Minnesota. BMI Project No. M

Transcription

1 Wastewater Treatment Facility Plan City of Paynesville Minnesota BMI Project No. M March 2009

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3 TABLE OF CONTENTS EXECUTIVE SUMMARY... 1 A. GENERAL... 1 B. DESIGN PARAMETERS... 1 C. COST ESTIMATES... 1 D. RECOMMENDATIONS... 2 SECTION 1 INTRODUCTION... 3 A. GENERAL... 3 B. REPORT ORGANIZATION... 3 SECTION 2 PROJECTED FLOWS AND LOADINGS... 4 A. POPULATION PROJECTION... 4 B. WASTEWATER FLOWS... 4 C. WASTEWATER LOADINGS... 5 D. SUMMARY... 6 SECTION 3 EXISTING FACILITY... 7 A. GENERAL... 7 B. EXISTING FACILTY ASSESMENT... 7 C. EXISTING FLOWS AND LOADINGS... 7 D. CONDITION OF EXISTING FACILITY... 8 E. 100 YEAR FLOOD PLAIN... 8 F. ELECTRICAL SERVICE AND POWER DISTRIBUTION... 8 G. WASTEWATER ORDINANCE AND USER RATE EVALUATION... 8 SECTION 4 FACILITIES SITING A. GENERAL B. ADDITIONAL LAND ACQUISITION C. FACILITY SITE SECTION 5 TREATMENT ALTERNATIVES A. GENERAL B. EVALUATION CRITERIA C. WASTEWATER TREATMENT OPTIONS General Alternative No. 1 - Construct a Parallel Aeration Cell...12 City of Paynesville, Minnesota M Wastewater Treatment Facility Plan Page i Prepared by Bolton & Menk, Inc.

4 3. Alternative No. 2 Maximize the Existing System Alternative No. 3 Activated Sludge Alternative No. 4 - Construct New Mechanical Treatment Facility...17 D. BIOSOLIDS TREATMENT & STORAGE Cold Storage Reed Beds...23 E. EFFLUENT DISCHARGE OPTIONS Spray Irrigation Rapid Infiltration Surface Water Discharge...26 F. ODOR CONTROL SECTION 6 COST CONSIDERATIONS A. GENERAL B. ESTIMATED CONSTRUCTION COSTS C. ESTIMATED OPERATION, MAINTENANCE AND REPLACEMENT COSTS D. ANNUAL EQUIVALENT COSTS SECTION 7 RECOMMENDATION & IMPLEMENTATION SCHEDULE A. RECOMMENDATION B. IMMPLEMENATION SCHEDULE LIST OF TABLES ES-1 Summary of 20 Year Design Criteria...1 ES-2 Cost Summary of Treatment Alternatives Population Projections Year Design Flows Design Loadings Summary of Design Parameters Historical Flows and Loadings App. B 5.1 New Aeration Pond Size Existing System Capacity Extended Aeration Design Criteria Spray Irrigation Summary Rapid Infiltration Basin Summary Alternative No. 1-Construct Parallel Aerated Pond Costs Alternative No. 2-Maximize the Existing System Costs Alternative No. 3-Modified Activated Sludge Costs Alternative No. 4-Construct New Mechanical Treatment Facility Costs Operation, Maintenance and Replacement Costs Annual Cost Summary City of Paynesville, Minnesota M Wastewater Treatment Facility Plan Page ii Prepared by Bolton & Menk, Inc.

5 LIST OF FIGURES Follows Page 2.1 Existing Wastewater Flow Schematic... Appendix B - Existing Facility Aerial Views... Appendix B 3.1 Historical Flows Alternative No. 1 Flow Schematic Alternative No. 3 Flow Schematic Alternative No. 4 Flow Schematic APPENDICES Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G NPDES Permit Existing Facility Details Industrial Agreements Presentation Materials, Public Comments and Resolution Environmental Assessment Worksheet Ordinance Flow Calculations City of Paynesville, Minnesota M Wastewater Treatment Facility Plan Page iii Prepared by Bolton & Menk, Inc.

6 EXECUTIVE SUMMARY A. GENERAL The purpose of this report is to provide the City of Paynesville, Minnesota with necessary information regarding the City s wastewater characteristics and quantities so that the City can establish priorities, plan, fund and implement future wastewater treatment facilities or improvements. This summary highlights the main points of the facility plan. B. DESIGN PARAMETERS Design parameters used in this report are summarized in Table ES-1. TABLE ES - 1 Summary Of 20 Year Design Criteria City of Paynesville, Minnesota Parameter Year 2030 Design Value City Service Population 3,369 Average Wet Weather (AWW) Flow MGD Peak Hourly Wet Weather (PHWW) Flow MGD Peak Instantaneous Wet Weather (PIWW) Flow MGD Average Day CBOD 5 8,173 lbs/day Average Day TSS 4,674 lbs/day Average Day NH 3 -N 451 lbs/day Average Day P 140 lbs/day C. COST ESTIMATES The estimated cost for each alternative studied includes both construction costs and operation, maintenance and replacement (OM & R) costs. In determining the cost effectiveness of the various alternatives, costs have been presented in terms of equivalent annual costs. The interest rate and time period utilized in the cost effective analysis is zero 5.5 percent and 20 years, respectively. Monthly costs per connection have been determined by population equivalent connections, which historically have been 2.7 persons per connection. City of Paynesville, Minnesota M Page 1 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

7 TABLE ES - 2 Cost Summary for Treatment Alternatives City of Paynesville, Minnesota Item Maximize Existing Facility Modified Activated Sludge System Capital Cost $1,948,000 $5,875,500 Annualized Capital Cost (1) $163,000 $492,000 OM & R $1,100,000 $925,000 Total Annual Cost $1,263,000 $1,417,000 (1) Assumes financing rate of 5.5% interest for 20 years. D. RECOMMENDATIONS Each of the alternatives discussed was considered in terms of cost, environment, treatment capabilities, and operational considerations. The best fit for the City is to construct a modified activated sludge system with reed beds and continue to use the spray irrigation system. This option handles the full design load from the community, actively manages the biosolids in the process, produces high quality effluent and is flexible to handle future growth in the community City of Paynesville, Minnesota M Page 2 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

8 SECTION 1 INTRODUCTION A. GENERAL The purpose of this report is to evaluate the City s existing treatment facilities ability to process projected flows and loadings, and identify, evaluate and recommend treatment alternatives that will best meet the City s goals, needs and State regulatory requirements. Based on this information the City Council can establish priorities, plan, fund, and implement future wastewater treatment facility improvements. After the City Council has reviewed and approved this report, a copy of the report should be submitted to the Minnesota Pollution Control Agency (MPCA) for review and approval. B. REPORT ORGANIZATION To adequately address the major areas which were evaluated, this report is organized into the following sections: Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Introduction Design Projections Existing Facilities Facility Site Treatment Alternatives Cost Considerations Recommendations and Implementation Schedule City of Paynesville, Minnesota M Page 3 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

9 SECTION 2 PROJECTED FLOWS AND LOADINGS A. POPULATION PROJECTION There are a number of methods available to predict population trends for cities such as Paynesville, which include a review of historical city and county population trends. These trends can be projected using a variety of mathematical projections including, arithmetic, geometric, and linear regression methods. A combination of methods, including local intuition and conversations with City staff are included in the future population estimate. The current population for the City of Paynesville is 2,775. Since the City is within close proximity to the quickly expanding metropolitan area of St. Cloud, a significant population increase is expected. Discussion with City Staff resulted in a projection of 10 new homes per year with approximately 2.7 residents per home that results in 27 new residents per year. Table 2.1 presents the population projections for the next 20 years. Table 2.1 Population Projections City of Paynesville, Minnesota Year Population , , , , , ,369 B. WASTEWATER FLOWS The design flows and loadings for the 20-year design period were developed using historical data, projected residential and industrial growth, and Minnesota Pollution Control Agency (MPCA) guidelines. Table 2.2 presents the 20-year design flows. The design flows include any projected increase in population or industrial growth. Industrial growth has been estimated based on conversations with Mastermark Plastics and AMPI. Both industries project no net increase in flow to the Paynesville Wastewater Facility. City of Paynesville, Minnesota M Page 4 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

10 Strong consideration was given to varying loads due to alternate disposal methods both industries are currently practicing. Both industries reviewed current practices and supported on the flow allocation summarized in this report. Table Year Design Flows City of Paynesville, Minnesota Average Flow Average Wet Weather Flow (AWW-30 days) Peak Hourly Wet Weather Flow (PHWW) Peak Instant Wet Weather Flow (PIWW) MGD MGD MGD MGD C. WASTEWATER LOADINGS The commonly used parameters used to measure wastewater strength are: Carbonaceous Biochemical Oxygen Demand (CBOD 5 ), Total Suspended Solids (TSS), Total Kjeldahl Nitrogen (TKN), and Phosphorous (P). CBOD 5 is the measure of the oxygen consumption capacity of the wastewater. TSS is a measure of quantity of solids in the wastewater. TKN and P are indicators of the amount of nutrients in the wastewater and are significant for surface water discharges and would need to be considered if the City pursued a discharge to the North Fork of the Crow River. The main focus for the City of Paynesville is CBOD 5 and TSS due to the land application of effluent. The design loadings, measured in pounds per day (ppd) were determined by using residential and industrial growth projections, existing data, and recommended standards. For residential loadings, a design loading of 0.17 lb/capita/day and 0.20 lb/capita/day were used for CBOD 5 and TSS respectively, in accordance with Ten-State Standards. A design loading of 0.03 lb/capita/day and lb/capita/day were used for TKN and total phosphorous respectively, based on recommendation by Metcalf & Eddy. The base industrial loading of 7,100 lbs/day for CBOD 5 and 4,000 lbs/day for TSS was used for the design year. Design loadings are presented in Table 2.3. City of Paynesville, Minnesota M Page 5 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

11 CBOD 5 Municipal Industrial-AMPI Industrial-MasterMark Industrial-Unallocated Total TSS Municipal Industrial-AMPI Industrial-Unallocated Total Table 2.3 Design Loadings Wastewater Treatment Facility City of Paynesville, Minnesota Parameter Design Condition 573 ppd 6,500 ppd 600 ppd 500 ppd 8,173 ppd 674 ppd 3,500 ppd 500 ppd 4,674 ppd D. SUMMARY A summary of the wastewater flows and loading for all the design conditions are presented in Table 2.4. TABLE 2.4 Summary of Design Parameters City of Paynesville, Minnesota Parameter Average Flow (ADF) Average Wet Weather Flow (AWW-30 days) Peak Hourly Wet Weather Flow (PHWW) Peak Instant Wet Weather Flow (PIWW) Average CBOD5/Day (lbs/day) Average TSS/day (lbs/day) Average TKN/day (lbs/day) Average P/day (lbs/day) Design Condition MGD MGD MGD MGD 8,173 lbs/day 4,674 lbs/day 451 lbs/day 140 lbs/day City of Paynesville, Minnesota M Page 6 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

12 SECTION 3 EXISTING FACILITY A. GENERAL The existing facility for the City of Paynesville, Minnesota is located NE of the City along County Road 33. The legal location of the facility is the NW ¼ of the NW ¼ of Section 10, T122 N, R32W and the SW ¼ of the SW ¼ of Section 3, T-122N, R-32W, Stearns County, Minnesota. B. EXISTING FACILTY ASSESMENT The existing facility consists of a main lift station, a grit chamber, an aerated pond, a 7-cell stabilization pond system, micro-screen, and a storm water retention pond. The facility also consists of 11 spray irrigation sites, a ground water monitoring well network consisting of 6 monitoring wells and a drain tile system under spray sites #2, 3,6,11 and 12. Paynesville s existing facility was previously renovated in The facility was constructed with a seasonal discharge by means of spray irrigation. The design flow for the facility is 887,000 gallons per day (gpd). The 5-day biochemical oxygen demand design concentration is 676 mg/l (5,000 lbs/day). The pond system consists of one 1.65 acre aerated pond, three primary cells measuring 36 acres, 36 acres, 40 acres respectively; two intermediate cells measuring 7.25 acres each; and two secondary cells measuring 14 acres and 24 acres respectively. The pond system provides a total detention time of 245 days at design flow. The retention basin is approximately 9 acres in size. The spray irrigation sites encompass a total of 1,139 acres. Appendix B presents flow schematic and aerial views of the existing wastewater treatment facility. C. EXISTING FLOWS AND LOADINGS The flows and loadings from January 2004 to June 2008 to the existing facility are summarized in Figure 3.1. Historical flows and loadings to the facility from January 2004 to June 2008 are tabulated in Appendix B. The average flow to the facility over the given time was 667,000 gallons per day and the maximum flow experienced was 892,000 gpd which occurred during the month of June The average CBOD 5 loading to the City of Paynesville, Minnesota M Page 7 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

13 existing facility is 5,519 lbs/day, which is greater than the design loading of 5,000 lbs/day. D. CONDITION OF EXISTING FACILITY The existing facility was expanded in The existing components and equipment are in moderate condition. The existing facilities are currently being overloaded with organics and need to be upgraded or expanded. E. 100 YEAR FLOOD PLAIN According to MPCA regulations, all structures, equipment and electrical controls must be protected to above the 100-Year Flood Plain. Reviews of the Federal Emergency Management Agency (FEMA) Flood Maps indicate that the City s wastewater treatment facility is not located within the 100 Year Flood Plain. F. ELECTRICAL SERVICE AND POWER DISTRIBUTION The electrical service at the wastewater treatment facility is satisfactory at this time. If there are any large-scale changes to the electrical load, the electrical service may need to be upgraded. G. WASTEWATER ORDINANCE AND USER RATE EVALUATION The City's existing ordinances regarding the water and wastewater user rate system have been reviewed. The ordinances appear to cover all of the major areas that are required by the MPCA. Since the City may be pursuing financing for wastewater treatment improvements, the MPCA will perform a review of the wastewater ordinances for general compliance with funding requirements. City of Paynesville, Minnesota M Page 8 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

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15 SECTION 4 FACILITIES SITING A. GENERAL An important consideration in wastewater treatment plant design is to develop a site plan that is both functional and aesthetically pleasing. This section presents the plant site considerations and the discharge locations. B. ADDITIONAL LAND ACQUISITION Minnesota Trunk Highway 23 currently enters the City of Paynesville on the northeast side of the City and exits on the southwest side of the City. The Minnesota Department of Transportation (MNDOT) is planning the future expansion of Trunk Highway 23 near the existing wastewater treatment facility site, bypassing the community. The expansion of Trunk Highway 23 will encroach on the existing spray irrigation fields. Additional spray irrigation sites will need to be added to replace the sites that will be lost. Construction of Rapid Infiltration Basins (RIBs) on existing City property is also an option that will be evaluated to replace the lost capacity. The proposed aerated pond and mechanical treatment facility have been preliminarily sited near the existing aerated pond. It will be necessary to acquire additional property. Advantages to this site are the proximity of power; minimize excess pumping and that the surrounding land owners are accustom to a wastewater facility at this location. Biosolids holding and treatment is preliminarily sited north of the existing stabilization pond site. The site is as far from the community as possible and is not affected by the proposed T.H. 23 alignment and the City currently owns the property. C. FACILITY SITE Improvements discussed in this report are assumed to be located on existing pond sites or directly adjacent to the existing facility or in the City owned irrigation fields. The proposed site for the proposed RIB addition to the wastewater treatment facility is located to the south of the existing spray irrigation sites Nos. 14 and Nos. 17. City of Paynesville, Minnesota M Page 10 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

16 SECTION 5 TREATMENT ALTERNATIVES A. GENERAL This section describes the treatment process and design criteria for the wastewater treatment improvements. The treatment process and design criteria are based on the design wastewater flows and loadings as discussed in Section 2 of this report. The design philosophy for the wastewater treatment facilities is to provide high quality treatment, ease of operation, and low maintenance cost as well as flexibility for future expansion. B. EVALUATION CRITERIA The major treatment processes required to effectively treat the wastewater and dispose of the wastewater will be evaluated separately. To aid in the evaluation of these processes, the following criteria will be used: The hydraulic capacity of each process will be determined using the 2030 design wastewater flow discussed in previous sections of this report. Consideration regarding size of each process will be evaluated using average flows and maximum flows for the entire design life of the facility. The maximum organic loadings for the wastewater facility were also developed in previous sections of this report. The size of each process will be determined using the average and maximum month loading for the design year. Several of the processes described here include additional sludge generation. With the construction of secondary treatment processes such as activated sludge reactors and final clarifiers, it may be necessary to construct biosolids handling facilities. The costs associated with handling the biosolids are included in the operation and maintenance evaluation, and the storage facilities are included in the capital improvements. City of Paynesville, Minnesota M Page 11 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

17 C. WASTEWATER TREATMENT OPTIONS 1. General The wastewater treatment facility processes were evaluated using the criteria from the Ten States Standards. The existing aeration pond is designed to treat approximately 2,700 ppd of CBOD 5 and approximately 55% of the influent flows. The expansion to design flows and loadings for 2030 exceeds the treatment capability of the pond. The following alternatives outline the several possible process flow patterns to meet the effluent standards. 2. Alternative No. 1 - Construct a Parallel Aeration Cell The construction of an additional aerated pond is an option for treating the additional CBOD 5 load to the Paynesville Wastewater Treatment Facility. The design parameters are similar to the construction of the existing aerated pond and would be operated similarly as shown in Table 5.1. The new aerated pond will be 3.25 acres. The two ponds could be operated in parallel or in series. The new pond will be constructed with earthen dikes and aeration headers on the floor of the pond. The combination of the two ponds would be designed to treat the entire raw wastewater flow. The flow to the secondary ponds is designed to have a CBOD 5 concentration of 250 mg/l. The stabilization ponds are adequately sized to treat the remaining CBOD 5 for land application. This option requires acquisition of additional acreage for construction of a new aerated pond. The process flow diagram for this alternative is given in Figure 5.1. Table 5.1 Additional Aeration Pond City of Paynesville, Minnesota Parameter Value Proposed /Existing Aeration Pond Depth 14 feet Area 3.25 acres Volume 1,981,980 ft 3 City of Paynesville, Minnesota M Page 12 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

18 City of Paynesville, Minnesota M Page 13 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

19 This option achieves treatment, but may generate excess solids in the existing pond system. The excess solids will reduce storage capacity and be an odor source. The City and industries are aware of this risk and believe if an approach like this is taken it should be to maximize the existing system and limit the land to the wastewater treatment plant. This alternative will not be given additional consideration in this report. 3. Alternative No. 2 Maximize the Existing System The existing aeration pond is limited by the available oxygen transfer to the water in the system. The existing facility capacity is presented in Table 5.2. This option is to modify the aerated pond to maximize stabilization of CBOD 5 prior to flowing to the pond system. The pond system capacity is also proposed to be maximized. A high intensity section of the aerated pond will be created with a curtain wall and modification of the aeration layout. This area will be the influent portion of the pond to quickly stabilize soluble CBOD 5. Wastewater will then flow to a second stage of the conventional mixed aerated pond. The aerated water would then flow to the existing stabilization pond system for further treatment. Solids stabilization and separation would be completed in the ponds. The residual solids may require periodic dredging to prevent accumulation in the primary cells. The owner will plan to clean the solids out every 3 years. The frequent cleaning may lead to liner integrity issues. Replacement of the liner should be anticipated every 15 years and considered part of the operation and maintenance costs. This option will be considered further. City of Paynesville, Minnesota M Page 14 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

20 Table 5.2 Existing System Maximum Capacity City of Paynesville, Minnesota Average Flow MGD CBOD ppd TSS 4674 ppd TN 450 ppd TP 140 ppd 4. Alternative No. 3 Activated Sludge The most efficient way to handle CBOD 5 load as proposed for the City of Paynesville is activated sludge. It is necessary to separate the solids from the liquids to introduce the activated sludge flow regiment. The most straight forward design is extended aeration given the resistance to shock loading and the ability to carry a high solids inventory. This will allow the City to confidently treat the City flows. To separate the solids and liquids a final clarifier is necessary. Clarified effluent will be designed for 10 mg/l CBOD 5, 20 mg/l TSS and 5.0 mg/l NH 4 during winter operation. One clarifier will be provided. The system will have the pond system as back up should a mechanical failure occur. The water can be held in the ponds until it meets effluent limits. The existing main lift station and aerated pond will remain in service. The main lift station is adequate for the flows and is in good condition. The 7.53 million gallon aeration pond is adequate to provide the necessary aeration volume and will be reused to minimize the capital cost of the alternative. Additional aeration capacity is necessary and the blower system will be expanded. Pumping for RAS and WAS will also be provided. The modified activated sludge system flow schematic is presented in Figure 5.2. Biosolids handling will be discussed later in this section. City of Paynesville, Minnesota M Page 15 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

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22 5. Alternative No. 4 - Construct New Mechanical Treatment Facility This alternative involves the construction of an activated sludge facility near the city s existing facility, while utilizing some components of the existing facility. The activated sludge facility would treat the flow from the entire city and discharge it to existing ponds. Figure 5.3 shows a process flow diagram for this alternative. Emergency generators would be provided for both the wastewater treatment facility and the main lift station. Flow measurement is proposed with a Parshall flume at the head of the wastewater treatment facility. The following is a brief description of the individual treatment components: i. Screenings A mechanical bar screen would provide removal of sticks, rags and other large materials. These are removed to protect subsequent process equipment. As the bar screen removes items in the wastewater, the head loss ahead of the screen will increase until a float switch comes on and allows the bar screen to clean itself. The dewatered screenings would be loaded into trash containers and hauled away. ii. Grit Removal Following screening, flow would pass through the grit removal facilities that remove sand, grit and other materials that reduce the volume of the aeration basin and cause premature wearing of pumps and equipment. A mechanical vortex grit removal unit would be utilized for this process. City of Paynesville, Minnesota M Page 17 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

23 City of Paynesville, Minnesota M Page 18 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

24 iii. Activated Sludge (Extended Aeration) Extended aeration plants are characterized by the following: introduction of raw wastewater directly to the aeration basin; long-term aeration; high mixed liquor suspended solids concentration (MLSS); high return activated sludge (RAS) rate; and low sludge wastage. The particular advantage of using a long retention time (usually 18 to 24 hours in the aeration basin) is that the design permits the plant to operate effectively even though flow and strength vary widely and allow biological organisms to consume the organic matter and nitrify the ammonia. Since activated sludge undergoes aerobic digestion in the aeration basin, more oxygen is required in the basin than is required in conventional single stage systems. To avoid excessively high MLSS and effluent solid losses, periodic solid wasting is required. The accumulation of inert solids actually controls the rate of sludge wasting. The extended aeration basin will be designed with a maximum solids retention time (SRT) of 25 days, organic loading between lb/day/1000 cubic feet of basin volume, a food to mass (F/M) ratio between lbs CBOD 5 /lbs MLVSS/D, MLSS between 2,500-3,500 mg/l and 1.5 lbs O 2 /lbs of peak hourly CBOD 5. iv. Final Clarifier Activated sludge final clarifier must be designed to meet thickening as well as solid separation requirements. Since the rate of recirculation of return sludge from the final clarifier to the aeration basin is quite high, the surface settling rate and weir overflow rates should not exceed 900 gallons per day per square foot (gpd/ft 2 ) and 20,000 gallons per day per linear foot, respectively. Using these surface settling rates and weir overflow rates, problems with sludge loading density currents, inlet hydraulic turbulence and occasional poor sludge settle ability will be minimized. Solids loading rates are also maintained at a 35 lb/day/ft 2 maximum. This is the determining factor in sizing Paynesville s clarifiers. A scum collection and removal facility will be provided as well as sludge suction withdrawal in order to minimize effects of nitrification in the final clarifier. The solids, Return Activated Sludge (RAS), are pumped back to the City of Paynesville, Minnesota M Page 19 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

25 aeration basin to maintain the high concentration of activated sludge. A portion of solids or Waste Activated Sludge (WAS) must be wasted to maintain a constant concentration of biosolids. The rate of RAS, according to Ten-States Standards, is % of design average flow. A submersible automatic pump station will be provided for RAS and WAS. The WAS rate is % of design average flow. Flow measuring, sampling and control equipment will be provided. Typically redundant clarifiers are necessary in an activated sludge process. For the City of Paynesville, a second clarifier is not required because the pond system will provide backup prior to discharge. Therefore, one clarifier capable of handling 100 % of loadings at peak hourly wet weather (PHWW) will be provided. Due to heat loss in an extended aeration system, covers for the final clarifier should be provided in order to avoid freeze-up of the scum collection mechanism. Effluent from this system is designed to be approximately 10 mg/l CBOD 5, 30 mg/l TSS and a portion of the ammonia will be nitrified to nitrate and nitrite. This effluent meets the effluent standards to be spray irrigated without the need for final filters and disinfection. Effluent standards to the North Fork of the Crow River would include an ammonia and phosphorus limit. The CBOD 5 and TSS limits would likely be 5 mg/l; confirmation of this would need to be done by completing the NPDES permit process. Currently, the MPCA is not granting new discharges to the watershed due to ongoing legal proceedings. Table 5.3 shows the sizes of the major unit processes for this alternative. City of Paynesville, Minnesota M Page 20 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

26 Table 5.3 Extended Aeration Design Criteria City of Paynesville, Minnesota Parameter Design Value Activated Sludge Tanks Total Basin Volume 4.10 MG Number 3 Basin Volume (each) 183,600 ft 3 Basin Dimension (each) Length 135 ft Width 85 ft Depth 16 ft Blowers Units 4 (3 operating) SCFM (each) 4000 Final Clarifiers Number 1 Diameter 40 ft Recycle Pumps Units 2 Horsepower (each) 5 HP Sludge Storage Existing Volume 7.53 MG Sludge Rate (2% solids) 22,376 gpd Storage Provided (2% solids) 336 days Sludge Rate (3% solids) 14,917 gpd Storage Provided (3% solids) 504 days City of Paynesville, Minnesota M Page 21 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

27 D. BIOSOLIDS TREATMENT & STORAGE Alternatives 2, 3 and 4 require biosolids handling and treatment in addition to the liquid process. Wastewater biosolids, or sludge, consists of solids removed from raw wastewater and biosolids generated in the treatment process. The proper handling and disposal of biosolids is an important aspect of wastewater treatment. A method that is economical and acceptable from health, environmental and aesthetic points of view must be selected. The most commonly practiced disposal method is land application. Prior to land application, the biosolids need to be stabilized to meet fecal coliform and vector attraction regulations. The following are two common methods of treatment that will be evaluated. 1. Cold Storage Cold storage consists of biosolids treatment using gravity thickening and cold aeration in buried concrete tanks. The sludge will be stored in a tank with a 180- day minimum capacity of 2.5% solids (TS). At the end of the storage period, the sludge will be applied to agricultural land. It is expected that the City would contract with a licensed applicator for sludge hauling and application. The fertilizing elements in the sludge would be available for plant growth, and the humus in the sludge act as a soil conditioner. Application to agricultural land would occur during periods when the crops are not growing or otherwise on property that was temporarily out of crop production. The facility would test for fecal coliform to meet the pathogen reduction requirements prior to land application. The vector attraction reduction would be expected to be met by injection of the solids, or if injection is not available, testing the oxygen uptake. The storage tank would be designed to allow lime treatment of the solids if the above method did not work. The existing aerated pond could be used for sludge storage. This pond has a volume of 7.53 MG. The aerated pond provides required storage volume for all City of Paynesville, Minnesota M Page 22 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

28 three design conditions. The summary of sludge production rate and storage provided is given in Table 5.3. Two options will be evaluated for cold storage. The first option is to use the existing aerated pond for an aeration basin and construct a new tank for storage. The second option is to construct a new aeration basin and use the existing pond for storage. 2. Reed Beds Reed beds are a three stage biosolids handling process. The first stage is similar to cold storage and consists of a 10 day holding tank. The second stage is reed bed application and storage. The third stage is reed bed excavation and land application. The layout for Paynesville includes using the existing facility for aeration and constructing a new 10 day tank and reed beds. The excavation and land application will be contracted out by the City when it is necessary. The 10 day holding tank is proposed to be 405,000 gallons total. The tank will be divided into three 135,000 gallon aerated cells. The primary goal in this stage is to gravity thickening the biosolids and secondary benefit is to reduce the volatile solids. The aeration process starts the digestion process and promotes volatile solids reduction. When the air is turned off the solids settle in the cell and the clear water is decanted off the tank and returned to the liquid process for further treatment. By repeating this process a solids content of 2.5% can be reached, which will maximize the use of the reed beds. The reed beds proposed are 24 cells, each 50 feet by 150 feet, with a total area of 180,000 square feet. The solids are applied to the reed beds in layers 3 to 5 inches thick. The reeds favor the wet conditions and high nutrient area in the biosolids. Natural processes of plant uptake and time dewatering improves the quality of the biosolids. Total depth in the bed can reach 5 feet and is estimated to take 4 to 10 years depending on influent sludge quality. City of Paynesville, Minnesota M Page 23 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

29 Once a bed is full, the reeds are cut and bailed. The sludge is hauled out and land applied or land filled. Final solids content can range from 30 to 50% solids and greatly reduces the volume that needs to be land applied compared to cold storage. E. EFFLUENT DISCHARGE OPTIONS 1. Spray Irrigation The existing facility is permitted to spray irrigate to 1,139 acres. The expansion of Trunk Highway 23 will encroach on the existing spray irrigation fields. The spray irrigation will need to be expanded to meet the needs of the additional projected flow in addition to replacing the area taken for the highway bypass. A total of 1,139 acres will be needed for the influent flow. If spray irrigation is used as the exclusive disposal method and the application rate remains the same. Table 5.3 is a summary of the spray irrigation and the impact of the Trunk Highway 23 Bypass. Table 5.4 Spray Irrigation Summary City of Paynesville, Minnesota Design Condition Existing Spray Irrigation Field 1,139 Acres Existing Spray Irrigation Rate 780 gpd/acres Inches per year Application 10 Inches Projected Impact of T.H Acres Usable Existing Spray irrigation Field 879 Acres Requires Land for Projected Flow 1,139 Acres Additional Land Required for Spray Irrigation 260 Acres Excess Flow Associated with Land Area 0. mgd 2. Rapid Infiltration Rapid Infiltration Basins (RIBs) are seepage ponds that are designed to discharge effluent to ground water via sand and gravel layers in the soil. RIBs are designed to discharge 150 to 600 gpm/ft 2 per year and can be an effective way to discharge effluent without having a surface water discharge. The effectiveness of each RIB is site specific and further investigation is required to determine final design for City of Paynesville, Minnesota M Page 24 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

30 application rates. For the purpose of this report, an application rate of 375 gpm/ft 2 per year was used based on the Stearns County Soils Index and tests summarized by American Engineering Testing in a report included in Appendix A. The construction route of Trunk Highway 23 will encroach approximately 260 acres of the existing spray irrigation sites. The city needs to replace this discharge capacity to allow municipal and industrial growth within the community. Construction of three 5.8-acre each RIBs for the influent flow will be required to will replace the lost capacity of spray irrigation field, handle the addition of flow, provide redundancy for disposal, and allow for the rotation of RIBs. A 270-day per year application schedule is used for the RIBs design and to prevent issues with frozen application. Table 5.4 shows the required area for the construction of RIBs to discharge the design flow for all of the design conditions. This area is in conjunction with the existing spray irrigation fields that will not be affected by the Trunk Highway 23 Bypass. Table 5.5 Rapid Infiltration Summary City of Paynesville, Minnesota Design Condition Excess Flow Associated with Land Area mgd Annual Volume for Disposal MG Application Rate 375 gpy/ft 2 Required Land 8.60 Acres Recommended Construction acre basins Paynesville owns property that is suitable for Rapid Infiltration Basins. Extension of the forcemain that services the northern spay irrigation fields is necessary to feed the proposed RIBs. Associated improvements include a new dedicated effluent lift station pump, due to different pumping conditions than the spray irrigation applicators, and necessary electrical improvements in the existing effluent lift station. The risks of water mounding and the unknown soil conditions have led the City to discount this disposal option. City of Paynesville, Minnesota M Page 25 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

31 3. Surface Water Discharge The most common method of effluent disposal in the State of Minnesota is to discharge the effluent to a receiving stream. The City of Paynesville Wastewater Treatment Facility is adjacent to the North Fork of the Crow River. The storm water retention pond has an outfall structure that discharges to the North Fork of the Crow River; however, there is no permitted discharge of effluent to the North Fork of the Crow River. Other facilities on the North Fork of the Crow River have requested new discharges in the past several years. The MPCA has approved several discharges with stringent effluent limits. However, due the impairment of Lake Pepin on the Mississippi River for phosphorous and having no Total Maximum Daily Load (TMDL) in place, the court system has denied the allocation of a phosphorous mass discharge to any new facility in accordance with the Clean Water Act. Therefore, Paynesville cannot be granted a surface water discharge permit until a TMDL is completed, which is currently scheduled for completion in A surface water discharge is not a viable option for the City of Paynesville. F. ODOR CONTROL With the expansion of State Highway 23 along a corridor north of the community, it is likely growth for the City of Paynesville will continue that direction and begin to encroach on the existing wastewater treatment plant location. Odor control becomes an issue any time wastewater and the community are in close proximity and this will soon be the case in the City of Paynesville. The primary and most offensive odors occur when an aerated pond treatment facility, such as Paynesville s Wastewater Treatment Facility, is organically overloaded and the treatment process becomes anaerobic. The anaerobic conditions generate methane and hydrogen sulfate and can be best described as rotten egg odors. Collecting and treating the potentially offensive gases is possible, but would involve constructing a roof or membrane cover for the aerated pond and constructing a biofilter large enough to handle City of Paynesville, Minnesota M Page 26 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

32 all the air off gassing from the system. The best protection against odor is constructing a facility that is capable of handling peak flows and loads and preventing anaerobic conditions. City of Paynesville, Minnesota M Page 27 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

33 SECTION 6 COST CONSIDERATIONS A. GENERAL Estimated costs have been prepared for all the alternatives evaluated in Section 5. Construction or capital costs and operation, maintenance and replacement (OM & R) costs are presented in this section. In determining the cost effectiveness of the various alternatives, costs will be presented in terms of equivalent annual costs. The interest rate and time period utilized in the cost-effective analysis is 5.5% and 20 years respectively. B. ESTIMATED CONSTRUCTION COSTS In order to prepare the preliminary construction cost estimates presented herein, various material and equipment manufacturers and suppliers were contacted. Published and unpublished data on costs for similar kinds of construction were also utilized. The estimated costs are for March Increases in construction costs due to inflation are not taken into account. The cost estimates presented here are meant to be used as a guideline in the decision making process. More refined cost estimates for the selected alternative will be available later during the design of plans and specifications. Capital costs assume spray irrigation as the disposal option. Negotiation with Mn/DOT to replace disturbed or displaced areas is underway. City of Paynesville, Minnesota M Page 28 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

34 Table 6.1 Alternative No. 1 Construct a Parallel Aerated Pond City of Paynesville, Minnesota Item Estimated Cost Mobilization, Bonds & Insurance $150,000 Site Work $500,000 Aeration Basin (with biological P removal) $300,000 Aeration System $300,000 Control Structure $20,000 Blowers $110,000 Blower Building Modifications $250,000 Process Piping, Valves & Fittings $300,000 Electrical & Control $180,000 Subtotal $2,110,000 10% Construction Contingency $211,000 Total Estimated Project Cost $2,321,000 15% Engineering, Administrative and Legal $316,500 Land (10 $5,000/acre) $50,000 Total Cost $2,687,500 Table 6.2 Alternative No. 2 Maximize the Existing System City of Paynesville, Minnesota Item Estimated Cost Mobilization, Bonds & Insurance $50,000 Site Work $150,000 Aeration Basin (with Curtain) $200,000 Aeration System (with Blowers) $140,000 Process Piping $150,000 Blower Building Modifications $150,000 Electrical & Control $100,000 Primary Pond Mixing $600,000 Subtotal $1,540,000 10% Construction Contingency $154,000 Total Estimated Project Cost $1,694,000 15% Engineering, Administrative and Legal $254,000 Total Cost $1,948,000 City of Paynesville, Minnesota M Page 29 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

35 Table 6.3 Alternative No. 3 Activated Sludge City of Paynesville, Minnesota Item Estimated Cost Mobilization, Bonds & Insurance $385,000 Site Work $150,000 Control Structure $40,000 Final Clarifier (with Cover) $300,000 Sludge Pumping (RAS & WAS) $100,000 Scum Manhole $40,000 Process Piping $200,000 Electrical & Control $200,000 Sludge Storage $600,000 Reed Beds $2,600,000 Subtotal $4,615,000 10% Construction Contingency $460,000 Total Estimated Project Cost $5,075,000 15% Engineering, Administrative and Legal $760,000 Land (10 $5,000/acre) $40,000 Total Cost $5,875,500 City of Paynesville, Minnesota M Page 30 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

36 Table 6.4 Alternative No. 4 Construct New Mechanical Treatment Facility City of Paynesville, Minnesota Item Estimated Cost Mobilization, Bonds & Insurance $500,000 Site Work $500,000 Preliminary Treatment Facility $600,000 Aeration Basin (with Biological P Removal) $2,500,000 Aeration System $300,000 Blowers $200,000 Control Structures $50,000 Clarifier (with Cover) $300,000 Sludge Pumping (RAS + Sludge Transfer) $100,000 Scum Manhole $40,000 Control Building $350,000 Lab & Safety Equipment $10,000 Samplers $15,000 Process Piping, Valves & Fittings $600,000 Electrical & Control $800,000 HVAC $150,000 Generator $300,000 Sludge Treatment & Storage Modification $200,000 Subtotal $7,515,000 10% Construction Contingency $751,500 Total Estimated Project Cost $8,266,500 15% Engineering, Administrative and Legal $1,127,250 Land (10 $5,000/acre) $40,000 Total Cost $9,433,750 City of Paynesville, Minnesota M Page 31 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

37 C. ESTIMATED OPERATION, MAINTENANCE AND REPLACEMENT COSTS Item The OM & R costs are presented in Table 6.5 for the treatment alternatives. The costs associated with OM &R represents a significant portion of the total annual cost. These costs are presented as increased costs above the existing annual costs and are not total annual costs. Table 6.5 Operation, Maintenance and Replacement Costs City of Paynesville, Minnesota Alternative Alternative Alternative Alternative No. 4 No. 1 No. 2 No. 3 Salaries and Benefits $25,000 $50,000 $75,000 $100,000 Utilities $100,000 $150,000 $500,000 $525,000 Biosolids Handling & Disposal $25,000 $100,000 $200,000 $225,000 Maintenance and Replacement $0 $800,000 1 $150,000 $175,000 Total Cost $150,000 $1,100,000 $925,000 $1,025,000 1: Annualized pond liner replacement cost. D. ANNUAL EQUIVALENT COSTS Table 6.6 summarizes the total increased cost for each treatment alternative. The initial capital costs were annualized with a 5.5% interest rate and a 20-year loan. Item Table 6.6 Annual Cost Summary City of Paynesville, Minnesota Alternative Alternative Alternative Alternative No. 4 No. 1 No. 2 No. 3 Capital Cost $2,687,500 $1,948,000 $5,875,500 $9,433,750 Annualized Capital Cost (1) $222,000 $163,000 $492,000 $779,000 OM & R $150,000 $1,100,000 $925,000 $1,025,000 Total Cost $372,000 $1,263,000 $1,417,000 $1,804,000 (1) Assumes financing rate of 5.5% interest for 20 years. City of Paynesville, Minnesota M Page 32 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

38 SECTION 7 RECOMMENDATION & IMPLEMENTATION SCHEDULE A. RECOMMENDATION The City of Paynesville has reviewed all the options outlined in this report. The best fit for the community is to construct Alternative No. 3 with Reed Beds and Spray Irrigation. This option handles the full design load from the community, actively manages the biosolids in the process, produces high quality effluent and is flexible to handle future growth in the community. B. IMMPLEMENATION SCHEDULE City Review and Approve Facility Plan February 2009 MPCA Approval of Facility Plan March 2009 Design Improvements April 2009 to September 2009 MPCA Review Plans and Specification October 2009 to December 2009 Advertise for Bid January 2010 to February 2010 Receive Bids/ Awards March 2010 Construction April 2010 to August 2011 City of Paynesville, Minnesota M Page 33 Wastewater Treatment Facility Plan Prepared by Bolton & Menk, Inc.

39 APPENDIX A NPDES Permit

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44 APPENDIX B Existing Facility Details

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54 APPENDIX D Presentation Materials, Public Comments and Resolution

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