9 of 291 prings, Arkansas | Crist Engineers, Inc. on Planning Summary – Beyond Planning Period – Long-Term – rio 3A Intended Disposal Units posting Land Application Landfill MGD oC rm (i.e., WAS to New Thickening to Aerated Sludge Storage No. 1/ 2 to - dry lbs./ day - - % TS - - dry lbs./ day - - days - weeks - wet lbs./ dewatering day - cubic yards (CY)/ dewatering day - tons/ year - CY/ year WWTP hauled biosolids. 2Specific gravity of the biosolids = 1.07.
Page 250 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Due to the sequencing of Scenario 3, the only option considered is landfill disposal of unclassified biosolids at this time. Additional analysis is recommended to be completed with future master plan updates to determine if the biosolids disposal market has changed. However, currently, the average annual cost of landfill disposal of unclassified biosolids is presented Table 5.33.
Page 25 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.33 – Proposed Davidson Dr. WW Scena Existing 1A 1A Alternative A 2A1 Total Scenario Weight 19,825 24,500 23,333 Drying Unit Cost - - Unit Cost - - Subtotal Weight - - Subtotal Annual Cost Estimate - - Composting - Windrow Unit Cost $446.28 $446.28 $446.28 $613.0 Unit Cost $70 $70 $70 $129 Subtotal Weight 11,951 11,951 11,951 15,492 Subtotal Annual Cost Estimate $832,000 $832,000 $832,000 $1,994 Composting - Rotary Drum/ Windrow Unit Cost - - - $690.0 Unit Cost - - - $145 Subtotal Weight - - - 15,492 Subtotal Annual Cost Estimate - - - $2,244
1 of 291 prings, Arkansas | Crist Engineers, Inc. WTP Biosolids Estimated Cost Summary arios 2A1 Alternative B 2A1 Alternative C 3A Unit 15,492 Annual Tons $476.71 - - $/ dry-ton $100 - - $/ wet-ton 15,492 - - Annual Tons $1,550,872 - - Annual Cost 01 - - - $/ dry-ton - - - $/ wet-ton 2 - - - Annual Tons 4,279 - - - Annual Cost 04 - - - $/ dry-ton - - - $/ wet-ton 2 - - - Annual Tons 4,864 - - - Annual Cost
Page 252 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.33 – Proposed Davidson Dr. WWTP Scena Existing 1A 1A Alternative A 2A1 2 Land Application Unit Cost - - - - Unit Cost - - - - Subtotal Weight - - - - Subtotal Annual Cost Estimate - - - - Landfill Unit Cost $737.18 $498.69 $498.69 $370.45 Unit Cost $115 $78 $78 $78 Subtotal Weight 7,874 12,549 11,383 15,492 Subtotal Annual Cost Estimate $905,514 $976,271 $885,510 $1,205,174
2 of 291 prings, Arkansas | Crist Engineers, Inc. P Biosolids Estimated Cost Summary (cont.) arios A1 Alternative B 2A1 Alternative C 3A Unit $523.88 - $/ dry-ton $110 - $/ wet-ton 14,343 - Annual Tons $1,577,965 - Annual Cost - $370.45 $/ dry-ton - $78 $/ wet-ton - 21,405 Annual Tons - $1,665,185 Annual Cost
Page 253 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.33 – Proposed Davidson Dr. WWTP Scena Existing 1A 1A Alternative A 2A1 Total Estimates Total Scenario Annual Average Cost Estimate (Min) $1,737,514 $1,808,271 $1,717,510 $1,205,17 Total Scenario 1 Near-Term Annual Average Cost Estimate (Min) - $1,717,510 - Total Scenario 2 Mid to Long-Terms Annual Average Cost Estimate (Min) - - - $1,205,17 Total Scenario 3 Beyond Planning Period Annual Average Cost Estimate (Min) - - - -
3 of 291 prings, Arkansas | Crist Engineers, Inc. P Biosolids Estimated Cost Summary (cont.) arios 2A1 Alternative B 2A1 Alternative C 3A Unit 74 $1,550,872 $1,577,965 Annual Cost - - - Annual Cost 74 - Annual Cost - - $1,665,185 Annual Cost
Page 254 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.4 SWWWTP ANALYSIS To compare the proposed intended use and intended disposal options, we first must quantify the estimated biosolids production. Biosolids production is based on the results of the biological modeling of the various near, mid and long-term scenarios. Scenario 1A does not include costs associated with biosolids processing associated with WAS, thickening, TWAS, biosolids conveyance into the truck. 5.2.4.1 SCENARIO 1A SWWWTP currently processes WAS through an aerobic digester, thickens and then hauls the thickened biosolids to a manhole within the collection system of Davidson Dr. WWTP. To alleviate conveying SWWWTP biosolids through the collection system, it is recommended that the ~12,000 gallons per week of biosolids be conveyed directly into the aerated sludge storage no. 1, located at Davidson Dr. WWTP. When the biosolids handling project is completed (Mid-Term) at Davidson Dr. WWTP it will include a receiving station for biosolids hauled as a liquid from SWWWTP. It should be noted that when hauling activities occur, it is anticipated that approximately 189 lbs. of T-P with 118 lbs. (~62%) being orthophosphate will be delivered to aerated sludge storage no. 1. To alleviate the concern of an instantaneous spike of orthophosphate in Davidson Dr. WWTP biosolids processing it is recommended that sodium aluminate be fed into the receiving station when hauling activities are occurring.
Page 255 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.18 – Proposed SWWWTP Simplified Proces Figure 5.19 – Proposed SWWWTP Simplified Proces
5 of 291 prings, Arkansas | Crist Engineers, Inc. s Flow Diagram – Solids Treatment (Near-Term CIP) ss Flow Diagram – Solids Treatment (Mid-Term CIP)
Page 256 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.34 – Proposed SWWWTP Biosolids Production Intended Use Biosolids Mass/ Volume Drying Com Design Annual Flow Rate 0.74 Design Annual Temperature 20 Biosolids Processing Scenario 1A - Mid to Long-Term (i.e., WAS to Ae Minimum WAS to Aerobic Digester 470 Design WAS to Aerobic Digester 600 Maximum WAS to Aerobic Digester 660 Thickening Performance 3 Minimum Thickened Biosolids (EST.) 360 Design Thickened Biosolids (EST.) 425 Maximum Thickened Biosolids (EST.) 480 Hauling Days Per Week 1.00 Hauling Weeks per Year 52.00 Wet Sludge Weight (@ 3 % TS) 99,167 Wet Sludge Volume1 11,113 Design Annual Wet Sludge Weight (@ 3 % TS) 2,578 Design Annual Wet Sludge Volume1 577,855 Design Annual Total Phosphorus (T-P) Weight (@ 6.35 %) 9,850 . 1 Specific gravity of the biosolids = 1.07.
6 of 291 prings, Arkansas | Crist Engineers, Inc. n Planning Summary – Near/ Mid-Term – Scenario 1A Intended Disposal Units mposting Land Application Landfill MGD oC erobic Digester to Hauling to Davidson Dr. WWTP) dry lbs./ day % TS dry lbs./ day days weeks wet lbs./ day gallons/ day tons/ year gallons/ year dry lbs./ year
Page 257 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The total conveyance from SWWWTP to Davidson Dr. WWTP is approximately 12,000 gallons per week. The total amount of biosolids applied to Davidson Dr. WWTP on an average annual basis has been included in the calculations. Due to the small amount of biosolids generated from SWWWTP when compared to Davidson Dr. WWTP, any individual cost analysis for biosolids handling for SWWWTP would far exceed the costs established for Davidson Dr. Therefore, the most cost effective, economical solution for SWWWTP is to continue to haul to Davidson Dr. WWTP. However, as a point of comparison, the A cost analysis was performed for Scenario 1A to determine an estimated unit cost for disposal to Davidson Dr. WWTP. The following assumptions were included in the analysis: 1. utilize existing 4,000-gallon liquid hauling truck and driver to deliver thickened biosolids from SWWWTP to Davidson Dr. WWTP located, approximately 35 miles round trip, at 25 miles per hour, 0.75 hours load time, 0.75 unload for a total turn around period of 2.9 hours, with a total hauling day of approximately ~9 hours or 1 full day. Scenario 1A includes utilizing existing equipment and fuel, labor, maintenance, and replacement of equipment was also included in this analysis. Table 5.35 – Proposed SWWWTP Biosolids – Scenario 1A – Davidson Dr. WWTP Disposal Costs Analysis Davidson Dr. WWTP Disposal Annual Volume to Davidson Dr. WWTP @ 3% TS 577,855 gal Annual Weight to Davidson Dr. WWTP @ 3% TS 2,578 wet-ton Analysis Duration 20 years Total Capital Cost $0 Total Present Worth Cost $334,463 Estimated Handling and Disposal Costs $0.03 $/ wet-gal Estimated Handling and Disposal Costs $6 $/ wet-ton Cost per Dry Ton @ 3% TS $216.20 $/ dry-ton Average Annual Cost $16,723
Page 258 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.5 BIOSOLIDS PROCESSING – THICKENING To minimize the volume of biosolids, for conveyance and treatment within the biosolids processing segment of a WWTP they are commonly thickened. Thickening is the procedure by which part of the liquid portion of the sludge is removed in order to increase the solids content. This helps with storage capacity and lower the amount of chemicals and energy necessary to stabilize the sludge. Thickening is generally a physical process such as co-settling, gravity settling (thickener), gravity belt, floatation, centrifugation and rotary drum. Conceptually, as WAS is removed from the secondary process, the proportionate amount not removed (i.e., uncaptured solids) by the thickening technology are recycled back to the influent and ultimately end up in the secondary process. The result is that at any given instant the biosolids may be comprised of a higher percentage of older sludge (wasted) than if the solids capture rate were higher. Generally, the solids capture rate isn’t as critical when considering the type of WWTP and/ or the effluent. For example, an extended aeration WWTP (i.e., oxidation ditch, complete mix, etc.) is a very common secondary treatment process used throughout the US, is not as negatively impacted by recycled solids as a conventional WWTP. The extended aeration process uses longer sludge retention times (SRT) (i.e., older biosolids) which typically results in poorer settling sludge. This poorer settling biosolids requires the use of larger secondary clarifiers (i.e., lower hydraulic loading rate) for treatment to obtain the same level of performance that a conventional WWTP with a lower SRT. If the proportion of biosolids is older (i.e., recycled biosolids from the gravity thickener) than it otherwise would be is compensated by the increased size or the secondary clarifier. However, when used in conventional WWTP, where the clarifiers are smaller, a higher percentage of recycled biosolids will likely negatively impact the overall performance of the secondary clarifier and result in a higher clarified effluent TSS. This higher concentration of secondary clarified effluent ultimately results in a higher loading to a tertiary filter (if applicable), higher cBOD (cBOD in effluent is primarily derived from TSS) and higher T-P (contained within the cell wall, non-orthophosphate portion). Therefore, recycled biosolids become more of a concern and consideration as the effluent TSS, cBOD or T-P effluent limit decreases and/ or if tertiary filter is present at the WWTP. Davidson Dr. WWTP contains all of these considerations, therefore recycled TSS through solids capture must be considered. Co-settling occurs when WAS is conveyed to the primary clarifiers to co-mingle and settle with primary sludge. This approach is rarely employed now as the process introduces primary VSS and cBOD to WAS in an anaerobic environment. The approach to biosolids management is odorous and decreased the performance of primary sludge settling/ thickening while simultaneously decreasing the performance of WAS settling/ thickening. Co-settling was not evaluated or considered for Davidson Dr. WWTP because of the elimination of primary sludge and clarifiers. However, repurposing the primary clarifier as an aerated sludge storage does provide advantages with decanting and thickening of biosolids. This approach will be discussed in other sections of the report.
Page 259 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.5.1 GRAVITY THICKENER Gravity settling is one of the most common methods used biosolids thickening. Typically, WAS is conveyed to a circular tank with rake arms/ center well/ overflow weirs (i.e., clarifier) where biosolids will settle to the bottom and the clarified water will then be conveyed back to the head of the WWTP (i.e., solids-liquid separation). Gravity thickening was historically used because it utilizes relatively small structures while requiring minimal horsepower input. One critical performance parameter of the gravity thickeners is to keep the primary sludge separate from the WAS, thus traditionally requiring two gravity thickeners. The main disadvantages of gravity thickener technology are that they provide limited ability to control the performance (i.e., % solids of the biosolids) while also being difficult to expand or add additional flow/ volumes. Gravity thickening process relies exclusively on the settling velocity of the biosolids vs. the escape velocity of the clarified water. These processes are highly dependent on the hydraulic loading rate, solids loading rate and settleability of the biosolids. Additionally, they provide relatively per performance related to solids capture rate. The solids capture rate of a process is determined as the amount of solids that are retained by the unit process (by weight) divided by the amount of solids applied to the unit process (by weight). Historically, gravity thickeners may have a performance of between 80 to 90 % solids capture. An example of this type of technology is presented in Figure 5.20 Figure 5.20 – Gravity Thickener Image found at https://www.sludgeprocessing.com/sludge-thickening/gravity-thickening/ on November 10, 2021 5.2.5.2 FLOATATION THICKENING Flotation thickening uses particle-particle interaction between a bubble and a solid particle to “float” the solid particle to the surface to perform solids-liquid separation. The technology works well on secondary biosolids because they have a specific gravity (i.e., density) close to water therefore have an affinity to stay suspended within the water column. Floatation can achieve higher levels of performance than gravity thickening of between 90 to 95% solids
Page 260 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. capture with the correct chemical dosage/ charge development of the biosolids as well as the correct generation of the necessary bubbles/ size to float the biosolids. Historically, floatation thickening achieved the highest removal efficiency when it is more lightly loaded, smaller biosolids (i.e., pin floc) and colder water temperature when compared to gravity thickening. Flotation thickening was used extensively in the 1970’s but then fell out of favor because the equipment required more maintenance when compared to gravity thickening. An example of this type of technology is presented in Figure 5.21. Figure 5.21 – Floatation Thickener Image found at https://www.westech-inc.com/products/dissolved-air-flotation-clarifiers-and-thickeners on November 11, 2021
Page 261 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.5.3 GRAVITY BELT THICKENING Gravity belt thickening is a process that uses a table that contains a rotating belt with small openings for solids-liquid separation. This process involves first mixing polymer/ biosolids to condition the sludge so then when conveyed onto the table where plows will spread the liquid mixture across the belt creating furrows which allow for the solids to remain while gravity pulls the liquid through the small openings. This conditioning step is critical because it provides the structure that allows for the biosolids to bridge the gap created between the openings on the belt mesh. The stronger and more stable this bridging the higher the solids capture and/ or the thicker the biosolid. However, with this type of technology, careful consideration must be given to how strong or stable the biosolids is because it only uses 1G (i.e., the force of gravity) to separate the liquid from the solid. This force, unlike other technologies cannot be increased or decreased. Therefore, this technology is highly dependent on polymer performance. Gravity belt thickening can achieve similar levels of performance to that of the floatation thickening with between 90 to 95% solids capture. An example of this type of technology is presented in Figure 5.22. Figure 5.22 – Gravity Belt Thickener Image found at https://www.komline.com/products/gravity-belt-thickener/ on November 11, 2021
Page 262 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.5.4 ROTARY DRUM THICKENING Rotary drum thickening is a process that is similar to the gravity belt thickening only instead of a rotating belt table this technology uses a rotating drum for solids liquid separation. First step involves conditioning the biosolids to allow for bridging across the small openings in the drum mesh. The openings and/ or space can be slightly smaller in this technology than a gravity belt because the force of gravity can be increased by the centrifugal forces (i.e., operates higher than 1G). Therefore, rotary drum screen can generally achieve either higher solids capture rate/ higher solids percentage with similar polymer dosages or can achieve a high performance with higher polymer dosages to that of a gravity belt. The rotary drum thickener also can allow for a level of control in the centrifugal force (i.e., rate of solids-liquid separation) thus allowing the user to have a level of control to the overall performance of the process. This higher level of control by the user can generally allow for thickening of a wider range of WAS types. WAS because it is biological, will vary depending on the environment and conditions created in the secondary process of the WWTP. Providing for an additional level of control with the thickening performance will ultimately create a more consistent biosolids processing environment. A rotary drum thickener can also achieve similar levels of performance to that of floatation and gravity belt thickeners with between 90 to 95% solids capture. An example of this type of technology is presented in Figure 5.23. Figure 5.23 – Rotary Drum Thickening Image found at https://vulcanindustries.com/products/sludge-thickening/ on November 11, 2021
Page 263 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.5.5 CENTRIFUGAL THICKENING Centrifugal thickening uses similar approach to thickening as to the rotary drum thickener where it uses centrifugal forces with conditioned sludge for solids-liquid separation. The primary difference between the rotary drum thickener is that it uses a higher speed rotating bowl instead of a low-speed drum, therefore creating much higher G forces. As discussed, this approach allows for ultimately a higher performance level and degree of control for the user. A centrifugal thickener can generally achieve a higher level of performance than any other technology with solids capture rate of between 92 to 98%. An example of this type of technology is presented in Figure 5.24. Figure 5.24 – Centrifugal Thickener Image found at https://www.sludgeprocessing.com/sludge-thickening/centrifugal-thickening/ on November 11, 2021 The downside to centrifuge thickening technology is that it takes more horsepower to generate the higher centrifugal forces. Site specifics ultimately dictate the efficiency as it relates to thickened biosolids to energy input ratio and ultimately that also must be balanced with the polymer dosage and labor. The sum of the cost generated by the energy input, labor and polymer dosage is used to develop an efficiency rating of cost per unit mass ($/ dry-ton). Generally, however, centrifuge thickening can achieve similar cost efficiency ratings to that of other thickening technologies. Therefore, ultimately, the selection of thickening technologies is based on level of performance needed vs. the labor/ maintenance preferences. In the situation of Davidson Dr. WWTP, the performance of the thickening technology is critical to the solids capture rate and therefore
Page 264 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. critical to the overall performance of the WWTP. Additionally, space is a premium on the site, therefore small footprint is also a critical parameter. It is recommended that centrifugal thickening be used for normal thickening activities at Davidson Dr. WWTP. 5.2.5.6 AERATED SLUDGE STORAGE As mentioned, thickening operations can be performed within basins if equipment. The proposed aerated sludge storage no 1 is to be developed from conversion of a primary clarifier which was originally constructed as a settling basin. Therefore, this basin, when aeration and mixing are turned off, will act like an ideal clarifier and thicken biosolids toward the center well. It is suspected that through decanting operations alone that this facility could achieve approximately 3% thickened biosolids. This is especially critical if Scenario 1A (Alternative A) were to be undertaken as it would minimize the volume (i.e., gallons) of TWAS conveyed to the existing belt press. It would also likely improve the dewatering performance of the existing belt filter press. To accomplish this approach, it is recommended that aerated sludge storage be equipment with decanting capabilities to draw off clarified effluent to the headworks during decanting activities. Once mechanical thickening activities are in place it is less critical to thicken biosolids in this manner, but it could still need to occur if the centrifugal thickener were sidelined due to maintenance or servicing.
Page 265 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.25 – Decanter Image found at https://www.parkson.com/products/dynacanter on November 10, 2021
Page 266 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.6 BIOSOLIDS PROCESSING –DEWATERING Dewatering is a physical process of separating biosolids from liquid for the purposes of creating a “dry” or dewatered product. Dewatered biosolids can have the appearance of being dry but they still contain ~88 to 73% liquid/ water by weight. When these biosolids are handled and disposed of most of the mass moved is water. Dewatering is the procedure by which part of the liquid portion of the sludge is removed through traditionally mechanical methods to increase the solids content of the solid. Dewatering is generally a mechanical-physical process utilizing belt filter press, screw press or centrifuge type equipment. 5.2.6.1 BELT FILTER PRESS Davidson Dr. WWTP currently uses a belt filter press for dewatering. As discussed in the thickening section, the belt filter press has a similar approach to dewater as a gravity belt thickener. A belt filter press is a process that uses a table that contains a rotating belt with small openings where it passes through a wedge zone where two sides of the belt squeeze together (with the biosolids between them) for solids-liquid separation. Most belt filter presses come with a gravity zone, which is a smaller version of a gravity belt thickener (i.e., gravity belt table mounted on top of the belt filter press, utilizing the same belt as the belts in the wedge zone) that will first utilize gravity to thicken the solids prior to entering the wedge zone. As with gravity belt thickening, biosolids conditioning step is critical because it provides the structure that allows for the biosolids to bridge the gap created between the openings on the belt mesh. As with gravity belt thickening, the stronger and more stable this bridging the higher the solids capture and/ or the thicker the biosolid. Sludge is conditioned with polymer and then fed onto a gravity belt section. However, with this type of technology, careful consideration must be given to how strong or stable the biosolids is because it can apply only minimal pressure to the biosolids in the wedge zone to separate the liquid from the solid. Therefore, the overall performance of a belt filter press with a gravity zone is traditionally between 14 to 17% TS. A belt filter press will also achieve with between 90 to 95% solids capture.
Page 267 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.26 – Belt Filter Press Dewatering Image found https://www.alfalaval.us/products/separation/filters-and-strainers/belt-press/as-h-belt-press-kpz/ on November 10, 2021 5.2.6.2 SCREW PRESS A screw press operates similarly to a rotary drum thickener in that it uses a low-speed rotation screw that forces the biosolids to the exterior if the drum where is presses against a porous mesh retaining the solids while allow the liquid to pass through. As with any technology utilizing wedge action of squeezing the biosolids it heavily relies on conditioning the biosolids to allow for bridging across the small openings in the mesh. The overall performance of a screw press is similar to that of a belt filter press with a gravity zone and achieved between 14 to 17% TS. A screw press can also achieve similar levels of performance to that of a belt filter press with between 90 to 95% solids capture. The advantages of a screw press over a belt filter press are that it is relatively simpler to operate, requires lower horsepower and is easier to maintain.
Page 268 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.27 – Screw Press Dewatering Image found https://ishigaki.de/en/products/screw-press-isgk-a/ on November 10, 2021 5.2.6.3 CENTRIFUGAL DEWATERING Centrifugal dewatering utilizes the same approach to dewatering as centrifugal thickening. The main difference between a centrifugal dewatering equipment is that it uses higher centrifugal forces with conditioned sludge for solids-liquid separation. The rotating speed of the bowed generated much higher G forces than a centrifugal thickener. This approach allows for ultimately and generally a higher performance level of centrifugal dewatering than compared to other continuous flow processes. Centrifugal dewatering can generally achieve dewatering performance of between 18 to 24% TS. They can also achieve a higher performance than any other technology with solids capture rate of between 95 to 98% in a traditional dewatering application. The main downside to centrifugal dewatering is that it traditionally is higher capital cost, uses the most horsepower and can require more specialized maintenance than other dewatering technologies. The main advantages of this technology over its competitors are that it produces a higher TS percentage and has a more compact footprint. As discussed in previous sections, solids capture rate is critical to the overall performance of the Davidson Dr. WWTP. Also, footprint was discussed as being a factor in the selection of the thickening unit. As shown in other sections, landfill disposal of unclassified biosolids is the lowest cost option for Davidson Dr. WWTP. Landfill disposal lends the dewatering technology toward one that achieves the highest level possible prior to transportation and disposal. Also, there are advantages to maintenance to also keep similar technologies between thickening and dewatering. Overall, due to the site specifics of Davidson Dr. WWTP it is recommended that centrifugal be used for the dewatering process.
Page 269 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Considering that the lowest cost biosolids disposal option is landfill the solid matter and water of the sludge. A higher solids content is easier to handle, results in lower transportation costs, and is beneficial for each form of disposal (incineration, land application, composting, or landfilling). While there are many alternative processes for dewatering, the following will be discussed below: belt filter presses, screw presses, and centrifuge. Figure 5.28 – Centrifugal Dewatering Image found https://www.gea.com/en/products/centrifuges-separation/decanter-centrifuge/thickening-decanter/biosolids-decanter-prime-sludgethickening%20.jsp on November 10, 2021 5.2.7 BIOSOLIDS PROCESSING SIDESTREAM TREATMENT Normal centrifugal dewatering generates two streams, (1) the dewatered biosolid product and (2) the wash water. Dewatered biosolid is handled and conveyed as discussed in other sections, however, the wash water is traditionally recycled back to the influent where it is aggregate and sent back through the WWTP. The higher the volume that the dewatering process generates the more successful the process is for generation of dewater solids. However, as discussed earlier, these processes are not completely efficient and can traditionally achieve a maximum of 95 to 98% solids capture. For example, at Davidson Dr. WWTP, even with centrifugal dewatering that is achieving 95% solids capture still produces an anticipated wash water TSS concentration of approximately 1,500 mg/L with an anticipated total concentration of with T-P. As discussed in the biological section, the effluent T-P concentration is a critical approach parameter for all processes within the Davidson Dr. WWTP. This effluent parameter is one of the most challenging parameters to effectively and efficiently address. Biological processes
Page 270 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. have been shaped to most efficiently address their removal within the Davidson Dr WWTP secondary processes. The primary approach is to address the removal in the most efficient manner which is to remove orthophosphate biologically and achieve a high level of TSS removal through a combination of clarification and tertiary filtration. Under normal operation, without dewatering, this process is anticipated to achieve 90% removal of T-P. However, when dewatering occurs the overall removal efficiency of T-P will decrease from 90% to 77% when modeled. The un-simulated mass balance corrected estimate decreases the overall T-P removal efficiency to 69%. During dewatering, the effluent T-P concentration is anticipated to increase to 1.15 mg/L or approximately 15% above current permitted effluent discharge limit. Ultimately, dewatering operation minimizes operational window related to achieving permit compliance if influent swings, upsets or challenges present themselves through the course of normal operation. Traditionally, the higher T-P concentration that is experienced during normal dewatering operation is addressed through aggregation of the permitted effluent discharge (i.e., weighted average on the DMR form). This is represented as shown in Table 6.1 as a modeled, a MA effluent increase of approximately 10%. It is anticipated however that this aggregated effluent flow increases by an approximate 16% from 0.39 mg/L to 0.452 mg/L, which is still well within the limits of the discharge permit. However, additional investigations were conducted to thoroughly evaluate and address the sidestreams generated by centrifugal dewatering. Table 5.36 – Davidson Dr. WWTP Projected Effluent Quality and T-P Removal Example Analysis Parameter Operational Dewatering In (lbs.) Out (lbs.) Removal % Sidestream Treatment 172.672 68.332 60.43% No Sidestream Treatment 201.152 201.152 0.00% Value Unit Davidson Dr. WWTP Effluent T-P1 Non-Operational Dewatering 0.37 mg/L Operational Dewatering w/ Sidestream Treatment 0.503 mg/L Non-Operational Dewatering w/ No Sidestream Treatment 0.853 mg/L Weighted MA Aggregate w/ Sidestream Treatment 0.39 mg/L Weighted MA Aggregate w/ No Sidestream Treatment 0.434 mg/L 1 Effluent T-P concentration simulations performed at 20oC. 2 Modeling does not and cannot completely account for dewatering days. Based on mass balance, it is suspected that T-P mass balance values will be 7/3 or 2.33x the identified modeled values. 3 Actual field values could be under reported by
Page 271 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. approximately 35% for operational dewatering days, multiply by 1.35. 4 Multiply effluent T-P aggregated concentration value by 1.05 to obtain a closer estimation of effluent T-P values during operational dewatering. A sidestream treatment system utilizing suspended air floatation (SAF) was proposed for Davidson Dr. WWTP. SAF utilizes a charged (typically anionic) surfactant coupled with mixing to generate micro-bubbles. These micro-bubbles then attach themselves to a solid thus increasing the buoyancy force and floating the solid to the surface to achieve solids-liquid separation. In the application for Davidson Dr. WWTP, the SAF would only operate when dewatering is occurring. SAF’s have the advantage that they require minimal start up time/ period therefore making this process ideal for wash water treatment. Generally, the solids that make their way through the centrifugal are going to be relatively small and have a low specific gravity (i.e., density close to water, WAS) as they were not captured by the mesh of the dewatering process. The solids that are uncaptured by a centrifugal are not likely to be captured by any other mechanical physical process. SAF traditionally have an advantage for removal of small, low specific gravity particles and are also less dependent on water temperature than other gravity settling based system. Therefore, the anticipated solids capture rate of wash water solids is approximately 96 to 98%. This approach will likely remove most of the solids that when recycled back to the headworks, would likely not be removed in secondary clarification and/ or tertiary filtration (size/ specific gravity). This process although not modeled, is anticipated to improve the overall removal efficiency of TSS through the WWTP during dewatering operation.
Page 272 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.29 – Suspended Air Flotation (SAF) Image https://heroninnovators.com/municipal-applications/ on November 10, 2021 The main purpose to the introduction of the SAF for treatment of wash water is to remove orthophosphate. During normal WAS handling/ storage (endogenous) operation, orthophosphate will be released. This orthophosphate will be conveyed in TWAS to the dewatering process, whereby it is soluble will not be capture by the centrifugal. Aluminum based chemicals (sodium aluminate for example) will be added to the SAF to chemical react and precipitate orthophosphate whereas the precipitant will be removed as a solid. It is anticipated that this overall process will remove approximately 60% of the T-P. A mechanical scraper is then used to remove these solids from the process and conveyed back to aerated sludge storage no. 2 while the clarified wash water is conveyed to the headworks of the WWTP. This system would treat wash water generated by the centrifugal dewatering activities and would only operate during dewatering days. Figure 5.30 presents the zoomed in process flow diagram of the sidestream treatment approach.
Page 273 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.30 – Proposed Davidson Dr. WWTP Simplified Proc
3 of 291 prings, Arkansas | Crist Engineers, Inc. cess Flow Diagram – Mid-Term – Scenario 2A1 – Zoomed In
Page 274 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The additional cost sidestream treatment system cost analysis is included in the following table. Table 5.37 – Davidson Dr. WWTP Sidestream Treatment System Cost Analysis Suspended Air Flotation (SAF) Parameter Value Unit Total Capital Cost $809,000 dollars Total Present Worth Cost $5,798,662 dollars Analysis Duration 20 Years Annual Additional T-P Removed 3,000 dry-lbs. T-P/ year Additional Total T-P Removed 60,000 dry-lbs. T-P PW Cost/ Total T-P Removed $97.16 $/ dry-lbs. T-P Average Annual Cost $289,933 1 Effluent T-P concentration of 0.5 mg/L or less during operational dewatering with sidestream treatment. Sodium aluminate addition of 126 gal/ dewatering day (159 lbs./ day (as Al+3)) lbs. As shown in the above table it costs approximately $96.64/ dry-lbs. T-P of additional T-P removed during sidestream treatment or an annual average cost of approximately $289,933.
Page 275 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 5.3 – CONCLUSION A summary of the proposed biosolids improvements for Davidson Dr. and SWWWTP are presented as follows: 5.3.1 DAVIDSON DR. WWTP Near-Term 1.8 Continuously WAS from the Davidson Dr. WWTP secondary process to biosolids handling. 1.9 Incorporate aerated sludge storage no. 1 as described in Scenario 1A (Alternative A) to generate a location for WAS holding, decanting and thickening. 1.10 Continue to utilize the compost facility and landfill for disposal of biosolids as currently described. 1.11 Compost facility to maintain current existing processing capacity with excess diverted to the landfill located in Saline County. Mid-Term 1.1 Implement new biosolids handling scheme as described in the Biological and Hydraulic Modeling TM. 1.2 Utilize centrifugal thickening and dewatering process technologies. 1.3 Implement sidestream SAF treatment system for centrifugal dewatering wash water. 1.4 Continue to utilize the compost facility and landfill for disposal of biosolids as currently described. Reevaluate assets as they need extensive repair thus minimize their processing costs. 1.5 Compost facility to maintain current existing processing capacity with excess diverted to the landfill located in Saline County. Long-Term 1.1 Expand/ modify the biosolids handling scheme as described in the Biological and Hydraulic Modeling TM.
Page 276 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.3.2 SWWWTP Near-Term 1.1 Maintain existing biosolids handling practices with SWWWTP, process through aerobic digestion, thicken to 3% TS. 1.2 Eliminate practice of hauling biosolids from SWWWTP and disposal into the collection system for Davidson Dr. WWTP. 1.3 Davidson Dr. WWTP aerated sludge storage no. 1 to provide liquid biosolids receiving station. a. Feed sodium aluminate at receiving station during hauling activities.
Page 277 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. CHAPTER 6 – CONTROL ENVIRONMENTAL LABORATORY AND MAINTENANCE BUILDING(S) EVALUATION SECTION 6.1 - INTRODUCTION The City of Hot Springs (CHS) Wastewater System Master Plan (WWSMP) is intended to establish criteria to be used as the basis for the proposed Capital Improvements Plan (CIP). Part of the CIP involves evaluating the size and functionality of the control, laboratory, and maintenance buildings at the Davidson Dr. wastewater treatment plant (WWTP).
Page 278 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 6.2 – DISCUSSION 6.2.1 DAVIDSON DR. WWTP The existing Davidson Dr. WWTP laboratory and control facility was installed in 1992. Recently, the laboratory/ office areas were recently renovated (2020) to address damage that occurred within the last 5 years. To accommodate secondary clarifiers 7, 8, 9 and 10, the existing laboratory and control facilities will need to be demolished. These clarifiers are not likely to be needed until after the planning period (2040), however, a new laboratory is planned to be constructed at the end of the planning period. The proposed potential location of the facility is to be located where the existing backwash tank is currently located (south of the animal control on the bluff that overlooks the wastewater treatment plant). The planning of the new laboratory space toward the end of the planning period will maximize the use of the existing renovated laboratory. This new building is tentatively planned at this time to include: 1. Operations/ control room, 2. Administration offices, 3. Conference room, 4. Break room, 5. Bathrooms, including showers, 6. Storm shelter area, 7. And maintenance garage for working on equipment The total space for the building is planned to be approximately 9,000 ft2. Additional support components of the facility are planned to include parking, standby power generation and access to the wastewater treatment plant. Additional evaluations and discussions may be needed for determination of the need for onsite maintenance of large over the road tractors and/ or large equipment. At this time, maintenance of large tractors or other equipment is planned to be completed offsite or in-situ. 6.2.2 SOUTHWEST (SW) WWTP The existing SWWWTP laboratory and control facility was installed in 2005. It appears to be in acceptable condition and is functional for the size of the staff located at the WWTP. Most of the operations and permit monitoring parameters are evaluated at Davidson Dr. WWTP or through an outside laboratory.
Page 279 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. At this time there are no recommended improvements for the laboratory and control facilities located at SWWWTP. SECTION 6.3 - CONCLUSION Layout and planning of a future laboratory and control building for Davidson Dr. WWTP can be conducted closer to implementation of the improvement. Engagement with an architect early in the process can establish the goals, purpose, needs and a revised budget for the project.
Page 280 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. CHAPTER 7 – MAJOR LIFT STATIONS AND FORCE MAINS EVALUATION SECTION 7.1 – INTRODUCTION The City of Hot Springs (CHS) Wastewater System Master Plan (WWSMP) is intended to establish criteria to be used as the basis for the proposed Capital Improvements Plan (CIP). Part of the CIP involves improvements to the existing major lift stations. Crist Engineers, Inc. staff along with CHS staff reviewed CHS 82 major lift stations to develop improvement recommendations based on the age, defects, condition and capacity of each lift stations. A review was also conducted to determine if existing lift stations could be consolidated, thus minimizing the total amount of major lift stations present within the CHS service area. Lift station CIP were grouped in near, mid- or long-term phases.
Page 281 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 7.2 – DISCUSSION 7.2.1 EVALUATIONS In April of 2020, each of the 82 major lift stations were evaluated using an evaluation form developed by Crist Engineers, Inc in conjunction with City of Hot Springs staff. These evaluations detail the station’s location, construction materials, electrical information, standby power, pump and motor information, HVAC and odor control information. There are also spaces for general comments about the condition of the structures, equipment, and any general comments that need addressed. Photographs of the station and site were also included with these evaluation forms. Lift station flow monitoring was not completed with the master planning effort, however, the 2010 SECAP with corresponding update and lift station specific technical memorandums were reviewed and noted for those specific lift stations that were identified needing capacity improvements. Apparent capacity challenges were also noted if the lift station visually showed signs of frequent high flows. The evaluations are provided as a separate document titled Major Lift Station Evaluations (December 2020). Several lift stations were also visited by the engineers to evaluate the overall condition of the four large stations and to determine if some of the smaller lift stations could be consolidated or eliminated. Lift stations were then ranked on the overall condition of the station as good, moderate, or poor. This would later help to determine the timeline on which the recommended improvements to the station will be accomplished. 7.2.2 IMPROVEMENTS Most recommendations were miscellaneous improvements and minor in nature. Miscellaneous lift station improvements included coating the wet well walls to prolong the life of the station, replacing a missing pump, or adding a water service line connection with a yard hydrant. Lift stations that appeared to be in good condition but showed signs of frequent high flow were also recommended to be replaced and upsized. Almost half of the stations are a dry well / wet well configuration that were put in place prior to 1990. This lift station configuration can be considered a confined space as well as experience code and maintenance challenges. Due to the age, safety, and complexity of modifying these types of lift stations, it has been recommended that they simply be replaced with new duplex submersible type lift station. Two of the largest lift stations, Gulpha and Hot Springs Creek, were discussed in depth in the 2010 SECAP with corresponding update. Previous modeling and flow monitoring indicated that these lift station as currently configured do not have sufficient capacity thus increasing the overflow potential within their corresponding collection system subbasin. To alleviate the overflow concerns, it was recommended Gulpha and Hot Springs Creek subbasin receive a peak flow lift station and flow equalization basin. Flow equalization basins within these subbasins
Page 282 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. provide inline storage which limits the peak flow pumping capacity needs at the lift station while potentially eliminating the need for an additional force main while also minimizing the instantaneous flow that is conveyed to the Davidson Drive WWTP. Additional flow monitoring, modeling and analysis will be completed to confirm the effectiveness and/ or sizes of the FEB’s at these locations. Each site is recommended to have an access driveway and black powder coated chain link fence with three strand barbed wire on the top along with the option of seeding or hardscape. This approach helps to ensure the station is easy to maintain and does not decrease the aesthetics if it is located in a neighborhood or near residences. Stainless steel enclosures and piping is recommended wherever applicable for longer life and lower maintenance. An underground drop for electric service is recommended to improve the resiliency of the of the lift station. Standby power was also considered for all lift stations with at least a 15-horsepower duty pump or greater. Also, through feedback from CHS staff a backup pumping system is preferred at the Malvern Highway, Mazarn #1, 70 West #14 and Quail House lift stations. The Godwin Dri-Prime Backup System (DBS) are preferred at these lift stations because they not only provide power when the electricity is out, but they can also still provide the ability to pump wastewater if there is a mechanical failure with the duty pumps. CHS staff indicated that mechanical failure takes a significantly longer time to repair than the time required to get electricity back to these lift stations. For lift stations less than 15 horsepower duty pump, a quick connection for bypass pumping is recommended to be installed to accommodate trailer-mounted emergency pumping at the lift stations. This approach eliminates the capital and maintenance related costs of standby power generators at these smaller stations. Odor control was only considered at lift station sites where it was being currently employed. If the existing lift station’s odor control was in poor condition at the time of the evaluation, it was recommended to be repaired or replaced with a new odor control system. Proposed new odor control systems or implementations were not considered for the master plan at this time. 7.2.3 CONSOLIDATION AND ELIMINATION In an effort to minimize capital and maintenance costs, some existing stations were considered for consolidation. If lift stations were close in proximity, in the same wastewater drainage basin or pumping to the same larger station, they were considered for consolidation. Lift stations that with relatively low flow were also considered for consolidation with any nearby stations to maximize efficiency. Lift stations 70 West #9, #11, and #13 on Airport Road were the best candidates for this as all three are within a mile of each other and within the same catchment areas / subbasin. Other locations were analyzed for potential consolidation such as Hot Springs #4, Lakeshore Drive, Scully Point, Moonlight Bay, Harold Drive and Brown Drive. These stations were close in proximity and pumping to a nearby, larger lift station; it was considered to eliminate all except the station lowest in elevation so raw sewage could gravity flow to one station and be pumped up to the larger station. However, the level of existing development on the lake front and topography precluded the feasible consolidation of these lift stations. Lift
Page 283 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. stations were not considered for consolidation if they had a significant enough flow already coming to them if they were on the lake front with existing development or more extreme topography. Using the ArcGIS software, an aerial image of Hot Springs was downloaded as the base layer. An exhibit was created for each lift station that showed an aerial image of the area and graphics to explain what the recommended improvements are for that station. Wastewater sub-basins were provided by CHS as a layer in ArcGIS. This layer grouped lift stations within a common wastewater drainage basin before they are pumped to one of the big four lift stations (Gulpha, Hot Springs Creek, Stokes and Fairwood) or to one of the WWTPs. These groups are displayed in the summary charts geographically from West to East. 7.2.4 RATING Lift stations were placed in the timeline based on what is recommended to be repaired or replaced, and how large the station is. Further discussion with CHS led to insight on some stations, causing reprioritization of lift station improvements. Stations were placed in the nearterm category if they needed capacity enhancement, were missing a pump, if they were one of the larger lift stations that needed repairs or if they were deemed important by CHS staff. Many of the mid-term and long-term improvements were stations that are recommended to be replaced with a wet well mounted self-priming lift station, have new electrical and standby power installed and site work completed; as the majority of these stations are the smaller, more minor stations, unless otherwise specified by CHS staff, these could be spread out evenly throughout the mid and long-term improvements in an attempt to evenly distribute the capital cost of improvements over the timeline of this CIP. Other long-term improvements included miscellaneous lift station improvements that are specific to the site. These could include cleaning and coating the wet-well, replacing vent pipes, rebuilding the valve box or other items. 7.2.5 FORCE MAINS Force mains that were identified to be rehabilitated in the SECAP or other documents previous to the wastewater masterplan but were yet to be addressed are contained within Appendices 13 and 14. These items have yet to be addressed as of the publishing of this document due to financial needs of other areas of the wastewater system.
Page 284 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 7.3 – CONCLUSION The estimated cost summary for the force main improvements is identified in Table 7.1. Table 7.1 – City of Hot Springs Force Mains – Cost Summary Phase Location Cost Summary Near-Term Gulpha Force Main $8,113,000.00 Near-Term Mazarn Force Main $3,950,784.00 Near-Term Albert Pike Rd Force Main $1,039,000.00 Total $13,102,784.00 Of the near-term total estimated cost of approximately $19 million, the Gulpha parallel force main represents approximately $16.4 million or 86%. Due to the cost and extent of the improvements related to this interceptor/ lift station/ force main conveyance system the evaluation is ongoing. The estimated cost summary for the major lift stations is identified in Table 7.2. Table 7.2 – City of Hot Springs Major Lift Stations – Cost Summary Phase Number of Stations in Phase Percent of Total Stations Total Phase Cost Phase Percent of Total Cost Near-Term Improvements 17 21% $14,490,500.00 34% Mid-Term Improvements 16 20% $17,285,200.00 41% Long-Term Improvements 49 60% $10,733,100.00 25% Total 82 - $42,508,800.00 - Of the near-term total estimated cost of approximately $14.49 million, Gulpha lift station represents approximately $6.52 million or 45%. Due to the cost and extent of the improvements related to this lift station the evaluation is ongoing. As of late 2021, preliminary
Page 285 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. evaluations were conducted to determine which approach is the most cost effective and ideal solution: Options 1. Inline flow equalization basin coupled with peak flow pump station (to pump to FEB) and misc. pump station repairs or, 2. Upsize Gulpha pump station and force main to convey wet weather flow to Davidson Dr. WWTP to permit the use of the existing equalization pond. At the time of production of this report, Option 2 was the selected alternative. Of the mid-term estimated cost of approximately $17.2 million, Hot Springs Creek lift station represents approximately $10.6 million or 62%. Additional analysis is recommended to be conducted with a similar approach of comparison between the two alternatives of utilizing inline storage or alternatively increase the capacity of the lift station/ force main. The remaining major lift stations CIP projects represented in the near, mid and long-terms are mostly comprised of individual pump station rehabilitations or replacements in the magnitude of approximately $500,000 to $1 million in cost albeit there are a large number of projects that are less than $100,000 in cost.
Page 286 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. CHAPTER 8 – COLLECTION SYSTEM AND MINOR LIFT STATIONS SECTION 8.1 – INTRODUCTION The City of Hot Springs (CHS) Wastewater System Master Plan (WWSMP) is intended to establish criteria to be used as the basis for the proposed Capital Improvements Plan (CIP). Part of the CIP involves evaluating the collection system and associated minor lift stations.
Page 287 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 8.2 – DISCUSSION SECAP The City of Hot Springs, with the assistance of RJN Group, Inc. developed a Sewer Evaluation and Capacity Assurance Plan (SECAP) in 2010. This evaluation included the inspection of approximately 12,000 manholes and survey of 10 inch or larger lines. Additionally, sixty-five (65) flow meters were installed in strategic locations for 75 days to determine the impacts associated with storm events and their corresponding generation of I/I. From those evaluations a series of recommended improvements were developed for the various pump stations, force mains, gravity mains and manholes. Initially, 4,735 manholes and approximately 19,000 LF of sanitary sewer line were repaired/ replaced. This resulted in a 21.9% reduction in I/I to the Davidson Dr. WWTP and a 10.4% reduction in I/I to SW WWTP. RJN Group, Inc. completed a SECAP status update in 2020 to review the current status of the previously developed recommended improvements.
Page 288 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. SECTION 8.3 – CONCLUSION 8.3.1 LIFT STATIONS AND FORCE MAINS Major lift stations and force mains that were identified to be rehabilitated but were yet to be addressed are contained within Appendices 13 and 14. These items have yet to be addressed as of the publishing of this document due to financial needs of other areas of the wastewater system.
Page 289 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 8.3.2 GRAVITY MAINS AND MANHOLES Gravity mains and manholes that were identified in the SECAP to be rehabilitated but were yet to be addressed are contained within Appendices 13 and 14. These items were not addressed at the date of publishing this document due to financial needs in other areas of the wastewater system. The CIP summary of those items are presented in the below summary table. Table 8.1 – Proposed Collection System Estimated Cost Summary – Near-Term Phase Location Cost Summary Near-Term Grand Ave $286,144.00 Near-Term Main St $726,975.00 Near-Term Spring Street (Gulpha), MH 3314 to MH 4015 $3,698,000.00 Near-Term Ridgeway Street, MH 1569 to MH 1713 $2,556,786.00 Near-Term Gulpha Interceptor, MH 4015 to MH 1750 $20,124,061.00 Near-Term Southwest Collection or Gravity Mains, MH 13480 to Mazarn #3 Lift Station $282,450.00 Near-Term Lakeside Lift Station, MH 5254 to Lakeside Lift Station $710,506.00 Near-Term Mazarn Capacity Enhancement $418,304.00 Total $29,073,226.00
Page 290 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 8.2 – Proposed Collection System Estimated Cost Summary – Mid-Term Phase1 Location Cost Summary Mid-Term Realignment MH 1899 to MH 1900 (Adams St) $378,000.00 Mid-Term MH Point Repair, Replace MH 8574 (Malvern Ave) $73,300.00 Mid-Term Rework MH 11481 to MH 1864 (Forest View Court) $258,500.00 Mid-Term Rework MH 5271 to MH 5257 (Carpenter Dam Rd) $1,494,500.00 Total $2,204,300.00 1 I/I investigations within the Hot Springs Creek and Stokes Tributaries may identify additional midterm collection system CIP projects. Recommendations were made to revisit and conduct additional I/I investigations within the Hot Springs Creek and Stokes Tributaries. These investigations may result in the development of additional mid-term collection system CIP projects. Table 8.3 – Proposed Collection System Estimated Cost Summary – Long-Term Phase Location Cost Summary Long-Term Hot Springs Creek Interceptor $9,229,500.00 Total $9,229,500.00 Table 8.4 – City of Hot Springs Collection System – Cost Summary Phase Total Phase Cost Phase Percent of Total Cost Near-Term $ 29,073,226.00 72% Mid-Term $ 2,204,300.00 5% Long-Term $ 9,229,500.00 23% Total $ 40,507,026.00
Page 291 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. The majority of the near-term costs are associated with Gulpha interceptor. Projects related to the Gulpha basin, including lift stations, parallel force main and integration with the Davidson Dr. FEB are currently in the process of being analyzed to determine the best wholistic strategy for rehabilitation. 8.3.3 MINOR LIFT STATIONS The City of Hot Springs currently has approximately 3,800 minor lift stations that they must rehabilitate, replace, and maintain. These small stations are located primarily around Lake Hamilton to provide sanitary sewer service to the associated lake front residences. The City of Hot Springs currently has an extensive repair and rehabilitation program that continuously addresses the needs of these minor lift stations. Each location and needs are site specific. However, the estimated costs presented by these lift stations are estimated to be between $5 million to $10 million. To address this cost an analysis was completed that includes a 3.5% average annual inflation over a term of 20 years. It is anticipated that an annual rehabilitation/ replacement fund of approximately $500,000 per year should be targeted each year to rehabilitate or replace these lift stations. Table 8.5 – Proposed Minor Lift Stations Estimated Annual Cost Summary Phase Location Annual Cost Summary1 - Minor Lift Stations $500,000.00 Total Cost Summary1 Total $6,669,000.00 1 Present worth analysis and completed in 2022 dollars when considering a 3.5% average annual inflation rate. Preliminary layout for duplex lift stations was developed in 2018 by the City of Hot Springs and contained in Appendices 11 and 12.
Wastewater System Master Plan (WWSMP) Appendices Volume 2 May 2022