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of samples taken direct from the wells show that the water is normally of a high standard of chemical
quality and bacterial purity. The results of the examinations indicate the water to be wholesome in
character and suitable for drinking and domestic purposes. With few exceptions the water is also
subjected to precautionary chlorination.
The possibility of the pollution of the water-bearing strata below the London Clay is always
kept in mind, particularly from the fractured bore tubes of abandoned wells. No official guidance
has been given on the most effective method of sealing such wells, but during the year, after consideration
of suggestions from various sources, the following method was adopted for the sealing of
an abandoned well in the City.
The problem is to prevent impure water from the strata above the impervious clay draining
down the disused bore tubes to the chalk below, whence the deep well water is drawn. This particular
well was bored in 1907 to a depth of 551 feet. The internal diameter of the bore was 8½ inches. The
level of the water in the bore was approximately 151 feet from the adjoining road level compared
with the level of 159 feet when the well was originally sunk. The strata sheet, prepared during the
course of the boring operation, showed that the chalk was reached at a depth of 329 feet. Immediately
above the stratum of chalk and flints was a bed of Thanet Sand and a bed of impervious clay
which holds up the contaminated water in the gravels above.
It was decided to fill the lower part of the bore with ¾ inch washed shingle to a point just above
the bed of chalk and flints, but below the bed of impervious clay, to provide foundation for the concrete.
From this point the remainder of the bore was filled in with concrete made with 4 parts of
1½ inch shingle, to 2 parts of sand and 1 part of cement , mixed with a waterproofing compound.
There is a consensus of opinion that this method is the most satisfactory, and it is proposed to
adopt it for the sealing of other disused wells.
It would be of advantage if it were made compulsory for the owner of any private well to notify
the local authority of his intention to discontinue its use. This would ensure that it is satisfactorily
sealed off. Many such wells have been sealed off merely by covering the top of the bore with a slab
of concrete, but this method becomes useless if, in the course of time, the bore tubes are fractured
through rust or other causes, thus allowing impure water to drain into and contaminate the underground
water supply.
ATMOSPHERIC POLLUTION.
I am indebted to Mr. McGrath for the following report:—
"The year 1951 was the third complete year of the recommencement of observations since
the original deposit gauge was destroyed in 1940. The Table sets out the results obtained in 1951
by the various methods employed in the City for the measurement of atmospheric pollution.
These methods were fully described in my Annual Report for the year 1949, The averages for
the last three years are set out at the foot of the Table. The average rainfall for 1951 was much
higher than in the previous two years, and although increased rainfall usually results in a higher
soluble deposit the figure for total solids was 0 40 tons per square mile less than that of 1950. It
will be seen, however, that the sulphur pollution estimated by the lead peroxide and volumetric
methods is in excess of that for the two previous years. The suspended impurity, i.e., soot and
tar pollution principally due to the burning of raw coal in domestic fires, also shows an appreciable
increase, but insufficient time has elapsed since observations were recommenced to
enable any significant conclusions to be drawn about the rate of emission of pollution. As I
pointed out in my last Annual Report, conclusions of any value cannot be drawn from observations
extending over less than five years.
The appearance on the sky line in recent months of the tall chimney stack of the large
electricity generating station in course of construction at Bankside on the south side of the River
focuses attention on the sources of pollution by sulphur; on the fact that it is impracticable to
remove sulphur compounds from the chimney gases of any but the largest coal-burning installations
; and that it is still impossible for economic reasons to stop this pollution entirely. It is
well known that these compounds cause damage to the fabric of buildings, metal work, textiles,
etc., and it will be recalled that the proposal to construct the generating station at Bankside
caused considerable concern that the emission of sulphur fumes would cause an undue acceleration
of the damage by atmospheric pollution to the fabric of St. Paul's Cathedral and other
public buildings in the City. This concern will be readily understood when it is remembered
that it has been calculated that for the country as a whole, electricity generating stations are
responsible for some 17 per cent. of the total amount of sulphur emitted. For the London Area
the corresponding figure is about 28 per cent. This does not mean that the generating stations
are responsible for this proportion of the local pollution of the atmosphere at ground level. Their
flue gases are emitted at a height of some hundreds of feet and are dispersed into the upper air
to an extent much greater than the gases from domestic fires at very much lower level.
Parliament has stipulated that the greater part of the sulphur compounds should be removed
from the chimney gases of the Bankside Station, and to secure this a large and expensive plant
is to be installed. Simply stated, the process—a modernised type of the one in use at the Battersea
Generating Station-—enables the chimney gases to be washed with very large volumes of river
water to which a little chalk is added. The sulphur dioxide is absorbed by the water and oxidised
and neutralised.
When the new station is in operation, the results obtained from the various methods for
measuring atmospheric pollution will be studied with interest. The British Electricity Authority,
no doubt with a full appreciation of its responsibilities in the matter, has established in the City
three observation sites for the measurement of sulphur dioxide by the lead peroxide method.
These are similar to those in use at the Corporation's sites at Golden Lane and Finsbury Circus."