Driven Wells of the Plainfield Water Supply System.
Plainfield, N. J., is located in a comparatively level valley, which is only seven miles long and from three-fourths to two miles wide. The valley it fairly well wooded, and slopes gently to the westward. It is divided by a small stream running to the southwest, having several short tributaries, and altogether they furnish excellent drainage for the city. The soil consists of strata sand, clay and gravel, rock being encountered at a considerable depth. Water has always been obtained for domestic use by driving pipe wells from 20 to 80 feet, and attaching pumps directly to them. For fire supply large brick curbs have been sunk 15 to 20 feet into the gravel, and give an abundant flow. Obviously, with the increasing population and no sewerage system, these wells became a source of danger to health, but nothing has been accomplished during 20 years towards an improvement in these conditions beyond the organization of a water company.
In 1890 active measures were inaugurated ; tests anti examinations were made, and, finally, pipe wells sunk about 1 miles from the city in a soil where the upper clay stratum was 30 feet or more thick, and underlaid by a course water-bearing gravel. This spot was selected on account of being higher than the city, convenient, and free from probable contamination.
The quantity of water obtained from ten wells by eight hours’ daily consecutive pumping, during two weeks of observation, was at the rate of from 2,000,000 to 2,250,000 in 24 hours.
The cast heads to the wells were of such construction as to transform each water tube into practically an open well, thus giving atmospheric pressure free play, rather than forcing its action through the earth, as in systems where a single tube is used.
The most distant well is 500 feet from the pumps and shows very strikingly by the vacuum at the well head and increased vacuum at the pump the cITeet of long suction and of friction in the main.
Tests from four 2-inch pipe test wells were made during several months by the writer; each pipe had a balanced float gauge which indicated the rise anti fall of the water. The test wells were very sensitive to draft on the main wells when pumping was going on, the nearest main wells being 150 feet distant.
Observation showed that in about 1,900 feet the undergroundwater level fell to the westward about 3 feet, which is about the grade of the surface of the ground. This showed conclusively that there was no danger of a backflow of contaminated water from the city.
The plant consists of 20 wells six inches in diameter, 35 to 50 feet in depth, ranged in double rows 25 feet apart and 1,000 feet long. Kach well has a full 4)-inch open-end suction tube, connected with a wrought iron main varying from 8 to 12 inches in diameter.
There are two compound, surface condensing, duplex plunger pumps of Worthington make; one of 3,000,000 and one of 2,000,000 gallons daily capacity, and a suitable boiler plant. The water is
After a partial completion of the work additional tests were made with the permanent pumping plant. The wells on the westerly line were found to yield more abundantly than the easterly when under equally good conditions, and gave a lower vacuum for the same quantity pumped. This simply indicates that the underground water was flowing in a southwesterly direction. Tests were made with the large pumps, under both free discharge and full working heads, singly and together, and drawing from the wells in groups of 5, to, 15 and 20 ; also by cutting off one by one until the smallest number that could be used was reached, and then adding one by one in a reverse order. The smallest number with which the pumps would run smoothly was five. The best results were obtained by using numbers 1 to 55 inclusive
During the long-continued dry weather of 1891 the groundwater level became so low that difficulty arose with the extreme suction lift obtained, which was from 20 to 28 feet, according to the rate of pumping. This was a fall in the ground-water of 6 to 7 feet since the earlier observations. For this reason in the summer of 1892 the pumps were lowered 9 feet below their former positions.
The wells have for two years furnished without difficulty or any signs of decrease in the supply a full amount, beginning with 200,000 gallons, which has been increased to 1,500,000 gallons daily at the present time. The water has been of excellent quality, both for domestic and manufacturing purposes, and the underground supply has thus far proved a decided success.