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(1) Sewer Mains and Laterals. (See Sewage Lift Stations, Article IV of this chapter, for force mains.)

Sewer mains to be installed shall be of material noted below:




Max. Slope

Gravity Sewer and Laterals


5' – 18'


Ductile Iron

3' – 5'


Ductile Iron



PVC AWWA C900 Class 200



Force Mains

Ductile Iron



PVC pipe shall be a minimum Class S.D.R. 35 and be manufactured in accordance with ASTM D3034. The pipe and fittings shall be furnished with bells and spigots, which are integral with the pipe wall. Pipe and fittings shall be of the same material. Pipe joints shall use flexible elastomeric gaskets conforming to ASTM D3212. Nominal laying lengths shall be 20 feet and 13 feet. PVC C900 pipe shall conform to AWWA C900 and will be allowed in deep trench construction at the discretion of the district.

The ductile iron pipe shall conform to AWWA C151 and shall be Class 52. Pipe and fittings shall be of the same material. Grade of iron shall be a minimum of 60-42-10. The pipe shall be polyethylene or epoxy lined to a nominal thickness of 40 mils. Minimum lining thickness shall be 30 mils. Products meeting the standard are U.S. Pipe “Polylined,” “Protecto 401,” and American Pipe “Polyband,” or equal. The exterior shall be coated with an asphaltic coating.

Each length shall be plainly marked with the manufacturer’s identification, year cast, thickness, class of pipe and weight. The pipe shall be furnished with mechanical joint or push-on type joint, except where plans call for flanged ends. Joints shall conform to AWWA C111.

Restrained joint pipe shall be push-on joint pipe with FIELD LOK® or TR FLEX® gaskets as furnished by U.S. Pipe.

All pipe shall be jointed by the manufacturer’s standard coupling, be all of one manufacturer, be carefully installed in complete compliance with the manufacturer’s recommendations.

All fittings shall be short-bodied, ductile iron complying with AWWA C110 or C153 for 350 psi pressure rated mechanical joint fittings and 250 psi pressure rated flanged fittings. All fittings shall be polyethylene or epoxy lined per the ductile iron pipe specifications and either mechanical joint or flanged, as indicated on the plans.

Fittings in areas requiring restrained joints shall be mechanical joint fittings with a mechanical joint restraint device. The mechanical joint restraint device shall have a working pressure of at least 250 psi with a minimum safety factor of 2:1 and shall be EBAA Iron, Inc., MEGALUG, or approved equal.

All couplings shall be ductile iron mechanical joint sleeves.

The sewer pipe, unless otherwise approved by the district, shall be laid upgrade from point of connection on the existing sewer or from a designated starting point. The sewer pipe shall be installed with the bell end forward or upgrade. When pipe laying is not in progress, the forward end of the pipe shall be kept tightly closed with an approved temporary plug. Wherever movable shoring (steel box) is used in the ditch, pipe shall be restrained by use of a winch mounted in the downstream manhole and a line of sufficient strength threaded through the pipe and set tight before each move. Any indication that joints are not being held shall be sufficient reason for the district to require restraints, whether or not movable shoring is being used.

All gravity pipe shall be laid in straight lines and at uniform rate of grade between manholes. Variance from 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 nonconcentricity of joining surface and pipe interior surfaces, does not exceed one-sixty-fourth of an inch per inch of pipe diameter, or one-half-inch maximum. Any corrections required in line and grade shall be reviewed with the district and shall be made at the expense of the developer.

All extensions, additions and revisions to the sewer system, unless otherwise indicated, shall be made with sewer pipe jointed by means of a flexible gasket, which shall be fabricated and installed in accordance with the manufacturer’s specifications.

All joints shall be made up in strict compliance with the manufacturer’s recommendations and all sewer pipe manufacture and handling shall meet or exceed the ASTM recommended specifications.

Pipe handling after the gasket has been affixed shall be carefully controlled to avoid disturbing the gasket and knocking it out of position, or loading it with dirt or other foreign material. Any gaskets so disturbed shall be removed, cleaned, relubricated if required, and replaced before the rejoining is attempted.

Care shall be taken to properly align the pipe before joints are entirely forced home. During insertion of the tongue or spigot, the pipe shall be partially supported by hand, sling or crane to minimize unequal lateral pressure on the gasket and to maintain concentricity until the gasket is properly positioned. Since most flexible gasketed joints tend to creep apart when the end pipe is deflected and straightened, such movement shall be held to a minimum once the joint is home.

Sufficient pressure shall be applied in making the joint to assure that it is home, as described in the installation instructions provided by the pipe manufacturer. Sufficient restraint shall be applied to the line to assure that joints once home are held so, until fill material under and alongside the pipe has been sufficiently compacted. At the end of the work day, the last pipe laid shall be blocked in an effective way to prevent creep during “down time.”

For the joining of dissimilar pipes suitable adapter couplings shall be used which have been approved by the district.

All gravity sewer pipe shall be bedded with pea gravel. The PVC pipe shall be bedded from a depth of four inches below the pipe to 12 inches above the pipe and ductile iron gravity sewer pipe shall be bedded from a depth of four inches below the pipe to the springline of the pipe. The bedding material shall extend across the full width of the trench and shall be compacted under the haunches of the pipe.

Special concrete bedding shall consist of a pipe cradle constructed of Portland cement concrete containing not less than four sacks of cement per cubic yard. Sand, gravel and water proportions are subject to approval by the district. Maximum aggregate size shall be one and one-half inches. Maximum slump shall be four inches. The bottom of the trench shall be fully compacted before the placement of pipe cradle. The developer shall protect pipe against flotation and disturbing the horizontal alignment of the pipe during the pouring of the concrete.

Clay or bentonite dams shall be installed across the trench and to the full depth of the granular material in all areas of steep slopes, stream crossings and wetland to prevent migration of water along the pipeline.

All backfill in roadway sections shall be placed and compacted in accordance with Snohomish County, city and/or state requirements and copies of the compaction results shall be provided to the district. All backfill in easements shall be placed and compacted to a minimum of 90 percent of the Modified Proctor dry maximum density per ASTM D1557. Copies of compaction results for all sewer system trenches shall be provided to the district. Recycled concrete is not allowed for use in district trench sections, no exceptions.

(2) Manholes. Manholes shall be of the offset type and shall be precast concrete sections with either a cast in place base, or a precast base made from a 3,000 psi structural concrete. Joints between precast wall sections shall be confined O-ring or as otherwise specified.

The minimum diameter for manholes shall be 48 inches to a depth of 20 feet, and 54 inches for depths of 20 feet and greater. The district may require the diameter to be increased beyond the minimum based on future needs.

For connections to existing systems, a concrete coring machine, suitable for this type of work, shall be utilized in making the connection. The existing manhole shall be rechanneled as required. The new pipe connection shall be plugged (watertight) until the new pipe system has been installed and approved. The developer shall be responsible for any existing defects in the existing manhole unless these defects are witnessed by a representative of the district prior to any work being performed to make the connection. The contractor shall be required to remove any and all deleterious material in the existing manhole and downstream reaches as a result of this work.

Manholes located in easements or outside of paved areas shall have concrete collars with a minimum size of 48 inches diameter by 12 inches thick and marked with a green carsonite marker.

(a) Manhole Sections. Manhole sections shall be placed and aligned so as to provide vertical sides and vertical alignment of the ladder steps. The completed manhole shall be rigid, true to dimension, and be watertight. Rough, uneven surfaces will not be permitted.

(b) Manhole Steps and Ladders. Manhole steps shall be polypropylene, Lane International Corp. No. P13938 or equal.

Ladders shall be polypropylene, Lane International Corp. or equal, and shall be compatible with steps.

(c) Grade Adjustment. The manhole shall be set to provide not less than 14 inches or more than 26 inches of adjustment between the top of the cone or slab and the top of the manhole frame.

Masonry units (manhole adjusting rings) shall conform to the ASTM C2, Grade MA. The outside and inside of manhole adjusting rings and the joints of precast concrete sections shall be plastered and troweled smooth with one-half inch (minimum) of mortar in order to attain a watertight surface. No wood shall be used for adjustment.

(d) Channels. Channels shall be made to conform accurately to the sewer grade and shall be brought together smoothly with well rounded junctions, satisfactory to the district. The channels shall be field poured with concrete, no other fillers are permitted, after the inlet and outlet pipes have been laid and firmly grouted into place at the proper elevation. Allowances shall be made for a one-tenths-foot drop in elevation across the manhole in the direction of flow. Channel sides shall be carried up vertically from the invert to three-quarters of the diameter of the various pipes. The concrete shelf shall be warped evenly and sloped three-eighths inch per foot to drain. Rough, uneven surfaces will not be permitted. Channels shall be constructed to allow the installation and use of a mechanical plug or flow meter of the appropriate size.

(e) Drop Manholes. Drop manholes on new construction require district approval and shall be constructed with outside drop(s). Approval will be limited to future extensions from deep sewers. Where extension from deep sewers is concurrent with deep sewer construction, drop manholes will not be allowed. Drop manholes shall, in all respects, be constructed as a standard manhole with the exception of the drop connection. Connection to existing district sewers may be allowed to use inside drop with prior district approval.

(f) Lift Holes and Steel Loops. All lift holes shall be completely filled with expanding mortar, smoothed both inside and outside, to ensure watertightness. All steel loops shall be removed, flush with the manhole wall. The stubs shall be covered with mortar and smoothed. Rough, uneven surfaces will not be permitted.

(g) Frames and Covers. Frames shall be cast iron and covers shall be ductile iron. Castings shall be free of porosity, shrink cavities, cold shuts or cracks, or any surface defects, which would impair serviceability. Repair of defects by welding, or by the use of “smooth-on” or similar material, will not be permitted. Frames and covers shall be machine finished or ground on seating surfaces so as to assure non-rocking fit in any position and interchangeability of covers. Frames and covers shall be provided with three bolt locking lids. Rings and covers shall be positioned so one of the three locking bolts is located over the manhole steps and shall be adjusted to conform to the final finished surface grade of the street or easement to the satisfaction of the district. Manhole frames and covers shall be as manufactured by East Jordan Iron Works Model 00371564, or equal. Must meet the (AASHTO) M306 specification and have replaceable lock down nuts.

(h) Manhole Marker Posts. A fiberglass manhole marker post shall be located adjacent to all manholes located in easement areas. The marker post shall be green in color, three and three-quarters inches wide (flat), 60 inches long and furnished with a three-inch by three-inch high intensity white reflector (250 Candle Power) and a flexible anchor barb. Each post shall include the following decal: “Caution Sewer Manhole. Before digging, Call 1-800-424-5555, Utility Underground Location Center.” Manhole markers shall be Carsonite Utility Marker CUM 375.

The marker posts shall be set so as to leave 36 inches of the post exposed above grade.

Distance from the marker to the manhole shall be stenciled on the marker with two-inch letters. [Res. 735 § 1, 2017.]