The largest sewage treatment plant in Norway is being constructed underground at Bjerkås, 30 km south of Oslo. The plant will serve 300 000 persons and is designed to treat a dry weather flow of 3.0 m3/s. The main reason for the subsurface location is environmental. The plant is being placed in 11 parallel caverns of 16 m span with 12 m wide pillars between. The rocks in the area are Cambro-Silurian shale and nodular limestone. The conditions revealed by excavation were very similar to those predicted from the combined results of surface mapping, drill core analyses and seismic measurements The support is systematic bolting and shotcrete, partly mesh reinforced. Some injection work has been undertaken to prevent inflow of water. The rock mass underlying an industrial area nearby is fed by water through several boreholes to prevent lowering of the ground water table in the overlying clay. INTRODUCTION Norway has long traditions of building underground. Our hydro-electric projects make up the corner stone of Norwegian expertise regarding major subsurface constructions. This technology has been converted into use for several other purposes: air raid shelters combined with sport arenas, subway systems, oil storages, general storage and public utility facilities such as water and sewage treatment plants. Although representing a rather unique feature it was not out of the ordinary when the communities of Oslo, Bærum and Asker in 1976 decided to go ahead and build a large regional sewerage facility consisting of 40 km full-face bored tunnels and a mechanical/chemical treatment plant excavated into the hill of Bjerkås in Asker, 30 km southwest of Oslo - adjacent to Oslofjord (Fig.l). During the early surveys - and the preliminary reports - several alternatives were considered - also surface locations. The main reason for choosing the subsurface alternative was of an environmental nature. A surface plant was considered less expensive. However, the difference was eventually considerably less than originally expected. The Bjerkås area was finally chosen for the plant mainly because of political considerations. The rocks were estimated to be of poorer quality here than at the other possible localities, but Bjerkås was already an established industrial area with few private homes. GEOLOGY The project is situated in the geological formation called the Oslo Graben. The bedrock at Bjerkås consists of sedimentary rocks of Cambro-Silurian age, mainly shale and limestone, cut by some Permian dykes. The Bjerkås area is a hill about 70 m high. Due to limitations of space the orientation could not be chosen in the most favorable direction and the minimum rock cover is approx. 15 m. Geological mapping showed that the northern slope of the hill consisted of nodular limestone, in the southern slope there was shale. Seismic refraction measurements showed velocities of about 5000 m/s in the nodular limestone and 2500 - 4000 m/s in the shale. Some crushed zones gave 2000 - 3000 mis, the same as a near surface weathered zone of about 10 m thickness.

Industrial complex around Korba face acute environmental pollution. Disposal of industrial, mine waste and domestic: refuse need coordinated.approach for evolving a sewage network controlled by local drainage system and geologic constraints. Utilisation of abandoned coal mines for waste disposal, sewage treatment and storage of water can provide viable economic return besides improving pollution problem. INTRODUCTION The Korba town, in an area of approximately 200 sq Jon locates four major industrial complex - such as thermal, alluminium, explosive and fertilizer factories besides an upcoming super thermal power station. The colonies are situated aouth of the industrial plants. The urban and industrial planning of the region, with the growing popUlation to about one million in the near future, calls for a sustained effort in tac:kling the problems relating to base water supply, atmospheric and aquatic pollution and disposal of industrial waste/domestic refuse. The present paper deals with the disposal of waste material in the available underground space. GEOENVIRONMENT AROUND KORBA AND FEATURES CONTROLLING ECOIMBALANCE The landscape around Korba is characterised by low, isolated hills and near flat crest lines with. general rising elevation from south to north. The isolated hills are aligned in E-lf direction with local deviation to NNE-SSW and NE-SWdirections and range in altitude from 274.32 m tg 304.8 m. The isolated hill s have a fairly steep rocky slope of about 50 to 70 and project out as ‘tors’ while the low ground slopes from 5 to 10. The principal drainage- river Hasdo, is aligned in N-S direction and drains mainly through a sedimentary area. The other major tributaries - Belgari and Dhengurnalas have a general ENE-WSW to E-W flow direction on the left bank of Hasdo while on the right bank, the Ahiran nala flows in NW-SE to WNW-ESE direction. The softer sedimentaries control the drainage pattern which is subparallel to subdendritic. The low undulating hills, occupied by clastic and ancient crystalline rocks form the denudation tract while the fan/talus, piedmount/slope wash and the terraces are some of the characteristic fluvial deposits. The valley form is V-shaped at the head reaches while it is flat bottom and rectangular in the main body section of the. streams/rivers, with 2–3 m high steep bank, sloping about 70° -80° to vertical. Banks of Hasdo and its tributaries like Ahiran, Belgari and Dhengur show evidences of mass wasting in the form of debris slip, erosion scar and land subsidence due to soft and erodible clastic rock. The sandstone is soft, friable, arkosic and granular,med1um to coarse grained with hiqh percentage of felspar. The perviousness of sandstone is indicated by porosity to about 15% and due to the presence of erosion channel and cavities. Large quantities of groundwater in the porespaces make the sandstone a good confined and unconfined aquifer due to interlayering with shale. The granite is medium to coarse grained with large size felspar. Physical and chemical weathering of granitic rock is less active on the protuding hills rot are erratic and intense on surfaces in the process of exhumation. This weathered zone, controlled by topography, has limited ground water.

The present paper presents methods for injection of brine solution into the subsurface investigated under the Compressed Air Energy Storage Project of the Department of Energy in the United States of America. The principal objectives in this investigation were two fold: Prevention of any possible pollution of ground water by the injected brine solution. Avoidance of over pressurizing the solution-deposit zone by the injection operation which will result in: induced undesirable fractures in both upper and lower confining formations, and inefficient and uneconomical injection operation. INTRODUCTION The continental United States has many rock salt deposits, as well as salt lakes and natural brines. Salt is found in 4 major basins as well as several minor basins (Fig. 1). Taken together, this means that over one half of the states contain salt deposits (Lefond, 1969). The injection of brine into geologic formations can cause contamination of existing portable ground water. The contamination is due to either extensive lateral spreading or vertical upward of downward movement of the brine. The direction and magnitude of brine movement is a direct function of the total geologic environment surrounding the injection point. The total geologic environment embraces the rock types, fractures, rock strengths and permeabilities, in situ state of stress, ground water regime(s), and geochemistry. During brine injection containment is ideally obtained by ensuring that the suitable injection sequence, which is highly permeable, is over/underlain by impermeable rocks. These rocks restrict both the vertical upward and downward movement of the brine. The lateral extent is dependent on the uniformity, isotropic aspects, of the injection formation. The operating fluid pressures active within the migrating brine, must be known to ensure that they do not cause either, a) tensile fractures or b) extend pre-existing fractures within the over/underlying confining rocks. The promotion of fractures markedly increases the permeability of the low permeability confining rocks, and consequently contamination of previously isolated ground water by the brine. CRITERIA FOR INJECTION FORMATION The injection formation should be: an extensive sedimentary formation: unfractured sandstone, limestone, dolomite, and unconsolidated sands are the general lithologic types used for injection; at least several hundred feet thick; hundreds of square miles in extent in order to minimize injection pressures and to provide a buffer zone against migration of brine to discharge areas; an area of relatively simple geologic structure without complex folds and faults (synclinal sedimentary basins are favorable; high formation pressures are unfavorable); of uniform hydraulic properties with high enough permeability so that excessive injection pressures can be avoided (according to Warner in 1977, a porosity of at least 10% to 20% and permeability greater than 100 millidarcys, or 0.2 ft/day, is required for large-scale brine injection); of low or negligible lateral movement of formation fluids, to a discharge point (grouting may be necessary to lower the permeability so that lateral confinement is maintained); a zone that is below the level of fresh-water circulation with the surface