Appendix J: Pipe Evaluation and Replacement Options and Costs

Transcription

1 Appendix J: Pipe Evaluation and Replacement Options and Costs STORMWATER SYSTEM INVENTORY The City of Olympia has an extensive stormwater conveyance system. As a matter prudent management of the Stormwater Utility, it is necessary to know the quantity of pipe in the system and its age, condition, and life expectancy. This study focuses on the age, condition, life expectancy, and expected replacement cost of the present stormwater conveyance system (pipes). Other elements of the stormwater system that are not considered in this study are manholes, catch basins, pump stations, and storm ponds. The goals of this study are identified as the following: 1. Identify and quantify the entire existing stormwater pipe within the City of Olympia; 2. Collect data on the life expectancy of different pipe types; 3. Video select pipes to determine their condition and rate of deterioration; 4. Adopt a reliable system for storing and retrieving pipe condition information; 5. Project a useful life span for stormwater pipes; 6. Prepare a conceptual pipe replacement schedule; and 7. Prepare a pipe replacement cost estimate. The pipe replacement cost estimate can be used to plan for future budgetary needs to replace the existing system as it reaches the end of the its useful life. Storm pipes that reach the end of their useful lives can and do crack, leak, and collapse. These failures can cause street and property flooding, resulting in damage to property and streets. Pipes that collapse can result in an emergency condition where additional resources and dollars are spent responding to the emergency. Proactively replacing worn-out conveyance systems pipe can prevent future damages and efficiently uses the stormwater utility resources for replacing its infrastructure. Section 1. Type and Quantity of Pipe in Existing System The City of Olympia stormwater piping system contains approximately 670,000 feet of pipe, 4 inches in diameter and larger, composed of 5 basic materials. These include vitrified clay (VC), concrete (RCP & CP), high density polyethylene (HDPE), metal pipe (CMP), and polyvinyl chloride (PVC), and range in diameter up to 72 inches. In addition, there is approximately 109,000 feet of pipe in the combined sanitary/storm sewer system that is not included in this study because it is considered to be sanitary sewer pipe. For the purposes of this study, the various pipe diameters are grouped into four size ranges to simplify replacement cost estimating: 4 inches to 10 inches, 12 inches to 16 inches, 18 inches to 32 inches, and 36 inches and larger. The amount of pipe type in each size range is shown in the following table: J-1

2 Table 1: Existing Stormwater Pipes Size Range in Inches Vitrified Clay Concret e HDPE Metal PVC Total Percent of Total 4 to 10 24, ,000 6,000 48,000 97, , to 16 10,000 77,000 17,000 36,000 24, , to 32 7,000 44,000 11,000 33,000 7, , to , , , Total 41, ,000 34, , , , Percent of Total Section 2. Life Expectancy of Storm Pipes To determine the service life of storm pipes, a variety of different information sources were consulted. Sources included pipe manufacturers, pipe manufacturers associations, cities, counties, and state agencies. Most pipe manufacturers state a long service life for their material and a lower period for their competitors pipe materials. The information collected is summarized in Table 2. J-2

3 Table 2. Summary of Storm Pipe Life Pipe Material Manufacturer s Claimed Life Longest Duration Installed Comments City of Seattle Comments City of Tacoma Comments Pierce County Concrete 100 years 100+ years Preferred product; 60-year-old minimal pipe rehab PVC 100 year 30 years Cracks Easily Installed for 40 years 60-year-old installed pipes are okay Only SDR35 40-year-old installed pipes are okay Not available CMP 30 to 80, depends on soil resistance 120 years Will not use due to short life Rarely used due to life concerns 30-year-old pipe in need of rehab Vitrified Clay years Majority of rehab work; oldest pipe is 120 years old No Comments No Comments HDPE 70 + years 50 years Limited use; Solid wall only; Use in some central areas Limited use; Solid wall only 20-year-old installation appears as new To get an idea of the age of the storm sewer system within the City of Olympia, a sampling study approach was taken. Using the City s as-built drawings, the ages of a random sampling of pipes were determined. The ages were determined by looking at the date on the as-built drawing. A sufficient number of pipes were examined to create a distribution of pipe ages and to have a high level of confidence in the age determined. The following Table 3 summarizes the findings of the random sample. Table 3. City of Olympia Storm System Age of Pipes From Random Sample Vitrified Clay Concrete HDPE CMP PVC Sample Size 1* Oldest pipe in sample (yr) Std. Dev. Of sample (yr) Median Age in Sample (yr) Average Age in Sample (yr) Percent Confidence Interval Of Population Average Age (yr) * Numerous records were researched but only one record could be found. J-3

4 Since the sample sizes are small in relation to the population size, the 90 percent confidence level of the pipe average age is typically plus or minus five years. Thus, this study should be thought of as providing replacement time estimates in the range of plus or minus five years or within a time span of one decade. Section 3. Video Select Pipes to Determine Condition and Rate of Deterioration The objective of video inspection is two-fold: 1) Assess the condition of existing pipes, and 2) Provide a baseline to determine how the condition of storm pipe changes with age. To complete the first objective, the condition of the storm pipes inspected will be compared to those of new pipes, and some prediction of pipe life or rate of deterioration will be made. The pipes to be inspected are the oldest pipes of different material types determined in the random sample. To meet the second objective, the video inspection will be repeated in a number of years, and the change in condition in the interim period will be used to assess the aging rate of pipes. This second objective will not be completed for many years until the video inspection is preformed several times. The locations and ages of the pipes to be video inspected are given in Table 4 below. J-4

5 Table 4. Location and Age of Video Inspection Monitoring Study Storm Pipes Pipe Number Material Size (In Inches) Location Age City 10 Series Reference CR57-1 VC 30 Outfall Market Street to inlet through the port 1929 None CR57-2 VC Capital Way, Thurston to Olympia? None CR57-3 VC 8-12 Legion, Washington to Franklin? None CR57-4 Conc Chestnut, 4 th to 5 th 1927 FB-242, 1-18 CR57-5 Conc Cherry, 11 th to 12 th CR57-6 Conc Franklin, A to D 1951? CR57-7 Conc San Francisco, Pear to Quince CR57-8 CMP 8-12 East Bay Drive, near Berry CR57-9 CMP th Court, Mid-block, off Lilly CR57-10 CMP Cooper Point Road, between Caton and Carriage Loop F CR57-11 CMP I-5 ROW stream crossing at Henderson CR57-12 PVC 8-12 Buckingham, Gainsborough to South Hampton CR57-13 PVC 8-12 Mapleview Drive, Mapleview Court to Maple Ridge Court E CR57-14 PVC 8-12 Sunnyvale Court, mid-block, east of Goldcrest CR57-15 PVC 10 Caton Way, off Cooper Point Road A-B CR57-16 HDPE 8 Thomas Street, end of, south of 15 th 1967 LID673 CR57-17 HDPE 8-12 Carlyon, Boundary to Central 1977? CR57-18 HDPE Martin Way, mid-block, Sleater-Kinney to College 1978 FB960,4 The initial video inspection of the storm pipes has not been completed due to the workloads of the video inspection personnel. When the video and condition rating is performed, this section will be completed and an addendum will be prepared for this report. Section 4. Adopt a Reliable System for Storing and Retrieving Pipe Condition Information Since scoping this study, the sanitary sewer utility has researched and purchased a set of software programs that allows for the video inspection, condition rating, and storage of pipe condition information. The use of this equipment for the video inspection of storm pipes would be ideal for rating, storing, and retrieving storm pipe condition information. J-5

6 The pipe rating and storage system is not fully operational yet due to the workloads of the information technology personnel required to set up the storage devices. When this system is fully operational, all storm sewers should be inspected with the software and the relevant condition information stored for future use. Section 5. Project a Useful Life Span for Stormwater Pipes From the information gathered, it appears as though the expected life of pipe materials is in line with manufacturer s claims. Concrete, PVC, and Vitrified Clay pipes is 100 years, HDPE can currently be assumed to be slightly less at 80 years, and metal pipe can need replacement in as little as 30 years in high groundwater areas, but 50 years may be an appropriate life span. The useful lives used in this study are given below. Table 5. Useful Life of Storm Pipes Pipe Type Useful Life Vitrified Clay Concrete HDPE Metal Pipe PVC 100 years 100 years 80 years 50 years 100 years The Washington State Department of Transportation recommends a minimum design life of 50 years for all pipes. Section 6. Conceptual Pipe Replacement Schedule Using the distribution of ages in the sample, the total length of pipe within the City storm sewer system was divided up into the same age distribution. For example, if the City has 30,000 feet of a type of storm pipe and the sample had an age distribution of 33 percent at 0 to 10 years old, 33 percent at 10 to 20 years old, and 33 percent at 20 to 30 years old, then 10,000 feet would be assumed to be 0 to 10 years old, 10,000 feet at 10 to 20 years old, and 10,000 feet at 20 to 30 years old. The expected life of different pipe types from Section 1 was used to project the replacement decades of the current system s total length. The projected replacement decades of the current storm system are shown in Table 6. Note that the vitrified clay pipe was evenly divided into the next three decades since the one pipe found was 70 years old and life expectancy is 100 years. J-6

7 Table 6. Projected Length of Storm Pipe to be Replaced in a Decade Decade Ending Vitrified Clay (feet) Concrete (feet) HDPE (feet) CMP (feet) PVC (feet) Total (feet) , , , , , ,600 11, , , ,900 35, , ,900 11, , ,300 11, , , , ,400 14, , , , ,700 45, ,900 58,900 Total 34, ,600 31,700 99, , ,800 Expected Life 100 years 100 years 80 years 50 years 100 years Section 7. Prepare a Pipe Replacement Cost Estimate Currently, the most cost-effective means of replacing a failed pipe is to rehabilitate the pipe with trenchless technology. Trenchless technologies avoid expensive road restoration cost. To utilize trenchless rehabilitation, the pipe cannot be collapsed, and the pipe route cannot be changed. It is anticipated that the majority of the pipes will be replaced by trenchless technology. Currently, the best prices for trenchless pipe replacement are using cured in-place relining technology. The City of Seattle has a one-year contract with Insituform West, Inc., to reline various sized pipes. Using the distribution of different pipe sizes in the City storm system and the contract price to reline that size pipe, a weighted average cost to reline the various pipe types can be determined. For example, if the City has 30,000 feet of a type of storm pipe and the sample had a size distribution of 33 percent at 4 inches to 10 inches in diameter, 33 percent at 12 inches to 16 inches in diameter, and 33 percent at 18 inches to 32 inches in diameter, then 33 percent would cost $50 per foot to reline, 33 percent would cost $70 per linear foot to reline, and 33 percent would cost $100 per linear foot to reline. The weighted average cost to reline a random section of the storm pipe would be {(0.33x$50)+(0.33x$70)+)(0.33x$100) }=$72.6 per linear foot. J-7

8 It could be expected that with the aging of the storm sewer system over the entire country that rehabilitation technologies will advance and become more cost efficient over the next century. If this is so, the cost projections in this study will be overly conservative. Since it is impossible to predict future costs, this study uses current costs. Table 7. Distribution of Storm Pipe Sizes and Average Cost to Reline Pipe Types Pipe Sizes in Inches Vitrified Clay (Percent of Total) Concrete (Percent of Total) HDPE (Percent of Total) CMP (Percent of Total) PVC (Percent of Total) Contract Reline Cost 4 to $50 12 to $70 18 to $ or Larger $150 Weighted Reline Cost $63.47 $65.60 $76.18 $83.33 $56.64 Applying the information in Tables 6 and 7, we can estimate the cost to replace the current system and when those expenditures will take place. Expenditures to reline pipe in the future will require more in future dollars than present dollars. To adjust to future dollars, 2 percent annually compounded inflation was added to the reline cost. Table 8 presents the estimated costs to repair the current storm system. The raw data provided in this analysis results in some large variations in storm pipe expenditure between decades. The reality of financial planning is that a constant or growing budget is needed for planning purposes. A curve of best fit was determined for the raw data of the average annual repair costs. The best-fit line was a straight line starting at $85,000 and increasing at $34,500 per year. J-8

9 Table 8. Estimated Cost to Repair the Existing Storm Sewer System in Future Dollars Decades Raw Cost in Decade Raw Average Annual Cost *Smoothed Average Annual Cost 2002 to 2010 $851,000 $106,375 $85, to 2020 $3,020,000 $302,000 $430, to 2030 $7,629,000 $762,900 $775, to 2040 $6,377,000 $637,700 $1,120, to 2050 $2,985,000 $298,500 $1,465, to 2060 $22,305,000 $2,230,500 $1,810, to 2070 $2,960,000 $296,000 $2,155, to 2080 $60,266,000 $6,026,600 $2,500, to 2090 $15,728,000 $1,572,800 $2,845, to 2100 $24,168,000 $2,416,800 $3,190,000 * Smoothed data is for the middle of the decade. The data in Table 8 is shown in Figure 1 in graph form. Conclusions and Recommendations From the information presented above the following conclusions and recommendations can be made. Conclusions 1. Potentially some of the storm sewer system is reaching the end of its useful life within this decade. These pipes are the vitrified clay and CMPs. 2. CMP should not be used in current storm sewer installations. It is not allowed in the City of Olympia for pipe less than 36 inches in diameter. 3. Over the next century, storm pipe rehabilitation will be a growing industry and increasing amounts of money will have to be spent on replacing or rehabilitating storm pipes. Recommendations 1. Set up a pipe rehabilitation program to be funded in the order of $85,000 for 2002 and increased annual funding at a rate of $34,500 per year, compounded. J-9

10 2. Look for partnering opportunities with roadway overlay and rebuild project to reconstruct vitrified clay and metal pipes. 3. The cost projections in this study should be updated as pipe rehabilitation technologies advance and become more cost effective. 4. Start rating pipes and storing conditions; assess for priority replacement and projecting future replacement schedules. J-10