Summary Report

CITY OF DAVIS WASTEWATER PLANNING CHARRETTE

January 29, 2010

Prepared by Edward Schroeder and George Tchobanoglous Davis, California WASTEWATER PLANNING CHARRETTE Davis, California

January 29, 2010

Mr. Bill Emlen, City Manager City of Davis 1717 Fifth Street Davis, California 95616

RE: Summary Report: Results of Wastewater Planning Charrette

Dear Mr. Emlen:

Please find enclosed the Summary Report: Wastewater Planning Charrette. The purpose of the Charrette, conducted on October 22 and 23, 2009, was to develop a cost-effective wastewater management plan for the City of Davis. The findings from the Charrette, presented in this report, have been reviewed and approved by the Charrette team members. It has been an honor to be of service to the City of Davis and it is hoped that this report will be of aid to the community in developing a satisfactory approach to wastewater management and dispersal.

Very truly yours,

______Edward Schroeder George Tchobanoglous

Cc. Bob Clarke, Interim Public Works Director

CONTENTS

LETTER OF TRANSMITTAL ...... ii LIST OF TABLES ...... v LIST OF FIGURES ...... v EXECUTIVE SUMMARY ...... vi 1. INTRODUCTION ...... 1 Purpose of Charrette ...... 2 Charrette Participants ...... 2 Charrette Schedule, Agenda, and Organization ...... 3 Organization of Report ...... 3 Acknowledgements ...... 3 2. THE RECOMMENDED WASTEWATER MANAGEMENT PLAN . . . . 4 The Recommended Wastewater Treatment System ...... 5 Treatment Processes Flow Diagram ...... 5 Description of Individual Treatment Processes ...... 6 Comparison of Proposed to Previous Treatment Process Flow Diagram ...... 9 Modes of Operation ...... 9 Flowrates Up to an Average Dry Weather Flow (ADWF) of 6.0 Mgal/d ...... 9 ADWF Flowrates Above 6.0 Mgal/d ...... 11 Innovative Features of the Recommended System ...... 11 Cost Saving Features of the Recommended System ...... 12 Continued Use of Existing Plant Components in Proposed System ...... 12 Reduced Size and Number of New Plant Components in Proposed System ...... 12 Constructing a System Having a Capacity for Future Growth . . . . 12 Constructing a System with a High Degree of Operability and Reliability ...... 12 Staging Modifications and New Construction ...... 13 Recommended Actions by the City ...... 13

iii 3. RATIONALE FOR THE RECOMMENDED PLAN ...... 15 Selection of Design Parameters ...... 15 Population Projections ...... 15 Plant Loadings ...... 16 Critical Wastewater Constituents ...... 19 Components of The RecommendedTreatment System ...... 19 Headworks ...... 19 Primary Sedimentation ...... 20 Biological Treatment ...... 20 Chemical Addition ...... 20 Disk Filters ...... 20 Disinfection/Dechlorination ...... 21 Post Aeration ...... 21 Oxidation Ponds ...... 21 Dissolved Air Flotation ...... 22 Anaerobic Digesters ...... 23 Sludge Disposal ...... 23 Yard Piping ...... 23 Support Facilities ...... 23 4. DISCUSSION OF RELATED ISSUES ...... 24 Future Reuse Opportunities ...... 24 Future Discharge and Reuse Requirements ...... 24 Opportunities For Energy Conservation And Sustainability ...... 24 Approach to Estimating Costs ...... 25 REFERENCES ...... 26

APPENDIXES A Charrette Participant Biographies ...... A-1 B. Charrette Agenda and Attendees ...... B-1 C. Specific Technical Details and Issues ...... C-1

iv TABLES

2-1 Identification of principal treatment processes and their function in the WWTP process flow diagram ...... 7 3-1 Characteristic Davis influent wastewater flow values ...... 15

FIGURES

2-1 Proposed process flow diagram for the City of Davis Wastewater Treatment Plant. Dashed lines indicate alternative flow pathways or intermittent flows ...... 6 3-1 City of Davis population projections based on the 2007 value ...... 16 3-2 City of Davis daily flowrates for the period from 2007 to 2009 ...... 16 3-3 Projected City of Davis daily flowrates based on average dry-weather flow during the period from 2007 to 2009 ...... 17

v EXECUTIVE SUMMARY

The City of Davis currently discharges treated wastewater to Willow Slough Bypass, an effluent dominated stream. In October, 2007 the Central Valley Regional Water Quality Control Board issued a new discharge permit to the City that requires significant upgrades to effluent quality and set a date of October, 2016 for compliance. In May, 2009 the City Council asked Ed Schroeder and George Tchobanoglous, both professors emeritus from the Department of Civil Engineering at the University of California, Davis to organize and conduct a wastewater planning Charrette. The purpose of the Charrette was to:

1. Develop a treatment process flow diagram that will allow the city to continue to discharge to Willow Slough Bypass, and 2. Insure the selected system will minimize ratepayer fee increases The Charrette was conducted on October 22 and 23, 2009. The results of the Charrette are presented in this report.

THE RECOMMENDED TREATMENT SYSTEM The panel developed a treatment system concept based on:

1. The need to meet the discharge requirements and schedule set by the Regional Board in October, 2007, 2. The assumption that the City will continue to discharge to Willow Slough Bypass, and 3. The recognition of the changes in wastewater quality that will result from the City’s development of a surface water source. Alternatives to discharge to Willow Slough Bypass are under consideration, but essentially all of the treatment steps in the recommended system will be required to meet reclamation requirements necessary for land dispersal. The most notable changes in wastewater quality will be a reduction in the concentrations of selenium alkalinity, total dissolved solids, and hardness. Meeting selenium requirements should be possible even during periods when groundwater must be used as part of the supply. The decrease in alkalinity will result in a decrease in effluent pH and a

vi significant increase in the allowable effluent ammonia nitrogen concentration. A decrease in total dissolved solids will become important as the basin wide salt management plan under development by the Regional Water Quality Control Board is actuated.

The recommended treatment system for the City of Davis is presented and discussed in detail in Section 2. Additional details on the rationale for the selection of specific treatment processes are presented in Section 3. Related issues are discussed in Section 4. Specific technical details and issues noted by Panel members during the report review process can be found in Appendix C.

INNOVATIVE FEATURES OF THE RECOMMENDED SYSTEM Six features of the recommended wastewater treatment system are noteworthy as being particularly innovative. 1. Redundancy required under Title 22 of the California Water Code is provided without construction of multiple treatment units. 2. Portions of the current facility will be rehabilitated and retained as components of the new treatment plant, resulting in significant cost savings. 3. The recommended treatment plant will be adaptable to future conditions such as the need to incorporate complete nitrogen removal or the use of a method of disinfection other than chlorination. 4. Use of the oxidation ponds for treatment of flows greater than the principal flow diagram capacity will result in lower overall oxygen requirements and hence decreased energy consumption. The algae produced will be a renewable energy source through methane production in the anaerobic digesters. 5. The City’s decisions about future growth will not be constrained by treatment plant capacity. 6. Decisions about treated wastewater dispersal options (e.g., discharge to Willow Slough Bypass or dispersal on land) will not be constrained. The recommended facility will produce treated wastewater meeting Title 22 reclamation requirements.

vii RECOMMENDED ACTIONS BY THE CITY Three specific recommendations were made by the Charette Panel for action in the near future. They are: 1. Headworks and primary plant modifications that have been planned should be completed as soon as possible. 2. The City should take the necessary steps to meet the time requirements laid out by the Regional Water Quality Control Board in the October, 2007 NPDES permit, and 3. A preliminary design and cost estimate, followed by value engineering, of the recommended system should be conducted as soon as possible.

viii 1 INTRODUCTION

In October, 2008, the City of Davis retained Ed Schroeder and George Tchobanoglous, both emeriti professors in the Department of Civil and Environmental Engineering at UCD and long-term residents of the City, to prepare a review of the water resources management plans, including the many past studies that had been commissioned by the City. The purpose of the review was to insure that all of the feasible alternatives had been examined. More specifically, the following questions were to be answered: 1. Do alternative solutions exist that have yet to be considered? 2. Can the water supply and wastewater dispersal issues be addressed in a manner that spreads capital investment over a longer period of time and that allows for lower rate increases? In May, 2009, the results of that study were presented formally to the City Council. Based on a series of guiding principles, the principal findings, in summary form, were: 1. The City with Woodland and the University should move rapidly to secure water from the Sacramento River. 2. Make interim modifications to the existing water supply to reduce the selenium concentration in the water supply and wastewater effluent. 3. Move ahead with an aggressive water conservation program. 4. Make interim modifications to the wastewater treatment system to enhance performance until a final dispersal alternative is available. 5. Undertake a comprehensive analysis of dispersal alternatives. 6. Once construction begins on a new water supply, reconsider the need for new wastewater treatment facilities Subsequent to the submission of the report and before the report was presented to the City Council, it was learned from the Central Valley Regional Water Quality Control Board (Regional Board) that the discharge limit for ammonia would not be relaxed and that progress had to be made towards the implementation of

1 appropriate wastewater treatment facilities. In the ensuing discussion that followed, it was suggested that a wastewater planning Charrette be conducted to examine all treatment alternatives in an effort to minimize ratepayer impacts. A proposal was prepared and submitted to the City on August 7, 2009. On August 13, 2009 the City of Davis authorized Ed Schroeder and George Tchobanoglous to organize and conduct the proposed Charrette. The purpose of this report is to present the findings from the Charrette along with the rationale for the specific elements of the recommended plan.

PURPOSE OF CHARRETTE The purpose of the wastewater management planning Charrette was to: 1. Develop a treatment process flow diagram that will allow the City to continue to discharge to Willow Slough Bypass, and 2. Insure that the selected treatment process will minimize ratepayer impacts to the extent possible.

CHARRETTE PARTICIPANTS The Charrette Panel was comprised of six members: Robert Emerick, Ph.D., P.E. Richard Ingram, P.E. Kevin Kennedy, P.E. Denny Parker, Ph.D., P.E. Dave Richards, P.E. David Stensel , Ph.D., P.E. The Charrette members were selected to represent a broad range of experience in the planning and design of wastewater treatment facilities and the associated technologies. Biographies of the Charrette Panel members may be found in Appendix A. Ed Schroeder and George Tchobanoglous served as facilitators for the Charrette; their bibliographies are also included in Appendix A.

2 CHARRETTE SCHEDULE, AGENDA, AND ORGANIZATION The wastewater management planning Charrette was held on October 22 and 23, 2009. The agenda for the planning Charrette and a listing of attendees may be found in Appendix B. The first meeting, October 22, 2009, was held in two locations: the morning session was held at the City of Davis wastewater treatment plant; the afternoon session was held at the City's corporation yard. The second meeting, October 23, 2009, was held at the City's corporation yard.

ORGANIZATION OF REPORT The report has been organized into the following sections: 1. Introduction 2. The Recommended Wastewater Management Plan 3. The Rationale for the Recommended Plan 4. Discussion of Related Issues The recommended wastewater management plan is set forth in Section 2, which also serves as the summary. The rationale for selecting specific technologies is presented and discussed in Section 3. A discussion of related issues is presented in Section 4. Technical details and issues noted by Panel members during the report review process can be found in Appendix C.

ACKNOWLEDGEMENTS The assistance of the following individuals is acknowledged gratefully: Keith Smith, and Michael Lindquist of the Department of Public Works of the City of Davis. Special thanks are due to Steve McDonald who served as recorder. His notes made the preparation of this report a much easier task.

3 2 THE RECOMMENDED WASTEWATER MANAGEMENT PLAN

The Panel developed a treatment system concept based on:

1. The need to meet the discharge requirements and schedule set by the Regional Board in October, 2007, 2. The assumption that the City will continue to discharge to Willow Slough Bypass, and 3. The recognition of the changes in wastewater quality that will result from the City’s development of a surface water source. Alternatives to discharge to Willow Slough Bypass are under consideration, but essentially all of the treatment steps in the recommended system will be required for unrestricted reuse of the treated wastewater. The most notable changes in wastewater quality will result from changes in the potable water supply. Reduction in concentrations of selenium, alkalinity, total dissolved solids, and hardness will occur through replacement of existing wells with water obtained from a surface water source. Compliance with selenium requirements should be possible even during periods when groundwater must be used as part of the supply through dilution among the various potable water sources. The decrease in alkalinity will result in a decrease in effluent pH with a corresponding increase in the permitted effluent ammonia nitrogen concentration for discharge to Willow Slough Bypass. The reduction in total dissolved solids concentration will aid the City in complying with basin-wide salt management plans being developed through the Regional Board.

The key water quality constituents driving process selection are the effluent organic (measured as biochemical oxygen demand) and ammonia nitrogen concentrations. The ammonia nitrogen requirements, particularly the expected maximum day value of between 3 and 5 mg-N/L, are stringent. The Charrette Panel addressed the nitrogen requirements by the selection of the biological treatment process and incorporation of the current oxidation ponds into the new facility.

4 The purpose of this section is to (1) present the recommended wastewater treatment system, (2) describe the mode of operation at different flowrates, (3) identify the cost saving features of the proposed treatment system, and (4) highlight the innovative features of the recommended treatment system. In addition, the recommended actions by the City are also presented in this section. Additional details on the rationale for the selection of specific processes are presented in Section 3.

THE RECOMMENDED WASTEWATER TREATMENT SYSTEM Municipal wastewater contains a wide range of particulate and dissolved constituents. Most of the particulate matter is organic and biodegradable. Separation of the larger particulate matter from the wastewater, using screens and sedimentation, is inexpensive and the resulting sludges can be stabilized, concurrent with energy recovery, using anaerobic digestion. Material remaining in the wastewater after primary sedimentation includes fine and colloidal particles and dissolved organic and inorganic material. The organic matter is mostly biodegradable and is usually treated using an aerobic biological process. The dissolved inorganic material is typically non-reactive and can be discharged to the environment. However, a few inorganic constituents [e.g., ammonia nitrogen (NH3)] are toxic to aquatic organisms and will need to be removed.

The recommended treatment process flow diagram is presented and described in this section. For ease of presentation, the liquid and solids processing operations are described separately. The recommended treatment process flow diagram is also compared to the previously proposed treatment process flow diagram (Carrollo, 2005). It should be noted that the Charrette Panel felt that significant cost savings can be achieved through innovative incorporation of the existing plant facilities in the proposed flow diagram and by staging modifications and construction of new facilities. The Panel acknowledged that their work was not done in isolation, but reflects the original plan (Carollo, 2005) and the subsequent value engineering report (Brown and Caldwell, 2009).

5 Treatment Process Flow Diagram A treatment process flow diagram is a pictorial representation of the sequential combination of treatment processes that are used to achieve specific treatment objectives. Flow direction is indicated by arrows. The amount of detail shown in a flow diagram (e.g., the volume, length, or depth of a unit and the quantity of flow) is governed by the purpose of the diagram and the amount of information available. Details would be limited in a flow diagram constructed during a projects conceptual phase and would increase as the design process proceeds. The treatment process flow diagram proposed for the City of Davis Wastewater Treatment Plant (WWTP), recommended unanimously by the Charrette Panel, is shown on Fig. 2-1.

Description of Individual Treatment Processes The identification and function of the treatment processes incorporated in the WWTP flow diagram shown on Fig. 2-1 are presented in Table 2-1. Specific technical issues

Figure 2-1 Proposed process flow diagram for the City of Davis Wastewater Treatment Plant. Dashed lines indicate alternative flow pathways or intermittent flows.

6 Table 2-1 Identification of principal treatment processes and their function in the WWTP process flow diagram. Liquid Processing

Process Function Description

Headworksa Influent pumping Wastewater arrives at the treatment plant headworks in a 66 in. and screening to diameter interceptor sewer at an approximate depth of 33 ft. remove coarse Wastewater pumped from the influent trunk sewer passes through solids bar screens and fine screens for the removal of coarse solids. The wastewater is pumped to a height that will allow gravity flow through the WWTP.

Primary Removal of grit Wastewater leaving the screens enters the primary sedimentation sedimentation and wastewater tanks where flow velocity is low and particles remaining after with integral constituents that screening either settle to the bottom of the tank or float to the aerated grit will either settle surface. The solids that settle to the bottom are known as primary removala or float to the sludge. After primary sedimentation, the effluent wastewater surface by gravity contains about 30 to 40 and 50 to 70 percent on the influent total suspended solids (TSS) and organic matter measured as biochemical oxygen demand (BOD), respectively.

Biological Removal of the Effluent from the primary sedimentation tanks enters the biological treatment organic matter in treatment process where the organic matter is metabolized by a (activated wastewater and microbial community that grows in particles known as flocs. sludge) the conversion of Products of metabolism include microbial cells and carbon dioxide specific (CO2). In addition to organic matter metabolism, ammonia - constituents such nitrogen (NH3) will be oxidized to Nitrate (NO3 ) by a specialized as ammonia group of slower-growing bacteria that require specific operating (NH3) nitrogen conditions (i.e., longer solids retention times within the treatment process). The activated sludge biological process consists of two units, the aeration tank where metabolism of the organic matter takes place and the secondary sedimentation tank where the biological sludge is separated from the treated wastewater. Additional details on the biological treatment process are presented in Appendix C.

Secondary Separation of Because the specific gravity of the microbial mass (flocs) from the sedimentation activated sludge activated sludge aeration tank is slightly greater that that of water, from treated it can be removed from the treated wastewater by gravity effluent separation. Deep sedimentation tanks are recommended to provide effluent that is consistently below 10 mg/L TSS (See also Appendix C).

Oxidation Treatment The existing oxidation ponds are used for three purposes: (1) pondsa process provide treatment process redundancy and enhanced reliability, redundancy, (2) temporarily store treated wastewater that does not meet temporary discharge requirements, and (3) partially treat flows in excess of storage, and the capacity of the activated sludge process design flow [nominally partial treatment 6.0 Mgal/d (million gallon per day)]. At least one pond will be maintained in a wet state (i.e., will contain wastewater and a population of algae and bacteria at all times). In addition, the use of oxidation ponds will allow the City the ability to meet higher recycled water demands through seasonal storage and subsequent treatment and distribution during peak irrigation demand seasons. Continued on following page 7 Table 2-1 continued Liquid Processing

Process Function Description

Chemical Enhanced removal If needed, chemical addition could be used to enhance the addition of residual solids removal of residual solids by the disk filter.

Disk filter Removal of Treated wastewater from the secondary sedimentation tank residual TSS contains small concentrations of suspended matter. remaining from the Concentrations are usually less than the 10 mg/L discharge secondary limit set by the Regional Board but to ensure the discharge sedimentation tank requirement is met disk filters will be installed. Solids collected on the disk filters will be conveyed to the DAF or to the oxidation ponds, if necessary.

Disinfectiona Inactivation and/or Disinfection by chlorination and carried out in the current destruction of chlorine contact tanks using gaseous chlorine (Cl2) is pathogenic recommended if the current contact time requirements are microorganisms modified for fully nitrified effluents (see Section 3). Dechlorination with sulfur dioxide (SO2) will be carried out to remove any chlorine remaining at the end of the disinfection process. The use of other disinfectants is discussed in Appendix C.

Post-aeration Addition of oxygen Oxygen must be added to the effluent to assure that aquatic life in the receiving water can be supported during effluent dominated conditions.

Discharge Dispersal to the The treated wastewater is discharged to Willow Slough environment Bypass or diverted for reuse.

Solids Processing

Dissolved air Thickening of Sludge from the primary and secondary sedimentation tanks, flotation (DAF) waste activated and the disk filters will be combined with flows from the sludge and the oxidation ponds and thickened in the DAF. A polymer removal of algae coagulant aid will be necessary to obtain maximum from pond effluent thickening. A coagulant specific to algae flocculation will have to be added separately to the oxidation pond return stream. The thickened sludge will be fed to the anaerobic digesters.

Anaerobic Biological The thickened solids will flow to the anaerobic digesters for digestersa conversion of stabilization. Digested sludge will flow by gravity to drying excess biomass to lagoons where it is stored and dewatered for further methane (CH4) processing. and carbon dioxide (CO2). Sludge Storage and drying Existing method now used for the management of sludge. At lagoons of digested sludge present a firm that produces compost takes the dried sludge once a year for a fee of $25,000. While sludge processing volume and costs will increase with construction of the new facility, continuing the method of management now employed may prove, on further evaluation, to be a cost effective option a Existing treatment plant components

8 related to the process flow diagram, raised by Charrette Panel members during the report review process, are presented in Appendix C.

Comparison of Proposed to Previous Treatment Process Flow Diagram The basic treatment scheme, consisting of headworks/screening, primary sedimentation, biological treatment, and disinfection consists of standard treatment steps and is essentially the same as in the design proposed previously by Carollo Engineers (2005). However, incorporation of a more robust activated sludge process and the oxidation ponds in the system recommended by the Charrette Panel are unique features that will result in smaller treatment units and lower energy requirements while providing emergency storage, redundancy, and a 7.5 Mgal/d treatment capacity.

MODES OF OPERATION Because of the unique features of the proposed WWTP, the mode of operation under varying flow conditions is described briefly in this section.

Flowrates Up to an Average Dry Weather Return Flow (ADWF) of 6.0 Mgal/d For ADWFs up to 6.0 Mgal/d, the incoming wastewater flows through the WWTP as shown on Fig. 2-1. It should be noted that the flowrate of 6 Mgal/d (the projected ADWF in 2030, see Section 3) is believed to be sufficient for the initial capacity of this plant. In this mode of operation, the oxidation ponds will be used for three purposes: (1) to meet redundancy requirements, (2) to temporarily store treated wastewater that does not meet discharge requirements, and (3) to provide flow equalization for peak flow events in excess of the capacity of treatment process shown on Fig. 2-1 (nominally 6.0 Mgal/d), such as might occur during an extreme rainfall event. As noted in Table 2-1, at least one pond will be maintained in a wet state at all times (i.e., will contain wastewater and a population of algae and bacteria).

Redundancy: Wastewater treatment plants must be able to operate when units are out of service for maintenance or due to equipment failure. In most cases the redundancy requirement is addressed by constructing enough units to allow operation with the largest unit shut down. The Charrette Panel recommended that

9 the current oxidation ponds be used to meet the redundancy requirement. If a treatment process unit is out of operation, flow in excess of the reduced plant capacity will be stored and partially processed in the oxidation ponds. In the oxidation ponds, bacteria will consume and oxidize the soluble and colloidal organic matter in the wastewater. The floating aerators already in the ponds can be maintained and used to support the biological oxidation process. The algae laden oxidation pond effluent, which will be very low in soluble BOD, will be pumped to the DAF where solids will be separated and thickened. The subnatant from the DAF will be sent to the activated sludge process where any residual ammonia will be oxidized to nitrate.

Temporary Storage: Wastewater treatment plants are subject to occasional upsets and short-term excursions from discharge requirements. In most cases the problems involve carry over of suspended matter from the secondary clarifier. Less frequent cases will involve exceedance of the effluent ammonia and chlorine residual limits. While upsets or excursions are rare in well operated systems, the potential damage to receiving streams, particularly those in which treated wastewater is the dominant flow, necessitates the ability to store material not meeting discharge requirements. If an upset or excursion should occur, wastewater can be diverted to the oxidation ponds following the bar screens, primary sedimentation, secondary sedimentation, disk filter, and disinfection without incurring a violation. The oxidation ponds will be operated in the same manner as described above when used for redundancy. The ability to divert and store water that does not meet discharge requirements economically provides an exceptional opportunity to protect receiving water ecosystems as well as avoiding permit violations and possible fines.

Flow Equalization: The oxidation ponds will also be used to provide flow equalization, to deal with periodic peak flow-events that occasionally occur as a result of unexpected rainfall events. Flow equalization allows the more costly activated sludge process to be sized much smaller, resulting in cost savings. The oxidation ponds will be operated in the same manner as described above when used for redundancy.

10 ADWF Flowrates Above 6.0 Mgal/d When the permanent flowrate to the plant exceeds 6.0 Mgal/d (or other value as discussed above), the portion of the flowrate beyond 6.0 Mgal/d will be diverted to the oxidation ponds for treatment. In this case, the oxidation ponds will provide the same functions as described above, but will be operated to provide partial treatment on a continuous basis. Under this condition, two oxidation ponds must be in service to have sufficient capacity for the additional flow.

INNOVATIVE FEATURES OF THE RECOMMENDED SYSTEM Six features of the recommended system are noteworthy as being particularly innovative. 1. The redundancy required under Title 22 of the California Water Code is provided without construction of redundant treatment units or dedicated off-line storage facilities. 2. Portions of the current facility will be rehabilitated and retained as components of the new treatment plant. 3. The recommended treatment plant will be adaptable to future conditions such as the need to incorporate complete nitrogen removal or use a method of disinfection other than chlorination. 4. Use of the oxidation ponds for treatment of flows greater than the principal flow sheet capacity will result in lower oxygen requirements and hence decreased energy consumption. The use of algae is a sustainable wastewater treatment concept that consumes carbon dioxide and can enhance methane production in the anaerobic digesters. 5. The City’s decisions about future growth will not be constrained artificially by treatment plant capacity. 6. Decisions about treated wastewater dispersal options (e.g., discharge to Willow Slough Bypass or beneficial reuse) will not be constrained. The recommended facility will produce treated wastewater meeting reclamation requirements.

11 COST SAVING FEATURES OF THE RECOMMENDED SYSTEM Four cost saving features of the recommended system, of particular importance in relationship to the objectives of meeting the discharge requirements with reduced ratepayer impacts, are described in this section.

Continued Use of Existing Plant Components in Proposed System The five existing treatment system components (headworks/screens, primary sedimentation, oxidation ponds, chlorine contact basins, and anaerobic digesters) that will be incorporated into the recommended treatment system were noted above. Additionally, much of the existing equipment (e.g., pumps, piping, etc.) will remain in use. The continued use of current system components will reduce the cost of the new treatment plant considerably.

Reduced Size and Number of New Plant Components in Proposed System Utilization of the oxidation ponds will result in reduction of the size and number of new treatment units in the principal process flow diagram. Smaller treatment units will be possible through shifting a portion of the required treatment capacity to the oxidation ponds. With treatment plant redundancy requirements addressed by the ponds, many key treatment components can be reduced in number by one-third.

Constructing a System Having a Capacity for Future Growth The system configuration recommended by the Charrette Panel will have a principal flow sheet capacity designed for slightly more than the current average flowrate but an actual capacity of 7.5 Mgal/d consistent with the Regional Board permit. Incorporation of the oxidation ponds and the addition of a DAF increase the plant capacity for little additional cost and will result in the City having flexibility in addressing future population, industrial, and commercial growth.

Constructing a System with a High Degree of Operability and Reliability The recommended system will be composed of units that are standard throughout the industry. Simplicity of operation using either automatic or manual control is a hallmark of the units. Because several units (activated sludge treatment, disk filters, DAF) will be new to the facility and because the mode of operation will be considerably different than at present, operator training will be required. Plant staffing is not likely to change in numbers but the training level will be increased 12 (e.g., at least one more grade V operator will be required). Thus, an opportunity for staff advancement will occur.

Activated sludge processes treating municipal wastewater are highly reliable in general. The recommended system should have greater reliability than conventional plants that incorporate redundant units and chemical addition to control excursions from discharge requirements. Using storage to manage excursions is a much better method of generating reliable operation, but in most situations is extremely expensive. For this project, the availability of the oxidation ponds, coupled with the addition of continuous real-time monitoring and automatic control valves will result in an inexpensive method of providing a higher degree of reliability than is normally provided by conventional means.

Increased reliability translates to cost savings through (1) decreases in discharge violations and subsequent fines, (2) less need for overtime pay for operations staff because of more robust treatment capability, and (3) ability to conduct maintenance and repairs of treatment units at scheduled times rather than under emergency conditions.

Staging Modifications and New Construction Modifications to the headworks and primary treatment units were planned prior to initiation of the Charrette evaluation. Carrying out the modifications in the near future should result in very competitive bids. Similarly staging other components of the new facility may result in cost savings.

RECOMMENDED ACTIONS BY THE CITY Three specific recommendations for action in the near future were made by the Charette panel: 1. Headworks and primary plant modifications that have been planned should be completed as soon as possible in view of current construction costs. As a panel member stated “treatment plants are on sale” and noted that bids for the construction of a new 6 Mgal/d plant in Atwater, CA, estimated to cost $72,000,000, were in the low to mid $40,000,000 range.

13 2. The City should take the necessary steps to meet the time requirements laid out by the Regional Board in the October, 2007 NPDES permit. 3. A preliminary design and cost estimate, followed by value engineering, of the recommended system should be conducted as soon as possible.

14 3 RATIONALE FOR THE RECOMMENDED PLAN

Wastewater treatment systems are designed to comply with discharge requirements based on national and state standards and the characteristics and use of the receiving waters. The principal wastewater characteristics are volumetric flowrate, temperature, the constituents carried with or in the wastewater and their corresponding concentrations. Wastewater characteristics change over the course of a day, seasonally, and because of changes in a community such as population growth or the addition of commercial or industrial enterprises. Discharge requirements are issued for set periods, normally five years – a period considerably shorter than the life of a treatment facility. Understanding of the potential impacts of discharges on the environment will improve with time and succeeding discharge requirements will become increasingly stringent. Thus, wastewater treatment plants must be designed to accommodate changes that can be expected in the basis for design during the planning period.

SELECTION OF DESIGN PARAMETERS Wastewater system design is based on the expected flow and constituent loadings that will occur over the life of the treatment plant. Davis is a primarily residential community and changes in wastewater flow and characteristics are expected to reflect population growth and increased water conservation measures by homeowners and commercial enterprises. The City has recently entered into an agreement with the City of Woodland and the University of California, Davis to develop a new surface water supply from the Sacramento River. Changing from a groundwater to a surface water source will have beneficial effects on the City’s wastewater characteristics.

Population Projections Average wastewater flow and constituent loadings in residential communities such as Davis can be characterized in units per capita terms. Each resident, on average, contributes a quantity of wastewater, organic material, and other constituents. Thus,

15 estimates of the future population are a critical part of the design process. Between 1970 and 2000 Davis grew at an average rate of 3.2 percent per year. Since 2000 the average growth rate has been approximately 0.6 percent per year. Population projections based on the 2007 population of 62,724 are shown on Fig. 3-1 for growth rates of 0.5, 1, and 2 percent, respectively. The City has taken a number of steps to minimize growth and future growth rates greater than 1 percent per year seem very unlikely.

Plant Loadings Treatment units are sized on the basis of hydraulic, suspended solids, and organic (BOD) and ammonia loadings. Plant influent flowrate is characterized in a number of ways, as shown Table 3-1 with average dry weather flow being the baseline reference that is normally used to describe plant capacity. Since 2000, flowrates have not increased significantly; since 2007, a decreasing trend has been observed (see Fig. 3-2), despite a significant population increase. Stable or decreasing flowrates are likely the result of the City’s water conservation program and public awareness.

Table 3-1 Characteristic Davis influent wastewater flow values Flowrate, Mgal/d

Flow parameter 2000 2001 2002 2003 2004 2005 2007 2008 Average annual (AA) 5.64 5.61 5.79 5.87 5.96 6.07 5.68 5.53 Average dry weather (ADW) 5.21 5.23 5.37 5.45 5.55 6.07 5.40 4.97 Average dry weather max month (ADWMM) 5.27 5.40 5.61 5.78 6.43 6.47 5.61 5.28 Average wet weather max month (AWWMM) 6.36 6.07 6.34 6.33 6.74 6.77 6.09 6.28 Max day 7.42 6.84 7.53 7.07 7.69 8.83 7.79 6.95

The per capita average dry weather flowrate is approximately 86 gal/person per day based on 2000 and 2007 populations. Decreasing per capita flow is more difficult when dwelling units are older and retrofitting is required. However the per capita flow value can be lowered considerably with increased conservation efforts. With a 0.5 percent per year growth rate and 86 gal/person per day wastewater generation

16 160

140 2 % growth

120

100 1 % growth

Historical 80 values

0.5 % growth Population in thousands 60

40

20 1960 1980 2000 2020 2040 2060 Year Figure 3-1 City of Davis population projections based on the 2007 value

Figure 3-2 City of Davis daily flowrates for the period from 2007 to 2009

17

Figure 3-3 Projected City of Davis daily flowrates based on average dry-weather flow during the period from 2007 to 2009 rate, hydraulic capacity (ADWF of 7.5 Mgal/day) of the recommended plant will not be exceeded for over 50 years, as shown on Fig. 3-3.

At a 1 percent growth rate the plant capacity will be reached in 30 years. Decreasing the per capita flow generation by 10 percent would extend the time before plant hydraulic capacity was exceeded at a 1 percent growth rate to 44 years. The panel agreed that designing for a projected 2030 hydraulic loading was prudent. Design flows would then be 6.0 and 6.8 Mgal/d for 0.5 and 1 percent growth rates, respectively. The Charrette Panel settled on a flowrate of 6.0 Mgal/d for the principal flowsheet capacity as a value that could accommodate a range of growth rate decisions by the City.

Organic and suspended solids loadings are used to size the biological treatment process and sludge digesters, respectively, and currently each averages approximately 8900 lb/d or 0.14 lb/capita•d. Because the per capita loading values are unusually low (typical values are about 0.2 lb/capita•d) these values should be 18 investigated further. The two mass loadings (BOD and TSS) should increase approximately linearly with population unless a significant change in the commercial and industrial make-up of the City occurs. The activated sludge process recommended by the panel will be sized for 2030 organic mass loadings associated with the projected 2030 population level. As flow and the associated loadings increase above design flow, the oxidation ponds will be used increasingly for treatment of the organic material.

Critical Wastewater Constituents: In addition to BOD and suspended solids, critical wastewater constituents that must be considered in the design of the treatment system are total Kjeldahl nitrogen (i.e., the summation of organic nitrogen and ammonia), salinity, and selenium. Ammonia is toxic to many aquatic organisms at extremely low concentrations. Fortunately, - microbial communities that oxidize ammonia to nitrate (NO3 ) can be established in biological treatment processes and the discharge requirements issued in 2007, adjusted for the expected pH, can be met by a conservatively designed and operated biological treatment process. Salinity is a problem because aquatic ecosystems change with increasing salinity and groundwater quality decreases due to saline water percolation. Selenium has been shown to cause reproductive problems in waterfowl at concentrations in the microgram per liter range. Both salinity and selenium problems will be addressed with the City’s change to a surface water supply.

COMPONENTS OF THE RECOMMENDED TREATMENT SYSTEM

The treatment system recommended by the Charrette Panel (see flow diagram Fig. 2-1) was introduced in Section 2. The recommended processes for the WWTP have been presented previously in Table 2-1 in Section 2. The rationale for process selections is discussed in this section.

Headworks Carollo Engineers and the subsequent value engineering team both concluded that the current plant headworks capacity of 60 Mgal/d peak wet-weather flow would be satisfactory for the foreseeable future, but noted a number of deficiencies in

19 operating strategy and equipment. Upgrading the headworks was found to be necessary and should be initiated as soon as possible.

Primary Sedimentation The primary sedimentation tanks were designed for an average dry weather flow of 7.5 Mgal/d and a peak wet weather flow of 19 Mgal/d and, therefore, are of sufficient capacity. Carollo Engineers and the value engineering team concluded that upgrades to the primary tanks were necessary, including new sludge collection mechanisms and adding variable control to the sludge pumps.

Biological Treatment The Charrette Panel recommended the activated sludge process be selected for biological treatment because of the low ammonia nitrogen discharge requirement placed on the treatment plant by the Regional Board. Nitrification (oxidation of ammonia to nitrate) can be achieved to a greater degree and more reliably with activated sludge than with alternative processes such as trickling filters. A number of activated sludge process configurations exist and the panel recommended that either the plug flow or oxidation ditch with selector configurations be chosen. Process performance data recently collected by a Water Environment Research Foundation committee, chaired by panel member Dr. Denny Parker (Bott and Parker 2009), are consistent with the recommendation. An additional advantage of selecting the activated sludge process is that modifications necessary to operate the plant as a nitrogen removal facility are straightforward.

Chemical Addition The potential benefits of chemical addition include: (1) the enhanced capture of residual solids, (2) the use of higher filtration rates, (3) the ability to filter oxidation pond effluent directly during certain times of the year. Chemical addition may also be necessary to satisfy the Department of Health Services reuse requirements.

Disk Filter During the past ten years, a number of new effluent filtration technologies have been developed and approved for use in reuse applications. The stainless steel (SS) disk filter, operating at a filtration rate of 30 m/h (12 gal/ft2•min) with a backwash water

20 percentage of about 3 percent, is one such development. The filtration rate for this filter is two to four times greater than other approved filters, while providing the same level of performance (Bourgeous et al., 2009). The advantages of this new filter technology as compared to conventional filter technologies are significant: (1) less use of resources (3 to 6 times less volume), (2) less energy consumption, and (3) reduced overall carbon footprint.

Disinfection/Dechlorination

The Charrette Panel believes that continued use of gaseous chlorine (Cl2) and declorination with sulfur dioxide (SO2) will be the most cost effective method for disinfection. At the present time, the California Department of Public Health requires a Ct value (the product of the residual chlorine concentration in mg/L, C and contact time in minutes, t ), of 450 mg-min/L with a modal contact time of at least 90 minutes under dry weather flow conditions. The current chlorination facilities do not provide this level of protection. However, exceptions have been approved for nitrified effluents. The Charrette Panel assumed that effort will be directed toward modifying the current discharge permit to allow for a less stringent disinfection requirement or that studies will be undertaken to satisfy the Department of Public Health that the degree of disinfection provided by the current chlorination system is adequate.

Post Aeration The discharge into Willow Slough Bypass must meet a 7 mg/L dissolved oxygen coldwater fishery requirement. Activated sludge effluent will normally contain less than 7 mg/L dissolved oxygen. The oxygen requirement can be met by post aeration.

Oxidation Pond The Charrette panel developed a unique method of addressing both emergency storage and plant capacity issues. Emergency storage is required when effluent does not meet discharge requirements and when portions of the treatment train are out of service. Title 22 of the California Water Code requires that the treatment system must be operational with the largest unit out of service for 20 days.

21 Up to an ADWF of about 6.0 Mgal/d, one oxidation pond will be maintained in a wet condition as emergency storage and for treatment of wastewater. Beyond this ADWF a second pond will be required. Diverting excess flow to an oxidation pond for treatment will avoid the necessity of providing multiple units or the need to construct new storage. Additionally, flows greater than the activated sludge process capacity can be diverted to the oxidation ponds for treatment. Effluent from the oxidation ponds will be high in algae concentration, moderately high in ammonia concentration and low in soluble organic concentration. Treatment by dissolved air flotation (DAF) will separate the algae and the liquid stream can be sent to the activated sludge process. Because of the low organic concentration, there will be little impact on activated sludge process performance. Secondary sedimentation is considerably more sensitive to solids than hydraulic loading and flows up to 7.5 Mgal/d should be acceptable because flow from the oxidation ponds will not result in additional microbial biomass production and in addition, the ponds will provide equalization of flow obviating the need for the secondary clarifiers to handle high wet weather related peak flows. Nitrogen in the liquid stream from the oxidation pond will need to be oxidized and the added aeration capacity needs to be included in the design.

Dissolved Air Flotation Dissolved air flotation (DAF) is used for thickening sludges from sedimentation tanks and, in the recommended plan, for removing solids (primarily algae) from the oxidation pond effluent. The DAF process works by supersaturating dissolved gases in a portion of the DAF effluent by injecting air under pressure. The pressurized flow is introduced into the DAF tank inlet where the pressure is released and small bubbles form, much as when the cap is taken off of a soda bottle. The bubbles in the DAF attach to solid particles, decreasing their density and a rapid flotation and separation of the solids occurs. Addition of coagulating polymers improves solid removal and float concentration. The DAF can be used to remove algae from oxidation pond effluents as well as for the more common purpose of thickening sludges to increase anaerobic digester capacity.

22 Anaerobic Digesters Primary sludge, waste activated sludge, and solids from the oxidation pond will be treated in the current anaerobic digesters. In the Strategic Master Plan report of 2005, it was noted that unthickened primary sludge from a flow of 22.5 Mgal/d would have a 20-day residence time in the digesters. The Panel concluded that current digester capacity is more than adequate for the new plant.

Sludge Disposal At present digested sludge is discharged to drying ponds. Periodically the sludge is removed by a contractor at an annual cost of $25,000. Continuation of the current method of sludge disposal will require additional drying ponds to accommodate increased sludge volumes and addressing safety problems noted during the Charrette. The Charrette Panel believes that alternative sludge disposal options should be evaluated.

Yard Piping The Charrette Panel noted that an activated sludge system will involve considerable new piping. Based on their experience, the panel strongly recommended that piping be above ground on racks or in tunnels to allow for maintenance and possible later modification.

Support Facilities The Charrette Panel observed that the current laboratory is inadequate in terms of space and that much of the equipment is obsolete. Increasing sampling and analysis is being required by regulators. A new, bare bones, stand-alone laboratory building needs to be constructed and adequately equipped. The current administration and laboratory building should be converted to a 100 percent administrative function.

23 4 DISCUSSION OF RELATED ISSUES

Water will be an increasingly valuable resource in the Sacramento Valley. Davis wastewater will be treated to reclaimed water standards and suitable for a wide range of uses. The City will be able to choose a final dispersal of the treated wastewater in a manner that will be beneficial to the environment, provide water to sustain local ecosystems, or improve the groundwater quality. The Charrette Panel noted that developers taking water from the Truckee River are required to return an equal quantity of treated wastewater. If such requirements were extended to the Sacramento River limitations on reuse may occur.

FUTURE REUSE OPPORTUNITIES The City has been studying the possibility of dispersal on Conaway Ranch for some time. There the water would be used for irrigation of alfalfa and other forage crops. There is a further possibility of using reclaimed water on rice fields during the winter. Enough City owned agricultural land exists to accommodate summer flows. Future re-piping could allow a good deal of reclaimed water to be used for parks, golf courses and other open space within the City.

FUTURE DISCHARGE AND REUSE REQUIREMENTS Discharge requirements, particularly those for reclaimed water (Title 22), are quite likely to become more stringent in the future. Possible changes include limits on total inorganic nitrogen (TIN) and phosphorous. The recommended activated sludge system can be modified easily for both TIN and phosphorus removal.

OPPORTUNITIES FOR ENERGY CONSERVATION AND SUSTAINABILITY A number of opportunities exist to save and/or produce energy at the Davis wastewater treatment plant.  With the oxidation ponds in the process train, there is the opportunity to avoid the cost of putting in new standby generators by diverting primary effluent to the ponds during a power outage.

24  Gas generation at the adjacent County landfill is to be expanded and sludge disposal from the treatment plant could be used as an additional source. Energy produced could be returned for use at the plant.

APPROACH TO ESTIMATING COSTS The panel agreed that a life-cycle cost estimate is needed. Initial high capital costs difference can by overcome by reduced operating and maintenance (O&M) expense. Also, there are a number of choices that require performance/cost trade-offs. For example, fine-bubble diffusers are hard to justify on a cost basis (vs. coarse bubble), but the fine-bubble allows for a better process turn-down ratio.

Additional sludge lagoons will be needed. The three existing sludge lagoons are satisfactory for the primary sludge, but addition of (digested) waste activated sludge and lagoon solids will at least double the quantity of digested solids. The panel agreed that that there needs to be a further analysis of two alternatives: (1) dewatering and trucking to landfill and/or beneficial use or (2) air drying (and more land).

25

REFERENCES

Bott, C., and D. Parker (2009, in preparation) "WEF/WERF Study Quantifying Nutrient Removal Technology Performance," Water Environment Research Foundation Project, WERF Nutrient Removal Challenge (NUTR1R06).

Bourgeous, K., N. Fontaine, J. Stokke, K. Marks, Sean Poust, D. Loy, and D. Popowitch (2009) "Pilot Testing of a High-Rate Disk Filter for Water Recycling Applications and Title 22 Approval," presented at WEFTEC.09, Orlando, FL.

Brown and Caldwell (2009) Value Engineering Study Report For City Of Davis Water Pollution Control Plant Improvements Project, Brown and Caldwell in association with Robinson, Stafford, & Rude, Inc., Davis, CA.

Carollo Engineers (2005) City of Davis, California Wastewater Facilities Strategic Master Plan, Draft dated November 2005, Carollo Engineers in Association with West Yost Associates, Walnut Creek, CA.

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Appendix A

Charrette Participant Biographies Wastewater Planning Charrette Davis, California Robert Emerick, Ph.D., P.E. Principal Eco:Logic

Robert Emerick has over 15 years of water quality experience, focusing primarily on small to medium sized municipalities discharging within the Central Valley and Sierra Nevada. He specializes in wastewater treatment process development, process design, pilot testing, negotiating cost-effective land discharge and NPDES permits, and the conduct of stream studies for priority pollutant regulation (e.g., water effect ratio, translator, dilution studies). Dr. Emerick has developed, pilot tested, and successfully implemented at the municipal scale many wastewater treatment processes, most notably for rice irrigation, broad spectrum priority pollutant control, and broad spectrum emerging contaminant treatment (e.g., endocrine disrupting contaminants, pharmaceuticals, personal care products). He is currently directing an alternative technology equipment testing facility used to obtain State of California Title 22 approval for the production of disinfected tertiary recycled water and is also teaching a series of classes through the State Water Resources Control Board on wastewater permitting, process design, and compliant operation for all State of California regulatory, enforcement, and financing staff. Dr. Emerick serves on the groundwater monitoring advisory committee for the Regional Water Quality Control Board (Region 5) and provides forensic engineering services to the State Water Resources Control Board Office of Enforcement. He received his B.S., M.S., and Ph.D. degrees from the University of California at Davis.

Richard Ingram, P.E. Vice President Brelje & Race Consulting Engineers

Richard Ingram has been with Brelje & Race for more than 25 years and has over 30 years experience as a civil engineer. For the past 22 years, Mr. Ingram has designed and managed projects exclusively for water, wastewater, and recycled water infrastructure, more specifically treatment, distribution, supply and storage. His experience in this service arena involves all phases of the project life cycle commencing with project evaluation including preparation of master plans; site and system design; cost estimation; contract administration; preparation and implementation of pilot tests; execution of plant start-up; and preparation of operation and maintenance manuals. Mr. Ingram’s broad range of project experience has allowed him to specialize in various treatment technologies such as UV disinfection, advanced waste treatment, extended air activated sludge, biosolids and recycled water planning and use. In addition to his technical expertise, Mr. Ingram has extensive experience in environmental permitting processes and has worked developing State of California Regional Water Quality Control Board permits. His broad client base includes both private and public agencies. Mr. Ingram holds a Master of Science in Environmental Engineering from the University of California in Berkeley.

A-1 Kevin Kennedy, P.E. Vice President, Business Class Leader HDR Engineers

Kennedy has more than 18 years of experience in hydraulics, water supply, wastewater treatment, and plant operations. He is experienced in water and wastewater treatment process and hydraulic modeling, master planning, as well as in the use of database management system applications. He specializes in wastewater treatment and permit strategy development, process design, ratepayer impact minimization, and other related utility management activities. Kevin has led the preparation of over 50 water, wastewater, and recycled water related master plans for municipalities located throughout California and Nevada. Two recent Master/Facility Planning projects include Conceptual Advanced Wastewater Treatment (AWT) Cost Estimate, City of Cloverdale, California Stillwater Wastewater Treatment Plant Facilities Plan, City of Redding, California. Two recent peer review projects include Wastewater Treatment Plant Peer Review and Lagoon Study - Santa Nella County Water District, Santa Nella, California. And Comparison of Independent and Regional Approaches for the Ironhouse Sanitary District's Wastewater - Delta Diablo Sanitation District, Antioch, California. He also currently serves as the Utility Management Business Class Lead for HDR’s Northern California Region and has specialized experience related to beneficial reuse on the Conaway Ranch. Kevin received his B.S. and M.S. degrees from the University of California, Davis.

Denny Parker, Ph.D., P.E., NAE Senior Vice President and Director of Technology Brown and Caldwell Consulting Engineers

Denny Parker has been with Brown and Caldwell for more than 25 years. Regularly serving as a process design reviewer for major wastewater projects, Dr. Parker participated in Blue Ribbon Panel design and operations reviews for major BNR programs in New York City, Jacksonville, Denver, Pima County, AZ, and Atlanta. He has lectured on nitrogen removal at EPA technology transfer sessions across the U.S. and was the senior author of the EPA’s Nitrogen Control Process Design Manual. Dr. Parker has invented, developed and implemented new wastewater processes including the flocculator clarifier, the TF/SC process, and a number of separate stage nitrification and denitrification processes He has won seven national awards for his process engineering work including election to the National Academy of Engineering 2004, and WEF’s Camp Medal in 2003. Dr. Parker received his undergraduate B.S., masters, and Ph.D. degrees from the University of California at Berkley.

A-2 Dave Richards, P.E. Vice President Nolte and Associates

Dave Richards is a senior project manager and water/wastewater discipline director for Nolte Associates in Sacramento, California. Mr. Richards received his BSCE from Michigan Technological University in 1978 with an emphasis in sanitary engineering and his Master of Engineering in environmental engineering from the University of California at Davis in 1992. He is a registered civil engineer in California since 1981. The focus of Dave’s 31-year professional career is wastewater treatment and reuse. He has lead the planning, design, permitting, and construction of over twenty treatment plant and reclamation projects, including the first 5 Mgal/d recycling plant in Sacramento County, the City of Ione wastewater reclamation plant serving the Castle Oaks golf course, and City of Lathrop Water Reclamation Plant One. His most recent tertiary treatment project is the $22 million Title 22 upgrade of the 10 Mgal/day Manteca Wastewater Quality Control Facility, including cloth disk filters and UV disinfection. Mr. Richard has published extensively in the field of water reuse including the Cost of Wastewater Reclamation in California through the University of California at Davis.

David Stensel, Ph.D., P.E. Professor of Civil and Environmental Engineering University of Washington, Seattle, WA

David Stensel is Professor of Civil & Environmental Engineering at the University of Washington. Prior to his academic positions, he spent 10 years in practice developing and applying industrial and municipal wastewater treatment processes. He received a B.S. degree in civil engineering from Union College, Schenectady, NY, and M.E. and Ph.D. degrees in environmental engineering from Cornell University. Prof. Stensel’s principal research interests are in the areas of wastewater treatment, biological nutrient removal, sludge processing methods, and water reuse. He has authored or coauthored over 100 technical publications and textbooks on biological nutrient removal and the 2003 edition of the M&E Wastewater Engineering book. Prof. Stensel has worked on process designs for over 100 wastewater treatment facilities including biological nutrient removal and a wide range of secondary and tertiary treatment processes. He has received the ASCE Rudolf Hering Medal, has twice received the Water Environment Federation Harrison Prescott Eddy Medal, and the Water Environment Federation George Bradley Gascoigne Medal for his research contributions. Prof. Stensel is a member of numerous professional societies, and has served as chair of the ASCE Environmental Engineering Division, treasurer of the American Association of Environmental Engineering Professors, and as associate editor of the Water Environment Research Journal. He is a registered professional engineer and a certified environmental engineer in the American Academy of Environmental Engineers. Currently Prof. Stensel serves as a technical advisor to New York City and Spokane, WA.

A-3

Edward Schroeder, Ph. D. Professor Emeritus University of California, Davis (Davis, California)

Edward Schroeder taught courses and conducted research on water quality, water supply, and water and wastewater treatment at the University of California, Davis for 36 years. During this period Schroeder supervised 25 doctoral and 100 MS students. He served as Visiting Professor at University College, Swansea (Wales), The University of Leeds, The Hong Kong University of Science and Technology, and Canterbury University (New Zealand). Professor Schroeder has authored or coauthored over 160 publications and three textbooks and served as coeditor of Global Sustainability: The Impact of Cultures. He has received the Academic Senate and Engineering Alumni awards for distinguished teaching and the Water Environment Federation McKee Medal for research. Schroeder served on the California Regional Water Quality Control Board – Central Valley Region for three years and has served as a consultant to local and state governments, consulting firms, and non-profit environmental groups and as an advisor for a number of university programs in environmental engineering. He received a B.S. in Civil Engineering and M.S. in Sanitary Engineering from Oregon State University and a Ph.D. in Chemical Engineering from Rice University.

GEORGE TCHOBANOGLOUS, PH.D., P.E., NAE Professor Emeritus University of California, Davis (Davis, California)

For over 35 years, wastewater expert George Tchobanoglous has taught courses on water and wastewater treatment and solid waste management at the University of California, Davis, where he is Professor Emeritus in the Department of Civil and Environmental Engineering. He has authored or coauthored over 350 publications, including 13 textbooks and five engineering reference books. Tchobanoglous has been past President of the Association of Environmental Engineering and Science Professors and currently serves as a national and international consultant to both government agencies and private concerns. Among his honors, he received the Athalie Richardson Irvine Clarke Prize from NWRI in 2003, was inducted to the National Academy of Engineers in 2004, and received an Honorary Doctor of Engineering degree from the Colorado School of Mines in 2005. Tchobanoglous received a B.S. in Civil Engineering from the University of the Pacific, an M.S. in Sanitary Engineering from the University of California, Berkeley, and a Ph.D. in Environmental Engineering from Stanford University.

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Appendix B

Charrette Agenda and Attendees Wastewater Planning Charrette Davis, California CHARETTE AGENDA

A. Day 1 Morning (8:00 a.m. to 12 a.m.) 1. Introductions 2. Objectives of the Charette Process a. Develop cost effective wastewater management system that will meet discharge requirements b. Minimize ratepayer fee increases 3. Background a. Short summary of past issues (toxicity, algae, erosion, flooding….) b. Operating issues with current system c. Changes in operation/configuration 4. Current discharge requirements and pending changes/possibilities a. Discharge requirements as of October, 2007 b. Recalculated ammonia limits proposed for February 2010 adoption c. Changes resulting from delivery of Sacramento River water 5. Discussion of current loading and flows 6. Field trip to treatment plant (led by EDS & GT and emphasizing points associated with Charette objectives B. Lunch at city conference room C. Day 1 Afternoon (1:00 p.m. to 5 p.m.) 1. Presentation of potential/possible treatment options a. With continued discharge b. With reclamation/reuse and storage requirements i. Summer only ii. Summer and winter 2. Potential processes, linkages, sequences, and winter/summer options a. Biological treatment including nitrification and denitrification b. Additional treatment process(es) required to meet discharge requirements 3. Operability and ability to meet requirements 4. Need for preliminary cost estimates 5. Preliminary engineering and construction schedules 6. Assignments to participants

D. Day 2 Morning (8:00 a.m. to 12 a.m.) 1. Discussion of options – Modifications – New Options 2. Selection of best alternatives based on operability and meeting requirements E. Day 2 Afternoon (1:00 p.m. to 4:00 p.m.) 1. Cost Estimates 2. Time to completion 3. Discussion & Outline of Letter Report

B-1 CHARRETTE ATTENDEES

THURSDAY OCTOBER 22, 2009

Charrett Panel Members Robert Emerick (Eco:Logic) Richard Ingram (Brelje & Race) Kevin Kennedy (HDR) (left mid-afternoon) Denny Parker (B&C) Dave Richards (Nolte) David Stensel (Univ. of Washington) Facilitators Ed Schroeder (UCD) George Tchobanoglous (UCD) City of Davis Jim Beatty (City of Davis) (Morning Session) Keith Smith (City of Davis) Observers Steve McDonald (Carollo) Steve Swanback (Carollo) (afternoon)

FRIDAY OCTOBER 23, 2009

Charrett Panel Members Robert Emerick (Eco:Logic) Richard Ingram (Brelje & Race) Kevin Kennedy (HDR) (left mid-afternoon) Denny Parker (B&C) Dave Richards (Nolte) Facilitators Ed Schroeder (UCD) George Tchobanoglous (UCD)

B-2 City of Davis Michael Lindquist (Davis) Keith Smith (City of Davis) Observers Steve McDonald (Carollo) Steve Swanback (Carollo)

B-3

Appendix C

Specific Technical Details and Issues Wastewater Planning Charrette Davis, California

SPECIFIC TECHNICAL DETAILS AND ISSUES

Charrette Panel members raised a number of specific technical issues during the report review process. The issues did not involve changes in the recommendations developed during the Charrette process, but were focused on design and regulatory factors that may of interest to the City Council and will be important to a future design team. The specific issues raised are addressed beginning with the wastewater source and extending through each treatment step. Surface Water Supply: 1. The surface water supply will eliminate a future need for salt removal due to restrictions in the proposed basin-wide salt management plan. 2. The decrease in hardness has the potential to exacerbate metals toxicity. It may be necessary to conduct various water effects ratio studies to demonstrate compliance with metals limitations upon conversion to the Sacramento River potable water supply Headworks: None Primary Sedimentation: None Biological Treatment: 1. As noted in Section 3, to ensure satisfactory nitrification the Panel recommended that the biological treatment process configuration be either plug flow or oxidation ditch with a selector. Selectors provide environmental conditions that promote formation of a well settling floc. In the selector, nutrient rich effluent from the primary sedimentation tanks is combined with microorganisms recycled from the main biological treatment process. Effluent from the selector is discharged to the nutrient poor aeration tank creating feast/famine conditions that promote the growth of a well-settling floc. 2. The oxygen free environment within anoxic selectors allows for denitrification (conversion of nitrate nitrogen to nitrogen gas) and corresponding reductions in oxygen and energy requirements. In a typical activated sludge process the recycle flow may vary between 25 and 50 percent of the plant influent flow and potential nitrogen removals are in about the same percentages.

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3. Fine-bubble diffusers are highly desirable for a plug flow activated sludge process configuration but lower cost brush aerators are used in oxidation ditches. However, an oxidation ditch will have a much larger footprint and reduced operating flexibility than a plug flow configuration. Secondary Sedimentation: 1. Solids stored on the bottom of the secondary sedimentation tank will become anoxic and in nitrified effluents denitrification will occur. The rising nitrogen gas bubbles will attach to solids and result in carryover of suspended matter. 2. It is essential to minimize the solids inventory in the secondary sedimentation tank of nitrifying systems to prevent denitrification and rising sludge. Oxidation Ponds: 1. The Midgen law requires automatic fines for violation of effluent limitations with the minimum fine equal to any economic benefit of non-compliance. With storage facilities in place, there is no reason that substandard water should be discharged to the environment, greatly limiting the likelihood of the City incurring discharge violation fines. 2. Depending on the number and size of ponds utilized, it may be possible to dispose of their contents solely on land or via evaporation. 3. The need to line any one of the various ponds will depend on groundwater degradation limits imposed by the Regional Board. Use of a surface water supply and past groundwater monitoring results will aid in determining the need for lining. Chemical Addition: None Disk Filter: None Disinfection: 1. The current permit requires enhanced disinfection, requiring a longer contact time than is currently available with existing facilities. An appeal of the disinfection requirement to the Department of Public Health should be undertaken based on the fact the proposed design involves complete nitrification. 2. An appeal of the disinfection requirement must be based on providing equal protection as described by statute.

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3. If the appeal is unsuccessful, conversion to ozonation should be considered because it allows for emerging contaminant control (i.e., expected future changes in regulation) while providing the necessary postaeration function. Postaeration: None Dissolved Air Flotation: None Anaerobic Digestion: None Sludge Lagoons: The use of the lagoon system for sludge processing has tentatively been selected as the sludge processing method, subject to a more detailed analysis of other sludge processing methods such as dewatering and land application.

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