Norwich bulletin., 1910-12-05
WELLS IN CRYSTALLINE ROCKS.

The boring or wells In crystalline iocJc is no new thing in Connecticut, and ths record of 2s0 wells bored in his state with results. it does not ap- pear to be at all surprising that the second attempt on the Norwich water sheds promises to prove unsatisfa ctory, 70 far as abundant yield is concerned.
 A bulletin issued by the geological survey on Underground Water Re sources of Connecticut" by Herbert E. Gregory. in 1909, shows that there nave been 61 wells drilled in eastern Connecticut, and II of these were in Norwich. The well of the Thames ville Iron works, having a capacity of lie gallons a minute. being the third argest yield in the state. The Ulmer tannery well. from which hundreds of citizens are being supplied with water free, is 115 feet deep and yields 1e gal Ions a minute. The average production of the wells here runs high because of he high yield of water by the Thames vile well. which is only GO feet deep.
 Mir. Gregory says on page 93 of the limit of depth of these wells that
 while supplies have been obtained at all depthe from 15 feet to 500, the largest percentage of failures is among the wells of over 400 feet in depth"
 Tn deciding at what depth an un- successful well should be abandoned a number of factors must be taken into consideration. The table on page 100 shows that the average depth of the wells varies considerably for ditereBt rocks. The average depth Of rock of 16g welis Wss Ss.s feet, and the total depth. including the surface rna- terial overlyang the rock is 1884 feet. About S9 per cent of the wells are Irsder 200 feet. Tn many of the wells which have gone below 250 feet the 11a4H supply, and in several the entire supply. has come from seams less than 150 feet in depth. From a study of the recorded wells it would appear, there fore, Shat II a we'll has penetrated 250 feet of rock without success the best policy is 10 abandon fR and sink in an- other location. For wells in a grand OrtSrtte, w1Iieh have been successful at an average greater depth than in other rocts. this depth might be somewhat 100 small. but for wells in other rocks it Is possible that a maximum depth of zoo feet should be adopted.
 "The average yield of 123 wells in he crystalline rocks is 12.7 gallons a minute. and as their average depth is 10s fest the cost of the average well for this yield Of water is $4.25 foot, or S45O
 The wells located on hills average .ess in cost than those in the valleys, but the average yield of both Is about the same
 These wells appear to maintain a remarl1a biy constant yield from year to vsar. Although tine drilling of wells in crystalline rocks is a comparatively new venture and almost all these wells nave been sunk in the past three years, TO woll In which water was obtained has feiIsd to yield a supply in contin- ned use"
 The city Of Norwich is estimated to be using about million gallons a day and with exceptional luck @ half hun dred wells of the average capacity of 12.7 gallons ought to be enough to meet Onr daily demand.
 Of these 2s0 wells in the state, g viejd TO gallons or less a minute, so comparatively speaking the drilled wells at Fairview have turned out as wafi as could have been expected.