+----------+------------------------------------------+-----------+
|DIAMETER: | | |
+-----+----+ Kind. | Length, |
| cm | in.| | in meters.|
+-----+----+------------------------------------------+-----------+
|24.3 | 8 | Fire-clay | 38,332.85 |
|25.4 | 10 | " | 16,400.69 |
|30.5 | 12 | " | 7,953.15 |
|38.1 | 15 | " | 4,850.56 |
|45.7 | 18 | " | 2,023.40 |
|50.8 | 20 | " | 1,450.53 |
|55.9 | 22 | Reinforced concrete tubes, 6.9 cm. thick | 3,134.20 |
|61.0 | 25 | " " " 7.6 " " | 357.40 |
|68.6 | 27 | Brick and concrete | 484.05 |
|76.2 | 30 | " " " | 662.69 |
| | | | |
| | | Total | 75,649.15 |
+-----+----+------------------------------------------+-----------+
The greater number of the manholes are of brickwork, 23 cm. thick, and
have concrete inverts. They have a diameter of 1.2 m., which is reduced to
0.61 m. at the top, and each is provided with a heavy cast-iron frame and
closed cover weighing about 190 kg. There are 521 manholes, and they are
placed at every block and on long lines about 80 m. apart.
[Illustration: FIG. 16.--STANDARD 300-GAL. FLUSH TANKS.]
The sewers are flushed with 15-cm. (6-in.) automatic flushing siphons of
the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of
these siphons, and they are placed in flush-tanks (Fig. 16) built of
brickwork and plastered with 1:1 cement mortar. Their capacity varies from
800 to 1,200 liters, and they discharge from 22-1/2 to 28-1/2 liters per
sec. They are timed to flush once in 24 hours.
The system is at present ventilated by 23-cm. (9-in.) steel ventilating
columns (Fig. 16), with ornamental cast-iron bases. There are 220 of these
columns. Most of them are 7.85 m. above the level of the edge of the
sidewalk, and are connected to special 15-cm. branch pipes leading from
the sewer on the outside of the flush-tanks. In the center of the city
they are provided with extension lengths, giving a total height of 12 m.
Table 13 gives the particulars of the average distributed cost of laying
the 75.6 km. of sewers.
TABLE 13.--AVERAGE COST, PER LINEAR METER, FOR 75.6 KM.
OF SEWERS, FOR MATERIALS AND LABOR COMPLETE.
+----------+-----------+--------+-----------------------------+--------+
| | INTERNAL |Cost of | EARTHWORK AND LABOR: | Total |
| | DIAMETER | mater- |-------+------------+--------| cost of|
| | OF | ials | | Cost of |Cost of | sewer |
| | SEWERS. |includ- |Average| excavation,|labor |complete|
|Kind of +------+----+ ing | depth | including | in | per |
| Sewer. | | |10-cm. | of | back- |laying | linear |
| | | |(4-in.) | sewer | filling, |(includ-| meter. |
| | cm. | in.|branches| | removing | ing | |
| | | |every | m. | surplus, |hauling,| |
| | | |4-1/2 m.| | etc. | etc.). | |
| | | |Pesos. | | Pesos. | Pesos. | |
+----------+------+----+--------+-------+------------+--------+--------+
|Fire-clay | 24.3 | 8 | 2.00 | 2.10 | 3.46 | 0.21 | 5.67 |
| " | 25.4 | 10 | 2.78 | 2.25 | 3.97 | 0.2625 | 7.0125 |
| " | 30.5 | 12 | 3.64 | 2.50 | 4.705 | 0.305 | 8.65 |
| " | 38.1 | 15 | 6.14 | 2.75 | 5.50 | 0.4375 |12.0775 |
| " | 45.7 | 18 | 8.80 | 3.00 | 6.745 | 0.645 |16.19 |
| " | 50.8 | 20 | 11.30 | 3.50 | 8.275 | 0.815 |20.39 |
|Concrete | 55.9 | 22 | 5.93 | 3.50 | 9.19 | 1.325 |16.445 |
| " | 61.0 | 25 | 7.30 | 3.75 | 11.245 | 1.685 |20.23 |
|One brick}| | | | | | | |
|thick on }| 68.6 | 27 | 7.17 | 3.75 | 11.735 | 3.93 |22.835 |
|concrete }| 76.2 | 30 | 7.925 | 4.00 | 14.53 | 4.515 |26.97 |
|founda- }| | | | | | | |
|tions }| | | | | | | |
+----------+------+----+--------+-------+------------+--------+--------+
[Illustration: FIG. 17.--SKETCH SHOWING DISCONNECTING TRAP ON HOUSE
DRAIN.]
The house connections are chiefly of 10-cm. (4-in.) pipes, laid on a
minimum gradient of 2-1/2%, from oblique branches on the sewer to siphon
intercepting traps near the house, as shown by Fig. 17. From this trap a
10-cm. fire-clay inspection pipe is carried up and capped at the sidewalk
level with a cast-iron box having a locked cover. From this inspection
pipe a branch is connected to a cast-iron fresh-air inlet, in most cases
set in the wall of the house, the inlet being 30 cm. above the level of
the pavement.
_Effect of the Flood on Sewers._--The flood of August 27th and 28th, 1909,
partly destroyed one of the main collectors, which was laid along the
banks of the river and encased in concrete. This has now been relaid
farther north, and out of the way of any future floods. The total length
of the new sewers replacing those damaged amounts to 1200 m., and they
vary in internal diameter from 20 to 55.9 cm. (8 to 22 in.).