§ A168-12. Drainage., Chapter A168. Street Specifications, Appendix, Code of Ordinances, Warwick, Town

The drainage system and/or culverts shall be designed in accordance with established engineering principles and approved by the Town Engineer. A design condition of a twenty-four-hour storm having a return frequency of 10 years shall be used. Plans for any drainage structure other than pipe culverts, when existing or proposed, shall be submitted in detail to the Commissioner of Public Works for approval. The minimum grade of any drainage pipe or culvert shall not be less than 1%. The approved plans shall show invert elevations of the inlet and outlet of all drainage structures. Any deviation from the approved plans shall be on approval of the Town Commissioner of Public Works or Town Engineer, in writing. No culvert pipe shall be less than 15 inches in diameter unless by approval of the Town Commissioner of Public Works and Town Engineer. Pipe for culverts may be reinforced concrete, which shall conform to the attached specifications for materials, or HDPE pipe, which shall be in accordance with the New York State DOT Specifications.

The width of the trench in which the pipe is laid shall be sufficient to permit thorough tamping of the backfill around the pipe. A cushion of select granular fill at least six inches shall be laid in line with grade prior to laying the pipe. No rock over three inches in thickness shall protrude or lie in this cushion. The soil below the cushion shall be stable enough that there will be no settlement of pipe after backfilling the trench. All pipe bedding and backfill shall conform with the subsections listed below, as excerpted from § 203-2.02C, 203-3.15 and 603-3.03 of the New York State Department of Transportation Standard Specifications for Construction and Materials, 2002, revised 2004. [Note: Dimensions have been converted from metric to imperial units for this specification.]

(1)

Select granular fill. Materials furnished under these items shall be suitable, well graded, and conform to the following requirements:

(a)

Gradation. Except when used as backfill material for plastic pipe, the material shall have the following gradation. When used as backfill for plastic pipe, 100% of the material shall pass the 19 mm sieve.

	Sieve Size	Percent Passing by Weight
	4 inches	100
	No. 40	0 to 70
	No. 200	0 to 15

(b)

Soundness. The materials shall be substantially free of shale and soft, poor-durability particles. A material with magnesium sulfate soundness loss exceeding 30% will be rejected.

(c)

Composition. Reclaimed asphalt pavement (RAP) shall not be used.

(d)

pH. Where the Town elects to test for this requirement, a material with pH of less than five or more than 10 shall be rejected.

(2)

Fill and backfill at structures, culverts, pipes, conduits and direct burial cables.

(a)

The type of material to be used in bedding, filling and backfill at structures, culverts, pipes, conduit and direct burial cable and payment lines therefor shall be in conformance with the details shown on the appropriate NYSDOT Standard Sheet or as noted on the plans or as ordered by the engineer. Do not use RAP. Do not use slabs or pieces or either concrete or asphalt.

(b)

Fill or backfill material at structures, culverts and pipes shall be deposited in horizontal layers not exceeding six inches in thickness prior to compaction. A minimum compaction of 90% modified proctor maximum density will be required. When placing fill or backfill around culverts and pipes, layers shall be deposited to progressively bury the pipe or culvert to equal depths on both sides. When filling behind abutments and similar structures, all material shall be placed and compacted in front of the walls prior to placing fill behind the walls to a higher elevation. The limits to which this subsection will apply shall be in accordance with the plans approved by the Town Engineer.

(c)

Fill or backfill for conduit or cable placed in a trench shall be carefully placed in a horizontal layer to a depth of six inches over the top of the conduit or cable. This layer of material shall not be compacted; however, the remaining portion of the trench shall be backfilled in accordance with the preceding Subsection B(2)(b). Where cables or conduits are placed and backfilled by a machine in one operation, the above requirements for backfilling do not apply.

(d)

Where sheeting has been used for the excavation, and incremental removal of sheeting is not specified in the plans or proposal, sheeting shall be pulled when the trench has been backfilled to the maximum unsupported trench depth of three feet.

(3)

Bedding and backfilling pipe. Apply the standards of Subsection B(2), Fill and backfill at structures, culverts, pipes, conduits and direct burial cables and the approved project plans.

The pipe shall be laid to true line and grade on the prepared bed of the trench. Backfilling of the trench shall be done with select granular fill or other suitable material approved by the Town Commissioner of Public Works and Town Engineer. The backfill shall be made in layers of no more than 12 inches, which shall be compacted as specified in § A168-10. In no case shall the top of any drainage pipe be less than 12 inches below the finished grade of pavement.

All drainage structures shall be of a size sufficient to carry natural water runoff and stormwater and also that which, in the opinion of the Town Commissioner of Public Works and Town Engineer, may be reasonably anticipated from future construction, both from within the development and from adjoining properties which normally drain across the area of the proposed development. Any additional drainage facilities not shown on the approved plan and which may be ordered by the Commissioner of Public Works shall be constructed by the developer at the developer's expense and in accordance with these specifications.