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<br />
<br />r f~,' .
<br />f.-V:"';
<br />
<br />
<br />Zone of
<br />oerO',on
<br />
<br />, {.~;4 'I .." > ..,~
<br />, ~ M;~,HHl
<br />~1t "1' J; . S~rfoce WOle,\
<br />W obl"'t; ~ ~.. 1__1'.
<br />
<br />Ion. of iOI",ot'on
<br />
<br />FIGl'RF. 4-Zmr.. of analion and ~oni' of saturation.
<br />
<br />towd, i~ ~uckt-d in and held ag-ain~t the pull of
<br />gra\it~,. The prC\-~ure in the water i~ Ies.." than
<br />the pn-'s,<'UTt' of the almosphere, so it L" foned by
<br />atmospht'ric pre.,,",url' to "tay where it is. Below
<br />the .....ater table. all the \~'ater i,,, under a prt'S<.un'
<br />wcater than atmospheric. This p~ure is suffi-
<br />cient to force the water to move from one pore
<br />into a larger one when the larger om.. is emptied.
<br />.-\ \H..11 is nothing bul an extra.large pore into
<br />.....hich the prCl'...ure forces the .....ater to mo\'e to
<br />r('place .....ater dra.....n out by the pump.
<br />
<br />
<br />',",
<br />, ~ ' # ~ '
<br />:'..:'::'
<br />'I','
<br />
<br />Thus, any .....e11 that txtends be1O\~' the .....ater
<br />table will fill .....ith water up to the levd of the
<br />.....al('r table. If the well is pumped dry, it .....ilI
<br />fill up again. The important thing is, .....ill the
<br />.....ater come in fasl enough to make the well useful
<br />for a continuing water supply? .-\ tight rock such
<br />a.... day or granite, with tiny pores or only a few
<br />hairline crack... may gin up its water so slowly
<br />that senoral days w-ould be T('quircd for a well to
<br />fill up to th(' len'l of the water table. Obviously,
<br />such a rock would not be a u~fuI .....ater bear('T.
<br />On the other hand, the openings in the rock may
<br />be lan;:e enouR'h to let waler through fredy, SO
<br />that it can he taken OUI in u~dul amounts. The
<br />amount... yield('d to a .....ell that ju!<tif)' calling a
<br />Tlx-k u'ata beadng range from a few hundred gal-
<br />Ion.. a day, where only a domestic supply L". needed,
<br />[0 a.". much a" ,<.('\'I."ral million gallons a day.
<br />The word aquifer comes from two Latin words:
<br />aqua, or walr-r, and far~, to bring. The aquifer
<br />liltTall~ brin~ waler (undt"rground, of course).
<br />The aquifer may he a layer of gravel or sand, a
<br />laYt"r of s,and!<IOIlC or of cavernous Iime>tone, or
<br />
<br />,
<br />. .
<br />.-
<br />. .'
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<br />'. '
<br />",#
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<br />"~ #
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<br />D~lo,1 of wale. in lon~
<br />of oerolion
<br />
<br />/..Rin9s..ofeCPillc,r....ctef
<br />(not g,ound ....cle.) i""ound~
<br />conloell of rod partIcles
<br />ci cbo...~
<br />
<br />."
<br />
<br />
<br />
<br />____ "pprcximole ____
<br />level 01 me ""cle. labl.
<br />
<br />"II Op~nings belc"" ""01..
<br />Icble full of ""oter~
<br />g.ound ....ole.
<br />
<br />Grov.1
<br />
<br />C.evie&<! rock
<br />
<br />FIGl'RE 'j~Hou' u'Qttr occurs in tht' rocks.
<br />
<br />6
<br />
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