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Home My WebLink AboutRP 05-12A; AGUA HEDIONDA OUTER LAGOON; SEWER STUDY; 2013-11-12Va ARCADIS The Water Division of ARCADIS Imagine the result Carlsbad Desalination Project Sewer Study FINAL November 12, 2013 PoS-c2A. cepor+5 Sewer Study Carlsbad Desalination Project November 12, 2013 Rick Kennedy, PE ARCADIS Project Manager Jena Prior, PE Design Manager Sewer Study Carlsbad Desalination Project 1. Introduction I Project Description 2 Design Criteria 2 3.1 Sources of Wastewater 2 3.1.1 Normal Daily Flows 3 3.1.2 Intermittent Daily Flows 3 3.1.3 Redevelopment Permit Requirements 4 Determination of Sewer Connection Fee 5 Conclusion 6 Figure 1: Vicinity Map I Figure 2: Annual Waste Water Flow Profile 5 Table I Carlsbad Desalination Facility - Normal Daily Wastewater Flows 3 Table 2: Carlsbad Desalination Facility - Intermittent Daily Flows 3 Appendix A: Sewer Exhibit with Sewage Connections Appendix B: EWA Meter Flow Data Sewer Study Carlsbad Desalination Project 1. Introduction The purpose of this sewer study is to provide response to Condition 37 of the amendment to the Redevelopment Permit for the Carlsbad Seawater Desalination Plant (RO 05-12(A)) contained in Planning Commission Resolution No. 6635 as promulgated by the City of Carlsbad Planning Commission on August 19, 2009. The condition states: "Prior to the issuance of precise grading permits or building permits, Developer shall submit a sewer study, prepared by a Registered Engineer, that identifies the peak flows of the project, required pipe sizes, depth of flow and velocity in pipe, and the capacity of the existing 6" sewer line serving this project. The study shall identify whether any sewer improvements are required to the existing 6" sewer line serving this project. Said study shall be submitted concurrently with the precise grading plans for the project and the study shall be prepared to the satisfaction of the City Engineer." The Carlsbad Desalination Facility (CDF) is located within site of the existing Encina Power Generating Station at 4590 Carlsbad Boulevard, Carlsbad, CA 92008 as shown on Figure 1: Vicinity Map. CITY OF OCEANSIDE i_NOT TO SCALE CITY OF VISTA CITY OF SAN MARCOS CITY OF ENCINITAS Figure 1: Vicinity Map Sewer Study Carlsbad Desalination Project 2. Project Description The proposed project consists of a nominal 50 MGD water desalination plant located on approximately 5.7 acres of land on the existing Carlsbad NRG Power Plant Site, located in Carlsbad just north of Cannon Road and west of the Amtrak railroad line. The plant includes an intake pump station that takes seawater from NRG's cooling water discharge line, pretreatment filtration facilities, high pressure pumps, reverse osmosis desalination followed by post treatment to recarbonate the water, and high pressure pumping facilities to transfer the desalinated water into piping that can feed potable water throughout San Diego County. The Carlsbad Desalination Facility (CDF) also has a chemical storage facility and an administration building where the operations and maintenance facilities are located. Brine and backwash water that is produced through the treatment processes are returned to the NRG cooling water discharge line and discharged to the ocean. Other flow streams produced during the desalination process are proposed to be conveyed to a private onsite sewage lift station within the CDF site. Wastewater from the sewage lift station will be pumped easterly through a private force main which will be installed in an existing tunnel underneath the railroad tracks to an existing sanitary sewer manhole (Manhole #21 D-1 1) on the City's Vista/Carlsbad Interceptor sewer (VCI). The VCI conveys flows southerly to the Encina Wastewater Pollution Control Facility (EWPCF) located south of Palomar Airport Road at 6200 Avenida Encinas. Appendix A contains an illustration of the onsite CDF sewer collection system and how it connects to the existing VCI. Design Criteria 3.1 Sources of Wastewater For the most part, the sources of wastewater at the CDF are non-continuous. Sanitary sewage is generated in the Administration Building by operating personnel and visitors. The CDF also houses a lab for routine water quality testing. Throughout the CDF, there are emergency eyewash/showers (total of 34) that are used only on an as needed basis and are typically operated for a very short period of time to assure they are in good operating condition. Other non-continuous flows are generated by operator washdown activities to concrete floors in work areas. This water typically discharges to sumps and is pumped or flows by gravity to the proposed private sewage lift station. There are also a number of small waste streams generated throughout the plant by analyzers that sample and determine the quality of the water. Many are in situ probes (pH, conductivity, ORP) that take measurements directly from a process line and others take a sample from a side stream that is either returned to the process, discharged to the brine line (that returns flow to the NRG cooling water discharge), or discharged to the sewer. Some of these, such as SDI and turbidity actually produce a waste stream of their own which is also discharged to the brine line or to the sewer. All waste streams from analysis on seawater are returned to the brine line. Only waste streams from analyses conducted on final product water that has been through the reverse osmosis process are directed to the sewer. Sewer Study Carlsbad Desalination Project 3.1.1 Normal Daily Flows Table I is a listing of the normal daily sources of wastewater from within the CDF. These include sanitary waste streams, emergency shower/eyewash testing, washdowns, and solids pipeline flushing. Table I Carlsbad Desalination Facility -Normal Daily Wastewater Flows Flow Duration Daily Fixture Number Rate, Frequency (mm) Average gpm Flow, GPD Emergency Eyewash/Shower 7 23 1/day 1 161 Measurement Panel 1 5 cont. 1,440 7,200 Washdown 3 20 2/day 30 3,600 Admin Building 7.7 220 gpd/EDU 1,694 Solids Handling - Pipeline Flushing 1 144 3/day 10 4,320 TOTAL 16,975 GPD 11.8 gpm Note: The solids pipeline flushing is from the solids handling process and consists of a service water connection upstream and downstream of each centrifuge sludge feed pump whose purpose is to flush residual solids from the piping and thus prevent the lines from becoming plugged. Since the flow stream consists of very little seawater and mostly service water from the plant's non- potable water connection, it is routed to the sewer. 3.1.2 Intermittent Daily Flows Table 2 is a listing of the intermittent daily source of wastewater from within the CDF. This once per month source is associated with the cleaning and flushing of the Neutralization Tank. Table 2 Carlsbad Desalination Facility - Intermittent Daily Flows Daily Q Max I Number Frequency Average Flow Structure (GPM) (MIN.) (GPO) Cleaning & Flushing 1 88 300 1/mo 26,400 Neutralization Tank Draining Total 26,400 GPD 18.3 gpm Note: Clean In Place is water used to clean the reverse osmosis cartridges. The cartridges are cleaned in place with a chemical solution to remove mineral scale, biological matter, colloidal particles, and insoluble organic constituents. The solution is made up of permeate water from the RO process and caustic or sulfuric acid as the cleaning process proceeds, Ultimately, the waste 3 Sewer Study Carlsbad Desalination Project from this cleaning process is neutralized to a pH neutral and solid free solution and discharged to the sewer. 3.1.3 Redevelopment Permit Requirements The City of Carlsbad Redevelopment Permit # 05-12(A) requires the preparation of this sewer study to identify "the peak flows of the project, required pipe sizes, depth of flow and velocity in pipe, and the capacity of the existing 6" sewer line serving this project..." The only existing 6" sewer line close to the CDF site is a private 6" sewer line located in the southwest corner of the NRG power plant site used for sanitary service to the power plant. However, all flow from the CDF is proposed to be routed to a private sewage lift station as shown in Appendix A and pumped to the existing 42" VCI gravity sewer that conveys wastewater to the Encina WPCF. Based on an analysis of the data from Tables 1 and 2, it has been determined that a sewage lift station with a maximum capacity of 150 gpm is sufficient. The private sewage lift station would consist of two pumps (1 operating; I standby) with a capacity of approximately 75 gpm each pump (maximum capacity of 150 gpm). The pumps are proposed to be submersible type within a 6-foot diameter wet well. The minimum run time is approximately 4 minutes. The peak flow rate from normal CDF activities, as depicted in Table 1, is estimated to be about 192 gpm. The peak flow rate for the CDF as a whole will occur once a month when the normal flows and the single intermittent flow occur on the same day. During this event, the peak flow rate from the CDF is about 280 gpm; well in excess of the sewage lift station pumping capacity. However, since the duration of this loading scenario is short, the volume of the sewage lift station wet well will be large enough to allow the lift station to store excess flow so that operation of 150 gpm will not cause an overflow within the CDF site or any backup in the facility's sewer collection system. Under maximum flow conditions, it is estimated that it will take about 35 minutes to pump down the combined peak flow rate. Based on the City of Carlsbad 2012 sewer master plan, the flowrate in the Vista/Carlsbad Interceptor Sewer in this area is measured at Meter Location C3 which is downstream of the proposed tie-in connection of the private force main to the VCI. A copy of the diurnal flow measured by Meter C3 during a wet weather event is included in Appendix B. The measured flows at this location are as follows (per City of Carlsbad): Average Dry Weather Flow = 7.56 mgd Peak Dry Weather Flow = 14.00 mgd Peak Wet Weather Flow = 23.96 mgd (See Appendix B) Ultimate Peak Wet Weather Flow = 32.00 mgd Existing Pipe Capacity - 20.5 mgd The depth of flow at the connection point during average and peak dry weather flow conditions is below the City's requirements for the d/D ratio not to exceed 0.75. However under peak wet weather conditions, the VCI is currently surcharged. Sewer Study Carlsbad Desalination Project 4. Determination of Sewer Connection Fee The Sewer connection Fee for the CDF is based on the Drofile shown in Fiaure 2: rugure : Annuai waste water now rrotuie As shown previously and illustrated in Figure 2, the normal daily flow is 16,975 GPD. Once a month, this daily flow increases to 43,375 GPO. This increase of 26,400 GPO is attributable to an intermittent maintenance flow described in more detail in Section 3.1.2. For the purposes of calculating the Sewer Connection Fee, a combined daily flow must be established. The normal daily flow already acts as an average daily flow and, therefore, can be considered adequate as is. Conversely, the intermittent daily flow acts as a peak. Therefore, it must be reduced by a peaking factor of 2.5 to yield the associated daily average. Considering all this, it is contemplated that the CDF will generate the following combined daily flow: 26,400 GPD 16,975 GPD + 2.5 = 27,535 GPD Therefore, the associated Sewer Connection Fee is: 27,535 GPD =126EDUs 220GPD 61 Sewer Study Carlsbad Desalination Project 126 EDU x $1,000/EDU = $126,000 5. Conclusion The wastewater generated at the Carlsbad Desalination Facility will not discharge into the private 6" sewer located in the southwest corner of the NRG site. Therefore, no sewer improvements are required to this existing 6" line. Flow from the CDF will be routed to the east and discharge into the existing 42" Vista/Carlsbad Interceptor. The increase in peak flow will not cause the depth of flow in the Vista/Carlsbad interceptor to exceed the City's design maximum depth D/d :5 0.75 during dry weather conditions. However, the Vista/Carlsbad Interceptor is presently surcharging during the peak wet weather conditions, as shown on the attached graph for December 17-26, 2010 in Appendix B, and summarized in Table 4-3 in the 2012 Sewer Master Plan. To resolve the VCI capacity constraint, the City has prepared plans and specifications for parallel pipeline improvements. The City is pursuing an easement from NRG, which is required to construct the City's improvements, and plans to initiate construction in 2014 with completion scheduled for 2016. The City has indicated that "Startup Testing" of the CDF can occur provided the wastewater is conveyed to the VCI during dry weather conditions. Until the parallel VCI improvements are constructed, Poseidon will defer CDF maintenance flows upon notice from the City of Carlsbad of an anticipated peak wet weather event. 5N JO- I3HS I pit sq,o1 I I OI aftI 3LYO 0000Too$c$O SNOIJ.O3NNOO OVM3S HIM .L191HX3 I3M3S Gx --- AS o] UW vxcIv INVid N011VN11VS30 NOI1VN'ON ONOW flVS ayssiivo IV)HV J3J..VM NOI3SOd LY SY CEO cc ma V. - -- ii— 1?— , I I j 1:2 I J / ji 5MaY10 1V3Y1319 - L_f 4 ii L Y1dJ IN—oi-oo p OdD rt ammm huh h/iE .4 /r-'-° D-o pi _IL MW Q350d=d \0 93M awdow OdD corL-o (WO V3110 GNV MWITU mud mm C-M mm am 3Y03 Y1d OIY1ILVOY1 s- . - - - _- — If VA -- - 0010YY1 SOVSNVJS j [ VY1Y3O 053E NYS r - -- --------------------- I T _ nVIS dOlid .11 — J_- ___I_- _---1zti_I —_I "--I-•_- -I -- c f---------— ---- — At —1 a - —__- -- Appendix B Encina WA Meter Flow Data - C3 Meter Flows, Rain event - December 17-26, 2010. EWA Meter Flow Data C3 METER FLOWS, RAIN EVENT DEC. 17-26, 2010