B08_Attach_6_Basis_of_Design_with_Civil_Calculations.pdf

Haleakala National Park (HALE)

BASIS OF DESIGN – FINAL SUBMITTAL

PROJECT: HALE 259822, Install 50,000 Gallon Buried Filtered Water Tank at Haleakala National Park, Maui, Hawaii, Title II – Design Development Services

DATE: March 29, 2024

LOCATION: Haleakala National Park (HALE), Maui, Hawaii

FROM: Kaula AE

Background

This project is located at Haleakala National Park (HALE) on the island of Maui and includes providing a filtered water tank within the existing water system. The objective of the project is to provide additional water storage for the existing water system.

Scope of Work

Major features of the project include the following:

A new 50,000 gallon, partially buried, cast-in-place concrete water tank.

A bypass water system for use during construction and for permanent installation after construction.

New water tank distribution piping, fittings, and appurtenances to connect the new filtered water tank to the existing water system.

Bid Option A: A vehicle turnout with a compacted gravel surface for one to two vehicles to park parallel to the existing service road with a low-profile masonry rock wall and metal railing.

Bid Option B: A vehicle turnout with a asphalt concrete pavement surface for one to two vehicles to park parallel to the existing service road with a low-profile masonry rock wall and metal railing.

Bid Option C: Exterior tank coatings for the filtered water tank.

The filtered water tank is intended to provide additional water storage for fire flow and drought conditions. The filtered water tank will be used to replenish the potable domestic water supply quickly by refilling the existing treated water tank to be chlorinated immediately.

Existing Conditions

The existing water system includes a rain catchment structure, which collects water and directs the water to two raw water tanks. The raw water tanks gravity feed the water to two slow sand filter tanks located near the project site. Water gravity flows from the slow sand filters via a 4-inch water distribution pipe. The pipe is partially buried and then runs aboveground for approximately two hundred feet in the project area. Filtered water flows by gravity to a chlorination room and treated water is stored in a 50,000-gallon buried water tank.

Treated water is used by the Headquarters area, maintenance, and Hosmer Grove.

The project site is located northwest of the existing slow sand filter tanks. The topography of the site for the filtered water tank slopes downward at varying degrees from approximately 15% to 20% grade. Nearby slopes have gradients between approximately 30% and 60%.

A topographic survey was performed in the earlier phase of this project.

Basis of Design – FINAL HALE 259822, Install 50,000 Gallon Buried Filtered Water Tank at Haleakala National Park, Maui, Hawaii

Filtered Water Tank Design Considerations

The water in the slow sand filter tanks will gravity feed to the filtered water tank. Based on the elevations obtained from the topographic survey, record drawings, and field measurements, the hydraulics of the system will control the position and location of the filtered water tank. The filtered water tank will be in line with the existing water distribution piping and flow by gravity to the existing chlorination room and treated water tank.

Based on the elevations from the topographic survey and field measurements, the water surface elevation in the slow sand filter tanks is approximately 7347.6 feet. The filtered water will gravity flow to the filtered water tank. The filtered water tank will be interconnected to the slow sand filter tanks; therefore, it is expected that the water level in the filtered water tank would be slightly lower than the water level in the slow sand filter tanks due to losses through the slow sand filter and the piping to the filtered water tank.

It was observed during the site visit in September 2023 that the slow sand filter outlet piping had been modified from the original installation and appeared to be causing a bottleneck in the system. However, after discussions with NPS, it was determined that the outlet piping had been modified for two purposes. According to NPS personnel, one of the purposes for the modification of the outlet piping was to provide a 1” vertical branch to provide an air relief to break any siphon that could occur. The second purpose for reducing the outlet piping to a 1” pipe was to reduce the flow rate in the slow sand filter to allow the water to filter properly. A high outlet flow rate caused the slow sand filter to drain the lower portion of the filter too quickly and would potentially impact the filter media above, which would result in a slower filtration rate.

During the site visit, it was observed from the flow meter on the 1” outlet piping, that the flow through one slow sand filter tank was 2.5 gallons per minute. During the site visit, the slow sand filter tank appeared to be full.

Therefore, it was assumed that each tank would produce a flow rate of approximately 2.5 gallons per minute for a total of 5 gallons per minute when both slow sand filter tanks were in operation. In the 1979 Haleakala National Park Headquarters Area Water System Improvements and Comfort Station Study Engineering Report, it was indicated that each slow sand filter would be sized to meet a flow rate of 5.0 gallons per minute. It appears that the existing slow sand filter tanks are operating at approximately half their design flows. The existing flow rate from the slow sand filter outlet measured during the site visit was used to determine the losses through the piping and appurtenances.

Based on the exterior slow sand filter tank water gauges, the existing slow sand filters had two slightly different levels of losses through the filter. It was assumed that filter media in one sand filter was cleaner than the other.

Losses through the slow sand filter tanks appeared to range between 9 inches and 12 inches. The higher loss was used to calculate the losses in the system. Based on the calculations, it was determined that the filtered water tank would have a water level of elevation of approximately 7346.5 feet. Hydraulic water calculations are included in Appendix A.

Downstream of the slow sand filter tanks, the existing water distribution pipe goes below grade for a short portion and returns above grade to an approximate elevation of 7345 feet. Because the topographic survey included limited pipe invert elevations for the existing pipe, field measurements were used to estimate the invert of the existing 4 inch pipe that would connect to the outlet of the filtered water tank.

To provide a filtered water tank with a 50,000-gallon nominal capacity, and fit within the existing hydraulic constraints of the site and existing system, a 4.5 feet water volume depth was selected. The selected water depth allows water to flow by gravity from the existing slow sand filters to the filtered water tank and flow by gravity to the existing treated water tank, which is located at an elevation several hundred feet below the filtered water tank.

Design Criteria

The filtered water tank will be cast-in-place concrete, partially buried. The filtered water tank will be provided with inlet and outlet piping, isolation valves, a bypass system, check valve, air relief valve, two roof access hatches, roof vent, a fill pipe that would allow trucks to haul water and fill the tank, and an overflow and drain

Basis of Design – FINAL HALE 259822, Install 50,000 Gallon Buried Filtered Water Tank at Haleakala National Park, Maui, Hawaii line daylighting to a concrete headwall. All wetted surfaces will be NSF-61 approved. The tank interior will be coated with an NSF-61 approved coating.

The tank will be partially buried and will have 2.5:1 earthen slopes down the sides.

The filtered water tank will have the following characteristics:

Nominal capacity: 50,000 gallons Tank interior length: 62.0 feet Tank interior width: 24.0 feet Tank design water level: 4.5 feet Freeboard: 1.0 feet Tank interior wall height: 5.83 feet Liquid to be stored: Filtered water

Operation of Filtered Water Tank

Due to the hydraulics of the existing system, the water from the existing slow sand filters will flow by gravity to the filtered water tank. However, due to the variation of head loss through the slow sand filters, the water level may fluctuate in the filtered water tank. Therefore, three outlet pipes at different vertical elevations will be provided for the filtered water tank. The top outlet pipe will be near the surface of the water level when the filtered water tank is full. The top outlet pipe will have an isolation valve that is normally open. The middle outlet pipe will be approximately in line with the existing water line downstream of the tank, where the outlet pipe manifold connects to the existing piping. The isolation valve on the middle outlet pipe will be normally open. The bottom outlet pipe will be near the bottom of the filtered water tank and have an isolation valve that is normally closed.

The isolation valves would allow the flow to be discharged from the selected outlet pipes. During normal operations, the top outlet pipe and middle outlet pipe will be open and the bottom outlet pipe will be closed.

This will allow the water to flow through continuously when the filtered water tank is filled. However, during a situation when the entire tank capacity is needed to replenish the potable domestic supply quickly, the bottom outlet pipe will be opened to allow the full tank volume to be utilized and discharged to the chlorination system and the treated water tank below. Isolation valves would also be utilized when bypassing the tank during maintenance.

HALE 259822, Install 50,000 Gallon Buried Filtered Water Tank at Haleakala National Park, Maui, Hawaii Basis of Design, Final Submittal March 29, 2024

A P P E N D I X A

Hydraulic Water Calculations

COMPUTED BY: ST

CHECKED BY:

DATE: 10/25/2023

Head Loss Calculations

Head Loss through Sand Filters

Maximum Reference 3 feet to 4 feet GFD #2 Water System Engineering Report (1979)

If losses reach the maximum level, filter must be cleaned

Range Observations 9 inches to 12 inches

Assumed 0.75 feet to 1 foot of head loss through sand filter

Based on observations during site visit, the flow meter readings indicated:

Flow through one tank was measured as 2.5 gpm Flow through two tanks was assumed to be 5 gpm

Hazen-Williams Equation for Head Loss through Pipe hf = 4.73 (Q/C)^1.852 (L/D^4.87) where:

hf = head loss due to friction, ft Q = flow rate, cfs C = Hazen Williams coefficient L = length of pipe, ft D= inside diameter of pipe, ft

Friction Losses through Pipe

Description

Diameter

(ID),

inches ID, ft Area, sf 3" DI pipe (existing) 3.46 0.29 0.065 1" copper pipe (existing) 1.025 0.09 0.006 3" galv steel pipe (existing) 3.068 0.26 0.051 4" galv steel pipe (existing) 4.026 0.34 0.088 4" galv steel pipe (existing) 4.026 0.34 0.088 4" DI pipe (new) 4.3 0.36 0.101

Calculate: Head losses through existing water system to determine appropriate water level in the filtered water tank.

From Site Visit on 9/8/23 - photos of tank

DATE: 10/25/2023

Friction Losses through Pipe (continued)

Conversion: 7.48 gal to cf

Description Flow rate, gpm Flow rate, cf/min Flow rate, cfs Velocity, ft/s

Pipe Length, ft

C, Hazen Williams coefficient hf, ft 3" DI pipe (existing) 2.5 0.334 0.006 0.085 1.8 120 0.000 1" copper pipe (existing) 2.5 0.334 0.006 0.972 5.7 130 0.035 3" galv steel pipe (existing) 2.5 0.334 0.006 0.109 1.7 100 0.000 4" galv steel pipe (existing) 2.5 0.334 0.006 0.063 15.1 100 0.000 4" galv steel pipe (existing) 5 0.668 0.011 0.126 14.3 100 0.001 4" DI pipe (new) 5 0.668 0.011 0.110 35.7 130 0.001

Total friction losses, ft = 0.037

Minor Losses through Pipe Fittings where:

hf = head loss, ft v = velocity, ft/s g = acceleration due to gravity, 32.2 ft/s^2 K = loss coefficient

1 inch fittings Flow rate = 2.5 gpm Velocity = 0.9721 ft/s

Description K coefficient # fittings head loss, hf Notes 1" 90 degree bend, copper 0.75 3 0.033 90 deg bend, medium radius elbow 1" gate valve 0.19 1 0.003 Wide open 1" copper increaser 0.19 1 0.003 sudden enlargement 1-1/2" flow meter 0.19 1 0.003 assume similar to a gate valve, wide open 1" copper reducer 0.25 1 0.004 reducer, ordinary 1" copper strainer 0.6 1 0.009 assume similar to standard run of tee 1" copper tee, flow through branch 1.5 1 0.022 Standard tee

Total losses, ft = 0.076 ft ℎ 𝑘 𝑣 2𝑔

DATE: 10/25/2023

3 inch fittings (flow from one tank) Flow rate = 2.5 gpm Velocity = 0.1085 ft/s

Description K coefficient # fittings head loss, hf Notes 3" gate valve 0.19 1 0.0000 gate valve, wide open 3" x 1" reducer 0.25 1 0.0000 Reducer, ordinary 3" galvanized steel tee, flow th 0.6 1 0.0001 Standard run of tee 3" x 4" galvanized reducer 0.19 1 0.0000 Sudden enlargement

Total losses, ft = 0.0002 ft

4 inch fittings (flow from two tanks) Flow rate = 5 gpm Velocity = 0.1105 ft/s

Description K coefficient # fittings head loss, hf Notes 4" 90 deg bend 0.3 1 0.0001 90 deg elbow regular flanged 4" tee (through) 0.6 2 0.0002 Tee, standard run of tee 4" 11.25 deg bend 0.09 1 0.0000 0.25 x sqrt (angle/90) 4" 22.5 deg bend 0.15 1 0.0000

Total losses, ft = 0.0003 ft

Total minor losses = 0.076 ft

Total losses through system, upstream of water tank

Loss through sand filter = 0.75 to 1 ft observed through site photos, approximate, to be confirmed Losses through pipe = 0.037 ft

Minor losses = 0.076 ft Total losses = 0.863 ft Lower range Total losses = 1.113 ft Upper range

Range = 0.863 feet to 1.113 feet

Water level elevation in existing sand filter tank = 7347.6 ft Based on field measurements and topographic survey elev.

Losses (lower range) = 7346.7 ft

Losses (Upper range) = 7346.5 ft

22 1/2 deg bend - use half of loss of 90 deg

Use this elevation to set the water level in the new filtered water tank