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LARCHMONT

sewers. .

LINSLY R. WILLIAMS, M.D., Acting State Commissioner of Hcalth:

I beg to submit the following report on our examination of plans for the interception and disposal of the sewage of the village of Larchmont, Westchester county, recently submitted to this Department for approval by the board of trustees.

Plans for the disposal of sewage for the more developed portions of the village were first submitted for approval on October 1, 1915, in compliance with the conditions of a permit previously issued to the village in connection with the approval of plans for the discharge of sewage from proposed

This permit required in general that plans for the interception and disposal of the entire sanitary sewage should be submitted to this Department for approval within a certain specified time. The plans first submitted, however, did not include plans for the interception and treatment of the sewage from the whole village although the report of the consulting engineers who prepared the plans for the disposal works outlined in a general way a proposed method of intercepting and disposing of the entire sewage of the village. The village authorities were, therefore, advised that the requirements of the permit referred to had not been fully complied with inasmuch as no plans had been submitted showing the proposed method of caring for the sewage of the entire village. After a number of conferences and considerable correspondence with representatives of the village a general plan showing the location of existing sewers and a general scheme for the collection, interception and disposal of the entire sewage of the village was submitted on January 11, 1917.

According to these plans and the engineering reports submitted with them, the village is divided by a ridge which runs in a northerly and southerly direction through the village. The general slope of the ground is toward Larchmont harbor on the east, toward Pine brook and Premium creek on the west and toward Long Island sound on the south. The topography and conditions of the village appear to be such that it is not practicable to collect and convey the sewage of the entire village to one suitable point for disposal by gravity flow. A general plan submitted shows the area of the village divided into 7 drainage areas, designated as districts Nos. 1, 2, 3, 4, 5A, 5B and 5C.

District no. I

This district comprises a fairly large area in the northeastern section of the village east of Larchmont avenue and north of Cherry street. This area is at present provided with a separate sewer system which discharges into Larchmont harbor through a 20-inch sewer at a point about 700 feet from shore, where the water is about 3.5 feet deep at low tide. According to the report of the consulting engineers the tide backs up in this outfall sewer as far as Cherry avenue, and possibly as far as Larchmont avenue, at times of extreme high tide. This outfall sewer also receives the sewage from a portion of Larchmont park in district No. 5A, which sewage is pumped from a small pumping station located near the lower end of Lincoln

avenue.

It is proposed to treat the sewage from district No. 1 and probably from district No. 5A in a sewage disposal plant consisting of an Imhoff tank to be located along the line of the outfall sewer in Bonnet avenue, about 700 feet north of Cherry creek.

In order to make the sewage from the portion of district No. 1 in Cherry street and south of Cherry street, as well as from district No. 5A tributary to this disposal plant, it will be necessary to reconstruct the sewer in Monroe avenue, Cherry avenue and a portion of Bonnet avenue. The location and alignment of the proposed sewers in these streets are shown in general by the plans. Detailed plans for these sewers should, however, be submitted before the disposal works are constructed.

District no. 2

This district is a small area situated south of District No. 1. The sewage from this district at present discharges into Larchmont Harbor through a ten-inch sewer at a point about 200 feet from shore. The report on the disposal of sewage of the village states that there are at present 30 connections with the sewers in this district and that although these sewers were originally built on the separate plan storm water connections have been made with them. It is proposed to treat the sewage from this district in a small screen chamber to be located near the foot of Woodbine avenue.

District no. 3

This district comprises a relatively small area in the southern part of the village west of District No. 2. The sewage from District No. 3 is at present discharged into Larchmont Harbor through a 10-inch sewer at a point about 200 feet from the shore. There are about 80 connections to the sewer system in this district which includes a number of summer hotels so that there is considerable fluctuation in the number of people served by this system. It is proposed to treat the sewage from this district as well as from District No. 4 located west of District No. 3, in a sewage disposal plant consisting of an Imhoff tank designated on the plans as the Village Park Plant.

District no. 4

This district as noted above is situated west of District No. 3 and extends from Willow avenue, on the north to Long Island Sound on the south. The sewage from this district discharges into Long Island Sound at a point about 200 feet from the shore west of Horseshoe Harbor. There are about 75 connections to the sewer system in this district. According to the plans and report of the consulting engineers the greater portion of the sewage from this district is to be intercepted by a sewer in Park avenue, extending from Grove strect, to Circle avenue, a distance of about 950 feet. The details of this sewer are not shown, however.

District no. 5a

This district comprises a comparatively large area in the northwestern part of the village extending both north and south of the Boston Post road and east and west of Pine brook. Although this district is sparsely populated at present it is estimated by the consulting engineers that the ultimate population tributary to the sewers in this area will probably exceed 5,000.

The sewage from the so-called Larchmont Park section of this district is at present conveyed to a small pumping station located near the lower end of Larchmont avenue, from which the sewage is pumped over the ridge into District No. 1. This pumping station consists of a covered concrete collecting well and a covered pump chamber and is equipped with a small centrifugal pump, belt driven froni a hand operated electric motor. Although the report of the consulting engineers proposes two alternate schemes for the collection of the sewage in District 5A involving the remodeling of the existing pumping station and the construction of one or two additional pumping stations, it is recommended that the existing pumping station be abandoned inasmuch as it is obsolete and inadequate and would have to be entirely reconstructed to make it efficient and that a 15-inch intercepting sewer be constructed from a point near the pumping station extending southerly to a proposed pumping station to be located near the lower end of Oak avenue, to care for the sewage from the northerly portion of District No. 5A east of Pine brook. The location of the proposed sewer is shown by the general plans. The plans also provide for a 10-inch sewer extending northerly from Helena avenue, to the proposed pumping station near Oak avenue, to care for the southerly portion of this district. A sewer in Boston Post road and in Oak avenue, connecting with the proposed pumping station near Vak avenue, is also proposed to care for the sewage of District No. 5A north and west of Pine brook. Details of these sewers are not shown, however, nor are there any details shown of the pumping station.

The report of the consulting engineers recommended, however, that the proposed pumping station be equipped with two centrifugal pumps driven by automatically operated electric motors and that an auxiliary gas engine to be used in case of emergency be provided. It is proposed according to the report and plans to pump the sewage from the pumping station through a force main laid through private property and in Willow avenue, to Prospect avenue, from which point the sewage will flow by gravity to the Bonnet avenue sewage disposal works. The report of the consulting engineers also recommends that whenever the cost of pumping the sewage becomes greater than the cost of operation of the pumping station plus the interest on the cost of construction of a sewage disposal plant for this section that a disposal plant consisting of settling tanks, sprinkling filters and final settling tanks be constructed in the low area near the Oak avenue pumping station in which case this pumping station would be used to lift the sewage into the proposed disposal plant.

District no. 5b This district consists of a very small area on either side of the northerly portion of Pryer Lane. The plans show that it is proposed to care for this sewage in the future by the construction of a sewer in Helena avenue, and Pryer lane tributary to the existing sewers in District No. 4. The plans do not show details of the proposed sewer.

District no. 5C

This district comprises a small area located in the southwestern corner of the village. The plans provide for the future treatment of the sewage from this district in a small screen plant from which the effluent will be discharged into Long Island Sound. No details of the sewer and screen chamber are shown.

avenue.

Bonnet avenue sewage disposal plant The proposed sewage disposal plant in Bonnet avenue which is to serve District No. 1 and District 5A is to consist of a covered settling tank 24 feet in diameter, 3242 feet deep with a maximum depth between the flow line of 2244 feet. It is planned to locate this tank under the street in Bonnet

It is designed to care for a population of 2,000. The plans also provide for an additional tank having the same capacity to be located under the street of Bonnet avenue, adjacent to the proposed tank.

The proposed settling tank has a settling capacity of about 19,000 gallons and will, therefore, provide for a detention period of about 214 hours when serving a population of 2,000 assuming a per capita rate of sewage contribution of 100 gallons a day. The sludge compartment has a capacity of about 2,800 cubic feet equal to about 1/4 cubic feet per person served.

Although the proposed settling tank if properly constructed and properly maintained should provide for a satisfactory preliminary treatment of the sewage there are certain features which should be modified. In the first place the tank should not be located in the street. It would appear that this could be obviated by changing slightly the location of Bonnet avenue, opposite the disposal plant. I am also of the opinion that there would be danger of explosion from gases generated in the tank if covered as proposed unless proper means be taken to ventilate the tank by forced draught. It would appear that if for any reason this cannot be done the concrete cover should be omitted and the tank covered by a small building.

Village park plant This plant which is to care for the sewage from Districts Nos. 3, 4 and 5B is similar to the Bonnet avenue plant and is designed to serve a population of 2,000. As in the case of the Bonnet avenue plant provision should be made for properly ventilating the tank by forced draught or for leaving it open and covering it with a small building.

Woodbine avenue plant The plant consists of a screen chamber, 6 feet long, 312 feet wide by 6 feet deep inside dimensions. The screen chamber is to be provided with an inclined bar screen composed of 2-inch by 3/8-inch bars placed 1 inch apart in the clear. The screen chamber is to be located near Larchmont Harbor on the line of the existing outfall sewer and the screened effluent is to be discharged into the Harbor through the present outlet.

Conclusions and recommendations

From our careful examination of the plans, it is found that provisions have been made for the preliminary treatment of the sewage from the more thickly developed portions of the village and for the future collection and interception and treatment of the entire sanitary sewage of the village. Although the disposal plants to be constructed at first are shown in detail the scheme for the future collection and interception of the sewage in the more sparsely settled section of the village is shown only in general by the plans and it is, therefore, impracticable to finally pass upon the adequacy of the proposed intercepting sewers before detailed plans are submitted. Before the proposed disposal works are constructed the detailed plans for intercepting sewers and pumping station shown in general by the present plans should, therefore, be submitted.

It appears also that although the preliminary treatment provided for by the plans should produce an effluent that might be discharged into Larchmont Harbor and Long Island Sound without objection at present it might be necessary at some time in the future when the village becomes more fully developed to provide for a more complete treatment of the sewage than that contemplated by the present plans and consideration should, therefore, be given by the village authorities to the possible necessity in the future of intercepting the effluent from the proposed sewage disposal plants and conveying it to a suitable site for more complete treatment.

I would, therefore, recommend that the plans be approved and a permit be issued allowing the discharge of effluent from the proposed sewage disposal plants into Larchmont Harbor and Long Island Sound and that the permit contain in addition to the usual revocation and modification clauses the following conditions:

1. That the Bonnet avenue works be located outside of the street or that the location of the portion of the street near the plant be changed and that plans for such modifications be submitted before this disposal plant is constructed.

2. That before the Bonnet avenue plant is constructed plans for the sewers in Willow avenue, Monroe avenue, Cherry avenue and Bonnet avenue, so designed as to permit of conveying the sewage from District 5A and from the Cherry avenue section to the Bonnet avenue disposal plant be submitted for approval.

3. That before the Village Park Plant is constructed detailed plans for the intercepting sewer in Park avenue, for the interception of the sewage in District No. 4 be submitted for approval.

4. That provisions be made for ventilating the proposed Imhoff tanks by forced draft or that the concrete covers be omitted and the tanks covered with suitably ventilated buildings and that plans for such changes be submitted for approval before the tanks are constructed.

5. That whenever required detailed plans for the intercepting sewers and for the proposed pumping station in District 5A be submitted for approval.

6. That detailed plans of the proposed sewer and screen chamber in District 5C be submitted before the construction of the sewer and screen chamber.

7. That whenever required, plans for the interception and more complete treatment of the effluent from the proposed sewage disposal plants at a suitable point be submitted to this Department for approval.

Respectfully submitted,
THEODORE HORTON,

Chief Engineer ALBANY, N. Y., February 14, 1917

Law »

PERMIT Application having been duly made to the State Commissioner of Health, as provided by section 77 of chapter 49 of the Laws of 1909, the “Public Health

as amended by chapter 553 of the Laws of 1911, constituting chapter 45 of the Consolidated Laws, permission is hereby given to the Board of Trustees of the village of Larchmont to discharge effluent from the proposed sewage disposal plants into the waters of Larchmont Harbor and Long Island Sound at the points indicated by the plans within the municipality of Larchmont in accordance with the plans accompanying the petition, under the following conditions:

1. That this permit shall be revocable at any time or subject to modification or change when in the judgment of the State Commissioner of Health such revocation, modification or change shall become necessary.

2. That the issuance of this permit shall not be deemed to affect in any way action by this Department on any future application that may be made for permission to discharge additional sewage or effluent into the waters of this State.

3. That both the sewer system and sewage disposal works shown by the plans approved this day shall be fully constructed in complete conformity with such plans or approved amendments thereof as herein provided.

4. That only sanitary or domestic sewage and no storm water or surface water from streets, roofs or other areas shall be admitted to the proposed sewers or sewage disposal works.

5. That no sewage sludge from any part of the disposal works shall be discharged into Larchmont Harbor, Long Island Sound or any other watercourse or body of water.

6. That the Bonnet avenue works shall not be built within the street lines or that the location of the portion of the street near the plant be changed; and that plans for such modifications shall be submitted before such works are constructed.

7. That, before the Bonnet avenue works are constructed plans for sewers in Willow avenue, Monroe avenue, Cherry avenue and Bonnet avenue, so designed as to permit of conveying the sewage from District 5A and from the Cherry avenue section to such works, shall be submitted for approval.

8. That before the village park works are constructed detailed plans for an intercepting sewer in Park avenue to intercept the sewage in District No. 4 shall be submitted for approval.

9. That provision shall be made for ventilating the proposed Imhoff tanks by forced draft or that the concrete covers shall be omitted and the tanks covered with suitable ventilated buildings; and that before these tanks are constructed detailed plans for such changes shall be submitted for approval.

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