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Appendix B Sourdough Reservoir Evaluation Report
Page 1 of 27 City of Bozeman Montana SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Technical Memorandum From: Brain Viall, PE Ken Weber, PE Jordan Geiger, PE AE2S To: Brian Heaston PE, Planning and Engineering Director Jill Miller, Water Plant Superintendent Jac Miller, Asst. Water Plant Superintendent City of Bozeman, MT Date: 11/19/2020 I. EXECUTIVE SUMMARY The Sourdough Reservoir is an important asset for the City of Bozeman’s distribution and WTP operations: it is the primary finished water storage facility within the City’s South distribution zone – sometimes referred to as the Sourdough Zone – and its water surface elevation establishes the operation pressure within this zone. Having been built in the 1950’s, this asset is nearing 70-years of operation and has had some rehabilitation improvements completed within the last 20 years. The City recognizes additional improvements are required for reliable operations into the future. AE2S was hired to complete a condition assessment and to identify the preliminary scope of planning for the anticipated improvements. Within this document, the City will learn of the existing conditions of the Sourdough Reservoir (Section II, III, & IV) and find alternatives considered for both rehabilitation and replacement. The Engineer’s Opinion of Probable Construction Costs (EOPCC) and other considerations are outlined in Section V – Proposed Alternatives. However, since the usable life of the alternatives evaluated are drastically dissimilar (20 and 80 years, respectively) a life cycle cost analysis (LCCA) compares the options to provide a basis upon which to identify the least cost alternative more confidently. The LCCA’s take into consideration the City’s preparedness to acquire debt for these capital improvements knowing similar investments are required at the Lyman Creek Reservoir (Section VI – Life Cycle Cost Analysis). Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 2 of 27 A. Alternatives Evaluated: 1. Reservoir Rehabilitation: EOPCC: ............................................................................ $2,971,550.00 Anticipated Usable Life: .................................................. 20 to 30-years 2. Reservoir Replacement EOPCC: ............................................................................ $9,075,200.00 Anticipated Usable Life: ........................................................... 80-years B. Life Cycle Cost Analysis (50-yr) Alternative No. 1 - Rehabilitation ....................................... $18,395,023 Alternative No. 2 – Replacement ........................................ $19,080,506 The results of the 50-year LCCA (found in Tables 6 & 7, respectively) show the reservoir rehabilitation is more favorable to the City’s financial, long-term storage, and distribution needs. The assumptions reflected in the LCCA’s are documented in Section VI. Even though these LCCA’s have nearly negligiable cost differences, it is reasonable to believe there is still usable life remaining in the facility and investing in rehabilitation and a replacement cover now will allow the City to capitalize on this remaining life. This strategy also benefits the City’s financial interest by post-poning the considerable debt payments concentrated in the first 20 years of Alternative No. 2. These financial considerations for debt repayment play an important role in identifying how these improvements fit within the City’s overall capital improvements plan – especially knowing similar improvements are presently under consideration at the Lyman Creek Reservoir. C. Benefits of Least Cost Alternative: 1. Reservoir Rehabilitation: i. Saves the City of Bozeman roughly $500,000 over the next 50 years. · Note this difference is almost negligible – mostly due to the investment in a new reservoir cover to increase the usable life of the existing facility. ii. Capitalizes on the remaining usable life of existing reservoir infrastructure. iii. Strategically post-pones the debt payments for a future Sourdough reservoir replacement project beyond those payments for more critical infrastructure improvements at Lyman Creek Reservoir. · This is based on a similar life cycle cost analysis of the Lyman Reservoir condition assessment. II. BACKGROUND A. Project Background The Sourdough Reservoir is a partially buried concrete storage tank for potable water dating back to the 1950’s and is situated at the intersection of Sourdough Road and Goldenstein Ln in Bozeman, MT. The tank is approximately 150’ in diameter, has a storage depth of thirty (30) feet, and a nominal storage volume of 4 million gallons. Discussions with Water Treatment Plant (WTP) Operators and record drawings indicate the walls and floor are a cast-in-place concrete structure with existing Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 3 of 27 horizontal preload wires reinforcing the walls with a design working stress of 105,000 psi – see record drawings in Appendix F. The structure has a reinforced concrete dome with a post-tensioned ring around the perimeter of the dome’s edge. A vent opening in the top of the dome allows air movement in and out of the reservoir’s headspace to compensate for volume changes of varying water levels. Water enters the reservoir through one 24” influent pipe and exits through a single 14” transmission main. A 24” overflow pipe ensures the maximum water surface elevation is not exceeded. B. City Concerns 1. City operators have no knowledge of the reservoir ever having been taken offline. iv. Therefore, the City is concerned the structure may not be able to support itself without water pressure against the walls. v. More detailed structural evaluation should be performed before dewatering the tank completely. vi. The reservoir can be isolated from the distribution system with valves but cannot be fully drained by gravity due to existing piping configuration and elevation constraints. vii. Pumping will be required to remove the lower portion of the tank volume. 2. The drainage ditch intended to convey water away from the facility during dewatering activities contains debris from private landowners. City Operators need to coordinate with landowners to prevent property damange caused by flooding. 3. Overflow pipe and bracing are corroded. 4. A known crack in the wall requires ongoing maintenance and is a source of vulnerability. 5. Operators suspect the tank leaks and have no knowledge of prior leak testing. 6. Ladder, hatches, and vents are in poor shape. 7. Concrete spalling appears on the interior of the roof dome. Additionally, the rate of spalling seems to have increased with time in recent years (as noted by inspections and recent cleanings). 8. Previous inspections by LEC have not been incredibly detailed. 9. Sourdough tank is an instrumental facility for the City’s WTP operating philosophies. C. Past Maintenance and Repairs Over the life of the reservoir, City Operators have conducted basic maintenance and contracted for minor repairs – each requiring the reservoir to have been isolated from distribution. However, current City staff interviewed have no knowledge of the reservoir having ever been fully dewatered, citing both Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 4 of 27 hydraulic limitations and concerns over unloading the internal walls. The reservoir can be operated down to about mid-depth: the lower half of the reservoir will need to be drawn down through the reservoir drain. The reservoir drain system discharges into an existing water way. The condition of the waterway is a concern due to various obstructions in the waterway created by adjacent property owners. The following is a list of current and ongoing maintenance and repair activities: 1. General Cleaning: i. The City removes sediment every three to five years. ii. Most recently, LEC performed this cleaning in 2017. 2. Maintain Identified Cracking: i. Periodically seal interior cracks in concrete walls and floor joints with epoxy treatment. ii. First sealed in approximately 2010. 3. Dome Cover Condition Assessment of Post-Tensioning Cables and Concrete End- Cap: i. In the mid-to-late 2000’s, the City observed the post-tensioning cable system was failing: the concrete endcap was crumbling and exposed the rebar to accelerated corrosion. An improvement project rehabilitated the dome roof’s tensioning system in 2008-2009 along with a new endcap. ii. Regular inspection of the compression ring along the dome’s perimeter tensioning system and concrete endcap is now included in the City’s regular maintenance and condition assessment check-list. Figure 1 - Tank Compression Ring - Before rehab (left), After rehab (right). 4. Maintain Flow Control Valves in the Control Vault. i. In February/March 2019, the city isolated the reservoir and replaced a valve in the vault structure outside of the reservoir. ii. Recommended maintenance includes exercising the valves to preserve operation and function. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 5 of 27 D. Previous Studies Previous facility inspections and studies informed repairs of the domed roof and compression ring. Additionally, the City performs condition assessments every 3-5 years. The most recent condtion assessment report is summarized below. 1. 2017 LEC Storage Reservoir Inspection Report i. LEC performed a limited, nondestructive tank inspection in 2017. It is important to note that the reservoir was in service and visual inspection was provided by a dive team and documented via video. The inspection reported no concerns regarding the structural concrete nor identified any surface defects on the concrete which may lead to future structural concerns. The report did mention the need to address corrosion on the ladders, over flow pipe, hatches, and ventilation pipe. ii. Recommentations included, regular inspections every three to five years and annual leakage testing in accordance with ACI 350. III. 2020 RESERVOIR EVALUATION A. Background The City’s current standard operations and maintenance plan includes completing a condition assessment on the Sourdough facility every three (3) to five (5) years. Abiding by that schedule, the City hired AE2S to lead the condition assessment and engineering evaluation. During this condition assessment, the tank underwent a non-destructive, in-service field assessment with Liquid Engineering Corporation’s (LEC) dive inspectors on June 17, 2020. The dive was recorded via video, photographs, and written record of LEC’s observations. The tank’s interior and above grade, exposed portions of concrete wall and domed roof were also observed and documented. LEC’s field report is included in Appendix A of this technical memorandum. B. Visual Assessment Visual assessment can help identify obvious areas of concern such as the following: cracked or peeling coating systems; spalling concrete; debris on the reservoir floor; exposed and corroded reinforcing steel; interior and exterior appurtenance condition; efflorescence; etc. Though the quantitative data gleaned from a visual inspection alone comprises only part of the data necessary for a more comprehensive assesment. Obvious improvements required are discussed and included in the proposed scope of rehabilitation but the City should also be aware of how collecting additional quantitative data through more invasive methods can identify deficiencies that are not obvious from visual inspection alone. The alternatives evaluated attempt to capture the scope of these unknown conditions through some contingency planning. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 6 of 27 C. Exterior Overview The exterior portions of the reservoir are composed of cast-in-place concrete and horizontal preload wires reinforcing the walls with a design working stress of 105,000 psi. The roof dome is also concrete and original to the 1950’s construction. Finished grade around the structure slopes to provide drainage from south to north. Along the south, grade fully burries the walls of the structure but reveals as much as ten feet of cast-in-place concrete walls on the north side of the storage tanks vertical walls. D. General Observations: 1. The walls have several visible cracks and show signs of minor efflorescence and staining. i. The visible cracking appears to be non-structural and likely due to settlement and age. Figure 2 - Tank exterior walls with black staining. 2. Tension Ring: A concrete tension ring is present along the perimeter of the roof dome. The dome has a limited amount of cracking and a few minor concrete spall locations. i. The tension ring appears to be in good condition. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 7 of 27 Figure 3 - Sourdough Roof Dome Tensio Ring 3. Roof Dome: The roof dome structure is exposed cast-in-place concrete with a relatively recent rehabilitation to its post-tensioning cables and concrete end-cap. The dome has several small visible cracks and shows signs of minor staining. i. The visible cracking appears to be minor. 4. Reservoir Access: A walkway from the east side of reservoir provides access to a hatch through the dome and into the reservoir. i. The access hatch appears in good condition for its design but is showing signs of corrosion and does not contain a watertight seal ii. The railing system leading to the hatch is in good condition with a small amount of paint failure. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 8 of 27 Figure 4: Tank Appurtenances - Hatch (left); Railing (right) 5. Other Exterior Appurtenances: i. The vent is a “mushroom” type. It appears to be in good shape but is not frost proof. Figure 5: Tank Appurtenances - Mushroom Vent E. Interior Overview 1. The concrete dome shows spalling in several areas. 2. Other than the previously repaired concrete cracks, walls appear acceptable condition for a 65-year old structure. 3. The overflow pipe has scale build-up and signs of corrosion. Additionally, one of the three supports for the overflow tank is completely corroded and no longer offers support. 4. Ladder is scaled, corroded, and missing rungs Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 9 of 27 Figure 6 - Concave interior of concrete dome with areas of concrete spalling outlined. Figure 7 - Concave interior of concrete dome with areas of concrete spalling outlined. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 10 of 27 Figure 8 - Interior walls, overflow pipe (background), and access ladder (foreground). Figure 6, above, shows the top of the overflow pipe in the background from the perspective of the access ladder – seen in the foreground. Spalling is captured on the walls behind the ladder. This concrete deterioration is likely attributed to icing. Figure 9 - Photo of overflow pipe support (separation from wall circled in red). Figure 7, above, shows the separation of an overflow pipe support bracket from the wall. While Figure 8, below, provides context for the overflow inlets vertical relationship with the tank’s maximum operationg level. Note the water level in this photo is the maximum operating level of the reservoir. Spalling can be observed on the wall above the water level. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 11 of 27 Figure 10 - Overflow pipe bell inlet Figure 11 - Interior Access Ladder (existing crack previously maintained with epoxy pictured in left background) Figure 9 depicts a severely corroded access ladder. Also pictured are some of the previously repaired cracks. Neith these photos nor LEc’s written report identify any defects in the existing epoxy crack repair. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 12 of 27 IV. EVALUATION AND KEY FINDINGS NOTE: Appendix B offers a glossary of terms used to describe the concrete conditions discussed in the following section for the readers’ reference. F. Exterior Evaluation 1. Walls: The dome shows some signs of cracking but few signs of delaminating or spalling concrete. Exposed portions of the concrete tank have blackened over time. This can either be a condition of the coating system or the effects of efflorescence. Staining is minor and does not present a concern at this time. 2. Roof: Reservoir roof shows signs of minor efflorescence as well as cracking, settling, and minor stains in all quadrants. This indicates the dome is experiencing some minor level of distress. This distress could lead to additional future concerns regarding the structural integrity of the dome. 3. Appurtenances: i. Access Hatch is a steel cover with a steel frame cast in place. Consider replacement due to age, it shows signs of deterioration and and lacks a proper seal. ii. Mushroom vent is generally in good condition but lacks frost protection and screens to prevent intrusion from insects and birds. Consider replacement during a rehabilitation project. G. Interior Evaluation 4. Roof: i. The concave interior surface of the roof dome has areas of spalling and exposed rebar, though no significant areas of delamination. The spalling is likely caused by a combination of the following factors: humidity, condensation, suseptability to freeze-thaw cycles, and age of the concrete dome. ii. This type of concrete deterioration may be caused by minimal concrete cover over the reinforcing steel and can be aggressive. These areas will spall and release as soon as rebar corrosion causes the rebar to expand enough to crack and deteriorate the concrete. In these cases, large delaminated areas are unlikely to occur. The presence of widespread spalling and no delamination indicates this could be occurring at the Sourdough Tank. iii. Due to the geometry of a dome, gravity also aids in removing potential delamination. If left untreated the interior environment will continue to cause damage, negatively affecting the structure. To mitigate and decelerate the deterioration to the concrete roof dome, coat areas with spalling and exposed rebar with an epoxy based paint and resurfacer. Because the ceiling was inaccessible for close up inspection, additional Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 13 of 27 inspection is required while the tank is out of service to identify potential rehabilitation needs not identified in LEC’s inspection. 5. Walls: i. The interior concrete surface of the tank has areas of spalling, no significant concrete delamination, no significant areas of exposed rebar, and some previously repaired cracks. 6. Previously Repaired Cracks: i. The previous epoxy crack repair areas appears to be in good condition and seems to be protecting water intrusion as intended. With the exception of the spalled areas, the interior walls of the reservoir appear visually acceptable. An epoxy based coating and/or concrete resurfacer would decelerate further deterioration. Again, the structure would benefit from further inspection with the tank completely dewatered to identify additional rehabilitation needs. 7. Appurtenances: i. Metal appurtenances within the reservoir have experienced normal corrosion and degradation for a structure of this age. The metal access ladder is in poor condition, missing rungs, and is in an overall weakened condition. Therefore the existing ladder is unsafe for continued service and requires replacement. Overflow pipe is in good condition however the supports are showing signs of failure. If supports continue to corrode, the overflow pipe could break away from the wall which would result in a loss of storage and trigger an emergency replacement project to bring the reservoir back online. The City should replace these supports prior to such an event. H. ADDITIONAL EVALAUTION CONSIDERATIONS 1. Icing: ii. Icing may be occurring during cold weather. iii. To counter icing effects, operators operate the tank between 27’ and 30’during the winter to ensure maximum storage is available in the event the supply source freezes. iv. In contrast, summer time operations range between 24’to 30’. 2. Stratification: i. Operators noted the reservoir is experiencing thermal stratification in the summer. This is caused by two conditions: the treated water is much colder than tank water; and the proximity of the inlet to the outlet pipe readily allows for short circuiting (especially after thermal stratification has occurred). By adding means of mixing to sourdough reservoir, the city would see improvements to water quality and reduce risk of icing in the winter. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 14 of 27 3. Isolation Operations: i. The City operates the WTP to effectively maintain water surface elevation of Sourdough at a safe operating level for emergency preparedness and a shortage of overall system storage. Hilltop Reservoir is used when Sourdough reservoir is offline; however, reliance on this tank requires tighter plant operations. The amount of time the reservoir is offline should be minimized and the tank should only be taken offline during periods of off-peak demand. V. PROPOSED IMPROVEMENTS ALTERNATIVE NO. 1 – REHABILITATION A. Rehabilitation Improvements The approach to rehabilitation improvements is two-tiered: Level 1 components are clearly identifiable based on the assessment information available; and Level 2 components are yet to be identified and require additional assessment and evaluation. The following table summarizes Level 1 improvements for the City to consider. Table 1: Overview of Assessment Conditions COMPONENT Concern Condition ACTION Concrete - Exterior Walls Spalling Minor Continue to Watch Cracks None Exposed Rebar None Delamination None Concrete - Exterior Dome Spalling None Cracks Minor Continue to Watch Exposed Rebar None Delamination None Concrete - Interior Walls and Floor Spalling Minor Visual Inspection Cracks No New Visual Inspection Exposed Rebar None Visual Inspection Delamination Minor Visual Inspection Concrete - Interior Dome Spalling Minor Visual Inspection Cracks None Exposed Rebar Minor Railing Functionality Acceptable New Coatings Vent Cover Functionality Degraded Replace Hatches Functionality Degraded Replace Access Ladder Functionality Degraded Replace Overflow Pipe Functionality Degraded Replace Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 15 of 27 All proposed repair materials that will be in contact with potable water must be ANSI/NSF 61 rated for use in this environment. These standards provide third party verification that use of these products will not have any adverse health effects on water system users when installed in accordance with the manufacturer’s recommendations. B. LEVEL 1 REHABILITATION 1. Conduct a leakage test in fall of 2020 using ACI 350 Standards. Testing will require isolating the tank for 48-72 hours and measuring drop in water surface elevation. 2. If leakage testing results are within acceptable limits, then conduct a rehabilitation project to perform the following improvements: i. Replace access ladder. ii. Replace access hatch cover – consider adding intrusion alarms. iii. Replace overflow pipe supports. iv. Replace vent assembly. v. Add tank mixing to mitigate stratification. vi. Conduct further detailed visual inspection while reservoir is dewatered. Conduct step 1 thru 4 of Level 2 Assessment & Rehabilitation. vii. Perform leak testing and implement results into an annual leak testing protocol to determine if conditions are worsening. viii. Continue inspections and cleaning every 3-5 years. ix. Closely monitor changes in dome and wall conditions. x. If deterioration continues, plan a future rehabilitation project to address condition of concrete dome. xi. Continue to assess needs for future rehabilitation projects. Relying solely upon an underwater visual inspection for a condition assessment does not always provide the whole picture of the tank’s conditions. Underlying conditions may be present and warrant further investigation. Failed leak tests are one indication that further investigation is needed. If the Sourdough tank fails a leak test, then the City should consider Level 2 Assessment and Rehabilitation. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 16 of 27 Table 2: EOPCC for Sourdough Reservoir – Level 1 Rehabilitation C. LEVEL 2 ASSESSMENT & REHABILITATION: 1. With the reservoir completely drained and offline, and with concrete surfaces having been hydro-blasted, conduct hammer sounding tests and detailed visual concrete condition assessments. 2. If the hammer testing and detailed visual concrete inspections indicate unacceptable conditions, direct a specialty contractor to perform additional physical testing. Appendix E offers an overview of the additional testing methods that a Contractor would perform depending on the observations and deficiencies identified. 3. Determine and conduct appropriate physical testing. 4. Findings: i. Conduct an engineering evaluation of findings from the physical testing. Depending on feasibility findings, a rehabilitation project may include the work described in the following Level 2 action. ii. The scope of work identified in the Engineer’s Opinion of Probable Construction Cost (EOPCC) for the Level 2 Assessment & Rehabilitation for Sourdough Reservoir are not based on final quantities identified in LEC’s June 2020 inspection. Rather these quantities are assumed based on possible deficiencies identified in LEC’s observation and the Engineer’s past experience with storage facilities of similar construction, age, and condition. Actual Level 2 costs will need to be Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 17 of 27 confirmed through additional assessment and will likely vary from the EOPCC presented in Table 3. 5. Interior Tank Rehabilitation i. Interior Tank Spalling: Repair spalled or delaminated areas with appropriate concrete repair system. Repair exposed or damaged rebar with a suitable protection system. Apply an appropriate coating system to seal concrete from further moisture penetration. ii. Crack repair: Apply structural epoxy pressure injection system in old repairs and in any new cracks identified. 6. Prestressed Wire Condition Assessment i. Conduct non-destructive testing to assess the condition of the prestressed wire support. 7. Interior Dome Options i. Dome Option 1 Repair spalled or delaminated areas with appropriate concrete repair system. Repair any exposed or damaged rebar with a suitable protection system. Apply an appropriate coating system to seal concrete from further moisture penetration. ii. Dome Option 2 Demo existing concrete dome to top of exising tank wall. Modfiy top of existing tank wall to receive new dome. Install an aluminum geodesic dome with matte finish. iii. Dome Option 3 Demo existing concrete dome to top of exising tank wall. Modfiy top of existing tank wall to receive new cover. Install precast double tee concrete decking, support beams and columns. Install sloped roof system. iv. NOTE: If City elects to replace the dome cover, a replacement cover in-kind (prestressed concrete) should also be considered. Prestressed Contractors have specific knowledge of the demo and construction requirements of a prestressed tank like Sourdough. Rough estimates from suppliers indicate costs similar to the options listed above. 8. Long Term Maintenance i. Leak Testing: Continue annual leak testing per ACI 350. ii. Condition Assessment and General Cleaning: Continue to perform every 3-5 years. Monitor changes and assess future needs. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 18 of 27 Table 3: EOPCC for Sourdough Reservoir – Level 2 Assessment & Rehabilitation Table 3, above, includes a line item for dome replacement. The amount included is an average of three (3) alternatives considered: rehabilitation of concrete; geodesic aluminum dome; or a precast concrete cover and roof system. A fourth alternative should also be considered to evaluate replacement of the cover in-kind with a prestressed concrete dome. Budgetary discussions with prestressed tank manufacturers indicate similar pricing. Additionally, the Contractors qualified to perform a prestressed dome replacement bring specific knowledge of demolition and rehabilitation of components of prestressed concrete structures such as the Sourdough tank. That knowledge and experience may be beneficial to the success of a dome replacement project. Final pricing for the dome replacement selection will be considered during final design. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 19 of 27 D. SUMMARY TABLE FOR EOPCC Table 4: Total EOPCC for Alternative No. 1 - Sourdough Rehabilitation E. Other Rehabilitation Considerations 1. LEVEL 1 OPERATIONAL IMPACTS: o Minor Impact. o Level 1 rehabilitation methods will require the reservoir to be taken offline for 3-4 Weeks. o Conduct Level 2 assessment items including hydro-blasting, hammer sounding tests, and detailed visual inspections. 2. LEVEL 2 OPERATIONAL IMPACTS: o Impact significant. o The Level 2 rehabilitation methods will require the reservoir to be taken offline for an additional 4-6 weeks. o Total offline time needed to conduct both Level one and Level 2 improvements is estimated to be 7-10 weeks. o As discussed earlier, there is a concern with lateral pressure on walls when offline for extended periods of time. To address this concern, lateral bracing would need to be evaluated prior to commencing work and is considered in the rehabilitation costs. 3. SCHEDULE: o Level 1 Rehabilitation project carries an anticipated schedule as follows: o If findings indicate Level 2 Improvements are favorable, the schedule would include the additional time estimated below. Final construction schedules will be evaluated in greate scrutiny during final design if this is the City’s chosen alternative. Schedule Duration Design/Bidding 6 Months Construction 3 Months Tank Down Time 2 Months Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 20 of 27 4. PROJECT BIDDING STRATEGY AND EXPECTATIONS. o Bidding a Level 1 and Level 2 rehabilitation project separately adds administrative costs to the City’s projects. Efficiency can be gained if all the activities identified for both Level 1 and 2 can be included in the scope of a single public bid. The contract would include controls for the Owner to stop work in order to make decisions about the project’s feasibility based on initial findings and engineering evaluations. The activities for Level 2 would not be completed if Level 1 observations indicate the tank is beyond repair. o If a Contractor is procured in this manner, the City should be prepared to see variability between a Bid Price and the Final Contract Price. o The City should be aware that most of the cost of a Level 1 rehabilitation will be primarily sunk if findings indicate the Level 2 improvements are not feasible – though in the case for Sourdough there is less uncertainty about the needed repairs. o Again, since most of the work is obscured from direct observation to quantify the extent of work to be performed, the Engineer would build the bid schedule on a series of line items for unit price work with estimated quantities only. The City may desire to include relatively conservative quantities in the Bid Form in hopes that the final contract price be reduced by change order. o This Project would require extensive observation and coordination with the Contractor during Construction to measure and negotiate the final quantities of rehabilitation tasks performed – recognizing that measurement of final quantities of this nature can be an exercise in detailed estimation as opposed to precision measurement. This task places most of the complexity in engineering services in the Construction phase of the project – as reflected in the EOPCC table for Engineering Services. o Upon finalization of quantities for work performed, a balancing change order would be issued to adjust the Contract price for the Contractor. o Additionally, the City should consider authorizing its internal Project Manager to approve changes in quantities as they are identified to avoid additional costs caused by schedule delays waiting for approval from the City Commission. Additional Schedule Duration Construction 4 Months Tank Down Time 2-3 Months Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 21 of 27 ALTERNATIVE NO. 2 – REPLACEMENT OF EXISTING RESERVOIR A. Replacement Considerations This alternative evaluates construction of a new 4.0 million gallon prestressed concrete tank using AWWA D110 construction methods. This replacement includes piping modifications, and site grading. The reservoir will be a partially buried ground storage reservoir on the existing site. Improvements will include the following: 1. Geotechnical Investigation: i. A geotechnical investigation will be completed in the proposed reservoir location to confirm existing soil conditions. 2. Sitework: i. The tank would sit on the adjacent open land within the boundaries of the existing Sourdough facility. ii. Tank will need to be mostly buried to match hydraulic grade lines along the existing transmission main. This has the added benefit of providing frost protection for footings and foundation slab. iii. The drain and overflow pipe for the new reservoir will tie into the existing infrastructure – design should consider modifications to drain to the reservoir’s full depth. iv. Site pipe will be modified to allow water to be directed to the new reservoir and out to distribution. 3. Prestressed Reservoir: i. Reservoir construction will consist of a cast in place mat-slab foundation with prestressed concrete panel walls and dome in accordance with AWWA D110 standards. 4. Mixing: i. Add mechanical tank mixing to mitigate stratification. ii. Link external controls into WTP SCADA system (similar to the Hilltop Tank Mixing Improvements). Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 22 of 27 Table 5: EOPCC for Alternative No. 2 – Sourdough Reservoir Replacement B. Construction Schedule 1. Operational Impacts: i. Minimal. ii. Existing reservoir would remain in service while the new reservoir is constructed. iii. There would be minor impacts during site piping connections as needed. Schedule Design/Bidding 8 months Construction 18 months Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 23 of 27 VI. LIFE CYCLE COST ANALYSIS Identifying the lowest cost alternative is difficult when the two alternatives evaluated have drastically dissimilar usable lifespans (20 and 80 years, resptectively). A selection on capital cost alone is not a fully equivalent comparison. The life cycle cost analyses (LCCA) of Table 6 and 7, found in the following pages, provides a basis upon which to inform a recommendation based on the least cost alternative. Additionally, the LCCA’s reflect the assumptions listed below. A. LCCA Assumptions: 1. Economics: i. Standard cash flow factors are assumed to adequately model the life cycle costs for comparison purposes. ii. Capital Improvements Projects are assumed to be repaid over a 20-year period with 3% interest and no up-front payment on the principle. iii. Costs for future capital improvements assume a 4% inflation rate. iv. Actual interest and inflation rates will vary but are assumed to impact each alternative equally. v. Because the existing Sourdough Reservoir is not known to have significant water loss, the opportunity cost of the lost revenue water is not factored into this LCCA. 2. Salvage Value: i. Though the probability of liquidation for either asset in 50-years is essentially zero, the life cycle cost analyses include credits for the salvage value of the respective remaining life as a fraction of the original capital investment. 3. Alternative No. 1 – Rehabilitation i. The exected usable life of the rehabilitation proposed for Sourdough Reservoir is between 20 and 30-years. ii. Annual O&M costs are increased during the iterim period to account for additiona monitoring and conditions assessments to determine the appropriate time for future improvements. iii. A reservoir replacement project is assumed to occur in the year 2048. At that time, the reservoir will be nearly 100-years old. It is therefore not unreasonable to assume it will have reached the end of its usable life – though could potentially be operated for longer and will require future engineering and condition assessments. The assumption reflects conservativism in the LCCA. iv. At the end of the 50-year LCCA, the city will have paid all debts on the replacement reservoir’s construction. v. The assumed reservoir constructed in 2048 as a salvage value of $21.3- million or ~71% of the Total Project Cost since. This represents 57-years of expected usable life remaining of the total 80-year usable life. 4. Alternative No. 2 – Replacement i. The 50-year LCCA reflects a 20-year debt repayment period starting in the year 2021 covering the Total Project Cost for the Reservoir Replacement. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 24 of 27 ii. A repair and rehabilitation project is scheduled in the year 2061 and is assumed to be similar in scope to the Alternative 1 – Rehabilitation Project defined previously (with the exception of the replacement dome cover). The future rehabilitation project is inflated for the future value of present money. iii. By the year 2070, the City will have only paid 10 of the 20-year financing period for the future rehabilitation project and therefore has just over $5- Million in outstanding debt. iv. 30 years of usable life is credited back to the Alternative No. 2 5. FURTHER DISCUSSION: i. The reservoir replacement project in Alternative No. 1 was originally assumed to occur in 2051 to provide Alt. No. 1 with the benefit of the doubt that the rehabilitation work would have 30-years of reliable performance. However, that schedule actually showed Alternative No. 1 as the more expensive option. ii. Scheduling the replacement just 3 years earlier avoids additional costs due to inflation and results in Alternative No. 1 as the lowest cost alternative. iii. The primary reason the two alternatives prove to have such similar 50-year LCCA’s is attributed to the cost of a new dome cover for the rehabilitation project. This cost is excluded from the rehabilitation project included in Alternative No. 2, scheduled to begin in 2061. iv. By shifting the construction of a replacement tank at Sourdough three years earlier, Alternative No. 1 gains an advantage in the comparison but does not drastically change the nature or intent of the analysis. After all, the financial models will vary based on many factors: scope of final design; measurement and payment of final quantities; interest rates; inflation; and others. v. However, the shift considers the City’s financial interests and its preparedness to take on the considerable debt payments concentrated in the first 20 years of Alternative No. 2. Strategically staggering these debt payments is important when considering the overall capital improvements plan – especially similar improvements currently under consideration at the Lyman Reservoir. Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 25 of 27 Table 6: 50-Year Life Cycle Cost Analysis for Alternative No. 1: Sourdough Reservoir Rehabiltation Year Capital Cost Annual Operations & Maintenance Costs Repair and Rehabilitation Outstanding Debt Salvage Value 2021 199,688.16$ 2022 199,688.16$ 2023 199,688.16$ 2024 199,688.16$ 2025 199,688.16$ 8,487.20$ 2026 199,688.16$ 2027 199,688.16$ 2028 199,688.16$ 2029 199,688.16$ 2030 199,688.16$ 9,839.21$ 2031 199,688.16$ 2032 199,688.16$ 2033 199,688.16$ 2034 199,688.16$ 2035 199,688.16$ 11,406.60$ 2036 199,688.16$ 2037 199,688.16$ 2038 199,688.16$ 2039 199,688.16$ 2040 199,688.16$ 13,223.67$ 2041 2042 14,302.72$ 2043 2044 15,469.82$ 2045 2046 16,732.16$ 2047 2048 18,097.50$ 1,758,451.41$ 2049 1,758,451.41$ 2050 19,574.26$ 1,758,451.41$ 2051 1,758,451.41$ 2052 1,758,451.41$ 2053 1,758,451.41$ 2054 1,758,451.41$ 2055 22,692.44$ 1,758,451.41$ 2056 1,758,451.41$ 2057 1,758,451.41$ 2058 1,758,451.41$ 2059 1,758,451.41$ 2060 26,307.34$ 1,758,451.41$ 2061 1,758,451.41$ 2062 1,758,451.41$ 2063 1,758,451.41$ 2064 1,758,451.41$ 2065 30,498.10$ 1,758,451.41$ 2066 1,758,451.41$ 2067 1,758,451.41$ 2068 2069 2070 35,356.45$ SUB-TOTAL: 3,993,763.20$ 204,315.72$ 35,169,028.18$ -$ (20,972,083.87)$ 18,395,023.22$ ALTERNATIVE NO. 1: SOURDOUGH RESERVOIR REHABILITATION TOTAL 50 Yr Life Cycle Cost 50 Year Life Cycle Cost Analysis Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 26 of 27 Table 7: 50-Year Life Cycle Cost Analysis for Alternative No. 2: Sourdough Reservoir Replacement Year Capital Cost Annual Operations & Maintenance Costs Repair and Rehabilitation Outstanding Debt Salvage Vlue 2021 609,853.44$ 2022 609,853.44$ 2023 609,853.44$ 2024 609,853.44$ 2025 609,853.44$ 8,487.20$ 2026 609,853.44$ 2027 609,853.44$ 2028 609,853.44$ 2029 609,853.44$ 2030 609,853.44$ 9,839.21$ 2031 609,853.44$ 2032 609,853.44$ 2033 609,853.44$ 2034 609,853.44$ 2035 609,853.44$ 11,406.60$ 2036 609,853.44$ 2037 609,853.44$ 2038 609,853.44$ 2039 609,853.44$ 2040 609,853.44$ 13,223.67$ 2041 2042 2043 2044 2045 15,330.20$ 2046 2047 2048 2049 2050 17,772.30$ 2051 2052 2053 2054 2055 20,603.43$ 2056 2057 2058 2059 2060 23,885.55$ 2061 505,314.85$ 2062 505,314.85$ 2063 505,314.85$ 2064 505,314.85$ 2065 27,690.52$ 505,314.85$ 2066 505,314.85$ 2067 505,314.85$ 2068 505,314.85$ 2069 505,314.85$ 2070 32,101.62$ 505,314.85$ SUB-TOTAL: 12,197,068.80$ 180,340.29$ 5,053,148.52$ 5,053,148.52$ (3,403,200.00)$ TOTAL 50 Yr Life Cycle Cost 19,080,506.13$ 50 Year Life Cycle Cost Analysis ALTERNATIVE NO. 2: SOURDOUGH RESERVOIR REPLACEMENT Technical Memorandum SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 27 of 27 VII. SUMMARY AND RECOMMENDATIONS A. OVERALL SUMMARY B. RECOMMENDATIONS Based on the results of the 50-year life cycle cost analysis, the City’s least cost alternative is to pursue Alternative No. 1 – Sourdough Reservoir Rehabilitation: Pursuing reservoir rehabilitation provides the City with the following benefits: · Saves the City of Bozeman roughly $500,000 over the next 50 years. o Note this difference in life-cycle cost is almost negligible – mostly due to the investment in a new reservoir cover to increase the usable life of the existing facility. · Capitalizes on the remaining usable life of existing reservoir infrastructure. · Strategically staggers the debt payments for a future Sourdough reservoir replacement project opposite of the cost of more critical infrastructure improvements at Lyman Creek Reservoir. o This is based on a similar life cycle cost analysis of the Lyman Reservoir condition assessment. 2020 Capital Investments 50 Yr LCCA Alternative No. 1 - Reservoir Rehabilitation 2,971,550.00$ 18,395,023.22$ Alternative No. 2 - Reservoir Replacement 9,075,200.00$ 19,080,506.13$ Table 8: Overal Summary of Alternatives' Capital Costs and 50-Yr LCCA SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 1 APPENDIX A – LIQUID ENGINEERING CORPORATION DIVE INSPECTION REPORT ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Concrete Water Reservoir Inspection Report QUADRANT 1 QUADRANT 2 QUADRANT 3 QUADRANT 4 INTERIOR RESERVOIR ROOF Coating: Roof Slab(s) Expansion Joint(s) Support Beam(s) Beam Joint(s) General Appearance: All expansion Joints: Uniform width: Uniform Level: Gaskets Intact: INTERIOR RESERVOIR WALLS Coating: Leaking: Wall‐Roof Joint ‐ ‐ Wall Structure General Appearance: INTERIOR RESERVOIR SUPPORT COLUMNS Coating: Columns Column Capitals Column Bases General Appearance: INTERIOR RESERVOIR FLOOR Coating: Sump System: Leaking: Perimeter Joint Floor Slabs General Appearance: All expansion Joints Uniform width: Uniform Level:Gaskets Intact: CONCRETE CONDITION CODE A - Abrasion B - Bug HolesC - Cracking D - Deformation E - EfflorescenceF - Fissure G - Contraction H - Deflection I - Delamination V - VoidX - Exposed Reinforcement S - Spalling T - Exposed Aggregate P - Popouts Q - Settling R - Stains M - ErosionN - Peeling O - Curling J - Chalking K - Checking L - Expansion Additional Comments: Job Number: Utility: Tank: Inspector: Dive Controller: Date: Capacity:Dimentions: ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Concrete Water Reservoir Inspection Report Job Number: Utility: Tank: Inspector: Dive Controller: Date: QUADRANT 1 QUADRANT 2 QUADRANT 3 QUADRANT 4 EXTERIOR RESERVOIR ROOF Coating: Vents: Level Indicator: Roof Slab(s) Expansion Joint(s) General Appearance: All expansion Joints Uniform width: Uniform Level:Gaskets Intact: EXTERIOR RESERVOIR WALLS Wall‐Roof Joint ‐ ‐ Wall Structure General Appearance: Overflow Structure: Coating: Leaking: All expansion Joints Uniform width: Uniform Level: Gaskets Intact: EXTERIOR RESERVOIR FOOTINGS / FOUNDATION Coating: Leaking: Perimeter Joint Footing Ring General Appearance: All expansion Joints Uniform Width: Uniform Level: Gaskets Intact: Ground Subsidence: INTE RIOR RESERVOIR PLUMBING COMPONENTS SSPC Rating Corrosion Blistering Delamination Chalking Checking Cracking Cratering Pinholes Staining Sags/Runs Average Blister Size Inlet Plumbing Outlet Plumbing Manways Floor Drains Interior Overflow Other Plumbing Coating Deficiencies: Over All Coating Condition Over All Structural Condition Weld Condition Average Pit Depth Grade 10 9 8 SSPC Rating Description - Good Condition No Rusting, or <0.01% of surface is rusted Minor rusting, or <0.03% of surface is rusted Isolated rust, <.01% of surface is rusted Grade 7 6 5 SSPC Rating Description - Fair Condition Isolated rust, <.03% of surface is rusted Extensive rusting, <1% of surface is rusted Approximately 3% of the surface is rusted Grade 4 3 2 1 0 SSPC Rating Description - Poor Condition Approximately 10% of the surface is rusted Approximately 17% of the surface is rusted Approximately 33% of the surface is rusted Approximately 50% of the surface is rusted Approximately 100% of the surface is rusted CONCRETE CONDITION CODE A - Abrasion B - Bug Holes C - Cracking D - Deformation E - Efflorescence F - Fissure G - Contraction H - DeflectionI - Delamination V - Void X - Exposed Reinforcement S - Spalling T - Exposed Aggregate P - Popouts Q - SettlingR - Stains M - Erosion N - PeelingO - Curling J - Chalking K - Checking L - Expansion QUADRANT 1 QUADRANT 2 QUADRANT 3 QUADRANT 4 SSPC Rating Corrosion SSPC Rating Corrosion SSPC Rating Corrosion ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Potable Water Reservoir Contamination, Health and Safety Report (Primary) Job Number: Utility: Tank: Inspector: Dive Controller: Date: FACILITY SAFETY & HEALTH Primary Air Vent Pressure Vacuum / Frost Proof: Exterior Overflow Screen : Screen: Cathodic Protection Gasket: Cathodic Access Covers #: Water Level Indicatior Condition: 1st Access Hatch Size: Lid Height: Hatch Height: 2nd Access Hatch Size: Hatch Height: Type: Flapper: System Installed: Type: Installed: Type: in. (min 4") Type: in. (min 4") Lid Height: Pennetration Points in. (24" - 24" x 15" min) in (min 2") in. (24" - 24" x 15" min) in (min 2") Condition: Properly Sealed: Properly Sealed: Properly Sealed: Properly Secured: Properly Sealed: Properly Secured: Primary Manway Locations Wall: Leg: Roof: Riser Pipe: Other: Type and Size Type: Size: in (24" - 18"x22") Support Structure Type: Condition: WT Integrity Leaks: Condition: Primary Exterior Ladder Location Wall: Leg: Roof: Riser Pipe: Other: Vandal Guard Present: Locked: Ladder Rails & Rungs Condition: Anti-Skid Rungs: Missing/Damaged Rungs: Rung Spacing & Depth Spacing: in. (max 12") Toe Depth: in. (min 7") Rail Spacing & Size Width: in. (min 2") Thickness: in. (min 1/4") Rail to Rail: in. (min 16") Safety Climb System Type: Condition: Primary Balcony & Railing Location On Roof: Around Bowl: Deck / Walkways Condition: Width: At Interior Landing: Other: in. (min 24") Top Rails Condition: Height: in. (min 42" +/- 3") Swing Gate Present: Mid Rails Condition: Height: in. (half the distance between top rail and floor) Toe Boards Condition: Height: in. (min 4") Roof Integrity: Cracking: Standing Water: Other: Wall Integrity: Cracking: Leaks: Other: Safety Tie-Off Points #: Condition: Antennas #: Location(s): Roof: Bowl: Leg: Other: Water Clarity Odor: Surface Debris: Hypalon Floating Cover Holes: Tears: Grounding System Holes: Holes: Type: Type: General Appearance: Condition: Present: Overall Ladder Condition: Height: Offset Landing: Heater System Type: ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Circular Tank Diagram / Information Worksheet Job Number Utility Name Tank Name Quadrant 1 Quadrant 2 Quadrant 3 Quadrant 4 ROOF Testing and Discrepancy Locations FLOOR Q4 Q1 Q3 Q2 Q4 Q1 Q3 Q2 Plumbing & Structure location Plumbing and structure codes O=Outlet X=Inlet Z=Manway V=Vent D=Drain S=Sump L=Ladder H=Hatch P=Overflow F=Float Level Indicator T=Telemetry Sediment Depth Measurements Average Sediment Depth = The sum of all measurements taken, divided by the number of measurements taken Avg. Depth Cubic Yardage Sediment Type Column Placement Type of Column Base Structure Top Structure Column Construction ©Copyright 1998 - 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Rectangular Tank Diagram / Information Worksheet Job Number Utility Name Tank Name N Q-4 Q-1 Q-3 Q-2 N Plumbing & Structure location Plumbing and structure codes O=Outlet X=Inlet Z=Manway V=Vent D=Drain S=Sump L=Ladder H=Hatch P=Overflow F=Float Level Indicator T=Telemetry Sediment Depth Measurements Average Sediment Depth = The sum of all measurements taken, divided by the number of measurements taken Avg. Depth Cubic Yardage Sediment Type Column Placement Type of Column Base Structure Top Structure Column Construction Liquid Engineering Corporation Potable Water Reservoir Security / Measurement Worksheet Job Number Utility Name Tank Name Security Is the area surrounding the tank well lit? Is the tank surrounded by a Security Fence? Are the access gates locked? Is the tank equipped with a Vandal Guard on the primary access ladder? If so, is the Vandal Guard locked? Are the access roads in good repair? Are all of the hatches equipped with electronic monitoring devices? Are the external plumbing components housed in a secure vault or out-building? Does the surrounding geography of the tank obscure it from public view? Does the exterior of the tank show signs of trespass? Measurements Vent Roof Outside Circumference Inches Inlet Outlet Drain Overflow Inches Inches Inches Inches Inches Inches Inches Inches Overflow Wall Inlet Riser Outlet Riser Inches Inches Feet/Inches Inches Floor Floor Floor Flange Metal Thickness Inches Roof to Screen or Flange Inches Flange Number of Bolt Holes Inches Size of Bolts Inches DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise no ted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved Page 1 of 1 ©Copyright 1998 ‐ 2020 Liquid Engineering Corporation – All rights reserved DISCLAIMER Liquid Engineering does not provide consulting engineering services. Unless otherwise noted, the findings contained in this report were neither prepared nor reviewed by a licensed Professional Engineer, but are based on experience, training and visual examination of the Dive Maintenance Technician Liquid Engineering Corporation Potable Water Reservoir Immediate Needs Assessment Job Number: Utility: Tank: Inspector: Dive Controller: Date: 1.Health and Safety Items Safety Climb System Installation: Vent Screen Repairs: 2.Testing Items Dye Testing for Leak Evaluation: Presence of Lead Test (Interior/Exterior): 3.Repair Items Epoxy Coating Repairs: Temporary Leak Repairs: Float Operated Level Indicator Repairs / Maintenance: Hypalon Repairs: 4.Security Related Items (Critical security upgrade information is immediately available) Tank vents are not equipped with a security vent shroud: Tank hatches are not equipped with a security hatch locking device: Tank perimeter not adequately secured: The above mentioned additional work is considered immediately necessary and is recommended to be completed. Some items may be completed in conjunction with work currently being performed while the crew is on site. Reservoir Inspection Condition Supplemental SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 1 APPENDIX B – GLOSSARY OF CONCRETE CONDITIONS i. Concrete delamination is the separation of the bond between the cement and aggregate in the concrete mixture causing damage to the concrete. Many times this type of concrete damage is indicative of decline of structural integrity and also results in cosmetic issues. ii. Concrete spalling is the flaking of the concrete surface. This type of defect is seen in a concrete slab or a layer of concrete in locations that have colder climates and experience the constant destructive forces of freeze-thaw cycles. iii. Cracking at the walls and floor can be the result of change in structural forces, concrete shrinkage or settlement. Cracking can be narrow to wide in width and variable in length. Larger cracks can allow water to enter causing corrosion and/or freeze-thaw action and therefore present a concern for potential damage. iv. Efflorescence is the migration of a salt solution to the surface of the concrete. The solution evaporates leaving a coating of the salt. On porous construction materials, it may cause staining but at its worst can indicate internal structural weakness. Efflorescence may clog the pores of concrete, resulting in the destruction of those materials by internal water pressure, resulting in spalling. v. Exposed rebar is an obvious sign the structural rebar is no longer properly covered or encased by concrete. This rebar is subjected to the elements of the environment and can corrode leading to loss of structural integrity and potential failure. Exposed rebar can be a result of several factors but most commonly the intrusion of water and freezing action within the cover concrete. Exposed rebar is a cause for concern and requires prompt remedy. SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 1 APPENDIC C - LEVEL 1 REHABILITATION DETAILS: 1. Access Modification: a. Replace existing 36” x 36” hatch with new watertight surface mounted aluminum hatch. Add intrusion switches to hatch to monitor authorized and unauthorized entry. b. Replace existing steel access ladder with fiberglass, aluminum, or stainless steel ladder. 2. Overflow Pipe a. Replace the entire internal overflow pipe system. The new overflow pipe is anticipated to be ductile iron with coated steel supports. All submerged and exposed metal pipe components will require an appropriate coating for protection. As an alternate to overflow pipe replacement, the existing overflow pipe could be cleaned and inspected but effort to remove tuberculation will be significant and it will be more cost effective to simply replace. 3. Dome Vent Assembly: a. Replace existing dome vent assembly with a new aluminum assembly. New assembly to be sized to accommodate airflow of both current and future water volume movements and will be structurally suited for the expected snow loads. Assembly to include updated mounting system and bird screen. 4. Tank Mixing a. Add one or two electric mixing units operating either intermittently or continuously. Equipment will be submerged within the reservoir. Mixing system will be connected to SCADA and controlled remotely. Equipment will require periodic maintenance and access to equipment is essential. 5. Additional Physical Testing a. The reservoir will require draining to install the overflow pipe and ladder. Consider conducting additional physical testing as detailed in Tasks 1-4 of Level 2. SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 2 APPENDIX D - LEVEL 2 REHABILITATION DETAILS: 1. Interior Dome Repairs a. Access for Repairs: Interior dome repairs such as concrete spalling repair, delamination repair, and crack repair will be from inside the reservoir. Dome height at center is estimated at 50 feet with wall height at approximately 30-feet. The height above the floor will make access to the repair areas challenging and scaffolding systems and/or a portable scissor lift will be required. b. Temporary Lateral Bracing: Temporary bracing may be required to support and stabilize the wall if the reservoir is offline for an extended period. This will be confirmed by a detailed structural review of the record drawings. c. Debris Removal and Surface Preparation: High-pressure washing would be used to blast the underside of the reservoir dome to remove any loose material and prepare the surface. Additional sand blasting may be required if visual inspection indicates removal of additional loose materials is required. d. Additional Testing: Hammer sounding should be completed on the underside to ensure all loose/delaminated concrete is removed and a sound substrate is provided for repair work. e. Structural Repair: Repairs should include the use of a special mortar structurally applied to the underside of the dome and subsequently provide proper cover over the reinforcing steel. A suitable product is a fiber reinforced mortar specifically designed for corrosion prevention and structural enhancement. f. Corrosion Protection: A distributed surface applied galvanic anode system could be added for long term corrosion protection. The system consists of a special zinc coating installed on the exterior of the reservoir that is electrically connected to the embedded reinforcing steel and will act as a sacrificial anode to protect the reinforcing steel. This will protect both the repaired and unrepaired areas and will last approximately 15 to 20 years before needing replacement. Appearance would be grey and lighten over time as zinc corrodes. 2. Reservoir Wall and Floor a. In the upper regions of the reservoir wall water levels routinely fluctuate (Between 24’ and 30’ operating level) and ice action is present during winter operation. In this region, any loose materials should be mechanically removed down to sound substrate and appropriately repaired according to paragraph 3.a below b. The lower regions of the wall the surface concrete appears to be in good condition excepting the documented cracking. c. The floor surface concrete appears to be in good condition excepting the documented cracking. 3. Potential Concrete repair options: a. Wall and Floor Sealants: Interior walls should be resealed to protect the concrete from any further water intrusion. b. Cold joints and cracks should be repaired and sealed. There are several newer products that can be used to seal existing joints and cracks. i. Epoxy Injection: Epoxy would be injected into visible cracks to restore the concrete to its original condition. Note that the effectiveness of this repair method will be dependent on the ability to visually identify cracks. Epoxy injection also requires a dry surface for installation. Alternate urethane SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 2 of 2 injection products are applicable for wet conditions and may be an alternate solution. ii. Special Repair Mortar and Concrete Waterproofing System: Visible cracks would be sealed with a repair mortar and then the walls sealed with a concrete waterproofing system. SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 2 APPENDIX E – OTHER AVAILABLE EVALUATION TECHNIQUES FOR CONSIDERATION B. Infrared Delamination Survey Infrared thermography is a non-destructive testing method capable of identifying delaminated concrete near the concrete’s surface using temperature differentials. As ambient temperatures heat or cool concrete, areas that are delaminated change temperatures at a different rate due to thin delaminated concrete sections separated from the main concrete mass. Results typically indicate: · Concrete delamination. · Areas of concrete deterioration. · Areas of potential distress or porous concrete. C. Reinforcing Steel Cover Survey Ground penetrating radar provides an indication of concrete cover depth over reinforcing steel in accessible areas. Typical design standards for reservoirs detail a minimum of 2-inches of concrete cover over reinforcing steel. Without proper cover, reinforcing steel is susceptible to corrosion and can cause spalling on the concrete surface. Results typically indicate: · Concrete Cover Depth · Rebar Spacing D. Electrical Continuity Verification can help determine if the existing reinforcing is continuous throughout a slab section. The test measures electrical resistance between reinforcing steel in several locations by contacting intentionally and strategically exposed sections of rebar with electrodes. Reinforcing must be electrically continuous to perform corrosion potential measurements and is also an integral part of cathodic protection systems. Non continuous sections of rebar indicate areas where corrosion may have compromised the integrity of the rebars intended function. E. Corrosion Potential Survey Corrosion potential surveys identify areas of active corrosion on reinforcement within a structure. If the reinforcement is electrically continuous, it can be connected to a reference electrode which measures the voltage differential between the two points. Table E-1 below, outlines the interpretation of corrosion potential measurements per ASTM C876. The spatial variation of measurements along with magnitude can also be indicators of active corrosion. Table E.1 - Interpretation of Corrosion Potential Measurements per ASTM C876 Reading vs. Cu-CuSO4 Reference Electrode Probability of Corrosion Activity More positive than -200 mV > 90% probability of passive steel -200 to -350 mV Uncertain More negative than -350 mV > 90% probability of active corrosion * From VCS Investigation Report SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 2 of 2 Corrosion potential measurements are typically collected at accessible locations thought to have the greatest potential for active corrosion. These areas include the joints and pipe protrusions through the concrete. F. Chloride Concentration The presence and concentration of chloride ion by weight of concrete is an indicator for corrosion potential for reinforcing steel. A chloride ion concentration below 0.030% by weight of non- carbonated concrete measurement at the reinforcing steel cover depth is considered below the corrosion initiation threshold and has a low corrosion potential. . Technicians collect and analyze concrete samples at varying depths to determine if chloride concentrations exceed the 0.03% by weight threshold. G. Concrete Compressive Strength Testing Core samples are collected from various locations of the reservoir for compressive strength testing. The dome may not be thick enough to provide samples of adequate size for testing. Typical design strength for new reservoir concrete is a minimum of 4,000 psi. Concrete will continue to gain strength over time (assuming other environmental factors have not compromised strength). “Healthy” samples for structures of this age should return tests results with strengths well beyond the typical design strength. SOURDOUGH RESERVOIR – CONDITION ASSESSMENT, EVALUATION, AND RECOMMENDATIONS Page 1 of 1 APPENDIX F – RECORD DRAWINGS OF SOURDOUGH RESERVOIR