1 2 3 General tax, 5c per 100. Front-foot charge, (13c water, 13c sewer) 26c Ready-to-serve charge Water consumption charge, 18c per 1,000 gal. Total annual expense $2.50 $0.25 $2.50 13.00 13.00 4.00 7.20 $2.50 $13.25 $26.70 It is evident from the above that the cost to the inaccessible property is trivial; that the owner of the ordinary undeveloped lot ascessible to service, while not heavily burdened, has considerable urge to develop; and that an average residence obtains all the advantages. of a complete water and sewerage system for less than $2.25 per month. The front-foot rates given are the maximum obtaining for subdivision property. Many of the early rates were considerably less, and some are still substantially so even since the advance was made effective. The local characteristics of the territory have given rise to many interesting problems. Most of these follow from the effort to secure, in this large suburban area, systems not only adequate for the near future but capable of extension to meet the demands of a later period-and to do this at moderate cost and without the probability of extensive replacements. Much difficulty and expense are caused by the ungraded condition of a substantial proportion of the streets at the time it becomes necessary to install the pipe lines. It is not at all unusual for the water main trenches to be from seven to nine or ten feet deep for some distance, to avoid the necessity of a later lowering of the main; and probably the average depth is more than six feet, in spite of the fact that a distance of slightly more than four feet from finished street surface to top of pipe is the aim. The Commission now refuses to lay water pipes and sewers in new real estate developments until streets are substantially graded to the elevations it establishes, but in existing developed sections service must be given regardless of the condition of the streets. Ungraded streets not only cause trouble with pipe line construction but they also affect the setting of hydrants and meter housings. Early experiences disclosed the desirability of using fire hydrants which could be replaced easily by those of greater or lesser length without the necessity of expensive excavation. This led to the designing, in the Commission's office, of a hydrant having a sliding frost ease which permits adjustment to changing grades over at range of two feet. The barrel of the hydrant itself is an adaptation of that of a well-known make. This form of hydrant, now used universally in the District, has proved highly satisfactory. In set ting this hydrant on a street which has not been brought to final grade, it is only necessary to place the top of the upper section of the frost case slightly above the existing ground level and to use a barrel of length to suit the elevation of the ground. When the street is either excavated or filled, only a small amount of labor is involved in lowering or raising the upper section of the frost case to conform with the changed ground surface and in replacing the existing barrel with another of suitable length, in case the grade was altered sufficiently to make a barrel of another length necessary or desirable. The resetting of meter housings to new grades has occasioned considerable expense and an effort has been made to design a housing which can be easily adjusted to small changes in ground elevation without the necessity of digging up the setting. As yet no satisfactory solution, involving reasonable expenditure, has been found. The following additional notations concerning details of the Commission's engineering practice may be of interest : 1. The engineering office is organized with divisions of accounting, drafting and design, and plumbing inspection, under the deputy chief engineer; and departments of surveys and street plan, construction, and maintenance and operation, each under a department engineer. 2. The surveying and mapping of the District are founded on a co-ordinate system, using the head of Liberty on the dome of the United States Capitol as origin. Main control for the traverse system is based on the triangulation stations established in the vicinity by the United States Coast and Geodetic Survey. 3. Most of the construction work is done by day labor, but some projects of considerable volume are carried out by contract. Day labor jobs are accomplished by thoroughly experienced forces, unaffected by politics, and using machinery where possible. Contrary to usual experience, day labor unit costs here are lower than contract prices. 4. Transportation of men and materials is somewhat difficult owing to the large area covered, the scarcity of circumferential highways, and the unpaved condition of many streets. The Commission uses about fifty automobiles and trucks in its various operations. 5. About 100 miles of water mains have been laid with de Lavaud centrifugal pipe, using all sizes from 6 to 20-inch. The use of this pipe has resulted in a considerable saving in cost. Except for some trouble experienced from split pipe in the lines, this kind of pipe has given satisfaction. 6. During the more recent years the use of leadite has been standard practice. This material has given complete satisfaction in connection with bridge and railroad crossings, as well as with ordinary trench work. Water mains laid with leadite now total about 120 miles. 7. Water services are ordinarily of 14-inch pre-calked cast iron pipe connected to the main by means of a corporation cock and lead goose-neck. A slight amount of difficulty has occurred due to shearing of the pipe, which is laid in the same trench with the sewer connection where practicable. The use of copper pipe for small services is contemplated. One connection from the main to the meter housing serves two houses wherever this arrangements proves feasible. 8. Housings for small meters consist of a two-foot length of 18inch vitrified pipe upon which is placed a concrete truncated cone with top and bottom diameters of 15 and 18 inches, respectively, and height of 18 inches. Above this comes a cast iron cover. The housing is thus approximately four feet deep. The meter is set with top about 15 inches below ground and is held in an iron yoke. These yokes have a cut-off on the inlet side which eliminates the necessity of using a curb cock and box. Where one pipe from the main serves two houses, two meters are placed in one housing and two pipes leave the housing. 9. Standard manhole frames and covers weigh approximately 350 pounds per set. The frame has a clear opening of 22 inches, a height of 8 inches, and the width of bottom flange is 41⁄2 inches. Not a single cover has been broken, even under the heaviest traffic conditions, and the frame opening has proven sufficient in size for easy maintenance of the sewer lines. All fire hydrants are painted dark green and light graythe domes green and the barrels gray. This color scheme 'gives a pleasing contrast and is effective both in daylight and at night. The green shows up well against a background of snow or concrete, and the gray against one of grass. 11. Coagulating periods from thirty minutes to an hour are all that are used in the District's water purification plants, and they have been found ample with the local water. Coagulation is under pH control at all times. Filter effluents are constantly observed. through turbidity detectors attached to the effluent piping of each filter. Liquid chlorine application is controlled through residual chlorine tests at hourly intervals, and oftener with rapidly changing quality of raw water. The Commission has power to install storm-water drains, operate a refuse disposal system, control plumbing, subdivision plats and street grades (except in municipalities), and to plan a system of highways. Owing to the pressing necessity of extending water and sewerage service, however, nothing has been done so far on drainage and refuse disposal projects. Subdivision plats cannot be placed on record until the Commission has approved them. This requirements has been productive of much good and, together with grade establishment, has aided materially in designing and constructing the water and sewerage systems. The communities in the District were developing in a haphazard manner; subdivisions were being laid out with no thought of adhering to a general highway plan; streets were mostly narrow and poorly suited to topography; the only desire seemed to be to obtain the greatest possible number of lots. Progress toward preventing further disfiguration of the territory was slow at first, as land developers resented what they believed to be unwarranted interference with their rights; but gradually most of them have learned that a logical street plan generally results in at least as many salable lots and in much lower grading expense. The Commission now works out practically all subdivision layouts and then turns them over to the landowner for completion of the plats for record and the staking out of streets and lots. The Commission has experienced the usual difficulties that befall a new form of administrative body in executing a large project. Charges of autocracy, secrecy, lack of sufficient check on authority, of imposing high rates, and of creating a burdensome public debt, have been made; but these have been shown to be without foundation in fact. The law undoubtedly can be improved in some particulars and this will probably take place. Rapid growth of the District in recent years, and the passage of similar legislation establishing several additional suburban districts in Maryland, bear witness, however, to the fundamental propriety and value of the original legislative act and the success attending its administration. SEPARATE SLUDGE DIGESTION By Jerry Donohue, Consulting Engineer, Sheboygan, Wis. The science of Sewage Disposal as it has been developed from studies and experiments made of the various plants which have been in operation during the past twenty years has given to the engineering profession a good working knowledge of the art, and the available data is of great value to the designer in planning new systems. It is needless to point out the necessity of all municipalities undertaking the analysis of their problem of Sewage Disposal, for it is apparent that no two cities have exactly the same problem confronting them. Some cities may have a large proportion of industrial waste, which may make the problem of disposal more difficult, and some cities may be geographically favored with a location on a large stream which has volume enough to secure proper dilution without complete treatment. Sewage treatment is one of the most important matters that governing bodies of any community have to deal with. Our present standard of living demands that our homes be equipped with sanitary improvements of all kinds. Even the workingman's cottage now has the conveniences that a few years ago were found only in expensive houses. It is an interesting fact that in 1860 even the white house was not equipped with a bath tub, and now there are 10,000,000 bath rooms in this country. Sanitary engineering, therefore, as a profession, will greatly facilitate the home building of the future in that it will be up to Sanitary Engineers to keep upto-date in the art, which has made such rapid strides during the past twenty years. The State of Wisconsin, with a population of three million people and an area of 56,000 sq. miles, is happily blessed with over 10,000 inland lakes, thousands of miles of wonderful streams and rivers, that annually attract red blooded men and women to enjoy the fishing and recreation that the great out-of-doors offers. It has within its borders, 132 municipalities that discharge raw sewage into some adjacent water course. There are 83 sewage disposal plants serving cities and villages in Wisconsin. Fifty-five percent of the urban population is now tributary to some type of disposal plant. The first municipal sewage disposal plant was built in the city of Madison about 1890, and Madison has now under construction it's fourth disposal plant. Settling tanks, supplemented with Separate Sludge Digestion replaced two of the old plants, but the city of Madison is this year adding Imhoff tanks in another part of the city. Each year Wis |