Novel Sewer Experiment.
THE out-fall sewer just completed from Los Angeles to the Pacific Ocean is a notable departure from the sewer system of this country in two ways. First, in its siphons three miles in length made of wood. Second, in utilizing the sewage for fertilizer and irrigation. It is 12 1/2 miles long, with brick conduits, barrel-stave pipe and cement tunnels following an almost direct air-line, burrowing through hills, siphoning under deep, wide valleys, piercing the sand dunes that line the sea coast, and projecting an iron tube out upon the bed of the ocean. It has been constructed in one year at a cost of $375,000. A drainage outlet to the sea was necessary because the city is situated on the small Los Angeles river, which most of the year is only a brook. Under the former outlet system the sewage was allowed to run out on the sandy bed of this river, forming noxious pools and polluting its shallow flow, a condition that would seriously endanger the health of the city as it increased in size. Instead of the sewer following the natural drainage course, making a long detour to the sea through swampy ground, it was found cheaper to follow the short air line and build the necessary siphons and tunnels, and in addition to this reclaim a tract of thirty thousand acres of high lying lands that could be watered in no other way. The novel features begin with the settling chamber, situated half a mile south of the city limits, and at the beginning of the first siphon. It is a cementlined cellar, 26×62 feet and 12 feet deep, covered by movable iron slabs one foot below the surface of the ground. I his settling chamber is so arranged as to catch all large substances, as boots, hats, cans, etc., that will find their way into a city sewer, and to sift out the sand by iron screens, thus removing all substancesthat would lodge in the lowest part of the siphon and choke it Up. Here will accumulate whatever valuables may fall into any branch of the sewer throughout the city. This chamber will be cleaned once or twice a year. In the lower wall of the settling chamber is the orifice of the siphon—a thirty-eight inch circular barre’tave pipe, made of black-heart redwood because of its solidity and capacity to resist decay. It is banded by steel 5-S inch rods dipped in asphalt to prevent rust. Where any hard wood is kept watersoaked it will last for hundreds of years ; for instance, when the old London bridge was removed timbers in good condition were taken out which had been under water 300 years. The siphon is expected to be constantly water-soaked, as the entire siphon is below the grade level, and the water is consequently’ under pressure. The life of the pipe will depend on the tenacity of the steel bands. This use of wood pipe is without precedent. It was suggested by City Engineer J II. Dockweller, and adopted on account of its cheapness compared with large size cast iron pipe required to extend over six miles. It was shown that the wood pipe could be renewed every five years on the interest of the original cost of cast iron pipe. Inverted siphons for sewers are used in Paris under the river Seine, being about 800 feet long and 39 inches in diameter. Similar sewer siphons under rivers are used in other European cities, but the pipe is always of iron.
This first siphon is 3.1 miles long. In the low places are blow-offs, large iron pipes projecting upward on an incline, with valves attached, through which the water can be thrown out with great force so as to eject any settlings in the pipe. Irrigation hydrants are placed at convenient points in the farmers’ fields and orchards. They are six-inch iron pipes, with caps that look like inverted pans, which throw the water down into a fountain pool whence it will be drawn in ditches over the fields.
The farmers were at first horrified at the idea of using sewage for fertilizing and irrigation. The city officials delegated to get the right-of-way, so plausibly set forth the merits of sewage as a fertilizer that they overcame the farmers’ prejudice. As a charge will be made for the use of sewage, it is estimated the revenue realized will pay the five per cent, interest on the sewer bonds. It is expected that during nine months of the year the sewage will be consumed before reaching the ocean.
At the end of the first siphon is a throttle valve to back up the water in the pipe to secure any desired pressure on the blow-offs and hydrants. From this point a forty-inch circular brick conduit, lined with cement, a quarter of a mile long, begins on the regular grade of one-foot fall in every 800, giving a velocity of feet per second. It leads to the portal of the first tunnel, which is an underground man-hole chamber vaulted and arched with brick. l’he tunnel is egg-shaped, with the larger end downward, six feet high by 4 L feet wide. It is cemented, and as smooth on the bottom as a sidewalk, and before the turning on of the sewage could easily he walked through. It is 5,800 feet long, and comes to an abrupt end at the west portal by a perpendicular fall of 12 feet upon a 2-foot water cushion. A short conduit connects with the second siphon. For : ix miles from the beginning of the tunnel to the ocean the server runs through the land of one man, Daniel Freeman. When he was aware of the project to run a sewer with three tunnels, a siphon and a conduit through his bonanza farm, he put in a claim of $530,000 damages, but a jury awarded him $12,500. He is now selling land at $100 an acre that a year ago was valued at only’ $50. It is through this tract that the second siphon extends for 3.2 miles. It will distribute water for five miles north and south over a broad rolling valley, now but partially cultivated.
As the grade of the second siphon is steeper, its diameter is reduced to 36 inches. After crossing the wide valley it discharges into a 40-inch brick conduit, which is laid through sandy elevations in a trench 10 to 23 feet deep, and extends 12,080 feet to the sand dunes bordering the ocean. Here at the bottom of a 10-foot drop is the entrance to the second short tunnel, 950 feet long. It is connected by a conduit to the third and last tunnel, 1,250 feet long, l’he greatest difficulty was experienced in driving this tunnel, for it runs through a hill of shifting sand. Heavy timbering was required, planks were driven horizontally into the top and sides while the earth was removed below. Only two feet headway could be made a day. The framework was left standing to protect the iron braced and arched brick-work till the cement and mortar should become hard enough to resist the pressure of the caving sands. These tunnels are made large enough to drain a city of 300,000, while the capacity of the conduits and siphons is for only 135,000, but provision is made for lay’ing a parallel line of siphons and conduits, and thus double the sewer’s capacity without the expense of enlarging the tunnels.
From the end of the last tunnel an iron pipe extends on a steep incline through 600 feet of beach sand, and reaches as much farther out into the ocean. The pipe was launched by sealing the end, mounting it upon rollers, and forced out bv capstans placed on either side on the beach. A tug out beyond the surf guided its direction. 1 he point where the sewer enters the ocean is just half way between the two pleasure resorts, Santa Monica and Redondo beaches, five and a half miles from either.
While the I.os Angeles sewer is as yet an untried experiment, it may prove an object lesson to larger cities in this country; and may demonstrate Victor Hugo’s theory that * a sewer is a misunderstanding, and when drainage with its double functions of restoring what it takes away is every where substituted for the sewer, the problem of food production will be reduced tenfold, and the problem of misery singularly attenuated.”
Los Angeles, Cal., April 2.