BIBE_Stantec_Tech_Memo_Oak_Springs_Fill_Line_Cond_Assess_Final_2022_11_03_0003.pdf

Technical Memorandum

To: Steven Splitek National Park Service, Denver Service Center, US

From: Olugbenga Ibikunle, PhD., P.Eng.

Stantec 910 Louisiana Street, Suite 2600 Houston TX 77002-4916

Project/File: Big Bend National Park Condition Assessment of Park Water Systems /BIBE 317515 / Stantec #177311653

Date: November 03, 2022

Reference: BIBE 317515: Big Bend National Park-Rehabilitate Park Water Systems

1 INTRODUCTION

Stantec was retained by the National Park Service (NPS) to conduct a condition assessment of the water fill line that supplies water from Oak Springs to the storage tanks at Chisos Basin Water Plant in the Big Bend National Park, Chihuahuan Desert, Brewster County, Texas. The approximately 3 miles (16,000 ft) long pipeline is a 3.5 inches (88.9 mm) galvanized steel pipe that was installed in 1950s along a popular trail route and over a steep ridgeline. The pipeline was verified to have nominal outside diameter of 4 inches (101.6 mm) during field inspection. To our knowledge, the pipeline has not been inspected since 2002 when the last condition assessment was conducted, therefore the current condition assessment will help ascertain the as-is condition of the pipeline to establish degradation rate and determine the need for any rehabilitation and/or replacement work.

The field inspection was completed by Pipeline Inspection and Condition Analysis Corporation (PICA), whose core business is the inspection and condition assessment of pipelines ranging in size from 3 inches (75 mm) to 78 inches (1,975 mm).

This Technical Memorandum (TM) reports the outcome of the efforts associated with the condition assessment scope of work, and recommendations on necessary or applicable courses of action the NPS may take to manage the pipeline going forward. The TM focuses on the following:

• Establishment of the current condition(s) of the pipeline

• Estimation of pipe degradation rate

• Estimation of remaining service life of the pipeline

• Recommendation of renewal timelines and potential Operations and Maintenance (O&M) needs

1.1 Description of the Water Fill Line

The 3.5-inch diameter galvanized steel pipe was installed in 1955 and is about 3 miles long and jointed using mechanical couplings. The pipeline runs through a mountainous rocky area from Oak Springs to Chisos Basin. The inspection measurements were taken along the pipeline alignment from Chisos Basin (Station 0+00) to Oaks Springs. Appendix A presents a map of the pipeline route.

November 03, 2022 Steven Splitek

The following are the unique characteristics of the water fill line:

• Pipe Nominal Diameter: 3.5 inches (88.9 mm)

• Nominal Wall Thickness: 0.250 inches (6.35 mm)

• Pipe Length: 3.0 miles (~16,000 ft)

• External Coating: Zinc coating

• Internal Coating: Unknown

1.2 Failure Modes in Water Mains

The deterioration or failure of metallic water transmission mains can occur from a structural, hydraulic or water quality perspective or combination of two or more aspects. Steel watermains are subject to both internal and external corrosion, resulting in pitting and wall thinning that can eventually lead to leaks or burst failures.

• Structural failures occur when the structural integrity of the pipe or its ability to withstand the various applied loads imposed upon it is diminished. Structural failures result from an increase in applied loads, the deterioration of the pipe’s wall through corrosion or a combination of both.

• Hydraulic failures occur when the watermain is not able to supply water at the required flow rate or pressure, especially due a process known as tuberculation or scaling causing an increase in inner surface roughness and/or the reduction of pipe internal cross-sectional area, resulting from the build-up of corrosion products and/or deposition of minerals.

• Lastly, failure due to water quality in a watermain is also a result of internal corrosion, leading to discoloration of the conveyed water.

Table 1. Potential Failure Modes in Water Transmission Pipes

Mode of Failure Evaluation Considerations Concerns / Cause of Failure Internal Pressures • Hydraulic and surge modeling

• Review of operating history/data

• Pressures in excess of pipe rating

• Vacuum conditions in pipeline

• Increasing operating pressure

External Loading • Burial depth (dead load))

• Traffic loads (live loads)

• Bedding material and compaction

• Pipe ovality

• External loads in excess of pipe's strength

• Substandard construction

Corrosion • Remaining pipe wall thickness

• External corrosion

• Internal corrosion

• Reduced pipeline strength for internal pressure and external loading

Joint Failure • Inspect joints/welds

• Leak detection

• Weak points in pipeline

• Differential settlement and associated bending stresses

• Loss of beam support due to erosion of bedding

2 SUMMARY OF 2002 INSPECTION/ CONDITION ASSESSMENT PROGRAM

2.1 Project Aim and Methodology

In 2002, the National Park Service engaged the services of ConCeCo Engineering Inc. to complete a condition assessment survey of the 3.5-inch diameter galvanized steel water fill line. The purpose of the condition assessment program was to evaluate the impact of internal and external corrosion of the pipeline and to determine its remaining service life.

The condition assessment survey involved:

• Interviewing Park service personnel to gather background information and history of the pipeline,

• Visual inspection of the pipeline,

• Collection of representative soil samples for testing,

• Collection of close intervals potential readings along the pipeline,

• Collection of water samples at Oak Springs and Chisos Basin for testing,

• Collection of pipe wall thickness readings at bell-hole excavations and all exposed pipe locations,

• Visual inspection of the above ground piping and water tanks at Oak Springs and Chisos Basin to assess the impact of atmospheric corrosion.

2.2 Summary of 2002 Inspection Results

The summary of the findings from the 2002 condition assessment is as follows.

• There was no evidence of water leaks in the form of heavy vegetation growth or unexpected moist soil locations

• Operating pressure was 750 psi while static pressure when pumps are off is at 640psi

• Flow rate was found to be 50 gallons per minute with a water velocity of 1.688 ft/sec

• Flow meter at Chisos Basin is regularly clogged by small rust colored scale particles

• Soil was found to be moderately corrosive

• Soil moisture content indicated a low to mild corrosive environment

• Soil Sulfides levels, Sulfates levels and Chloride concentrations were negligible indicating no presence of depolarizing agents or microbiologically influenced corrosion

• Water sample analysis indicated slight tendency for internal corrosion although internal corrosion was not expected to be a major problem

• Visual inspection indicated some external corrosion and pitting at Stations 69+00 and 71+85.

Concrete cover was also observed to be worn off at the creek crossings at Stations 91+30 and 94+25

• Air release valve exhibited atmospheric corrosion at Station 119+60

• The remaining service life of the pipeline was calculated to be in excess of 15 years

• Internal pits ranging from 0.020 to 0.070 inches were detected with ultrasonic measurements.

The overview of the ultrasonic measurements taken at 16 locations is shown in Table 2.

Table 2. 2002 Ultrasonic Measurements of the Remaining Wall Thickness

Station Min (inches) Max (inches) Average (inches)

0+00 0.229 0.242 0.235

6+50 0.216 0.260 0.242

9+40 0.230 0.254 -

20+00 0.216 0.252 0.234

68+00 0.203 0.254 0.239

69+00 0.239 0.284 0.253

71+80 0.196 0.277 0.243

71+90 0.226 0.265 0.247

91+30 0.214 0.250 0.230

91+50 0.212 0.248 0.237

94+25 0.206 0.254 0.230

96+65 0.228 - 0.236

108+00 0.220 0.251 -

114+70 0.229 - 0.240

115+30 0.225 0.239 0.245

148+30 0.199 0.277 0.240

3 CURRENT INSPECTION/CONDITION ASSESSMENT PROGRAM

3.1 Phase 1: Pressure Test

Due to suspected leaks in the pipeline, NPS engaged HECO Engineering in February 2022, to complete pressure testing on the fill line as part of Phase 1 of the condition assessment program. The test was conducted by installing a pressure transducer and ball valve to the water line at the Park’s supplied connection. The beginning of the test pressure stabilized at 645 psi after 8 hours and the pressure at the end of the 24-hour testing period was approximately 642 psi. Based on the results, it was concluded that the pipeline was not experiencing excessive leakage as the water loss estimated was found to be below the allowable leakage loss. The details of the Pressure Test are included in Appendix B: Static Pressure Test on 3.5” Water Transmission Line Technical Memorandum.

3.2 Phase 2: Field Inspection

3.2.1 PROJECT METHODOLOGY

In May 2022, a condition assessment inspection including visual inspection of the water fill line was completed by PICA and Stantec. An outline of all the project tasks is shown below:

• Task 1: Desktop Assessment and Inspection Planning Support

• Task 2: Field Investigation: Structural Integrity Assessment

• Task 3: Field Investigation: Water Quality Testing

• Task 4: Data Analysis, Condition Assessment, Action Plan and Reporting

Table 3. Summary of the Current Inspection Program Approach

Approach Description Comments

Structural Integrity

This was designed to non-destructively assess the structural integrity through remaining wall thickness measurement, utilizing an Ultrasonic tool. Ultrasonic measurements were taken at 16 pre-determined locations that were close to the locations of the 2002 condition assessment. Additional measurements were also taken at 5 other locations along the pipe.

• Excavation of about 72 inches in length with a minimum clearance of 6 inches underneath the exposed pipe was required at the two pre-determined excavated locations. The two locations were also selected to be in close proximity, as much as possible, to the 2002 test locations

Water Quality Testing

Water samples were collected at Oak Springs and Chisos Basins to be analyzed for conductivity, dissolved solids, calcium levels, alkalinity, and pH to compare against the 2002 test results.

• Sample kits (sample containers and cooler) and a UPS shipping label was provided to Park staff to facilitate sampling and shipment of samples to the lab for analysis.

3.2.2 VISUAL ASSESSMENT

Visual inspection of the pipeline was conducted at nineteen (19) already exposed and two (2) excavated sections along the pipeline. During the visual assessment survey, no evidence of water leaks was observed at any of the inspected sections of the pipeline, but, as shown in some of the images in Table 4, external corrosion and pitting were observed at multiple locations along the pipeline. A summary of the visual inspection observations and images of the pipeline sections are shown in Table 4. Prior to the field inspection, NPS deployed GPR system to estimate the depth of the pipeline at locations where the pipeline is fully buried. The GPR results are shown on the map in Appendix A.

Table 4. Summary of the Observations and Images from the Visual Inspection

Test Location Name Location Lat/Long & Observation Image

TL#1 • N 28⁰ 54.69' W103⁰ 15.146'

• Minor external corrosion observed

TL#2 • N 29⁰ 16.150' W 103⁰ 18.1214'

• No pitting or external corrosion observed

TL#3 • N 29⁰ 16.527' W 103⁰ 18.997'

• Moderate external corrosion at the section of the pipe in contact with soil and at the spring line

Exc#1 • N29⁰ 16.544' W 103⁰ 19.144'

• Moderate external corrosion was observed all over the pipe circumference

Test Location Name Location Lat/Long & Observation Image

TL#4 • N 29⁰ 16.521' W 103⁰ 19.201'

TL#5 • N 29⁰ 16.538' W 103⁰ 19.263'

• Moderate to major external corrosion observed over the section under investigation.

• Pipe appears to be bent. This was likely done during construction.

TL#6 • N 29⁰ 19.084' W 103⁰ 12.641'

• Moderate external corrosion and pitting at section of the pipe in contact with soil

TL#7a • N 29⁰ 16.689' W 103⁰ 19.531'

TL#7b • N 29⁰ 16.689' W 103⁰ 19.528'

• Pipe appears bent with minor corrosion. Again, this was likely done during construction.

TL#8 • N 29⁰ 16.682' W 103⁰ 19.530'

• Significant and major corrosion along the exposed pipe and across the pipe flange

• This section is at the creek crossing that is known to be constantly under water and debris during flash flood events

TL#9 • N 29⁰ 16.712' W 103⁰ 19.507'

• Minor external corrosion all over the entire pipe circumference under investigation

TL#10 • N 29⁰ 16.718' W 103⁰ 19.507'

TL#11 • N 29⁰ 16.729' W 103⁰ 19.529'

• Minor external corrosion observed especially at the part in contact with the soil.

TL#12 • N 29⁰ 16.741' W 103⁰ 19.639'

TL#13 • N 29⁰ 16.783' W 103⁰ 19.701'

• Longitudinal scratches, probably relating to construction activities, were observed on the pipe

• No external corrosion or pitting

TL#14 • N 29⁰ 16.844' W 103⁰ 19.748'

TL#15 • N 29⁰ 16.855' W 103⁰ 19.760'

TL#16 • N 29⁰ 16.879' W 103⁰ 19.778'

• Small numerous scratches (probably relating to construction activities) were observed along the section of the pipe

TL#17 • N 29⁰ 16.886' W 103⁰ 19.776'

• Exposed pipe has numerous small scratches, probably relating to construction activities

TL#18 • N 29⁰ 16.919' W 103⁰ 19.771'

Exc#2 • N 29⁰ 16.920' W 103⁰ 20.175'

• Moderate pitting and corrosion along the excavated pipe section

• Pipe appears bent

3.2.2.1 LOCATION OF SPOT REPAIR

During the visual assessment survey, a section of the pipeline, at Station 118+25 was observed to have been spot repaired as shown in Figure 1. The spot repair appears to be fit for purpose and in good condition.

Figure 1. Evidence of Spot Repair at Station 118+25

There is no historical information available on this repair or why the repair was necessitated. It was gathered that; the repair must have occurred before the current operations staff started working at the Park.

The only information available on leaks on the pipeline was reported in the 2002 condition assessment report to have occurred at Station 148+30. Given that there is no sign of corrosion or pitting at the upstream and downstream sections of the repair, the damage to the pipe, which warranted this repair, may have been a result of a third-party impact or accidental damage.

3.2.3 ULTRASONIC MEASUREMENTS RESULTS

Ultrasonic measurements were taken at twenty-one (21) locations along the pipeline alignment including two excavated locations and already exposed pipe locations, with the main purpose of using the data to determine the extent of internal wall corrosion and pipe wall loss. At every test location, after the exposed section of the pipe has been cleaned and prepared, measurements were taken at 12, 3, 6 and 9 o’clock positions, starting from the upstream section of the pipe to the downstream. Thirteen (13) individual measurements were taken at each clock position, spaced along the length of the exposed section of the pipe. This yielded fifty-two (52) measurements from each test location and 1,092 measurements for the entire twenty-one (21) locations tested as part of the 2022 inspection program.

The detailed Ultrasonic measurements data are presented in Appendix C while Table 5 shows the summary of the measurements in terms of minimum, maximum and average values at each test location.

Table 5. Summary of UT Measurements

Test Location Name# GPS Location Min. (inches) Max. (inches) Average WT

(inches)

TL#1 N 28⁰ 54.690' W 1030 15.146' 0.193 0.230 0.215 + 0.008

TL#2 N 29⁰ 16.150' W 103⁰ 18.214' 0.196 0.237 0.219 + 0.008

TL#3 N 29⁰ 16.527' W 103⁰ 18.997' 0.187 0.239 0.217 + 0.012

Exc#1 N 29⁰ 16.544' W 103⁰ 19.144' 0.195 0.241 0.225 + 0.009

TL#4 N 29⁰ 16.521' W 103⁰ 19.201' 0.201 0.239 0.220 + 0.009

TL#5 N 29⁰ 16.538' W 103⁰ 19.263' 0.206 0.227 0.215 + 0.006

TL#6 N 29⁰ 19.084' W 103⁰ 12.641' 0.193 0.237 0.222 + 0.007

TL#7a N 29⁰ 16.689' W 103⁰ 19.531' 0.210 0.236 0.223 + 0.007

TL#7b N 29⁰ 16.689' W 103⁰ 19.528' 0.211 0.238 0.222 + 0.008

TL#8 N 29⁰ 16.682' W 103⁰ 19.530' 0.210 0.238 0.229 + 0.007

TL#9 N 29⁰ 16.712' W 103⁰ 19.507' 0.198 0.234 0.216 + 0.011

TL#10 N 29⁰ 16.718' W 103⁰ 19.507' 0.211 0.233 0.223 + 0.006

TL#11 N 29⁰ 16.729' W 103⁰ 19.529’ 0.203 0.236 0.219 + 0.008

TL#12 N 29⁰ 16.741' W 103⁰ 19.639' 0.220 0.263 0.233 + 0.007

TL#13 N 29⁰ 16.783' W 103⁰ 19.701' 0.211 0.237 0.226 + 0.006

TL#14 N 29⁰ 16.844' W 103⁰ 19.748' 0.204 0.228 0.217 + 0.005

TL#15 N 29⁰ 16.855' W 103⁰ 19.760' 0.211 0.233 0.221 + 0.005

Name# GPS Location Min. (inches) Max. (inches) Average WT

(inches)

TL#16 N 29⁰ 16.879' W 103⁰ 19.778' 0.212 0.236 0.228 + 0.006

TL#17 N 29⁰ 16.886' W 103⁰ 19.776' 0.215 0.239 0.229 + 0.006

TL#18 N 29⁰ 16.919' W 103⁰ 19.771' 0.211 0.239 0.224 + 0.005

Exc#2 N 29⁰ 16.920' W 103⁰ 20.175' 0.204 0.239 0.224 + 0.008 #’TL’ and ‘Exc’ represent ‘Test Location’ and ‘Excavated Location’, respectively

The distribution of the measured ‘as-is’ wall thicknesses of the water fill line, across the circumference of the pipe (i.e., at the aforementioned clock positions and at 21 test locations) is shown in Figure 2. The results suggest that the wall thinning ongoing in the pipe appears to be evenly distributed across all clock positions. This is particularly important, as it suggests that, the sections of the pipe not embedded in the soil (especially from 9 to 3 o’clock) are deteriorating at the same rate as the sections of the pipe that are buried (especially from 3 to 9 o’clock). This supports the 2002 findings that the contribution of the embedded soil characteristics, to the recorded corrosion or wall thinning along the pipeline is secondary.

This by extension suggests the pipeline is deteriorating due to internal degradation processes, i.e., from ‘inside-out’.

Figure 2. Scatter Diagram showing UT Measurements at Different Clock Positions Along the Pipe

0.18

0.19

0.20

0.21

0.22

0.23

0.24

0.25

0.26

0.27

U T

M ea su re m en ts (i nc he s)

12 o' clock 3 o' clock 6 o' clock 9 o' clock

As per ASTM A53M, for Grade A or Grade B, the minimum wall thickness for a 3.5-inch nominal diameter galvanized steel pipe, can either be 0.250 inches (6.35 mm) or 0.281 inches (7.14 mm) depending on hydrostatic test pressures as shown in Table 6.

Table 6. ASTM A53 Pipe Specifications: Dimensions and Hydrostatic Test Pressures

Nominal Pipe Diameter OD (inches)

Nominal Wall thickness (inches)

Test Pressure (psi)

Grade A Grade B

3.5 4.0 0.250 2,250 2,500

3.5 4.0 0.281 2,500 2,500

Based on the available historical information on the pipeline, including the 2002 ConCeCO Engineering Inc.

report, the nominal wall thickness of 0.25 inches appears to be more applicable to the pipeline in question.

The percentage wall loss for the steel pipe under consideration was calculated assuming nominal wall thickness of 0.250 inches and minimum measured wall thickness of 0.187 inches. Therefore, based on the available data and recent results, it is conservatively, assumed that the water fill line has lost approximately 25% of its original nominal wall thickness.

Note: The 2002 UT testing was completed with ‘Panametrics 26DL Plus’ (with Standard Measurement Range: 0.020 - 10 inches; and resolution up to 0.001") and the 2022 testing used ‘Olympus-38 DL PLUS’ (with Standard Measurement Range: 0.003 - 25 inches; and resolution of 0.001"). They both combine the benefits of an ultrasonic thickness gage, internal datalogger, and digital waveform display. Although there may be differences in features such as battery life, display types, measurement ranges, ruggedness, UT testing instruments work based on similar principles irrespective of the manufacturers. So, provided best industry practices are followed, including proper calibration, using certified UT Technician and selection of instrument with right measurement range, the UT testing results will be similar, irrespective of the manufacturer of the UT instrument used. Based on the nominal WT of the water fill line and the ranges of results recorded in 2002 and 2022 inspections, the two UT instruments were suitable for the inspection programs.

3.3 Water Quality Assessment

The NPS team collected water samples at the inlet piping at Chisos Basins Tank and Oak Springs Box overflow. These water samples were analyzed for alkalinity, specific conductance, total dissolved solids and pH. Table 7 shows the summary of the results of the water quality assessment performed. Detailed water quality analysis reports are in Appendix D.

Table 7. Summary of Water Quality Assessment Results

The Langlier indices calculated from the two water samples are -0.40 and -0.3, respectively for Oak Springs and Chisos Basin. A negative Langlier index value indicates higher probability of corrosion in the pipeline while a positive Langlier index value indicates an increase in tendency for scaling. The Ryzner stability indices calculated from both water samples are 8.5 and 8.4, respectively for Oak Springs and Chisos Basin. As Ryzner stability index increases above 7, the tendency for corrosion increases while when it decreases below 6, the tendency for scaling increases. The results of both the Langlier and Ryzner indexes calculated for the water samples, indicate a higher tendency for internal corrosion in the pipeline. These indexes also show that scaling or build-up, if any in the pipeline, is insignificant.

Interestingly, this finding is supported by the fact that, as shown in Figure 2, only one (1) of the 1,092 individual UT measurements taken during this inspection program is greater than the nominal wall thickness of the pipe, i.e., 0.265 inches as against nominal wall thickness of 0.25 inches. Therefore, as discussed earlier, this water fill line appears to be undergoing internal corrosion.

3.4 Water Fill-line Design Evaluation

Steel pipes design standards have evolved over time as more information about the performance of these pipes become available. The evaluation of the pipeline design, to determine if it meets the requirements of the current American Water Works Association (AWWA) M11, AWWA C604, AWWA C207 and AWWA C206 design standards, has been completed as part of the current condition assessment program.

In line with best industry practices, pipe wall thickness is used as the basis for verifying the adequacy of the overall steel pipe design. The primary design consideration for the determination of pipe wall thickness is the pipe’s ability to withstand applicable internal and external pressures.

3.4.1 INTERNAL PRESSURE: DETERMINATION OF PIPE WALL THICKNESS

When designing for internal pressure, AWWA M11 recommends that the pipe wall thickness should be calculated to limit the circumferential tensile stress or hoop stress to an allowable level. For this evaluation, the actual working pressures (and transient pressures) to which the water fill line has been subjected to during its service life is taken as the internal pressure (design pressure). This, according to available information about the pipeline from the report titled: “Static Pressure Test on 3.5” Water Transmission Line

Collection Location

Total Alkalinity

(mg/L)

Calcium Hardness as CaCO3

(mg/L)

Specific Conductance

Total Dissolved

Solids (mg/L)

*Temp °C pH Langlier

Index Ryznar Index

Oak Springs 133 129 446 283 4.9 7.7 -0.397 8.494

Chisos Basin 121 144 396 267 0.7 7.9 -0.274 8.449

*This is the sample’s temperature at the laboratory.

Technical Memorandum” is 645 psi, with this value, the pipe wall thickness required to withstand this performance requirement is determined using Eq. 1 (AWWA M11) below:

𝑡𝑡 = 𝑝𝑝𝑝𝑝𝑜𝑜 2𝑠𝑠

Eq. 1

Where: t = pipe wall thickness for the internal pressure, in; p = internal pressure, psi; Do = outside diameter of steel pipe cylinder (not including coatings), in; and s = allowable design stress, psi.

Furthermore, working stress is determined based on the steel’s yield strength instead of its ultimate strength. An allowable design stress equal to 50% of the steel specified minimum yield strength (SMYS) for working/transient pressure is assumed for this design calculation as per AWWA M11 guidelines. Table 8 shows the design evaluation calculation. The design assumptions and parameters used for the design evaluation include the following:

• Diameter = 4.00 inches

• Working pressure = 645 psi

• Surge allowance (assumed) = 100 psi

• Transient pressure = 745 psi

• SMYS = typical yield strength of 30,000 psi is assumed

Table 8. Design Evaluation Calculation

Working Pressure Design Transient Pressure Design

Calculation 645 ∗ 4

(2 ∗ 0.5 ∗ 30,000)

745 ∗ 4 (2 ∗ 0.5 ∗ 30,000)

Result 𝑡𝑡 = 0.086 inches 𝑡𝑡 = 0.099 inches

For further analysis 𝑡𝑡 = 0.099 inches will be assumed, and it is henceforth referred to as 𝒕𝒕𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓.

3.4.2 EXTERNAL LOADS ON BURIED PIPE

The external load(s) on the buried water fill line is assumed to be from the weight of the backfill (geostatic load) and hydrostatic load only. As described in Section 3.4.1, internal pressure is typically used to determine pipe wall thickness. This section focuses on the analysis of the effects of applicable external loads and the principles of pipe/soil interaction to determine the performance of the water fill line under these applicable external loads, for the calculated minimum wall thickness (i.e., 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) obtained in the preceding section. The results of the analyses are summarized in Table 9. The following additional assumptions were made to complete the analyses:

• Pipe Diameter = 4 inches

• Minimum Wall Thickness Required (𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) = 0.099 inches

• Depth of soil cover = 6.5 ft

• The water table is assumed to be at ground surface along the pipeline alignment.

• Unit Weight of Saturated Soil = 127 pcf

• The stresses in the pipe wall will be limited to 50% of its specified minimum yield strength (SMYS

= 30,000 psi), i.e., 15,000 psi.

• Ultimate Yield Strength = 48,000 psi

• Modulus of Elasticity of Steel = 2.9 x 107 psi

• Factor of Safety (FOS) = 2.5.

Table 9. Design Evaluation Calculation Results

The results presented in Table 9, suggest that at 𝒕𝒕𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓 of 0.099 inches, the pipe will still be able to withstand the geostatic and hydrostatic loadings acting on it within the assumed operating condition listed above. It should be noted that, we have taken a conversative approach in completing the calculation.

3.5 Pipe Deterioration Rate and Remaining Service Life Calculation

Average life expectancy of a galvanized steel pipe typically varies between 35 and 75 years, depending on operational conditions, external loads, bedding support and characteristics of embedment soil. There are multiple methods and/or processes available in the industry to estimate the remaining service life of buried pipelines. It should be noted, however, that these processes are subjective and often, result in divergent outcomes. This is due in part to a wide variety of factors that can influence buried pipeline structural integrity. Furthermore, another main reason for the lack of correlation in the outcome of these methods is the uncertain nature of the underground environment in which the pipeline is buried. In a laboratory setting

Key Loading Parameters Values Comment (s)

Allowable Yield Stress, Fyr (psi) 15,000 i.e., 0.5 * Fy

Total External Load, (psi) 6.73 Acceptable: Value < Critical Ring Buckling Pressure

Critical Ring Buckling Pressure (psi) 247 Acceptable: Value < Pipe Allowable Yield Stress and > Total External Load

Calculated Ovality under Loading, ∆𝑦𝑦 𝐷𝐷� (%), 0.29% Acceptable: The permissible deformation is less than 5%

Crushing of Pipe Side Walls; using D/t ratio 40.6 Unlikely: D/t < 100 for example, “the effect of individual factors on corrosion can be described with a greater confidence, whereas in reality, underground corrosion is an intricate and time-dependent interaction of all the factors”1.

Based on the available data, for this assessment, the following three (3) approaches have been used to estimate the remaining service life (RSL) of the water fill line. It should be noted that, the minimum WT of

0.187 inches was used to complete each of the calculations, because failure of pressurized pipeline generally occurs at its weakest points.

Approach 1

Over a period of 67 years that the pipe has been in service, the estimated maximum wall loss in the fill line is 0.063 inches (1.60 mm), based on the minimum wall thickness recorded in Section 3.2.3. Assuming a galvanized zinc coating of 3.35 x 10-3 inches (85 µm) (including inside and outside of the pipe wall) as per ISO 1461:2009(E)2, the average corrosion rate over the 67 years can be obtained from the equation (Eq. 2) below:

𝐴𝐴𝐴𝐴𝐴𝐴 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑜𝑜𝑜𝑜 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 (𝑍𝑍𝑍𝑍𝑍𝑍𝑍𝑍)

+ 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 (𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆)

Eq. 2

Assuming that the corrosion rate of steel is 25 times that of zinc, the above equation becomes:

67 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 =

3.35 𝑥𝑥 10−3 𝑖𝑖𝑖𝑖

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 (𝑍𝑍𝑍𝑍𝑍𝑍𝑍𝑍)

0.063 𝑖𝑖𝑖𝑖

[25 ∗ 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 (𝑍𝑍𝑍𝑍𝑍𝑍𝑍𝑍)]

Solving for the Average Corrosion Rate (Zinc) as follows:

(25 ∗ 3.35 𝑥𝑥 10−3) + 0.063

25 ∗ 67

• This yields a value of 8.76 x 10-5 in/year.

• This corresponds to a steel pipe corrosion rate of (8.76 x 10-5x 25) = 0.0022 in/year.

The remaining service life of a buried pipeline can be estimated by relating the pipe’s corrosion rate, measured current wall thickness (i.e., 𝑡𝑡𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎) and required wall thickness (i.e., 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) as shown in Eq. 33.

For this estimation, required wall thickness (i.e., 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) is adjusted by manufacturing tolerance of 12.5% and factor of safety (FOS) of 2 (calculated at 50% of the yield stress).

1 Jyrkama, M., et al. (2018). Estimating external corrosion rates for buried carbon steel piping in different soil conditions. CNL Nuclear Review, 7(1) 2 International Standard (ISO) 1461: Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods, 3rd ed (2009-05-15) 3Naik, S. J et. al (2016) Determination of Corrosion rates and remaining life of piping using API and ASME standards in oil and gas industries (IRJET)

Eq. 3

• Minimum Wall Thickness Measured (𝑡𝑡𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎) = 0.187 inches

• Minimum Wall Thickness Required (𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) = 0.099 inches

• Minimum wall thickness required (𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟) increased with manufacturer’s tolerance and FOS of

2 = (1.25 x 0.099) which yields 0.124 inches

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 =

0.187 − 0.124

0.0022 = 29 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦

• This yields a RSL value of 29 years

Approach 2

The ANSI/NACE standard SP0502-20104 recommends a default pitting rate of 0.0157 in/year (16 mpy) for buried pipelines constructed of ferrous materials. Following this recommendation and using Eq. 3 above with adjusted 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 of 0.124 inches, the remaining service life of the water fill line based on the lowest remaining wall thickness of 0.187 inches (4.750 mm) is estimated as:

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 =

0.187 − 0.124

0.0157 = 𝟒𝟒 𝒚𝒚𝒚𝒚𝒚𝒚𝒚𝒚𝒚𝒚

• This yields a RSL value of 4 years

Approach 3

API 5815 recommends the soil-side corrosion rate to be estimated as a function of a base rate, modified by a set of multiplicative factors, which account for soil resistivity, temperature, cathodic protection (CP), and coating. API 581 therefore provides three deterioration rates based on the embedded soil types, as follow:

• 0.00098 in/year (1 mpy) for sand,

• 0.005 in/year (5 mpy) for silt, and

• 0.01 in/year (10 mpy) for clay.

4 ANSI/NACE Standard SP0502-2010, 2010, “Pipeline External Corrosion Direct Assessment Methodology,” Houston, TX.

5 API 581, “Risk Based Inspection Technology. Annexure 2.B: Determination of Corrosion Rates,” American Petroleum Institute, Washington, USA

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 (𝑅𝑅𝑅𝑅𝑅𝑅) =

𝑡𝑡𝑎𝑎𝑎𝑎𝑡𝑡𝑢𝑢𝑢𝑢𝑢𝑢 − 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟

𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟

Clear information on the construction method(s) for the water fill line is not available but given the physical environment or terrain where it is buried, it can be assumed that the pipeline is embedded in all of these soil types at multiple sections along its alignment. Therefore, using Equation 2 and the adjusted 𝑡𝑡𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 of

0.124 inches, the three deterioration rates have been used to estimate the pipeline remaining service life, as follows:

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿(𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) = (0.187 − 0.124)/0.00098 𝑖𝑖𝑖𝑖/𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 = 64 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿(𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) = (0.187 − 0.124)/0.005 𝑖𝑖𝑖𝑖/𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 = 13 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿(𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐) = (0.187 − 0.124)/0.01 𝑖𝑖𝑖𝑖/𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 = 6 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦

The three approaches estimated the water fill line RSL to vary between 4 and 64 years. Part of the reasons for this significant variation has been discussed at the beginning of this section. The pipeline has already been in service for 67 years; based on the rule of thumb, the estimated life span of galvanized steel pipes, used in water system applications, varies between 40 to 70+ years. For the pipeline under consideration, the condition assessment results have shown that, it is unlikely that external factors are playing significant roles in deterioration or wall thinning of the pipe, i.e., the pipeline appears to be experiencing internal corrosion/metal loss. Therefore, combining the preceding condition assessment results and findings, it is safe to assume that, if all the current external and internal factors currently at play on the pipeline remain constant, the pipeline may serve for the next 13 years to 29 years.

Note: According to the 2002 report, the predominant soil types encountered was clayey formation, followed by sandy formation, this notwithstanding, the lower RSL values (i.e., 4 years and 6 years) and the 64 years value are considered to be unrealistic, based on the other condition assessment results, hence not considered.

4 COMPARISONS BETWEEN 2002 AND 2022 CONDITION ASSESSMENT

PROGRAM

4.1 UT Testing

Due to some site constraints, ultrasonic measurements could not be taken at the exact locations of the 2002 test locations, but as much as possible, the 2022 measurements were taken close to the 2002 test locations. The comparison between the two sets of measurements described below considers the bulk results from each set of data. The highpoints of the two sets of data are presented in Table 10.

Table 10. UT Measurements: 2002 Versus 2022

2002 2022 % Decrease

Minimum Wall Thickness (WT) (inches) 0.196 0.187 4.6

Average Wall Thickness (WT) (inches) 0.239 0.222 7.1

Maximum Wall Thickness (WT) (inches) 0.284 0.263 7.4

Furthermore, Figures 3 to 5, respectively, show the comparison between all the minimum, average and maximum UT measurements taken along the pipeline from the two field inspection efforts.

Figure 3. Comparison between 2022 and 2002 Minimum UT Measurements

0.18

0.19

0.2

0.21

0.22

0.23

0.24

0.25

W al l T hi ck ne ss (i nc he s)

2022 Measurements

2002 Measurements

Figure 4. Comparison between 2022 and 2002 Average UT Measurements

Figure 5. Comparison between 2022 and 2002 Maximum UT Measurements

From results presented in Table 10 and in Figures 3 to 5, the trend of progressive wall thinning is evident along the pipeline over the last 20 years, with the % decrease values for Min. WT, Average WT and Max.

WT, of 4.6%, 7.1%, and 7.4%, respectively. Going with the highest value, the result suggests that, in the last 20 years, the percentage decrease in the water fill line WT is approximately 7.4% of the wall thickness measured during the 2002 inspection program, which may be assumed to be 0.4% per year.

4.2 Water Quality Testing

The water quality analysis results were compared with the 2002 analysis as shown in Table 11. The 2022 water analysis showed an increase in the dissolved solids content, Calcium hardness and total alkalinity values from the 2002 results. From the Langlier index and Ryzner index calculations, the 2002 analysis indicated a slight tendency for internal corrosion while the latest test results also indicated some tendency for internal corrosion. For the two testing points, the results also suggest that, over the years, the tendencies of the water to promote corrosion and/or scaling have increased.

0.21

0.22

0.23

0.24

0.25

0.26

W al l T hi ck ne ss (i nc he s)

2022 Measurements

2002 Measurements

0.21

0.23

0.25

0.27

0.29

W al l T hi ck ne ss (i nc he

s) 2022 Measurements 2002 Measurements

Table 11. Water Quality Analysis Comparison

Water Quality Tests Oak Springs Chisos Basin

Year of Inspection 2002 2022 2002 2022

Total Dissolved Solids (mg/L) 255 283 244 267

Ca Hardness (mg/L) 113 129 112 144

Total Alkalinity (mg/L) 104 133 110 121 pH 7.3 7.7 7.9 7.9

Langlier Index -0.4 -0.4 0.2 -0.3

Ryzner Stability Index 8.1 8.5 7.5 8.4

5 CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

Based on the available information and the findings of the condition assessment efforts, the following can be concluded:

• The results of the pressure test performed indicated that the pipeline was not experiencing excessive leakage as the water loss estimated was found to be within the allowable leakage loss.

• Visual inspection showed no leakage along the pipeline route, but multiple external corrosion and pitting occurrences at various locations along the pipeline.

• Ultrasonic measurements taken during the inspection indicated maximum pipe wall loss of about 25%, minimum pipe wall loss of 3.6% and average pipe wall loss of about 11.2 %

• Comparison between the 2002 and 2022 ultrasonic measurements indicated that, in the last 20 years, the percentage decrease in the water fill line wall thickness is approximately between 4.6% to 7.4% of the wall thickness measured during the 2002 inspection program, which may be assumed to be 0.2% to 0.4% per year.

• The results of the water quality analysis indicated that water that flows through the pipeline has a tendency to cause internal corrosion of the pipeline. Furthermore, analysis and comparison of the 2002 and 2022 UT measurements, suggested that the contribution of the embedded soil characteristics, to the recorded corrosion or wall thinning along the pipeline is secondary.

Therefore, the pipeline is believed to be deteriorating, although at reasonably slow pace, from ‘inside-out’.

• If all the external and internal factors currently at play on the pipeline remain constant, the pipeline may still serve for the next 13 years to 29 years.

5.2 Recommendations

The following are the three main reasons for watermain renewal:

i) water quality improvement,

ii) hydraulic improvement and

iii) structural improvement of the watermain.

The condition assessment results and findings, presented in the preceding sections, suggest that no immediate major renewal or rehabilitation of the water fill line is necessary at this time. This notwithstanding, the following are recommended for NPS consideration:

• Short Term: The visual assessment revealed that some of the pipe sections inspected are showing minor to significant external corrosion, the most significant of them is at TL#8 (i.e., the section of the pipeline at the creek crossing that is known to be constantly under water and debris during flash flood events). To address the evidence of external corrosion and improve the structural integrity of the water fill line at this location, it is recommended that this section should be protected with appropriate coating system, within the next 6 to 12 months. It may be necessary to further expose the upstream and downstream of the section in question, to capture all the corroded sections of the pipe at this location. Other locations that may be considered for coating are TL#5 and Exc#2. It is also advisable to monitor the other sections with evidence of external corrosion as part of the NPS O&M regime. Examples of such coating systems include:

o Epoxy o Polyethylene/propylene coating o Polyurethane Coating

• Short Term: Given the age of the pipeline, it is important for NPS to put in place an O&M plan which should include annual to biennial routine inspections to identify potential problems before they lead to catastrophic failures. Some of the industry best practices that can be employed in prolonging the life and maintaining a watermain in good condition are summarized as follows:

o Pressure Monitoring: Keeping the operating pressure of a pressurized pipeline below its Maximum operating pressure (MOP) based on its ‘as-is’ mechanical properties, especially when it is aging, can extend its service life and reduce the risk of sudden failure. Pressure monitoring can be completed by utilizing telemetry units or sensors that are attached to the pipe to measure or monitor the operating pressure within the pipeline over a period of time.

If pressure anomalies are observed, e.g., if lower than expected pressure is recorded over a period of time, an in-line inspection of the pipeline, utilizing an advanced acoustic leak detection system, may be performed to verify the cause of the pressure drop, such as leakages (see the point below for more information on leak detection). Also, if higher than expected pressure is recorded, this might be due to flow restriction probably due to build-up along the inside of pipeline. Additionally, the information from the exercise should be documented and benchmarked against design or ideal performance expectations.

o Leak Detection: Leaks often occur before the failure of a pressurized pipe. Early identification of leakage locations in a buried pipeline can help prevent catastrophic failure of the pipeline. An advanced acoustic leak detection system could be used to identify the presence/location(s) of leaks along the pipe. Advanced acoustic leak detection can be performed internally using free swimming leak detection tools under pressure conditions.

The need for leak detection should be triggered by anomalies from the pressure monitoring exercise. It should be noted that, while there is a risk of the leak detection tool getting stuck inside the pipeline, the need for leak detection as part of the current scope of work was dropped mainly because, the pressure test completed on the water fill line in February 2022, suggested that the pipeline was not experiencing excessive leakage as the water loss estimated was found to be below the allowable leakage loss. There are specialized tools and/or approaches to minimize or eliminate the risk of the tool getting stuck.

o NPS may consider including pressure monitoring telemetry unit as part of the water transmission system. This will provide real time operating pressure data, which can provide valuable guidance to NPS during O&M decision making processes. The data from this unit can particularly identify the need and timing for additional probing or inspection, such as leak detection.

• Long Term: Given that the UT testing was completed only on 0.26% of the entire length of the pipeline, additional UT testing is further recommended to be completed within the next 5 years, at other locations along the pipeline, especially at the locations where the pipe is fully buried.

Also, to be able to correctly track corrosion rate, the 2022 test locations may be re-tested in 5 years, especially at the locations identified as having significant corrosion, see Table 4. (Note:

The pipeline is 16,000 ft long, in the current inspection program, an approximately 2 ft length of the pipe was tested at each of the 21 locations, which is 42 ft out of 16,000 ft).

It is expected that, the frequency of the recommended activities, should be adjusted if their outcome or results warrant such changes.

Other recommendations for the Park’s consideration include:

• As it has been previously recommended that, given the length of the pipeline, the ideal assessment approach should include division of the pipeline into segments for data gathering.

While there are multiple industry approaches for achieving this, e.g., node-to-node, chamber-to-chamber, valve-to-valve, material, size and location based, etc., the peculiarity and terrain of this pipeline have shown that such segmentation approaches are not feasible. Therefore, a ‘fit-for-purpose’ arbitrary approach will need to be developed for the water fill line, such as ‘equidistant segmentation’ and segmentation based on accessibility, soil characteristics or existing station numbers.

• Due to the condition assessment results, showing that the water chemistry is predominantly responsible for the wall thinning recorded to date on the pipe, NPS could evaluate the potential treatment option(s) for modifying the water chemistry in a way that will minimize its corrosion potential, without compromising the safe drinking water quality requirements. A pilot study may be necessary to pre-determine the effectiveness of such treatment option(s).

STANTEC CONSULTING SERVICES INC.

Olugbenga Ibikunle, Ph.D., P.Eng., AWAM, CRL.

Associate, Civil Engineer

Phone: (780) 969-2134 olugbenga.ibikunle@stantec.com

Ray Plummer III, P.E., Wet Weather Technical Leader, Principal

Phone: (208) 916-8113 raymond.plummer@stantec.com

Attachment: Appendix A – Drawing showing Pipeline Route and GPR Locations Appendix B - Pressure Test Technical Memorandum Appendix C –Detailed Ultrasonic Measurements Report Appendix D – Water Quality Analysis Reports

Appendix A Drawing Showing Pipeline Route and

GPR Locations

0+00

20+00 Bell Hole #1

59+50 Crosses

Trail

61+50 Crosses Trail

68+00 Bell Hole #2

69+00 Bell Hole #3

71+70 Bell Hole #4

91+30 Creek Crossing

91+25 Bell Hole #5

94+25 Creek Crossing

104+60 Junction - Oak Springs Trail

119+60 Air Release Valve

126+40 Stopped Locating

132+00 Started Locating Pipe

148+30 Leak Site158+90 Oak

Springs Box

161+00 Oak Springs

Pump House

GPR 1

GPR Point 3

GPR Point 4 GPR Point 4.1

GPR

Point 5

GPR Point 6

GPR Point 7 No Data Found

Oak Spring

Chisos Basin Tanks

Big Bend National

Park

0 10.25 0.5 0.75 Mile

0 10.25 0.5 0.75 Kilometers

Á North

1:11,000

Legend Original point (2002 condition assessment) Exposed Pipeline Oak Spring pipeline (updated with GNSS, 5/3/2022) GPR detected pipe GPR did not detect pipe

Map developed 5/4/2022 | M. Landis, Big Bend National Park File: BIBE_2022_FACILITIES_GPR_20220502 î

GPR Points 5/2/2022 National Park Service U.S. Department of the Interior

Big Bend National Park Texas

GPR 1 GPR detected pipe 35 664863.383675 3238913.30965 29.268377 -103.303093

GPR Point 3 GPR did not detect pipe 0 663646.691478 3239678.4002 29.275437 -103.315499

GPR Point 4 GPR detected pipe 10 663034.946814 3239710.44072 29.275806 -103.321789

GPR Point 4.1 GPR detected pipe 10 663033.300004 3239710.48795 29.275806 -103.321806

GPR Point 5 GPR detected pipe 26 662477.707743 3240068.85756 29.279111 -103.32747

GPR Point 6 GPR detected pipe 15 662323.82214 3240410.11604 29.28221 -103.329004

GPR Point 7 No Data Found GPR did not detect pipe 662134.660271 3240512.59837 29.283159 -103.330935

Pipe Track 1 Start GPR detected pipe 663544.935139 3239678.90074 29.275455 -103.316546

Pipe Track End Point GPR detected pipe 663700.612141 3239635.19023 29.275041 -103.314951

Pipe Track Poimt 4 GPR detected pipe 663670.964474 3239641.80854 29.275104 -103.315255

Pipe Track Point 2 GPR detected pipe 663641.447262 3239654.87603 29.275226 -103.315556

Pipe Track Point 3 GPR detected pipe 663662.245237 3239649.19098 29.275172 -103.315343

Point 2 Shallow: Metal Detector GPR detected pipe 664799.245619 3239022.23822 29.269368 -103.303737 name Pipe Depth to pipe cm UTM Easting UTM Northing Latitude WGS84 Longitude WGS84

30+00 GPR

Point 2

GPR Point 1 - Trail

Crossing

GPR Point 3 - Trail Crossing

81+50 GPR

Point 4

104+00 GPR Point 5

118+25 GPR

Point 6

GPR

Point 7 at

Trail CrossingGPR Point 8 at leak site

GPR Point 9 at Oak Springs Pump Station discharge

0+00

20+00 Bell Hole #1

59+50 Crosses

Trail

61+50 Crosses Trail

68+00 Bell Hole #2

69+00 Bell Hole #3

71+70 Bell Hole #4

91+30 Creek Crossing

91+25 Bell Hole #5

94+25 Creek Crossing

104+60 Junction - Oak Springs Trail

119+60 Air Release Valve

126+40 Stopped Locating132+00 Started

Locating Pipe 148+30 Leak Site

158+90 Oak Springs Box

161+00 Oak Springs

Pump House Oak Spring

Chisos Basin Tanks

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Map developed 4/29/2022 | M. Landis, Big Bend National Park File: BIBE_2022_FACILITIES_GroundtruthedGPRPoints î

GPR Points Groundtruthed 4/28/2022

National Park Service U.S. Department of the Interior

Big Bend National Park Texas

0+00 628916.551114 546484.375515 29.267205 -103.301934

Air Release Valve 72+60 623144.79899 549637.951999 29.275287 -103.320392

Air Release Valve 119+60 620596.756267 552320.238297 29.2824 -103.32869

Bell Hole #1 20+00 627831.050513 548007.610122 29.271282 -103.305513

Bell Hole #2 68+00 623569.162053 549775.311112 29.275708 -103.319077

Bell Hole #3 69+00 623466.478818 549746.815426 29.275619 -103.319396

Bell Hole #4 71+70 623226.383287 549627.900488 29.275268 -103.320135

Bell Hole #5 91+25 621658.963337 550526.48951 29.277578 -103.325152

Creek Crossing 91+30 621639.534467 550480.283168 29.277449 -103.325208

Creek Crossing 94+25 621618.714479 550762.14054 29.278222 -103.325306

Crosses Trail 59+50 624317.526504 549642.617586 29.275419 -103.316716

Crosses Trail 61+50 624146.645583 549587.34566 29.27525 -103.317245

GPR Point 1 - Trail Crossing 628553.148128 546872.246784 29.268234 -103.303118

GPR Point 2 30+00 626857.853824 548290.535923 29.271961 -103.308596

GPR Point 3 - Trail Crossing 624720.85954 549578.212412 29.275283 -103.315444

GPR Point 4 81+50 622701.138448 549775.820442 29.275621 -103.321798

GPR Point 5 104+00 620923.718425 551122.370757 29.279141 -103.327526

GPR Point 6 118+25 620507.330936 552204.999793 29.282075 -103.328957

GPR Point 7 at Trail Crossing 619918.021335 552581.086217 29.283048 -103.330849

GPR Point 8 at leak site 618145.366787 552237.230847 29.281923 -103.336366

GPR Point 9 at Oak Springs Pump Station discharge 617836.469471 552249.652276 29.281925 -103.337336

Junction - Oak Springs Trail 104+60 620883.881179 551189.017469 29.279321 -103.327659

Leak Site 148+30 618047.22531 552257.24132 29.281968 -103.336676

Oak Springs Box 158+90 617161.315394 552424.209253 29.282336 -103.339473

Oak Springs Pump House 161+00 617002.454813 552553.186509 29.282674 -103.339986

Started Locating Pipe 132+00 619628.59241 552519.819389 29.28285 -103.331749

Stopped Locating 126+40 620158.717077 552700.268633 29.2834 -103.330108

Station Name Station Number Easting - UTM 13N Northing - UTM 13 N Latitude WGS84 Longitude WGS84

TL#2

W103.304

N029.269

TL#3

W103.317

N029.275

TL#4

W103.320

N029.275

TL#5