35
Presumably this state of affairs is due to the last rains. It is not easy to explain
why the pollution should be present nearly a fortnight after the rain has ceased,
as in former occasions an improvement was usual about this time after rain.
Sample No. 26.—Very much the same remarks apply to this sample. No rain has
fallen. Fcal bacilli are present in .01 cc. which is very bad for this Well. The
bacilli present are extremely interesting and show a very large number of species.
Rare organisms Nos. 38 and 9, already referred to are present, and also coli communis.
The explanation for this high degree of pollution is, as already stated, not very
apparent. The water at this period is obviously of a very dangerous character.
Sample No. 27.-Fcal bacilli are present in 1 cc., eoli communis being also
present. Practically the same remarks apply to this sample as were made about the
last two.
Sample No. 2 8 . — F œ c a l b a c i l l i a r e p r e s e n t i n 1 c c . T h e b a c i l l i a p p e a r t o b e g e t t i n g
more nearly to the normal. Coscoroba and grunthal are beginning again to
predominate.
Sample No. 29.—Focal bacilli are present in 1 cc., no rain having fallen for some
weeks. 1 coli communis was observed in this sample the rest are mostly bacillus
grunthal.
Sample No. 30.—Still there is no very great improvement in the quality of the
water. Fecal bacilli are present in 1 cc. The organisms, however, are getting
cnsiderably less objectionable in kind. Coscoroba and grunthal are predominating.
Sample No. 31.—A marked improvement in the quality of the water is noticed.
Fecal organisms . are now present in 5 cc. Cloaca and another resistant organism
No. 73 are beginning to reappear.
Sample No. 32.—Still further improvement is noticed. Fcal bacilli are present
in 10 cc.
Sample No. 33.—The improvement appears to be maintained, but on this date 3
coli communis were found in the water, with bacillus grunthal. The reason for
this improvement in quality during the last 3 weeks is not by any means obvious.
The following may however be the explanation : The heavy rains that took
place early in January at first, increased the number of organisms in the well,
and then caused a temporary improvement in the quality of the water ;• but
they washed into the ground a large number, of fœ cal organisms that were lying
on the surface. They also laised the level of the sub-soil water and rendered
the whole of the catchment area of the well damp. After the rains had ceased,
and during the whole month of February, there was a very decided and steady
deterioration in the quality of the water, followed by a second improvement. The
samples during this period of pollution. nearly all contained cob communis and showed
the typical mixture of organisms which indicates surface pollution. As long as the
sub-soil water was high, and the ground surrounding the well was damp, this satu-
rated earth would yield a certain quantity of highly polluted water, whenever pumping
was in progress. Gradually as March came in, there being no rain, the ground in
the immediate neighbourhood of the well became thy, and only its lower layers
were tapped. The drier the ground became, the less water would be drawn
from the upper layers by pumping, and consequently the purer the water
became. The correctness of this explanation is confirmed by the results of the
chemical analysis of sample 27 taken on 4th February 1909. This sample is consider-
ably worse than all the others and contains nitrates in an appreciable amount. The
presence of coli communis in the last sample is probably explained in this way also,
for, as has already been stated, whenever coli communis is present in a well, without
the usual mixture of faecal organisms, the probabilities are that it comes from the
deeper layers of the soil. This point however is one which requires much careful
investigation before a definite statement can be made.
The table of the chemical analysis of certain samples, herewith appended, shows
that the water on the whole is a good one. Samples Nos. 19 and 23 are the best.
Both of them were taken within very short intervals after heavy rain. Samples
Nos. 27, 28 and 33 were taken after several weeks of drought and show a falling off
in quality seen particularly in the increased amount of free ammonia.