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t'~ <br />• 2. DEEP WILL I_' ^CTI0;1 PRP.CTZCES <br />, <br />• <br />~' I?~TRODC;CTION <br />4', <br />Ceeo well waste disposal is the injection of a liquid waste, under <br />pressure or by gravity, into a corpus geological strata. U~.,+ard <br />migration from the disa~sal zone, mtentially resulting in ground <br />water or surface water contaninatinn, will occur if the confining <br />beds contain natural per?n°able channelways, such as faults and <br />fractures, and if hydraulic pressures are sufficient. Injection <br />pressures, if high enough, can fracture the overlying formations. <br />Abandoned, poorly constructed and improperly plugged ooreholes may <br />also aid utward migration. <br />Fran 1958 to 1976, disposal :.ells discharged about S x 106 m3 of <br />industrial wastes at pressures up to 450 psi into the Cetroit River <br />Group in the Sarnia ar=_a. These activities oere teninatc~ as a <br />result oE,breakouts of brine and wastes at the surface. The types <br />of waste injected wore primarily sent caustics, acids, ci:enols, <br />hydrocarbons, and brines (see attached Tables). <br />Since 1976, provincial authorities have allrnred gravity dis~sal of <br />wastes (cavern washing and oil field brines) five miles away frari <br />the river. The deep well orx rations were approved by the Ministry <br />of Natural P.esources and tcerators sere requires' to submit :ninthly <br />r_ports on injection volumes to tie Pinistry of the Envirorrent <br />Geology and Hvdrxeolooy of La:ton Cn. in the 9icinity of Sarnia <br />A vertical 'section' cut through khe ground in this area would <br />display, beginning at the too: 30 to 50 meters of clay (lake and <br />• glacial deposits) overlying cedrock consisting primarily of shale <br />(Lambton and Hamilton groups) over limestone a:r dolomite (Detroit <br />River Groua), over limestone, shale and sa'_t ('Salina Fors=t ion', <br />see attached diagram). Sand and gravel occurs bet~aen the clay and <br />upixr shale; groundwater within this zone cgnstitutes the primary <br />source of X11 water in the area. This zone is referred to as the <br />'freshwater aquifer'. <br />Oil and gas deposits occur at various depths within the rock units. <br />Wells drilled into these rocks for exploration and productirn over <br />the last 100 years have resulted in an abundant= of abandoned and <br />often improperly plugged oil a:d gas wells. <br />The ideal concept of dee? wall injection of ~.,astes is to plat= the <br />material at sufficient depths and under 'confining' rock units <br />(such as shale) r,~ich will pr=_vent their subsequent entry into t:ie <br />e msystem. However, the 'Detroit River Group', into which rtnst of <br />the wastes were injected, does rot fully tre et the generally <br />accented criteria applied to disp'zsal zones ar.3 confining beds. <br />Unknrnan, abandoned wells, natural Fractures (joints and faults) <br />arid, mssibly caves, as well as man-irduc~ Fractures (Fran <br />pressure injection of the wastes) all provide agtential, ciar,nels <br />for the wastes to tmve uo into the Er=_shwater anuifer. <br />,i <br />