Chapter 19.40
SEWER SYSTEM
Sections:
19.40.010 Introduction and applicability.
19.40.010 Introduction and applicability.
A. The items herein contained are the sewer system standards, conditions, and specifications of the town of Waterville, and are to be considered in conjunction with other provisions of town plans and/or regulations governing the public sewer system. These are minimums only and may be increased or altered to fit particular site conditions and/or situations. The town by this reference adopts the latest edition of the “Standard Specifications for Road, Bridge and Municipal Construction” (hereinafter referred to as the “standard specifications”) as prepared by the Washington State Department of Transportation and the Washington State Chapter of the American Public Works Association to govern all aspects of sanitary sewer system improvements including but not limited to materials, labor, equipment for installation, workmanship, testing, etc. Any material, design, standard, or testing not specifically addressed within this document shall be as per the standard specifications. The town also by this reference adopts the latest version of the “standard plans” (engineering drawings hereinafter referred to as the “standard plans”) published by the Washington State Department of Transportation.
B. In addition to the specific standards set forth in this chapter, the town may develop a technical specifications guidebook containing drawings that graphically depict the provisions of this chapter and the standard specifications. This guidebook may also specify where the town may choose to add to, remove from, and/or replace (in whole or in part) certain aspects of the standard specifications and standard plans adopted by reference herein. The guidebook is a technical reference document that may be updated periodically based on changes in engineering standards, whether those be town standards or updated standards in the design and construction documents that are adopted by reference in this chapter.
C. These standards and specifications shall apply to any work that is done to the town’s sewer system, whether required as a condition of development permit approval or as a result of an individual request for sewer extension. (Ord. 612 § 2, 2001).
19.40.020 Design standards.
The design and construction of sanitary sewer system improvements shall be dependent on local site conditions, and shall conform to the following minimum standards:
A. General Requirements.
1. The design and construction of extensions of the sanitary sewer system shall be consistent with the town’s approved comprehensive plans and all other applicable state, county and local agency standard regulations, including without limitation the Washington State Department of Ecology’s publication “Criteria for Sewage Works Design,” December 1998 Edition (hereinafter referred to as “DOE standards”). Obtaining necessary permits issued by an agency or authority other than the town shall be the responsibility of the developer.
2. If future extension of the system is deemed probable by the town, the proposed system shall be designed and sized to service tributary areas and future customers. Easements shall be provided to facilitate the same. Sewer lines shall be extended to the boundaries of the property being served, providing access for future service to adjacent properties. Sewer lines shall be designed and constructed for the ultimate development of the service areas and as may be further established in the town’s water comprehensive plan.
3. Whenever sewer lines are located outside of public streets or alleys, the easement shall be of sufficient width to allow for future replacement of the facility without damage to permanent adjacent improvements. In general, if the sewer line is located in the center of an easement, the easement shall be a minimum width of 15 feet. Special circumstances may require additional widths as determined by the town.
4. Detailed plans shall be submitted for the town’s review and approval that provide the location, size, type and direction of flow of the proposed sewers and the connection with existing sewers. Horizontal locations and elevation information shall be to a datum acceptable to the town. Computations and other data used for the design of the sewer system improvements shall be submitted to the town for approval.
5. Construction of new sewer systems or extension of existing systems will be allowed only if the existing and downstream receiving systems are capable of supporting the added hydraulic load.
6. Sewer facilities, including collection and interceptor sewers, shall be designed and constructed for the ultimate development of the tributary areas and as may be further established in the town’s sewer comprehensive plan. The location and size of oversized sewer lines shall be designated by the town engineer. Sewer facilities shall also be designed and installed to achieve total containment of sanitary wastes and maximum exclusion of infiltration and inflow. Sewers installed below water table shall require special design and inspections.
7. All materials shall be new and undamaged, and the same manufacturer of each item shall be used throughout the work. Material and installation specifications shall contain appropriate requirements that have been established by the industry in its technical publications, such as ASTM, WSDOT, WEF and APWA standards. Requirements shall be set forth in the specifications for the pipe and methods of bedding and backfilling so as not to damage the pipe or its joints, impede cleaning operations and future tapping, nor create excessive side fill pressure or deformation of the pipe, nor seriously impair flow capacity.
8. All sewers shall be designed to prevent damage from superimposed loads. Proper allowance for loads on the sewer main due to the width and depth of the trench should be made. When standard-strength sewer pipe is not sufficient, extra-strength pipe shall be used, as determined by the town.
9. All pipe shall be laid in straight lines and at uniform rate of grade between manholes. Variance from town-approved established line and grade shall not be greater than one-half inch; provided, that such variation does not result in a level or reverse sloping invert; provided also, that variation in the invert elevation between adjoining ends of pipe, due to non-concentricity of joining surface and pipe interior surfaces, does not exceed one-sixty-fourth-inch per inch of pipe diameter, or one-half inch maximum. Any corrections required in line and grade shall be reviewed with the town and shall be made at the expense of the developer.
10. Deflection tests shall be performed on all PVC sewer mains and the deflection test limit shall be five percent of the base inside diameter of the pipe.
11. Prior to final inspection, all pipelines shall be tested, flushed and cleaned and all debris removed and disposed of at a location approved by the town. A pipeline “cleaning ball” of the proper diameter for each size of pipe shall be flushed through all pipelines prior to final inspection. Hydrant meters shall be acquired from the town and utilized by the contractor for all water withdrawn from the town’s system for flushing, construction, cleaning and testing purposes.
12. Before sewer lines are accepted, the developer shall perform a complete televised inspection of the sewer pipe and appurtenances and shall provide the town an audio-visual tape recording of these inspections. All equipment and materials shall be compatible with existing town equipment and it shall be the developer’s responsibility to confirm equipment compatibility with the town prior to inspection. At all times during the televised inspection process, the public works superintendent shall be present.
13. After all other work is completed and before final acceptance, the entire roadway, including, without limitation, the roadbed, planting, sidewalk areas, shoulders, driveways, alley and side street approaches, slopes, ditches, utility trenches and construction areas shall be neatly finished to the lines, grades and cross-sections for a new street consistent with the provisions of this title and the original street section.
14. Sanitary sewer extension projects shall be conveyed to the town for operation and maintenance upon final project acceptance.
B. Design Elements.
1. Sewer pipelines shall be laid only in dedicated streets, alleys or easements which have been, or will be prior to final acceptance, exclusively granted to the town.
2. The minimum size sewer main permitted shall be eight-inch diameter.
3. The sewer pipelines shall be located such that a minimum of 10-foot horizontal separation from proposed or existing parallel water pipelines is maintained at all times.
4. PVC pipe shall be a minimum Class SDR 35 and be manufactured in accordance with ASTM D3034. Class 52 ductile iron pipe is required for force mains.
5. The allowable cover (finished grade) for PVC pipe shall be no less than four feet nor more than 25 feet, as approved by the town engineer. The town reserves the right to require a minimum of four feet of cover unless topography, existing facilities or other future improvements prohibit this minimum cover for installation.
6. Sewer lines shall be designed such that the invert elevation of the side sewer stub at the property line is four feet below the lowest expected floor elevation of the structure to be served. The invert elevation of the side sewer stub shall be calculated based on the invert elevation of the lateral sewer at the side sewer connection plus the rise of the side sewer to the property line based on its length and a minimum slope of 0.02 feet/foot plus 1.0 feet. Where the service elevation is critical, the design elevation of the side sewer stub shall be shown on the construction plan.
7. All side sewers shall be constructed with a “wye” or tap, and shall be extended a minimum of five feet past the street right-of-way line (or property line). Extended side sewers on easements shall be avoided wherever possible.
8. Minimum slope shall be maintained unless specifically waived by the town engineer. All mains shall be designed to have a minimum scouring velocity of two feet per second. Minimum slope on all sewer pipe shall comply with the DOE Standards except for the following:
a. Six-inch side sewer laterals shall be two percent;
b. Eight-inch gravity mains shall be 0.5 percent;
c. Ten-inch gravity mains shall be 0.4 percent;
d. Twelve-inch gravity mains shall be 0.3 percent.
9. Wherever possible sewer lines shall be terminated in a manhole. Should design considerations indicate a future manhole located beyond the current sewer termination, a temporary lamp hole may be used to terminate the sewer, provided the distance to the downstream manhole is 200 feet or less.
10. All sewer manholes shall be located at street centerline or six feet left or right of street centerline. The maximum distance between manholes shall be 400 feet unless specifically approved otherwise by the town.
11. Connection of side sewers to manholes shall be avoided if possible. If side sewers must be connected to a terminating manhole, such as in a cul-de-sac, no more than two side sewer connections will be allowed and shall enter at apron elevation.
12. Where the combined slope of the sewer line entering or existing a manhole is less than 0.05 feet per foot, a drop of 0.1 foot shall be provided between the invert of the entering and exiting sewer pipes.
13. All sewer pipe invert elevations at manholes shall be computed to the center of the manhole.
C. General Construction Practices.
1. Except as otherwise noted herein, all work, including without limitation, materials, installations and testing, shall be accomplished as recommended in the current standard specifications, DOE standards and according to the recommendations of the manufacturer of the material or equipment used. The contractor shall have a copy of the specifications on the job site at all times. The system shall not be placed into service until the town provides written permission.
2. Each side sewer lateral shall have an approved watertight cap at the termination of the stub, and it shall be adequately “blocked” to satisfactorily resist the air pressure testing.
3. All side sewer laterals shall be of the same material as the main line and shall be provided with a six-inch by six-inch clean-out, sweep tee with an approved watertight cap located on private property to be utilized as a clean-out. A watertight six-inch capped stub shall be installed which extends vertically form the six-inch by six-inch tee to within 18 inches of finished grade.
4. Front lot corners shall be staked prior to construction for side sewer tee locations.
5. Each side sewer lateral shall have a treated two-inch by four-inch wood marker at the termination of the stub. The marker shall extend from the bottom of the trench to 24 inches above finished grade. Above the ground surface, it shall be painted white with “S/S” and the depth, in feet, stenciled in black letters two inches high.
6. Side sewer connections, if allowed directly into manholes, shall be constructed to match the sewer main crown (outlet) and the manhole channeled accordingly.
7. Manholes, where sewer extension may occur as determined by the town, shall be provided with knock-outs and channeled accordingly.
8. Locking lids shall be provided for all manholes located outside pavement areas, and all manhole lids shall have the word “sewer” cast integrally onto its surface.
9. Concrete collars shall be placed around all manhole frames.
10. Pipe connection to manholes shall be as follows:
a. PVC pipe: cast or grout a watertight manhole coupling into manhole wall.
b. PVC optional: core the manhole and connect sewer pipe with a watertight flexible rubber boot in manhole wall, Kor-N-Seal boot or equal. Special approval by the public works superintendent is required if this option is used.
11. Trenches shall be excavated to the line and depth designated by the approved plans and shall be excavated only to such widths as are necessary for adequate and safe working space. No manned trench width less than 30 inches will be allowed. The trench shall be kept free from water until complete. Surface water shall be diverted so as not to enter the trench. The developer shall maintain sufficient pumping equipment on the job to insure that these provisions are carried out.
12. The developer shall perform all excavation. Where material is removed from below subgrade, the trench shall be backfilled to grade with material satisfactory to the town. Unsuitable material below the depth of the proposed pipe shall be removed and replaced with satisfactory materials as determined by the town. The developer shall be responsible for meeting current Labor and Industry Trench and Shoring Protection and Washington State Safety Standards.
13. When trenching operations cut through asphalt/concrete pavement, the pavement shall be removed to a solid edge along the width of the trench as approved by the town engineer. The pavement shall be sawcut on a straight line and shall be beveled so that the cut will be approximately one inch wider at the top than at the bottom.
14. Trenching operations shall not proceed more than 200 feet in advance of pipe laying without written approval of the town.
15. Special treatment may be required at the discretion of the town for pipe laid in filled areas. This treatment may consist of compacting the backfill in six-inch layers, use of select backfill materials, use of mechanical joint ductile iron pipe in short lengths, welded HDPE pipe, or such other reasonable methods or combinations as may be necessary in the opinion of the town based upon topography, soil type and any other unique characteristics of the area.
16. Pipe shall be placed on a prepared subgrade of stable bedding material consisting of clean, granular, unfractured material. Bell holes shall be excavated so the pipe, when laid, will have a uniform bearing under the full length of the pipe. The developer shall be responsible for adequate support and bedding for the pipe. The trench shall be backfilled and compacted to no less than 95 percent of the maximum theoretical density.
17. Whenever the trench is excavated below the depth required for proper bedding, it shall be backfilled with bedding gravel and compacted, as provided above.
18. Backfilling and surface restoration shall closely follow installation and testing of pipe, so that not more than 200 feet of pipe is left exposed without express approval of the town. The backfill shall be compacted to current WSDOT standards. Where other agencies have jurisdiction over roadways, the backfill and compaction shall be done to the standard of the agency having jurisdiction.
19. Pipe trenches shall not be backfilled until the pipe and bedding installation has been inspected and approved by the town.
20. Manhole rim and invert elevations shall be field verified after construction by the developer’s engineer and the “as-built” drawings individually stamped attesting to the fact that the information is correct.
21. Final air testing shall not be accepted until after the asphalt treated base or finished paving is accomplished, all other underground utilities have been installed, and the lines have been satisfactorily flushed, cleaned deflection tested and television inspected.
22. Any material, design, standard or testing not specifically addressed within these standards shall be as per the current edition of the standard specifications and the DOE standards.
23. The developer shall give town customers whose service may be disrupted no less than 24 hours’ notice prior to the interruption. (Ord. 612 § 2, 2001).
19.40.030 Plans and profiles.
A plan and profile of the proposed sanitary sewer system improvements showing the following data shall be submitted to the town for approval prior to any final development approval and construction. The plan shall be prepared and designed by a civil engineer currently licensed to practice in the state of Washington and shall contain the engineer’s stamp and signature certifying the design. It shall be submitted on a sheet size of 24 inches by 36 inches, and shall be drawn at a scale of one inch equals 50 feet. A one and one-half-inch margin shall be provided on the left edge, and a one-half-inch margin shall be provided on the other edges of the map. All maps shall be drawn on mylar sheets.
A. Plan. The plan shall contain the following information:
1. Show the locations of existing streets, rights-of-way, adjacent property lines, easements, utilities, driveways and water mains;
2. Show all proposed rights-of-way, easements and or proposed property lines;
3. Site topography shall be shown at a minimum of five-foot intervals, to include a minimum of 20-foot intervals within adjacent areas;
4. Show a vicinity and site location map;
5. Include all known existing structures, both above and below ground, that might interfere with the proposed construction, particularly sewer lines, gas mains, storm drains overhead and underground power lines, telephone lines and television cables;
6. Show station and offset to each manhole. Number each manhole consecutively in the new sewer system preceded by the initials of the development. Begin at the connection to the existing system and proceed upstream. Branch lines shall use the subnumber of the manhole from which they branch. For example a line branching from manhole SR4 would have the first manhole on the line numbered SR4-1. All manholes shall be numbered on the plans and correspondingly numbered on the profile;
7. Show the size, material and length of each sewer line between manholes;
8. Show the location of all side sewer stubs and the invert elevation at the end of the stub if critical to the service of the parcel. Where there is any question of the sewer being sufficiently deep to serve any residence, the developer shall indicate building and basement floor elevation in the profile;
9. Show details as necessary to direct the contractor in making connections to the existing system and to protect existing facilities during construction of the new sewers. Details shall be to scale drawings, which clearly show special sewer joints, connections, cross-sections, sewer appurtenances such as manholes and related items, and all other items as required by the town to clearly identify construction items, materials and/or methods.
B. Profile. A separate drawing showing the vertical profile of the proposed water system is required. The scale of these drawings shall be one inch equals 50 feet horizontal and one inch equals five feet vertical with horizontal grid of 50 feet and vertical grid of five feet.
1. For each manhole, show the ground elevation, invert elevation of all sewers entering or leaving the manhole, the depth of the manhole, and the manhole number and location (street station and offset). Ground surface, pipe type, class and size, manhole stationing, invert and surface elevation at each manhole and grade of sewer between adjacent manholes shall be identified.
2. Show the sewer line in profile and the existing and proposed ground lines. Identify the size, type of pipe, slope and horizontal length of the sewer line.
3. Above the ground line, indicate the profile location by street name or other right-of-way designation.
4. Show all crossing utilities and designate special materials or construction procedures that may be required.
5. Provide a legend to clearly illustrate the composition of the profile. (Ord. 612 § 2, 2001).