+-----------------------------------------+-----------+-----------+
| | Pesos per | Pesos per |
| | cubic | cubic |
| | meter. | meter. |
+-----------------------------------------+-----------+-----------+
| LABOR : | | |
| Mixing and placing | 5.20 | |
| Carpenter work in forms, framing, etc. | 4.20 | |
| | _____ | |
| Total labor cost | | 9.40 |
| | | |
| MATERIALS : | | |
| Screened gravel | 4.04 | |
| Sand (from neighboring arroyo) | 4.98 | |
| Cement (including hauling) | 15.19 | |
| Lumber, nails, and other supplies | 1.90 | 26.11 |
+-----------------------------------------+-----------+-----------+
| Total cost of concrete per cubic meter 35.51 |
+-----------------------------------------------------------------+
_Sludge-pit._--The sludge-pit, used when cleaning out the tanks, is
carried 639 m. northward, far enough to get the available fall to drain
the bottom of the detritus chambers and liquefying tanks. The drainage
pipe was formed of 56-cm. (22-in.) concrete tubes. The sludge-pit is
merely an excavation in the earth 20 m. square and 2 m. deep, the sides
having a slope of 1-1/2 to 1. An overflow drains the pit to an irrigation
ditch, the solid matter being allowed to settle and the liquid to drain
off. From time to time it is proposed to dig out the solids and plow them
into the land.
_General._--To the east of the tanks a 3-roomed house has been built for
the inspector.
In order to provide a good supply of water for cleaning operations, a well
22 m. deep has been sunk and is fitted with pumps operated by an Eclipse
windmill, 4 m. in diameter, on a tower 22 m. high, which delivers the pump
water to a circular wooden tank of 20,000 liters capacity.
The work in connection with the purification tanks was carried out by the
Company's own staff; it was begun on September 10th, 1908, and practically
completed by the first week in January, 1909.
At the time of writing, the tanks have to deal with the sewage from a
population of only 10,000 persons, as only from 15 to 20% of the
connections have been made. The sewage, therefore, has been diluted with
several times its volume of surplus water, and the necessary scum on the
top of the sewage in the tanks has not yet assumed the usual thick matty
condition observed in most systems. As there are no available means in
Monterrey of having proper determinations made of the degree of
purification which takes place in the passage of the sewage through the
liquefying tanks, a few simple tests have been made. These tests were
limited to the determination of the amount of oxygen absorbed in 4 hours,
and show a purification of 50% in passing from the detritus chambers to
the outlet. The sewage, although very black and full of suspended matter
as it enters the tanks, leaves them in a very clarified condition.
Of the total area of land acquired by the Company, 904 hectares (2,234
acres) have been leased to the Monterrey Railway, Light, and Power
Company, for 99 years, the Water-Works Company reserving 5 hectares (12
acres) absolutely for future extensions of the sewage works. By giving 12
months' notice, the Company also reserves the right to utilize any part of
145 hectares (358 acres) near the tanks, should it be required at any time
in the future for sewage purification purposes.