Deep waste water injection has been practiced since the middle of the last century. More recently, massive solid waste injection technology has been developed, first in the oil industry for non-hazardous waste (~1988), since late 2008 for municipal biosolids (Los Angeles) for treatment and energy recovery (CH 4 generation). C-sequestration through deep injection in the form of solid carbon (biosolids injection), supercritical CO2, or dissolved CO2, is being studied through a number of projects worldwide. The future will bring new applications for deep injection disposal, including certain classes of radioactive wastes, toxic liquids and solids, mine tailings wastes, and other materials. This will happen because sedimentary basins are ideal sites for permanent isolation of wastes at a much higher environmental security level than any form of surface or shallow placement. Deep injection is a coupled geomechanics process, involving temperature changes, stress changes, volume changes, and perhaps chemical changes (e.g. dissolution of CaCO 3). Furthermore, the physical state of the target formation (generally porous sandstones or naturally fractured carbonates) is altered by the process. Understanding these changes is paramount, and must precede attempts to carry out full physics-based simulations of deep waste injection A general methodology and some guidelines for developing deep disposal technology for more toxic solid and liquid wastes are given; these methods involve dilution, adsorption and isolation. will be presented. Finally, it is noted that the Ganga Basin is an ideal place for deep waste disposal: it possesses all the required rock mechanics and hydrogeological conditions necessary to give extremely high levels of environmental security.
Deep injection disposal of waste water has been practiced in the oil industry since the 1960's (OGP 2000), of sour acid gas (H2S and CO2) since the 1970's (Bachu and Gunter 2004), and of ground drill cuttings since about 1988 (see article by Dusseault, this conference). Permeable sandstone and carbonate reservoirs (depleted) or saline aquifers are preferred target strata in all cases so that excess pressures can dissipate rapidly. Though less widely used, permanent non-hazardous solid waste placement into dissolved caverns in salt (Veil et al. 1998) is used in Alberta, Saskatchewan and Texas. Salt is essentially impermeable as well as viscoplastic, so a cavern will slowly close around the solid waste, and once sealed by salt, leachate generation no longer takes place. Given the age of stable (non-flowing) salt deposits, >million year security of waste placement seems achievable. However, suitable salt beds are not everywhere present, and salt cavern disposal development requires a lengthy dissolution period to create a cavern that can then be used for waste placement. Deep solids injection (DSI) into permeable strata involves placing aqueous slurry through continuous hydraulic fracturing as it is not possible to force slurry into a porous medium without filtration of the solids and pore blockage. One must increase injection pressures to values greater than the overburden stress. Because the target stratum is permeable, pressure dissipation occurs after DSI and solids are permanently entombed by large effective stresses.
