EVALUATION OF ODOR EMISSIONS AND THEIR CONTROL AT THE CHIQUITA WATER RECLAMATION PLANT, AND SAN JUAN AND ORTEGA LIFT STATIONS

Transcription

1 EVALUATION OF ODOR EMISSIONS AND THEIR CONTROL AT THE CHIQUITA WATER RECLAMATION PLANT, AND SAN JUAN AND ORTEGA LIFT STATIONS Prepared for: RANCHO MISSION VIEJO Ortega Highway San Juan Capistrano, CA by: BOWKER & ASSOCIATES, INC. CONSULTING ENGINEERS 477 Congress Street, Suite 1004 Portland, ME May, 2013 i

2 EXECUTIVE SUMMARY INTRODUCTION The Ranch Plan prepared by Rancho Mission Viejo was approved in 2004 by the County Board of Supervisors. A portion of the proposed development is in relatively close proximity to the Chiquita Water Reclamation Plant (CWRP) in the unincorporated County of Orange, CA. The sewage treatment plant currently has no neighbors, but the location of the proposed development has raised concerns with regard to the potential for odors to be detected by the residents and other occupants. Also, the San Juan and Ortega Lift Stations are sources of odors that could potentially impact the development. The purpose of this study is: 1. To determine the extent to which CWRP odors will be detected by future residents in Planning Area Determine the adequacy of existing odor control systems to meet target odor levels in the proposed development. 3. Evaluate needed improvements at the treatment plant and lift stations to prevent odor complaints. 4. Make recommendations to upgrade, expand, or replace odor control systems to ensure that odor impacts on the community are minimized. DESCRIPTION OF FACILITIES Chiquita Water Reclamation Plant The Chiquita Water Reclamation Plant (CWRP) is a 9 million gallon per day (mgd) wastewater treatment plant owned and operated by the Santa Margarita Water District (SMWD). It is located in Chiquita Canyon. The original Phase I facility came on-line in 1987 using the trickling filter-solids contact process for wastewater treatment. The plant currently treats approximately 5 mgd through a conventional activated sludge process with tertiary filtration, producing reclaimed water suitable for landscape irrigation and agriculture. An additional 1 mgd is treated through the original trickling filter solids contact process. The plant appears to be well operated and maintained, and was in a clean and orderly condition at the time of the visits. The CWRP was constructed with four odor control systems having a total combined air treatment capacity of 58,000 cubic feet per minute (cfm). Since the plant has no current neighbors, the odor control systems were installed to meet permit requirements only for hydrogen sulfide. Apparently, the SMWD was able to demonstrate that the permit requirements ii

3 are met without operating the chemical feed systems, and only the fans are operated to provide adequate ventilation of the enclosed spaces. In 2009, a Master Plan was developed for SMWD by AECOM to evaluate the need for additional capacity and plant upgrades. Recommendations for the Phase 4 expansion included increasing liquid treatment and solids handling capacity, replacement of sludge dewatering systems, adding a thermal sludge drying system, and installing a new central biofilter odor control system. San Juan and Ortega Lift Stations The San Juan Lift Station was constructed in 2001, and houses four pumps, each rated at 2,000 gpm. It is located east of Antonio Parkway and north of San Juan Creek. The pumps discharge into a 16 force main approximately 7,000 ft. long. Current wastewater flows through the San Juan Lift Station are approximately 2 mgd. Peak capacity is 8 to 9 mgd. The San Juan LS receives the discharge from the Horno LS, which serves the community of Ladera Ranch. The Horno LS currently pumps about 2 mgd through 9,500 ft of 16-inch force main. The Ortega Lift Station Lift Station was built in 1991, and has three pumps, each capable of 1,600 to 1,700 gpm. It is located north of Ortega Highway near its intersection with a private road (Christianito Rd). The pumps discharge into a 16-inch force main approximately 17,000 ft. long. Current flows through the station are about 0.7 mgd. Peak capacity is 4 to 5 mgd. The Ortega Lift Station receives the discharge from the Talega Lift Station, which pumps approximately 0.7 mgd through a 10-inch diameter, 12,000 ft long force main, which transitions to a 16-inch force main for the remaining 8,000 ft. The District has installed a system at the Talega LS to inject oxygen and ozone into the force main to prevent sulfide generation. The Ortega LS also has a 300 cfm Biocube biofilter system to treat the air from the wet well. SAMPLING PROGRAM A sampling program was developed for the Chiquita Water Reclamation Plant (CWRP) and the San Juan and Ortega Lift Stations. The purpose of the sampling program was to quantify the odor emissions from the facilities, and understand the conditions under which the odors are generated and released. The sampling program consisted of the following elements: 1. Collection of air samples from major odor sources for laboratory odor panel analysis 2. On-site measurement of hydrogen sulfide (H 2 S) at all sample locations 3. Installation of datalogging H 2 S analyzers (Odalogs) 4. Collection and field analysis of wastewater grab samples iii

4 ODOR DISPERSION MODELING Odor dispersion modeling was used to predict off-site odor impacts from odor sources at CWRP to evaluate odor mitigation alternatives. The software used to complete the modeling was Breeze AERMOD developed by Trinity Consultants Inc. AERMOD is the preferred U.S. Environmental Protection Agency model for simulating the impacts of emissions from a variety of sources. The information input into the model for this study was the Odor Emission Rates (OER) for each odor source, location and discharge height of source, local meteorological conditions from the Costa Mesa and Mission Viejo weather stations operated by the South Coast Air Quality Management District, and digital terrain data. The OER is the odor concentration or Dilutions to Threshold (D/T) multiplied by the air flow rate. The model output predicts the highest D/T level, estimated over the area of analysis. The resulting peak D/T levels are shown graphically on odor contour plots. In addition, the model output provides a plot of odor frequency, that is, the number of hours per year that the odor concentration exceeds a pre-selected target level of nearly non-detectable odor. The target parameters used in the modeling were a peak odor concentration of 7 D/T or less, and an odor detection frequency of less than 100 hours/year. The following scenarios were evaluated using the model: 1. Existing conditions with odor control systems operating. 2. With improved performance of upgraded odor control systems 3. With improved scrubber performance; primary clarifier and sludge transfer scrubbers upgraded to achieve 99% odor reduction. CONCLUSIONS AND RECOMMENDATIONS Conclusions Chiquita WRP 1. The Chiquita Water Reclamation Plant (CRWP) and the lift stations that contribute wastewater flow are well operated and maintained facilities, and poor maintenance is not a factor contributing to odor emissions. 2. Based on sampling of the odor emissions from various processes, the discharge of the chemical scrubber serving the primary clarifiers had the highest odor concentrations and the highest odor emission rate. 3. The existing chemical scrubbers were designed only for hydrogen sulfide removal using sodium hydroxide, and are only partially effective at controlling odor emissions, with odor removal efficiencies of zero to 70 percent. iv

5 4. The second largest odor contributor based on odor emission rate was the chemical scrubber serving the sludge thickening and holding processes. Odors from these sources tend to be strong, and sulfur compounds other than H 2 S typically contribute to the strong odor. 5. The trickling filters were estimated to be the third largest odor emission source. 6. Odor dispersion modeling using AERMOD showed significant predicted downwind odor impacts from the CWRP on the area slated for development (Planning Area 2). Predicted peak odor levels were as high as 1,000 D/T, compared to target levels of 7 D/T. 7. The scrubbers serving the primary clarifier and sludge transfer processes were responsible for almost 98% of the total plant odor emissions, with the primary clarifier scrubber accounting for 90 percent of the plant odor emissions. 8. The existing chemical scrubbers serving the CWRP appear to be capable of being upgraded to use sodium hypochlorite (bleach) which will greatly enhance performance. 9. Even with the assumption of 90% odor reduction through upgraded chemical scrubbers, dispersion modeling still shows an odor impact on the proposed Planning Area 2. This impact is largely due to the primary clarifier scrubber. Predicted peak odor levels were as high as 200 to 300 D/T near the plant fence-line compared to target levels of 7 D/T. 10. With 99% odor reduction assumed for the primary clarifier scrubber and sludge transfer scrubber, predicted odor impacts closely approach the target range for acceptable odor concentrations and detection frequency (less than 7 D/T peak odor concentration; less than 100 hr/yr above 7 D/T). 11. Under the scenario of 99% odor reduction in the primary clarifier scrubber and sludge transfer scrubber, the trickling filters become a more significant source of odor. 12. The remaining odor sources, including the aeration tanks, dewatering building, sludge loading operation, and grit storage are relatively minor and do not appear to be capable of off-site detection. Ortega and San Juan Lift Stations 1. The Ortega Lift Station experienced significant spikes in H 2 S of over 350 ppm during morning hours. The remainder of the day, H 2 S concentrations were zero. 2. The biofilter serving the Ortega LS is not providing effective treatment due to overloading and the need to replace the organic media. 3. The San Juan Lift Station showed a relatively high odor concentration in the wet well air. Due to a steeply-sloped influent sewer, the sewer is conveying large volumes of air to the wet well. This causes the air to become pressurized and escape around seams on hatches, pipe or conduit penetrations, etc. Recommendations Chiquita WRP 1. The primary clarifier scrubber should be upgraded to achieve outlet odor concentrations of 300 D/T or less. The cost of rehabilitating the scrubber and adding a second chemical (bleach) is estimated to be $196, Additional sampling should be conducted on the primary clarifier scrubber to verify the high inlet loading and to measure performance using bleach. v

6 3. The chemical scrubber serving the Chiquita influent pump station should be replaced with a larger, 5,000 cfm biological odor control system such as a biofilter or bioscrubber. The estimated cost of a pre-engineered biofilter system is $362, The sludge transfer scrubber should be rehabilitated and upgraded to use bleach, and the activated carbon in the downstream carbon adsorber should be replaced. Estimated cost of odor control system improvements for the sludge transfer processes is $285, Bowker & Associates concurs with a choice of a central biofilter system to handle odorous air from an expanded Chiquita WRP in accordance with the 2009 Master Plan. If space is not available for a large biofilter, biotrickling filters (aka bioscrubbers) should be evaluated. Ortega and San Juan Lift Stations 1. The San Juan LS should be fitted with a 1,000 cfm (conservative) activated carbon adsorber to treat odorous air from the wet well. This will ensure no off-site odors even if upstream chemical treatment is compromised. Estimated cost of this system is $112, Oxygen injection rate at the Talega LS should be increased to eliminate spikes of H 2 S at the downstream Ortega LS. 3. The media in the Ortega LS biofilter should be replaced. 4. The Santa Margarita Water District should continue their effort to control sulfide in the collection system using cost-effective control technologies such as oxygen injection. Oxygen injection is likely to be more cost-effective and reliable compared to the existing chemical (nitrate) addition system at the Horno LS, even though the current system may be effective.. SUMMARY OF ODOR CONTROL RECOMMENDATIONS Recommendation Est. Capital Cost, $ 1. Install activated carbon adsorber at San Juan LS $112, Upgrade primary clarifier scrubber $196, Upgrade sludge transfer scrubber $285, Install biofilter at influent pump station $362, Replace media in Ortega LS biofilter $ 10, Increase oxygen injection at Talega LS $ 0 vi

7 TABLE OF CONTENTS Page No. EXECUTIVE SUMMARY... i 1. INTRODUCTION DESCRIPTION OF FACILITIES Chiquita Water Reclamation Plant San Juan and Ortega Lift Stations SAMPLING PROGRAM Methodology Results Odor and H 2 S Measurements Continuous H 2 S Dataloggers Wastewater Grab Samples ODOR DISPERSION MODELING Odor Emission Rates Description of Dispersion Model General Description Dispersion Model Output Modeling Protocol Description of Modeling Scenarios Modeling Results EVALUATION OF ODOR CONTROL ALTERNATIVES San Juan and Ortega Lift Stations Chiquita Water Reclamation Plant Interim Odor Control Measures Long-Term Odor Control CONCLUSIONS AND RECOMMENDATIONS Conclusions Recommendations vii

8 LIST OF TABLES Page No. Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Odor Control Systems at the Chiquita WRP...5 Summary of Odor and H2s Data from Air Sampling Program Chiquita Water Reclamation Plant Liquid Stream Sampling Data Santa Margarita Water District...20 Ranking of Existing Odor Sources by Odor Emission Rate Chiquita Water Reclamation Plant...22 Estimated Cost of 1,000 cfm Activated Carbon Odor Control System for San Juan Lift Station...36 Estimated Cost of Primary Clarifier Scrubber Upgrade...39 Estimated Cost of Sludge Transfer Scrubber And Carbon Adsorber Upgrade...41 Estimated Cost of 5,000 cfm Pre-Engineered Biofilter for Chiquita Influent Pump Station...42 viii

9 LIST OF FIGURES Page No. Figure 1 Chiquita WRP and Planning Area No. 2 Map...2 Figure 2 Site Plan of Existing Chiquita WRP...6 Figure 3 Diagram of Flux Chamber Sampling System...10 Figure 4 H 2 S Concentration vs. Time Ortega LS Wet Well March 9-13, Figure 5 H 2 S Concentrations vs. Time San Juan LS Wet Well Figure 6 March 9-13, H 2 S Concentration vs. Time Chiquita WRP Influent PS Wet Well March 9-13, Figure 7 Predicted Peak Odor Levels - Existing Conditions (Costa Mesa Met Data)...26 Figure 8 Predicted Odor Detection Frequency - Existing Conditions (Costa Mesa Met Data)...27 Figure 9 Predicted Peak Odor Levels - Existing Conditions (Mission Viejo Met Data)...28 Figure 10 Predicted Odor Detection Frequency - Existing Conditions (Mission Viejo Met Data)...29 Figure 11 Predicted Peak Odor Levels - 90% Control in Scrubbers...31 Figure 12 Predicted Odor Detection Frequency - 90% Control in Scrubbers...32 Figure 13 Predicted Peak Odor Levels - 99% Control in Primary Clarifier and Sludge Transfer Scrubbers...33 Figure 14 Predicted Odor Detection Frequency - 99% Control in Primary Clarifier and Sludge Transfer Scrubbers...34 ix

10 1. INTRODUCTION The Ranch Plan developed by Rancho Mission Viejo was approved in 2004 by the County Board of Supervisors. A portion of the proposed development is in relatively close proximity to the Chiquita Water Reclamation Plant (CWRP) in the unincorporated County of Orange, CA. The sewage treatment plant currently is surrounded by ranching and farming operations. The location of the proposed development has raised concerns with regard to the potential for odors to be detected by residents and other occupants. Also, the San Juan and Ortega Lift Stations are sources of odors that could potentially impact the development. A map showing the location of the Chiquita WRP and Planning Areas 2 and 3 are shown in Figure 1. The closest residence may be as little as 1,000 feet from the wastewater treatment plant. In addition, there are two lift stations (San Juan and Ortega) that are odor sources that could impact future residents. The purpose of this study is: 1. To determine the extent to which CWRP odors will be detected by future residents in Planning Area Determine the adequacy of existing odor control systems to meet target odor levels in the proposed development. 3. Evaluate needed improvements at the treatment plant and lift stations to prevent odor complaints. 4. Make recommendations to upgrade, expand, or replace odor control systems to ensure that odor impacts on the community are minimized. 1

11 FIGURE 1 VICINITY MAP SHOWING SMWD FACILITIES AND RANCH PLAN 2

12 2. DESCRIPTION OF FACILITIES 2.1 Chiquita Water Reclamation Plant The Chiquita Water Reclamation Plant (CWRP) is a 9 million gallon per day (mgd) wastewater treatment plant owned and operated by the Santa Margarita Water District (SMWD). It is located in Chiquita Canyon (see Figure 1). The original Phase I facility came on-line in 1987 using the trickling filter-solids contact process for wastewater treatment. The plant currently treats approximately 5 mgd through a conventional activated sludge process with tertiary filtration, producing reclaimed water suitable for landscape irrigation and agriculture. An additional 1 mgd is treated through the original trickling filter solids contact process. The plant appears to be well operated and maintained, and was in a clean and orderly condition at the time of the visit. Unit liquid stream processes at the facility include: 1. Influent screening and pumping 2. Vortex grit removal system 3. Primary clarification 4. Activated sludge or trickling filter solids contact 5. Final clarification 6. Tertiary filtration 7. Disinfection Solids handling processes include: 1. Gravity thickening 2. Mechanical disk thickening 3. Anaerobic digestion 4. Sludge holding 5. Belt filter press dewatering 6. Off-site disposal of dewatered biosolids 3

13 Digester gas is burned in boilers to heat the digesters, and excess gas is burned to generate electricity via micro turbines. Ferric chloride is added to the digesters to control hydrogen sulfide. The CWRP was constructed with four odor control systems having a total combined air treatment capacity of 58,000 cubic feet per minute (cfm). Since the plant has no current neighbors, the odor control systems were installed to meet permit requirements for only hydrogen sulfide. Apparently, the SMWD was able to demonstrate that the permit requirements are met without operating the chemical feed systems, and only the fans are operated to provide adequate ventilation of the enclosed spaces. Table 1 provides a summary of the available information on the odor control systems. Figure 2 shows a site plan of the existing Chiquita WRP. In 2009, a Master Plan was developed for SMWD by AECOM to evaluate the need for additional capacity and plant upgrades. Recommendations for the Phase 4 expansion include: 1. Increasing influent pumping capacity 2. Constructing a new 3 million gallon emergency raw sewage holding basin 3. Installing new screens at influent lift station, and adding one new vortex grit chamber 4. Constructing one new primary clarifier 5. Constructing two new aeration tanks and two secondary clarifiers 6. Installing new 1.5 million gallon (secondary) flow equalization basin 7. Constructing additional filter and chlorine contact tank 8. Installing additional disc thickener 9. Constructing new anaerobic digester and sludge holding tank 10. Replacing the belt filter presses with centrifuges 11. Constructing a 39 wet-ton-per-day thermal sludge drying system 12. Installing 3 new micro turbines 4

14 TABLE 1 ODOR CONTROL SYSTEMS AT THE CHIQUITA WRP Odor Control System Processes Served Air Flow Capacity, cfm Type 1. Influent Lift Station Screen room, old wet well 4,000 Cross-flow, caustic-only chemical scrubber; approx. 5.5 ft of horizontal media 2. Primary Clarifiers Grit chambers, primary clarifiers 24,000 Vertical, counter-current packed tower scrubber, causticonly; 8 ft. diam., 9 ft. packing depth 3. Dewatering Building Biosolids dewatering room 22,000 Vertical, counter-current packed tower scrubber, causticonly; 8 ft. diam,, 9 ft. packing depth 4. Sludge Transfer Building Sludge thickening, holding 8,000 Cross-flow caustic-only scrubber followed by 12 ft. diam. activated carbon adsorber 5

15 FIGURE 2 6

16 13. Installing new 4-cell central biofilter for odor control at the treatment plant, as well as a new odor control system for the influent pump station (capacities not provided). 2.2 San Juan and Ortega Lift Stations San Juan Lift Station The San Juan Lift Station was constructed in 2001, and houses four pumps, each rated at 2,000 gpm. It is located east of Antonio Parkway and north of San Juan Creek (see Figure 1). The wet well is 6 W x 45 L x 20 H. The pumps discharge into a 16 force main approximately 7,000 ft. long. Current wastewater flows through the San Juan Lift Station are approximately 2 mgd. Peak pumping capacity is 8 to 9 mgd. The San Juan LS receives the discharge from the Horno LS, which serves the community of Ladera Ranch. The Horno LS currently pumps about 2 mgd through 9,500 ft of 16-inch force main. From there, the flow transitions to gravity for approximately 1 mile before reaching the San Juan LS. Ortega Lift Station The Ortega Lift Station was built in 1991, and has three pumps, each capable of 1,600 to 1,700 gpm. It is located north of Ortega Highway near its intersection with a private road (Christianito Rd) as shown in Figure 1. The wet well is 6 W x 22 L x 20 H. The pumps discharge into a 16- inch force main approximately 17,000 ft. long. Current flows through the station are about 0.7 mgd. Peak pumping capacity is 4 to 5 mgd. The Ortega Lift Station receives the discharge from the Talega Lift Station, in San Clemente, which pumps approximately 0.7 mgd through a 10-inch diameter, 12,000 ft long force main, which transitions to a 16-inch force main for the remaining 8,000 ft. With the long detention times in these force mains, there is high potential for sulfide generation. The SMWD has installed a system at the Talega LS to inject oxygen and ozone into the force main to prevent sulfide generation. At the time of the sampling, oxygen was being injected at a rate of 150 L/min. The system can inject up to 280 L/min of oxygen. 7

17 The Ortega LS has a 300 cfm Biocube biofilter system to treat the air from the wet well. The system is designed to handle 150 ppm of H 2 S over a 24-hour period, with a max 1-hr peak of 300 ppm. 3. SAMPLING PROGRAM A sampling program was developed for the Chiquita Water Reclamation Plant (CWRP) and the San Juan and Ortega Lift Stations. The purpose of the sampling program was to quantify the odor emissions from the facilities, and understand the conditions under which the odors are generated and released. 3.1 Methodology The sampling program consisted of the following elements: 1. Collection of air samples from major odor sources for laboratory odor panel analysis 2. On-site measurement of hydrogen sulfide (H 2 S) at all sample locations 3. Installation of datalogging H 2 S analyzers (Odalogs) 4. Collection and field analysis of wastewater grab samples Although the odor control systems at the CWRP have not been operated for many years, they were brought into services and operated long enough to collect air samples from the inlet and outlet ductwork. Air samples were collected from the following locations: 1. Inlet and outlet of scrubber serving CWRP influent LS 2. Inlet and outlet of scrubber serving primary clarifiers and grit chambers 3. Inlet and outlet of scrubber serving dewatering building 4. Inlet and outlet of scrubber serving sludge transfer processes 5. Surface of trickling filters 6. Surface of aeration tanks 7. Surface of solids contact tank 8

18 8. Surface of grit piles in container 9. Surface of dewatered sludge cake in biosolids trailer 10. Inlet and outlet of biofilter odor control system at Ortega LS 11. Wet well of San Juan LS Samples were collected on March 11, 12, and 13, The air sampling procedure involved use of the EPA surface isolation chamber or flux chamber that is placed over an area odor source such as the primary clarifier. After a 20-minute equilibration period, a sample was withdrawn from the chamber at 3 liters/minute using Teflon tubing, a vacuum chamber, and air sampling pump. The sampling pump induced a vacuum in the vacuum chamber containing a 10L Tedlar bag. This allowed sample air to flow directly into the Tedlar bag without potential contamination from the sampling pump. A diagram of the sampling apparatus is shown in Figure 3. Air samples were shipped by overnight carrier to St. Croix Sensory in Stillwater, Minnesota for determination of odor concentration in accordance with ASTM E-679. The samples were analyzed within 24 hours of collection. This laboratory test measures the odor strength in dilutions to threshold, which is the number of times that the sample must be diluted with equal volumes of odor-free air before it is no longer detectable by 50% of a trained 6-member odor panel. The dilutions of the sample and the presentation of the air to the odor panelists was accomplished using a forced-choice dynamic triangle olfactometer having a presentation rate of 20 liters/minute. In addition to the odor testing, hydrogen sulfide concentrations were measured at each sample location using an Interscan 4170 H 2 S analyzer with a range of 0.1 to 200 ppm. To measure the diurnal variation in hydrogen sulfide levels with time, datalogging H 2 S analyzers (Odalogs) were installed in the wet wells of the Ortega LS, the San Juan LS, and the Chiquita WRP influent lift station. The devices recorded H 2 S concentrations every five minutes from March 8 until March 13,

19 Regulator Teflon "sweep air" line Stainless steel dome Teflon sample line Tedlar bag Flowmeter "Ultra Zero" compressed air Flotation collar 16" Vacuum chamber Sampling pump FIGURE 3. DIAGRAM OF FLUX CHAMBER SAMPLING SYSTEM Bowker & Associates, Inc. 10

20 Single grab samples of wastewater were collected from the Ortega LS, the San Juan LS, and the Chiquita WRP plant influent. The ph, temperature and oxidation-reduction potential were measured in the field using a Myron L Model 3P analyzer. Total sulfide was measured in the field using a Chemetrics Sulfide Test Kit with a range of 0 to 10 mg/l. 3.2 Results Odor and H 2 S Measurements Table 2 summarizes the results of the air sampling program, which are discussed below in the order shown on the table. The aeration tank odor emissions were relatively low as expected (Samples 1 and 5), with odor concentrations of 140 and 80 dilutions to threshold, and low H 2 S of 0.1 ppm. The trickling filters exhibited a higher odor concentration of 2,400 D/T, but with low H 2 S levels of 0.1 to 0.2 ppm. (Samples 2 and 6). Air samples from the surface of the open sludge cake trailer showed odor levels of 1,100 D/T from freshly-deposited biosolids (Sample 4), and lower odor concentration of 320 D/T from partially dried material (Sample 8). H 2 S levels were 2.7 to 4.4 ppm. The solids contact tank exhibited odor concentrations of 360 D/T and 830 D/T, with low H 2 S of 0.2 ppm (Samples 3 and 7). Samples were collected from the inlet an outlet of the four chemical scrubber systems. All scrubbers were put into service for the sampling, and the ph of the scrubbant solution was adjusted to achieve a minimum ph of 10. The large scrubber serving the grit chambers and primary clarifiers had the highest odor concentration of any of the samples collected. Inlet and outlet odor concentrations were reported as 29,000 and 28,000 D/T, respectively (Samples 11 and 12). Although the H 2 S concentrations were reduced by about 55% through the caustic scrubber, the odor data did not show a similar decrease. The influent pump station scrubber did 11

21 TABLE 2 SUMMARY OF ODOR AND H 2 S DATA FROM AIR SAMPLING PROGRAM CHIQUITA WATER RECLAMATION PLANT March 11, 2013 Sample No. Location Time Odor Concentration (D/T) H 2 S Concentration (ppm) 1 Aeration Tank #1 9:40 AM Trickling Filter #3 10:20 AM 2, Solids contact tank 11:15 AM Sludge cake trailer, fresh 12:00 PM 1, Aeration Tank #2 1:20 PM Trickling Filter #1 2:05 PM 2, Solids contact tank 2:35 PM Sludge cake trailer, dried 3:10 PM

22 TABLE 2 (cont d) SUMMARY OF ODOR AND H 2 S DATA FROM AIR SAMPLING PROGRAM CHIQUITA WATER RECLAMATION PLANT March 12, 2013 Sample No. Location Time Odor Concentration (D/T) H 2 S Concentration (ppm) 9 Influent PS Scrubber Outlet 10 Influent PS Scrubber Inlet 11 Primary Clarifier Scrubber Outlet 12 Primary Clarifier Scrubber Inlet 13 Dewatering Scrubber Outlet 14 Dewatering Scrubber Inlet 15 Sludge Transfer Scrubber Outlet 16 Sludge Transfer Scrubber Inlet 9:20 AM 1, :40 AM 6, :10 AM 28, :25 AM 29, :20 AM :40 AM :55 AM 8, :10 AM 6,

23 TABLE 2 (cont d) SUMMARY OF ODOR AND H 2 S DATA FROM AIR SAMPLING PROGRAM CHIQUITA WATER RECLAMATION PLANT March 13, 2013 Sample No. Location Time Odor Concentration (D/T) H 2 S Concentration (ppm) 17 Ortega LS Biofilter Outlet 18 Ortega LS Biofilter Inlet 19 San Juan LS Wet Well 20 Chiquita WRP Grit Dumpster 9:20 AM 6, :50 AM 9, :30 AM 8, :30 PM 3,

24 show greater than 70% odor and H 2 S reduction, reducing the odor concentration from 6,000 to 1,600 D/T (Samples 9 and 10). Odors in the sludge dewatering room were mild at the time of the sampling. Inlet and outlet odor concentrations from the dewatering room scrubber were only 80 and 50 D/T respectively (Samples 13 and 14). No H 2 S was detected. The low odor and H 2 S concentrations may be due to the addition of ferric chloride to the anaerobic digester, which binds up the hydrogen sulfide. The air entering the sludge transfer scrubber has a relatively high odor concentration of 6,900 and an H 2 S of 2.8 ppm. Much of the odor is likely due to non-h 2 S reduced sulfur compounds. Although the scrubber showed some H 2 S reduction, the outlet odor sample showed a similar odor concentration to the inlet (Samples 15 and 16). The biofilter serving the Ortega LS was sampled (Samples 17 and 18). The system was receiving a relatively high odor loading of 9,700 D/T but odor reduction through the system was only about 30 percent. Inlet H 2 S was only 0.5 ppm, which is much lower than the peaks recorded by the dataloggers (see next section). The organic media in the system is approximately 5 years old and has reached the end of its useful life, which is typically 2 to 5 years. The air sample from the San Juan LS (Sample 19) wet well showed a similar odor concentration of 8,500 D/T and an H 2 S of 1.2 ppm. Peak values may be higher based on datalogger results. Finally, the sample collected from the surface of the grit dumpster at the CWRP showed an odor concentration of 3,700 D/T and H 2 S concentration of 6.5 ppm (Sample 20) Continuous H 2 S Dataloggers Figures 4, 5 and 6 show approximately five days of H 2 S data from March 8 to March 13 for the Ortega LS, San Juan LS, and CWRP influent LS, respectively. The Odalog devices were hung in 15

25 Mar, 8 Mar, 9 Mar, 10 Mar, 11 Mar, 12 Mar, 13 13:50 17:50 21:50 1:50 5:50 9:50 13:50 17:50 21:50 1:50 5:50 9:50 13:50 17:50 21:50 1:50 5:50 9:50 13:50 17:50 21:50 1:50 5:50 9:50 13:50 17:50 21:50 1:50 5:50 H 2 S, Concentration ppm Temperature, F 1000 FIGURE 4 H 2 S Concentration vs. Time Ortega LS Wet Well March 9-13, Temperature; Avg. = 69 F H 2 S; Avg. = 15 ppm Date/Time 16

26 Mar. 8 Mar. 9 Mar. 10 Mar. 11 Mar. 12 Mar :52 18:52 22:52 2:52 6:52 10:52 14:52 18:52 22:52 2:52 6:52 10:52 14:52 18:52 22:52 2:52 6:52 10:52 14:52 18:52 22:52 2:52 6:52 10:52 14:52 18:52 22:52 2:52 6:52 H 2 S Concentration, ppm Temperature, F 7 FIGURE 5 H 2 S Concentrations vs. Time San Juan LS Wet Well March 9-13, Temperature Avg. = 72 F H 2 S; Avg. = 0 ppm Date/Time 17

27 Mar. 8 Mar. 9 Mar. 10 Mar. 11 Mar. 12 Mar :37 19:04 21:31 23:58 2:25 4:52 7:19 9:46 12:13 14:40 17:07 19:34 22:01 0:28 2:55 5:22 7:49 10:16 12:43 15:10 17:37 20:04 22:31 0:58 3:25 5:52 8:19 10:46 13:13 15:40 18:07 20:34 23:01 1:28 3:55 6:22 8:49 11:16 13:43 16:10 18:37 21:04 23:31 1:58 4:25 6:52 9:19 H 2 S Concentration, ppm Temperature, F 11 FIGURE 6 H 2 S Concentration vs. Time Chiquita WRP Influent PS Wet Well March 9-13, Temperature; Avg. = 61 F H 2 S; Avg. = 0 ppm Date/Time 18

28 the wet wells of the Ortega and San Juan LS and in the influent channel upstream of the screens at the CWRP lift station. At the Ortega LS (Figure 4) significant spikes of H 2 S were detected in the morning hours between 6 AM and 10 AM. Peaks of 200 to over 350 ppm were recorded. Smaller spikes were twice detected between 5PM and 6PM. Much of the flow entering this lift station is pumped from the Talega LS, where oxygen/ozone are injected into the force main to control sulfide generation. It would appear that not enough oxygen is being added to prevent sulfide generation during low-flow periods during late evening/early morning hours. At the San Juan LS (Figure 5), average H 2 S concentration was 0 ppm, with only an occasional spike of H 2 S. This lift station receives flow from the Horno LS, where a nitrate product is injected to control hydrogen sulfide generation. The influent pump station for the Chiquita WRP showed low H 2 S concentrations, but with occasional spikes of 8 up to 10 ppm (Figure 6) Wastewater Grab Samples Single grab samples of wastewater were collected from the Ortega LS, the San Juan LS, and the Chiquita influent LS and analyzed in the field for ph, oxidation-reduction potential (ORP), temperature, and total sulfide. ORP is a measure of the relative septicity of the wastewater. Positive values indicate aerobic conditions with presence of dissolved oxygen, while negative values indicate septic or anaerobic conditions conducive to sulfide generation. Results from the wastewater testing are shown in Table 3. Samples collected from the Ortega and San Juan LS wet wells showed no sulfide, with a positive ORP. The sample of the Chiquita WRP influent, on the other hand, exhibited a sulfide concentration of 0.8 mg/l and a highly negative ORP of -240 mv. 19

29 TABLE 3 LIQUID STREAM SAMPLING DATA SANTA MARGARITA WATER DISTRICT March 13, 2013 Location Time ph, s.u. ORP, mv Temp, C Total Sulfide mg/l Ortega LS wet well San Juan LS wet well 8:55 AM :40 AM Chiquita Inf. PS 11:15 AM

30 4. ODOR DISPERSION MODELING 4.1 Odor Emission Rates A key input into the odor dispersion model is the odor emission rate for each odor source. Odor emission rate is the product of the odor concentration and the air flow rate. This provides an estimate of the mass of odor being released from each odor source. Table 4 shows the ranking of the odor sources at the Chiquita Water Reclamation Plant (CWRP) by odor emission rate. This shows that the scrubber serving the grit chamber and primary clarifiers dominates the emissions, accounting for nearly 90 percent of the total measured odor emissions. The second highest odor contributor is the sludge transfer scrubber (9% of total emissions). The trickling filters account for about one percent of the total odor emissions, followed by the influent pump station scrubber and dewatering room scrubber. The aeration tanks, grit dumpsters, solids contact tank, and sludge cake trailers are relatively minor sources that collectively account for less than one percent of total plant odor emissions. 4.2 Description of Dispersion Model General Description Odor dispersion modeling has been used as a reliable and cost-effective approach for predicting offsite odor impacts from odor sources and evaluating odor mitigation alternatives. The odor dispersion model is a computer program designed to predict what impact an odor source, or group of odor sources, will have on an area based on a number of factors that are input into the program. The primary inputs include: Odor emission rates from individual odor sources Odor source dimensions and characteristics Historic meteorological data Local terrain data 21

31 Source TABLE 4 RANKING OF EXISTING ODOR SOURCES BY ODOR EMISSION RATE Chiquita Water Reclamation Plant Odor Concentration (D/T) Estimated Air Flow, cfm Odor Emission Rate D/T x cfm 1. Primary clarifier scrubber 28,000 24, x Sludge transfer scrubber 8,500 8, x Trickling filters (2 in service) 2,400 3, x Influent PS scrubber 1,600 4, x Dewatering bldg. scrubber , x Aeration tanks (2) 140 3, x Grit dumpsters (2) 3, x Solids contact tank x Sludge cake trailers (2) x 10 6 TOTAL X

32 The software used to complete the modeling is Breeze AERMOD v developed by Trinity Consultants Inc. AERMOD is the preferred U.S. Environmental Protection Agency model for simulating the impacts of emissions from a variety of sources where a near field (less than 50 km) condition exists. AERMOD is a comprehensive, steady state Gaussian plume dispersion model that is commonly used for odor assessments as it assumes direct transport from a source to a receptor for every hour of meteorological data, which is designed to yield a conservative result in terms of odor impacts in the community surrounding the facility. The model was be used to predict and simulate the dilution of odors from the sources, measured in terms of Dilutions to Threshold (D/T) for the maximum hourly value of the year throughout the study area. AERMOD uses the pre-processor program AERMET which processes meteorological data for input to AERMOD. The modeling in this study used actual meteorological data obtained from the South Coast Air Quality Management District s monitoring stations in Costa Mesa and Mission Viejo. The data includes the actual hourly meteorological data (wind speed, wind direction, temperature, and cloud cover, ceiling height, and mixing height) from every hour of the year. The information input into the model for this study was Odor Emission Rates (OER) for each point source (sources with stacks &/or exhaust fans); Odor Emission Rate per square foot for each area source (open surfaces and tanks); odor source locations, discharge heights and size; local meteorological conditions from the Costa Mesa and Mission Viejo weather stations, and digital terrain data. The OER is the Detection Threshold (D/T) at the source multiplied by the air flow rate Dispersion Model Output The model output predicts the highest D/T level, estimated over the area of analysis. The resulting peak D/T levels are shown graphically on odor contour plots. In this study, the hourly average D/T levels at particular receptor points were converted to peak one-minute D/T levels by applying a multiplier to account for short exposure to odors. The peak D/T is more relevant for odors, since the odor plume meanders and is very transient. Perceived odor complaints are generally related to peak odor levels, as opposed to an hourly average odor level. 23

33 plant. In other words, it predicts the number of times per year odors may be detectable for a oneminute period at any point in the study area. For example, a person standing at a point where a frequency of 100 is predicted would be expected to experience an odor that exceeds the selected odor detection threshold 100 times (or during 100 hours) per year. In this study, an odor detection threshold of seven (7) D/T has been selected. An odor with a detection threshold of seven dilutions or less may not be detected because it could be overwhelmed by other natural odors in the area such as grass, trees, soil and flowers, or it may not be detectable at all Modeling Protocol The modeling scenarios were completed with the following modeling protocol settings: Peak-to-mean multiplier of: (Averaging Period / Peak Duration) 0.5 = (60 min / 60 sec) 0.5 = 7.75, based on one hour averaging period, one minute average peak duration, and 0.5 power factor. Elevated terrain option Digital local terrain data 2011 surface and mixing height meteorological data, upper air data collected from the Costa Mesa and Mission Viejo meteorological stations operated by the South Coast Air Quality Management District. Threshold of 7 D/T used for the odor frequency modeling Description of Modeling Scenarios Three modeling scenarios were evaluated in this odor evaluation. Following is a description of each of the modeling scenarios. 24

34 Current 2013 Conditions This scenario simulates the odor impact of all significant existing processes at the Chiquita Water Reclamation Plant (CWRP) as tested on March 10-12, All significant existing plant processes are simulated in this modeling scenario, and the odor control systems were operating in accordance with their design. 90% Odor Control Scenario This scenario simulates the odor impact of all significant plant processes, assuming that the existing odor control systems have been upgraded to provide 90 percent odor reduction. 99% Odor Control Scenario This scenario assumes upgrade of the primary clarifier and sludge transfer scrubber to achieve 99% odor reduction, with the remaining two scrubbers operating at 90% control. 4.3 Modeling Results Current 2013 Conditions Figures 7 and 8 show the Peak D/T and Odor Frequency contour maps for the current conditions scenario with odor control systems operating as designed. These model results use meteorological data from the Costa Mesa station based on recommendations from the South Coast Air Quality Management District. Figures 9 and 10 shows the model output using the meteorological data from the Mission Viejo station. Figures 7-10 clearly show a significant predicted odor impact on areas surrounding the CWRP. Not only are the predicted odor concentrations well above the target of 7 D/T, but the frequency of detectable odors is above the target of 100 hours per year. Comparison of the model outputs using 25

35 FIGURE 7 Predicted Peak Odor Levels Existing Conditions (Costa Mesa Met Data) 26

36 FIGURE 8 Predicted Odor Detection Frequency Existing Conditions (Costa Mesa Met Data) 27

37 FIGURE 9 Predicted Peak Odor Levels - Existing Conditions (Mission Viejo Met Data) 28

38 FIGURE 10 Predicted Odor Detection Frequency- Existing Conditions (Mission Viejo Met Data) 29

39 Costa Mesa meteorological data (Figures 7 and 8) vs. Mission Viejo data (Figures 9 and 10) shows only a minor difference in predicted odor impacts, with the Costa Mesa meteorological data having a slightly greater impact. The Costa Mesa data was used in all subsequent modeling. Figures 11 and 12 show the predicted odor impacts from the CWRP assuming that all four chemical scrubbers are upgraded to achieve 90% odor removal efficiency. This is well within the capabilities of packed tower scrubbers that use a combination of sodium hypochlorite (bleach) and sodium hydroxide (caustic soda). The exception to the 90% removal efficiency was the dewatering building scrubber, which is currently receiving such dilute odors that the outlet D/T was assumed to be 100. Even with improved performance of the scrubbers, predicted odor levels beyond the Chiquita WRP properly line still exceed the target 7 D/T in all locations. The odor impact from this scenario is again due largely to the primary clarifier scrubber that showed a measured inlet odor concentration of 29,000 D/T. Assuming 90 percent removal, the outlet odor remains a relatively high 2,900 D/T. Combined with the high air flow rate of 24,000 cfm, the odor emission rate is still greater than from all other sources combined. Figures 13 and 14 represent a scenario in which the primary clarifier scrubber is upgraded to achieve 99% odor reduction, and the sludge transfer scrubber exhaust is polished by the existing activated carbon adsorber. This would produce an outlet odor concentration of about 300 D/T from the primary clarifier scrubber, which is achievable by many chemical scrubber systems treating odor sources that are comprised mostly of hydrogen sulfide. It is difficult to predict whether this outlet odor level is achievable in the existing scrubber without adding a second polishing stage. The outlet from the combined scrubber-carbon system serving the sludge transfer processes is assumed to be 85 D/T, which is achievable. This scenario represents over 95% reduction in total odor emissions from the CWRP. Under this scenario, the odor impacts on Planning Area 2 are greatly reduced, and for the most part meet the target peak odor concentration of 7 D/T (Figure 13) and target odor detection frequency of <100 hours per year (Figure 14). Although there are still limited areas on the east and south borders of the plant where predicted peak odor levels exceed the target of 7 D/T, the frequency that these peak odors would be detectable is very low. With the assumption of very efficient odor control in the primary clarifier scrubber, the trickling filters become a more significant source of odor. 30

40 FIGURE 11 Predicted Peak Odor Levels - 90% Control in Scrubbers 31

41 FIGURE 12 Predicted Odor Detection Frequency- 90% Control in Scrubbers 32

42 FIGURE 13 Predicted Peak Odor Levels 99% Control in Primary Clarifier and Sludge Transfer Scrubbers 33

43 FIGURE 14 Predicted Odor Detection Frequency 99% Control in Primary Clarifier and Sludge Transfer Scrubbers 34

44 5. EVALUATION OF ODOR CONTROL ALTERNATIVES 5.1 San Juan and Ortega Lift Stations Because of the proximity of the lift stations to the first phase of development of Planning Area 1, as well as other Rancho Mission Viejo property, they are considered to be high priority for evaluation and control. San Juan LS This lift station is near the south entrance to Planning Area 1. Currently, the only odor control is upstream chemical addition (nitrate) at the Horno LS. Very little H 2 S was detected in the wet well of the San Juan LS during the March, 2013 monitoring. However, odor concentration was still quite high, and odorous air can escape around hatches, pipe penetrations, etc. The steeply-sloped 18-inch HDPE sewer approaching the lift station is contributing to the pressurization of the wet well headspace and the escape of odorous air. Under worst-case conditions, this pipe could contribute as much as 700 cfm of air to the wet well. This is due to the friction between the flowing wastewater and the air above it that drags the air down the pipe. Average velocity of the air is typically about one third the velocity of the sewage. Escape of odorous air can be prevented by evacuating enough air to maintain a slight negative pressure in the wet well. This air would require treatment prior to release to the atmosphere. Based on the low H 2 S levels, an activated carbon adsorber would be an appropriate odor control technology for this application. The process is very simple and reliable, and with the low H 2 S loadings, a media life of at least two years is anticipated. A biofilter is also feasible, but will have greater capital and O & M costs. Performance would be equivalent. A carbon adsorber has been conservatively sized for an air flow rate of 1,000 cfm. This estimate accounts for the contribution of air from the inlet sewer. Table 5 provides a breakdown of estimated 35

45 TABLE 5 ESTIMATED COST OF 1,000 CFM ACTIVATED CARBON ODOR CONTROL SYSTEM FOR SAN JUAN LIFT STATION Item Estimated Cost 1. 6 ft diam adsorber with fan, carbon media, control panel $46, Sound enclosure for fan 8, Pre-filter 5, Ductwork 15,000 Subtotal $64,000 30% 19,200 $83,200 Engineering & 35% 29,100 TOTAL $112,300 36

46 costs for an activated carbon odor control system to treat the air from the San Juan LS wet well. The SMWD is considering an oxygen injection system at the Horno LS to replace the chemical addition system. In the experience of Bowker & Associates, a properly designed oxygen injection system will provide more reliable and consistent control of hydrogen sulfide, and will provide long-term economic benefits in reduced O & M costs. Ortega LS The Ortega LS has historically been a source of odors, due largely to the long force main from the Talega LS. Although a 300 cfm biofilter was installed at Ortega to treat the air from the wet well, the organic media is exhausted and needs to be replaced. H 2 S data collected by the Odalog datalogger showed several significant spikes of H 2 S (> 300 ppm) during morning hours, with no H 2 S detected during the vast majority of the day. This may indicate that the upstream oxygenation system is not providing enough oxygen to prevent sulfide generation during low-flow periods when detention times in the force main can exceed 12 hours. However, the current injection rate is approximately 150 L/min, and the capacity is reported to be 280 L/min. Thus, it would appear that the system has sufficient capacity to bring H 2 S levels down to zero during all times of the day. With the optimization of the upstream oxygen injection system to consistently control sulfide, and the change-out of the biofilter media, odors from the Ortega LS should be adequately controlled. 5.2 Chiquita Water Reclamation Plant In order to prevent odors from the Chiquita WRP from impacting new development planned for east and north of the facility, it will be necessary to either upgrade the existing chemical scrubbers to achieve higher odor removal efficiency, or replace the scrubbers with new, more operator-friendly odor control systems. Given the age of the existing scrubbers, upgrading the scrubbers to use sodium hypochlorite (bleach) to improve performance is considered an interim solution until the odor control recommendations in the 2009 Master Plan are implemented. The schedule for 37