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West Grand
Chelsea Middlesex Junction
Company. Company. Company.
Amount of storage 13 days ... 6.3 days ... 3.5 days
Average thickness of sand on
filters 4 feet ... 2.6 feet ... 1.9 foot
Average rate of filtration per
square foot per hour ... 1.75 gallon ... 1.39 gallon ... 1.75 gallon
Maximum percentage of microbes
removed 99.93 ... 99.96 ... 99.91
Mininum percentage of microbes
removed 93.94 ... 97.88 ... 76.37
Average percentage of microbes
removed ... ... ... ... 98.78 ... 99.29 ... 97.57
Except in February, the Chelsea Company delivered,
during the whole year, water of a high degree of bacterial
purity, rivalling, in some cases, deep-well water. In November,
when the Thames at the intake contained no less than 29,260
microbes per c. c., this Company's water, which was being
pumped from the general filter wells into the supply mains
contained only 20. The West Middlesex Company, except in
January, February, and March, when intense cold prevailed,
delivered water of a high degree of organic purity, rivalling
that of the deep well water of the Kent Company. In November,
the number of microbes was only 12 per c.c. It is stated
that " the small amount of storage possessed by the Grand
Junction Company renders it difficult for them at all times to
maintain efficient bacterial filtration," so that, on several occasions,
the samples collected at the works (at Hampton Court
and Kew) contained an excess of microbes, or their spores, over
100 per c. c., this being the " bacterial standard." It is added
that " most of the abnormal results occurred when the raw
river water was bacterially in a bad condition, and during
severe frost." Professor Frankland concludes his report with a
statement of the results of investigations with respect to
bacterial filtration, as practised by tins Massachusetts State
Board of Health, which are gradually enlarging our knowledge
of this important subject.