13.B.
City Council Meeting - FINAL
- Meeting Date:
- 02/18/2020
- Co-Submitter:
- Brad Hill
- From:
- Ryan Roberts, Water Services Engineering Manager
Information
TITLE
Discussion on the Wastewater Biosolids Master Plan prepared by Carollo Engineers
STAFF RECOMMENDED ACTION:
Discussion with City Council on the Biosolids Master Plan Report and its recommendations.
EXECUTIVE SUMMARY:
Water Services began conducting a Biosolids Master Plan (BMP) in November 2017, to provide a roadmap and framework for sustainable and cost-effective biosolids management. The BMP Report evaluated the City of Flagstaff's solids handling facilities, studied solids treatment alternatives and evaluated the impacts on the liquid treatment process due to increased wastewater strength entering the plant. Wildcat Hill Water Reclamation Plant was identified to be nearing operational capacity limits on biosolids treatment/handling and unexpectedly, liquids treatment. The upgrades needed at this facility range from immediate (solids handling), within the next four years (liquid capacity) and within the next five to 10 years (solids dewatering and drying). The BMP Report also identified needs at the Rio de Flag WRP and contains immediate recommendations for future capital improvements at both plants. The next step is to start planning for and design upgrades to these facilities. Carollo Engineers, who conducted the Biosolids Master Plan Report, will be presenting the findings and recommendations to the Council. Attached is an Executive Summary of the BMP Report for Council and public review.
INFORMATION:
The City of Flagstaff has two separate, but operationally connected, water reclamation plants (WRP); the Rio De Flag WRP (RDFWRP) located in the center portion of the City; and the Wildcat Hill WRP (WHWRP) in the far northeast portion of the City.
The Wildcat Hill WRP treats wastewater solids by first thickening and then processing them in anaerobic digesters that destroy harmful bacteria. The solids are then sent to the Solids Storage Basins (SSBs) and temporary Geotube bags prior to disposal in the Dedicated Land Disposal (DLD) area. Biosolids may be described as a nutrient-rich material that results from the biological treatment of municipal wastewater and can help build healthy, productive soils, and increase vegetation growth when applied to land. Biosolids can be used as a key ingredient in the fabrication of high-quality soil products. The Wildcat Hill WRP is permitted at six (6) million gallons per day (MGD) Maximum Monthly Average Day Flow (MMADF). This plant serves as our regional solids handling facility designed to produce Class B quality biosolids, treating biosolids produced at both Rio De Flag WRP and Wildcat Hill WRP facilities. Because of their relatively high-water content, the biosolids are primarily disposed of at the DLD site. Landfill disposal requires further dewatering to be a viable option.
One of the unexpected findings of the study was Carollo's identification that Wildcat Hill's liquid treatment will reach capacity within approximately four (4) years. Wildcat Hill WRP's liquid capacity was designed to handle six (6) MGD, and Rio de Flag's WRP was designed to handle four (4) MGD for a combined total of ten (10) MGD. Based on Carollo's analysis, due to the increasing strength of the wastewater entering the plant, the total capacity for both plants combined under Carollo's analysis is estimated to treat only 6.3 MGD. Increased wastewater strength is due, in part, to less water entering the sewer system relative to the total flow. One factor that has contributed to this phenomenon is our successful water conservation program. Carollo suggested two options for the City to consider in order to solve this issue; #1) divert wastewater flows from Wildcat Hill WRP to the Rio de Flag WRP within the four (4) year timeframe; and #2) remove residual solids from the Rio de Flag WRP and haul directly to Wildcat Hill WRP, most likely via truck.
The Rio De Flag WRP is currently permitted as a four (4) million gallon per day (MGD) facility, based on Maximum Monthly Average Day Flow (MMADF). The Rio De Flag plant produces Class A+ reclaimed water and has no digesters or solids handling capabilities at the current time. This plant currently treats 2 MGD of wastewater flow.
The BMP Report discusses and recommends ways to transform the biosolids produced at Wildcat Hill WRP into end products that may be beneficially reused and/or disposed of at the DLD or landfill, in a cost-effective and environmentally friendly manner.
The BMP Report addresses Biosolids produced at both the Rio De Flag WRP and the Wildcat Hill WRP, as well as liquids capacity, and provides a prioritized list of the major Capital Improvement Project needs that have resulted from the different evaluations conducted in this Biosolids Master Plan (BMP).
The result of this Biosolids Master Plan was the development of a fiscally responsible and implementable 10-year Capital Improvement Plan for wastewater improvements at the Rio De Flag WRP and Wildcat Hill WRP. The Biosolids projects that Carollo recommends include the expanding digester capacity by adding two more, followed by new mechanical dewatering and solar drying facilities at the Wildcat Hill WRP. To address the upcoming liquids capacity limitation identified at Wildcat Hill, Carollo provided two recommendations for the City to consider including diverting wastewater flow from Wildcat Hill WRP to the Rio de Flag WRP. The projects shown below form the basis of the 10-year Biosolids Master Plan-related Capital Improvements.
During the course of this study, Water Services reached out to inform the public through both Water Commission and public meetings to provide updates on the status and receive input on ideas and on capital projects, and to discuss future solids handling options.
The full report is quite extensive and too lengthy to adequately cover as an agenda item. Carollo Engineers' project team will present an overview of the executive summary and discuss their final report and recommendations with the Council.
The Wildcat Hill WRP treats wastewater solids by first thickening and then processing them in anaerobic digesters that destroy harmful bacteria. The solids are then sent to the Solids Storage Basins (SSBs) and temporary Geotube bags prior to disposal in the Dedicated Land Disposal (DLD) area. Biosolids may be described as a nutrient-rich material that results from the biological treatment of municipal wastewater and can help build healthy, productive soils, and increase vegetation growth when applied to land. Biosolids can be used as a key ingredient in the fabrication of high-quality soil products. The Wildcat Hill WRP is permitted at six (6) million gallons per day (MGD) Maximum Monthly Average Day Flow (MMADF). This plant serves as our regional solids handling facility designed to produce Class B quality biosolids, treating biosolids produced at both Rio De Flag WRP and Wildcat Hill WRP facilities. Because of their relatively high-water content, the biosolids are primarily disposed of at the DLD site. Landfill disposal requires further dewatering to be a viable option.
One of the unexpected findings of the study was Carollo's identification that Wildcat Hill's liquid treatment will reach capacity within approximately four (4) years. Wildcat Hill WRP's liquid capacity was designed to handle six (6) MGD, and Rio de Flag's WRP was designed to handle four (4) MGD for a combined total of ten (10) MGD. Based on Carollo's analysis, due to the increasing strength of the wastewater entering the plant, the total capacity for both plants combined under Carollo's analysis is estimated to treat only 6.3 MGD. Increased wastewater strength is due, in part, to less water entering the sewer system relative to the total flow. One factor that has contributed to this phenomenon is our successful water conservation program. Carollo suggested two options for the City to consider in order to solve this issue; #1) divert wastewater flows from Wildcat Hill WRP to the Rio de Flag WRP within the four (4) year timeframe; and #2) remove residual solids from the Rio de Flag WRP and haul directly to Wildcat Hill WRP, most likely via truck.
The Rio De Flag WRP is currently permitted as a four (4) million gallon per day (MGD) facility, based on Maximum Monthly Average Day Flow (MMADF). The Rio De Flag plant produces Class A+ reclaimed water and has no digesters or solids handling capabilities at the current time. This plant currently treats 2 MGD of wastewater flow.
The BMP Report discusses and recommends ways to transform the biosolids produced at Wildcat Hill WRP into end products that may be beneficially reused and/or disposed of at the DLD or landfill, in a cost-effective and environmentally friendly manner.
The BMP Report addresses Biosolids produced at both the Rio De Flag WRP and the Wildcat Hill WRP, as well as liquids capacity, and provides a prioritized list of the major Capital Improvement Project needs that have resulted from the different evaluations conducted in this Biosolids Master Plan (BMP).
The result of this Biosolids Master Plan was the development of a fiscally responsible and implementable 10-year Capital Improvement Plan for wastewater improvements at the Rio De Flag WRP and Wildcat Hill WRP. The Biosolids projects that Carollo recommends include the expanding digester capacity by adding two more, followed by new mechanical dewatering and solar drying facilities at the Wildcat Hill WRP. To address the upcoming liquids capacity limitation identified at Wildcat Hill, Carollo provided two recommendations for the City to consider including diverting wastewater flow from Wildcat Hill WRP to the Rio de Flag WRP. The projects shown below form the basis of the 10-year Biosolids Master Plan-related Capital Improvements.
| Priority No. | Project Description | Timing |
|---|---|---|
| 1 | Digester capacity expansion at Wildcat Hill WRP | Immediate |
| 2 | Removal and Replacement needs at WHWRP & RDFWRP | Immediate |
| 3 | Additional flows/diversion to Rio De Flag WRP | By 2024 |
| 4 | Mechanical dewatering and solar drying at WHWRP | 2025-30 |
During the course of this study, Water Services reached out to inform the public through both Water Commission and public meetings to provide updates on the status and receive input on ideas and on capital projects, and to discuss future solids handling options.
The full report is quite extensive and too lengthy to adequately cover as an agenda item. Carollo Engineers' project team will present an overview of the executive summary and discuss their final report and recommendations with the Council.