The Filter Gallery at the Lowell WaterWorks.
FIRE & WATER
Among the questions engaging the attention of the water board at Lowell, Mass., is that of a change in connection with the inlet pipe and filter gallery of the works, with a view to obtaining a more uniforndy pure quality of water. The greater part of the supply flows from the river into the conduit at the lower end of the filter gallery, through a thirty-inch pipe in the river bank. The board entertains a theory that this direct water as it reaches the gallery has a tendency to hold the water in the gallery above the direct inlet pipe in check, that the direct supply being sufficient for the demand the water above it in the gallery is not drawn upon and practically remains “ dead water,” whenever the direct draft is used. There is another theory entertained by some that the water in the vicinity of the direct inlet pipe, being near the dam, is liable to hold oflmsive matter in suspension, especially when there is nth water enough to flow over the dam.
The water board, at a recent meeting, discussed the feasibility of obviating these objections by carrying the inlet pipe further up the river. Should the inlet pipe enter the filter gallery at the upper end, it is assumed that this supply would at least keep the water in the filtei gallery constantly moving, and benefit would be derived from whatever water entered the gallery through the filter inlet. The advisability of extending che gallery further up the river, even as far as Stony Brook, and entering it there w ith a direct pipe, has also been discussed. The accompanying diagram shows the filter gallery ami the plan suggested cl admitting the direct water at its upper end. Concerning this gallery. Superintendent M. F. Wright of the l,owell water-works writes to KIRK AND WATKR :
“ The filtering gallery was substituted for settling basins and artificial filters, and was not intended to be used as the principal source of supply, but only during times of freshet, when the water in the river contains a considerable amount of matter in suspension. When the water is clear, it is to be taken from the river through the inlet pipe, shown on the plan.
“ The gallery is situated about 1500 feet above Pawtucket bridge, on the northerly shore of the Merrimack river, and parallel with it, about 100 feet from the water’s edge. Its length is 1300 feet, width eight feet, and height (inside) eight feet. The top (inside) is level with the Pawtucket dam. The side walls have ail average thickness of two and three-fourths feet, and a height of five feet, and are constructed of heavy rubble masonry, laid water tight in hydraulic mortar. The walls support a semi-circular brick arch one foot thick, made water tight. Along the bottom stone braces, one foot square and eight feet long, are placed, ten feet from centre to centre, between the walls, to keep them in position.
“ The bottom is covered with coarse gravel, screened, one foot deep, to the level of the brace stones. There are three manholes of three feet interior diameter, which are built up to the elevation of 47.5 or 1.7 feet above the highest known freshet, and covered with cut-stone covers, and located about 400 feet apart. The depth of the excavation aveiaged about sixteen feet, which carried it into the natural gravel bed.
“ The filter inlet shown on the plan was an afterthought and constructed in 1876, but it has of late been considered of little value. It has been claimed that the 1300 feet of gallery would allow about 1,500,000 gallons of water through it in twenty-four hours, but as we are using at the rate of about 5,500,000 in that time, it can be seen at once that it is of very little use.”