immediately above the latter which has been converted into a park and the lake shore of which now affords a clean bathing beach. The city is to be congratulated upon having effected this improvement. Early in 1925 there was brought to our attention the matter of a sewer for Appleton Street, to discharge into the Lake at the foot of this street and at a point opposite from and a little above the intake of the Laconia Water Works, (a chlorinated supply), located on the east shore. The plans call for disposal through a septic tank, to be located near the lake shore just above the railroad tracks. This department examined this project, the following letter being transmitted: Mr. C. A. French, Dear Mr. French : Concerning the Appleton Street sewer project as looked over yesterday, the following statement is given you. This project involves the construction of a sanitary sewer to serve at present some eight or ten houses, to connect with a septic tank located near the railroad tracks on the shore of the lake, the untreated effluent to go into the lake on the west side at a point a few rods above the point opposite from the water pumping station on the east side. It is regretted we must advise you that this department does not view this project favorably and that the sanction here provisionally given is extended only because it is understood there is absolutely no other feasible way of handling the situation, such sanction being with the understanding that the arrangement is emergency and temporary in character and that it shall not be viewed as a precedent for the later installation of similar disposal devices in this locality. While it may be rather improbable that any of this sewage discharge would, under normal conditions and because of the lake current at this point, ever reach the water intake, yet we have no positive assurance of this, and at best we are obliged to regard the proposal as one more distinct pollution hazard by which your public water supply will be confronted. Later, as a measure of safety it was recommended to the city that it give consideration to extending the effluent line from the tank to a point well below the water intake, and this feature is now pending. The Winnepesaukee Water Company, which furnishes water to The Weirs from Lake Winnepesaukee, has been ordered by the Board to install chlorination. This treatment the company is arranging to provide during the 1926 sum mer season. LEBANON The following report was addressed to the board of water commissioners embodying observations made in connection with an inspection of the plant of the Lebanon Water Works, such inspection having been made in consequence of difficulties having been experienced. Board of Water Commissioners, Lebanon, N. H. Gentlemen: October 24, 1925. The following report, with recommendations, is handed to you relative to our inspection of your plant as made October 1st. Results of previous analyses have, on the whole, been generally indicative of unsatisfactory quality-this particularly so in view of the fact that the system includes a filtration plant, which, if properly constructed, equipped and operated, should afford a water substantially equal to one of ground origin. By this is meant a water not only having the minimum bacteria content, but one which contains but a small proportion only of the turbidity, vegetable matter and color originally present. ous one. Thanks very largely to the chlorination part of the treatment the criticism from a bacteriological standpoint is not at this time a seriThat there is general improvement in this respect at this time is largely due to the fact, probably, that the chlorine treatment is now so arranged as to be applied to the water as it leaves the clear water well in the pump intakes. However, the degree of improvement in the physical quality is not now, and never has been, satisfactory, this largely due to defects or deficiencies in the original construction. PLANT Originally using water from the Mascoma River direct, an attempt was made during 1901 to obtain a form of filtration through the construction of two filter galleries near the stream, one of these, 30'x 65'x15' being at present used as the filtered water collecting well. As these galleries were a failure, three artesian wells were bored, but these too have proved to be failures, in point of both quality and quantity. Because of the inferior quality contributed and the very small volume available it is recommended that the only one now producing be cut out entirely. The present fitration plant, constructed in 1906 or 1907, includes two 15' mechanical filter units, of a combined capacity of 1,000,000 gallons per twenty-four hours operation. Filtered water is accumulated in the old filter gallery just mentioned, from which it is pumped a distance of 1900 feet, under a 250-foot head, to an open distributing reservoir of about 1,000,000 gallons capacity. About two years ago a second storage reservoir of larger capacity was constructed near the original one. This also is uncovered, and has a foundation in a very soft shale rock. The latter is peculiar in that the cleavage is in nearly a vertical line and an unfortunate circumstance is that under the action of air and water it is disintegrating very rapidly. Tests have indicated this rock to include a very large amount of readily soluble iron. As the slope of this rock floor within the new reservoir is some 30-35 degrees, there are times when much of the upper side is uncovered by water. The surface is, moreover, extremely jagged, which renders cleaning very difficult and tends to favor the accumulation and development of organisms giving rise to odors and tastes. It may prove feasible to cover this present rough surface with cement. FILTRATION There is no means of ascertaining more than approximately the water consumption. However, on the basis of an estimated consumer population of 6,000 and a daily per capita consumption of 100 gallons this would mean in the neighborhood of 600,000 gallons daily. Making due allowance for slippage in the old pump and on the basis of an average of 15 to 17 hours pumping, this figure checks fairly well with that deduced from the pumping rate. This also agrees with the rate for the electrically operated pump held in reserve. The above is at the rate of about 85,000 gallons per 24 hours, and as the combined area of the two filters is 354 square feet, this is equivalent to a filtration rate of 104,000,000 gallons per acre per day. As good practice recognizes a rate of 125,000,000 gallons per acre per 24 hours, or two gallons per square foot per minute, it will be seen that the present rate is not excessive, also that there is a substantial margin for increment, if needed. This plant includes no such modern devices as loss of head 1 gauges and rate controller, items needed for careful and intelligent operation. COAGULATION An indispensable adjunct to filtration under this system is the use of a coagulating medium, the dosage of which should be adequate and should be constantly and carefully proportioned to the needs of the raw water supply as determined by its varying character. A low color and turbidity mean a lower alum demand than where these are high. It must be evident therefore that where turbidity is increased, as a result of rains or flood conditions, an increase in the alum dosage is called for. Properly speaking, the chemical used is not true alum but is a basic sulphate of alumina. Its action is similar to that of the white of egg in clarifying coffee, as its addition to a turbid or colored water occasions a flocculation of the fine dirt particles, with precipitation of the vegetable and coloring matter. As this precipitated matter serves as the true filtering material on the surface of the sand, it is indispensable that, after washing the filter, the water be run to waste for a sufficient period until a film of this material has reformed. Analysis of a sample of the sulphate of alumina in use this date, supplied by the Merrimack Chemical Company, indicated 17.22% of alumina as oxide, with 3.41% of oxide equivalent insoluble in water. Good filter alum should contain not less than 17% of alumina, with not more than 7% of insoluble. There is, however, now obtainable a soluble filter alum containing not exceeding 0.5% insoluble. The latter is more desirable for use in small plants because it does not necessitate frequent stirring of the alum solution tank, and there is much less tendency to clogging of the feed valve in the orifice box. Incidentally it should be noted that the orifice valve has apparently been out of commission here for some time, while the box itself is in very poor shape. There should be a new box and valve provided at once, and an extra one kept in reserve. Also the alum solution tank should be provided with mixing paddles set on a vertical shaft and actuated by a crank. Of course if soluble alum is used, this will be unnecessary. The present position of the orifice box, close up under the ceiling, is most unfavorable to frequent inspection, cleaning and adjustment, and apparently it does not get this. PRESENT RATE OF ALUM DOSAGE In making up the alum solution fifty pounds are said to be weighed out for each tank-ful, and it is claimed that this amount always serves for a day's run, and sometimes more. On the basis of 600,000 gallons filtered per day this means a dose per gallon of less than 0.6 grain. This is a very low dosage-too low for any satisfactory accomplishment. Good practice seldom involves less than 1 grain and there are many waters for which considerably more is needed. Thus at Exeter as much as 2.5 is used. At the new West Lebanon plant of the Hartford Water Company, the dosage is varied on a scale, determined by the needs but the amount used approximates 75 pounds per day for the 325,000 gallons pumped, equivalent to about 1.6 grains, or nearly three times that used at your own plant. Incidentally it is recommended that your Board arrange to make a study of the West Lebanon plant with a view to securing the introduction of improvements at Lebanon. That the present alum dosage is comparatively very small is also revealed by the alkalinity values as indicated in the accompanying analyses, but the alkalinity reduction as a result of the alum addition being but slight. LACK OF SEDIMENTATION AND COAGULATION BASIN The absence of any provision for pre-settlement of sediment and of the matters precipitated by the alum before the alumed water goes to the filters is a vital and fundamental defect, the reason for which can only be explained on the assumption that it was thought to save money by its omission. If so, it was a short-sighted bit of economy. At present the alum solution is conducted directly into the 10′′ raw water feed main at a point about 75 feet back from the filters, which means that there is no adequate provision whatsoever either for settlement or for the time needed to complete the chemical reaction involved. The result is that the filters are constantly overloaded and much of the floc. which should form and be dẹposited before reaching the filter actually must occur on and in the filter and in the filtered water well, in which latter place it tends to be deposited and to some extent be carried up into the reservoirs. To just what extent this may be responsible for the foul-smelling accumulation recently noted in the reservoir cannot be stated, but there would seem to be no doubt that such must be an important contributing factor. Modern practice demands the provision of sedimentation basins permitting of a detention period for the treated water of two to six hours before entering the filters. Until this deficiency is supplied you cannot expect to turn out an acceptable water supply. Also, because of this lack, there would be no particular point in materially increasing your present alum dosage, because there is no opportunity afforded for the alum to do effective work. The alum should, however, be increased up to about 1 grain, even for present conditions. |