Page 130 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.34 - Davidson Dr. Existing and Proposed Simplified
0 of 291 prings, Arkansas | Crist Engineers, Inc. d Process Flow Diagram – Hydraulic Improvements – Area 3
Page 131 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. As demonstrated in the above figure, during normal operation (non-high flow events), clarified effluent near (up to 25.8 MGD) and long-terms (up to 53.3 MGD) will be conveyed to the tertiary filter’s junction box. During normal operation the tertiary filters will provide exclusive tertiary treatment of clarified secondary effluent. However, in the near-term, during normal high flow events (between 25.8 and 48 MGD), the tertiary filter junction box will provide as a location for clarified secondary effluent and peak flow to aggregate before being conveyed to the tertiary filters. During this operational scenario, the tertiary filters will process the aggregated flow (combination of secondary treated and screened/ de-gritted peak flow wastewater) in “storm” mode. The tertiary filters have been designed and manufactured to accommodate “storm” mode. In the near-term, during abnormal high flow events (exceed 48 and 73.8 MGD), valves are closed that prevent secondary clarified effluent from being conveyed to the tertiary filter’s junction box. Secondary clarified effluent during this operational scenario will be conveyed directly to UV disinfection without tertiary filter treatment. The purpose of this approach is to maximize treatment of peak flow through the tertiary filter’s “storm” mode. As discussed in previous sections of the report, during this mode of operation, 48 MGD of wastewater (screened and de-gritted) from headworks and ~24 MGD (25.8 MGD) from the FEB (primary clarified because of FEB volume) to the peak flow junction box. At this point ~24 MGD (25.8 MGD) will be conveyed to secondary treatment and 48 MGD will be conveyed to the tertiary filter’s junction box. This approach will permit the peak flow to then be conveyed to the tertiary filters for treatment and then conveyed to UV disinfection. At UV disinfection, ~24 MGD (25.8 MGD) of secondary clarified effluent is then aggregated with 48 MGD peak flow tertiary treated effluent. The total flow ~72 MGD (73.8 MGD) is then disinfected, passed through flow measurement, and conveyed to the outfall. It is anticipated that most flows conveyed through the Davidson Dr. WWTP will not fall into the abnormal high flow category. In the long-term, during normal high flow events (between 53.3 and 94 MGD), the tertiary filter junction box will provide as a location for clarified secondary effluent and peak flow to aggregate before being conveyed to the tertiary filters. During this operational scenario, the tertiary filters will process the aggregated flow (combination of secondary treated and screened/ de-gritted peak flow wastewater) in “storm” mode. Also, in the long-term post aeration may need to be employed post UV disinfection and prior to outfall flow measurement. It is anticipated that this can be completed using fine bubble diffused aeration in a tank with a sidewall depth of 16 ft. In the near-term new flow measurement device capable of at least measuring at least 96 MGD will be installed. A new 54-inch outfall conveyance pipe will also be installed in the near-term to convey at least 96 MGD to the outfall (Lake Catherine).
Page 132 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.35 - Davidson Dr. Existing and Proposed Simplified
2 of 291 prings, Arkansas | Crist Engineers, Inc. d Process Flow Diagram – Hydraulic Improvements – Area 4
Page 133 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. In Figure 3.35, in the near-term it has been proposed that conveyance piping modifications be made to convey waste activated sludge (WAS) directly from the secondary clarifiers to the existing dewatering unit. Although this is not ideal long-term solution it does permit for midterm improvements to be completed with minimal interruption to the existing biosolids handling process. It has also been proposed in the near-term to install new WAS pumps (with VFDs). These new pumps will continuously convey WAS to the dewatering unit. This approach should maximize the existing dewatering performance (i.e., continuous, and consistent) as well as improve the biological efficiency of the near-term proposed secondary treatment process. Wasting and dewatering are planned to be completed approximately 20 hours per day, 7 days per week under this near-term approach. This approach will also permit for the anaerobic digesters to be removed from service thus eliminating the liability that they pose. Alternatively, it has been proposed in the mid-term that improvements be made to install new piping to convey WAS to a new centrifugal thickener. The proposed mid-term biosolids handling improvements will include new thickening that will permit continuous WAS and thickening to new aerated sludge storage no. 1. The aerated sludge storage will be accomplished through repurposing an existing primary clarifier. The aerated sludge storage is essentially a wide spot in the conveyance scheme that will provide for ~ 63 to 127 hours (or 2.6 to 5.2 days) of storage during normal operations. TWAS will then be conveyed to aerated sludge storage no. 2 (consisting of a and b basins). Aerated sludge storage no. 2 is repurposed existing gravity thickeners. Aeration sludge storage no. 2 (combined a and b) will provide for an additional 20 to 41 hours of storage during normal operations. Thickened sludge will then be dewatered using new centrifugal dewatering units to be loaded onto a truck for disposal. All the conveyance piping uses for conveyance of WAS and TWAS is planned to be 6 inch in size. Dewatered biosolids are planned to be conveyed utilizing shafted or shaftless screw conveyors. Preliminary hydraulic scenarios were developed utilizing the recommendations provided within the simplified process flow diagrams. These intent of utilizing hydraulic simulations are the planning level is to ensure that the recommendations will essentially function as described. It is by no mean at this planning stage to be considered a design level effort, therefore it is strongly recommended that additional hydraulic investigations be conducted during preliminary design to determine an overall effective/ efficient design approach to conveyance of these various liquid streams. The preliminary proposed hydraulic simulation for the near and long-terms piping improvements is presented in the below figures.
Page 134 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.36 - Davidson Dr. Proposed Hydrau
4 of 291 prings, Arkansas | Crist Engineers, Inc. ulic Simulator Configuration – Upper Reach
Page 135 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.37 - Davidson Dr. Proposed Hydraul
5 of 291 prings, Arkansas | Crist Engineers, Inc. lic Simulator Configuration – Middle Reach 1
Page 136 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.38 – Davidson Dr. Proposed Hydraul
6 of 291 prings, Arkansas | Crist Engineers, Inc. lic Simulator Configuration – Middle Reach 2
Page 137 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 3.39 - Davidson Dr. Proposed Hydrau
7 of 291 prings, Arkansas | Crist Engineers, Inc. ulic Simulator Configuration – Lower Reach
Page 138 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Preliminary hydraulic simulations indicate that the proposed near, mid and long-terms improvements will improve the hydraulic conveyance capacity of the Davidson Dr. WWTP. However, it is recommended that detailed hydraulic analysis and simulations be completed during the preliminary design phase of the improvements. A detailed analysis at that time will ensure that future modifications or updates are accounted for to minimize the risk of generating hydraulic constraints or errors. 3.2.5.5 SWWWTP HYDRAULIC MODELING RESULTS SWWWTP simulation does not appear to identify any hydraulic constraints. There are no recommended hydraulic improvements to this WWTP.
Page 139 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 3.3 – CONCLUSION 3.3.1 CAPITAL IMPROVEMENTS PLAN SUMMARY A summary of the proposed biological and hydraulic improvements for Davidson Dr. and SWWWTP are presented as follows: 3.3.1.1 DAVIDSON DR. WWTP Near-Term 1.1 Chemical Feed Building and Non-Potable Water System a. Magnesium Hydroxide feed system for supplemental alkalinity b. Sodium aluminate and aluminum chlorohydrate for T-P removal and settlement aid 1.2 Aeration Basin and Blowers a. New waste activated sludge pumps (WAS) 1.3 Secondary Clarifier No. 5 a. Secondary Peak Day Hydraulic Capacity to 25.8 MGD 1.4 Tertiary Filters No. 1 and 2 a. Tertiary Filter Hydraulic Capacity to 48 MGD 1.5 Add 4th Bank of UV Lamps to Channel 1 and 2 a. Disinfection Hydraulic Capacity to 75 MGD 1.6 Piping Improvements a. WAS b. Parshall Flume c. Outfall d. Peak Flow Piping e. Primary Clarifier f. Influent g. Tertiary Filter h. WAS Pumping 1.7 New dewatered biosolids hauling trailer (x2)/ heavy haul tractor (x1) Mid-Term 1.1 Biosolids Handling a. Demolition of existing anaerobic digesters b. New centrifugal sludge thickening c. Conversion of existing one (1) primary clarifier to new aerated sludge storage d. Receiving station for SWWWTP biosolids
Page 140 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. e. New centrifugal sludge dewatering 1.2 RAS Pumping Improvements a. Sidestream Treatment System b. Suspended Air Flotation (SAF) No. 1 Long-Term 1.1 Secondary Clarifier No. 6 a. Secondary Peak Day Hydraulic Capacity to 31.3 MGD 1.2 Secondary Clarifier 3 Rehabilitation 1.3 Secondary Clarifier 4 Rehabilitation 1.4 Secondary Clarifier 1 Rehabilitation 1.5 Secondary Clarifier 2 Rehabilitation 1.6 Primary Treatment Expansion to 72 MGD a. Headworks Screen No. 3 b. Headworks Grit Removal No. 3 1.7 Tertiary Treatment Expansion to 72 MGD a. Tertiary Filter No. 3 1.8 New Operations and Maintenance Building Long-Term (Beyond Planning Period) 1.9 UV Disinfection Expansion – 3rd Channel a. Disinfection Hydraulic Capacity to 96 MGD 1.10 Post Aeration Basin 1.11 Primary Treatment Expansion to 96 MGD a. Headworks Screen No. 4 b. Headworks Grit Removal No. 4 1.12 Tertiary Treatment Expansion to 96 MGD a. Tertiary Filter No. 4 1.13 Secondary Clarifiers No. 7 and 8 a. Secondary Peak Day Hydraulic Capacity to 42.3 MGD 1.14 Secondary Clarifiers No. 9 and 10 a. Secondary Peak Day Hydraulic Capacity to 53.3 MGD 1.15 IFAS a. Biological capacity to 24 MGD b. Influent piping and splitter box modifications c. Conversion of existing two (2) primary clarifiers to anaerobic selector basins d. RAS pumping improvements
Page 141 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. e. Modify RAS piping, add additional piping to convey RAS to anaerobic selection basins f. WAS pumping improvements g. WAS piping improvements h. Conversion of existing anoxic basin to aerated/ mixed basin i. Centrifugal Thickening No. 2 j. TWAS pumping improvements k. TWAS piping improvements l. Aerated sludge storage 1 and 2 aeration/ mixing improvements m. Centrifugal Dewatering No. 2 n. Dewatered biosolids conveyance improvements 1.16 Sidestream Treatment System a. Suspended Air Flotation No. 2 1.17 New Internal Recycle Process a. New piping and pumping station A summary of the cost of the corresponding biological and hydraulic improvements for Davidson Dr. are presented as follows:
Page 142 Wastewater System Master Plan (WWSMP) – Hot Sp Table 3.34 - Proposed Davidson Dr. WWT WWTP Simplified Process Flow Area1 WWTP Process Type Improvement1 Phase 3 Physical Near-Term Tert 2 Chemical/ Biological Near-Term Che 2 Biological Near-Term Aera 2 Biological/ Hydraulic Near-Term Seco 3 Physical Near-Term UV D and 1,2,3 Hydraulic Near-Term Pipi 4 Biosolids Near-Term Dew Trac 1 WWTP simplified process flow area and associated subgrouping process type Arrangement/ subgrouping is not necessarily a representation of improvement phase at this time. 3 Total budget amount identified within the CIP, individual p Table 3.35 - Proposed Davidson Dr. WWT WWTP Simplified Process Flow Area1 WWTP Process Type Improvement1 Phase 4 Biosolids Mid-Term Bios 2,4 Biological Mid-Term Retu 4 Biological Mid-Term Side No. 1 WWTP simplified process flow area and associated subgrouping process type Arrangement/ subgrouping is not necessarily a representation of improvement phase at this time.
2 of 291 prings, Arkansas | Crist Engineers, Inc. TP Estimated Cost Summary – Near-Term Description Cost Summary tiary Filter No. 1 and 2 $6,398,000.00 mical Feed Building and Non-Potable Water System3 $17,664,203.00 ation Basins and Blowers3 ondary Clarifier No. 53 Disinfection - Add 4th Bank of UV Lamps to Channel 1 23 ng Improvements3 watered Biosolids Hauling Trailer (x2)/ Heavy Haul ctor (x1) $149,900.00 improvement is arranged upstream to downstream of associated WWTP. t needs, cost, importance, risk or other potential qualifying subgrouping with each project estimated costs are identified under each individual projects herein. TP Estimated Cost Summary – Mid-Term Description Cost Summary solids Handling $14,293,000.00 urn Activated Sludge (RAS) Pumping Improvements $1,099,000.00 estream Treatment System - Suspended Air Flotation 1 $837,000.00 improvement is arranged upstream to downstream of associated WWTP. t needs, cost, importance, risk or other potential qualifying subgrouping with each
Page 143 Wastewater System Master Plan (WWSMP) – Hot Sp Table 3.36 – Proposed Davidson Dr. WWT WWTP Simplified Process Flow Area1 WWTP Process Type Improvement1 Phase 2 Biological/ Hydraulic Long-Term Sec 2 Biological/ Hydraulic Long-Term Sec 2 Biological/ Hydraulic Long-Term Sec 2 Biological/ Hydraulic Long-Term Sec 2 Biological/ Hydraulic Long-Term Sec 1 Physical Long-Term Hea 1 Physical Long-Term Hea 3 Physical Long-Term Ter 1 Physical Long-Term Equ - - Long-Term Ope 1 WWTP simplified process flow area and associated subgrouping process type Arrangement/ subgrouping is not necessarily a representation of improvement phase at this time.
3 of 291 prings, Arkansas | Crist Engineers, Inc. TP Estimated Cost Summary – Long-Term Description Cost Summary condary Clarifier No. 6 $2,605,000.00 condary Clarifier No. 3 Rehabilitation $2,018,000.00 condary Clarifier No. 4 Rehabilitation $1,933,000.00 condary Clarifier No. 1 Rehabilitation $1,933,000.00 condary Clarifier No. 2 Rehabilitation $1,933,000.00 adworks Screen No. 3 $1,129,000.00 adworks Grit Removal No. 3 $1,987,000.00 rtiary Filter No. 3 $4,938,000.00 ualization Pond $4,452,000.00 erations and Maintenance Facility $6,644,000.00 improvement is arranged upstream to downstream of associated WWTP. t needs, cost, importance, risk or other potential qualifying subgrouping with each
Page 144 Wastewater System Master Plan (WWSMP) – Hot Sp Table 3.37 - Proposed Davidson Dr. WWTP Estimated WWTP Simplified Process Flow Area1 WWTP Process Type Improvement1 Phase 3 Physical Long-Term (Beyond Planning Period) UV Cha 3 Physical/ Chemical Long-Term (Beyond Planning Period) Pos 1 Physical Long-Term (Beyond Planning Period) Hea 1 Physical Long-Term (Beyond Planning Period) Hea 3 Physical Long-Term (Beyond Planning Period) Ter 2 Biological/ Hydraulic Long-Term (Beyond Planning Period) Sec 2,4 Biological/ Biosolids Long-Term (Beyond Planning Period) Bio 2 Biological/ Hydraulic Long-Term (Beyond Planning Period) Sec 4 Biosolids Long-Term (Beyond Planning Period) Side 2 2 Biological Long-Term (Beyond Planning Period) Bio 1 WWTP simplified process flow area and associated subgrouping process type Arrangement/ subgrouping is not necessarily a representation of improvement phase at this time.
4 of 291 prings, Arkansas | Crist Engineers, Inc. Cost Summary – Long-Term (Beyond Planning Period) Description Cost Summary Disinfection Expansion - Add 3rd UV Disinfection annel with 4 Additional Banks of Lamps $3,045,000.00 st Aeration $4,822,000.00 adworks Screen No. 4 $1,732,000.00 adworks Grit Removal No. 4 $2,195,000.00 tiary Filter No. 4 $4,938,000.00 condary Clarifier No. 7 & 8 $6,745,000.00 logical/ Biosolids Expansion and Upgrade - IFAS $26,729,000.00 condary Clarifier No. 9 & 10 $5,145,000.00 estream Treatment System - Suspended Air Flotation No. $798,000.00 logical Improvements - Internal Recycle $4,875,000.00 improvement is arranged upstream to downstream of associated WWTP. t needs, cost, importance, risk or other potential qualifying subgrouping with each
Page 145 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 3.38 – Proposed Davidson Dr. WWTP Estimated Cost Summary - Near, Mid and LongTerms Total Improvements Phase Total Phase Cost Phase Percent of Total Cost Near-Term $24,212,103.00 35% Mid-Term $16,229,000.00 23% Long-Term $29,572,000.00 42% Total $70,013,103.00 - As shown in the above table, approximately $70 million dollars are planned for Davidson Dr. WWTP within the 2040 planning period. Table 3.39 - Proposed Davidson Dr. WWTP Estimated Cost Summary – Long-Term (Beyond Planning Period) Total Long-Term (Beyond Planning Period) $61,024,000.00 As shown in the above table, approximately $61 million dollars are planned for Davidson Dr. WWTP beyond the 2040 planning period.
Page 146 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 3.3.1.2 SWWWTP Near-Term 1.1 Magnesium Hydroxide feed system for supplemental alkalinity 1.2 Programming modifications to accommodate anaerobic and anoxic sequences Mid-Term 1.1 Deliver thickened biosolids to Davidson Dr. WWTP Aerated Sludge Storage No. 1 receiving station A summary of the cost of the corresponding biological and hydraulic improvements for SWWTP are presented as follows:
Page 147 Wastewater System Master Plan (WWSMP) – Hot Sp Table 3.40 – Proposed SWWWTP Est WWTP Simplified Process Flow Area WWTP Process Type Improvement Phase - Chemical/ Biological Near-Term - Biological Near-Term Table 3.41 – Proposed SWWWTP Es WWTP Simplified Process Flow Area WWTP Process Type Improvement Phase - Biosolids Mid-Term Th
7 of 291 prings, Arkansas | Crist Engineers, Inc. timated Cost Summary – Near-Term Description Cost Summary Chemical Feed Improvements $375,000.00 Sequencing Batch Reactor (SBR) Programming Improvements $75,000.00 stimated Cost Summary – Mid-Term Description Cost Summary ickened Solids Receiving Station at Davidson Dr. WWTP $464,000.00
Page 148 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 3.42 – Proposed SWWWTP Estimated Cost Summary - Total Improvements Phase Total Phase Cost Phase Percent of Total Cost Near-Term $450,000.00 49% Mid-Term $464,000.00 51% Long-Term $- 0% Total $914,000.00 - As shown in the above table, approximately $1 million dollars are planned for SWWWTP within the 2040 planning period.
Page 149 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. CHAPTER 4 – WWTP UNIT PROCESS EVALUATION SECTION 4.1 – INTRODUCTION Sequential treatment processes are used to chemically, physically, and biologically remove contaminants to create wastewater effluent that achieves NPDES permit requirements prior to being released into the environment. To aid in the development of the City of Hot Springs (CHS) Wastewater System Master Plan (WWSMP), existing unit process evaluations were completed prior to completion of the biologically and hydraulic modeling (simulator) efforts. The intent was to consider unit processes, concurrently with the biological/ hydraulic and biosolids evaluations, in ascending order the unit processes: 1. type of treatment (chemical, physical or biological), 2. purpose or necessity (goal of the unit process/ targeted function/ contaminant, et al.), 3. performance for achieving purpose, 4. and physical attributes (age, condition, efficiency, capacity).
Page 150 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 4.2 – DISCUSSION 4.2.1 DAVIDSON DR. WWTP Davidson Dr. WWTP is a traditional activated sludge wastewater treatment plant consisting of the following unit processes: Liquid Treatment 1. Equalization Pond 2. Headworks a. Screening b. Grit Removal 3. Primary Clarification 4. Secondary Treatment a. Aeration b. Secondary Clarification 5. Tertiary Filtration 6. UV disinfection Solids Treatment 1. Gravity Thickening 2. Anaerobic Digestion a. Stage 1 b. Stage 2 3. Belt Filter Press Dewatering 4. Solids Disposal to Landfill or Compost The simplified process flow diagrams for the Davidson Dr. WWTP are presented in the following Figures.
Page 15 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 4.1 - Existing Davidson Dr. WWTP Simpl
1 of 291 prings, Arkansas | Crist Engineers, Inc. ified Process Flow Diagram – Liquid Treatment
Page 152 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 4.2 - Existing Davidson Dr. WWTP Simplifi
2 of 291 prings, Arkansas | Crist Engineers, Inc. ied Process Flow Diagram – Biosolids Treatment
Page 153 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 4.2.1.1 EQUALIZATION POND 1. Treatment Type: Physical 2. Purpose: Wastewater storage generated from wet weather events. 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~32 years old b. Condition: Acceptable c. Efficiency: Acceptable d. No. of Units: 1 e. Total Capacity: 78 MG The equalization pond was installed in the 1990’s as an approach to store wet weather flow generated during storm events. The original approach was to convey screened, de-gritted and primary clarified wastewater to the equalization pond during wet weather flow events. However, the to achieve acceptable performance the primary clarifiers are limited to a hydraulic capacity of approximately 16 to 20 MGD, whereas screening and grit removal are effectively sized for ~48 MGD. Therefore, primary clarifiers generate a hydraulic bottleneck thus causing wastewater to be diverted to the equalization during normal wet weather events immediately after screening. Also, during significant wet weather events wastewater is also diverted prior to screening. Equalization pond is not a treatment process per say, however, it does provide for physical treatment. When screened wastewater is diverted to the equalization pond, grit will settle in the pond due to the detention time of the structure. Additionally, when unscreened wastewater is diverted to the equalization pond some of the floatables or settleable solids will be removed. The total capacity of the equalization pond is approximately 78 MG at elevation 374, however, when the elevation of the equalization pond exceeds 369, wastewater can flow hydraulically via gravity from the equalization pond to the diversion structure (located adjacent to primary clarification). The significance of this hydraulic conveyance capability is it permits wastewater to flow from the equalization pond to UV disinfection where it is aggregated with secondary flow during periods of significant wet weather. The parameters of the equalization pond at elevation 369 are as follows: 1. Depth: 19 ft 2. Step: 11th 3. Capacity: 51.5 MG Ideally, the volume above elevation 369 should not be utilized during normal wet weather events because of the potential risk to effluent violations or impacts to downstream processes. At the conclusion of the storm event, diverted wastewater is to be pumped back to the headworks or to the diversion box. Ideally, after normal wet weather events, wastewater
Page 154 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. would be pumped back to the headworks and the equalization pond be emptied of liquid and solids. The total existing pumping capacity from the equalization pond to the headworks or called the pump back, is approximately 12 MGD. The pump back occurs when wastewater stored in the FEB is pumped back to the headworks of the wastewater treatment plant. The equalization pond also includes aeration that is used to minimize odors generated during storage periods. Improvements, discussed in other sections of the report, address elimination of the hydraulic bottleneck to ensure only screened and de-gritted wastewater is conveyed to the equalization pond during normal wet weather events. These hydraulic improvements will also minimize the amount of wastewater that is needed to be stored within the equalization pond. Storage of wastewater within the equalization pond negatively impacts the overall biological performance of the wastewater treatment plant during pump back. Additional analysis/ modeling is currently being undertaken to determine the overall normal storage volume and planned operation during normal wet weather events. The recommended operation of the lift stations within the collection system coupled with the recommended operation of the wastewater treatment may result in needed improvements to the equalization pond. Additional CIP recommendations may be developed from these or future analysis. The volume of the solids that are currently contained within the equalization pond is unknown. A future project will investigate the volume of solids as well as develop a potential strategy, if required for the removal of those solids. During this future project, investigations can be conducted to specifically determine if components (aeration, pumping, controls, etc.) will need to be rehabilitated or replaced as a part of normal maintenance program or if a specific CIP needs to be developed for those components. Based on the review completed during the WWSMP investigations, it was determined that the components were in acceptable condition at this time. At this time, it has been identified that the equalization pond will require long-term improvements, likely in the form of: 1. Cleaning/ removal of deposition material 2. Inspection of the liner a. Rehabilitation of the liner 3. Pump station replacement 4. Odor/ ammonia production mitigation strategies a. Rehabilitation/ expansion of the aeration equipment The cost for rehabilitation of this unit process is presented in the long-term CIP improvements.
Page 155 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 4.2.1.2 SCREENING 1. Treatment Type: Physical 2. Purpose: Removal of solids, bar spacing 0.25 inches 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~2 years old b. Condition: Acceptable c. Efficiency: Acceptable d. No. of Units: 2 e. Total Capacity: 48 MGD Figure 4.3 – Davidson Dr. WWTP Headworks Screens The existing Huber screening system was installed in 2018 with a nominal screen opening of 0.25 inch. The screens appear to be in good condition and providing acceptable solids removal. Each screen is capable of conveying 24 MGD with a total capacity of 48 MGD.
Page 156 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. There are no rehabilitations identified for this unit process during the planning period, however, an additional screen has been identified in other sections of the report to be added in the long-term increasing the total capacity at that time to 72 MGD. The cost of the additional unit is presented in the long-term CIP improvements. 4.2.1.3 GRIT REMOVAL 1. Treatment Type: Physical 2. Purpose: Removal of grit, 95% of 105 micron at 24 MGD (total) and 95% of 150 micron at 40 MGD (total) 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~2 years old b. Condition: Acceptable c. Efficiency: Acceptable d. No. of Units: 2 e. Total Capacity: ~48 MGD; (decreased removal performance above 40 MGD)
Page 157 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.4 – Davidson Dr. WWTP Headworks Grit Removal System The existing Hydro International grit removal system was installed in the 2018 with an identified performance of 95% removal of 105-micron particles or larger when total flows are 24 MGD or less. Alternatively, the grit removal system will achieve 95% removal of 150-micron particles when between 24 to 40 MGD. When flows are in excess of 40 MGD the removal performance decreases but is capable of hydraulically conveying those flows. During normal wet weather flow events flows are not anticipated to be in excess of 40 MGD. There are no rehabilitations identified for this unit process during the planning period, however, an additional grit removal system has been identified in other sections of the report to be added in the long-term increasing the total capacity at that time to 60 MGD with achieved performance or 72 MGD with decreased performance. The cost of the additional unit is presented in the long-term CIP improvements.
Page 158 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 4.2.1.4 PRIMARY CLARIFICATION 1. Treatment Type: Physical 2. Purpose: Removal floatable/ settleable solids, grit, TSS, cBOD 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~47 years old b. Condition: Marginal c. Efficiency: Poor at flows in excess of 20 MGD d. No. of Units: 3 e. Total Capacity: 16 to 20 MGD
Page 159 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.5 – Davidson Dr. WWTP Primary Clarifiers The existing primary clarification process is undersized for the conveyance needs associated with the hydraulic improvements. It also is detrimental to the overall biological nutrient removal targets discussed in other sections of the report. It is recommended that this unit process be abandoned, and one (1) of the structures/ primary solids pumps be repurposed in the mid-term for aerated sludge storage. The remaining two (2) primary clarifiers have been slated to be utilized as anaerobic selectors in the long-term, beyond the planning period. The cost of re-purposing these structures is presented in the mid and long-term CIPs.
Page 160 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 4.2.1.5 AERATION 1. Treatment Type: Biological 2. Purpose: Removal cBOD/ ammonia 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~32 years old b. Condition: Marginal c. Efficiency: Poor, aeration undersized d. No. of Units: 3 e. Total Capacity: 20 MGD Figure 4.6 – Davidson Dr. WWTP Aeration Basins The aeration basin provides for biological treatment of cBOD, ammonia and phosphorus through contact with biomass with wastewater and electron acceptor (oxygen).
Page 161 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The existing diffusers, aeration laterals and blowers have been identified as undersized for the near, mid and long-terms needs of the WWTP. The aeration capacity is approximately ½ the size that is needed for the future capacity. The aeration basin appears to be sufficiently sized. It is recommended that this unit process be rehabilitated with new aeration diffusers, laterals, piping, and blowers to increase the capacity of the unit process. The existing anoxic zones and associated vertical mixers appears to be in acceptable condition. The cost of rehabilitation/ expansion of this unit process is presented in the near-term CIP improvements. 4.2.1.6 SECONDARY CLARIFICATION 1. Treatment Type: Physical 2. Purpose: Solids/ liquid separation/ recycle biosolids to aeration 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~32 to 47 years old b. Condition: Poor c. Efficiency: Acceptable d. No. of Units: 4 e. Total Capacity: ~20 MGD (20.38 MGD)
Page 162 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.7 – Davidson Dr. WWTP Secondary Clarifiers This unit process provides for the removal of TSS from wastewater through gravity sedimentation achieving liquid/ solids separation. The biosolids that separate to the bottom of the structure are then recycled back to the aeration basin for participation in biological removal of contaminants. Some of the biosolids are removed from the system to maintain a specific balance between contaminants and biosolids through “wasting”. The pumps that are used to recycle biosolids from the secondary clarifier to the aeration basin are called return activated sludge (RAS) pumps and have been identified for replacement in the mid and long-term. The cost of these rehabilitation/expansions have been identified in the mid and long (beyond the planning period) improvements CIP. The pumps used for “wasting” or the waste activated sludge (WAS) pumps have been identified to be rehabilitated in the near-term CIP. Due to the condition and age of the existing secondary clarifiers (1 – 4), they have been identified for rehabilitation in the long-term improvements. The secondary clarifier’s performance has been acceptable, and an additional clarifier has been identified for installation in the near-term improvements which will increase the capacity from ~20 MGD to ~24 MGD (25.8 MGD). To accommodate secondary clarifier no. 5, the cost of demolishing of these structures is presented in the mid-term CIPs.
Page 163 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The cost of the additional unit is presented in the near-term CIP improvements. To perform the rehabilitation of the existing clarifiers it is necessary to construct secondary clarifier no. 6 to ensure that five (5) clarifiers are in operation to maintain ~24 MGD (25.8 MGD) capacity during rehabilitation of clarifiers 1 – 4. Due to the size and configuration, it is recommended that the secondary clarifiers be rehabilitated in the following order: 1. Secondary Clarifier No. 3 2. Secondary Clarifier No. 4 3. Secondary Clarifier No. 1 4. Secondary Clarifier No. 2 The existing anoxic zones and associated vertical mixers appears to be in acceptable condition. The cost of rehabilitation of this unit process is presented in the long-term CIP improvements. 4.2.1.7 TERTIARY FILTRATION 1. Treatment Type: Physical 2. Purpose: Removal of TSS 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~47 years old b. Condition: Poor c. Efficiency: Poor d. No. of Units: 4 e. Total Capacity: ~20 MGD
Page 164 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.8 – Davidson Dr. WWTP Tertiary Filters This existing unit process is used for solids/ liquid separation to further remove TSS from clarified secondary effluent. The existing tertiary filtration process is undersized for the conveyance needs associated with the hydraulic improvements. It also is in disrepair and in need of replacement. The design and construction of the replacement of this unit process was underway during the wastewater system master plan development with final completion in January 2022. The improvement consisted of installing two (2) Aqua-Aerobic AquaStorm cloth disc filters. These disc filters are capable of operating in two modes: 1. Treatment of Clarified Secondary Clarifier Effluent (Tertiary Mode) 2. Treatment of Screened/ De-Gritted Effluent (Storm/ Wet Weather Mode) The new tertiary filters will be capable of removing TSS from secondary clarified effluent as well as TSS from screening/ de-gritted wastewater. Each unit is size for 24 MGD with a total treatment capacity of 48 MGD.
Page 165 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The estimated cost of the replacement/ expansion of this unit process is included in the nearterm CIP improvements. An additional tertiary filter has also been identified in the long-term CIP improvements to expand the capacity from 48 to 72 MGD. The cost of the additional unit is presented in the long-term CIP improvements. 4.2.1.8 UV DISINFECTION 1. Treatment Type: Physical 2. Purpose: Inactivation of bacteria 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~2 years old b. Condition: Acceptable c. Efficiency: Acceptable d. No. of Units: 2 e. Total Capacity: 44 MGD
Page 166 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.9 – Davidson Dr. WWTP UV Disinfection This existing unit process uses ultraviolet light to inactivate bacteria found within wastewater effluent. The existing TrojanUV disinfection system was installed in 2018 with a total capacity of 44 MGD. The existing system has acceptable performance and is planned to be expanded to 75 MGD though the addition of the 4th banks to the two-channel system. The cost of the expansion is presented in the near-term CIP improvements. 4.2.1.9 GRAVITY THICKENING 1. Treatment Type: Physical 2. Purpose: Primary and secondary solids settling to thicken 3. Achieve Purpose: Yes 4. Physical Attributes a. Age: ~32 years old b. Condition: Poor c. Efficiency: Marginal d. No. of Units: 2 e. Total Capacity: 18,600 dry-lbs./ day
Page 167 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 4.10 – Davidson Dr. WWTP Gravity Thickening The existing gravity thickening process is in poor condition and has marginal performance when compared to other technologies. Thickening discussions and performance are discussed in other sections of the report. It is recommended that this unit process be abandoned, and the two (2) structures be repurposed in the mid-term for aerated sludge storage. The cost of re-purposing these structures is presented in the mid-term CIP. This unit process is intended to be replaced with centrifugal thickening as discussed in other sections of the report. The cost of centrifugal thickening is presented in the mid-term CIP improvements. 4.2.1.10 ANAEROBIC DIGESTION 1. Treatment Type: Physical 2. Purpose: Digestion of primary and secondary solids 3. Achieve Purpose: No 4. Physical Attributes