TO AVOID THE EXPENSE OF FILTERS.
A new plan has been proposed at Pittsburgh, Pa., to avoid the expense of filtration as the board of public works intends the process to be carried on. The city should buy Six-Mile or Nine-Mile island and dredge out a basin twenty feet deep, 300 or 400 feet in width and 1,000 feet long; throw up an embankment around the outside ten feet higher than highwater mark, and riprap around the outside so that it should not be washed away or damaged during floods. The water of the Allegheny river flows over sand and gravel with a thickness of twenty feet and there is an undercurrent of water passing through this gravel and sand. By the building of the mammoth well suggested it is figured the basin would fill with water passing through this sand bed— thus ridding it of the impurities with which it is impregnated in its raw state. The fear of some that the sand and gravel would become clogged in years and render the process of cheap filtration ineffective is held to be groundless. The flow of the water through the gravel has continued for generations, and it fills all the water wells that are put down on both sides of the valley. Official tests, however, have demonstrated that at Brilliant while the filtering of the water through the sand and gravel of the bed of the river rendered the water somewhat purer, still it added hardness to it, and Superintendent Shepherd declares that it could not be used for steam-making purposes. The quality of water would doubtless be the same in the proposed big basin plan as in the driven -wells at the side of the river.