W as tew ate r T re atm en t P lan t E v a l u a t I o n City of Stayton OREGON Stayton WWTP Evaluation 103003/3/03-707 TOC - 1 February 2006 TABLE OF CONTENTS Page No. Chapter 1 Introduction 1.1 History ........................................................................................... 1-1 1.2 Existing Facilities ........................................................................... 1-1 1.3 Purpose of Study ........................................................................... 1-3 1.4 Abbreviations ................................................................................ 1-3 Chapter 2 Flow and Load Projections 2.1 General .......................................................................................... 2-1 2.2 Existing Flow ................................................................................. 2-1 2.3 Existing Plant BOD and SS Loads ................................................ 2-2 2.4 Future Plant Flow Rates ................................................................ 2-3 2.5 Future Plant BOD/SS Loads ...........................................................2-4 Chapter 3 NPDES Permit Limits 3.1 General ......................................................................................... 3-1 3.2 Previous Permit Conditions.............................................................3-1 3.3 New Permit Requirements ..............................................................3-2 3.4 New Permit Impacts ........................................................................3-4 Chapter 4 Process Evaluation 4.1 General .......................................................................................... 4-1 4.2 Plant Liquid Process Unit Evaluation ............................................. 4-1 4.3 Plant Solids Handling Process Evaluation ..................................... 4-9 4.4 Miscellaneous Facilities ................................................................4-14 Chapter 5 Operational Analysis 5.1 General .......................................................................................... 5-1 5.2 Staffing Levels................................................................................ 5-1 5.3 Operations, Monitoring, and Controls............................................. 5-3 5.4 Operation and Maintenance Procedures.........................................5-4 5.5 Testing ............................................................................................5-5 5.6 Industrial Pretreatment and GIS Programs .....................................5-5 5.7 Operation and Maintenance Costs..................................................5-5 Chapter 6 Recommended Improvements 6.1 General .......................................................................................... 6-1 6.2 NPDES Permit and I/I Related Improvements.................................6-1 6.3 Headworks Improvements ..............................................................6-4 6.4 Sequencing Batch Reactor Improvements......................................6-5 6.5 Equalization Basin Improvements ...................................................6-8 6.6 UV Disinfection System Improvements ...........................................6-9 Stayton WWTP Evaluation 103003/3/03-707 TOC - 2 February 2006 6.7 Solids Handling Facility Recommendations ..................................6-10 6.8 MBR Alternative to SBR Expansion ..............................................6-18 6.9 Miscellaneous Plant Improvements...............................................6-21 6.10 Recommendation Summary..........................................................6-23 Tables 2.1 Existing and Design Conditions - Influent Flow Rates (MGD) ........ 2-1 2.2 Existing and Design Conditions – Influent BOD/SS Loads..............2-2 2.3 Projected Future Plant Flow Rates..................................................2-3 2.4 Projected Future Plant BOD/SS Loads ...........................................2-4 4.1 Estimated Sludge Production – (tons/day) ......................................4-9 6.1 Sludge Treatment and Disposal Alternative Costs ........................6-16 6.2 MBR/SBR vs SBR Capital Cost Comparison ................................6-20 6.3 MBR/SBR vs SBR Annual O & M Costs .......................................6-20 6.4 Opinion of Most Probable Cost .....................................................6-24 Appendix A Figures Figure 1.1: Site Plan Figure 1.2: Schematic Flow Diagram Figure 2.1: Plant Hydraulic Profile Figure 3.1: Proposed Outfall Extension Figure 6.1: Wastewater Treatment Master Plan Appendix B NPDES Permit Appendix C Plant Staffing Level Estimate Appendix D O & M Costs Appendix E Industrial User Summary Stayton WWTP Evaluation 103003/3/03-707 1 - 1 February 2006 CHAPTER 1.0 – INTRODUCTION 1.1 HISTORY The City of Stayton has provided wastewater treatment for the Stayton- Sublimity area since 1962. The original wastewater treatment plant (WWTP) was an oxidation ditch type plant which was upgraded in 1972 and 1975 and operated until 1996. The plant consisted of the following elements: • Headworks (included comminutors and flow measurement) • Oxidation ditch • Secondary clarifiers • Chlorine contact chamber and equalization pond • Gravity filters • Aerobic digester and sludge lagoons Some of the old plant features are still in existence. Most have been abandoned except for the aerobic digester and sludge storage ponds. 1.2 EXISTING FACILITIES In the late 1980’s the oxidation ditch plant became overloaded and required expansion as a result of continuing growth in the Stayton- Sublimity area. A facilities planning study was undertaken at that time to evaluate future treatment alternatives. Considering the expected tougher future effluent discharge limitations, the City elected to construct a new mechanical sequencing batch reactor (SBR) plant. Additional land was purchased expanding the plant site to the west. The first phase of construction occurred in 1996 and consisted of the following process units: Abandoned Oxidation Ditch Stayton WWTP Evaluation 103003/3/03-707 1 - 2 February 2006 Phase I – SBR Plant Improvements (1996) • Operations building and lab • Headworks − Parshall flume flow measurement − Rotomat inclined screen − Vortex type grit separator − Automatic influent sampler • Influent pump station • Batch reactors (2) • Blower building and SBR process support facilities • Decant equalization basin • UV disinfection facilities • Reuse of the existing aerated sludge storage tank • Belt press and lime stabilization • Onsite paved biosolids storage basin (originally to be abandoned, but put into use because of a lack of a winter biosolids application site) A site plan showing existing facilities and existing plant process flow schematic are included on Figures 1-1 and 1-2, respectively. The current facilities are relatively new and the plant normally meets discharge permit requirements with a few exceptions as discussed in Chapter 3. A second phase of improvements was projected to occur approximately in the year 2006 as follows: Existing Treatment Plant Stayton WWTP Evaluation 103003/3/03-707 1 - 3 February 2006 Phase 2 – SBR Plant Improvements (previously anticipated by 2006) • Batch reactors (1) • Filters (2) 1.3 PURPOSE OF STUDY The purpose of this study is to provide an assessment of the existing SBR plant and to develop a master plan and capital improvement plan that address: • Compliance with existing and anticipated future NPDES permit limits • Plant process performance and potential improvements • Condition of existing facilities and equipment • Staffing and O & M protocol • Process monitoring procedures • Development of future facility needs and capital improvement plan This evaluation of the wastewater treatment plant is being performed simultaneous with the wastewater collection system master plan which is bound in a separate document. Some of the flow data developed in the wastewater collection system master plan has been used in this study. 1.4 ABBREVIATIONS The following abbreviations have been used in this report: • BOD 5-day biological oxygen demand • cfs cubic feet per second • DEQ Oregon Department of Environmental Quality • EPA United States Environmental Protection Agency • FPS Facilities Planning Study • fps feet per second • gal gallon • gcd or gpcd gallons per capita per day • gpd gallons per day • gpm gallons per minute • Hp horsepower • Hp-hr horsepower per hour • I/I Infiltration and Inflow • lbs pounds Stayton WWTP Evaluation 103003/3/03-707 1 - 4 February 2006 • lbs/day pounds per day • mg/L milligrams per liter • MG million gallons • MGD million gallons per day • MLSS mixed liquor suspended solids • ml milliliter • NH3N ammonia nitrogen • O&M operation and maintenance • SCS Soils Conservation Service • SS or TSS total suspended solids • TKN total kjeldahl nitrogen • TMDL total maximum daily load • TN total nitrogen • TP total phosphorus • WW wastewater • WWTP wastewater treatment plant • yr year Stayton WWTP Evaluation 103003/3/03-707 2 - 1 February 2006 CHAPTER 2.0 – FLOW AND LOAD PROJECTIONS 2.1 GENERAL This chapter provides an analysis of existing and future plant flow and water quality to determine load conditions (biochemical oxygen demand and suspended solids). It is necessary to look at existing influent flow and biochemical oxygen demand and suspended solids loads to provide a comparison to plant design criteria so as to determine remaining capacity available. Historical data is also useful in projecting future flow and load conditions. 2.2 EXISTING FLOW Discharge monitoring reports were reviewed for January 2000 through December 2004 to determine flow conditions for those years. Flow data is summarized along with the original Phase I (Year 2006) plant design criteria in Table 2.1. Please note that these flows reflect the contributions of both Stayton and Sublimity. Table 2.1 Existing and Design Conditions - Influent Flow Rates (MGD) Flow Condition 2000 2001 2002 2003 2004 Phase I Plant Design Criteria Annual Average Flow 1.34 1.34 1.60 1.94 1.55 1.72 Dry Weather (May – Oct) Average Daily Flow 1.08 1.00 1.16 1.17 1.41 1.37 Max. Month Flow 1.34 1.12 1.26 1.81 2.01 2.18 Max. Day Flow 1.57 1.29 2.12 2.50 2.72 3.10 Wet Weather (Nov - April) Average Daily Flow 1.89 1.37 2.18 2.75 2.26 1.96 Max. Month Flow 2.30 2.97 2.70 3.06 3.46 2.71 Max. Day Flow 2.96 3.98 4.98 5.46 5.37 3.91 Peak Flow unknown unknown unknown 5.74 unknown 6.87 Stayton WWTP Evaluation 103003/3/03-707 2 - 2 February 2006 From the above data, it can be seen that dry weather flows are approaching the original Year 2006 Phase I plant design capacity. The wet weather flows have already exceeded the design conditions. Looking at the difference between dry and wet weather flows, it is apparent the City has a high degree of inflow and infiltration (I/I) from its sewer collection system. The plant design hydraulic profile is shown on Figure 2-1 at previously anticipated peak flow instantaneous rates of 6.87 (Phase I 2006) and 9.27 MGD (Phase II 2016). More current population and flow projections are presented in Table 2.3 which shows that a peak flow of 6.87 MGD would correspond more closely to Year 2010. 2.3 EXISTING PLANT BOD AND SS LOADS Plant BOD and SS data from the year 2000 to 2004 Discharge Monitoring Reports were also reviewed and are summarized in Table 2.2 for Stayton and Sublimity. Year 2006 plant design criteria loading data is also shown. Table 2.2 Existing and Design Conditions - Influent BOD/SS Loads Load Conditions 2000 2001 2002 2003* 2004 Phase I Design Criteria Biochemical Oxygen Demand (BOD) Average Annual (mg/l) 183 145 139 135 110 157 Average Annual (lbs/day) 1862 1487 1661 1781 1422 2254 Max. Month (mg/l) 248 178 198 220 161 211 Max. Month (lbs/day) 2027 1889 1978 1965 1783 4760 Suspended Solids (SS) Average Annual (mg/l) 131 109 109 109 102 157 Average Annual (lbs/day) 1341 1121 1330 1462 1319 2254 Max. Month (mg/l) 190 133 164 184 161 211 Max. Month (lbs/day) 1630 1601 1689 1863 1693 4760 *Population 9460 From the above information, it can be seen that organic loading is significantly lower than the year 2006 Phase 1 plant design capacity. The mass loading is currently less than half of the Phase 1 maximum month design capacity. As a part of this study, the City also completed an Stayton WWTP Evaluation 103003/3/03-707 2 - 3 February 2006 inventory of all non-residential users to better characterize the type of wastewater entering the City’s conveyance and treatment systems. A summary of this survey can be found in Appendix E. 2.4 FUTURE PLANT FLOW RATES Existing plant per capita flow rate was evaluated and determined to have a significant amount of I/I. The City is implementing a program to remove excess I/I where economically feasible. In addition, future new construction should not have the same I/I problems. Taking the above into account, flows were projected based on an approximate 3.35% geometric growth rate for the wastewater collection system and are presented in the table below. The projected flow rates reflect the combined flow of Stayton and Sublimity. For a more comprehensive discussion of flow rates, documentation can be found in the “Wastewater Collection System Master Plan.” Table 2.3 Projected Future Plant Flow Rates 3.35% Growth Projection Flow Condition Estimate 2015 Flow (MGD) Estimate 2025 Flow (MGD) Estimate UGB Buildout Flow (MGD) Population 14,000 19,400 34,200 Annual Average Flow 2.8 3.9 6.9 Dry Weather (May – Oct) Average Daily Flow 1.9 2.7 4.9 Max. Month Flow 2.4 3.4 6.1 Max. Day Flow 3.2 4.6 8.3 Wet Weather (Nov - April) Average Daily Flow 3.6 5.0 8.9 Max. Month Flow 4.2 5.7 10.0 Max. Day Flow 6.7 8.4 13.3 Peak Flow 8.0 10.1 16.1 Stayton WWTP Evaluation 103003/3/03-707 2 - 4 February 2006 The following sections of this report are based upon the above flow rate projections. 2.5 FUTURE PLANT BOD/SS LOADS As more I/I is removed from the system, BOD and suspended solids concentrations will increase. Plant BOD and SS loads will also increase as a direct result of increased growth. Taking the above into account and using flows projected from master planning for the wastewater collection system, future projected BOD and SS loads were estimated as shown in Table 2.4 for Stayton/Sublimity. Table 2.4 Projected Future Plant BOD/SS Loads 3/35% Growth Projection Load Condition Estimate 2015 Loads Estimate 2025 Loads Estimate UGB Buildout Loads Population 14,000 19,400 34,200 Biochemical Oxygen Demand (BOD) Average Annual (mg/l) 160 160 160 Average Annual (lbs/day) 3,740 5,200 9,210 Max. Month (mg/l) 210 210 210 Max. Month (lbs/day) 4,200 5,960 10,680 Suspended Solids (SS) Average Annual (mg/l) 140 140 140 Average Annual (lbs/day) 3,270 4,550 8,060 Max. Month (mg/l) 220 220 220 Max. Month (lbs/day) 4,400 6,240 11,190 Based on projected organic loads, the existing two SBR basins will reach average annual organic loading design BOD capacity by approximately the year 2010 and maximum month BOD capacity by the year 2018. Based on peak design flow, the two SBR basins will reach design flow capacity by the year 2010. Stayton WWTP Evaluation 103003/3/03-707 3 - 1 February 2006 CHAPTER 3.0 – NPDES PERMIT LIMITS 3.1 GENERAL The National Pollutant Discharge Elimination System (NPDES) permit limits are important as the plant must be capable of meeting existing permit limits as well as anticipated future limits. The City’s permit expired in December 2003 and the new permit was issued in June 2004. Following is a review of previous permit conditions and how new permit limits may impact future plant operation and facility improvements. 3.2 PREVIOUS PERMIT CONDITIONS The City operated under the previous permit since startup of its SBR plant in 1996. The primary limits of the permit varied according to season as follows. (1) May 1 – October 31: Parameter Average Effluent Concentrations Monthly Weekly Monthly* Average lb/day Weekly* Average lb/day Daily* Maximum lbs BOD5 10 mg/l 15 mg/l 110 160 220 TSS 10 mg/l 15 mg/l 110 160 220 (2) November 1 – April 30: Parameter Average Effluent Concentrations Monthly Weekly Monthly* Average lb/day Weekly* Average lb/day Daily* Maximum lbs BOD5 30 mg/l 45 mg/l 340 510 680 TSS 30 mg/l 45 mg/l 340 510 680 *Mass load limits are based on a dry weather flow of 1.35 MGD. Note that this dry weather flow was the rated design flow for the old oxidation ditch plant which was not increased when the SBR plant went online. (3) Other Parameters (Year-Round): E. coli Bacteria Shall not exceed 126 organisms per 100 ml monthly geometric mean. No single sample shall exceed 406 organisms per 100 ml. pH Shall be within the range of 6.0 – 9.0 BOD5 and TSS Removal Efficiency Shall not be less than 85% monthly average Stayton WWTP Evaluation 103003/3/03-707 3 - 2 February 2006 The permit’s dry season BOD and SS permit limits were relatively stringent. However, the City has done an exceptional job in meeting previous permit conditions over the last 4 years with only a few exceptions as follows: • Exceedance of effluent BOD/SS limits as a result of one batch reactor being taken out of service for repairs. • Effluent pH violations as a result of incorrect pH meter readings. • E coli violation as a result of one batch reactor being taken out of service for repairs. • Mass load limit violation in May 2003. 3.3 NEW PERMIT REQUIREMENTS The State of Oregon Department of Environmental Quality (DEQ) has several areas of concern regarding future discharges to the North Santiam River and Willamette River drainage basin. These areas of concern include: • Heat load discharge which can raise the temperature of the North Santiam River and adversely affect aquatic life. • Potential ammonia levels discharged, which may be toxic to aquatic life. • BOD and SS loads to the North Santiam River. DEQ currently has a policy of limiting future new discharges to the river, and limiting any future increase in mass loads from existing discharges to the river. • Total mass daily load (TMDL) investigations by DEQ may lead to future discharge limits on metals, in particular mercury, and nutrients (nitrogen and phosphorus). Metals and nutrient limits will not impact the new permit, but could impact the City’s next permit in 2009. Considering the above, it is unlikely that limitations in future permits will be relaxed and it can be stated that a higher degree of treatment will be necessary to maintain and even improve effluent quality as future growth occurs. DEQ has conducted an evaluation of the City of Stayton’s discharge over the last few years, and how it might impact the North Santiam River with Stayton WWTP Evaluation 103003/3/03-707 3 - 3 February 2006 regard to heat load, ammonia, and BOD/SS mass loads. The results indicate a potential risk to the river in those areas and are reflected in the new permit limits as indicated below: (1) May 1 - October 31: Parameter Average Effluent Concentrations Monthly Weekly Monthly* Average lb/day Weekly* Average lb/day Daily* Maximum lbs CBOD5 10 mg/L 15 mg/L 110 160 220 TSS 10 mg/L 15 mg/L 110 160 220 (2) November 1 - April 30: Parameter Average Effluent Concentrations Monthly Weekly Monthly* Average lb/day Weekly* Average lb/day Daily* Maximum lbs BOD5 30 mg/L 45 mg/L 340 510 680 TSS 30 mg/L 45 mg/L 340 510 680 *The mass load limits are based upon average dry weather design flow of 1.35 MGD, and are uncharged from the previous permit. (3) Other Parameters (year-round except as noted) Parameter Limitations E. coli Bacteria Shall not exceed 126 organisms per 100 mL monthly geometric mean. No single sample shall exceed 406 organisms per 100 mL. pH Shall be within the range of 6.0 - 9.0 CBOD5 Removal Efficiency (May 1 through October 31) Shall not be less than 85% monthly average. BOD5 Removal Efficiency (November 1 through April 30) Shall not be less than 85% monthly average. TSS Removal Efficiency Shall not be less than 85% monthly average. Excess Thermal Load (September 1 through June 15) Shall not exceed a weekly average of 30 million Kcals/day. Ammonia-N (May 1 through October 31) Shall not exceed a monthly average concentration of 12 mg/L and a daily maximum concentration of 27 mg/L. The complete new permit is attached in Appendix B and became effective on June 1, 2004 and expires on May 31, 2009. Stayton WWTP Evaluation 103003/3/03-707 3 - 4 February 2006 3.4 NEW PERMIT IMPACTS The above limits required by the new permit will have an impact on current operation of the plant and will eventually require facility improvements to meet some limits. These impacts are discussed below. 3.4.1 Heat Load Limit DEQ provided an evaluation of Stayton’s historical effluent temperature and flow and arrived at the conclusion that the City would exceed the heat load limit of 30.2 million kcals to the North Santiam River during the salmon rearing and migration period of September 1 through June 15. That conclusion was based on a theoretical model calculated dilution of 14:1 in the existing mixing zone. The City and DEQ question the dilution accuracy and DEQ has requested that the City conduct an evaluation to determine the actual mixing zone dilution. If the actual dilution is determined to be substantially higher DEQ will consider deletion of the heat load limit from the permit. Therefore, it is important that the City conduct the evaluation to determine actual mixing zone dilution. Should the mixing zone dilution be inadequate, a strategy is needed for the City to insure compliance with the heat load limit. Mixing conditions are complicated by the fact that the City discharges to a sidestream branch of the North Santiam River. The river splits about one half mile upstream with the smaller amount of river flow passing over the Stayton outfall discharge. There appear to be several strategies and alternatives for meeting the heat load limit: 1) Measure the effluent temperature at a manhole as close to the river as possible to account for some cooling of effluent that occurs downstream of the UV disinfection process. 2) Extend the outfall about 700 feet across the dividing island to the main branch of the North Santiam where dilution would be much greater (See Figure 3-1). Hydraulic analysis is needed to better define feasibility. An amended or new NPDES permit would likely be required for the new point of discharge. It may also be advantageous to discharge to both channels. 3) The US Army Corps of Engineers could be consulted about dredging of the entrance to the river branch flowing past the Stayton plant to allow greater flow diversion in that section, Stayton WWTP Evaluation 103003/3/03-707 3 - 5 February 2006 thereby increasing dilution. The disadvantage is that dredging would probably need to be repeated annually to maintain the higher branch flow rate, especially since previous sandbar formation has partially closed the channel. It is highly unlikely that the USACOE would allow annual dredging of this channel. 4) The Santiam Water Control District operates a canal which discharges several hundred yards upstream of the WWTP outfall. The District has discussed increasing flows through its hydroelectric plant to the canal in the future, thus providing increased dilution water. The District is currently negotiating the flow increase under licensing renewal with the FERC. If flow increases are substantial (>250 cfs) it could improve dilution such that the City would not have potential to violate their permit. 5) There has been discussion of the City purchasing land adjacent to the treatment plant. However, it appears Norpac controls most adjacent land which they are currently irrigating. During high effluent temperature periods, it may be possible to irrigate adjacent lands, or provide storage to hold all or part of the effluent until higher effluent temperature periods pass and then slowly return stored wastewater to the river. 6) It may be possible to create a labyrinth of underground piping and use the ground as a heat sink and reduce effluent discharge temperature. This would have to be pilot tested to determine feasibility. 7) It has been indicated that wetlands can reduce effluent temperatures as well as provide additional treatment. The City could consider this option as well. 8) Other alternatives would include trading credits such as planting trees to shade and cool the river, or purchasing credits through a trading program that cools the river. Other possibilities include buying upstream water rights to limit withdrawals so as to maintain greater river flow and dilution. The above alternatives are discussed further in Chapter 6. Evaluation of actual existing mixing zone dilution achieved will dictate whether further measures are necessary to meet heat load limits. The mixing zone study is scheduled for completion by August 2006. Stayton WWTP Evaluation 103003/3/03-707 3 - 6 February 2006 3.4.2 BOD/SS Mass Load Limits Dry weather mass load limits of 110 lbs/day were exceeded in May 2003 and were in the 90 to 100 lbs/day range for several other months despite reasonable effluent BOD and SS concentrations in the 10 mg/L range. Well designed and operated SBR plants can achieve effluent quality less than 10 mg/l, however, that concentration is the reliable threshold which can be guaranteed to be met and satisfy permit limits. As population growth continues, effluent mass loads discharged will also increase. To meet the limit, additional treatment will be necessary. Filtration would provide the greatest immediate benefit, as approximately 80 to 90 percent reduction of BOD and suspended solids is possible in the filters, and filters would also provide an additional barrier if upset conditions occur in the batch reactors. 3.4.3 Ammonia Limit The May 1 through October 31 ammonia limit of 12 mg/L monthly average and 27 mg/L daily maximum has been consistently met by the plant over the last several years. There has been discussion by DEQ of possibly raising the ammonia limit even higher. The plant has significant organic capacity remaining and should not have any difficulty meeting the current mandated limit over the next 5 years, particularly since it is a warm weather limit. Beyond 5 years additional basin capacity and aeration would need to be added. Nitrification and reduction of ammonia is much easier to achieve during warm weather months. The City will need to monitor plant alkalinity since ammonia removal decreases significantly below a pH of 6.5. Should influent pH drop below that level, chemical addition may be necessary to raise alkalinity and pH. 3.4.4 Future TMDL Related Limits At this time it is difficult to know if DEQ’s future total mass daily load (TMDL) studies on the Willamette Drainage Basin, including the North Santiam River, will have any impact on the City of Stayton. It is critical the City continue to monitor the river and plant effluent in accordance with permit requirements to gather sufficient data to allow DEQ to make rational decisions should future TMDL limits be proposed. The SBR process can be readily modified to remove phosphorus and nitrogen should nutrient limits be imposed; however, additional reactor tank volume may be necessary. Mercury can either be controlled at the source (dental offices, etc.), by isolating mercury laden products from discharge to the sewer, or removed at the WWTP by use of absorbents and chemical precipitation. Stayton WWTP Evaluation 103003/3/03-707 4 - 1 February 2006 CHAPTER 4.0 – PROCESS EVALUATION 4.1 GENERAL Plant process evaluation is necessary to determine the plant’s present and future capability of meeting its NPDES permit requirements as well as addressing operation and maintenance issues. Recommendations can then be made for improvements to comply with permit requirements, ensure adequate capacity is available, and assist in ease of future operation and maintenance of the plant. Facility improvement alternatives and recommendations are presented in further detail in Chapters 5 and 6. 4.2 PLANT LIQUID PROCESS UNIT EVALUATION A plant process flow schematic is shown on Figure 1-2. An evaluation was made for capacity of each process flow unit and discussions were held with plant staff to determine process performance, facilities conditions, and any deficiencies which might exist. An evaluation for each process unit is presented in the following paragraphs. 4.2.1 Headworks The headworks facilities are located near the plant entrance and consist of a parshall flume influent flow meter, automatic sampling equipment, manual and Rotomat fine screen (indoors), influent pump station and vortex type grit separator. Flow measurement and automatic influent sampling take place just upstream of the screening facility. The screening facility consists of two parallel concrete channels, one channel with an inclined Rotomat screen, and the other with a backup manually cleaned bar screen. The Rotomat screen has a nominal capacity of 5 MGD but will handle 6.8 MGD per the manufacturer. It operates automatically based on either upstream channel depth or by timer. The collected screenings are washed of fecal and organic materials by spray system, compressed to remove excess water, and discharged to an adjacent dumpster. Stayton WWTP Evaluation 103003/3/03-707 4 - 2 February 2006 Influent Screen and Grit Washer The influent pump station consists of a below grade 30 foot diameter by 18 foot deep concrete wetwell with four submersible pumps, two pumps each with a capacity of 1390 gpm and two pumps each with a capacity of 3680 gpm. With one of the larger pumps out of service, the total capacity is 9.3 MGD, which is capable of meeting the original plant year 2016 design flow. One additional pump will be required to meet the year 2025 peak flow rate of 10.1 MGD. The pumps automatically cycle on and off based on wetwell level. Influent Pump Station The influent pump station discharges to an elevated vortex type grit basin with a peak flow capacity of 9.3MGD. At the projected year 2025 peak flow rate of 10.1 MGD there may be some minor carryover of grit; however addition of more capacity is not warranted until the year 2025. Settled grit is removed by recessed impeller grit pump to a cyclone separator and grit washer and classifier. Clean grit is then discharged to a dumpster. The headworks facilities generally operate with few problems. Concerns or deficiencies noted include the following: Stayton WWTP Evaluation 103003/3/03-707 4 - 3 February 2006 • The Rotomat inclined screen has ¼ inch openings which allow some smaller plastics and material to get through. According to plant staff the screen is also difficult to maintain and repair. • At times, excessive amounts of grease in the influent stream is reported by plant staff. Excessive grease can clog pipelines and cause operating problems with plant equipment. • Original influent pump level floats would hang up and come off. An electronic level sensing device is currently used to monitor level; however, a backup level sensing system is needed in event of failure to prevent pump station overflow conditions. 4.2.2 Batch Reactors The plant has two 1.3 MG concrete batch reactors each with jet aeration headers (2), floating decanters (2), scum skimmers, and reactor mixing pumps. Two positive displacement blowers provide air for process needs, and a field programmable process control panel with PLC provides sequencing and control of process functions. The PLC operating process parameters can be adjusted by a computer located in the operations building. Each reactor typically goes through a staggered 6 hour batching process except when high peak flows occur when the cycle time is reduced to 4 hours. Typical plant process sequencing is as follows: • Anoxic fill (80 minutes) • Mixed fill (60 minutes) Batch Reactor Stayton WWTP Evaluation 103003/3/03-707 4 - 4 February 2006 • Aerated mixed fill (40 minutes) • Aerated react (15 minutes) • Settle (130 minutes) • Decant (20 minutes) • Sludge waste (3 minutes) • Idle (12 minutes) Solids are typically wasted at a rate as needed to maintain a desired mixed liquor suspended solids (MLSS) concentration and solids residence time in the basins. The plant has been operated over a MLSS range of 2000-3000 mg/l for the past few years in an attempt to increase sludge age and minimize solids production downstream since onsite solids storage is limited. Water depth in the reactors varies from 16 to 22 feet based on influent flow rate. The SBR process is supported by two 200 Hp positive displacement blowers each with a capacity of 3400 scfm. Dissolved oxygen (DO) sensors in each basin are used to control and maintain a DO concentration of 2-3 mg/l during the aerated react phase. Blowers are constant speed and are turned on and off during the aerated mixed fill and aerated react phases to provide the required DO concentration. Process Blowers Plant design solids residence time (SRT) is not shown on the plant design criteria drawings; however, the plant appears to be designed for a calculated Phase I minimum solids residence time of 12.5 days based on a MLSS concentration of 2,500 mg/l and sludge mass loading data shown on the plant solids balance diagram in Stayton WWTP Evaluation 103003/3/03-707 4 - 5 February 2006 the WWTP plans. The calculated current maximum month SRT is approximately 24 days. Therefore, the reactors have considerable additional organic capacity available. It should be noted that current wet weather average, peak month, and peak day hydraulic loading rates exceed previously established Phase I Year 2006 design criteria. Peak day flows result in decreased detention time, which reduce aeration, settling, and decant cycle times. This can have a negative impact on treatment. Fortunately, these peak events normally occur during wet weather months when effluent BOD/SS limits are less stringent. Should permit violations occur, 1) peak flows will need to be reduced through a program of collection system I/I reduction, 2) flow equalization will need to be added, 3) increased reactor capacity will need to be added, or 4) filters added. There are some issues with the batch reactors that make operation and maintenance more difficult and less efficient than it could be. • It is difficult to take one of the reactors out of service as that transfers all load to a single reactor which, in most instances, results in overload. That was the case in July 2002 which resulted in exceedence and violation of permit requirements. It would be advantageous to add a third basin which would assist in meeting wet weather peak flows and allow one basin to be taken offline when maintenance and repairs are needed. An equalization basin could be added to reduce peak flows, however, would not provide treatment capability. • The SBR process is highly automated with programmable logic controller (PLC), automatic operated valves, and individual pumping systems. The process is extremely difficult to operate manually. Loss of any of the above components usually results in single basin operation, overload, and effluent violation. It would be desirable to have a spare pneumatic valve actuator of each size, a spare pump of each size, and spare PLC with important cards. This would provide redundancy, and minimize single basin operation situations. • The high capacity mixing pumps (11,000 gpm) are also used for sludge wasting by extreme throttling to lower flow rate. There are several disadvantages to wasting in that manner, including excessive backpressure on the mixing pumps leading to seal failures, very high sludge draw-off rates for Stayton WWTP Evaluation 103003/3/03-707 4 - 6 February 2006 brief periods (1-3 minutes) which can result in “coning” (drawing in excessive water with sludge), and poor regulation of sludge flow. Instead it is recommended that separate sludge wasting pumps with variable frequency drives be installed to allow separate sludge withdrawal at lower and adjustable flow rate (200-500 gpm for 10-30 minutes). • One mixing pump recently has suffered impeller damage with erosion and holes reducing flow by half. It appears severe cavitation or other problem has occurred. Pumping conditions should be reviewed to determine if head and flow conditions are abnormal. • Recent cold weather in the low 20° F range resulted in plant overflow due to water freezing inside outdoor exposed pneumatic air piping controlling the SBR valves. A sequencing batch reactor plant may experience dormant periods in pipelines up to 6 hours, which also allows adequate time to freeze conveyance pipelines and valves. Although freezing conditions are rare, they can occur and preventative measures are needed to protect exposed valves and pipelines from freezing. Reactor Mixing Pump Outdoor Process Piping Stayton WWTP Evaluation 103003/3/03-707 4 - 7 February 2006 • Excessive foaming which is difficult to remove has occurred in the reactor basin. This can be a symptom of filamentous organisms, in particular Nocardia, which can lead to foaming and poor settling sludge. The mixed liquor has been checked by microscope for filamentous organisms and found to be present. • Backflushing of the jet aeration system is difficult as it requires manual operation of up to four valves with up to 300 turns to open each valve. The process is time consuming, and therefore is not performed as frequently as desired. 4.2.3 Equalization Basin The 215,000 gallon concrete equalization (EQ) basin provides storage for the SBR short duration high decant flow rates (16.2 MGD = 11,200 gpm). That allows a lower flow rate (6.9 MGD = 4,760 gpm) to be pumped to the UV disinfection process. The basin has adequate capacity; however, there are several issues with the basin that require resolution as follows: • The bottom of the basin accumulates settled solids since the floor is relatively flat. This requires periodic maintenance to remove the solids between decant cycles. • The basin walls accumulate algae which can slough off and impact UV disinfection performance. • Access to the basin for cleaning is poor. Equalization Basin Stayton WWTP Evaluation 103003/3/03-707 4 - 8 February 2006 4.2.4 UV Disinfection System The existing UV disinfection system consists of two parallel channels each with two horizontal banks of low pressure, low intensity lamps (288 total). The system is manufactured by Trojan Technologies (Model UV3000), and is designed for a peak flow of 6.87 MGD. The existing system lacks redundancy (separate third channel and lamp banks); however, redundancy is not essential since loss of several lamps involves a relatively simple replacement resulting in minimal downtime. The system normally meets E coli NPDES permit limits except in cases of abnormally high suspended solids conveyed from the batch reactors and EQ basin as a result of poor settling, biological process overload/upset, excessive high flow rates, or algae sloughing and cleaning of the EQ basin. The effluent channel level control gate controls the high water level over the lamps and is not designed to be water tight, and can lose water and expose the top lamps between discharge cycles. The lamps also must be manually cleaned once a month which is time consuming. Current plant peak flow rate is 6. 5 MGD, so expansion of the system will be necessary in the next 5 years, based on projected future flow rates (or perhaps longer if I/I is reduced). When expansion is required, consideration should be given to upgrading to the new low pressure high intensity disinfection systems currently on the market. These latest technology lamps have several advantages including: • Significantly fewer lamps required to treat the same flow rate. UV Disinfection Process Stayton WWTP Evaluation 103003/3/03-707 4 - 9 February 2006 • High intensity lamps are able to penetrate flow with higher suspended solids and thus achieve pathogen inactivation even during poor upstream process performance. • The lamps are now made with self-cleaning systems which eliminate the necessity of manually cleaning as currently practiced. • Replacement can be phased in as each new bank will provide improved inactivation of pathogens. 4.3 PLANT SOLIDS HANDLING PROCESS EVALUATION Solids wasted from the batch reactors are pumped to a concrete solids storage tank (aerated and mixed) with a volume of 225,000 gallons, or to a sludge storage pond with an additional volume of 180,000 gallons. Every day, sludge is pumped by a transfer pump at a rate of approximately 100 gpm through a sludge grinder, dosed with a polymer, and dewatered by a 1.7 meter belt filter press. Sludge cake from the press is then lime stabilized to Class B standards, and is land applied offsite in dry weather periods. When land application is not possible during wet weather months due to wet field conditions, the sludge cake is stored onsite. Existing and estimated future sludge production quantities are shown on Table 4-1 below. Table 4.1 Estimated Sludge Production - (tons/day) Description 2005 2015 2025 Buildout Average month with lime 0.80 1.10 1.50 2.60 Average month without lime 0.60 0.80 1.10 1.95 Maximum month with lime 1.20 1.60 2.20 3.90 Maximum month without lime 0.90 1.20 1.70 2.90 An evaluation of solids processing units is discussed in the following paragraphs. 4.3.1 Liquid Solids Storage The reactor mixing pumps are used to pump waste solids from the batch reactors at approximately 0.4 to 1.0% total solids content to Stayton WWTP Evaluation 103003/3/03-707 4 - 10 February 2006 the aerated storage tank or sludge storage pond. Current peak month pumping results in an average of approximately 40,000 gpd solids wasted. The storage tank volume is 225,000 gallons. As noted, the plant has an additional liquid solids storage pond with a capacity of 180,000 gallons if needed. Therefore, the plant has a current peak month holding capacity of 10 days. Year 2025 (population 19,400) sludge would be 80,000 gpd and holding capacity of 5 days. Additional liquid sludge storage should be provided for a minimum duration of two weeks should downstream dewatering equipment require repair. The existing aerated storage tank typically holds very thin solids with no means of decanting excess water. It is recommended the aerated sludge storage tank be equipped with a decanting mechanism so as to allow thicker solids on the order of 3-4% to be pumped to the belt press and/or separate thickener facilities be provided to accomplish the same result. This would significantly increase belt press production capability and provide a dryer sludge cake on the order of 20-25% from the belt press. Aerated Sludge Storage Tank Liquid Sludge Storage Pond Stayton WWTP Evaluation 103003/3/03-707 4 - 11 February 2006 4.3.2 Sewer Cleaning Disposal Area The plant operates a small sand filter containment area for separation of deleterious materials discharged by the City sewer cleaning truck. Material is discharged to the sand surface and a standpipe well used to remove filtered water. The sand area is cleaned by hand. The water is currently removed manually by installation of a temporary pump and hose discharge to the plant drain system. The water removal process should be automated to simplify operation, and a manual screen added to collect and remove larger debris. 4.3.3 Dewatering Facilities Sludge is dewatered from 0.4 to 1% to approximately 15 to 20% solids by belt filter press. Prior to dewatering the Waste Activated Sludge (WAS) is conditioned with a liquid polymer and pumped by a variable speed progressive cavity pump or constant speed centrifugal pump to the press. The standby centrifugal pump is quite old (1962), lacks adequate capacity, and should be replaced. Dewatered filtrate is drained and conveyed back to the influent pump station. Solids capture typically exceeds 90%. The belt press performance is within the range typically obtained by other plants. Belt Filter Press The belt press has a specified dewatering capacity of 130 gallons per minute, however only operates at approximately 100 – 110 gpm due to transfer pumping equipment limitations. The current average month daily sludge flow is approximately 40,000 gpd and can be dewatered in approximately 6 hours. Therefore, sludge dewatering currently requires approximately 40 hours per week. Dewatering operation is currently excessive and will become worse as future sludge production increases. Solids thickening needs to be provided to feed a sludge concentration of 3-4% to the belt filter Stayton WWTP Evaluation 103003/3/03-707 4 - 12 February 2006 press. This will significantly reduce BFP run time from 40 hours to 8 hours per week and also meet future dewatering needs. Adequate dewatering capacity appears to exist for current sludge production, but will be inadequate for future production without some changes as discussed in Chapter 6. The primary shortcomings of the dewatering system are transfer pumping capacity limitations and that the plant has only one belt press. If the press were to go down and require repairs over an extended period, there would be no way to dewater the sludge. In that case, liquid sludge would need to be stored (2 week future capacity) onsite until the press was repaired. 4.3.4 Lime Stabilization System The plant achieves a Class B solids per EPA 503 regulations for land disposal by lime stabilization. Lime is stored in a 1255 cubic foot silo with bin activator (the silo provides 3-4 weeks storage at current maximum feed rates). Lime is fed by volumetric feeder to a screw conveyor that has a capacity of 10 lbs/minute. The lime feed system is automatically controlled. Lime is uniformly fed by screw feeder and mixed with dewatered sludge cake at the belt press conveyor. The lime treated sludge is discharged to a covered concrete containment stabilization area just outside the building for the required Class B stabilization period. Sufficient lime is added to achieve a pH over 12 for a minimum of 2 hours and a pH of at least 11.5 over an additional 22 hour period. The lime stabilization system is adequately sized and achieves the desired Class B stabilization requirements. As with the belt press, only single components of the system are available and if repairs are needed, the system could be down for an extended period. Lime Storage Silo Stayton WWTP Evaluation 103003/3/03-707 4 - 13 February 2006 The lime stabilized sludge in the biosolids stabilization area was observed during a site visit draining to adjacent grounds from the containment area. A more reliable means of total containment is needed. 4.3.5 Onsite Biosolids Storage Upon achieving sludge stabilization, the biosolids are loaded and conveyed by truck to a land application site. In wet weather conditions biosolids are stored in an asphalt lined sump (with drain) south of the dewatering building and stabilization area. Filtrate from the drain is returned to the influent pump station. At current sludge production levels, the sump is filled to capacity at the end of the wet weather season. To address onsite storage limitations either, 1) additional onsite lined storage must be provided, 2) storage provided at the disposal site, 3) or sludge volume reduced through additional onsite drying. The dewatered sludge also accumulates a great deal of water from precipitation in the wet season making it very difficult to load and haul at the start of the dry season. A permanent cover is needed to keep the sludge dry. Biosolids Stabilization Area Onsite Biosolids Storage Stayton WWTP Evaluation 103003/3/03-707 4 - 14 February 2006 4.3.6 Biosolids Disposal The City currently disposes of biosolids at a DEQ approved offsite land application site known as the Studnick site located approximately 12 miles from the plant. It consists of approximately 200 usable land application acres of grass pasture out of 580 acres total. In addition, the City is currently pursuing agreements and DEQ approval for disposal on two alternative sites, referred to as the Tracy and Lamb sites. Test results of the City’s sludge show levels of metals significantly lower than DEQ’s allowable spreading requirements. Maximum land application rates are typically dictated by total nitrogen applied. The Oregon DEQ permit allows application of 100 pounds of available nitrogen per acre per year at the Studnick site. The plant currently produces an average of approximately 290 tons of biosolids per year which contains about 25-30% lime (70 tons). Therefore, approximately 220 tons of biosolids per year at a typical total nitrogen content of 3% represents 6.6 tons of nitrogen per year. That amount requires approximately 130 acres of land for spreading per year. It should be noted that total nitrogen content of the City’s biosolids has ranged up to 6 – 7% TN which would require 260 acres for land spreading. The biggest concern with the Studnick site is that no long-term agreement exists with the owner, and the City would have to look elsewhere if the owner no longer wanted the biosolids. The relatively long haul distance of 12 miles also results in increased biosolids disposal cost. The City also has a single hauling truck which makes disposal time consuming. Other concerns include numerous state restrictions placed on land disposal of Class B biosolids and the tendency for tighter future restrictions which may ultimately require biosolids to be treated to Class A standards. Treatment to Class A standards and benefits are discussed further in Chapter 6. 4.4 MISCELLANEOUS FACILITIES The plant is supported by a potable water/utility water system, electrical and emergency power, and general site space requirements. Following are comments regarding miscellaneous existing plant facilities and needs. Stayton WWTP Evaluation 103003/3/03-707 4 - 15 February 2006 4.4.1 Plant Facility Conditions The plant is still relatively new as it was constructed in 1996. It has been maintained very well and all structures, piping, and facilities still appear to be in good condition. 4.4.2 Utility Water System The plant utility water system comes off the City’s potable water distribution system through a backflow preventer. Potable water utilization at times has been in excess of 100 gpm which is on the high side. Holding water in the UV channel at a constant level accounts for over half of this amount. It would be worth investigating a solution to the UV channel problem and the use of plant effluent instead of potable water for plant utility water. It would be worth investigating a solution to the UV channel problem and the use of plant effluent instead of potable water for plant utility water 4.4.3 Plant Electrical System The plant receives utility power from PPL and is distributed from a 2000 amp 480 V switchboard in the Blower Building Electrical Room. The switchboard distributes electrical power through 8 MCC distribution panels throughout the plant. Emergency backup power is provided by a 1250 KW diesel engine generator which powers all of the key plant components as needed to meet plant discharge permit requirements until normal utility power can be restored. The electrical and emergency power systems appear adequate to meet plant needs until the year 2025. 4.4.4 Plant Facility Siting The plant encompasses approximately 8 acres. The existing plant has adequate space for incorporating two additional SBR basins and filters. Adequate room appears to exist to meet facility needs for the next 25 years. A feature that would greatly assist in meeting plant O&M requirements would be a new maintenance building and garage as the City currently has no place to perform equipment maintenance work indoors, or provide covered storage for plant spare parts or equipment. Stayton WWTP Evaluation 103003/3/03-707 5 - 1 February 2006 CHAPTER 5.0 – OPERATIONAL ANALYSIS 5.1 GENERAL This chapter provides an evaluation of the existing WWTP in regard to staffing levels, plant operations, monitoring, and controls, O&M procedures, testing procedures, industrial pretreatment, and O & M costs. 5.2 STAFFING LEVELS The plant is currently manned on a daily basis by a full staff from 6:00 a.m. to 4:00 p.m. Monday through Friday and 7:00 a.m. to 4:00 p.m. on weekends by a combination water/wastewater operator. The sewer utility staff includes the following: • Wastewater collection system supervisor (Level 4) • WWTP supervisor in training (Level 1) • Wastewater operators (2 @ Level 3, 0.5 @ Level 2) Therefore, the sewer department has 4 ½ people which are allocated to both the sewer collection system and the wastewater treatment plant. The plant operators also serve as lab technicians. One operator is allocated strictly to sludge hauling during the summer months. A number of tasks are contracted out as follows: • Sewer system cleaning/TV inspection • Mechanical maintenance • Electrical maintenance and repairs • Collection system repairs • Instrumentation/controls repairs Landscaping maintenance is performed by both the City Parks Department and plant staff when available. 5.2.1 Recommended Staffing Level EPA publishes a manual entitled “Estimating Staffing for Municipal Wastewater Treatment Facilities” dated March 1973. Staff operation and maintenance hours can be projected based on the size of plant, type of plant, unit processes, employed, type of waste treated and adjustments for local conditions. Local adjustments are made for plant layout, climate, training, type of waste stream treated, etc. The staffing estimates are based on a survey of staffing levels for 35 small to large wastewater treatment facilities across the country. Stayton WWTP Evaluation 103003/3/03-707 5 - 2 February 2006 Using the manual a staffing estimate worksheet was filled out as applicable to the City of Stayton plant. This worksheet is included in Appendix C. Following is a summary of personnel recommended for the wastewater utility: • Collection system and pump stations (1.0 person) • TV inspection and collection system cleaning (if undertaken) (0.5 person) • Pretreatment and GIS programs (if undertaken) (1.0 person) • Treatment plant per EPA guidelines (6.5 people) TOTAL 9.0 People The City currently budgets 4.5 personnel to the wastewater utility. Note that the equivalent of 1.5 personnel are recommended above for new programs. Therefore, it appears the wastewater utility is currently understaffed by 3.0 people not including the new programs. That condition is reflected in the level of services either being contracted out or personnel being borrowed from other City operating groups to do wastewater related work tasks. Of the nine total staff recommended for the wastewater utility group, the following management organization is recommended. Wastewater Utility Group Supervisor: This person would be responsible for the entire wastewater utility group and supervise the following personnel: • Wastewater Treatment Plant Chief Operator would be at least a Level III operator and be responsible for efficient and effective operation of the wastewater treatment plant. • Wastewater Collection System Supervisor would be at least a Level III operator in collection and pumping station operations and be responsible for those facilities. • Treatment plant and collection system operations staff. Please note that due to the small size of the current utility group, supervisory personnel could serve multi-supervisor functions and would also assume part-time operations and maintenance duties as needed. As the system grows to twenty or more staff, fulltime supervisory personnel should be provided as discussed above. Stayton WWTP Evaluation 103003/3/03-707 5 - 3 February 2006 5.3 OPERATIONS, MONITORING, AND CONTROLS As previously indicated the sequencing batch reactor plant is highly automated due to the batching process which provides step by step treatment from “fill to idle”. The basic process is monitored and controlled by PLC’s and computer system. There is a great deal of flexibility built into the control system in that any of the discrete process timed sequences can be easily varied by computer to optimize the type of treatment desired and the effluent quality. Operating parameters of the plant are currently set to provide a long solids residence time and to minimize sludge production. Another control goal is to minimize effluent BOD and SS concentrations so as to remain within NPDES permit mass load limits. At times the City has experienced sludge settling problems. An extended settling period up to 2 hours has been necessary to settle solids. This problem appears to be a result of a long solids residence time and growth of filamentous organisms as verified by recent microscopic analysis. Filamentous organisms, particularly Nocardia, in the mixed liquor, cause bulking and difficult to settle sludge. Growth of filamentous organisms in SBR’s is not uncommon. The filamentous organisms can be temporarily eliminated by chemical treatment. Spraying of foam with chlorine solution is also necessary to temporarily eradicate the organisms. Even with chemical treatment, the organisms will usually reappear. Long-term measures to minimize growth of filamentous organisms is discussed further in chapter 6. The City appears to be meeting anticipated future ammonia limits; however, the plant control scheme may need to be modified in the future should ammonia levels increase. A longer solids residence time and aeration period will allow nitrification and ammonia removal to occur. Computer Monitoring and Control System Stayton WWTP Evaluation 103003/3/03-707 5 - 4 February 2006 US Filter/Jet Tech, the manufacturer of Stayton’s system, is available to assist in troubleshooting SBR process issues and problems. Because they have a large number of these plants in operation they can be a valuable resource in solving unique operating problems. Some installations can be direct telephone connected into the computer control system and allow process evaluation. Alternatively, data can be provided to Jet Tech for analysis. Other plant process unit monitoring and controls appear to be adequate. The City is able to remote monitor key plant alarm functions by telephone dialer which is important since the plant is unmanned overnight. The City is currently doing a comprehensive review of all plant alarms to be sure all needed alarms are in place and to insure the most important alarms are placed on the after-hours dialer. 5.4 OPERATION AND MAINTENANCE PROCEDURES The City currently uses a manual system for scheduling and logging equipment maintenance. In addition, a significant amount of specialized electrical and mechanical maintenance is contracted out. Based on present staff levels as indicated above, general maintenance duties such as painting, cleaning, and landscaping are performed as time allows. Currently most plant maintenance is performed as corrective maintenance, rather than preventative maintenance Most mechanical treatment plants are converting to computerized O&M which greatly facilitates scheduling and record keeping of O&M requirements. It allows for logging of equipment information, spare parts inventory, prompting for scheduled maintenance, printout of maintenance instructions, record keeping, budgeting, summary reports, etc. There are numerous O&M software packages on the market ranging in cost from less than $1,000 to greater than $25,000 depending on amount of information and the level of detail desired. It is recommended that the City convert to computerized O&M. Keller Associates can assist the City in searching for a software package to meet its needs. Upon purchase of the O&M software, the City should set up a comprehensive maintenance management program which would incorporate all of the functions indicated above. By installation of a computer O&M system, it is anticipated more attention will be paid to a regular scheduled preventative maintenance program and less repair time will be necessary. Stayton WWTP Evaluation 103003/3/03-707 5 - 5 February 2006 5.5 TESTING The City’s laboratory does all required testing for its NPDES permit except for biosolids analysis and only a few tests that require specialized needs and equipment. The level of testing performed appears adequate and acceptable. Future testing mandated by the plant’s new permit will require significant additional specialized testing to be contracted out. Once or twice a year dual samples should be sent to another lab as a confirmation of the City’s lab results. It is recommended that a full-time lab technician be hired to oversee all future testing needs. 5.6 INDUSTRIAL PRETREATMENT & GIS PROGRAMS The City currently does not have an industrial pretreatment ordinance and therefore has no legal means of controlling what substances are discharged to the treatment plant. This can result in toxic chemical upsets of the biological process, process overloading, excessive grease, and other discharges detrimental to plant operation. Most municipalities have extensive industrial pretreatment ordinances in place to track and control undesirable chemicals or high strength wastes from impacting plant operations. The ordinance provides for pretreatment of industrial waste at the source and for charging commercial and industrial dischargers additional costs as required to treat their wastes. It is recommended that a comprehensive industrial pretreatment ordinance be written and adopted by the City. It is recommended that a pretreatment person be hired to organize and track the above activities. This would be approximately a ½ to 2/3 time effort with remaining time assisting in plant or sewer system operation and maintenance. The City is also in the process of implementing a GIS utility tracking system for all City utilities. The GIS system will greatly assist the City in documenting the location, condition, inventory, etc. of existing facilities and in planning for system expansions. A full-time person would be required with about 1/3 of that person’s time allocated to wastewater GIS work. Considering the above, the equivalent of one additional staff will be required by the wastewater utility for industrial pretreatment and GIS work. 5.7 OPERATION AND MAINTENANCE COSTS The year 2004 sewer O & M budget, not including capital improvements, or bonded indebtedness is $719,000. This includes O & M for both the treatment plant and collection system. Stayton WWTP Evaluation 103003/3/03-707 5 - 6 February 2006 An article on the internet by EPA summarizes O & M costs for sequencing batch reactor plants according to maximum month design flow. Based on Stayton’s Phase I plant maximum month design flow of 2.5 MGD the EPA cost curve shows an estimated annual O & M budget of $1,150,000. Stayton’s budget of $719,000 is about 65% of the EPA recommended average. The above data is bound in Appendix D. Recent work by Keller Associates for the City of Blackfoot, Idaho (approximate population of 10,000 people similar to Stayton) showed an annual sewer department budget (not including bonded indebtedness or capital improvements) of approximately $1,300,000 for treatment plant and collection system O & M. Based on the above it can be stated that the City of Stayton’s operation of its sewer collection system and wastewater treatment plant is very efficiently run and is budgeted considerably under similar sized communities. Stayton WWTP Evaluation 103003/3/03-707 6 - 1 February 2006 CHAPTER 6.0 – RECOMMENDED IMPROVEMENTS 6.1 GENERAL Chapters 2 through 5 presented an assessment of the existing plant with regard to its capability to meet new permit conditions as well as continued City growth. Those chapters also discussed areas where operating facilities could be more efficient and could be improved to assist in ease of operation and maintenance of the plant. Recommended improvements and their costs will be discussed in further detail in this section 6.2 NPDES PERMIT AND I/I RELATED IMPROVEMENTS Improvements will be needed to meet new NPDES permit conditions as well as high inflow and infiltration flows. Related improvements are discussed below. 6.2.1 Filtration The City’s previous and new permit conditions allow a monthly dry weather CBOD and SS mass discharge load of 110 lbs/day. It should be noted that in May 2003, the dry weather monthly mass load limit for BOD of 110 lbs/day was exceeded. In addition, several dry weather months have resulted in mass load discharges in the 90 and 100 lbs/day range. This upward trend indicates additional treatment will be required to decrease effluent CBOD and SS mass loads. The most likely alternative to significantly reduce mass load discharged is to provide filtration prior to UV disinfection. Filters would also provide a measure of protection in the event of plant upsets or solids washout due to high peak flows. Several alternative filtration processes should be evaluated including various media bed type filters and membrane disk filters. Of these, mechanical membrane disk type filtration appears to be the most promising based on performance and cost. Reduction of 80 to 90% of suspended solids and BOD is possible. It is recommended that two filters be constructed to meet the projected year 2025 peak flow rate of 10.1 MGD. Estimated total project cost for 2 filters at 5.05 MGD each is $1,000,000. These filters could be phased with one constructed now and a second as needed in the future. 6.2.2 Outfall Improvements Depending on the results of the City’s mixing zone dilution analysis, improvements may also be necessary to either 1) reduce effluent Stayton WWTP Evaluation 103003/3/03-707 6 - 2 February 2006 discharge heat load during the September 15 to June 1 period; 2) cease discharge to the river during excessive temperature periods; or 3) obtain greater effluent dilution by dredging and expanding flow to the existing channel, or extending the outfall to the main branch of the river to obtain greater dilution. Regardless of dilution findings, it appears likely heat load will be a future issue as plant flows increase as a result of growth. The most practical alternatives to mitigate heat load limits during the critical months of September and possibly October are as follows: • Outfall Extension: One alternative would be extension of the outfall into the main branch of the Santiam River to achieve greater dilution. Estimated total project cost for this alternative is $500,000. • Potential Upstream Flow Increase: A canal operated by the Santiam Water Control District discharges several hundred yards upstream of the WWTP outfall. The District is currently negotiating with the Federal Energy Regulatory Commission (FERC) to substantially increase flow through its hydroelectric facility which discharges to the canal and could potentially add up to 250 cfs or more in that branch of the river during the critical months of September and October. The City should track the outcome of these proceedings and determine viability of increased dilution upon completion of negotiations. • Land Application: It is estimated that approximately 300 acres would be currently required to irrigate for September and October when effluent temperatures may cause violations. Norpac appears to control all of the available land adjacent to the WWTP, which they are using for irrigation of their own effluent. It is unlikely a deal with Norpac could be negotiated and the City would need to purchase or lease lands at a site remote from the plant. Estimated costs for land purchase alone, is approximately $2,100,000, plus additional costs for conveyance and application facilities. • Wetlands Cooling: It has been reported by others that constructed wetlands can provide effluent cooling benefit as well as provide additional treatment. A wetlands could be constructed south of the existing plant on approximately 7 acres of City owned land. The effluent would likely need to be collected and chlorinated/dechlorinated prior to discharge Stayton WWTP Evaluation 103003/3/03-707 6 - 3 February 2006 to the river. Average wetlands construction costs are approximately $50,000 per acre for surface flow wetlands. Distribution, collection, and chlorination/dechlorination costs would be approximately $200,000. Including engineering and contingency, the total project cost is estimated at approximately $750,000. • Credit Trading: This alternative would consist of planting I trees along upstream riparian zones to cool the river by shading equivalent to the amount~ wastewater effluent heat added. This has been done by at least one industry on the Willamette drainage already. Other credit trading would consist of water rights purchase upstream to maintain a higher 7Q10 river flow. A significant amount of investigation would be required to establish credit trading as a viable alternative for Stayton. For the purpose of this report and budgeting, the outfall extension alternative would appear to be the most feasible at this time. However, the above alternatives are all conceptual in nature and warrant further evaluation prior to commitment to a course of action. 6.2.3 Reactor Expansion Inflow and infiltration flows and increased flow from growth impact SBR hydraulic cycle times. Decreased cycle times, particularly in the settle and decant phases during high I/I flows can increase effluent suspended solids and BOD concentrations. That has occurred in the recent past when sustained peak flows have resulted in washout of suspended solids from the reactors. To resolve this problem, either I/I must be reduced in the collection system to Phase I design flow rate conditions (See Chapter 2) or Existing Outfall Location Stayton WWTP Evaluation 103003/3/03-707 6 - 4 February 2006 additional reactor basin capacity provided. I/I reduction is discussed in the collection system evaluation and basin capacity increase under the batch reactor recommendations below. Filtration, as previously recommended above, will also help alleviate high suspended solids loads, however, would result in increased backwashing during those events. 6.3 HEADWORKS IMPROVEMENTS The existing headworks appear to function relatively well and few improvements appear to be needed. The plant occasionally has some problems with grease. A hot water spray wash system could be implemented. A portable hot water pressure washer would cost approximately $7,500, however, this alternative would be labor intensive. Rather than provide grease removal facilities at the plant, that problem is normally better handled at the source(s) through the City’s sewer use ordinance. The ordinance should require all major grease producers such as auto repair shops, restaurants, and other food establishments to install grease traps or grease interceptors and provide routine cleaning. Consumer education and random periodic verification by staff may be necessary to ensure compliance and reduce grease problems at the plant. Correcting the grease problem at the service also provides the added benefit of reducing buildup in sewer collection pipelines. Nationwide, grease blockings are responsible for close to one half of all Sanitary Sewer Overflows (SSO’s), although grease blockings have not been a major source of SSO’s for Stayton to this point. 6.3.1 Screening Improvements The influent Rotomat screen is operating at recent peak flow rates up to 6.5 MGD. The screen has a peak flow capacity of 6.8 MGD (per Lakeside, the manufacturer). The screen has 1/4-inch openings which allow some smaller material to get through. Lakeside was contacted about retrofitting the screen with 1/8-inch opening mesh. The manufacturer indicated the existing type screen mesh size could only be decreased to 3/16”, which would lower the screen capacity to 6.2 MGD. The City has two alternatives. The existing screen could be retrofitted with a 3/16” mesh which would cost approximately $40,000. However, the capacity would be reduced to 6.2 MGD which is less than current peak plant flows. It would not be worth the cost to retrofit the screen, since it will require replacement within five years to meet higher flows anyway. Instead, it is recommended that the screen be replaced in the next 5 years (or sooner if desired to provide better screening) with a 11 MGD 1/8- Stayton WWTP Evaluation 103003/3/03-707 6 - 5 February 2006 inch fine screen that will remove smaller material and meet peak flow conditions for at least a 20-year period. It is recommended that the existing manually cleaned bar screen be left in place as a backup. The larger 11 MGD capacity screen may require channel modifications and is estimated to cost approximately $270,000 total project cost. 6.3.2 Influent Pump Station Improvements A third 3680 gpm pump should be added about the year 2020 to bring total pumping capacity to 12.7 MGD with a small and large pump on standby. Estimated project cost for the pump and rail facilities would be $30,000. Addition of a backup influent pump level control by a top mounted electronic sensing device or pressure transducer would provide pump control redundancy and prevent overflow conditions. A backup liquid level sensing system is estimated at $10,000 total project cost. 6.4 SEQUENCING BATCH REACTOR IMPROVEMENTS Issues and problems with the existing SBR units and support equipment were discussed in Section 4 and 5. A description of recommended process improvements and costs are discussed below: 6.4.1 Additional SBR Basin Capacity Basin capacity should be expanded for several reasons. First, it will allow basin maintenance to occur without violating permit conditions. Second, it will provide increased hydraulic capacity to better handle peak flows. Third, it would provide additional operational flexibility. Only a single basin expansion is needed to handle flows and loading to the year 2025. Auxiliary equipment such as piping, valves, pumping equipment, etc. must also be expanded. Following are estimated costs for a single basin expansion: Stayton WWTP Evaluation 103003/3/03-707 6 - 6 February 2006 SBR Expansion Estimated Costs Description Construction Cost Total Project Cost Sitework $60,000 $78,000 Piping/Valves 600,000 780,000 Concrete Basin 800,000 1,040,000 Decanters / Scum Skimmer 100,000 130,000 Blower / Piping 125,000 163,000 Pump Equipment 100,000 130,000 Electrical / Control 150,000 195,000 Miscellaneous 100,000 130,000 TOTAL $2,035,000 $2,645,000 A second batch reactor will be required in 2025. 6.4.2 Reactor Batch Fill Tank Addition As previously discussed, many SBR plants have a chronic tendency to repeatedly generate filamentous organisms. This has been confirmed by microscopic evaluation of the City’s plant biomass. These organisms significantly impact sludge settling and, thus, effluent quality. It also limits operational flexibility since the settling phase takes up to 2 hours or 33% of the treatment cycle versus 20-30 minutes for a normal well settling sludge. One way to permanently alleviate this problem is to create an anaerobic environment prior to the fill–mix phase in which the filamentous organisms do not grow. Experience has shown that a complete anaerobic environment cannot be obtained in the reactor itself. A batch fill tank is needed in the process train prior to the batch reactors. The anaerobic batch–fill tank typically is sized about 1/4 of the reactor tank size to limit filamentous growth. Experience at other plants has shown the batch fill tank to significantly reduce filamentous organisms and improve solids settling. Additional piping, pumping, mixing, and process sequencing changes are also needed to incorporate the batch–fill tank. Total project cost of a batch fill tank and appurtenances is estimated at $850,000. Stayton WWTP Evaluation 103003/3/03-707 6 - 7 February 2006 6.4.3 Waste Sludge Pump Additions Addition of separate waste sludge pumps will allow more efficient operation of the SBR mixing pumps and will provide better control of sludge withdrawal from the SBRs. Some modifications of piping will be necessary to convey sludge to the new pumps and sludge discharge line. Reprogramming will also be needed to eliminate throttling of the mixing pump and coordinate sequencing of WAS pump operation. Estimated project cost for addition of waste sludge pumps for the existing two reactors is $110,000. 6.4.4 Spare SBR / Process Equipment The SBR process is a complex highly automated system that is very difficult to run in a manual mode. If one of the automated components breaks down, single basin operation would be required until a repair could be made. It is recommended that all key pumps, automated valves, and PLC’s/software cards susceptible to malfunction be provided with spare equipment to allow easy replacement in event of outage. The following spare equipment should be provided: • Mixing pump • Waste sludge pump (to be provided above) • 24-inch spare for the mixing pump discharge valve, SBR inlet valve, decant valve • 14-inch air inlet valve • Spare software cards and PLC for the SBR operating system A spare valve for the 18-inch WAS line may or may not be needed depending on how the new waste sludge piping is configured. The estimated project cost for the above spare equipment is approximately $65,000. 6.4.5 Freeze Protection The exterior SBR valves and pipelines exposed to the weather should be protected against freezing. This could be done by constructing a heated shelter over the area, or providing heat tracing and insulation for exposed valves and piping. The insulation Stayton WWTP Evaluation 103003/3/03-707 6 - 8 February 2006 system is typically covered with an aluminum jacket for protection. The latter method would be much less expensive with an estimated project cost of approximately $40,000 for applicable exposed piping to / from both basins. 6.4.6 Aeration System Backflush Valving As previously indicated backflushing of the aeration system is a manual process not very easily accomplished. It should be done weekly to ensure jet aeration nozzles are clean and oxygen transfer efficiency maintained. The simplest and least cost alternative would be to provide a portable hydraulic or pneumatic valve operator at a cost of approximately $7,000. To automate the backflush process would require several valves for each reactor to be equipped with pneumatic operators and control system. It is estimated automation of the aeration backflush system would be approximately $75,000 total project cost utilizing the existing valves. Considering US Filter Jet Tech recommends weekly backflushing, it is recommended an automated system be provided. 6.5 EQUALIZATION BASIN IMPROVEMENTS There are several O & M issues associated with the EQ basin as follows; • It cannot be taken out of service for cleaning for more than a 2-hour period as the basin is always needed. • Algae tend to accumulate on the walls and floor slab. The floor has very little slope and solids tend to accumulate. • There is no easy way to clean the basin as all intermediate pumps route flow to the UV disinfection system, then to river discharge. • Cleaning of the basin is difficult and can be hazardous due to the lack of permanent access to the basin. The EQ basin has a capacity of 215,000 gallons. At current maximum day flow rate that allows a decant period of approximately one hour which is adequate. Based on future flow rates, it appears a second EQ basin will be required when peak flow rates reach 6.9 MGD or approximately year 2010. Also, another intermediate pump will be required when maximum day flows reach 6.9 MGD. Algae accumulation could be mitigated by covering the basin which would deny light as needed for algae growth. Or a very smooth wall lining, such Stayton WWTP Evaluation 103003/3/03-707 6 - 9 February 2006 as epoxy or polyurethane could be applied to minimize algae adherence and assist in ease of cleaning. Basin cleaning could be improved by steepening the floor slope, and lining the basin, as well as providing a separate pump or valving an existing pump to convey flow to the digester via the WAS line, instead of to the UV disinfection system. Access for cleaning could be improved by adding a stairwell, platform, catwalk, and ladder with cage on the west wall. The above recommended improvements estimated project costs are as follows: • Either 1) install a cover over the existing and new EQ basins - $150,000, or 2) line existing EQ basin tank – Cost would range from $26,000 to $60,000 depending on coating type and thickness, durability, and longevity desired. Lining the basin is recommended. • Install a 4th intermediate pump and piping - $60,000 • Steepen basin bottom slope to 2%, add pump to existing sump or valving to use an existing pump, and pipe to WAS line - $65,000 • Construct access improvements including stairwell platform, catwalk and ladder with cage - $75,000 • Construct a 215,000 gallon second EQ basin including pumps and piping - $650,000 The above in-basin improvements must be made between decant periods, preferably during low flow dry weather conditions, or a temporary bypass system provided while improvements are made. 6.6 UV DISINFECTION SYSTEM IMPROVEMENTS Although the existing UV system is functional and normally meets E coli permit limits, it could be improved. As discussed previously, newer technology is currently available that provides better performance and is self cleaning. The new low pressure high intensity system uses less than ½ the lamps so flow capacity could be easily expanded using the existing UV basin channels. The estimated cost for an 10.2 MGD high intensity automatically cleaned system to meet year 2025 requirements is approximately $600,000 total project cost. This improvement is solely at the discretion of the City as the most pressing current issue is the time Stayton WWTP Evaluation 103003/3/03-707 6 - 10 February 2006 required to manually clean the lamps. It could be phased in if desired by the City. It is also noted that the UV structure is uncovered, which makes maintenance during the winter months difficult and hazardous. It would greatly help to cover and enclose the structure to allow for better wet weather O & M conditions. A covered metal structure is estimated to cost approximately $100,000 total project cost. The level in the channel could be automatically maintained during periods of no discharge by adding a small tank and recycle pump at a cost of approximately $25,000. 6.7 SOLIDS HANDLING FACILITY RECOMMENDATIONS Solids handling facilities currently create the greatest level of concern for plant staff, particularly in the area of dewatered sludge storage and disposal. Following is a discussion of solids handling facility recommendations: 6.7.1 Liquid Sludge Storage Liquid sludge storage is needed for sludge wasted from the SBRs to provide holding capacity prior to dewatering. The City has a 225,000 gallon sludge storage tank and 180,000 gallon sludge storage pond onsite. The old oxidation ditch is also available for storage with an estimated capacity in excess of 500,000 gallons. Thus, total liquid sludge storage is approximately 1,000,000 gallons, which is 25 days current capacity, or 13 days Year 2025 (population 19,400) capacity. Should the lime stabilization or dewatering equipment fail, adequate capacity appears to be available to allow repairs and put equipment back online. It is recommended that the oxidation ditch be cleaned and provided with piping and pump to easily fill and draw off sludge should it ever be necessary. Aerators should also be provided to minimize odors. Estimated total project cost is $250,000. It is recommended that the old low capacity standby liquid sludge pump be replaced with a 130 gpm progressive cavity pump. Estimated total project cost for pump, piping, and valves is approximately $50,000. In the short-term, it is recommended that decanting facilities including supernatant discharge and piping be provided for the aerated storage tank to allow thicker solids to be pumped to the belt Stayton WWTP Evaluation 103003/3/03-707 6 - 11 February 2006 press. This will assist in increased belt press production and dryer cake from the press. The estimated project costs for decant facilities is $100,000. In the long-term, it is recommended to provide a thickener to reduce 2025 sludge volume of 80,000 gpd at .5% solids to 13,300 gpd at 3.0% solids. With a thickener, the aerated sludge storage tank alone would have a storage capacity of 18 days at 2025 sludge production levels, which would be adequate. It would also substantially decrease belt press operating time. A gravity belt thickener with polymer feed equipment, piping, housing, and pump equipment would have an estimated total project cost of $830,000. It is recommended that the City install both decanting facilities and the gravity belt thickener for redundancy. This will substantially decrease belt filter press run time. These improvements will also assist in providing increased liquid storage capacity since the aerated storage tank will hold much thicker solids. 6.7.2 Dewatering and Lime Stabilization Facilities The belt filter press should be adequate to meet year 2025 needs providing the following is implemented: • Make repairs as needed to bring capacity up to 130 gpm, the specified rated capacity. • Install liquid sludge thickening facilities as indicated above, which should allow the dry weight of feed sludge to the belt press from the digester to be increased by a factor of 6. Due to the expense involved and liquid sludge storage available to allow time for repairs of this equipment, duplication of dewatering and lime stabilization facilities for redundancy is not recommended. However, it is recommended that spare parts be provided for those elements that may be susceptible to breakdown, such as spare drives, bearings, belt press belt, conveyor drive and belt, etc. such that they can be quickly replaced if needed. It is recommended that approximately $65,000 be set aside to purchase the components most susceptible to outage. Should the belt press be inoperable for an extended period of time (>21 days) it may be necessary to contact a dewatering equipment supplier and temporarily lease trailer mounted dewatering equipment until repairs can be made. Stayton WWTP Evaluation 103003/3/03-707 6 - 12 February 2006 It is also recommended that the existing sludge containment area, where the sludge conveyer discharges, be modified to allow complete containment without leakage. This could be done by extending the drain trench across the opening with a grating and providing a removable stop log wall in front of the drain trench. These improvements are estimated to cost $8,000 total project cost. 6.7.3 Dewatered Sludge Onsite Storage Alternatives Biosolids disposal impacts onsite storage in that adequate onsite storage is needed during periods when biosolids cannot be land applied. Biosolids disposal can be very difficult for the City at times for a variety of reasons, particularly during the winter months: • Crop uptake of biosolids nutrients (nitrogen and phosphorus) in the winter months slows considerably and DEQ is hesitant to permit winter application sites. • Fields become wet during the rainy season and farmers do not want biosolids spreading vehicles leaving ruts and damaging fields. • Application is susceptible to farming schedules in that biosolids spreading cannot occur during planting or harvesting or other periods at the farmers discretion. • Should farmers graze their fields, animals are not allowed to graze on fields during and up to 30 days after biosolids application per DEQ regulations. • It is very difficult to obtain a long-term agreement with a farmer to guarantee a place for continued sludge disposal. Without an agreement the farmer can refuse biosolids at any time leaving the City in a bind. • Application regulations are becoming increasingly difficult to adhere to as there are numerous restrictions which must be met. As a result of the above, the City must either find a reliable winter land application site or store biosolids onsite for long periods when biosolids land application is not possible. Existing onsite dewatered sludge storage is barely adequate to meet existing sludge production during wet weather months. The Stayton WWTP Evaluation 103003/3/03-707 6 - 13 February 2006 storage area is uncovered and susceptible to precipitation that reintroduces water that was previously removed by the belt press. Either the sludge volume must be reduced (as discussed further below under sludge disposal), or more onsite or offsite sludge storage needs to be provided. It is recommended that stored dewatered sludge be provided with a permanent cover to prevent accumulation of water and facilitate sludge handling and disposal. The existing effluent pond immediately east of the dewatering building could be converted to onsite storage. It is almost twice the size of the existing sludge storage area. Note that additional onsite sludge storage will not be needed if a reliable winter disposal site can be found or the sludge drying alternative as discussed in the next section is selected. Following are estimated costs for onsite storage improvements: • Cover existing sludge storage pond with a permanent cover. A permanent structure with adequate access and ventilation is estimated at a total project cost of $250,000. • Prepare (pave) existing effluent pond for additional sludge storage and cover the pond with 140’ x 160’ steel framed cover. A Brown Bear should also be provided to assist in turning over the sludge and drying. Estimated project cost for these improvements is $1,025,000. 6.7.4 Sludge Disposal Recommendations Average sludge production quantities projected for Year 2025 are estimated at 1.1 dry tons per day (not including lime). Assuming the City’s sludge continues to contain low levels of heavy metals, and land application is governed by total nitrogen (TN) at 3% of total sludge quantity and at an application rate of 100 lbs/acre per year, approximately 240 acres of land application area will be needed (not counting buffers, etc). There are a number of disposal alternatives to consider including continued disposal of lime stabilized Class B biosolids, or enhanced treatment and disposal of Class A biosolids. These alternatives are discussed further below. Class B Biosolids Disposal: This method is currently being practiced with disposal at the Studnick site. Additional sites (Lamb and Tracy) are currently being pursued as temporary alternative application sites particularly during the winter. DEQ is willing to Stayton WWTP Evaluation 103003/3/03-707 6 - 14 February 2006 permit winter disposal on these temporary sites for two years until the City arrives at a permanent disposal solution. Disadvantages of the present Class B disposal method include the lack of sufficient improved onsite biosolids storage facilities, the current relatively long haul distance, and the lack of a long term disposal agreement should the landowner no longer want the biosolids. The landowner also controls when the biosolids may be applied. A second Class B solids winter reuse alternative would be similar to the method reported to be used by the City of Salem and several other western Oregon communities. They contract for hauling biosolids to eastern Oregon during the winter where year-round application is possible and permitted. Another alternative would be for the City to purchase their own land for continued land application of Class B biosolids so as to have better control of the disposal site. Two hundred and seventy acres allowing for buffer area at an estimated cost of $4,000 per acre would result in a land purchase cost of $1,080,000. Additional covered onsite storage facilities would still be needed. Class A Biosolids Disposal: The City has expressed a desire to provide a higher degree of biosolids treatment meeting EPA 503 Class A standards, instead of Class B treatment as presently practiced. That desire is motivated by more restrictive EPA/Oregon DEQ land application standards for Class B sludge and less restrictive and more readily available application sites for Class A biosolids (including nurseries, golf courses, landscaped public rights-of-way, home gardens, and more readily available agricultural sites). Following are EPA accepted Class A treatment technologies: • Composting (in vessel, static aerated pile, or windrow) • Lime stabilization (in vessel under tightly controlled conditions) • Pasteurization (in vessel heat treatment to 70 degrees C > than 30 minutes) • Thermophilic aerobic digestion (heat to 55 degrees C > 10 days) • Anaerobic digestion processes Stayton WWTP Evaluation 103003/3/03-707 6 - 15 February 2006 - TPAD (temperature phased digestion) - Thermophilic digestion - Acid phased digestion - Three phased digestion (acid, thermo, meso) • Beta and gamma ray radiation • Heat drying (heat to 80 degrees C > 3 hours) Of the above Class A processes, composting, lime stabilization and heat drying are the three Class A processes that appear most suited to meet the City’s needs. • Composting is a relatively simple process and can be either in-vessel, aerated static pile, or windrow composting. Windrow and aerated static pile composting involve minimal capital cost; however, extensive land and labor is required as multiple piles are needed which must be mixed every few days. In addition, variations in weather, mixing, and inadequate monitoring can lead to inconsistencies in meeting Class A criteria for the windrow and aerated static pile process. In-vessel composting is the composting process most likely to consistently produce Class A biosolids since the process is performed under more tightly controlled conditions than the other composting methods. • Lime stabilization to meet Class A requirements is also performed in-vessel to allow tighter control of mixing and heating conditions. Also, the City has lime feed facilities already onsite. • Heat drying offers the benefit of volume reduction which would alleviate onsite storage conditions and reduce biosolids hauling costs. Estimated annual costs for the above six Class A and Class B processes are presented in Table 6.1. Stayton WWTP Evaluation 103003/3/03-707 6 - 16 February 2006 Table 6.1 Sludge Treatment and Disposal Alternative Costs Alternative Biosolids Disposal Cost Comparison Existing Disposal Class B Land Purchase Class B E. Oregon Hauling Class B In Vessel Compost Class A In Vessel Lime Stab. Class A Heat Drying Class A CAPITAL COSTS (includes 30% for engineering and contingency) Land $0 $1,.080,000 $35,000 Leased $0 $0 $0 Equipment (installed) 0 0 0 850,000 900,000 1,520,000 Housing 0 0 0 120,000 150,000 450,000 Onsite Covered Sludge Storage 1,200,000 1,200,000 250,000 1,200,000 1,200,000 65,000* Sludge Load/Dry Equip. 75,000 75,000 0 150,000 75,000 0 Sub-Total $1,275,000 $2,355,000 $285,000 $2,320,000 $2,325,000 $2,035,000 Annual Capital Cost* $94,400 $174,000 $21,100 $171,700 $172,600 $150,600 *4%, 20 years OPERATING COST Materials - Lime $40,000 $40,000 $40,000 $0 $33,000 $0 Materials - Amendment 0 0 0 15,000 0 0 Power / Heat 3,000 3,000 0 10,000 15,000 50,000 Labor 25,000 25,000 25,000 65,000 65,000 65,000 Sludge Hauling 36,000 18,000 75,000 0 0 0 Sub-Total $104,000 $86,000 $140,000 $90,000 $113,000 $115,000 Total Annual Cost $198,400 $260,000 $161,100 $261,700 $285,000 $265,600 Cost/Dry Ton Biosolids $500 $650 $400 $650 $710 $660 * Fill in existing sludge storage basin if heat drying used The City could continue with Class B biosolids reuse at lowest cost, by transporting biosolids to eastern Oregon region in the winter similar to the City of Salem, and summer spreading similar to current practices. This method would require long-term agreements with landowners and still be susceptible to restrictive spreading schedules plus DEQ regulation constraints for reuse of Class B solids. Stayton WWTP Evaluation 103003/3/03-707 6 - 17 February 2006 Of the Class A processes, heat drying appears to provide the greatest benefits for the following reasons: • Disposal of Class A biosolids should be much easier. The final product will be an excellent dry pathogen free soil amendment with a nutrient value such that it should be in demand by the public. It may be possible to sell the final product, however, would require extensive marketing. Experience with smaller plants has shown that marketing costs usually offset any sales benefit. Even those plants that are able to sell biosolids only realize a gain in the range of $10 - $60 per dry ton. • Heat drying is the only process that provides significant volume reduction (on the order of 4 to 5 times less sludge volume) as total solids after drying are in the 90% range. Volume reduction means the City will not have to provide increased covered sludge storage capacity onsite. That is a significant benefit to the City. • Hauling and application tasks are reduced by a factor of 4 to 5 as a result of reduced volume to be hauled. It is anticipated that demand will be such that the public may pick up the product and haul it themselves. • The process is not as structurally intensive as most of the other Class A processes are and will occupy less area onsite. The entire process comes skid mounted. • Odors are better controlled as the sludge is contained and off gases can be scrubbed. The primary disadvantage of heat drying is the need for fuel for the drying process which would be susceptible to energy cost increases. However, the advantages are considered to far outweigh the one disadvantage. A manufacturer’s quote for 3.6 dry ton per day heat drying process equipment operating for 30% of the time at 1.1 dry tons per day (year 2025 average rate) is approximately $750,000. An additional $300,000 should be allowed for installation, sitework, piping, and electrical requirements. It is recommended the sludge drying equipment be housed. Housing consisting of an approximate 120’ x 60’ metal building would be at an estimated cost of $350,000. Ventilation and odor scrubbing would cost approximately $100,000 and abandoning the existing biosolids storage basin would be Stayton WWTP Evaluation 103003/3/03-707 6 - 18 February 2006 $65,000. Therefore, the entire housed installation is estimated at $1,565,000 construction cost and $2,035,000 total project cost. Being a relatively new process, it is strongly recommended that the City visit at least two operating biosolids heat drying installations and discuss equipment performance with operating staff and establish a comfort level with this type of process prior to making a final commitment to the heat drying process. Should the heat drying process be installed, the City could terminate the current lime stabilization process, saving on operation and maintenance expenses. Additional onsite sludge storage volume would also not be needed. On a short-term basis, it is recommended the City explore winter land application as practiced by the City of Salem and summer spreading as currently practiced. In the long-term, it is recommended the City consider Class A biosolids reuse and implement the heat drying process. It is also recommended the City purchase 80 acres near the WWTP to serve a dual purpose as follows: • It would provide a reliable backup means of disposal of biosolids for the winter months should the Class A biosolids not be picked up at the plant and avoid dependence on others during the winter period. • It would provide a backup area for partial land application of effluent during September and October to mitigate effluent temperature issues. The total cost of 80 acres is estimated at $560,000 based on recent appraisals. 6.8 MBR ALTERNATIVE TO SBR EXPANSION The existing plant will require significant upgrade in the next twenty years to meet growth and stricter NPDES permit requirements. The major facilities needed, will include two additional SBR reactors, two filters, batch fill tank, and an EQ basin. Instead of expanding the existing SBR process it may be worth considering addition of a parallel membrane bioreactor process. This process is increasingly being employed by many municipalities across the U.S. as it provides the highest quality effluent of current biological Stayton WWTP Evaluation 103003/3/03-707 6 - 19 February 2006 wastewater treatment plants. Benefits of the membrane bioreactor process include reduced space required, it is not susceptible to bulking (poor settling) sludge since solids separation is by filtration not settling, lower sludge production, decreased disinfection dose, and simplicity of operation. A 2 MGD (maximum month flow) membrane bioreactor addition which would meet the City’s needs for the next twenty years is estimated at a total project cost of $5,900,000. In comparison, the cost of two additional SBR reactor trains, one filter (the existing plant would still require one filter at peak flow capacity of 7.5 MDG, and another EQ basin would be approximately $ 6,690,000. There are advantages and disadvantages to adding the MBR process as follows: • Disadvantages - It would require operating essentially two different types of processes simultaneously, in addition, the SBR process would be batch flow, and the MBR process would be continuous flow. - The expansion would require a significant capital expenditure in the next five years. - The membrane filter cassettes must be replaced approximately every 10 years at a cost of approximately $675,000. Filter longevity should increase and replacement costs decrease in the future as more competition enters the market and improved lower cost membranes surface. • Advantages - The MBR process provides the highest level of treatment in the wastewater industry to date with effluent BOD/SS usually less than 2 mg/l. This would allow expansion to 6.6 MGD max month flow (buildout conditions) without violating mass load limits. - Due to high MLSS and long sludge age characteristic of the MBR process solids production is decreased. - The process takes up minimal room. The complete 2 MGD expansion would be contained inside a basin 90 feet by 65 feet versus two 100 foot square SBR reactors. Stayton WWTP Evaluation 103003/3/03-707 6 - 20 February 2006 - Once the initial MBR expansion is made, it may be possible to use existing SBR tankage for further expansions thus decreasing future expansion cost. - The MBR process is capable of nutrient removal (phosphorus and nitrogen) should that be added to the City’s future permit. - The MBR process is easy to operate and permit violations are rare since the filter membrane serves as a safeguard against plant upsets or operator errors. A cost comparison of the two alternatives is shown in Table 6.2 and Table 6.3: Table 6.2 MBR/SBR vs SBR Capital Cost Comparison Item MBR/SBR SBR Only Filter(s) $750,000(1) $1,000,000(2) Batch Fill Basin 850,000 850,000 Batch Reactors(2) 0 5,290,000 Two MGD MBR Expansion 5,900,000 --- EQ Basin 0 650,000 UV System 500,000 600,000 TOTAL $8,000,000 $8,390,000 Table 6.3 MBR/SBR vs SBR Annual O & M Costs Item MBR/SBR SBR Only Labor Cost $450,000 $390,000 Power Cost 130,000 160,000 Chemical Cost (Filter Cleaning) 10,000 0 Repair Cost 50,000 50,000 Equipment Replacement 120,000 132,000 Membrane Replacement 88,000 ---- Solids Disposal 180,000 240,000 Annual O & M Cost 1,028,000 972,000 Annualized Capital Cost 640,000 671,000 TOTAL ANNUAL COST $1,668,000 $1,643,000 Based on the above two tables, the two alternatives are approximately the same cost. However, as the City approaches buildout conditions, the MBR alternative would be lower cost by approximately $1.5 million since existing SBR process tankage could be retrofitted with membrane filters. Stayton WWTP Evaluation 103003/3/03-707 6 - 21 February 2006 The decision can be delayed until the next SBR reactor is needed in 2010. At that time membrane cost could decrease even further. History has shown that effluent limits continue to become more restrictive and the MBR process is currently the best available technology for providing a high quality effluent. Keller Associates recommendation would be to make the transition to the MBR process prior to the addition of a 3rd SBR basin, or approximately year 2010. 6.9 MISCELLANEOUS PLANT IMPROVEMENTS In addition to all of the process related improvements discussed above there are some additional improvements which would assist in improving plant operation and maintenance as follows: 6.9.1 Plant Utility Water System In evaluating plant water uses it was determined that the treatment plant is the City’s second largest water user with an average of approximately 110,000 gallons per day of potable water used for plant functions such as belt press and influent screen spray wash systems, foam spray, general washdown, landscaping, etc. Approximately 40-50% of that amount is used for keeping the UV channel full. Many plants use disinfected plant effluent for many plant water uses. Discussion with Oregon DEQ staff indicate UV disinfected water (without chlorination) can be used for plant utility water purpose including landscape irrigation. Therefore, significant potable water savings are possible. A recycle system for the UV channel would significantly reduce potable water use, however, the lamps could warm the water which would be detrimental to the effluent temperature limit. A separate onsite well or Ranney collector could also serve as a source of plant utility water. An approximate cost for a utility water system would be in the range of $75,000 – 100,000. 6.9.2 Sewer Debris Disposal Area The City currently disposes of debris cleaned from sewers at the plant site to a sand filter. The process could be enhanced by addition of a larger wetwell and an automated pump which would pump filtered water directly to the headworks and a manual bar screen to remove larger debris. The project cost for this addition is estimated at $30,000. Stayton WWTP Evaluation 103003/3/03-707 6 - 22 February 2006 6.9.3 Maintenance Management Program As indicated in Chapter 5, a comprehensive maintenance management program should be set up to maximize preventative maintenance and minimize corrective maintenance. This will require purchase of computerized software and organization of the program to allow the plant to operate more efficiently with less repairs and equipment downtime. Purchase of the O&M software and incorporation of the maintenance management program is estimated at $200,000. 6.9.4 Aerated Sludge Storage Tank Rehab This tank was part of the original plant and has been in use for over 40 years. It is reported by staff that the interior concrete shows evidence of corrosion and should be replaced or rehabilitated. This would require sand blasting the interior surface, spot repair of significant damaged areas and resealing of the entire interior surface with a polyurethane sealing system. Estimated total project costs would be approximately $100,000. 6.9.4 Maintenance and Storage Building The existing plant has no place for weather protected storage of spare equipment and supplies, vehicles, or for doing any mechanical repairs, etc. A maintenance building would greatly assist in providing for the above functions and improving plant O&M. It is anticipated that four (4) bays (one side open) for vehicles and an enclosed maintenance shop and separate equipment/materials storage area would require approximately 3,750 square feet with 14-foot wall height. Estimated project cost including a paved drive would be approximately $350,000. It may be possible to reduce this cost by common wall construction with the heat drying equipment building. 6.9.5 Plant Buffer Space The existing plant is currently surrounded by agricultural land. In the future, it is likely that development will occur closer to the plant with resulting complaints regarding esthetics, noise, and odors. For this reason it is recommended that land be purchased around the plant to maintain buffer space between the plant and future development. The buffer distance is very subjective, however, the WEF Manual of Practice for Design of Municipal Wastewater Treatment Plants recommends a distance of 150 to 250 feet between the plant and residential growth. At a distance of 250 feet Stayton WWTP Evaluation 103003/3/03-707 6 - 23 February 2006 approximately 20 acres would need to be purchased at a cost estimated at $200,000. In addition to the buffer space, it is recommended the City provide for industrial zoning for at least an additional 750 feet beyond the buffer space. 6.10 RECOMMENDATION SUMMARY A summary of recommended improvements, their cost, and priority is shown on Table 6.4 below. Improvements indicated as 1 are immediate needs with 1A as highest need and 1B as lower priority depending on available funds. A site layout is provided on Figure 6-1 showing anticipated locations of new facilities requiring significant land use. Stayton WWTP Evaluation 103003/3/03-707 6 - 24 February 2006 Table 6.4 City of Stayton WWTP Improvements Opinion of Most Probable Cost Priority Improvements Description Capacity or Permit Related Need Needed to improve Plant Operations & Reliability Estimated Total Project Cost (2005) Estimated Population/Year (Marion County) Headworks: 2 Provide a new 1/8” fine screen at 11MGD 9 $270,000 11,900 / 2010 1B Backup pump station level controls 9 10,000 Present 3 Influent pump addition 9 30,000 2020 Batch Reactors: 1B Batch Fill Basin 9 $850,000 Present 1B Heat trace / insulate exterior piping / valves 9 40,000 Present 1B Waste sludge pumping separation 9 110,000 Present 1B Spare process equipment / valves 9 65,000 Present 1B Automate backflush system 9 75,000 Present EQ Basin: 2 Line interior of EQ basin 9 $60,000 Present 1B Basin drain improvements 9 65,000 Present 2 Add Intermediate pump and piping 9 60,000 11,900 / 2010 1B Access improvements 9 75,000 Present UV Disinfection System: 2 Cover existing structure 9 $100,000 Not Time Dependant (Taking Bids) Convert and expand existing UV system to high intensity system @ 10.2 MGD capacity 1A Phase 1 (3.4 MGD) 9 200,000 Present 2 Phase 2 (3.4 MGD) 9 200,000 2010 3 Phase 3 (3.4 MGD) 9 200,000 2015 2 Channel level control system 9 0 Completed Stayton WWTP Evaluation 103003/3/03-707 6 - 25 February 2006 Solids Handling Facilities: 1B Clean and convert oxidation ditch to aerated sludge storage 9 $250,000 Present 1B Replace liquid sludge transfer pump 9 50,000 Present 1B Provide spare parts for stabilization / dewatering equipment 9 65,000 Present 1A Improve existing sludge containment 9 0 Completed 1B Provide aerated sludge tank decanting facilities. 9 100,000 Present 1B Sludge Thickener Facilities 9 830,000 Present 3 Provide Class A sludge heat drying system (housed) Future DEQ Requirement? 9 2,035,000 2015 2 Purchase 80 acre biosolids application site near plant 9 560,000 2010 or as Available 1A Provide improved permanent cover for solids storage 9 250,000 Present 1B Rehab aerated storage tank 9 100,000 Present Miscellaneous Improvements: 1A Provide filter to lower effluent BOD/SS mass loads 9 $750,000 Present 1B Plant utility water system 9 100,000 Not Time Dependant 1B Maintenance and storage building 9 350,000 Not Time Dependant 1B** Extend river outfall 9 500,000 By 12-31-08 2 Buffer around WWTP 9 200,000 Present 2 2 MGD Parallel MBR Plant 9 5,900,000 2010 1B Sewer debris cleaning area upgrade 9 30,000 Present 1B Maintenance management program 9 200,000 Present Total Cost By Priority: 1A $1,300,000 Present 1B 3,765,000 See Above 2 7,350,000 See Above 3 2,265,000 See Above Total Improvements Cost $14,680,000 1A = Needed Immediately 1B = Recommended Immediately, but can be delayed 2-5 Years depending on availability of funds 2 = Medium Priority 3 = Low Priority **Assumes existing mixing zone dilution is inadequate to meet NPDES permit heat load limits. A pp en di x A Fi g u re s A pp en di x B N P D E S P er m it A pp en di x C P la n t St af fi n g L ev el E st im at e A pp en di x D O & M C o st s A pp en di x E In d u st ri al U se r Su m m ar y