Nevada County Municipal Code Ch. 7 Design and Construction Standards

A. Scope. The design and construction of sanitary sewers in the unincorporated area of Nevada County within public rights-of-way and sanitary sewers and sewage treatment plants subject to control or permit requirements of the District shall be in accordance with good engineering practice. The work shall comply with these standards except where specific modifications have been approved by the District Engineer in writing.

B. Interpretations. The District Engineer shall decide all questions of interpretation of "good engineering practice," being guided by "Design and Construction of Sanitary and Storm Sewers" (ASCE Manual of Engineering Practice No. 37) and "Sewage Treatment Plant Design" (ASCE Manual of Engineering Practice No. 36), both prepared by joint committees of the American Society of Civil Engineers and Water Pollution Control Federation.

C. Plumbing Code. All work on house laterals and house sewers outside of public rights-of-way or sewer easements will be governed by the provisions of the Uniform Plumbing Code and other applicable ordinances of the local sewerage agencies.

D. Other Standards. Where purveyor's requirements and standards are more restrictive than this manual, the purveyor's requirements shall govern.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

Provisions of this Chapter shall be enforced by the District Engineer.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

The following plates are included as part of this Chapter:

(SD-5. (03/26/1979); SD-73. (08/11/2015); SD-75. 11/07/2023)

A. Average Sewage Flow Rates. The average flow rate shall be determined by the owner's or purveyor's engineer based on good engineering practice. The ranges shown in the following table may be used as a guide but flows outside of these ranges may occur. If flows are used which are less than those listed in the column headed "Minimum for Design," the engineer's approval must be obtained in advance of design.

Acreage in table is gross acreage including roads, yards, parking, etc.

Average Sewage Flow Rates (Table referred to in Section 30.07.040.A)

* To be determined by Engineer

B. Peak Sewage Flow Rates. Peak sewage flow rates shall be obtained from chart on Plate 10 by entering the chart with average daily flow rates.

C. Hydraulic Design.

1. Use Mannings' "n" = 0.013 or Hazen-Williams "C" = 100 for hydraulic design. A minimum full-conduit velocity of 2fps is required.

2. For pipe ten (10") inches or less in diameter, design pipe so peak flow rate will be carried when pipe is flowing at one-half (½) depth. Discharge at one-half (½) depth equals one-half (½) discharge when full and velocity equals velocity when full. Tables and formulas to find slope may be used by entering with two times the peak flow rate.

3. For pipe twelve (12") inches and larger in diameter, design pipe so peak flow will be carried when pipe is flowing at two-thirds (⅔) depth. Discharge at two-thirds (⅔) depth equals three-fourths (¾) discharge when full and velocity equals one and sixteen one-hundredths (1.16) times velocity when full. Tables and formulas to find slope may be used by entering with one and thirty-three one-hundredths (1.33) times the peak flow rate.

4. When low early year flows are anticipated, a slope will be selected to provide self-cleansing velocities. If initial flows are to be so low that self-cleansing velocities aren't practical, the design engineer will clearly designate that relatively frequent flushing will be required.

D. Minimum street sewer size shall be six (6") inches.

E. Oversizing and extra depth of tract sewers will be required where such sewers can logically serve an upstream tributary area and extra size and/or depth are required for such future use.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

A. Purpose. Minimum slope requirements are necessary to assure self-cleaning and self-oxidizing velocities in order to avoid significant generation of hazardous, odorous, and corrosive sulfur compounds.

B. Minimum Slopes. Slopes of sewers shall equal or exceed those set forth in the following table:

C. Substandard Slopes. Slopes below the minimum slopes may be used in order to avoid pumping only upon specific approval of the engineer. Such approval should be solicited well in advance of completion of design.

D. Pipe for Substandard Slopes. Pipe, in substandard slope areas and pipe in all areas downstream from substandard slope areas to the point where the peak flow rate is four (4) times that in the section with substandard slope, shall be corrosion-resistant sewer pipe in accordance with Section 30.07.090.D.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

A. Roads. The centerline of sewers constructed in County roads shall not be closer than four (4') feet to the centerline of the road nor closer than four (4') feet to the curb or edge of the shoulder. On divided highways, a separate sewer shall be installed to serve each side of the highway. Exceptions to these location requirements may be made only on approval of the Engineer.

B. Easements.

1. Sewer easements shall be not less than twelve (12') feet wide.

2. Where easements follow common lot lines, the full easement width shall be on one (1) lot, in such a manner that access to manholes will not be obstructed by walls, trees, or permanent improvements. Where this requirement cannot be met without interfering with existing buildings, easements may straddle lot lines on approval of the engineer.

3. Deeds for easements shall provide for restrictions of permanent construction within easement to provide ingress and egress for maintenance.

C. Future Extensions. When an area outside the tract can be logically served by future extension of a tract sewer, the tract sewer shall extend to the tract boundary or to the end of a paved street in a manner to facilitate the future extension.

D. Alignment.

1. Sewers shall be laid on a straight alignment and grade between manholes except that curved sewers may be used subject to the following requirements.

2. Curved Sewer Requirements.

a. Minimum radius = one hundred fifty (150') feet for horizontal curves.

b. Minimum invert slope of horizontally curved sewers shall be zero and one one-hundredths (0.01) except that sewers with a radius of two hundred (200') feet or more will have the same requirements as straight sewers.

c. Vertical curves may be used in combination with horizontal curves where invert slopes exceed zero and one one-hundredths (0.01) throughout the reach between manholes.

d. Maximum combined horizontal and vertical deflection at any joint shall be as recommended by the manufacturers but in no case more than three (3) degrees.

e. The arithmetic sum of all horizontal and vertical deflection in curved sewers between adjacent manholes shall not exceed sixty (60) degrees.

E. Water-Sewer Separation.

1. Purpose and Scope.

a. Minimization of public health hazards created by sewage contamination of water supplies dictates a need for facility separation standards. The provisions herein are intended to govern the separation of water supply and sewerage facilities not already regulated by the Uniform Plumbing Code. This should not be interpreted to change separation regulation of building sewer, drainage, and water pipes as provided under the Uniform Plumbing Code.

b. If, in the opinion of the County Health Officer, the Director of Sanitation, or the civil engineer designing and/or supervising the construction of the facilities, the standards herein are inadequate to provide reasonable protection due to unusual circumstances, said individuals will prescribe more effective separation and/or protection.

2. Required Water and Sewer Facility Separation.

a. Horizontal separation between a water main and a sanitary sewer line laid approximately parallel shall not be less than ten (10') feet.

b. When a water main or service line and a sanitary sewer line cross, the water shall be higher than the sewer by a vertical separation of not less than three (3') feet. See Plate 9 for construction requirements when three (3')-foot separation cannot be maintained.

c. The following minimum separations shall be maintained between water supply and sewerage facilities.

3. Exceptions to Standard Separations. When it is impractical to locate water supply facilities and sewerage facilities in accordance with the preceding separation standards, they may be located in closer proximity provided that:

a. Line joints where standard separation is not maintained must possess the strength and durability needed to prevent line leakage under such adverse conditions as corrosion, temperature change strains, settlement and superimposed loads.

b. Facility designs not maintaining the standard required separation shall be approved in advance by the Director of Sanitation. Construction requirements by the Director of Sanitation for separations within the ten (10')-foot zone shall be generally in agreement with Plate 9 of this Chapter.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

A. Basic Requirements. Sewers shall be installed at a depth which will provide suitable service to the properties connected and will allow subsequent installation of water lines in accordance with Water Sewer Separation requirements with a minimum of special construction of the water lines other than joint spacing.

B. Standard Depths. Compliance with Subsection A will usually be assured if the main sewer is located at a depth of five (5') feet to top of pipe below the flow line of the existing or proposed gutter or, where no gutter exists, from the elevation of the outermost edge of the traveled way; and the house laterals are located either: (1) four (4') feet to top of pipe below the ground surface at the property line, or (2) at a depth below the ground surface at the property line that will provide for the construction of a straight run of private sewers at a slope of zero and two one-hundredths (0.02) from one (1) foot below the surface at any point within the established building setback lines, excluding any areas steeper than five (5) horizontally to one (1) vertically, whichever depth is greater.

C. Exceptions. Designs not in accordance with Subsection B shall be submitted to the engineer for approval together with evidence that it complies with Subsection A.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

A. Manholes.

1. Locations. Manholes shall be located at all abrupt changes in alignment or grade and at all junctions. Manholes shall be located at least every four hundred (400') feet along lines smaller than twenty-four (24") inches in diameter. Spacing of manholes on lines twenty-four (24") inches in diameter and larger will usually be at four hundred (400') feet but may be extended subject to the approval of the engineer.

2. Drop Manholes. Drop manholes shall be used wherever sewers enter manholes at more than twelve (12") inches above the outlet elevation of the manhole. Vertical curves may be used to eliminate drop manholes in accordance with the requirements of Section 30.07.060.D.2.

3. Design. Manholes shall be constructed generally in accordance with Plates 5, 6, and 7. Manhole designs which, in the opinion of the engineer, provide access to the sewers, a stable working platform, and freedom from splash and turbulence, equivalent to or better than the design shown herein, will be approved.

4. Protection. Where new tract sewers are to be connected into a manhole which is in active use, the designer shall call for such protection as is necessary to prevent construction debris from being washed into the active sewers. Plugged inlets or other suitable protection shall be called for in the active manhole before beginning manhole modifications or tract sewer cleaning.

5. Elevations. Finished elevations of frames and covers shall be set in relation to finished grades of the completed road surface or finished surrounding grade when outside of roads. They should be depressed one-quarter (¼) inch in finished roadways to facilitate snow removal and installed in general accordance with Plate 5 outside of roadways.

B. Cleanouts.

1. Requirements. Dead end sewers not over two hundred (200') feet in length shall terminate in standard manholes or cleanouts. Dead ends over two hundred (200') feet long shall terminate in standard manholes unless future extension of said dead end will include a manhole within four hundred (400') feet of the uppermost manhole, in which case a temporary cleanout is permitted. Where dead ends are on a slope of zero and one one-hundredths (0.01) or greater, the length for use of a cleanout may be extended to three hundred (300') feet.

2. Location. End structures shall be located ten (10') feet up grade from the down grade lot line of the last lot served unless greater length is necessary to serve the property.

3. Design. Cleanouts shall be constructed generally in accordance with Plate 8.

C. Service Laterals.

1. Requirements. Wherever it is known or can be reasonably assumed that a building sewer connection is required, a service lateral shall be shown on the plans and installed to the property line as a part of the street sewer construction, prior to paving. Service laterals shall be installed whenever possible during construction of the sewer main using prefabricated fittings.

2. Size. Service laterals for single dwellings and small single stores or offices shall be four (4") inches or larger, providing the Plumbing Code does not require the building sewer to be larger than four (4") inches. All other service laterals shall be six (6") inches or larger and at least equal to the size of the building sewer.

This Subsection shall not apply to the Penn Valley Sewer System in District Zone No. 6.

3. Depth. Service laterals shall be at the minimum depths herein provided and in addition such depth shall be sufficient to provide a connection to any point on the lot within the established building setback lines (excluding any area steeper than five (5) horizontally to one (1) vertically) with a cover of one (1) foot and a slope on not less than zero and two one-thousandths (0.02.) Any exception to this requirement may be had only upon approval by the Director of Sanitation.

4. Design. Service laterals shall be constructed in general conformity with Plates 3 and 4.

5. Future Connections. Unused openings shall be tightly sealed, supported and permanently marked in a manner to facilitate their future location and use. Developer's engineer shall select appropriate service lateral locations and shall instruct contractor to locate laterals according to the design elevations and locations. The locations shall be shown on As-Built Plans by the developer's engineer.

Installation of service laterals not included in the original construction and all lateral maintenance will be the responsibility of the user.

6. Backflow. Sewers shall be designed to preclude the backflow of sewage into laterals. To prevent sanitary sewer overflows for municipal sewer customers, sewer laterals for new connections, significant remodels of fifty percent (50%) or more, and for replacements or repairs made to an existing sanitary lateral shall include:

a. Installation of pop-off relief devices (pop-off caps) in the caps of all sewer cleanouts on the property.

b. Installation of a backflow prevention device (backwater valve), to prevent sewage from the main sewer backing up into the private sewer lines due to cleaning or blockages in the main.

Backflow prevention and pop-off relief devices shall be installed as shown in Plate 11 of Section 30.07.030 of the Sanitation District Code.

7. Connection to Cesspools or Septic Tanks. A person shall not connect or cause to be connected any cesspool seepage pit or septic tank to any main line sewer or to any service lateral leading thereto.

This Subsection shall not apply to the Penn Valley Sewer System in District Zone No. 6.

8. Curb Markings. The location of all sewer service laterals shall be marked at completion of construction, either on the curb or by permanent stake if there are no curbs.

D. Structural.

1. Roads. All structures and pipe placed under public roads shall be of sufficient strength to support with an adequate factor of safety the backfill, road surfacing and H-20 truck loading with impact.

2. Other Pipes and Structures. Sewers under other pipes and structures shall be protected from damage and shall be constructed so as not to endanger the other pipe or structure. Minimum clearance between outside of pipes or between pipes and other structures is six (6") inches unless approved by the engineer.

3. Flexible Joints. Flexible joints which will allow for differential settlements or other movement of sewer pipe, sewer structures, adjacent pipe and adjacent structures shall be provided where sewer lines enter encasements, manholes or other structures. Flexible joints shall be within four (4') feet of such structures.

4. Steep Grades. Sewers laid on grades steeper than ten percent (10%), which are not under pavements, shall be anchored in place and protected from erosion in a manner approved by the engineer.

E. Force Mains and Lift Stations.

1. Requirements. All sewage shall reach the system by gravity flow, in a fresh condition susceptible to conventional sewage treatment processes. Where extreme hardship conditions prevail, and a substantial area cannot be sewered by gravity sewers in accordance with these requirements a sewage pumping station may be installed. No pumping facilities shall be incorporated in sewer plans without approval of the engineer.

2. Lift Station Design. Lift stations, where allowed, shall be of the dry-pit type incorporating the following features:

a. Pumps or other devices shall be provided in duplicate arranged for positive priming.

b. Capacity shall be provided to handle ultimate peak flow from the tributary area with the largest pump out of service. Stage installation of pumps is allowed, providing space is provided for future installations. Single pump installations will not be allowed.

c. Access shall be provided to site for removal and repair of equipment.

d. A means for dewatering force mains shall be provided.

e. An overflow to natural channel or storm drain shall be provided or an alternate method of protection approved by the engineer.

f. The lift station shall not be in a County road right-of-way except with permission from the engineer.

3. Force Main Design. Force mains need not comply with the requirements for gravity sewers. Force mains shall be designed in accordance with good engineering practice.

(SD-5. (03/26/1979); SD-17. (02/04/1992); SD-73. (08/11/2015); SD-75. 11/07/2023); SD-75. 11/07/2023)

A. Requirements. Materials shall be chosen for their strength, durability, and ease of maintenance, with due consideration for dead and live loads, beam strength, and resistance to corrosion. Pipe joints shall be selected to provide positive protection against entrance of roots and groundwater, and sufficient flexibility to adjust to the trench bedding. In general, the joints shall be non-rigid, and the joint sealer shall be restrained against lateral and axial movement. The installed joint shall provide positive separation between adjoining pipe sections to prevent failure of rigid materials by axial expansion during wetting.

B. Plans. For each section of sewer, the plans shall show that materials and strengths are required in accordance with Plate 1. Pipe strength, pipe bedding, and trench width shall be specified on the plans (see Plate 1).

C. Materials Specifications. All materials for which specifications are provided by the Nevada County Standards shall meet those specifications. Specifications for materials not covered by the Standards are subject to the approval of the engineer.

D. Pipe Material.

1. Corrosion resistant sewer pipe material shall be vitrified clay, rigid polyvinyl chloride, reinforced plastic mortar, plastic lined asbestos cement pipe or other pipe material approved by the engineer.

2. Other sewer pipe material not required to be corrosion resistant shall be vitrified clay, plastic lined asbestos cement, unlined asbestos cement, reinforced concrete, reinforced plastic mortar, cast iron, or other pipe material approved by the engineer.

E. Pipe Joints. Mechanical compression joints shall be used. Standard Land Development Specifications Type "A" and "B" joints for clay pipe and any other poured or formed joints utilizing cement, sulfur compounds, bituminous materials or other materials forming a rigid joint are not permitted. Special adapters using approved type joints shall be used in connecting to old work or in joining different types or classes of materials.

F. Concrete.

1. All concrete for sewer structures and sewer pipe encasement shall be Class 6.0 C-3000 unless otherwise approved or required by the engineer.

2. Testing and Final Acceptability of Material. The engineer will require such tests and certifications as he or she deems necessary to show that the specified materials are being used on the work. Notwithstanding prior factory or yard inspections, the Engineer will have the right to reject any damaged or defective materials found on the job which in his or her opinion will affect the durability of the installation, and the engineer may order its removal from the site.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

A. Specifications. Construction shall be in accordance with Nevada County Standards except where the requirements of this Chapter are more restrictive.

B. Bench Marks. A system of bench marks on the U.S.C. & G.S. Sea Level Datum of 1929 and adequate to construct the work shall be shown on the profile. The elevation of the sewer at the point where the system is to be discharged shall be shown as determined in the field from the above shown datum.

C. Excavations. All excavations shall have sufficient width to allow proper workmanship and permit adequate inspection and shall be supported in the manner set forth in the rules, orders and regulations prescribed by the Construction Safety Orders of the Division of Industrial Safety of the State of California. Sheet piling and other timbers shall be withdrawn in such a manner as to prevent caving of the walls of the excavation or disturbance of the sewer. Trenches wider than provided for on Plate 2 may require stronger pipe. Before any trench excavation five (5') feet or more in depth, the Contractor shall secure a permit from the California Division of Industrial Safety. A copy of this permit must be available at the construction site.

D. High Groundwater. No work shall be commenced on sewer construction in an area having a subsurface water level above the level of the sewer, unless and until sufficient pumping equipment is available on the job to keep the excavation unwatered.

E. Work and Plans Shall Conform. All plans required for the construction of main line sewers and house laterals shall conform to the standards of design prescribed. Construction shall conform to the plans unless a change is approved in writing by the engineer.

F. Inspection by Engineer Required. All work done shall be subject to inspection by and shall meet the approval of the engineer.

G. Testing. Prior to testing, the pipe installation shall be cleaned by the use of an inflatable rubber ball fit snugly in the pipe and forced through by water pressure. Each section of sewer constructed shall be tested in accordance with acceptable "Low Pressure Air Test for Sanitary Sewers" methods such as presented in the Journal of Sanitary Engineering, Division ASCE, April 1964.

H. As Built Plans.

1. Plans. The actual location and grade of all sewers shall be accurately determined after construction and shall be recorded on "As Built" plans. Accurate locations and elevations of all service laterals, manholes, cleanouts, lift stations and other sewer appurtenances shall also be marked on the "As Built" plans.

2. Certification. The "As Built" plans shall be certified as being correct by the Developer's Engineer or the Purveyor's Engineer.

3. Filing. A reproducible mylar or equivalent of the "As Built" plans shall be filed with the Engineer.

(SD-5. (03/26/1979); SD-75. 11/07/2023)

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