CHEMIC.IL EXAMINATION OF THE WATEE SUPPLY. 289 
1904,® before the filter plant was put into operation, and for the 
same period of 1906, after the filter plant had been in operation for a 
period of six to nine months. Considerable and significant differ- 
ences are noticeable, especially in showing the dirninution in the 
amount of total solids and in free and albuminoid ammonia and in 
nitrites, which has been effected bv sand filtration. 
DEEP WELLS. 
At the present time there are 24 deep wells in use as a part of the 
pubhc water supply of Washington and the District of Columbia. 
Most, if not all, of these deep wells have been found to contain small 
amounts of iron, and while less attractive than the waters of many 
of the shallow wells these waters are characterized bv great chemical 
purity. It vfill be seen from an examination of Table 8 that as a 
rule thev are low in total solids. In the greater number of them 
chlorine is present only in very small amounts, and in the few in- 
stances in which it is present m larger quantities it is associated with 
very small amounts of nitrates, indicating that the larger quantity 
of chlorides in these few instances is probably derived, not from 
remote sewage pollution, but from saline deposits. These waters 
are also free from nitrogen in its various combinations. Albuminoid 
ammonia, nitrites, and nitrates are either absent altogether or, if 
present, only in very small amounts, and in only two instances, viz, 
Nos. 108 and 110, has the free ammonia been found to be present in 
such quantities as to cast some suspicion on the purit}’ of the water. 
In these two waters the bacterial count was also foimd to be some- 
what higher than in the waters of other deep wells. It has been 
found, however, that the waters of deep wells may often contain 
rather large amomits of ammonia, which in such cases is believed to 
result from the gradual reduction of nitrates.^ The fact that these 
waters contain practically no nitrates, in most instances even a 
smaller amount than the surface water of this region, is in keeping 
with this view regarding the origin of ammonia in deep wells, so that, 
taking all things into consideration, we find no reason to regard 
these waters as in anj^ way polluted; indeed, so far as we have been 
able to deternfine the waters of these deep wells leave practically 
nothing to be desired so far as purity is concerned. The presence of 
iron in these waters doubtless has a great deal to do with their purity 
and freedom from pollution. In the main at least, this iron exists 
in the form of ferrous carbonate. This is derived from ferric oxide 
contained in the rocks and soil through which the water flows by the 
“The Potomac River Basin, Water-Supply Paper No. 192, by Horatio M. Parker. 
& See ‘‘Air, Water, and Food,” by Richards and Woodman (1901), p. 76, and also 
Mendel ejeff. Chemistry, p. 223. 
29643—07 19 
