30 HISTORY OF COLCHESTER CORPORATION WATER WORKS.
was deemed prudent to look for a supplemental supply, as the
demand was gradually overtaking the yield of the well, as the rest
level was gradually falling, due to continuous pumping and a
series of dry years. It is difficult to at once trace the connection
of a dry year in a well situated as this is, so far away from the
outcrop of the chalk, and at such a small elevation above sea
level. The rest level records have, however, since clearly
shown that as soon as the pumping ceased to be continuous,
due to the supplemental supply and a series of wet years, the rest
level speedily recovered.
As the present wells could not be touched or deepened under
any circumstances, an entirely independent source had to be
found, but there was not much necessity to search far, as the
Lexden Gravel Springs were close at hand with the water in
sight. When I was first consulted in 1888, a suggestion was
then made that the Lexden Springs might be used to supplement
the then existing supply to the town. The springs were carefully
gauged, and the whole nest, including the two eastern springs,
which rise close to the village, were found to yield some 513,000
gallons per day, but 1887 was a dry year. They were then
carefully examined by the late Dr. Tidy, a then eminent chemist
and authority, also by the late Dr. Foster, but as the analysis
revealed a rather large proportion of nitrates, they suggested
that a well supply from the chalk would be preferable, hence it
was that the new well was constructed. At that time a certain
prejudice existed by a particular school of chemists against so-
called surface springs containing nitrates, for the reason that the
method of protecting them against unoxidised manurial matter
was not so fully developed or understood, nor was so much
importance then attached to the purifying action of the soil.
From 1888 until 1902, the matter was allowed to sleep, until
Dr. Thresh was consulted, when he was so impressed with their
importance and the possibility of protecting them, that he re-
ported most favourably on their adoption.
The springs are situated on the western boundary of the
Borough, in the valley of the River Colne, in the Parish of
Lexden; they consist of a group of very strong gravel springs,
which are thrown out to the surface by a junction of extensive
sand and gravel beds with the London-clay, and are shown on
Ordnance Map (25 inch scale), sheet xxvii. 7. They unite to