USA > Massachusetts > Worcester County > Milford > Town Annual Report of the Officers of the Town of Milford, Massachusetts 1921 > Part 5
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The work done on the present field during the past year has included the placing of outlet weirs on the settling tanks so as to increase the depth and capacity of the tanks, the re- laying of a considerable part of the under-drain system and the cleaning of the remainder, and the refilling with sand of the sludge bed to the elevation of the original surface. By these improvements the original capacity of the field should be regained, but this capacity is well below the present flow of sewage, and it must be recognized that the work done during the past year did not by any means do away with the necessi- ty of enlarging the plant. The board has for several years de- ferred making a definite recommendation because of the high cost of construction, but prices of material and labor have now substantially dropped, and we believe the time has come to undertake the necessary extension of the disposal plant. Furthermore, by requiring in the contract that preference shall be given to citizens of Milford, this extension can be made the means of providing employment for men now out of work.
We submit herewith a report from our engineer and, in accordance with his conclusions, we recommend that the town appropriate the sum of $60,000.00 for the construction of ad- ditional disposal works
The following figures indicate the condition of the assess- ment account :-
Total amount certified 1908 to December 31, 1921 $102,243 09 Total amount paid, not including interest $97,574 02
Balance of assessments not paid . $4,669 07 Total interest accruing 1908 to December 31,
1921 ·
$10,223 38 ·
Total interest paid to date
$8,842 29 .
Unpaid interest
$1,381 09
Total outstanding assessments and interest . .
$6,050 16
No assessments were certified in 1921.
The total present number of connections is 1355, 30 hav- ing been added during the past year.
FRANK P. DILLON, LOUIS P. PRATT, ALFRED F. MARTIN, Sewerage Commission.
Report to Sewerage Commission on the En- largement of the Sewage Disposal Works.
February 15, 1922.
SEWERAGE COMMISSION, MILFORD, MASSACHUSETTS.
DEAR SIRS :- In accordance with your instructions we are submitting the following report on the necessity of addi- tional disposal works.
CONCLUSIONS.
For, your convenience we will at once set down our con- clusions, which are as follows :-
That the plant has been seriously overloaded for five years and the present load is from 40-50 per cent in excess of the reasonable capacity of the works.
That the discharge into the river of a large [quantity of untreated sewage will be unavoidable until additional filters are constructed, and that an enlargement of, the disposal plant should be at once undertaken.
That to provide the increased capacity-filters of coarse stone can be constructed at about two-thirds the cost of addi- tional sand filters and that the approval of the State Depart- ment of Health should be asked of the plans, herewith submit- ted, of a trickling filter preceded by sedimentation in two- story tank-the additional plant to bejtsufficient for 5000 people and to cost $56,000.00.
That permanent carriers should be constructed in the present sand beds at a cost of $3,000.00 and that a total appro- priation, by the town, of $60,000.00 shouldibe requested for the necessary improvement and enlargement of the disposal works.
THE CAPACITY OF THE PRESENT PLANT, AS ORIGINALLY ESTIMATED.
The present plant, consisting of four settling tanks of a total capacity of 300,000 gallons and 9.4 acres of sand filters was estimated in our original report of 1906 to be capable of
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treating 800,000 gallons of sewage per day, and to be proba- bly sufficient for the requirements of the town for ten years, or until 1916. It is, therefore, of interest to inquire as to the present flow of sewage.
FLOW OF SEWAGE IN 1921.
Observations made during the past year show that during the spring and early summer the discharge varied from a minimum of 1,000,000 gallons per day to a maximum of 2,- 900,000 gallons per day ; that from June 1st the flow gradu- ally decreased from 1,000,000 gallons per day to a minimum of 450,000 gallons per day on September 15th, after which date it again increased to approximately 1,000,000 gallons per day in December. Because of extremely low rainfall in Aug- ust and September, the minimum flows recorded during the late summer months are undoubtedly less than under average conditions. The maximum observed flow of 2,900,000 gallons per day was noted at 9 A. M. on May 1st, following a rainfall which exceeded 3 inches in the preceding 24 hours. From this peak the flow gradually decreased to 1,650,000 gallons per day on May 5th. The maximum of May 1st is undoubt- edly exceptional, but the observations indicate that the dis- charge will frequently approach 1,750,000 gallons per day dur- ing the spring months. As a general summary, it may be fairly concluded that, with present connected population, the flow will approximately average 1,000,000 gallons per day during the winter months; 1,250,000 gallons per day during. the spring months, and 750,000 gallons per day during the summer and autumn. As will appear later, these average flows are equal to 100, 125 and 75 gallons per capita per day for the respective seasons.
The records also indicate that following rainstorms these averages, as just stated, may be increased by amounts vary- ing from the insignificant to more than 1,000,000. gallons per «lay. It is impossible as yet to determine the cause of these increased flows following rainfall. In some storms the quick rise suggests that roof or surface drains have been connected with the sewers ; in the case of other storms the response is
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too slow to be thus accounted for, although quicker than can be reasonably explained by leakage due to rising ground water. It is true that, following the observations of last spring, some open inspection holes, which admitted ground water from the underdrains to the sewer, were discovered and closed, but a further investigation under high spring flow con- ditions is necessary to determine whether there is direct en- trance ;of rain water from roof and surface drains. It is be- lieved that, by such an investigation, it may be found possible to reduce the peak flows which follow rainfall, but even, if the peaks were eliminated, the amount of sewage reaching the plant during six months of the year will range from 25 to 75 per cent in excess of the capacity of the plant, as originally estimated.
POPULATION CONNECTED WITH THE SEWERS.
A more logical way of estimating the capacity of filters is on the basis of connected population rather than quantity of sewage. Accordingly an analysis of the 1921 list of sewer connections has been made with the following results : -
Number of People.
Resident population in connected premises
(based on 1920 census) 9,420
Floating population in hotels, boarding houses, etc. 100
From 22 connections in Hopedale
150
Factory operatives and workers in business district who reside outside sewer dis- trict 250
Total present connected population 9,920
In like manner the connected population has been ap- proximated for each of the years from 1913 to date as follows :
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Connected Population
Connected Population
Per acre of filters.
1913
7050
750
1914
7600
820
1915
8200
880
1916
8650
930
1917
8850
950
1918
9100
980
1919
9700
1040
1920
9800
1055
1921
9900
1070
CAPACITY OF PRESENT FILTERS ON BASIS OF CONNECTED POPU- LATION PER ACRE OF SAND AREA.
The following table shows the yearly average of analyses of the disposal plant effluent from 1911 to 1921 (Records of State Department of Health )
Ammonia
Total
Free
Albuminoid Chlorine Nitrates (Parts per 100,000)
Nitrites
Iron
1911
.72
.0357
10.13
1.1683
.0056
.0236-
1912
.69
.0393
9.79
1.5040
.0087
.0591
1913
.38
.0292
9.02
1.3917
.0067
.037
1914
.47
.0405
9.36
1.1358
.0072
.070
1915
.87
.0751
8.45
.8558
.0093
.146
1916
.84
.0583
7.58
1.0350
.0178
.219
1917
1.55
.1208
7.16
.8943
.0162
.494
1918
1.45
.1028
7.46
.8358
.0086
.513
1919
1.13
.0816
5 91
.5266
.0093
.609
1920
2.02
.1002
7.06
.4415
.0114
.777
1921
2.53
.0885
5.68
.4588
.0118
1.050
The progressive deterioration of the effluent-as shown by the increasing ammonias and iron, and decreasing nitrates -indicates that the load on the filters reached its sate limit in 1913. This load, by reference to the table of connected populations, is found to have been in that year 7,050 people, or 750 people per acre. From the record of the Milford plant.
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it, therefore, appears reasonable to conclude that 750 people per acre may be accepted as the safe capacity of the present sand beds, or of any addition thereto constructed of the sa me material.
The present situation then is that the existing plant with capacity sufficient for 7,000 people is overloaded 42 per cent by a connected population of 9,990 people-making mainten- ance difficult and costly, and rendering it necessary to dis- charge substantial quantities of untreated sewage into the river.
Since 1917 the State Department of Health has yearly called attention to this overloaded condition of the dispos al works and without question-unless enlargement is immedi- ately undertaken-the town is facing the responsibility of seriously contaminating the river to the detriment of down- stream proprietors-including those communities which draw water from wells in the valley of the stream.
ENLARGEMENT OF THE DISPOSAL WORKS BY CONSTRUCTION OF ADDITIONAL SAND FILTERS.
. The present plant is of the type, which for many years has been accepted as the standard practice in Massachusetts - the essential features being sand filters and the intermittent application of the sewage after preliminary sedimentation. The high degree of purification possible, the simplicity of operation and the availability of suitable natural soils in this state are responsible for this quite general adoption of sand filters in the treatment of sewage. By this method, under favorable condition and proper control, a higher degree of purification can be effected than in any other practicable way. Also, where the sand can be used in natural position, the cost bas compared favorably with that of other available methods.
It is natural, therefore, in undertaking the enlargement of the present disposal works to assume that the project will simply involve the building of additional sand beds. The settling tanks of 300,0 00 gallons capacity are large enough to provide adequate sedimentation for some years to come. The distributing system, radiating in four lines, suggests at once
12[
the construction of four additional beds on the north, and another four on the south of the present field, in order to bal- ance the filter units in reference to the dosing tank. With the new filters made the same size as those now in use, the additional area thus provided will equal 4 82 acres, or suffi- cient for 3,600 people, at 750 people per acre. The sand, as shown by numerous test-pits (see plan and sections) is of the same character as in the present field, the samples varying from an effective size of .04 m. m. to .20 .n. m. and approxi- mately averaging .12 m. m. with a uniformity coefficient of 2.5. As a general statement the material is finer than is de- sirable, and 750 people per acre is probably as high a rate as can be justified. On this basis the eight additional beds to. gether with the present field will provide for 10,600 people, or 700 people in excess of the population now contributing sew- age. It is obvious that this is the minimum extension of the plant which can be considered.
The estimated cost of this increased area of sand filters is as follows :-
GENERAL WORK.
Clearing and grubbing
$150 00
Loaming and seeding embankments
300 00
Excavation and grading
27,600 00
$28,050 00
UNDERDRAINS.
Excavation
$2,750 00
Pipe and specials
1,110 00
Laying
.
.
5,179 00
Manholes
154 00
$9,193 00
DISTRIBUTING SYSTEM.
Excavation
$ 500 00
Pipes, gates, etc.
.
1,502 00
Laying
387 00
Gate chambers, outlet abutments,
etc.
663 00
Carriers
.
1,600 00
·
$4,652 00
122
DRAIN FOR BROOK CHANNEL.
Excavation
$ 800 00
Segmental· tile block drain (36 in.)
3,750 00
Masonry abutments
120 00
$4,670 00
Re-location of river
1,300 00
Total
$47,855 00 ·
Add 20 per cent for land, engineering and con-
tingencies
$9,573 00
Total
: $57,438 00
This total cost-equivalent to $15,700.00 per 1000 people is much higher than has obtained in similar work in the past. The explanation is found in the fact that topography is not favorable-involving heavy cutting in the northern line of beds and the building of the southern line almost entirely by filling with sand transferred from the northern area. The cost is also substantially increased because of the necessity of constructing a 36-inch drain to provide a water way for the brook.
No more economical layout appears to be possible for fil- ters constructed adjacent to the present plant at an elevation which will permit the application of sewage to the additional area by the present automatic dosing apparatus, or through an extension of the present distribution system. A saving of some $6,000.00 can be made, if the filter surfaces are placed at a higher elevation and the advantages incident to automatic intermittent dosing are disregarded, but this saving would be largely offset by the necessity of greater attendance in shift- ing gates by hand. Further an examination of the territory along the river has made evident that there is no site (be- tween the present plant and South Milford) where additional sand filters can be constructed more economically than adja- cent to the present plant. In other words, the construction of an additional line of beds on the north and south of the present plant, as already described, is apparently the cheapest
123
available method of providing increased disposal capacity-if sand filtration is to be used.
ENLARGEMENT BY CONSTRUCTION OF IMHOFF-TRICKLER PLANT.
The excessive cost per unit of capacity of additional sand filters, and the undesirable fineness of the sands available, has led to the consideration of the method of treatment in success- ful use at Fitchburg, Mass., Mansfield, Ohio, Columbus, Ohio, Baltimore, Md., and many other places. In these plants, in- stead of a fine filtering medium, such as sand, crushed stone ranging from 1 to 2 inches in size of particle is used, and the sewage, applied by spraying from nozzles, trickles through the filter and by the action of bacteria, lodged on the stone and working in an ample supply of air, is rendered non-putrescible although not purified to the degree possible with sand filters under favorable conditions. The economy of the method lies in the higher rates at which the tricklers are operated and which vary from 10 to 40 times the rates possible with sand filters. It is obvious that the relative economy in any particular case depends upon the rate adopted as feasible for the sand and the trickling filter.
Preliminary treatment to remove the heavier suspended matter from the sewage before application to the filter is nec- essary, and clarification of the trickler effluent by settling tanks is also generally desirable.
The plans and estimates, which have been prepared for this method of treatment, are based on provision for 5000 people, or at 75 gallons per capita, for a normal summer and autumn flow of 375,000 gallons per day.
The plant includes a two-story settling tank, dosing tank, a trickling filter, a settling tank for the filter effluent, and sludge beds. The location proposed is adjacent to the river at the northeastern corner of the present disposal field, and one-third mile distant from the highway to South Milford. The total area occupied is about 1} acres.
It is planned to lay a branch outfall of 15 inch vitrified pipe and 10 inch and 12 inch cast iron pipes to the new plant from a diversion chamber to be cut into the present main
I24
sewer. The 10 inch and 12 inch pipes will operate an invert- ed siphon and are used to avoid unnecessary embankment.
The settling tank is of the two-story or Imhoff type, the sewage flowing through the upper compartment'and the set- tled solids passing through a bottom slot into the digestion chamber below. One advantage of this two-story arrange- ment is that the sewage does not come in contact with the accumulated stale sludge, and the tank effluent is, therefore, fresher and less liable to create trouble by odors when sprayed from nozzles in its application to the filter. The effluent of the present settling tanks could not, in our judgment, be sprayed without serious danger of nuisance. Another advan- tage of the deep pyramidal-bottomed settling tank is the im- proved digestion of the sludge and better control of its dis- charge and drying on the sludge beds.
The tank, as planned, is 43 by 27 feet in horizontal di- mensions and 26 feet deep. The settling chamber will provide a 23 hours period of retention for a flow of 375,000 gallons per day, or 2 hours for a flow of 500,000 gallons per day. The sludge compartment is designed on the basis of 24 cubic feet per person for 5000 people, measuring from a point 18 inches below the level of slot. The horizontal free surface for the escape of gas is equal to 25 per cent of the total area of the tank. Provision is made for reversing the flow through the settling chamber and an 8-inch sludge pipe will make possi- ble the discharge of sludge under ample head ou the adjacent sludge beds, the elevation of the surface of which is 10.5 feet below high water in the Imhoff tank. Pipes for flushing the pyramidal bottom of the digestion chamber and the sludge outlet pipe with water under control are also provided.
The sludge beds have a depth of 12 inches of cinders and an area of 5,000 square feet, or one square foot per person for 5,000 people. This area and the volume of the digestion chamber has been made particularly liberal.
From the Imhoff tank the effluent flows to the dosing tanks, two in number, each of 1,750 gallons capacity, or suf- 1 ficient for 63 minutes flow at rate of 375,000 gallons per day,
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these tanks to discharge alternately through 14 inch, 10 inch and 6 inch cast iron pipes and 120 spray nozzles spaced on the filter, as shown on plan.
The trickling filter 28 acre in area, with a depth of 6 feet, is to be constructed of hard crushed stone screened be- tween 1 and 2} inches. The area proposed is based on pro- viding for 5,000 people at a rate of 3,000 people per acre per foot of depth, and in quantity is equivalent to a rate of 1,350,- 000 gallons per day per acre of average summer flow of sew. age at Milford.
The total difference in elevation between water level in the Imhoff tank and the average summer level in the river is 14 feet, and with due allowance for the necessary head in dosing the filter and in flowing through the tanks and con_ necting piping, the depth of six feet adopted for the trickling filter is the maximum possible, unless the sewage is to be ele- vated by pumping. By some expenditure the river channel can be cleaned out so as to lower the summer flow line ap- proximately one foot, but in our judgment, this expense can- not be justiffed at the present time.
The estimated cost of the Imhoff-trickler plant is as fol- lows :-
BRANCH OUTFALL SEWER :-
Excavation and embankment . . $ 390 00
Piping and laying · ·
1,129 00 ·
Diversion chamber and manholes
600 00
-$ 2,119 00
IMHOFF TANK :-
Excavation
. $3,375 00
Concrete masonry
8,062 00
Piping, valves, stop planks
.
625 00
Imhoff royalty .
250 00
12,312 00
DOSING TANK :-
Excavation
·
.
$ 15 00
Concrete masonry
700 00
·
.
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Dosing apparatus, etc. .
.
. $2,500 00
Miscellaneous .
·
.
25 00
$3,240 00
TRICKLING FILTER :-
Excavation
. $1,260 00
Concrete masonry walls
. 2,875 00 ·
Floor system . ·
. 4,230 00
Distributing system, nozzles
£ 3,750 00 .
Crushed stone .
. 11,200 00
23,315 00
SECONDARY TANK :-
Excavation . $1,000 00
Concrete masonry
1,300 00 .
Piping, valves, etc
2.0 00
Sludge and water pumps and piping .
1,500 00
4,050 00
SLUDGE BEDS :-
Excavation
$950 00
Filter material .
620 00
Underdrains
200 00
Concrete masonry
150 00
Stop plank, guides
100 00
2,020 00
Miscellaneous piping
629 00
General grading, seeding, walks, etc.
1,150 00
Total
$48,835 00
Add 15 per cent for land, engineering and con-
tingencies
7,325 25
Total
$56,160 25
.
.
.
.
The addition of 15 per cent to the summation of the de- tailed figures instead of 20 per cent, as in the case of sand filters, is due to the lesser area of land required for the trick. ler plant.
The preceding estimate of $56,160.00 for works designed
127
to provide for 5000 people is equivalent to $11,200.00 for 1000 people, which compares with $15,700.00 per 1000 people, esti- mated as the cost of additional sand filters. It, therefore, ap pears that the Imhoff trickler method of treatment can be pro- vided for approximately two-thirds the cost of additional sand filters under the conditions to be met at Milford, or, stated differently, an Imhoff-trickler plant to care for the sewage of 5000 people, or adequate for the probable disposal require- ments of eight years in the future can be constructed for $56,- 000.00, while sand filters to care for 3600 people, or sufficient for the requirements of only three years in the future, will cost $57,400.00.
The Imhoff-trickler method of treatment should also prove substantially cheaper in maintenance. The average cost per capita of connected populations at Fitchburg and Brock- ton for the past five years have been less than two-thirds of the corresponding figures at Milford for sand filters.
As has already been stated, the degree of purification pos- sible by trickling filters is materially less than that obtaina- ble by sand filters under favorable conditions. In actual practice, however, as indicated by comparison of plants of the two types in Massachusetts, the difference is not so outstand- ing, and it is of interest to note that while the average reduc- tion of free ammonia by 24 sand filter plants for the five years from 1915 to 1919 was 67 per cent-the corresponding figures for the trickling filter plants at Fitchburg and Brockton was 70 per cent. Again making comparison on the basis of albu- minoid ammonia, the trickling filters removed 77 per cent as compared with 87 per cent for the sand filters. The practical question, however, in the problem under discussion is whether Imhoff-trickler treatment will produce an effluent sufficiently purified to permit its discharge into the river without detri- ment to the interests of downstream proprietors, or, better stated, whether the Imhoff-trickler plant, as planned, will prove a better all-round instrument for the protection of the river than such additional area of extremely fine sand filters, as the town at the present time can afford to construct.
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In our judgment, the relatively unfavorable conditions for further extension of sand filtration and the substantially low- er cost, both in construction and maintenance, of trickling filters points to the advisability of adopting this latter method in the necessary enlargement of the disposal works.
We therefore recommend that you request the approval of the State Department of Health of the plans, herewith sub- mitted, for an Imhoff-trickler plant.
The improvement of the present works carriedout dur- ing the past year included the relaying of a considerable part of the underdrain system, the building of new outlet weirs in' the settling tanks, so as to increase the effective storage capa- city, and the refilling of the sludge bed to the original eleva- tion. The replacement by some permanent construction of the wooden carriers, which served to distribute the sewage over the sand beds for ten years and then rotted to the point necessitating removal, remains to be done. The estimated cost of this necessary work is $3,000.
We, therefore, recommend that you request the town to appropriate the sum of $60,000.00 for the enlargement of the disposal plant, and the construction of carriers in the present beds, and that steps be taken to obtain whatever legislation is required to make this appropriation possible.
Respectfully submitted,
F. A. BARBOUR.
1
REPORT OF THE CHAIRMAN OF THE BOARD OF Trustees of Milford Town Library.
The outstanding features of the fiscal year just ended were :
The unexplained increase in circulation, especially in the departments of the lighter fiction and the juveniles. This increase almost imperceptible in the earlier months of the year made itself more noticeable during the Spring season and reached its height about the middle of November.
The exorbitant, almost prohibitive, prices demanded for standard and current fiction and the consequent limitation of our program of expansion as originally mapped out.
The imperative need for immediate replacement of a large number of the more popular of the juveniles, which have been in constant demand and which, although rebound time and again, seem never to lose their popularity with the young folk who daily swarm our reading room.
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