**NATURAL RESOURCES CONSERVATION SERVICE**

**Idaho**

**CONSTRUCTION SPECIFICATIONS**

**FOR**

> **IRRIGATION WATER CONVEYANCE**
>
> **LOW PRESSURE UNDERGROUND PLASTIC (LARGE DIAMETER)**

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

(Owner/Operator)

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

(Project/Title)

GENERAL

This specification covers the installation and materials for
low-pressure plastic pipe larger than 18-inch diameter. Pipelines shall
be installed in accordance with a design and plan approved by the
responsible technician. Details of construction shown in the design and
plan but not included here shall be considered as a part of this
specification. Construction activities shall be in accordance with
applicable OSHA regulations.

TRENCH CONSTRUCTION

Trench width at any point below the top of the pipe should be only wide
enough to permit the pipe to be easily placed and joined and to allow
the initial backfill material to be uniformly placed under the haunches
and sides of the pipe. The minimum trench width shall be 24 inches
greater than the pipe diameter for mechanical compaction and not less
than 18 inches greater than the pipe diameter for water saturated
compaction. The maximum trench width should be no greater than 36 inches
wider than the diameter of the pipe. Trench banks that are more than 5
feet high shall be shored or sloped. Refer to Figure 1 for typical
trench details.

Where rock, hardpan, cobbles or other hard material which might prevent
the pipe from being uniformly supported is encountered in the bottom of
the trench, the trench shall be undercut a minimum of four inches below
final grade. The over cut area of the trench will then be filled with
sand or fine-grained soil.

BEDDING

The pipe shall be firmly and uniformly bedded throughout its entire
length. Bedding material shall be placed and spread in uniform layers
and in such a manner as to fill the trench so there are no unfilled
spaces below the pipe. For pipe with bell joints, holes shall be dug in
the bedding at the bells to permit the body of the pipe to be in contact
with the bedding along its entire length. Blocking or mounding shall not
be used to bring the pipe up to final grade.

PIPE INSTALLATION

Pipe shall be the diameter, length, material and pressure class as
specified on the drawings.

The pipe shall not be dropped into the trench or handled in a manner to
cause damage. Individual joints of pipe shall be inspected and any
damaged pipe shall be removed and replaced. The pipe will be allowed to
come within a few degrees of the temperature it will have after it is
completely backfilled before placing fill other than that needed for
shading or before connecting the pipe to other facilities.

Hand, mechanical or water packing are optional methods for placing and
compacting pipe backfill.

[Initial Backfill]{.underline}. Pipe with a pressure rating of less than
50 psi shall be filled with water prior to placement of backfill
materials and maintained near the design working pressure during the
backfilling operations. The initial backfill material shall be either
(1) angular 1 to ¼ inch size crush stone with a maximum of 10 percent
cohesive fines or (2) sand and gravels (Soil types GW, GP, SW, and SP)
with a maximum particle size of 1 inch containing a maximum of 12
percent of noncohesive fines. Sands shall have a maximum of 45 percent
passing the \# 40 sieve. The initial backfill materials shall be placed
in a manner as not to displace, deform or damage the pipe. The initial
backfill materials shall be placed in four to six inch lifts. Each lift
shall be shoveled and tamped between the pipe and the edge of the trench
wall. Care shall be taken to assure that all voids are filled under the
haunch of the pipe.

When backfilling is done by hand or mechanical means the initial fill
shall be compacted firmly around and above the pipe to achieve a soil
density equal or greater than the density of the undisturbed side walls
of the trench. When water packing is used, the pipe shall be filled with
water. The initial backfill, before wetting, shall be of sufficient
depth to ensure complete coverage of the pipe with backfill after
consolidation has taken place. Water packing shall be accomplished by
adding water to diked reaches of the trench in such quantity as to
thoroughly saturate the initial backfill. After the backfill is
saturated, the fill shall be consolidated by rodding or with a vibrator.
The wetted fill shall be allowed to dry until firm before completing the
final backfill. The pipeline shall remain full of water until after the
final backfill is made. Water packing shall be only used on sites with a
freely draining subgrade.

[Final Backfill]{.underline}. The final backfill material shall be soil
or sand free of rocks, frozen clods or other debris larger than 1inch in
diameter within 6 inches of the pipe and 6 inches in particle size for
the remaining portion of the final backfill unless otherwise specified
on the drawings. The material shall be placed and spread in
approximately uniform layers so there are no unfilled spaces in the
backfill. Rolling equipment shall not be used until a minimum of 18
inches of compacted backfill material has been placed over the top of
the pipe. Final backfill may be mounded over the top of the trench above
ground level, but in no case shall the final backfill be lower than the
natural ground along the top of the trench.

All special backfilling requirements of the pipe manufacturer shall be
followed.

[Cover]{.underline}. The minimum depth for backfill over the top of the
pipe shall be 30 inches.

At low places on the ground surface or at locations where it is shallow
to rock, extra fill may be placed over the pipeline to provide the
minimum depth of cover. In such cases, the top width of the fill shall
be no less than 10 feet and the side slopes no steeper than 6 horizontal
to 1 vertical.

Vertical alignment of pipe shall be uniform and such as to maintain the
cover requirements unless otherwise noted on the drawings. If irregular
grades are required, thrust blocks, air releases, drains and other
appurtenances as needed shall be installed.

[Thrust Blocks]{.underline}. Thrust blocks shall be formed against a
solid trench wall. They shall be of the minimum size and materials as
specified on the drawings.

[Joints and Connections]{.underline}. All joints and connections shall
be constructed to withstand the design working pressure for the pipeline
without leakage and shall leave the inside of the pipeline free of any
obstruction which could reduce the pipe capacity below design
requirements, except that insert fittings for joining PE pipe are
permitted.

All fittings, such as couplers, reducers, bends, tees and endives shall
be made of material that is recommended for use with the type of pipe
specified and shall be installed in accordance with the recommendations
of the pipe manufacturer. Fittings made of steel or other materials
susceptible to corrosion shall (1) be wrapped with plastic tape meeting
the requirements of AWWA C 209 for Type I or II tape, or (2) coated with
coal-tar epoxy paint (Kippers-Bitumastic No. 300-M is an approved off
the shelf product), or (3) painted with one coat of urethane primer
applied at a rate of 2 to 3 mils thick and two or more coats of gloss or
semi-gloss Alkyd Enamel to provide a minimum thickness of 6 mils or (4)
coated with epoxy paint in accordance with the Steel Structures Council
(SSPC) Paint Specification \# 16.

Pipelines with solvent welded joints shall have expansion-contraction
couplers as indicated on the drawings. Couplers shall have a minimum
length of 14 inches.

Solvent for solvent cement joints shall conform to ASTM D 2564 for PVC
pipe and fittings, to ASTM D 2235 for Acrylonitrile-Butadiene-Styrene
pipe and fittings.

Rubber gaskets shall conform to ASTM D 3139.

MATERIALS

[Quality of Plastic Pipe]{.underline}. The compound used in
manufacturing the pipe shall meet the requirements of one of the
following materials:

1.  Polyvinyl chloride (PVC) as specified in ASTM D 1784 for Type I,
    Grade 1 or Type I, Grade 2 or Type II, Grade 1.

2.  Acrylonitrile-butadiene-styrene (ABS) as specified in ASTM D 1788
    for Type I, Grade 2 or Type I, Grade 3 or Type II, Grade 1.

3.  Polyethylene (PE) as specified in ASTM D 1248 for Grade P14, Class C
    or Grade P23, Class C or Grade P33, Class C or Grade P34, Class C.

Pipe shall have a maximum standard dimension ratio (SDR) of 51. Iron
pipe size (IPS) plastic pipe and I.D. controlled PE pipe meeting one of
the following ASTM specifications are acceptable under this Practice
Standard.

[ASTM SPECIFICATION]{.underline}

D 1785 Polyvinyl Chloride Plastic Pipe,

Schedule 40, 80 and 120

D 2241 Polyvinyl Chloride Pressure Rated Pipe

D 2672 Joints for IPS PVC Pipe Using Solvent

Cement

D 2740 Polyvinyl Chloride Plastic Tubing

D 1527 Acrylonitrile-Butadiene-Styrene Plastic

Pipe, Schedules 40 and 80

D 2282 Acrylonitrile-Butadiene-Styrene Plastic

Pipe

D2104 Polyethylene Plastic Pipe, Schedule 40

D 2239 Polyethylene Plastic Pipe Based on

Controlled Inside Diameter

D 2447 Polyethylene Plastic Pipe, Schedules 40

and 80, Based on Outside Diameter

D 2737 Polyethylene Plastic Tubing

D 3035 Polyethylene Plastic Pipe Based on

Controlled Outside Diameter

F 771 Polyethylene Thermoplastic High-Pressure

Irrigation Pipeline Systems

Plastic irrigation pipe (PIP) installed under this specification shall
be classified as low-head irrigation pipe or 50 psi plastic irrigation
pipe meeting the requirements of ASTM D 2241 or of ASTM D 2282 except
that:

1.  The outside diameters, wall thicknesses and tolerances in ASAE
    S376.1 "Design Installation and Performance of Underground,
    Thermoplastic Irrigation Pipe" shall apply.

2.  The minimum burst pressure requirements for water at 23 degrees C
    for PVC 1120 and 1220 plastic pipe, SDR 51 is 260 lb/in^2^ and for
    ABS plastic pipe SDR 32.5 and SDR 41 is 380 and 300 lb/in^2^.

Plastic pipe shall be marked with nominal pipe size (for example 10 in),
applicable material designation code (for example PVC 1120), pressure
rating for water at 23 degrees C (50 ft head or 22 psi, 50 psi, or
63psi), specification designation with which the pipe complies and
manufacture's name or trademark.

[Valves and Appurtenances]{.underline}. The pipeline valves and
appurtenances shall be of the size, type, material and pressure rating
as shown on the drawings. Unless otherwise shown on the drawings all
Butterfly valves shall be equipped with geared operators.

# Air and vacuum relief valves and/or combination air and vacuum relief valves shall be installed at locations shown on the drawings.

# 

# Pressure relief valves shall be stamped with the pressure at which the valve starts to open. Adjustable valves shall be sealed or otherwise altered to insure that the setting marked on the valve is not changed.

# 

# Check valves shall be rated as quick-closing, non-slamming.

# 

TESTING

When water is available at the time the pipe is installed the system
shall be given an operational test. This test shall consist of filling
the pipe with water, taking care to bleed of any air in the pipe. All of
the system components shall operate without difficulty. Leakage or
defects caused by poor materials or workmanship shall be replaced or
repaired. When water is not available to complete a test on 50 psi and
63 psi rated pipe, the installer shall provide a guarantee stating they
will return and fix leaks that are found when the pipe is initially
filled with water.

GUARANTEE

The installing Contractor shall certify that the installation conforms
to the requirements of this specification and furnish a written
guarantee protecting the landowner against defective materials and
workmanship for a period of less not than 1 year. The guarantee will
identify manufacturer of pipe and pipe markings.

ADDITIONAL SPECIFICATIONS

FIGURE 1

> TRENCH WIDTH AND BACKFILL REQUIREMENTS
>
> NATURAL GROUND
>
> FINAL BACKFILL
>
> 6" FINAL BACKFILL
>
> (Maximum particle size 1 inch)
>
> INITIAL BACKFILL

OD (Compacted select

0.7 OD 4" bedding materials)

> MINIMUM DIMENSIONS
>
> (If Necessary) 9 inches-Water Saturation
>
> 12 inches -- Mechanical Compaction
>
> TYPICAL TRENCH DETAIL
>
> 5 FT DEPTH, MAXIMUM
>
> NATURAL GROUND
>
> 1
>
> FINAL BACKFILL \*\*
>
> FINAL BACKFILL
>
> (Maximum particle
>
> size 1 inch)

OD

0.7 OD INITIAL BACKFILL

> (Compacted select
>
> bedding materials)
>
> 4" (If Necessary) MINIMUM DIMENSIONS
>
> 9 inches-Water Saturation
>
> 12 inches -- Mechanical Compaction
>
> ALTERNATIVE TRENCH DETAIL

DEPTH GREATER THAN 5 FEET

> \*\* Slope typically varies from ¾ to 1/1/2:1 or greater based upon
>
> material classification and other factors such as wetness, vibration,
>
> surcharge, etc. Refer to OSHA Subpart P for details.