(a) Shirley Gut Siphon.

Largely on account of the dredging in the harbor in the vicinity of Shirley Gut, a considerable portion of the siphon through which the sewage is conveyed under the bed of the harbor from Point Shirley to Deer Island was uncovered. During the year there has been heavy riprap placed along the line of the siphon in order to defend it against further moving of the material and possible injury to the pipe.

(b) Siphon under Alewife Brook.

The work of the Metropolitan Park Commission in moving the channel of Alewife Brook near the Alewife Brook pumping station has caused considerable changes to be made, and the channel has been carried to a greater distance from the station. It has also been found necessary, in order to conform to the deepening of the channel of the brook, to introduce a siphon into the branch of the metropolitan sewer leading across the brook to Arlington. Two siphon pipes have been carried in the bed of the channel in substitution of the main pipe for a length of 54 feet. The local Arlington sewer was also affected and various changes were required. All the changes now in progress are made by the Board, but it is understood that the expense is to be paid by the Metropolitan Park Commission.

(c) Changes caused by the Cambridge Subway.

The plans for the subway being built by the Boston Elevated Railway Company through Main Street in the city of Cambridge interfere with the Metropolitan Sewer where it crosses the line of the subway at Portland Street, the bottom of the sewer being 6 feet above the bottom of the subway. It is therefore necessary to carry the sewage under the subway by means of two siphon pipes. The work involves many complications and is performed by the Railway Company. The introduction of siphons in the line of sewers will not only involve a large additional cost in the maintenance of the sewer, but results in a substantial reduction in its carrying capacity. The construction of the subway involves still further interference with the sewer, and the Board has notified the Company of a claim for damages by reason of the largely increased expense resulting to the Sewerage District.

(d) Winchester and Woburn Sewers.

The condition of the branch of the North Metropolitan Sewer which receives the sewage of the city of Woburn and the town of Winchester has been such as to cause considerable trouble and complaint. The increasing population and at the same time the apparent reduction of the capacity of the sewer have rendered it at certain periods of heavy rain incapable of disposing of the sewage, and consequently there were short periods during a few days in the early spring when slight overflows occurred.

Careful investigations have been made during the past year of the capacity of this system, and it is believed that the troubles which have arisen have largely been caused by the improper discharge of tan bark, hair and other objectionable substances from the tanneries into the sewer. When permission was given to connect the tanneries with the Metropolitan Sewer it was on the distinct condition that all such matter should be excluded. These substances being admitted clog the sewer and consequently obstruct the flow of sewage, and in fact diminish the capacity of the sewer. The attention of the authorities of the two municipalities has been called to the condition, and demands have been made that proper works should be introduced, through settling tanks or otherwise, by which the objectionable matter shall be disposed of, and that only proper matter shall be allowed to enter the Metropolitan Sewer.

The officials of the town of Winchester have caused measures to be taken which will apparently remove the difficulty, but so far the authorities of the city of Woburn have not complied with the requirements of the Board. It is the opinion of the expert advisers of the Board that if only proper matter is allowed to enter the sewer, the present system will be sufficient for a long period to come properly to dispose of the sewage of this district.

(5) SOUTH METROPOLITAN SYSTEM-MAINTENANCE.

There are operated in the South Metropolitan System main sewers of a length of 43.42 miles, an increase of 0.64 of a mile during the The connections from local sewers have been increased during the year by 18 public connections and 1 special connection, in all, 31.15 miles in length. The local sewers connected with the South

year.

Metropolitan System are now 524.01 miles in length, and the number of these connections has increased from 117 to 136.

The Back Bay, Roxbury, West Roxbury, Brighton and Dorchester districts of Boston and the towns of Brookline and Milton still maintain both separate and combined sewers, but all the other districts contributory to this system maintain separate sewers.

There are two pumping stations operated in the South Metropolitan System. The Ward Street pumping station elevates into the Highlevel Sewer the sewage from the original Charles River valley sewer and also that which is contributed from a portion of the city of Boston. The sewage from the city of Quincy is also pumped into the High-level Sewer from the Quincy pumping station. Although the sewage is carried by gravity to the outfall pipes in the harbor, a screen-house is maintained at Nut Island for the purpose of removing the more objectionable matter contained in the sewage before it is finally discharged from the outfall.

There has been pumped at the Ward Street station an average of 22,700,000 gallons of sewage per day, with an average lift of 40.57 feet, at a cost of $0.077 per million gallons per foot lifted; and at the Quincy station 4,163,000 gallons, 21.17 feet lift, at an average cost of $0.208 per million gallons per foot lifted. From all the stations the average cost per million gallons per foot lifted has been $0.089.

An average of 40,400,000 gallons of sewage has been discharged daily from the outfalls into the outer harbor. The maximum rate of discharge per day, which was 135,500,000 gallons, was reached on February 20.

The average discharge of sewage in the South Metropolitan System was at the rate of 173.37 gallons per day per person of the estimated number contributing sewage in the District. This larger per capita discharge is in part because, on account of its greater size, more storm water is admitted into the High-level Sewer at periods of heavy rainfall.

The total amount of coal, all of which is bituminous, which was purchased for use at the stations, was 2,373.303 gross tons. The contract price per gross ton varied from $3.97 to $4.33.

There has been considerable increase in the number of gallons of sewage discharged into the harbor, largely owing to the additional