B08_-_Atch_1_-_Oasis_irrigation_SOW.pdf

Joshua Tree National Park

Project Title: Restore Hydrologic Conditions and Enhance Vegetation at the Oasis of Mara

PMIS Number: 265252

Location: Oasis of Mara at Joshua Tree NP Oasis Visitor Center Twentynine Palms, CA

Statement of work (SOW) for the removal and replacement of existing Oasis of Mara Irrigation system

Synopsis: Project will replace irrigation water system in the Oasis of Mara from and including the Utility Vault to farthest west fan palms as shown on included map. All fan palm locations except for location D will be watered by the replacement irrigation system. Note that 1” lateral lines travel underneath a sidewalk in up to six locations. If cutting the concrete sidewalk is required, contractor to repair sidewalk back to existing condition.

TASKS

Item Task__________________________________________________________________________

1. UTILITY VAULT

a. With a Cultural monitor present, shut off water service and remove existing utility vault, backflow prevention device, shut off valves, piping, and meter.

b. Install and reconfigure equipment and fittings to include: 2” galvanized steel pipe to 2” ball valve and union, 2” x 1 ½” reducer, new strainer with a minimum of 150 mesh (Uniram may require 200 mesh), new check valve with support stand and 14” x 14” x 6”concrete footing, new pressure reduction valve with a pressure gauge upstream and downstream, 1 ½” x 2” reducer, hose bib, ball valve, and union, and other necessary galvanized fittings (as per vault schematic).

c. Replace existing gate valves for service to nursery and oasis with same sized ball valves and reconnect to correct lines. Abandon 1” gate valve and PVC line.

d. Install new 2” water meter on oasis main line. After the water meter on the oasis main line install, below grade and within an irrigation box, a 2” DIG (305DC-200) solar powered irrigation valve with a union on each side to facilitate replacement. Outside of the box install the accompanying LEIT-2ET solar panel to power the valve.

e. Replace vault with precast or fiberglass structure of appropriate size to contain valves, piping, meter, etc. (5’ length minimum). Fill bottom 2” of vault with pea gravel.

2. OASIS IRRIGATION SYSTEM

a. PHASE 1: Dividing the removal and installation of irrigation pipe in the main part of the oasis into four phases will reduce the linear feet of open trench. Using a ditch witch, or hand digging, excavate and remove existing irrigation pipe and irrigation boxes from utility vault to the branch for the main oasis pool, and then on to the main pool and watering site A. All open trenches shall be identified with bollards or folding traffic barricades and caution tape for the entire duration that they are open.

i. Install new 2” schedule 40 PVC main line irrigation pipe at a depth of 18” from the utility vault to the main pool branch.

ii. Install 2” x 1” tee in the same location where the old system branched to the main pool (site A is located on a secondary branch from the lateral leading to the main pool)

iii. Install a new irrigation box and 1” PVC ball valve on 1” lateral line within 6’ of the 2” main line to provide a shut off for maintenance of each section of the system.

iv. Pound in one 12” piece of rebar next to the irrigation box to allow for location with a metal detector should the box get buried.

v. For the main pool, connect to the existing line to the southeast of the concrete oasis walkway thereby avoiding need to bore under or cut concrete sidewalk.

Do not disturb anything inside the walkway. Near the point of the connection install within an irrigation box a 1” brass adjustable pressure regulator with a union upstream, a 1” brass ball valve immediately downstream followed by a union.

vi. A branch upstream from this irrigation box will serve tree A (see map). Install 1” tee in the same location where the old system branched to tree A.

vii. At tree A, a 1” PVC tee will terminate the lateral line with reducers and fittings to connect to the Uniram poly pipe (Netafim Uniram AS XR 16012 providing 0.7 L/H and with a 1.0 meter spacing between emitters) which shall be installed at a depth of 12” and in a complete circle around the tree. The polypipe trench will be dug by hand and will be a circle with a radius of 10’ from the base of the tree (circumference of roughly 63’ or 19 m).

viii. Backfill and compact soil into trench.

b. PHASE 2: Dividing the removal and installation of irrigation pipe into four phases will reduce the linear feet of open trench in the oasis at any given time. Using a ditch witch, or hand digging, excavate and remove existing irrigation pipe and irrigation boxes from the branch for the main oasis pool to the oasis trail midpoint (roughly: E 588458 N 3776800). All open trenches shall be identified with bollards or folding traffic barricades and caution tape for the entire duration that they are open.

i. Install new 2” schedule 40 PVC main line irrigation pipe at a depth of 18” from the main pool branch to the oasis trail midpoint (approximately location of branch to site D).

ii. Install 2” x 1” tees in the same locations where the old system branched to sites B and C.

iii. Site D will be abandoned, and any existing main line PVC tee will be replaced by straight pipe.

iv. Install a new irrigation boxes and 1” PVC ball valve on each 1” lateral line within 6’ of the 2” main line to provide a shut off for maintenance of each section of the system.

v. Pound in one 12” piece of rebar next to the irrigation box to allow for location with a metal detector should the box get buried.

vi. Connect to existing line where it crosses under the sidewalks at sites B and C. If not possible, bore or cut concrete to lay new pipe. Repair cut sidewalk back to existing condition if applicable.

vii. At tree groups B and C, a 1” PVC tee will terminate the lateral line with reducers and fittings to connect to the Uniram poly pipe (Netafim Uniram AS XR 16012 providing 0.7 L/H and with a 1.0 meter spacing between emitters) which shall be installed at a depth of 12” and in a complete circle around the group. The polypipe trench will be dug by hand and will be a circle with a radius of 10’ from the base of the tree (circumference of roughly 63’ or 19 m).

viii. In tree groups where a complete circle isn’t possible, the uniram will be installed in both directions around the circle as far as possible and folded and terminated with a figure 8 closer at each end.

c. PHASE 3: Using a ditch witch, or hand digging, excavate and remove existing irrigation pipe and irrigation boxes from the oasis trail midpoint to tree group J. This phase of the project will focus on tree groups E, G, H, I, and J. All open trenches shall be identified with bollards or folding traffic barricades and caution tape for the entire duration that they are open.

i. Install new 2” schedule 40 pvc main line irrigation pipe at a depth of 18” from the oasis trail midpoint (approximately site D) to just beyond tree group H.

ii. Install 2” x 1” tees in the same locations where the old system branched to sites F, G, H, and I.

iii. Install a new irrigation box and a 1” PVC ball valve on each 1” lateral line within 6’ of the main line to provide a shut off for maintenance of each section of the system.

iv. Pound in one 12” piece of rebar next to each irrigation box to allow for location with a metal detector should the box get buried.

v. Connect to the existing line to sites E and F thereby avoiding need to bore under or cut concrete sidewalk. If not possible, bore or cut concrete to lay new pipe.

Repair cut sidewalk back to existing condition if applicable.

vi. At trees E and J, a 1” PVC tee will terminate the lateral line with reducers and fittings to connect to the Uniram poly pipe (Netafim Uniram AS XR 16012 providing 0.7 L/H and with a 1.0 meter spacing between emitters) which shall be installed at a depth of 12” and in a complete circle around the tree. The polypipe trench will be dug by hand and will be a circle with a radius of 10’ from the base of the tree (circumference of roughly 63’ or 19 m).

vii. At groups G, H, I and J a 1” PVC tee will terminate the lateral line with reducers and fittings to connect to the Uniram poly pipe (Netafim Uniram AS XR 16012 providing 0.7 L/H and with a 1.0 meter spacing between emitters) which shall be installed at a depth of 12” and in a complete circle around the group. The polypipe trench will be dug by hand and will be a circle with a radius of about 10’ from the base of the tree/ group (circumference of roughly 63’ or 19 m).

viii. Tree group E and I will be flood irrigated and will not need polypipe installed.

The 1” line to these groups will have a 1” brass adjustable pressure regulator with a union upstream, a 1” brass ball valve immediately downstream followed by a union within an irrigation box 10’ from the base of the tree. Pound one 12” piece of rebar next to the irrigation box to allow for location with a metal detector should the box get buried.

ix. Termination will be 5’ from the base of the tree and will consist of an aboveground PVC riser that rises 8” above grade and curves 180 degrees to face the ground.

x. NPS employees may place sandbags (filled with weed free sand from outside the oasis) in a circle 6-8’ from the tree trunk to prevent water runoff and increase availability to the tree’s root system.

d. PHASE 4: Using a ditch witch, or hand digging, trench from tree group H (E 588407, N 3776805) west to the Julie Miller extension trail and down the trail to the point where irrigation should turn north to tree group K (roughly E 588337, N 3776800) and then further along the trail to the end of the main line where irrigation should turn north to tree group L (roughly E 588251, N 3776795) which is the end point for the 2” main line. This phase deviates from the existing route of the irrigation and must be kept within 10 feet of the walkway near the western end of the oasis. All open trenches shall be identified with bollards or folding traffic barricades and caution tape for the entire duration that they are open.

i. Install new 2” schedule 40 PVC main line irrigation pipe at a depth of 18” from tree group H to end of main line.

ii. Use 2” x 1” tees for each tree groups K and L.

iii. Install a new irrigation box and 1” PVC ball valve on each 1” lateral line within 6’ of the main line to provide a shut off for maintenance of each section of the system.

iv. Pound in one 12” piece of rebar next to each irrigation box to allow for location with a metal detector should the box get buried.

v. At each tree group K, L2, and L3 a 1” PVC tee will terminate the lateral line with reducers and fittings to connect to the Uniram poly pipe (Netafim Uniram AS XR 16012 providing 0.7 L/H and with a 1.0 meter spacing between emitters) which shall be installed at a depth of 12” and in a complete circle around the group.

The polypipe trench will be dug by hand and will be a circle with a radius of about 10’ from the base of the tree/ group (circumference of roughly 63’ or 19 m).

vi. Tree group L1 will be flood irrigated and will not need polypipe installed. The 1” line to this group will have a 1” brass adjustable pressure regulator with a union upstream, a 1” brass ball valve immediately downstream followed by a union within an irrigation box 10’ from the base of the trees. Pound one 12” piece of rebar next to the irrigation box to allow for location with a metal detector should the box get buried.

vii. Termination will be in the ditch at the base of these trees and will consist of an aboveground PVC riser that rises 8” above grade and curves 180 degrees to face the ground. Sandbags will probably not be needed for this location.

3. When all three phases are complete, approximately 2800 linear feet of existing PVC pipe will be removed and approximately 2800 linear feet of new PVC pipe will be installed. The ditch witch is 3 feet wide and will be used to excavate main and lateral lines (polypipe lines will be dug by hand) resulting in the disturbance of 8310 square feet of surface area that will require vegetative restoration. To the greatest extent possible, new PVC irrigation line should be laid in the footprint of existing line after it has been removed.

GENERAL INFORMATION

1. ENVIRONMENTAL COMPLIANCE REQUIREMENTS

a. Joshua Tree has identified a threatened species, the desert tortoise (Gopherus agassizii), in and around the Oasis of Mara. As such, any open trench in the oasis must be filled or fenced at the end of each workday. Fencing can consist of plastic construction fencing or chicken wire/ hardware cloth folded out away from the trench along the ground for 6” and installed on posts (rebar) driven into the ground.

b. An NPS cultural resources monitor shall be present whenever ground disturbance is occurring.

c. The Contractor and all employees working on the Project will be required to take “Desert Tortoise Awareness Training” which will be provided by the Government at no cost to the Contractor. This training will take approximately 30 minutes or less.

d. The Contractor’s employees shall never handle a desert tortoise.

e. The Contractor and employees shall immediately report the presence of any desert tortoise to the COR.

2. PERIOD OF PERFORMANCE

a. The total performance period for this contract is 120 days after notice to proceed is issued.

3. HOURS OF OPERATION

a. Hours of operation shall be Monday through Friday between the hours of 7:00 AM and

5:00 PM unless alternate hours are approved by the Contracting Officer (CO). Any requests to work outside of normal working days and hours shall be submitted to the CO and COR at least 3 business days before the requested event for authorization.

4. PROJECT COORDINATION AND COMMUNICATION

a. Contractor shall coordinate with the COR on the schedule. The contractor shall notify the COR of any changes to the schedule as soon as possible.

DIAGRAM