The record-union., 1899-10-28

possible to arrange filter plants SO that
/ the eff1uent water can be given any
degree of purity that may be desired.
There are, generally speaking, two
methods in use, the slow and the rapid
| filtration.
The slow filtration requires bed OF
sand several feet thick and arranged IN
specially prepared basins, having an
impervious bottom and sides. The water
| is allowed to percolate through TINS
sand and escape by specially arranged
drains at daily rates varying from hive
| to ten cubic feet per square foot OF
filter surface. Various appliances are
necessary to insure a proper rate and
to enable a top layer of sand to pc re-
moved when it becomes clogged, 10
wash the sand thus removed and there
after to redistribute it upon the inter.
The rapid filtration requires tanks
made Of wood or iron and supplied with
mechanical appliances to wash the sand
| in the tanks. These rapid filters are
| intended daily to clean about 3OO CUBIC
feet of water on every square foot OF
! sand surface In order that this rapid
percolation may be accomplished, and
yet effectually cleanse the water, it is
necessary to use coaguDating mater
ial. such as alum, in order to have on
the surface of the filtering material, a
film which retains the bacteria and
| finer particles of suspended matter.
There are other, but minor, differ
ences between the slow and rapid filters
which it is not necessary to enter into
at present.
Prior to the successful operation of
| either, it is necessary to allow for a
sedimentation of the heavier suspended
matte. This is accomplished, in the
case of slow filters, by allowing the
water to enter large settling reservoirs,
where 1T can obtain a state of compara-
tive rest The suspended matter then
naturally settles to the bottom. In
the case of the rapid filters, there is a
| mechanical contrivance in use in some
of them, which accomplishes similar
! result in a smaller space and in direct
connection with the filters.
a final comparison of the different
available projects should be made
along three lines of inquiry, namely:
| First, the quality Of the water to be
furnished; second, the quantity of wat
er obtainable, and third, the cost of
building the necessary works and OF
| operating them.
Quality. In the case of the river
waters, there seems to be no indication
that they would not be suitable for the
city's supply. A sewage pollution is
and will be almost absent and nearly all
Of the suspended matter is mineral A
Qualification of the water is therefore
the main object to be secured, rather
than the purif1cation of water polluted
with foul organic matter. For such a
purpose, there is no difference between
the results of the slow and the rapid
| filtration, and both these methods may
in the present case, be considered as
having equal merits from sanitary
point of view.
The known geological and Topographic
| cal features of the water sheds of these
streams, indicate that the water should
have good quality for municipal pur-
poses. The mining industry causes
much of the turbidity, and perhaps
some slight chemical change, but adds
no sanitary impurities.
If the analysis of the ground water
after long continued pumping shows re-
suits equal to those heretofore obtained
| after long pumping, the quality of the
ground water supply can be relied upon
as being satisfactory. Inasmuch as
this water has been clarified by nat
ura1 process, such a supply is there
fore ordinarily considered preferable
because more reliable than one which
requires an artificial process.
| While the water from mountain
streams, when it is naturally clear will
also generally be pure, it will not al
ways be free from pollution, owing to
the fact that it is at least exposed to
the incidental defilement by animals
and human beings A ground water
supply or one that has been artificially
filtered, can be guarded against every
subsequent pollution.
Quantity. There is no question that
either the Sacramento or American
River has a sufficient quantity of water
during the driest year to supply the
needs Of the city. of Sacramento.
The North Fork Ditch Company Of
fers TO deliver 1000 miners inches or
l5,O00,0O0 gallons daily to the city
This quantity is stated to be third
Of that which is made available by the
ditch.
Regarding the quantity of water OBJ
tainable from the ground water sup
ply. it must be said that there is in
sufficient knowledge TO foretell how
much water could be permanently
drawn therefrom. The indications are
that a supply of considerable magni-
tude may be available. A city should
however, not rely upon such indications
until the actual minimum supply has
been demonstrated by a proper test
Regarding the supply Of pure and
clear water from the mountains 1t
would be necessary to have a deter
mination of the minimum flow during
| the driest years. Should this flow BE-
insufficient, then it would be further
necessary to investigate sites for stor-
ing the larger flow of water during the
wet season, so that it may supplement
the insufficient flow during the dry sea
son.
Cost. After the best Of the above
mentioned projects have been ascer-
tanned, SO far as the quality and guam
tity Of water which they will yield are
concerned, it is then necessary to make
a careful estimate of the cost of each
one, including different methods of fl
tration, so as to ascertain their re-
lative economy. In order to be of
value, such estimates of cost should be
based on good judgment, experience
and when necessary on surveys and
other practical physical examinations.
/ A comparison necessitates first the
! making Of an estimate of the entire