Section 4 Standards for Sanitary Sewer Systems (PDF, 367KB)

8/6/2019 Section 4 Standards for Sanitary Sewer Systems (PDF, 367KB)

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SECTION 4: STANDARDS FOR SANITARY SEWER SYSTEMS

4.0 General

These specifications contain the design criteria and improvement standards for the extension

of or connections to the City of Kent Sanitary Sewer System. The conditions as stated hereinand in the City of Kent Development Assistance Brochures apply to all improvements made

by private developers. These improvements may include the following:

A. Sewer main extensions, modifications and replacements.B. Side sewer connections to City mains.

4.1 Easements and Rights-of-Way

Permanent onsite easements for access, maintenance, and construction are required for all

Sanitary Sewer Extensions located outside of public right-of-way. When easements arerequired, legal descriptions for same shall be submitted with a professional land surveyors

stamp thereon. Also, at this time, a current title report covering the properties to be

encumbered by the easements shall accompany said description. Under no circumstancesshall a Bill of Sale be placed on the City Council agenda for action until all easement have

been approved and recorded.

When offsite easements and/or onsite easements for the extension of approved

comprehensive sewer plans are required, these easements shall be approved and recorded prior to any preconstruction meeting being held. Also the same conditions shall apply

regarding legal descriptions and title reports.

Certain private improvements are not allowed under the terms of the Citys easement.

Where any encroachment interferes with the Citys easement, the contractor, or his/her

assign, shall remove and relocate the conflicting private improvement immediately upon

direction from the Public Works Director or his representative.

A. Easement Requirements The minimum easement widths are as follows:1. Sanitary Sewers under ten (10) feet deep) fifteen (15) feet wide.2. Sanitary Sewers ten (10) fifteen (15) feet deep) twenty (20) feet wide. Note:

large diameter or deeper sewers may require wider easements as determinednecessary by the Director.

3. Access roads are required to each sanitary sewer manhole for maintenance. Wherealignment of manholes will allow maintenance, access can be to every other manhole


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4.2 Plan Approval and Permits

The construction of sanitary sewer extensions within the City and approved franchiseservice areas requires the approval of the City of Kent, the State Department of Ecology, and

King County DNR-WTD. No construction shall be permitted until the design plans and

specifications have been reviewed and approved by these agencies, unless a Hold HarmlessAgreement is executed. Said construction is also subject to Permits and plan Review Fees

(See Appendix C for Fee Schedule).

4.3 Sanitary Sewer System Design Requirements

4.3.1 General

All sanitary sewer systems shall conform to the design requirements of the Criteria for

Sewage Works Design by the Washington State Department of Ecology, and the StandardSpecifications, as may be amended by the City of Kent design requirements. When

connections are made to the King County DNR-WTD system all work shall comply with the

design requirements of King County DNR-WTD. Permits and Plan Review Fees are

required as shown in Appendix C.

4.3.2 Comprehensive Sewerage Plan

The City of Kent has developed a comprehensive sewerage plan to allow the orderly and

cost effective development of sewerage facilities to serve existing and future users of the

Kent sewer system.

The Comprehensive Sewerage Plan includes a map of proposed sewer extensions to service

areas presently unsewered. The plan shows the general location of interceptor and trunksewers, intended to provide the framework of the collection system for the service area. Allproposed sewer improvements and extensions shall be consistent with the Comprehensive

Sewerage Plan.

4.3.3 Service Area Considerations

All sewer extensions shall be designed for the ultimate development of the service area inaccordance with current land use plans. The determination of the tributary area shall be

based on the Comprehensive Sewerage Plan and detailed studies of the areas affected. The

Director shall assist in the determination of the tributary area and must approve the service

area plan prior to detailed design of the sewer system.

Ne se er s stems shall be designed on the basis of per capita flo s or other methods as


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4.3.4 Extent of Sanitary Sewer Improvements

The Sanitary Sewers shall be extended to the limits of the respective property being served

in accordance with the Comprehensive Sewerage Plan. The extension shall be of size and

grade as necessary to be extended in the future. In cases where the plan does not requirefuture extension, the sewer system shall be extended as necessary to service the affected

property.

4.4 Sanitary Sewer System Design Standards

A. The minimum diameter sanitary sewer main shall be eight (8) inches. Larger diametersmay be required for capacity or to minimize grades.

B. All sanitary sewers shall be designed and constructed to provide a minimum velocity oftwo (2) feet per second flowing full. The maximum allowable velocity shall be ten (10)

feet per second. Where velocities are greater than ten (10) fps or slopes greater than 20percent pipe anchors shall be required with a detailed drawing submitted to the City for

approval by the Director.

The following are the minimum, acceptable slopes for sanitary sewers as permitted byD.O.E. and the City:

Sewer Size Minimum Slope*(Inches) (feet per 100 feet)

4 inches 2.00 % Private Side Sewer 6 inches 1.00 % Private Side Sewer

8 inches 0.40 %10 inches 0.28 %12 inches 0.22 %

15 inches 0.15 %

18 inches 0.12 %

21 inches 0.10 %

*Based on Mannings n value of 0.013.

C. All sewers shall be designed and constructed with a straight alignment and continuousgrade between manholes.

D. All sewer mains shall be buried deep enough to prevent freezing, breakage, and provideadequate depth to service the lowest fixtures on the properties served. The minimum

cover for PVC sewer pipe is three (3) feet (Minimum SDR 35)


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4.5 Sanitary Sewer Manholes

A. Sanitary sewer manholes are required at the following locations:1. At the end of all sewer mains eight (8) inch and larger. When the main is to be

extended in the future, the end of the line shall be a bell, plugged and marked with a2 x 4 stake. (See standard detail 4-3(a) for staking requirements only.)

CLEANOUTS ARE NOT ACCEPTABLE IN MAIN LINE INSTALLATIONS.

2. All changes in slope.3. Changes in sewer main pipe diameter.4. All connections to the main line eight (8) inch and larger.5.

Changes in sewer alignment.6. Manholes shall be located at no more than four hundred (400) foot intervals.

B. The minimum diameter of sewer manholes shall be forty eight (48) inches for sewerpipes up to eighteen (18) inches in diameter. Larger diameter manholes will be requiredfor special configurations and sewer pipe larger than eighteen (18) inches.

C. All standard City manholes shall have precast eccentric cones except special shallowmanholes shall have concentric cones. All manholes shall be equipped with City

approved drop rung type safety steps. Flat slabs shall not be used unless preapproved bythe Director of Public Works. (See Standard Details 4-1(a), 4-1(b) & 4-8 in Appendix

B)

D. Outside drop connections shall be required at all locations where the entering sewer is 24inches or more above the outfall invert elevation. Line connections to manholes or to

stubs integral to a manhole shall be made with approved flexible joints. (See Standard

Detail 4-7 in Appendix B). Inside drop connections are not allowed.E. The Sanitary Sewer Manholes shall be fully channeled to conform to the inside diameter

of the sewer line from invert to spring line, then the channel shall be vertical to the top ofthe pipe. The top edge of the channel shall have a radius of to inch. The shelvesshall slope at 2% to the top of the channel. All manhole section joints and pick holes

shall be filled with grout and smooth finished outside and inside after installation. (See

Standard Details 4-1(a) and 4-1(b) in Appendix B).

F. Where possible, a one tenth (0.1) foot drop from invert to invert across manholes isdesirable. Where diameters change, the downstream invert shall be lowered so that the

elevation of pipe crowns match. The maximum drop from invert to invert across

manholes shall be one (1) foot.G. Care must be taken to insure that pressures exerted on the soils beneath the manholes

and the adjacent mains are approximately uniform. Unequal soil pressures may result in

excessive settlement at manholes. A spread foundation or other measures may berequired to reduce the unit load imposed by the manhole. All manholes shall be

provided with KOR-IN-SEAL type flex joints or sand collars meeting ASTM D-303H-


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I. Manholes installed outside of the traveled City Right-of-Way shall have locking rings

and covers. (See Standard Detail 4-6(a) in Appendix B).

J. Where the possibility of odors, gasses or corrosive discharges could be present in the

sewer line or where required by the Director, corrosion protection of the inside of the

manhole may be required. The material to be discharged and the Director will determinethe particular type of corrosion protection in the manhole. Sealed manhole covers shall

be required for this type of installation. (See Standard Detail 4-6(b) in Appendix B).

4.6 Private Side Sewer Systems

Sanitary sewer lines that extend from the mainline to service one legal lot and/or one

building (or two single-family residential lots) are considered private side sewers. Sidesewers are to be constructed and maintained by the property owner in accordance with theCity of Kent Side Sewer Standards adopted by Ordinance #2374. Handouts are available

upon request.

4.6.1 Side Sewer Permit

Prior to construction, replacement, repair, connections or additions to a side sewer, the

owner or authorized agent must obtain a Side Sewer Permit from the City. To obtain theSide Sewer Permit, the owner or authorized agent must file an application with the Public

Works Engineering Department. The application shall include the name and address of the

owner, the legal description of the property to be serviced, the design plans andspecifications for the side sewer installation in accordance with the side sewer application

instructions, and any submittals and attachments for review as required by the Director. The

City shall review the application, require or make changes if needed, approve the side sewer plan, and assess the property owner for applicable latecomer charges, charge in lieu of

assessments, traffic mitigation fees, permit fees, tapping charges, street restoration bondsand other charges, as required. (See Appendix C for Fee Schedule). (See the City of KentSide Sewer Standards Handout for additional information).

4.6.2 Side Sewer Design Standards

A. The minimum diameter of a side sewer shall not be less than six (6) inches, exceptservice to a single-family residence shall not be less than four inches in diameter from

right of way or easement line to the building. All side sewers eight (8) inches indiameter shall be designed in accordance with the requirements of Section 4.3 thru 4.5

and 4.7 thru 4.8.

B. All side sewers shall have cleanouts located on the straight run after each total 90change of direction and/or change in slope, and at the termination of the sewer within

five (5) feet outside of the building The maximum length of a six (6) inch side sewer


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D. The minimum allowable slope for six (6) inch side sewers shall be 1.0%. The minimum

slope for four (4) inch side sewers shall be 2.0%. All side sewers shall function on a

gravity basis, unless a specific exception is preapproved by the Director.

4.6.3 Connections

Each legally defined property or building or up to two single family residences shall beserviced by a separate side sewer stub connected to the City main. For multi-tenant sites or

if the property is planned to be platted at a later date, consideration should be given to

providing separate six (6) inch side sewers for each building.

The maximum number of services permitted on a six (6) inch diameter sewer shall be thirty

(30) persons. In general, up to ten (10) units in a multi-family dwelling may be serviced ona single six (6) inch diameter sewer.

4.6.4 Grinder Pumps

Where gravity flow for side sewer is not possible, a privately owned and maintained grinder

pump system to service individual structures requires specific approval by the Director.

These assemblies shall be located adjacent to the structure, and shall be equipped with bothhigh level and pump failure alarms. The alarms shall be both audio and visual, and be on a

separate circuit from the pump.

Residential systems will be a package-type simplex systems hydromatic SPG 200 or

approved equal. Each pressure system shall have an individual connection to the Citysewer. Lift systems for commercial and multi-family structures require special maintenance

agreements and specific approval of the Director. Submittal is required for each permit prior

to approval. Solid handling waste pumps are not allowed. Refer to Section 4.9C for airtesting force main systems. (See Standard Detail 4-4(a) in Appendix B).

4.6.5 Connection to City Sewer System

All lots adjacent to a City sewer main shall be serviced with a six (6) inch side sewer stubout

extended to the property line. Where possible, the sewer service shall be six (6) feet deep at

the property line. The location of sewer stubouts shall be marked with a 2 x 4 post and

tracer wire. The development shall be designed to utilize the stubout supplied. (See Detail4-3(a) & 4-4 in Appendix B).

The City maintains records concerning the location and approximate depth of recent side

sewer stubouts. These records are for informational purposes only and it shall be the

developers responsibility to verify the location and depth of existing services.


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4.6.6. Waste Discharge Permits

Storm water, surface water, ground water, cooling water and industrial processes that have

been polluted as determined by the City of Kent Director of Public Works and King County

Department of Natural Resources Industrial Waste Division are required to be dischargedto the City sewer main through an approved pretreatment system and metering method.

Pretreatment requirements of the discharge shall be determined and approved by King

County Department of Natural Resources Industrial Waste Division.

Metering, billing and authorization to discharge shall be determined and approved by the

City of Kent. A waste discharge permit shall be required from the City and can be obtained

as outlined in 4.6.1 of this section. The City of Kent will not issue waste discharge permitswithout prior discharge approval from King County DNR-IWD.

Metering methods shall be determined and approved by the City of Kent Director of Public

Works on a case by case basis. See Section 3.5.5 for Sewer Rate Meter applications.

The type and size of oil/water separator(s) when required shall be approved by King County

DNR-IWD.

The type and size of grease interceptor(s) when required shall be approved by the City of

Kent Director (See Standard Detail 4-9(a) and 4-9(b) in Appendix B).

4.7 Sanitary Sewer System Materials

4.7.1 Standards

All materials used for construction of City sewer mains, side sewers, and appurtenances,shall be new and undamaged. All materials to be used shall be subject to inspection by the

City of Kent prior to use. The contractor shall provide the City with shop drawings and

material certificates, as requested. All materials and equipment shall be installed in

accordance with the manufacturers recommended installation procedures and the City ofKent Standards.

4.7.2 Gravity Sewer Pipe

Unless otherwise approved, all sewer pipe shall be PVC (Polyvinyl Chloride), SDR 35,

conforming to ASTM 3034 or 3035 specifications or ductile iron pipe, Class 50.

The sewer pipe shall be clearly marked with the type class thickness and manufacturer


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4.7.4 Manholes and Covers

Sanitary sewer manholes shall be precast concrete units constructed in accordance with the

Standard Specifications. (See Standard Detail 4-1(a) & 4-1(b) in Appendix B).

Manhole frames and covers shall be cast gray or ductile iron. Locking type lids are required

outside of traveled public right-of-way. (See Standard Detail 4-5, 4-6(a) & 4-6(b) inAppendix B).

4.7.5 Pipe Bedding

Pipe bedding for sewer pipe shall be 5/8th

inch minus crushed rock, (Pea gravel is not

allowed). A continuous and uniform bedding shall be provided in the trench for all buriedpipe. Bedding material shall be tamped in layers six (6) inches under the pipe, around the

pipe and six (6) inches above the pipe to adequately support and protect the pipe to 95%

compaction ASTM D-1557, in accordance with the standard specifications and details and in

conformance with the following gradation:

Sieve Size Passing

Inch 100%

5/8 Inch 95 100%

Inch 45 65%U.S. No. 40 6 18

U.S. No. 200 7.5 Max.% Fracture 75 Min.

Sand Equivalent 40 Min.

L.A. wear 500 rev. 35% Max., Degradation 25% min.

Free from wood waste, bark and other deleterious material.

The pipe shall be protected from damage when compacting. At least two (2) feet of cover isrequired over the pipe prior to using heavy compaction equipment.

Where determined necessary by the Director, ballast material shall be used below the

bedding to stabilize the trench. Ballast shall conform to the requirements of Section 3.8.2herein.

4.7.6 Backfill

Pipe trench backfill shall be bank run gravel if, in the opinion of the Director, existing trench


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In paved areas the material used shall match the existing street section unless otherwise

directed by the Engineer. In no case shall the thickness of the asphalt concrete be less than

three (3) inch of Class B asphalt concrete.

4.8 Sanitary Sewer System Installation

4.8.1 Connection to Existing Sewer System

The connection between the new sanitary sewers and the existing sewer mains shall be

plugged and tied off to the top manhole step and left in place until the new piping and theplugged manhole has been cleaned, pressure tested, TV camera inspected, and is ready for

City Council acceptance.

4.8.2 Cleaning

All sewer pipe shall be thoroughly cleaned to remove any solids or construction debris thatmay have entered the pipe during construction by jet cleaning and pigging as approved by

the City of Kent.

The contractor shall be responsible to insure that material flushed from sewers are trapped,and do not enter the existing downstream system. The City shall approve the contractors

method prior to cleaning sanitary sewer mains. The rate of flushing shall be such that the

flow will not overload the downstream sewers. The flushing of a sewer main tributary to alift station shall be coordinated with the Operations Division to insure that the lift station is

not overloaded.

City water used for cleaning sewer lines is not metered, but shall pass through an approved

double check valve assembly.

4.8.3 Pressure and Leakage Tests

All testing shall be verified by the City inspector. All sewer mains and appurtenances shall

be air pressure tested for leakage in accordance with Section 7-17 of the StandardSpecifications as modified in the following:

Procedure for Air Testing Sanitary Sewer Lines (Based on PBC and Ductile Iron Pipe)The Contractor shall furnish all facilities and personnel for conducting the test under the

observation of the Director. The equipment and personnel shall be subject to the approval of

the Director.

The Contractor may desire to make an air test prior to backfilling for his own purposes


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pressure reaches 4.0 pounds per square inch greater than the average back pressure of any

ground water that may submerge the pipe. At least two minutes shall be allowed for

temperature stabilization before proceeding further. Then, disconnect the air supply and

wait until the pressure drops to 3.5 psig greater than the average back pressure of

groundwater. The pressure shall be held on the time indicated on the table on page 4-13 thru4-15 and recorded on the form on page 4-16.

Groundwater Pressure

p = 0.4332 (z)z = Distance between groundwater surface and centerline of pipe in feet.

p = Average back pressure of groundwater above the centerline of the pipe in psi.

For Concrete Pipe The time it takes the pressure to decrease from 3.5 psig to 2.5 psig

greater than the average back pressure of groundwater (p), shall not be less than half that

indicated in the attached tables for the section under test.

If the pipe installation fails to meet these requirements, the Contractor shall determine, at his

own expense, the source of leakage and he shall repair (if the extent and type of repairs

proposed by the contractor appear reasonable to the Director) or replace all defectivematerials or workmanship. The completed pipe installation shall meet the requirements of

this test before being considered acceptable.

Caution When air testing adequate bracing is required to hold plugs in place to prevent the

sudden release of compressed air. A pressure of 4 psig against an eight (8) inch plug willcause a force of approximately 200 lbs.; against a twelve (12) inch plug, 450 lbs. The

compressed air acts as a spring. Proper precaution must be taken to prevent this force from

propelling the plug from the pipe like a bullet.

For systems where groundwater is negligible at the inspectors discretion pressure shall be

maintained at 4.0 psig with no drop at the time indicated on the attached tables on page 4-13

thru 4-15 and recorded on the form on page 4-16.

4.8.4 Television Inspection

All new sanitary sewer extensions shall be TV camera inspected by the City OperationsDivision prior to acceptance. All construction must be completed and approved by the

inspector prior to the TV inspection. All manholes shall be channeled, and grade rings set inplace prior to TV inspection by the City. The casting and top grade rings do not have to be

mudded in until after the final grade is established. It is the responsibility of the contractor

to string each sewer main prior to inspection. The string shall be a nylon cord of sufficient


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4.8.5 Vacuum Testing Sewer ManholesAll new sanitary sewer manholes shall be vacuum tested by the City Operations Division prior toacceptance to ensure it is air-tight and not susceptible to infiltration. On projects with more than

one manhole, the Contractor shall have all of the manholes ready for testing prior to scheduling theair-testing with the project inspector. Manholes will not be considered ready for testing until all

grouting has been performed and the frame and cover have been grouted in place. It is the

responsibility of the contractor to ensure all manholes are ready for testing prior to scheduling thetesting through the inspector. Manholes not ready for testing shall receive a failing mark and a re-

test shall be scheduled through the inspector once the manhole is ready.

The contractor shall bear all costs for correction of deficiencies found during the vacuum testing,

including the costs for additional vacuum testing to verify the correction of deficiencies.

4.9 Sewage Pump Stations

A. General Sewage pump stations will be approved on an individual basis. The proposedpump station must be designed with adequate capacity to provide service for the ultimatedevelopment of the potential service area. The service area for any proposed pump

station shall not be less than seventy five (75) acres or provide service to less than twohundred and fifty (250) potential single-family residences or its equivalent in revenue.

B. Design Requirements1. All sewage pump stations shall be designed in accordance with the Department ofEcologys design requirements for sewage pump stations and force mains.2. Pump stations shall be of Smith and Loveless (or approved equal) manufacture, and

have separate wet well and dry well structures.

3. All stations shall have an on-site emergency power supply with automatic switchingcapacity.

4. All stations shall be equipped with a telemetry system compatible with the existingCity equipment.

5. No discharge from a new pump station shall be discharged to an existing City pumpstation.

6. The developer shall post a cash bond to cover the estimated costs of operation andmaintenance of the new pump station during the first year of service.

C Pressure Tests


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LENGTH OF 6 PIPE (FEET)

0 50 100 150 200 250 300 350 400

0 0 40 80 118 158 198 238 278 316

50 70 110 150 190 228 268 308 348 356

100 140 180 220 260 300 338 374 372 368

150 212 250 290 330 370 390 386 382 378

200 282 322 360 400 404 398 394 390 386

250 352 392 428 418 410 404 400 396 392

300 422 440 430 422 416 410 404 400 396

350 454 442 434 426 420 414 410 404 402LENGTHO

F8PIPE

(FEET)

400 454 444 436 428 422 418 412 408 404

Time in seconds required for decompression from 3.5 psig to 3.0 psig.


0 50 100 150 200 250 300 350 400

0 0 40 80 118 158 198 238 278 316

50 110 150 190 228 268 308 348 384 380

100 220 260 300 338 378 418 420 414 406

150 330 370 410 448 466 454 444 434 428

200 440 480 514 496 482 470 460 450 444

250 550 542 522 506 494 482 472 464 456

300 566 544 528 514 502 492 482 474 466350 566 548 534 520 508 494 490 482 474

LENGTHO

F10PIPE

(FEET)

400 566 550 538 526 514 504 496 488 482



0 50 100 150 200 250 300 350 400

0 0 40 80 118 158 198 238 278 316

50 158 198 238 278 316 356 396 416 408

100 316 356 396 436 476 492 476 464 454

150 476 514 554 566 544 526 510 496 48612PIPE

T)


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0 50 100 150 200 250 300 350 400

0 0 40 80 118 158 198 238 278 31650 248 288 326 376 406 446 486 476 462

100 496 534 574 614 624 596 572 552 530

150 742 782 742 704 672 646 624 604 586

200 850 804 766 732 704 680 658 640 624

250 850 812 780 752 726 704 684 666 652

300 850 818 790 766 742 722 704 688 672

350 850 822 798 776 756 736 720 704 690LENGTHO

F15PIP

E

(FEET)

400 850 826 804 784 766 748 732 718 704



0 50 100 150 200 250 300 350 400

0 0 40 80 118 158 198 238 278 316

50 356 396 436 476 314 554 566 544 526

100 712 752 792 794 748 710 680 654 632

150 1020 952 896 850 810 778 748 722 700

200 1020 968 922 884 850 820 794 770 748

250 1020 978 940 906 876 850 826 804 784

300 1020 984 952 922 896 872 850 830 810

350 1020 990 960 916 912 890 868 850 832LENGTHO

F18PIPE

(FEET)

400 1020 992 968 944 922 902 884 866 850



0 50 100 150 200 250 300 350 4000 0 40 80 118 158 198 238 278 316

50 634 674 712 752 792 794 748 710 680

100 1268 1246 1156 1082 1020 968 922 884 850

150 1360 1282 1214 1156 1106 1060 1020 984 952

200 1360 1300 1246 1200 1156 1118 1082 1050 1020

250 1360 1312 1268 1228 1190 1156 1124 1096 1068THO

F24PIPE

(FEET)


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CITY of KENT

SANITARY SEWER TEST RESULTS

Project: Date: Contractor: Engineer:

Type of Test: Air Water Tested By:

Manhole Number Pipe TimeTestDat

eFrom To

Lengthof

RunDia. Type

Groundwater

Head

TestPressur

eSpecifie

dActual

Remarks

Send a copy of completed form to: King County, Water Pollution Control Division, Department of Natural Resources, 821 Second Ave. M.S. 117 Seattle, WA

98104-1598 Fax: 206-684-1710

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Section 4 Standards for Sanitary Sewer Systems (PDF, 367KB)

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