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HomeMy WebLinkAbout; Buena Interceptor Sewer and Vallecitos Interceptor Sewer; ASSESSMENT REPORT; 2004-02-14Assessment Report on the Buena Interceptor Sewer and Vallecitos Interceptor Sewer February 14, 2004 PAL AA AIRPORT RO .. ,~it~(; ' ·, ..• . . -''" , . ., ' ;.;1 .,:.,-.-,_. 1 INTRODUCTION This assessment report is an engineering evaluation of the Buena Interceptor sewer and the Vallecitos Interceptor sewer. The combined capacity of both interceptors convey over 5 million gallons per day (MGD) of Carlsbad's average dry weather wastewater flow to the Encina Water Pollution Control Facility. Therefore, these interceptors are an important component of Carlsbad's wastewater conveyance system, and must be maintained in a reliable condition. The information presented is being submitted to comply with the threshold and target requirements outlined in City Goal number 476. Threshold required developing background information on each interceptor sewer to determine the condition of each pipeline, the current flow rates and pipeline capacity, and Carlsbad's capacity rights. The background documents are listed in Appendix "A" of this report. Requirements for target include preparation of this assessment report, which utilized the information gathered in threshold, to provide conclusions and recommendations regarding: • Capacity rights • Pipeline condition • Current maintenance activities • Budgets for fair share capital improvements • Recommended changes to existing capacity share agreements This assessment report is separated into two main sections. The first section discusses the Buena Interceptor sewer and the second section discusses the Vallecitos Interceptor sewer. The following team members developed this report. Sincerely, William E. Plummer Deputy City Engineer Carrie Loya-Smalley Senior Engineer BUENA INTERCEPTOR SEWER ASSESSMENT REPORT Background The Buena Sanitation District constructed the Buena Interceptor Sewer in 1964, which is referred to on the original plans and capacity agreements as the "Outfall Sewer'' or the "Encina Outfall". Carlsbad's Sewer Master Plans for 1987, 1992, 1997 and 2003 refer to the sewer as the Buena Interceptor. The Buena Interceptor consists of a gravity flow pipeline and a sewage forcemain. It extends from the Encina Water Pollution Control Facility, located in the City of Carlsbad on Avenida Encinas south of Palomar Airport Road, to the Buena Creek Lift Station located in the City of Vista east of Melrose Drive and north of Sycamore Avenue. The Buena Interceptor is owned and maintained by the Buena Sanitation District, which is now a subsidiary district of the City of Vista. Capacity Share Agreements A series of agreements between the Buena Sanitation District and the City of Carlsbad defines capacity rights in the Buena Interceptor between the two agencies. The original agreement approved on June 20, 1966 was replaced on December 15, 1981 with a new agreement. The 1981 agreement established the City of Carlsbad's percent share capacity in the interceptor, which is as high as 35 percent in the downstream reach, refer to Table 1. The 1981 agreement had a termination or "sunset" clause of July 1, 1996. This agreement, however, was amended in 1987 for an additional 0.8 MGD of "temporary" capacity. Copies of the 1981 and 1987 agreements are located at the back of this report. The 1987 agreement is intended to provide Carlsbad with additional capacity until a replacement sewer is constructed. Table 1 Carlsbad's Caoacitv Riahts in Buena lnterceotor Sewer Pipeline Carlsbad's Percent Share of Total Station to Station Line Capacity (a) 0+00 20+81.43 34.88 20+81.43 33+36.43 31.71 33+36.43 42+28.18 28.21 42+28.18 67+42.43 28.21 67+42.43 87+57.43 21.13 87+57.43 190+93.29 18.84 190+93.29 204+08.65 17.65 204+08.65 209+56.94 17.65 (a) In addition to the percent share, a 1987 agreement provides Carlsbad an additional 0.8 MGD in each pipeline reach. 3 Pipeline Reaches The gravity flow portion of the Buena Interceptor extends from El Camino Real west to the Encina Water Pollution Control Facility, and is divided into eight pipeline reaches noted as B1 through B8. Each pipeline reach corresponds to the eight different percent share allocations noted in Table 1. Connecting to the upstream end of pipeline reach B1 is a sewer forcemain, which is designed only for pressure flow, and conveys wastewater from two lift stations serving the City of Vista and Buena Sanitation District. For reference, these reaches are shown on Figure 1. The capacity of each pipeline reach is dependent on its pipe size and minimum slope of the pipe in the reach. The size and the different slopes of each pipeline reach are shown on Figure 2 for reference. A summary description of each pipeline reach is shown in Table 2. Table 2 Buena Interceptor Sewer Enqineerinq Data Enqineerinq Data Citv of Carlsbad Ownership Reach Pipe Minimum Length Capacity Percent Capacity Available Size Slope (a) Ownership Rights Capacity (in.) (Percent) (Feet) (MGD) (MGD) (mgd) /bl B8 30 0.10 2,081 7.64 34.88 3.46 0.8 B7 24 0.32 1,255 7.53 31.71 3.19 1.4 B6 24 0.27 892 6.92 28.21 2.75 0.9 B5 21 0.56 2,514 6.98 28.21 2.76 0.9 B4 21 0.46 2,015 6.32 21.13 2.14 0.3 B3 18 1.00 10,336 6.18 18.84 2.13 0.4 B2 15 2.60 1,315 6.17 17.65 1.89 0.8 B1 18 2.20 548 9.17 17.65 2.41 1.3 force 14 (c) N/A 14,612 N/A 00.00 0.0 0.0 main (a) "Capacity" assumes the maximum depth of flow in the sewer pipe does not exceed ¾ of the pipe diameter using a Manning's "n" value of 0.013. (b) Carlsbad's capacity rights include percent share ownership of the pipe "capacity" plus 0.8 MGD. (c) Portions of the 14" forcemain have been replaced with 16", 18" and 24" diameter pipelines. Flow Monitoring Existing flow-monitoring data was available from reports prepared by the City of Carlsbad and the Encina Wastewater Authority. This data is from calendar years 2001, 2002, and 2003. The capacity of each gravity sewer is based on the relative depth of flow within the respective pipeline reach. Sewer interceptors are not typically designed to flow full, as unoccupied space at the top of the pipe is required for conveyance of sewage gases and to provide contingent capacity for wet weather inflow. Interceptor sizing is typically based on the pipeline flowing 75 percent full at peak wet weather flow (PWWF). 4 The 1987 agreement states, "When peak flows reach 75% of the depth of the pipe in any reach of the Encina Outfall as determined by the Buena Sanitation District, Carlsbad shall construct a replacement outfall". The agreement also states lease payments in the amount of $7,500/year "shall double when depths exceed the 75% depth of the pipe threshold and double again each year until flows are removed". Buena Sanitation District has not provided Carlsbad any determination or notice on the depth of flow in the pipe nor have they submitted a request for Carlsbad to construct a parallel sewer. Flow depth measurements have approached the 75 percent of pipe diameter criteria. Following is a discussion on the results of the flow monitoring performed by each agency. Flow Monitoring by Carlsbad -Flow monitoring was preformed by the City of Carlsbad at four locations along the Buena Interceptor over a period of three years. The four locations were selected based on inflow from major connections to the interceptor. The information is contained in three reports, which include Bi- Annual Flow Monitoring For 2001, October 2001, Bi-Annual Temporary Flow Monitoring 2002, Submittal May 8, 2002, and the Bi-Annual Temporary Flow Monitoring 2003 Wet Weather Submittal, May 16, 2003. From downstream to upstream, the monitoring locations include manholes at: • Motel 6 parking lot on Paseo Del Norte • Palomar Oaks Way near Palomar Airport Road • Yarrow Drive at Camino Vida Roble • El Camino Real near Palomar Airport Road. Monitoring periods include: • April/May, 2001 • AugusUSeptember 2001 • February/March 2002 • February/March 2003 A summary of the average and peak flow rates measured is shown in Table 3. 5 Table 3 Summarv of City Flow Measurement Data Date of Location of Measurement Measurement Paseo Del Palomar Oaks Yarrow Drive PAR near Norte -Motel Way (1) @Camino ECR(3) 6 Parking (5) Vida Roble (2) (MGD) (MGD) (MGD) (MGD) April 2001 2.95 avg. 1.63 avg. 1.64 avg. 0.94 avg. (wet weather) 5.55 peak 4.31 peak 3.34 peak 5.16 peak Sept. 2001 2.22 avg. 1.93 avg. 2.02 avg. 3.34 avg. (dry weather) 4.24 oeak 4.06 peak 5.67 oeak 7.12 peak February 2.58 avg. 2.42 avg. 2.23 avg. none 2002 4.88 oeak 4.18 oeak 4.45 oeak March 2003 3.27 avg. 3.19 avg. 2.45 avg. none 5.70 oeak 6.83 oeak 8.74 peak Results of the flow monitoring at the four locations noted above indicate the following: • At average day dry weather flow rates the depth of flow is always below 75 percent of the pipe diameter for all locations monitored. • At peak day dry weather flow rates, the depth of flow approached 75 percent of the pipe diameter except at one location. • At peak hour wet weather flow rates, spikes occurred at three of the locations resulting in the flow depth exceeding 75 percent of the pipe diameter. These locations were the Motel 6 parking lot on Paseo Del Norte, Yarrow Drive at Camino Vida Roble, and El Camino Real near Palomar Airport Road. At Palomar Oaks Way near Palomar Airport Road the depth of flow was measured to be just below 75 percent of the pipe diameter. Flow monitoring by EWA -The Encina Wastewater Authority (EWA) monitors flow rates at three locations along the Buena Interceptor on a continuous basis. The flow rate measurements are taken at the Buena Creek Lift Station (82 meter), the Raceway Lift Station (V2 meter) and at the Encina Water Pollution Control Facility (81 meter). The data is used to establish Carlsbad's flow rate for treatment at the Encina Water Pollution Control Facility. Carlsbad's flow rate is determined by subtracting the flow rate measured at the Buena Creek Lift Station and the Raceway Lift Station from the Encina Water Pollution Control Facility. The resulting difference in flow rates is a measure of Carlsbad's flow rate entering the interceptor sewer and being treated. 6 The data collected by EWA is tabulated continuously on an hourly basis at each of the three metering sites. In reviewing the recorded data for calendar year 2002 and 2003 the following was determined. • The highest average monthly flow rate recorded in the Buena Interceptor was 1.91 MGD, which occurred in November 2003. • The highest peak day flow rate entering the Encina Water Pollution Control Facility from the Buena Interceptor was 4.24 MGD, which occurred on November 12, 2003. • The highest recorded peak hour flow rate entering the Encina Water Pollution Control Facility from the Buena Interceptor was 6.15 MGD, which occurred on November 12, 2003 at 11 :00 AM. The combined flow for Buena and Carlsbad is within the capacity limits of the pipeline with depth of flow theoretically not exceeding 75 percent of the pipe diameter. • Carlsbad's highest average monthly flow rate in the Buena Interceptor was 0.97 MGD, which occurred in November 2003. • Carlsbad's highest peak hour flow rate was 2.11 MGD measured on November 12, 2003 at 9:00 AM. The peak hour flow rates for Carlsbad are within the capacity limits established in the capacity agreement between Buena Sanitation District and Carlsbad. Carlsbad's Tributary Collector Sewers The City of Carlsbad has fourteen collector sewers that connect to the Buena Interceptor. These are labeled C1 through C14 on Figure 1. Build out of the service area tributary to each collector sewer primarily has occurred except for C13 and C14. Both C13 and C14 collector sewer pipelines have additional undeveloped or unoccupied industrial lots that could connect to the sewer system. Since these two collector sewers are at the upstream reach of the Buena Interceptor, the new connections would add more flow to Carlsbad's capacity share at all gravity flow pipeline locations along the Buena Interceptor. The ultimate peak wet weather flow in each reach was determined in the March 2003 Sewer Master Plan, and is shown in Table 4. Table 4 -Buena Interceptor Carlsbad's Ultimate Peak Wet Weather Flow Rates Per Pipeline Reach B1 B2 83 84 B5 B6 87 B8 1.1 1.1 1.7 1.7 1.8 1.8 1.8 2.6 MGD MGD MGD MGD MGD MGD MGD MGD Pipeline Replacements Since its original construction, the forcemain has had sections replaced, and the remaining sections will be replaced within two years. Initial replacements 7 occurred in 1989, when the 14-inch diameter pipe was replaced with a 16-inch diameter pipe from the Buena Creek Lift Station to the intersection of Melrose Drive and Dawson Drive, and an 18-inch diameter pipe was installed from Dawson Drive to the intersection of Sycamore Street and Melrose Drive. A 24- inch diameter pipe was installed in Melrose Drive from Sycamore Street west to Faraday Avenue. The replacement pipelines coincided with the construction of new street improvements, which realigned the forcemain basically into Melrose Drive. Vista is pursuing a three-phase program to replace the remaining sections of the forcemain, which is noted in their May 1993, and July 2001 sewer master plans. Phase 1 was designed and constructed in 2003, and included replacing the forcemain from El Camino Real to a point 1,787-feet east with a 24-inch diameter PVC pipeline. The pipeline is referred to as BSD-FM1. Vista's 1993 Sewer Master Plan called for a parallel 16-inch diameter forcemain along with the existing 14-inch diameter forcemain from the intersection of Melrose Drive and Faraday Avenue to El Camino Real. However, to increase pumping capacity at its Buena Creek Lift Station, Vista replaced the old forcemain with a larger 24- inch diameter pipeline. The increase in pipe size reduces friction head loss, which compensate for a proposed extension of the forcemain occurring in Phase Ill. Although Phase 1 was constructed, the valves have not been opened to use it to convey wastewater. Phase 2 will relocate the old forcemain into the new alignment of Faraday Avenue when the developer for Carlsbad Oaks North constructs the Faraday Avenue extension from Orion Street east to the city limits of Carlsbad. The pipe size will be increased from 14 -inches to 24-inches. Vista indicates they have adequate funding for the project, and construction would probably occur in 2005. Phase 3 will extend the forcemain along Palomar Airport Road from El Camino Real west Yarrow Drive and then they will also construct an 18-inch diameter gravity sewer from Yarrow Drive to Camino Vida Roble. Phase 3 has not been placed in their capital improvement program; and therefore, construction may not occur for another five years or longer. Vista presently has no funding for the project in. The Phase 3 forcemain extension would remove Vista's flow from the gravity sewers in reaches B1, B2, B3, and B4. It would also place 50 percent of Vista's flow in the Vallecitos Interceptor sewer where Vista has capacity rights of up to 3.75 mgd. This project will relieve capacity concerns within the entire gravity flow section length of the Buena Interceptor. Pipeline Inspections In 1996 the City of Vista completed a manhole inspection of the 63 manholes along the interceptor from the Encina Water Pollution Control Facility east to El Camino Real. All but three manholes were found to need improvements at that time. Improvements range from a complete rehabilitation to replacement of the manhole covers. Below is a summary of the recommendations: • Rehabilitate eleven manholes. 8 • Recoat and repair approximately seventeen manholes. Recoating in most cases includes recoating the entire manhole. Repairs include any combination of the following: repairing or reconstructing channels, replacing concrete on the inside and outside of manholes, raising manholes, replacing top rings, replacing cones, and replacing or repairing a portion of the shafts. • Recoat and replace approximately eleven manholes. Recoating in most cases includes recoating the entire manhole and replacement of the manhole covers and or cover frame. • Recoat approximately nine manholes. • Replace five manhole covers and/or cover frames. • Five manholes were not located and most were expected to require rehabilitation. The work recommended in this inspection report was not initiated. Recent discussions with Vista indicate that when Vallecitos Water District completes a project to slipline the Vallecitos Interceptor Sewer where it crosses Interstate 5 in April 2004, then Vista plans on cleaning the Buena Interceptor Sewer along with performing a pipeline CCTV inspection. The CCTV inspection will result in a condition assessment report scheduled for completion in the summer of 2004. Vista has completed the bid documents for the inspection and cleaning project, which should be advertised and awarded in the next three months. Vista also is budgeting in their capital improvement program the anticipated funding necessary to make any recommended improvements that would be identified in the 2004 assessment report. They plan to construct the improvements sometime in FY 2004/2005. Inflow/Infiltration In May 2001 Vista assessed the condition of their collector sewer pipelines tributary to the Buena Creek Lift Station and the Raceway Lift Station. For the Buena Creek Lift Station they determined that infiltration from ground water is probably not a problem because they found no difference between summer and winter flows. However, for inflow they determined up to 1.4 MGD entered the sewer system during wet weather time periods. Similarly, they estimate that inflow is a major problem on Raceway Lift Station increasing the flows by as much as 0.22 MGD. No inflow/infiltration report was prepared for the Buena Interceptor. Since this pipeline was constructed in 1964 using vitrified clay pipe, it is anticipated that the joints are not watertight so infiltration is probably occurring in high ground water locations. In addition, as noted Vista did complete a manhole inspection report and it shows that repair work is needed. Therefore, inflow is probably occurring during wet weather time periods. Proposed Revisions to Capacity Agreements The City of Carlsbad receives sewer service· for a portion of its service area through the Buena Interceptor sewer. Carlsbad's current capacity rights are contained in two separate agreements, which are listed in Appendix A and were 9 previously described above. In reviewing these two agreements, there are four main issues that need to be addressed, which is described below. First, each agency's capacity rights are out of date and needs to reflect ultimate buildout conditions. For Vista their buildout capacity at peak wet weather flows at Buena Creek Lift Station is estimated at 7.09 MGD and 1.87 MGD for the Raceway Lift Station. The combined flow is 8.97 MGD, which would exceed the capacity of the existing gravity pipeline system. On an interim basis Vista estimates Raceway Lift Station will need to pump 1.32 MGD and Buena Creek Lift Station will need to pump 6.00 MGD. The combined flow of 7.32 MGD would not provide Carlsbad sufficient capacity to convey its own wastewater flows. With respect to Carlsbad, the flow capacity requirements vary for each pipeline reach depending on the tributary flow from collector sewers that connect to each reach. The current flows in each collector sewer can be determined from actual flow measurements or estimated on an equivalent dwelling unit basis. The ultimate peak wet weather flow rates are listed previously in Table 4 of this report. Second, maintenance of the interceptor sewer needs to be detailed in terms of frequency, the type of activity, and what each agency is responsible for. Third, an annual maintenance budget should be established to provide adequate funding for, maintenance and replacement of the gravity flow sewer portion of the pipeline. Based on recent bids that Carlsbad received, cleaning costs for a 24- inch diameter pipe is approximately $3.95 per foot to $4.42 per foot. Smaller pipe diameters would be lower in cost. On average cost would be $2.00 per foot for budget purposes. The cost for CCTV inspection is $2.00 per foot. Using these unit costs the pipeline could be inspected and cleaned every five years at $4 per foot. With a length of 20,957-feet the work could be budgeted at $84,000 to occur once every five years. Fourth, if Vista extends the forcemain to Camino Vida Roble, then they would no longer need pipeline reaches B1, B2, B3, and B4, and eliminating their flow contribution from these pipeline reaches should be addressed. Further, Vista's flow in the remaining reaches, B5 through B8, would be reduced by 3.75 MGD, which would change the percent share each agency would need the last three each pipeline reaches. Conclusions Based on the information contained in the documentation obtained for this report and discussions with Peter Nieblas and Carlos Mendoza of the City of Vista, and Mark Elliott and Larry Pierce of PBS&J (consultant for Vista) the following is concluded: 1. Pipeline Capacity -The dry weather flow rates measured in the gravity flow portions of the Buena Interceptor sewer are within the capacity agreement limits of 75 percent of the pipe diameter. However, under wet weather 10 conditions, spike conditions have occurred that reach or slightly exceeded the 75 percent pipe diameter criteria at several locations. The peak wet weather flow rate theoretically was calculated at 4.7 MGD, however, this is lower than the actual recorded highest peak wet weather flow rate at the Encina Water Pollution Control Facility of 6.15 MGD. Inflow is responsible for the high flow rate and this condition should be corrected. 2. Carlsbad's current flow rate -Based on flow metering results prepared by the Encina Wastewater Authority, Carlsbad's tributary peak wet weather flow is 2.43 MGD. This flow rate is within Carlsbad's capacity rights in Reach BS and B7, which limit Carlsbad's share to 3.46 MGD and 3.19 MGD, respectively. Reach B6 is also within Carlsbad's capacity rights because collector sewers C1 and C2 do not contribute flow to this reach. The remaining pipeline reaches are also adequate for Carlsbad when ultimate peak wet weather flow rates are compared to Carlsbad's peak wet weather capacity rights. 3. Vista's planned flow rate increases -Vista anticipates increasing the combined peak pumping capacity from the two lift stations from 7.33 MGD to 9 MGD. Upgrades to the Buena Creek Lift Station were recently completed, and Vista is preparing the design to replace Raceway Lift Station with a new facility within two years. This is Vista's highest priority project because of failure concerns with the existing pumping facility. However, the combined peak wet weather flows from these two lift stations would exceed the capacity of the gravity flow pipeline; and therefore, both lift stations need to limit their maximum pumping capacity to avoid surcharging the downstream gravity sewer pipeline. 4. Carlsbad's planned flow rate increases -Carlsbad's sewer service area will have an increase in development, resulting from future connections. Most new connections will occur on collector sewers C13 and C14. Since these two collector sewers are at the upstream end of the gravity flow portion of the Buena Interceptor, the new connections would add more flow to Carlsbad's capacity share at all gravity flow pipeline reaches. 5. Forcemain Replacement -Sections of the forcemain have been replaced and the remaining section will be replaced within the next two years when the Faraday Road extension is completed by the developer of Carlsbad Oaks North. 6. Forcemain Extension -Vista plans on extending the forcemain in Palomar Airport Road from El Camino Real west to Yarrow Drive using a 24-inch diameter pipe, and then constructing an 18-inch diameter gravity sewer from Yarrow Drive to Camino Vida Roble. The extension would occur sometime in the future, beyond the next five years. This forcemain extension project referred to, as Phase Ill would remove any future 11 capacity concerns in the Buena Interceptor for both Vista and Carlsbad. The forcemain/sewer extension will also divert up to 3. 75 MGD of Vista's wastewater flow, to the Vallecitos Interceptor where Vista has capacity rights to 3.75 MGD. 7. Forcemain Extension Impacts -It is important to note that when Buena Sanitation District constructs a planned new forcemain extension, that only flow from Carlsbad will be in the Buena Interceptor upstream of Camino Vida Roble. At that time, Buena Sanitation would be in a position to request that Carlsbad purchase the upstream reach of gravity sewer pipeline at a depreciated value since Vista would no longer contribute wastewater flow to the upstream sewer pipeline reaches. 8. Pipeline Maintenance and Repairs -Our records show that Vista has never cleaned the gravity flow sewer. However, in February 2004 Vista advertised to receive bids for cleaning the gravity sewer portion and also performing a CCTV inspection. The cleaning and video work should be completed within six months. Vista is planning to make any necessary repairs identified in the CCTV inspection in FY 2004/2005. Repairs are anticipated to be needed on the manholes based on a 1996 Manhole Inspection Report. The pipeline condition is not known at this time. However, because it is constructed of VCP, corrosion is probably not a problem. Broken pipe sections are possible and they would need to be replaced or sliplined with "lnsituform" or other material. 9. Lease Payments -There is no record that Carlsbad has been paying Vista the lease amount of $7,500 per year as described in the 1987 Capacity agreement for use of the Buena Interceptor. Back payments may need to be budgeted or discussed with Vista. 1 O. Infiltration/ Inflow -Because the pipe material on the gravity flow portion is vitrified clay pipe, the joints are not considered to be tight. In addition, the age of the pipeline would also impact the integrity of the pipe joints. Therefore, in locations where there is high ground water it is anticipated that infiltration is occurring through pipe joints and manholes. The amount of infiltration cannot be estimated without bypassing the collector sewers. However, during Vista's CCTV inspection of the Interceptor sewer, they will be able to determine whether infiltration is occurring. If infiltration were occurring, the agencies would have to determine the extent and the possible solutions to eliminate or reduce the problem, which may include sliplining work. Inflow is definitely occurring primarily in Vista's collection system. This is evident by the pumping capacity requirements used in sizing the expansion of each lift station. For Buena Creek Lift Station the peaking factor is 2.35. For the Raceway Lift Station the peaking factor is 3.1. For 12 the size of these pumping stations the peaking factors should be 2.1 or less. In addition, historically the Buena Creek Lift Station had a separate set of pumps to convey wastewater to the Shadowridge Treatment Plant. This was done to divert flows in wet weather periods for treatment at Shadowridge. Since Vista no longer is using the Shadowridge Treatment Plant, all the flows are now pumped to the Buena Interceptor. Carlsbad's collector sewers and the Buena Interceptor itself may also have inflow occurring through manhole covers that contribute to the inflow problem. Recommendations A. The combined peak wet weather flow from the Buena Creek Lift Station, which was recently upgraded, and the Raceway Lift Station, which is planned for an upgrade within two years, will exceed the capacity of the gravity flow pipeline reaches. Therefore, discussions need to occur with Vista regarding limiting the pumping capacity of the combined flow from the two lift stations to less than 5.8 MGD. This would provide sufficient capacity for Carlsbad's tributary flow. B. Vista should be encouraged to proceed with Phase 3 of their forcemain/gravity sewer extension project as soon as possible. This project would eliminate all flow capacity issues on the Buena Interceptor. C. Carlsbad should review the 2004 gravity flow pipeline condition assessment report, which will be prepared by a contractor for Vista and assist Vista in making any necessary repairs if requested. Funding could be budgeted for FY 2005/2006. D. Maintenance should occur on a regular basis, which may include periodic pipeline cleaning (every 5 years) and making repairs as required to maintain the useful life of the interceptor sewer. Sewer cleaning and CCTV contracts for this size pipeline are approximately $85,000. Assuming the work is performed every five years a budget in the amount of $20,000 per year could be established with each agency paying its proportionate percent share. Carlsbad may want to take a more proactive role to see that improvements planned to extend the useful life of the pipeline. The improvement work may be pursued by Carlsbad either by working directly with contractors, utilizing City maintenance staff, or proportionately funding Vista's activities. 13 VALLECITOS INTERCEPTOR SEWER Background The Vallecitos Interceptor Sewer (VIS) was originally designed in 1983 and constructed in 1984. The plans referred to the project as the "Land Outfall Sewer." Agreements between Carlsbad, Vista and Vallecitos Water District refer to the VIS as the "Palomar Joint Land Outfall Interceptor''. Carlsbad's Sewer Master Plan refers to the pipeline as the Vallecitos Interceptor Sewer. The VIS is owned and operated by the Vallecitos Water District (VWD). The VIS extends from the Encina Water Pollution Control Facility east approximately 8 miles to an existing sewer lift station located along San Marcos Boulevard in the City of San Marcos. The VIS consists of a gravity flow sewer, and three inverted siphons. Capacity Agreement Through an interagency agreement dated January 8, 1985, the City of Carlsbad has rights to 23.98% of the pipe capacity from El Camino Real west to the Encina Water Pollution Control Facility. Carlsbad also has peak wet weather capacity rights of 5.0 mgd. The maximum capacity of the pipeline is 20.85 MGD. Pipeline Reaches The VIS is divided into eight pipeline reaches. Reach V1 includes a gravity sewer pipeline, a portion of which is in a tunnel extending 50-feet below ground level. Reach V2 includes a long inverted siphon extending approximately from El Camino Real east to the intersection of San Marcos Boulevard near Discovery Street. Reach V2 does not allow any collector sewer connections. Pipeline reaches V3 through V8 consists of gravity flow sewer pipelines and two inverted siphons extending from the Encina Water Pollution Control Facility east to El Camino Real. Carlsbad has capacity rights in these last six pipeline reaches. At the upstream end of VIS is Lift Station No. 1, which can divert a portion of Vallecitos Water District's wastewater, up to 5 MGD, to the Meadowlark Water Reclamation Plant, see Figure 3. In addition another pump station called the "West Lift Station" also pumps flow to the Meadowlark Water Reclamation Plant. However, VWD must maintain at least 3 mgd in the VIS to have the large inverted siphon operate properly with enough scouring velocity. Therefore, the amount of flow diverted by Lift Station No. 1 is controlled to provide an acceptable minimum flow rate in the VIS sewer siphon. The capacity of each 14 pipeline reach is determined based on pipe size and minimum slopes of the pipeline reach. This information is shown on Figure 4. Table 3 below summarizes the capacity of each pipeline reach compared to the available capacity rights of Carlsbad. Table 1 Vallecitos Interceptor Sewer Enoineerina Data Enaineerino Data Citv of Carlsbad Ownership Reach Pipe Minimum Length Capacity Percent Capacity Available Size Slope Ownership Rights Capacity (in.) (Percent) (Feet) (MGD) (MGD) (MGD) V8 54 0.15 870 49.2 10.2 5.0 4.1 V7 39 0.16 2,130 21.3 23.5 5.0 4.1 V6 30 0.68 3,400 21.8 22.9 5.0 4.1 V5 30 0.68 1,670 21.8 22.9 5.0 4.1 V4 30 0.68 6,510 21.8 22.9 5.0 4.1 V3 30 0.67 3,260 21.7 23.0 5.0 4.1 V2 20 N/A 4,355 21.7 0.00 0.0 N/A 24 N/A 14,960 0.00 0.0 N/A V1 30 0.02 1,563 21.7 0.00 0.0 N/A 36 0.02 5,061 0.00 0.0 N/A Flow Monitoring Existing flow-monitoring data was available from reports prepared by the City of Carlsbad and the Encina Wastewater Authority. This data is current and therefore additional flow measurements were not needed to evaluate the capacity remaining in the pipeline. Following is a discussion on the results of the flow monitoring performed by each agency. Flow monitoring by Carlsbad -Flow monitoring was preformed by the City of Carlsbad at two locations along the Vallecitos Interceptor Sewer over a period of three years. The two locations were selected based on inflow from major connections to the interceptor. From downstream to upstream, the locations include manholes at: • Motel 6 parking lot on Paseo Del Norte • Las Palmas Drive at its east end within an existing dirt access road Monitoring periods include: • April/May, 2001 • August/September 2001 15 • February/March 2002 • February/March 2003 Results of the flow monitoring at the four locations noted above indicate the following: • At average day dry weather flow rates, the depth of flow is always below 75 percent of the pipe diameter at both locations monitored. • At peak day dry weather flow rates, the depth was always less than 75 percent of the pipe diameter. • At peak hour wet weather flow rates, spikes occurred at the Motel 6 parking lot resulting in the flow depth exceeding 75 percent of the pipe diameter with a measured depth "D" to pipe diameter "d" of 0.87 (i.e. D/d =0.87). At the other location the depth of flow was less than 50 percent. Significant inflow from the Vallecitos Water District resulting in the high peak flow rates is causing the flow depth to exceed 75 percent of the pipe diameter at the downstream reach. The capacity agreement between Carlsbad, the Vallecitos Water District and the City of Vista does not have any requirement to maintain the depth of flow below 75 percent of the pipe diameter, and is not possible since there are three siphons that will cause the flow to seal the pipe. However, it is desirable to not exceed this limit so that sewer gases may be transported with the wastewater. Flow Monitoring by EWA -The Encina Wastewater Authority (EWA) measures flows on a continuous daily basis on the VIS in order to determine Carlsbad's contributory flow into the Encina Water Pollution Control Facility. Flows are measured at El Camino Real and also at the Encina Water Pollution Control Facility. The difference between these flow rate measurements is Carlsbad's tributary flow entering the VIS and being treated by EWA. Using EWA's data over the calendar years 2002 and 2003 the following was determined: • March 2003 had the highest average monthly flow rate in the VIS, which was 8.434 MGD and the highest peak hour flow rate recorded was 11.35 MGD, which occurred on March 16, 2003 at 11 :00 A.M. • Carlsbad's peak wet weather flow rate also occurred in March 2003 with a flow rate of 0.69 MGD, and a peak hour flow rate of 0.89 MGD recorded on March 16 2003. • In December 2003, the average flow rate in the VIS was 5.69 MGD with a peak hour flow rate of 9.14 MGD occurring on December 27, 2003 at 11 :00 AM. During that same time, Carlsbad's tributary flow was 0.417 MGD with a peak hour flow rate of 0.536 MGD. • In all cases Carlsbad's flow rates were well below its capacity rights of 5.0 MGD. The peak flow rate measured is also within the capacity of the VIS. 16 Pipeline Replacements Two major replacements occurred on the VIS since its original construction. The first replacement occurred in 1997 when an inverted siphon failed near Las Palmas Drive, adjacent to property owned by the City of Carlsbad. At this location the pipeline was replaced with ductile iron pipe. The failure occurred when corrosion, caused by high levels of hydrogen sulfide gas, resulted in the formation of sulfuric acid, which attacked and penetrated the inner lining of the metal ductile iron pipe. The corrosion that followed caused the pipe to collapse and wastewater flowed through parking lots and City streets. The second replacement occurred in 1998 when a portion of the long inverted siphon was abandoned from the City limits of Carlsbad to El Camino Real. This portion of the sewer siphon was originally constructed of cement mortar lined and coated steel pipe, but was replaced with 24-inch diameter ductile iron pipe with a double cement mortar lining. This work occurred at the same time as the Rancho Carrillo land development project. In addition, a hydrogen peroxide injection manhole was installed on the sewer pipe near El Camino Real. Recent discussions with Vallecitos Water District indicate they are using Bauxite rather than hydrogen peroxide to control hydrogen sulfide gas levels. Vallecitos Water District is also preparing plans to replace the remaining portion of the sewer siphon extending from the city limits of Carlsbad east to the tunnel section of the gravity sewer pipeline. Vallecitos Water District plans to construct this pipeline replacement in 2005. At that time the entire sewer siphon extending from El Camino Real to the tunnel will have been replaced. Carlsbad's Tributary Collector Sewers The City of Carlsbad has twelve collector sewers that connect to the Vallecitos Interceptor. These are labeled C1 through C12 on Figure 3. Build out of the development tributary to the collector sewers has occurred except for C12. Collector sewer C12 will have major additional industrial, commercial and residential lots that will connect to the sewer system mainly in the Bressi Ranch and Villages of La Costa (The Greens) development projects. It is estimated that at buildout, C12 will have an average wastewater flow of 0.89 mgd and a peak flow of 2.14 mgd. Since this collector sewer is at the upstream reach of the Valecitos Interceptor, the new connections would add more flow to all downstream pipeline reaches. The future additional flow is not expected to exceed Carlsbad's capacity share in the Vallecitos Interceptor. Flow from collector sewer C7 will be eliminated in 2005 when the City's planned Cannon Road Lift Station is constructed. This project will allow the Upper Faraday Lift Station to be abandoned and the flow from Upper Faraday Lift Station will proceed by gravity to the Cannon Road Lift Station. From the 2003 Sewer Master Plan, Carlsbad's average flow rate is presently estimated at 0.97 MGD. Using a peaking factor of 2.36 results in a peak dry weather flow rate of 2.3 MGD, which is well below Carlsbad's capacity right of 5.0 MGD. 17 Pipeline Inspections In 2003, Vallecitos Water District performed a CCTV inspection of the pipeline. From the results of the inspection, two major improvement projects were subsequently designed. The first included rehabilitating the manholes from El Camino Real west to Interstate 5 using a spray on two-part epoxy resin by Raven Lining Systems. This work was completed in 2003 and the City of Carlsbad paid $48,182.51 for its proportionate cost share of the work. The second project includes sliplinning the ductile iron sewer pipe crossing under Interstate 5 with Hobas pipe. This work will be constructed in April 2004. Carlsbad's share of this project is $136,798.99, which was paid in December 2003. Corrosion and Odor Control The Vallecitos Water District has experienced some major failures along the pipeline at various locations. These failures are primarily a result a hydrogen sulfide (H2S) gas releasing and generating sulfuric acid that attacks the pipe interior above the water level. Because the siphon pipes were constructed using ductile iron pipe the sulfuric acid that was generated slowly attacked the interior lining of the pipe. To control this situation Vallecitos Water District is now using Bauxite. This is a proprietary chemical, which is added to the interceptor at El Camino Real at the rate of 400 gallons per day. Vallecitos Water District monitors the H2S levels at that point and also near College Boulevard. Their operations manager indicates that they are now maintaining H2S at acceptable levels. Revisions to Agreement Conditions Carlsbad's buildout peak wet weather flow rate varies depending on the pipeline reach. The projected flow rates were estimated in the 2003 Sewer Master Plan and are shown in Table 2. The current capacity rights of 5 MGD can accommodate all projected flow rates. Table 2 Carlsbad's Peak Wet Weather Flow Rates in Each Pioeline Reach V3 V4 V5 V6 V7 V8 2.1 MGD 2.3 MGD 2.3 MGD 3.2 MGD 3.2 MGD 3.35 MGD Carlsbad may want to amend the existing agreement to revise its capacity rights by lowering them to 4.0 MGD in the interceptor sewer. Conclusions Based on the information contained in the documents reviewed for this report and discussions with Dennis Lamb and Rich Arrant of Vallecitos Water District the following can be concluded: 1. In 2003, the VIS was inspected and problem areas where identified by Vallecitos Water District. The problem areas included rehabilitation of gravity sewer manholes, sliplining the sewer pipeline crossing Interstate 5, and replacing the long inverted siphon pipe from the City limits east to the 18 tunnel section. Provided all these improvements are completed the interceptor sewer is in acceptable condition. 2. The manholes were repaired in 2003 by Vallecitos Water District and the City of Carlsbad paid its proportionate share of the project cost. 3. The Interstate 5 Freeway Sliplining project was awarded and the work will occur in April 2004. 4. Vallectios Water District is presently in design with the replacement of the remaining portion of the long siphon (Portion of reach V1 ). 5. The City of Vista proposes in the future (no date specified) to connect their Buena Interceptor to the Vallecitos Interceptor near the intersection of Camino Vida Roble and Palomar Airport Road. At that time, one half of their flow in the Buena Interceptor, approximately 3.75 MGD, would be diverted to the Vallecitos Interceptor sewer. 6. Carlsbad's current flow rates are within its capacity rights of 5.0 MGD. In 2003 Carlsbad's peak hour wet weather flow rate was 0.9 MGD. At buildout of Carlsbad's tributary sewer system the flows will increase to 3.35 MGD. 7. Vallecitos Water District and Vista combined will have 11.04 MGD tributary to the interceptor sewer at buildout. The total combined flow with Carlsbad is projected to be 12.58 MGD. This flow rate will be accommodated in the capacity of the VIS, which is 21.8 MGD. 8. Inflow during wet weather periods remains a big problem. Most of the inflow is tributary to Valllecitos Water District. Recommendations The condition of the pipeline and appurtenances is being addressed by Vallecitos Water District and Carlsbad has been paying its share of the cost of those improvements. However, the following is recommended: A. The operation and maintenance procedures and programs employed by Vallecitos Water District should be listed and described in a report prepared by Vallecitos Water District to develop an understanding between all three agencies. This would help ensure that adequate measures are being taken to identify any corrosion problems that may be occurring along the pipeline alignment that would jeopardize the integrity of the pipeline. B. Carlsbad may want to consider reducing its capacity share in the pipeline from 5 MGD to 4 MGD to reflect current buildout flow conditions. 19 APPENDIX A SUMMARY LISTING OF BACKGROUND DOCUMENTS,REPORTS,PLANS,AND AGREEMENTS 20 TITLE DATE DESCRIPTION Documents and Renorts City of Carlsbad Sewer Master March 2003 Current and buildout flow Plan Update Final Report, rate estimates, description prepared by Dudek & Associates, of pipe condition, Inc. ownership agreements, l&I discussion City of Carlsbad Master Plan of January 1992 Current and buildout flow Sewerage, by Wilson rates, pipeline reach Engineering description, capacity ownership City of Carlsbad Bi-Annual Flow October 2001 Flow rates and depth Monitoring For 2001, prepared by measurements at 4 MGD Technologies, Inc. locations City of Carlsbad Biannual Maya, 2002 Flow rates and depth Temporary Flow Monitoring 2002 measurements at 4 Submittal, prepared by MGD locations Technologies, Inc. City of Carlsbad Biannual May 16, 2003 Flow rates and depth Temporary Flow Monitoring 2003 measurements at 4 Wet Weather Submittal, prepared locations by MGD Technologies, Inc. City of Vista and Buena May 1993 Land use & population Sanitation District Master Plan of data, design criteria, Sewerage by Wilson Engineering wastewater flow rates, costs, and capital improvement program. City of Vista Buena Outfall Sewer Manhole Inspections and May 13, 1996 Report on condition of all Recommendations, prepared by manholes. Wilson Enaineerina 21 Wastewater Flow Measurements 2002 and 2003 Continuous hourly flow taken at Buena Creek Lift Station, measurements Raceway Lift Station, El Camino Real, and Encina Water Pollution Control Facility by Jeff Parks at Encina Wastewater Authority 2003 Encina Water Pollution Control Average monthly flow rates Facility Wastewater Flows by by member agencies Encina Wastewater Authority Infrastructure Review Summary & July 2001 Flow estimates, Wastewater Master Plan Update inflow/infiltration analysis for the City of Vista, prepared by design criteria, capacity Powell/PBS&J analysis, condition assessment, and capital improvement program. Final Program Environmental April 2003 Environmental impact Impact Report for the City of report on Master Plan Vista and Buena Sanitation update. District Wastewater Master Plan Update, prepared by Dudek & Associates Buena Interceptor Upgrade March 2002 Shows options to extend Route Selection and Flow forcemain to connect to the Splitting Study Vallecitos Interceptor, and flow splitting structure. Raceway Sewer Pump station -January 30, Flow projections, pump Preliminary De.sign by PBS&J 2004 station design criteria, preliminary layout, estimated cost Letter to Property Owners by City January 22, Notice that the Buena of Vista providing notice of 2004 Interceptor will be cleaned maintenance program in April 2004 during eveninq hours. 22 Memo from Mark Biskup to Bill August 12, Discusses Vista's three Plummer regarding Phasing of 2003 phases to construct the Forcemain forcemain improvements on the Buena Interceptor Vallecitos Water District, Final July 1991 Water, Wastewater and Wastewater flows, Reclamation Master Plan, by collection system, capital John S. Murk Engineers, Inc. improvement program Vallecitos Water District Update October 1997 Wastewater flows, to the Water, Wastewater and collection system, capital Water Reclamation Master Plan, improvement program prepared by Camp Dresser & McKee Vallecitos Water District Capital April 28, 2000 A CCTV video inspection facilities Interceptor Video report of the Vallecitos Inspection Report, prepared by Interceptor indicating pipe Downstream Services size, material and general condition. Memo Re: Meadowlark July 8, 2003 Sewer flow projection data WWTP/EWA Phase V Flows, applicable to Phase V from City of Carlsbad Deputy PW expansion to be conveyed Director, Robert Greaney to by Vallecitos Interceptor. Deputy City Engineer, William Plummer Memo Re: Odors on Palomar October 21, Data recorders (odalogers) Airport road at College 2003 placed in manhole to Boulevard, from Rich Arrant, measuring H2S levels Systems Maintenance Supervisor summary of findings at Vallecitos Water District to Bill Plummer at the City of Carlsbad Meeting Notes Re: VWD Information on H2S control Interceptor Sewer Odor September measures performed by Problem/Maintenance from Bill 2003 Vallecitos Water District, Plummer's meeting with Rich chemical addition, quantity Arrent at VWD. and costs 23 Poinsettia Lift Station test results October 23, H2S results from for odor since bioxide treatment 2003 measurements taken at began. Results emailed to Bill Poinsettia Lift Station. Plummer from Louie Montanez Letter from Vallecitos Water October 30, Payment requests in District to Carlsbad regarding 2003 amount of $200,927.90 for manhole repair work on 23.98% cost share of Vallecitos Interceptor manhole rehabilitation work. Letter from Vallecitos Water November 21, Payment requests in the District to Carlsbad on 1-5 2003 amount of $136,798.99 for Crossing Sliplining Project 23.98% share of sliplinning project cost Plans and Drawinns Buena Sanitation District's 24-September 30, Plan and Profile Drawing inch Force Main Outfall Line 2002 Reconstruction (Approved Date) Plans for the Construction of December 12, Plan and profile drawing Land Outfall Interceptor SWRCB 1985 Project No. C-06-1571-100, (Record Schedule I Tunnel, Sewer Main Drawing Date and Appurtenances, and for Sched I) Schedule II Sewer Main and Appurtenances Odor Control, May 19, 1986 Meter Station and Connection to (Record Existing System, Conformed Drawing Date plans, Sheets 1 thru 48 of 48 for Sched II) Vallecitos Water District Land May 7, 1998 Plan and Profile Drawing Outfall Sewer Rehabilitation Sta (Approved 140+35 to Sta 156+85, Sheet 5 Date) of 7 24 San Marcos County Water May 5, 1981 Plan and Profile Drawing District Failsafe Outfall Sewer ("As-Built Date) City of Vista Plans for the September 1, Plan and Profile Drawing Construction of Realignment of 1992 Portions of Buena Sanitation (As Built Date) District Outfall and Failsafe Sewers, Sheets 2 and 3 of 3 Anreements Agreement Between the Buena December 15, Capacity allocation in Sanitation District and City of 1981 percent share per pipeline Carlsbad for the Lease of reach to Carlsbad Capacity in the Encina Outfall Agreement Between the Buena December 15, Increase of 0.8 MGD in Sanitation District and City of 1987 capacity to each pipeline Carlsbad for the Lease of reach and payment of Additional Capacity in the Encina $7,500 per year for leasing Outfall capacity Palomar Joint Land Outfall January 8, Capacity rights in Vallecitos Interceptor lnteragency 1985 Interceptor to Vista, Agreement Carlsbad and Vallecitos Water District, payment of capital and maintenance costs Agreement for Exchange of March 24, Purchase capacity for 80 Sewage Flows Between the 2000 residential units in Vallecitos Water District and the Vallecitos Water District City of Carlsbad (Meadowlark Estates/Rancho Carrillo Sewer Flow Agreement) 25