jan 1, 1974

By John M. Devine

The severe corrosion of equipment that is caused by the presence of hydrogen sulphide in oil and gas has been described in detail by several authors. Such corrosion, termed "low-temperature hydrogen sulphide corrosion", presents a somewhat different problem from the "high-temperature hydrogen sulphide corrosion" that is encountered in refinery operation and which has been described by various-investigators of refinery corrosion.

Jan 1, 1932

By P. T. Bissert, T. J. Lutz, J. A. Yonkey, G. T. Homce

"Underground refuge alternatives require an air source to supply breathable air to the occupants. This requires pressure relief valves to prevent unsafe pressures from building up within the refuge alternative. The U.S. Mine Safety and Health Administration (MSHA) mandates that pressure relief valves prevent pressure from exceeding 1.25 kPa (0.18 psi), or as specified by the manufacturer, above mine atmospheric pressure when a fan or compressor is used for the air supply. The U.S. National Institute for Occupational Safety and Health (NIOSH) tested a variety of pressure relief valves using an instrumented test fixture consisting of data acquisition equipment, a centrifugal blower, ductwork and various sensors to determine if the subject pressure relief valves meet the MSHA requirement. Relief pressures and flow characteristics, including opening pressure and flow rate, were measured for five different pressure relief valves under a variety of conditions. The subject pressure relief valves included two off-theshelf modified check valves, two check valves used in MSHA-approved built-in-place refuge alternatives, and a commercially available valve that was designed for a steel refuge alternative and is currently being used in some built-in-place refuge alternatives. The test results showed relief pressures ranging from 0.20 to 1.53 kPa (0.03 to 0.22 psi) and flow rates up to 19.3 m3/ min (683 scfm). As tested, some of the pressure relief valves did not meet the 1.25 kPa (0.18 psi) relief specification.IntroductionThe Mine Improvement and New Emergency Response Act of 2006 (MINER Act) was enacted in the United States in the wake of three mine explosions/fires that claimed 19 lives that year. Intended to help improve underground coal mine accident preparedness, the MINER Act includes provisions that target mine safety issues in areas such as emergency response planning, adoption of new technology, training and education, and mine safety standards enforcement (U.S. Mine Safety and Health Administration, MSHA, 2006). Section 13 of the MINER Act specifically directed the U.S. National Institute for Occupational Safety and Health (NIOSH) to provide for research into the effectiveness and viability of refuge alternatives for underground coal mines. This mandate culminated in the 2009 adoption of changes to Title 30 of the Code of Federal Regulations (30 CFR) mining health and safety regulations, requiring underground coal mines to provide mine emergency refuge alternatives and associated components, to provide a life-sustaining environment for persons trapped underground. Such refuge alternatives can be either self-contained mobile units or built-inplace facilities. The regulatory changes also include provisions establishing requirements for MSHA approval of refuge alternatives and their components, and among these provisions are numerous criteria for providing a safe breathable atmosphere under positive pressure within the refuge alternatives. One specific criterion for maintaining a safe refuge alternative atmosphere requires the inclusion of an air pressure relief valve that will activate at a maximum of 1.25 kPa (0.18 psi), or at a pressure above mine atmospheric pressure, in the refuge alternative, as specified by the manufacturer when the breathable air is supplied by a fan or compressor (MSHA, 2008)."

Jan 3, 2018

By Jerry M. Whiting, Neil J. Duncan

"Does Canada need a mining industry? Isn't it a chronically depressed collection of businesses that pollute the air and water and tear up the countryside? Wouldn't it be better if Canada's investors devoted their attention to high-technology endeavours, tourism, and other relatively pleasant tasks?Probably the answer to whether Canada needs a mining industry in the 21st century is to look at the real mining industry that is in operation today. The facts indicate that mining is a very important contributor to Canada. It has certainly encountered some challenging times during periods of recession, and it face s severe and continuing problems of cost and competition in world markets. However, uneconomic mines have been closed, others suspended, and productivity has risen dramatically with employment at 77 000, down from 101 000 in 1981. The country's metal and non-metal mines, metallurgical plants and semi-fabricated metals industries employed an estimated 378000 workers in 1986, and paid wages than any other sector of the Canadian economy. This effort resulted in the production of 60 different metals, non-metals and structural minerals valued at $13.5 billion.The trade aspects of the mining industry are of paramount importance. If there is a reason for this situation to change during the next century. it eludes the authors. Canada has the well-developed expertise to discover, evaluate, develop, operate and profit from existing and new businesses based in an enormous area endowed with a nearly unbelievable variety of mineral resources. Many countries throughout the world must rely on producers like Canada, if they are to maintain and/or improve their standard of living."

Jan 1, 1988

"A method is described for determining the viability of hard rock orebody extraction by block caving. Using a very limited amount of geotechnical data, the procedure enhances Laubscher’s empirical stability graph method by using the complex structural modelling system (ChaSM) to assess cavability and block cave tonnages.IntroductionIn considering the selection of suitable mining methods, block caving has gained popularity over other extraction systems in recent years (Butcher, 1999). This has been ascribed to the fact that block caving is the lowest cost per ton mining method, with orebodies that were in the past considered unsuitable for caving, now being successfully mined. However, even though all orebodies will cave, a problem exists in the evaluation of economic viability — it is necessary to be able to predict both when the orebody will cave and what will be the sizes of the initial ore fragments (and the associated tonnages) that report to the drawpoints. This problem is compounded by the fact that, during the scoping study phase of a project, only limited geotechnical data may exist on which to base an assessment of whether block caving is viable or not. Empirical and numerical methods of cavability assessment do not account for the full effects of geological discontinuity trace lengths, nor for the stress regime. Those require significant geotechnical data to be available. The result is that uncertainty may exist as to whether block caving is an economic option. This uncertainty is complicated by the fact that limited experience exists with the caving of more competent orebodies.This paper describes a method for assessing cavability, and for predicting the size of initial ore fragments and the tonnages reporting to block cave drawpoints, using only the level of data normally available during a scoping study. Fragment size and tonnages are assessed by identifying potentially unstable blocks and wedges in the undercut back using statistical joint data. The effects of lateral confining stresses are accounted for by comparing the in situ stress orientations with the joint orientations. To evaluate the accuracy of the method, a back analysis exercise was conducted to predict cavability and initial tonnage for a mine in which the actual behaviour is known. The method is then applied to cavability and tonnage predictions for a hard rock orebody."

Jan 1, 2002

By Henry H. Rubin

Rubber and its contributions to the economic solutions of environmental problems in the minerals industry. The intelligent applications of "Rubber" to systems of noise abatement, vibration isolation, dust containment, weak and corrosion resistance has proven economically beneficial. Intelligent application requires a thorough understanding of the nature of the material, knowledge of the process wherein it is going to be applied, and consideration of the environmental conditions in which it will serve, for these determine the proper amount, type, compound and configuration for an economically successful application.

Jan 1, 1979

By S. Ozbilen

"Al-Li binary alloys with nominal Li contents of0.15, 1.1and2.8 (in wt%) were aged naturally at room temperature for two months, aged at low temperatures ( 65 and 1 OOEC) for up to 2 months and aged artificially at 190EC for 4 days after water quenching to 25EC following solutionizing at 530EC for 20 minutes. Ageing behavior of these binary alloys were studied by Vicker's Hardness measurements and DSC thermal analysis. Thermal analysis results indicate the formation of GP zones of Al-Li system in Al-2.8wt%Li binary alloy. In the same alloy, rapid quenching from one phase region (a) gives rise to precipitation of small o' particles in a matrix (a) with still high supersaturation. During ageing of this alloy below lOOEC an additional transformation, i.e., GP zone formation occurs proceeding at a very high rate which is described on the basis of the theoretical analysis for the quenched Al-Li system proposed by Khachaturyan et al [6]. Ageing at temperatures below 11 OEC takes place slowly by the formation of small d' particles of lower thermal stability than the quenched-in d precipitates in addition to GP zones resulting in an increase in hardness compared to water quenched samples. During artificial ageing, GP zones transform by dissolution to d' precipitates while d' particles already in the microstructure coarsen during under aged condition at which hardness increases with time till peak aged condition.IntroductionIn binary Al-Li alloys the d' (Al3Li) fully coherent internally ordered inetastable phase of Li2 structure with a=0.4038d [1-5] forms homogeneously between 120 and 190EC before the formation of stable d' (A!Li) phase and cause the superior mechanical properties. This is due to an appreciable age hardening effect resulting because of the d' precipitation during ageing [1]. The response of d' to decomposition and its formation kinetics have been studied previously and it is believed that the decomposition of the a-supersaturated solid solution occurs in a two stage process; i.e., a 6 d' (Al3Li) 6 d(A!Li). Khachturyan et al [6] theoretically investigated precipitation of the d' phase and gave an interpretation of the transformation paths of the quenched Al-Li alloys. They predict that the disordered supersaturated solid solution congruently orders, and then the uniformly ordered solution decomposes into ordered regions that differ in Li-content. Finally, ordered d' phase forms in the disordered matrix."

Jan 1, 1998

By L. S. Breckon

This paper describes the methods and equipment used by the Utah Copper Co. in constructing a vehicular tunnel at Bingham Canyon, Utah, Completion and use of this tunnel for vehicular and pedestrian traffic permitted abandonment of the long-used county highway connecting Bingham and Copperfield. Expanding- operations of the Utah Copper open-cut mine, necessitated construction of a vehicular route away from the ore body. The site Of the tunnel is well beyond ultimate nit slopes and future mining operations. The tunnel not only diverts vehicular and pedestrian traffic is but also carrier, creek water, copper water, sewage, pipe lines, and. power and telephone cables between the two communities. The dimensions of the tunnel permit one-way traffic only. Traffic-control lights have been installed. Owing to the possibility of accumulation of carbon monoxide gas from automobile exhausts, automatic gas detectors has been installed at various stations. These detectors control the operation of a large exhaust fan situated at the upper portal of the tunnel.

Jan 1, 1940

Federal lands often contain extensive mineral resources and decisions affecting access to those lands are made with knowledge of the possible minerals-related consequences. Information is provided to the Bureau of Land Management (BLM) in this report for use in preparing environmental impact statements on the Western Mojave Management Area (WMMA) and the Desert Tortoise Priority Habitat (DTPH). To augment U.S. Bureau of Mines (USBM) efforts such as the Mineral Assessment of the Planned Foil Irwin Expansion, Modified Silurian Valley Alternative, San Bernardino County, California which is in progress, and the Economic Analysis of the Minerals Potential of the East Mojave National Scenic Area; California, the USBM studied mineral deposits and estimated the potential impacts of mining in a segment of the California desert; the 8.7-million-acre WMMA, an area which includes the 1.2-million-acre Desert Tortoise Priority Habitat (DTPH). In addition, this information is intended to assist administrators, legislators, and the concerned public in understanding the economic importance of mineral resources in the California desert, especially that portion designated as the WMMA. See figure 1.

Jan 1, 1993

By Fred Tarquinio, Giovanni Bonita, Lars Wagner

"A new embassy for the Peoples Republic of China is under construction in Washington, DC. The 475,000 square feet (44,125 m2) structure has five levels below ground and four above, making it the largest embassy in Washington DC. A vertical soil nail wall was used as the primary support of excavation system for the project. The soil nail wall was irregularly shaped, benched in areas, and up to 98 feet (29.9 m) in height. The soil nail and shotcrete system consisted of approximately 1,600 soil nails and 50,000 square feet (4,645 m2) of exposed shotcrete wall surface. Design and construction challenges included soft soil conditions, inside wall corners, underground utilities, seismic impacts from blasting, and logistical and political factors. Overall, wall movements were lower than expected, with maximum horizontal movement less than 0.25% of the total height of the excavation.INTRODUCTIONThe proposed Embassy of the Peoples Republic of China in Washington, DC, will consist of about 475,000 ft2 (44,125 m2) of building space and contain up to four fl oor levels above ground and fi ve levels of basement (Figure 1). When completed, the building will be the largest embassy in Washington, DC. The architect for the project, Pei Partnership Architects, along with the world-renowned architect I.M. Pei, made effi cient use of the site by inserting the building into the existing slope. Consequently, excavations reach heights up to 98 feet (29.9 m) on the southern side of the property and 42 feet (12.8 m) on the northern side.The soil nail and shotcrete system consisted of approximately 1,600 soil nails and 50,000 square feet (4,645 m2) of exposed shotcrete wall surface. The location of the building relative to the property line called for tight excavation requirements, including precise wall positions and shotcrete tolerances. Design and construction challenges included soft soil conditions, inside wall corners, arched walls, underground utilities, seismic impacts from blasting, and logistical and political factors.SITE INVESTIGATIONInformation obtained from the geotechnical investigation revealed about 10 to 20 feet (3.1 to 6.1 m) of a loose to medium dense fi ll material placed during previous site activities. The fi ll material was underlain by a silty sand and sandy silt residual soil derived from the natural weathering of the underlying bedrock. This soil sequenced naturally from a medium dense to very dense material through natural weathering of the underlying bedrock. This soil sequenced naturally from a medium dense to very dense material through natural weathering processes in the rock. The underlying bedrock was locally characterized as a gneiss. A water table elevation about 17 feet (5.2 m) above the fi nal excavation level was revealed, except in the “radius” area, where a leaking water main/hydrant generated a high local water table."

Jan 1, 2007