The record-union. [volume] (Sacramento, Calif.) 1891-1903, 1899-06-27
CONCERNING SEWAGE sunni.
An Overflow Basin Recommended
for Use During the Flood
Season.

tional report on the street stump mat
ter, and the same was read at last
nights meeting of the board. The re-
port will prove interesting reading to
all concerned. 1t follows in full:
San Francisco, June 10, 1899.
Hon. Board of Trustees of Sacra-
mento, Cal.-Gentlemen: Supplement-
ing my report of May Goth on the pro-
posed sewer work, 1 desire to state that
my attention was also called to the con-
dition of the stump and sewer termina-
ton at the foot of S street.
The pumping station was located just
at the eastern levee base The river at
this point Is close upon the other side
of the levee. The river slope of the
levee is faced with granite blocks. This
revetment Is an excellent protection
against its injury or destruction by cur.
rents or wave action, but is not a check
to the flow OF seepage water through
pervlous layers under the levee.
The stump or pit from which sewage
was lifted by the pumps was excavated
in rectangular form, to a depth con-
siderably below the low water plane of
the river During the winter, spring
and summer months the river for long
periods of time maintains a hight Of
twelve to sixteen and more feet above
the low water stage
: When the water within the stump at
the pumping station is kept down to or
near the level of the sewer invert, there
is difference of water level from river
to stump during the rivers high stages,
often exceeding sixteen to twenty feet.
If, now, the walls of the stump are
sufficiently
soil water freely, then this head or wa
ter pressure of sixteen to twenty feet,
becomes effective in forcing water from
the river through. amy intervening per-
vious material toward the stump.
Were the stump not near the levee so
that the soil in the immediate vicinity
OF the qevee could remain saturated
with water, then the effective pressure
forcing water through pervious layers
under the levee would have been con-
fined to smaller limits. Upon the
abandonment of the stump this spring,
when it filled with water, this pressure
was reduced by an amount equal to
the hight which water rose in the stump.
The driving of sheet piling along the
levee base between stump and levee, in
terposed an obstacle to the flow of wa
ter which was sufficient to cause the
water on the river side of this sheeting
to rise four or five feet higher than on
the land side, thus showing that the
sheeting was actually an impeachment in
the path of the water
AT the same time, the persistence with
which some water found it's way into
the shattered stump, even after the
sheeting was in place, was ample evil
dence Of the fact that pumping opera
ton, stimulating as they did the soil
water inflow, had aided in opening. or.
at least, clearing passages for the wa
ter from the river, and that a continu-
ance of pumping operations from a de-
fective stump might have endangered
the stability of the levee
From various statements made, it ap-
pears likely that the greatest inflow of
soil water was originally through a de-
feet in the bottom of the sewer at a
gate which had been placed in the
sewer after its completion, about thirty
feet east of the. stump. The inflowing
soil water at this point carried soil and
sand into the sewer undermining the
street surface, the sewer and the stump
itself, thus causing further injury and
increased leakage, which, when the
supply OF soil water was augmented by
rising river, quickly resulted in dis
aster.
There is no evidence that any of the
water came through the levee along the
line of the discharge pipes.
Had the stump and the sewer near
the levee been practically water tight
and capable of resisting water pressure
from without, the location of the sta
ton so near the levee would not have
been a menace to it's safety. The fact
that it rests upon sand is not to be
considered the cause of its failure, but
facilitated its rapid destruction after
| considerable leak had been developed
because the sand particles were readily
displaced and carried along by flowing
water and the sewer and stump were
thus soon deprived of their support
sand, or even quicksand, as founda-
ton does not necessarily condemn a
site for suction pit such as is re-
! quired in connection with the sewer
system, but adds to the difficulty of
construction.
Very little is gained in pump efficien-
cy by locating the pumping station
close to the levee An injudicious To-
cation too near the river may subject
the levee to a danger that might Just
as well be avoided; it will, therefore,
be better to keep from 200 to: 300 feet
away from the levee.
The. floor of the suction pit or sunni
should be capable of resisting upward
pressure of water. The best shape of
the pit is oval or circular.
RV thus Piyinr tbo n-a11s ,-ob =
shape they will be better able to with
stand pressure from without, and equal
strength can be obtained with less ma
sorry or concrete
Piling can be used under the stump
to advantage If the excavation extends
into very soft and unstable material
The sewer near the sump as we'll
as its connection with the. stump, should
be constructed with extra care. The
stump and the sewer near it must be
practically water-t tight, otherwise the
inflowing soil water may again under
mine parts of the system and interfere
with it's usefulness at a critical mo-
ment. The matter of making these
structures as nearly water-tight as
possible should not be overlooked, even
though only temporary pumping sta
ton be kept in service during the next
wet season.
1t seems hardly necessary to add that
the original stump should be filled up
in order that the flow of seepage water
from the river into it be checked as
much as possible Conduits leading
from it, particularly the sewer itself,
should be carefully closed AS an addi-
tional precaution it would be well to
d<aor, f,ror, L.. - L.