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PARKS 



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first impervious layer of rock. The water 

 in a shallow well should be considered to 

 be, and treated as, surface water. It is a 

 contaminated supply. A deep well is usually 

 driven, while a shallow well may be dug or 

 driven. Both deep and shallow wells are 

 frequently polluted by material entering at 

 the top of the well, and this is particularly 

 prone to occur in a dug well, because of the 

 wide shaft. The entrance of contamination 

 into the mouth of a well can be prevented 

 by sealing up the top of the shaft with a 

 cement platform and protecting the imme- 

 diate vicinity by fences and by intercept- 

 ing ditches to carry off the surface w r ater 

 (Plate 303). If a dug well is used the upper 

 part of the shaft should have a concrete lin- 

 ing to shut out the surface water coming 

 from the immediate vicinity of the well 

 (Plates 304 and 305). All well water should 

 be pumped either by hand or by power. A 

 bucket should never be used. 



Spring water may be derived either 

 from the water flowing above or that lying 



below the first impermeable stratum. In the former instance, the rate of 

 flow varies markedly with the volume of rainfall and, being surface water, 

 is to be regarded as contaminated. The spring water which rises from be- 

 low an impermea- 

 ble stratum has a Tight wooden or concrete 

 more constant flow cover- removab/e ^ 



and is usually po- x tenet box 



. . above gsour>cl : 



table unless it is 



polluted after 

 reaching the sur- 

 face. All springs 

 which supply 

 drinking water 

 should be inclosed 

 in a water-tight 



chamber (Plates 



Sprtnys 



306 and 307) to PLATE XQ ^ 6 CROSS SFCTION OF COLLECTION BOX FOR SPRINGS 



prevent the en- (Commission of Immigration and Housing of California.) 



PLATE No. 305. A DUG WELL 



Showing method of excluding surface 

 water by use of a concrete platform and by 

 making the upper part of the walls of the 

 shaft water tight with concrete masonry. 



(Iowa State College Bulletin No. 56, 1923.) 



