OF THE CHIEF OF ENGINEERS, U. S. ARMY. the District of Columbia that are under the supervision of the Chief of Engineers: GATEHOUSES, BUILDINGS, AND GROUNDS. At Great Falls the buildings and grounds were kept in good condition. At Dalecarlia Reservoir the two frame houses were painted, and filtered city water was supplied to the two houses south of the reservoir. At Georgetown Reservoir modern fixtures were installed in the bathroom in the overseer's house and filtered city water supplied. A fence of heavy concrete posts and panels and low steel pickets was built along the west side of the Conduit Road extending 339 feet south and 161 feet north of the west shaft gatehouse. The board fences around the grounds are being replaced with a heavy wire fence supported on reenforced concrete posts, 1,075 linear feet having been built during the fiscal year. At 2728 Pennsylvania Avenue a garage for the motor truck and a fireproof oil house were built and the old blacksmith shop was torn down and removed. At McMillan Park Reservoir a hot-water heating plant was installed in the foreman's house, and both this house and the one occupied by the superintendent were painted and repaired. THE CONDUIT. The conduit between the intake and gatehouse at Great Falls was cleaned out once, at which time about 80 cubic yards of deposit was removed. Mud deposited from the conduit upon opening waste weir No. 1 was removed from the Chesapeake & Ohio Canal in front of the waste weir. Several leaks in the conduit, near manholes Nos. 5 and 30 and at culvert No. 12, were repaired. THE ROADS. The total length of roads maintained under this office is 14 miles. For convenience in describing the condition of various parts of these roads they are divided into ten sections as follows: Sec. 1.-Foxhall Road to Elliott Place.. Sec. 4.-Little Falls Road to top of Dalecarlia Hill. Sec. 6. Culvert No. 20 to Cabin John Bridge. Total.. During the fiscal year the amount of work done on the roads and its cost is shown in the following table: TABLE 1.-Showing amount and cost of work on roads. The areas of road treated with tarvia A on section 6 were plowed, shaped, and rolled. About 0.7 gallon of tarvia per square yard was then applied hot from a tank wagon; a thin layer of screenings was then spread over the tarvia and rolled. The areas of road treated with tarvia B were swept reasonably free of dust and about 0.4 gallon of tarvia per square yard applied from sprinkling cans. Tarvia B was applied in the fall of 1910. In the spring of 1911 automobiles passing over portion of section 2 between Elliott Place and the Georgetown effluent gatehouse, where there are several sharp turns and the road has a grade of about 3 per cent, raveled the road badly. Tarvia A was then applied, about 0.9 gallon per square yard, and stone screenings placed on top while the tarvia was hot. The result is a smooth, practically dustless surface, with no raveling evident up to the latest inspection. The part of section 10 which was resurfaced, being a gravel and clay road, was covered with about 3 inches of broken stone (loose) in sizes between three-fourths inch and 1 inches. This layer of stone was rolled; about 1.4 gallons of tarvia X per square yard of surface was applied hot from tank wagons. Upon this it was intended to spread and roll a layer of stone screenings three-fourths inch and smaller in quantities slightly more than sufficient to fill the voids, and to cover this layer with about 0.7 gallon of tarvia A per square yard, followed by more screenings to take up excess tarvia, but on account of nonreceipt of materials ordered it will be necessary to do this work in fiscal year 1912. There were also 825 linear feet, or 550 square yards, of concrete sidewalk laid along the road in section 10. In repairing section 4 the method used was the same as described above for section 10, except that the tarvia A was not applied until the spring of 1911, by which time the road, especially on the 6 per cent grade and on curves, had raveled in certain small areas. Since final treatment this section has been in good condition. The value of this method of treatment will depend upon how the surfacing holds up during the next few years. The tarvia was a refined coal tar, being a by-product from the works of the Washington Gas Light Co. The designation and trade name are as used by the Barrett Manufacturing Co. A survey was made of the Washington Aqueduct property along the Conduit Road from Foxhall Road to the District line, and two sets of maps, one on a scale of 100 feet to the inch and the other on a scale of 40 feet to the inch, were made. THE TUNNEL. The Washington Aqueduct Tunnel was pumped out and inspected from Widow's Mite air shaft to the east shaft. On the last occasion as a preliminary to draining the tunnel the filters were filled to their full capacity several days before the work of pumping was begun. The McMillan Park Reservoir was filled as full as possible. The blow-off at Rock Creek was opened at 1.25 a. m. November 29, the tunnel discharging by gravity until 5 a. m., when the centrifugal pumps at Rock Creek were started. The air lifts at Champlain Avenue and east shaft were started at 6 a. m. and 6.45 a. m., and on account of the failure to maintain pressure of steam at Rock Creek, where only one centrifugal pump could be kept continuously in operation, the air lifts worked with the centrifugal pumps until the water was reduced below the level of the summit east of Rock Creek about 11 a. m. The section of the tunnel drained by the air lifts at the east shaft was emptied at 9.20 a. m. on the 30th, and that section drained by the air lifts at the Champlain Avenue pumping station was emptied at 1.30 p. m. An inspection party composed of the officer in temporary charge and the superintendents of the Aqueduct and the filtration plant made an inspection of the entire section of the tunnel east of the summit lying east of Rock Creek. This being the first time that this section of the tunnel was drained since the tunnel was put into operation in 1902, this inspection was the first made since the latter date. The brick walls of the tunnel and also the rubble masonry walls were found to be in excellent condition. The invert of the tunnel as well as all the walls were found to be free from any sedimentary deposit. The only obstruction found in the tunnel was some plaster which had fallen from the rubble masonry side walls, which was insignificant in amount and harmless to the operation of the tunnel. Seepage into the tunnel was small in amount and usually through holes which had been used for grouting or in very thin streams through joints in the brick. The entrances to the inlet of the air lifts were found to be unobstructed. The inspection having been completed, the filling of the tunnel began about 4.15 p. m. by opening two gates 6 inches at the west shaft, Georgetown Reservoir. The gates at the east shaft were kept closed until the tunnel was filled. The gates at the west shaft were opened an additional 6 inches at 5 o'clock and at each hour thereafter until the tunnel was filled. By this means the filling of the tunnel (capacity about 20,000,000 gallons) was accomplished in about four hours. The time occupied previously in filling the tunnel was eight hours. The waves and water hammer created by filling the tunnel caused the water to be forced up the air shafts at the different summits. At the Thirteenth Street shaft, the top of which is covered with a manhole cover in the west sidewalk above Florida Avenue, the water spouted through the holes in the manhole cover, rising several feet above the sidewalk. The tunnel was out of use for 43 hours. THE BRIDGES. The flooring on bridge No. 6 across Rock Creek was renewed and minor repairs were made to the bridges along the aqueduct. THE MAINS. Prior to August, 1905, the mains leading from the distributing reservoir were used for a gravity supply to the city. On August 21, 1905, the gates at the distributing reservoir were closed, and since that date the entire supply has passed through the tunnel to the McMillan Park Reservoir. The mains are now more than ever an integral part of the city distributing system. By mutual agreement they are now operated and maintained by the city water department. It is again recommended that their formal transfer to the city be authorized. TURBIDITIES. The practice of closing the inlet gates at Great Falls whenever the turbidity of the Potomac water reaches 500 or more, as described in the Annual Report of the Chief Engineers for 1906, pages 2090 and 2091, was continued during the fiscal year, with the results shown in the following table, which are, of course, only approximate. TABLE 1.-Table showing tons of suspended matter entering system, etc. From the above it is seen that the gates were closed 11.26 per cent of the time, thereby excluding 45.23 per cent of the total suspended matter that would otherwise have entered the system. CONSUMPTION AND WASTE OF WATER. Tables showing the average consumption of water per 24 hours, by years from 1874 to 1906 and by months from July, 1899, to January, 1903, will be found in the Annual Report of the Chief of Engineers for 1906, page 2092, and by months for the period January, 1903, to June, 1910, in the Annual Report of the Chief of Engineers for 1910, page 2632. The following table covers the fiscal years 1910 and 1911 and the accompanying diagram gives a graphic comparison with the consumption for previous years since 1899: TABLE 2.-Table showing average consumption of water for 24 hours. [In million gallons.] 59.19 60.38 173 173 Per capita consumption for 1911 is based on a population of 348,460, which is that assumed by the health department, District of Columbia. The maximum daily amount of water pumped to the filters during the year was 78,320,000 gallons. Appropriations for the Washington Aqueduct, dates of acts, and reversions to the Treasury. APPROPRIATIONS 1850-1900, INCLUSIVE. $87,500.00 20,000. 00 5,000.00 20, 000. 00 555,000.00 20, 000. 00 355, 000. 00 20, 000. 00 595, 000. 00 25, 500. 00 48, 396. 78 20,000. 00 20,000. 00 80,000. 00 82, 500. 00 June 4, 1880. Mar. 3, 1881. July 1, 1882. July 15, 1882. Mar. 3, 1883. July 5, 1884. July 7, 1884. 87,500.00 4,000. 00 71, 500. 00 25,000. 00 26, 000. 00 322, 210. 50 230, 000. 00 176, 034. 34 8, 296, 577. 92 15, 651. 39 8, 312, 229. 31 38,048. 27 Net amount expended. 8, 274, 181. 04 |