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<br /> <br /> <br />,- ",' <br />be u~d. If a ~'jJo"""'lle is to he drilled. a profes- <br />sional well driller may be hired to do the drilling. <br />'Ioe ~amples of earth material brought up by <br />drilling are examined and anal~-lcd to determine <br />which Mrata are watt'r bearing and how large <br />an area thq underlie. Drillin~ test holt~ is an <br />t'xpcnsi\"t' hu"in<.~s. generally CO-ling a Jollar or <br />more and ~m('times as much as SJO a foot. A <br />deep holt' (]b\'iously runs into a lot of money. and <br />unnccc~'Qry drilling would Ix wa~teflll. <br />Both on the~ t~t wells and on some of the <br />eXlstin,g wells. the hydrologist will mak~ pumping <br />tests. or aquifer tcstf. Thc--.e ~ientifkally (on- <br />troIled tests are not fi'ally te;ts of the well il"Clf. <br />hut arc designed to g1\'C infonnation 011 th(' <br />water-bearin~ properties of the aquifer tapped by <br />the well. The te,,1 enables the hydrologist to dc- <br />tcnninc the amount of water mo\"ing through <br />the aquifer, the \"olume of w'ater in the aquifer <br />that can enter the well. and \~hat the elIen of <br />pumping- will be on the water lenl in the pump('d <br />wdl and in other wells in the area, <br />Because quality is jU"1 as important as quan- <br />tity, he will collect s"1.mples of waler from certain <br />weill', and haw' the'm anak'ed {'hl"'miralh. From <br />this ht;' will know \\hal kind of water can be ob- <br />tained from different aquifer.,;. and if So1.mples arc <br />collected onr sen"ral year", how th(' quality may <br />chang:e when la~c quantities of water an' taken <br />out. <br />Thus you call see that there is no mar:ic about <br />the hydrologist"s work. It i~ based on common <br />~me and M"icntific ob"t'T\'ation. He u."Cs all the <br />clues he can gCl-whal he can ~('(" of thl" rocks as <br />they are exposed at the land surfac(' (lr in road- <br />cuts, quarries. tunnels, or mines. and what he can <br />learn from wells_ <br />Thl'se wound-water studies v.ny in l~omplcle- <br />ness with the need for infonn,1tioll. If Iht: need <br />is most!\" for dOlnc:-.til" supplies. an area the size <br />of a county can he studied in a slimmer. and the <br />report and maps prepared the follll\\'ing \\inter. <br />The hydrologist's repon and nMp" will shah <br />"heT(' wau'r (an lx- obtained, wh.11 kind of water <br />it is chemically, and in a Hry gcnc:-ral h'ay hOh' <br />milch i... a\'ailahle. If a n-ry larg(' supply is <br />needed or if there arc problems with the prCSC'nt <br />~upply. more detailrrl studi~ must lx- made, either <br />in the area \\ hl"re the large need exi...t" or. in some <br />cases, hhae a future need is anticipated. What- <br />('\-er the scope of the study. the reporl is designed <br />to pro\"idl' .1 sound basis for whate\'er may foliO', <br /> <br />it. hhether it i" nothing more than drilling home <br />and farm wells. or large-scale" ater projects for <br />a city, an industry. or an irrigation projcct. <br /> <br />WHAT IS GROU:'\'D WATER? <br /> <br />II is hard to picture unrlo:rground water. ~fO"t <br />people ha\"e a fanciful notion of an underground <br />lake. or a murky stream mO"ing along slo\\l}' in <br />dark underground channel:- scarcely high enough <br />to stand upright in. There are such underground <br />slreams in cavernous Iimcstonc or la\"a rock, but <br />Ihey arc not common. ~[ostly. ground water i~ <br />ju:st the water filling- pOfTS or crack<. in the rocks <br />(fi..,5). <br />But if g-round water is not a river or lake as we <br />Ihink of ;hem on the surface, how is it carried in <br />Ihe earth? \\"h>' do~n.t it soak through the <br />earth',' It d{)('S not becau.<.e the rock!> at great <br />dl:pdl lack opcnings-por~ or cracks----through <br />which water can mon', or if they ha\'e openings <br />they are too tightly packed to kt water move <br />through freely. <br />Between the land !>urface and the water table <br />there i~ a !>pace which the hydrologist calls the <br />::on(' of aeration (figs. 4, 5). In the lOne of <br />aeration th('re is usualIy at k;:u;t a little water, <br />mostly in Ihe smaller openings: the larger open- <br />ings in the rocks contain air instead of water. <br />After a heay} rain thi~ zone llIay lx- almost satu- <br />rated; in a long, dry spell it may become almost <br />dry. In the zonc of aeration. water is held to the <br />soil and roch by forces the hydrolog~ts call <br />capiUarit)" and it will not come into a well. <br />'nlcst' arc the same forces that hold enough water <br />in a wet towel to make il feel damp after it has <br />stopped dripping. <br />\\"hen rain fall'l, the first water that enters thl" <br />soil i'l hdd hy capillarity, to make up for the water <br />that has been e\'aporated or taken up by pla.nl'l <br />during the preceding dry spell. Then after the <br />thir;;t} plants and soil ha\e had enough. and if <br />the rain still wntinues to faU, thl- excess water <br />will reach the water table-the top of the zone in <br />w'hich the openings in the rock are saturated. <br />Below the w-ater table, all the opcllin~--crc\"iccs. <br />uannie:s_ P"~- art" complctel~ full of water (fig. <br />5). The raindrops han become ground water. <br />and thi:" water is free to come into a well. <br />The reason the wal('r below the \\ at('r table will <br />come into a well, and the w'ater ahon will not. <br />i:" a bit technical. but not too hard 10 undCr;;tand. <br />111e w'ater al>o\'e the water table. as in the damp <br /> <br />5 <br /> <br />