EXAMINATION OF RIVERS.

The regular monthly examination of the waters of three rivers has been continued during the past year. The Blackstone has been examined at four points, the Merrimack at two and the Taunton

at one.

Advantage was taken of a drier season than any other since the Board began its regular examinations of water supplies and rivers in 1887, to make special examinations of five rivers, viz., the Blackstone, Quaboag (a branch of the Chicopee), Merrimack, Nashua and Neponset.

Occasional examinations have been made of water from some of the other rivers of the State, and the results are printed in connection with the water supplies of the towns where the samples were collected, and can be found on previous pages of this volume as follows:

Nearly all of the examinations show an increasing pollution of the streams as compared with previous years. This is caused not only by the fact that the summer and autumn of 1891 were drier than for several years before, but also by an unusually rapid increase in population and manufactures during these years, little being done by the towns and manufacturers to keep the larger streams from becoming polluted.

BLACKSTONE River.

A detailed description of the Blackstone River and of the various ways in which it is polluted was given in the special report of the Board on the Examination of Water Supplies, 1890, page 383. As there stated, the Blackstone is the most polluted river in Massachusetts, due for the most part to the sewage and manufacturing refuse

BLACKSTONE RIVER.

of the city of Worcester, situated at the head of the river. Until Je 25, 1890, all of the Worcester sewage went directly into this stream through the Mill Brook channel; but since that date a portion of the sewage has been treated at the chemical precipitation works, located near the river, about one mile south of Quinsigamond Village.

In order to show clearly the points at which the Worcester sewage and the effluent from the precipitation works enter the river, and the relation of these points to the places where samples have been collected, a diagram is given upon the opposite page. This is not drawn to scale, but is merely a sketch showing the relation of the sewage outlets and sewerage works to the river, and the average quantity of water or sewage flowing in the different channels during the week ending July 29, 1891, when a special examination of the river was made.

As,

Nearly all of the sewage of the city flows into the channel of Mill Brook, which has practically been converted into a sewer. however, this brook receives the natural drainage from a water-shed of about 12.5 square miles, the sewage is diluted and its volume very greatly increased by mingling with the brook water. At the present time the main sewer leading to the precipitation works extends only up to the mouth of the Mill Brook channel, so that the sewage treated does not come directly from the sewers, but is the diluted sewage flowing in this channel. On account of the large volume, it is possible with the present works to treat only a portion of this sewage, even in the summer time when the flow is least. The precipitation works were designed to treat 4,500,000 gallons per day, but, during the drier portions of 1891, they were used to treat as much as 6,000,000 gallons, though this amount could not be treated quite as effectively as a smaller quantity. The greater part of the untreated sewage now, as in the past, flows into the river at the mouth of the Mill Brook channel; but it is the custom to divert to the precipitation works somewhat more sewage than can be treated, and to turn the surplus into the river through a by-pass.

At the precipitation works the sewage is treated with chemicals and then caused to flow slowly through settling tanks. The clarified effluent is discharged through a ditch into the river. The precipitated sludge is disposed of by pumping it upon land near the river, and some of it after drying has been burned.

Samples of Sewage collected here. Precipitation Tanks

BLACKSTONE RIVER.

Diagram showing the Relation of the Worcester Sewerage Works to the Blackstone River (not drawn to scale).

NOTE.-Figures in parentheses express the average flow in millions of gallons per twentyfour hours through the different channels during the week, beginning at 8 A.M., July 22, 1891.

By-pass for

(6.01) EFFLUENT

(35.84)

BLACKSTONE

(28.43)

RIVER

(Sampling and Measuring Station above Precipitation Works.

Sampling place below
Precipitation Works,

BLACKSTONE RIVER.

As the amount of sewage discharged without treatment is much greater than the amount treated, the river is still very foul and during the past year has been the cause of much complaint from those living near it below Worcester.

The regular monthly examinations of the river at several points have now been continued since June, 1887, and it is feasible to prepare tables by which the average results obtained in the different years can be compared. Two tables are presented, one showing the average results for each calendar year and the other giving the average results for the six months of each year from June to November, inclusive, the latter representing the drier half of the year. The Worcester precipitation works were first operated in July, 1890, and since that date samples have been taken from the river above and below the works, while before only one sample was collected. As no sewage then entered the river at the precipitation works it may be fairly assumed that for all previous months the water had the same character above and below the works.

Following these tables of averages will be found, first, the detailed tables of analyses of the regular monthly samples; second, a description of the special examination of the river and sewerage works, made in July, 1891, together with the general results of this examination; and, finally, the tables giving in detail the measurements of the flow of the river and all of the analyses made in connection with this examination.

AVERAGES OF CHEMICAL ANALYSES OF WATER FROM THE BLACKSTONE RIVER FOR THE YEARS 1888 TO 1891, INCLUSIVE.

Blackstone River between Mill Brook Channel and the Sewage Precipitation Works.