"/ !( !( !( !( Lakeside 5259 5260 Ü Hot Springs, AR "/ Pump Station Gravity Main !( April 12, 2020 SSO Manhole !( Feb 18, 2020 SSO Manhole Lakeside Pump Station Capacity Improvement Lakeside Pump Station Capacity Improvement Exhibit 9
"/ "/ "/ !( !( !( !( !( Hot Springs Creek 1866 1865 Ü Hot Springs, AR "/ Pump Station Gravity Main !( April 12, 2020 SSO Manhole !( Feb 18, 2020 SSO Manhole SECAP Recommended Hot Springs Creek Interceptor Evaluate I/I Removal Evaluate I/I Removal Exhibit 10
!(1684 Ü Hot Springs, AR Gravity Main !( April 12, 2020 SSO Manhole !( Feb 18, 2020 SSO Manhole Monitor For Additional SSOs Monitor For Additional SSOs Exhibit 11
APPENDIX 14 Tech Memo – Update on SECAP Projects for SSO Removal
Page 1 TECHNICAL MEMORANDUM – UPDATE ON SECAP PROJECTS FOR SSO REMOVAL WITHIN COLLECTION SYSTEM To: Craig Johnson, P.E. (Crist Engineers) From: Daniel Jackson, P.E. (RJN) / Mac Compton, P.E. (RJN) Date: August 20th, 2020 RE: Engineers Opinion of Probable Cost of Required Projects to Eliminate Remaining SSO’s INTRODUCTION This technical memo provides cost estimates for the remaining, required projects to eliminate the continuing SSO’s in the Hot Springs sewer system as well as additional remedial measures for SSO manholes without a designated project. Model predicted SSO volumes are given where applicable. Due to most of the model not being updated since 2011, several SSO’s reported by Hot Springs staff the last several years are not replicated orproduced within the model and subsequent volumes cannot be given. All of these improvements were outlined in the 2010 SECAP for the City to undertake, however have been re-evaluated based upon recent SSO information as well as updated for current costs to reflect 2020 dollars vs. 2011. EAST GRAND AVE TABLE 1 East Grand Ave Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 3109 3108 305 8 10 $114,375 3108 3106 295 8 10 $110,625 Total 600 $225,000 Segments 3109:3108 and 3108:3106 will both require upsizing from an 8-inch to a 10-inch pipe to limit the amount of surcharging occurring within the sewer line, along with recorded overflows. A sizeable
Page 2 area of the sewer system, approximately 9,500 linear feet conveys its flow thru this line. The hydraulic model predicts only heavy surcharging during the design storm and no overflows; however, the City of Hot Springs has reported repeating SSO’s at manhole 10578. The February 18, 2020 storm estimated overflow volume was 400 gallons. Exhibit 2 illustrates the East Grand Ave capacity improvement project. SPRING STREET (UPPER GULPHA) TABLE 2 Spring Street Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 1805 3299 56 10 15 $23,520 1806 1807 198 10 15 $83,118 1807 4115 238 10 15 $100,128 3279 3296 220 10 15 $92,484 3288 3279 245 10 15 $102,816 3289 3289A 213 10 15 $89,418 3290 3289 108 10 15 $45,360 3295 3290 290 10 15 $121,800 3296 1806 440 10 15 $184,842 3297 3295 185 10 15 $77,826 3298 3297 372 10 15 $156,156 3299 3298 155 10 15 $64,890 3938 4005 72 12 18 $32,400 4005 4006 154 12 18 $69,255 4006 4007 154 12 18 $69,075 4007 4008 39 10 18 $17,550 4008 4009 181 10 18 $81,450 4009 4010 122 10 18 $54,720 4010 4011 417 10 18 $187,695 4011 4012 302 10 18 $136,035 4012 4013 164 10 18 $73,935 4013 4014 202 10 18 $90,855 4014 4015 66 10 18 $29,790 4108 4116 62 10 15 $26,166 4114 4108 110 10 15 $46,368 4115 4114 294 10 15 $123,270 4116 4117 242 10 15 $101,682 4117 4118 202 10 15 $84,630 4118 4119 52 10 15 $21,966 4119 4143 78 10 15 $32,718
Page 3 TABLE 2 Spring Street Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 4142 3938 28 12 15 $11,844 4143 4142 128 10 15 $53,760 3289A 3288 98 10 15 $41,160 3315 3314 208 12 15 $87,360 3314 3313 96 12 15 $40,143 3313 3311 77 12 15 $32,278 3311 3309 471 12 15 $197,637 3309 3301 112 12 15 $46,930 3301 3300 146 12 15 $61,381 3300 1805 274 12 15 $115,068 Total 7,270 $3,109,479 Completion of the Spring street (Upper Gulpha) interceptor capacity improvement will eliminate SSO’s at manholes 4117 and 4118. Model predicted overflow volumes during the design storm for manholes 4117 and 4118 are 0.44 million gallons (MG) and 0.46 MG, respectively. Exhibit 3 illustrates the Spring Street capacity improvement project. RIDGEWAY STREET TABLE 3 Ridgeway Street Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 1564 4627 163 8 12 $47,427 1565 1564 153 8 12 $41,003 1566 1565 183 8 12 $49,043 1567 1566 369 8 12 $98,890 1568 1567 22 8 10 $5,559 1569 1568 316 8 10 $79,847 1753 1713 311 15 21 $98,587 1754 1753 141 15 21 $44,697 1755 1754 136 15 21 $43,112 1756 1755 84 15 21 $23,798 1757 1756 400 15 21 $122,512 1758 1757 322 15 21 $98,622 1759 1758 405 15 21 $133,347 1760 1759 246 15 21 $83,633
Page 4 TABLE 3 Ridgeway Street Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 1761 1760 178 15 18 $61,878 1762 1761 400 15 18 $134,763 1763 1762 278 15 18 $93,660 1764 1763 405 15 18 $136,448 1765 1764 390 15 18 $131,394 1766 1765 304 15 18 $102,420 1767 1766 491 15 18 $165,422 1768 1767 250 15 18 $84,227 1769 1768 376 15 18 $126,677 4561 4562 193 12 15 $50,245 4562 4563 65 12 15 $17,917 4563 4564 116 12 15 $36,417 4564 4565 350 12 15 $109,878 4565 4566 50 12 15 $14,548 4566 4567 364 12 15 $114,273 4567 4568 278 12 15 $87,274 4568 4569 96 12 15 $30,138 4569 1769 65 14 15 $18,913 4627 4543 262 10 12 $70,215 Total 8,162 $2,556,786 Completion of the Ridgeway street capacity improvement will eliminate SSOs at manholes 1754 and 1755. Manhole 1754 overflows because it is a relief point for the main trunk sewer running along Gulpha Creek. Infiltration and inflow (I/I) removal upstream will have minimal impact at relieving the SSO at manhole 1754. Model predicted overflow volumes for manhole 1754 is 0.40 MG. Exhibit 4 illustrates the Ridgeway Street capacity improvement project.
Page 5 GULPHA INTERCEPTOR TABLE 4 Gulpha Interceptor Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 1701 1702 394 21 30 $301,686 1702 1703 396 21 30 $294,121 1703 1704 207 21 30 $153,745 1704 1705 117 21 30 $86,899 1705 1706 293 21 30 $217,620 1706 1707 421 21 30 $322,360 1707 1708 197 21 30 $150,843 1708 1709 264 21 30 $202,145 1709 1710 160 21 33 $134,763 1710 1711 372 21 33 $313,324 1711 1712 399 21 33 $340,343 1712 1713 290 21 33 $164,319 1713 1714 312 21 33 $266,133 1714 1715 175 21 33 $147,397 1715 1716 269 21 33 $226,571 1716 1717 354 21 33 $298,164 1717 1718 185 21 33 $155,820 1718 1719 300 21 33 $252,681 1719 1720 99 21 33 $84,446 1720 1721 183 21 33 $156,097 1721 1722 101 21 33 $82,749 1722 1723 519 21 33 $437,138 1723 1724 311 24 33 $261,946 1724 1725 326 24 33 $274,580 1725 1726 377 24 33 $317,536 1726 1727 305 24 36 $287,252 1727 1728 396 24 36 $377,202 1728 1729 602 24 36 $573,424 1729 1730 371 24 36 $349,412 1730 1731 415 24 36 $390,852 1731 1732 101 27 36 $95,123 1732 1733 339 27 36 $319,274 1733 1734 390 27 42 $404,336 1734 1735 396 27 42 $406,311 1735 1736 402 27 42 $412,467 1736 1737 416 27 42 $426,832 1737 1738 130 27 42 $133,385
Page 6 TABLE 4 Gulpha Interceptor Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 1738 1739 351 27 42 $360,139 1739 1740 200 27 42 $205,208 1740 1741 353 30 42 $365,976 1741 1742 337 30 42 $345,775 1742 1743 366 30 42 $375,530 1743 1744 474 30 42 $491,423 1744 2351 370 30 42 $281,609 1745 1746 260 32 42 $266,770 1746 1747 335 32 42 $336,027 1747 1748 397 32 42 $407,337 1748 1749 63 30 42 $64,640 1749 1750 77 30 42 $77,236 1750 Gulpha PS 192 30 42 $199,057 2351 1745 102 30 42 $67,480 4004 4283 255 21 27 $169,871 4073 4074 213 21 24 $127,213 4074 4075 213 21 24 $127,213 4075 4076 504 21 24 $306,415 4076 4077 307 21 24 $183,355 4077 4078 321 21 24 $184,342 4078 4079 172 21 24 $102,726 4079 4080 162 21 24 $98,490 4080 4081 269 21 27 $182,080 4081 4004 455 21 27 $303,102 4083 4084 399 21 27 $265,797 4084 4141 376 21 30 $291,934 4100 4073 294 21 24 $175,590 4101 4100 271 21 24 $161,854 4102 4101 258 21 24 $154,089 4103 4102 254 21 24 $151,700 4141 1701 116 21 30 $88,821 4283 4083 199 21 27 $132,566 Total 20,199 $16,870,662 This project in conjunction with the Gulpha parallel force main project and Spring Street project will eliminate the SSOs at manhole 1750 and others further upstream. Model predicted overflow volumes for manhole 1750 is 2.80 MG. Exhibit 4 illustrates the Gulpha Interceptor capacity improvement project.
Page 7 GULPHA PARALLEL FORCE MAIN TABLE 5 Gulpha Parallel Force Main RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 Capacity Improvements Item Capital Cost ($) Additional Force Main 16,016 LF $6,622,346 Additional Pumping Capacity 24 MGD $9,848,433 Total $16,470,780 The Gulpha parallel force main project is critical in not only eliminating the SSO at manhole 1750, but for all SSO’s upstream of the Gulpha pump station. Without constructing the parallel force main and installing new pumps none of the other Gulpha related projects will result in any net impact, overflows upstream of the pumping station will still occur. As stated in the 2010 SECAP, the new, parallel force main should be 30-inches in diameter and 24 million gallons per day (MGD) of new pumping should be added to the existing 6 MGD pumping capacity for a total of 30 MGD worth of pumping capacity. Exhibit 5 illustrates the Gulpha parallel force main capacity improvement project. SOUTHWEST WWTP CAPACITY IMPROVEMENTS TABLE 6 SWWWTP Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 9292 9293 74 6 8 $25,900 9291 9292 63 6 8 $22,050 13483 13484 120 6 8 $42,000 13482 13483 99 6 8 $34,650 13481 13482 121 6 8 $42,350 9293 Mazarn #3 PS 15 6 8 $5,250 9291A 9291 17 6 8 $5,950 13484 13485 81 6 8 $28,350 13480 13481 217 6 8 $75,950 Total 807 $282,450
Page 8 Most of the west side of Hot Springs which includes the SWWWTP has not been updated in the model since 2009, therefore model predicted overflow volumes cannot be given at this time for manholes 13483 and 13484. However, the current model predicts approximately 0.16 MG of flooding upstream of Mazarn #3 pump station without taking into account the extra influence from the newly developed subdivision to the north. Nevertheless, RJN is recommending at a minimum, upsizing the 6-inch gravity mains north of Mazarn #3 pump station connecting the newly constructed subdivision to an 8-inch to appropriately handle the additional influent. Exhibit 7 illustrates the SWWWTP capacity improvement project. MAZARN #1 PUMP STATION The current model predicts 0.11 MG overflowing from manhole 9250. As previously stated, the west side of Hot Springs has not been updated in the model since 2009, so flow regimes into this pump station cannot be determined, consequently, preventing appropriate recommendations on required pump upgrades for the time being. Exhibit 8 illustrates the Mazarn #1 pump station capacity improvement project. LAKESIDE PUMP STATION TABLE 7 Lakeside Pump Station Capacity Improvements RJN Group Inc 2020 COLLECTION SYSTEM IMPROVEMENTS ENGINEERS OPINION OF PROBABLE COST Updated: 08/17/2020 USMH DSMH Length (Feet) Existing Diameter (Inch) Proposed Diameter (Inch) Capital Cost ($) 5257 5258 195 10 12 $78,029 5260 5257 338 10 12 $135,189 5258 5259 216 10 12 $86,360 5263 5260 276 10 12 $110,575 5259 PS 63 10 12 $25,353 Pump Station Upgrade to 2.8 MGD $275,000 Total 1,089 $710,506 Completion of the Lakeside pump station capacity improvement will eliminate the SSO at manhole 5260. The current model does not predict that any overflows will occur at manhole 5259 during the design storm. Model predicted overflow values for manhole 5260 are 0.23 MG. Exhibit 9 illustrates the Lakeside pump station capacity improvement project.
Page 9 HOT SPRINGS CREEK INTERCEPTOR AND PUMP STATION There is some uncertainty in the current model about which pumps are working at the Hot Springs Creek pump station. Judging from the results given by the model, it seems that not all three Flygt pumps are pumping into the new Fairwood force main as well as a diesel Fairbanks Morse pump discharging into the “old” 30-inch force main shared with Stokes. Clarification about pump station performance will determine which SECAP projects need to be addressed to eliminate the SSOs at manholes 1865 and 1866. The reported SSO volume by the City of Hot Springs for both manholes 1865 and 1866 for the February 18, 2020 storm were 10,000 gallons. Exhibit 10 illustrates the Hot Springs Creek capacity improvement project, which was outlined in the 2010 SECAP. However, due to the Fairwood Pump Station and force main project, along with the parallel force main out of Stokes Pump Station, the best solution here would be to remove I/I upstream of Hot Springs Pump Station. MANHOLE 1684 The current model does not predict that any overflow should occur at manhole 1684. RJN is recommending that the manhole be monitored for additional SSO’s and if SSO’s continue to occur, that further investigation immediately downstream of the manhole be pursued to check for blockage and/or collapsed pipe. Exhibit 11 illustrates the location of the SSO at manhole 1684. SUMMARY TABLE 8 SUMMARY OF REQUIRED PROJECTS Project Cost ($) SSO Volume Removed (MG) East Grand Ave $225,000 0.0004 Spring Street (Upper Gulpha) $3,109,479 0.90 Ridgeway Street $2,556,786 0.40 Gulpha Interceptor $16,870,662 2.80 Gulpha Parallel Force Main $16,470,780 4.101/ SWWWTP $282,450 0.16 Mazarn #1 - 0.11 Lakeside Pump Station $710,506 0.23 Hot Springs Creek - 0.02 Manhole 1684 - - Total $40,225,663 4.62 1/ Without completion of the Gulpha Parallel Force Main all other Gulpha projects will have no net impact
APPENDIX 15 Tech Memo – Hot Springs Rainfall Monitoring along with SSO Comparison
1 | Page TECHNICAL MEMORANDUM To: Monty Ledbetter (Hot Springs) From: Daniel Jackson (RJN) / Mac Compton (RJN) Date: May 27, 2020 RE: 2019-2020 Rainfall Monitoring along with SSO Comparison BACKGROUND In October 2019, the City of Hot Springs requested that RJN monitor rainfall at four different locations throughout the City with an emphasis in evaluating the “Gulpha” basin. In relation to a CAO that Hot Springs was placed under, the City has made efforts to increase the efficiency of their sewer system and reduce the number of sanitary sewer overflows (SSOs). This includes flow monitoring, sanitary sewer evaluation inspections throughout the City, hydraulic model development, resulting in capacity enhancements and rehabilitation of the sanitary sewer collection system across the service area. The purpose of the rainfall monitoring conducted from October 2019 through April 2020 was to associate recorded SSOs to the most intense storm events observed during this six-month period. It should be noted that Hot Springs’s collection system consists of over 445 miles of gravity sewer, 215 miles of force main, 180 pump stations and 3,300 grinder pumps. In 2009, the City experienced 18 SSOs per 100 miles of gravity sewer during high intensity rainfall events. DESIGN STORM The design storm event was selected after consulting with the City of Hot Springs staff and was constructed according to NRCS design methods in 2009. The NRCS design storm is a 24-hour duration event that contains all 2-year events of smaller durations within it and has a cumulative depth of 4.3 inches. The cumulative depth for a 2-year/24-hour rainfall event has since increased to 4.51 inches (NOAA Atlas 14 Volume 9, Version 2). Figure 1 shows the current, cumulative depth of the 2-year/24-hour storm in Hot Springs.
2 | Page Figure 1 - DDF Table for Hot Springs, AR from NOAA Atlas 14 Volume 9, Version 2
3 | Page RAINFALL MONITORING Four rain gauges, identified as HS1, HS2, HS3 and HS4, were installed on October 16, 2019 with the first full day of monitoring beginning on October 17, 2019. The rain gauges are still active at the time of this technical memorandum. The purpose of their installation was to measure rainfall contributing to SSOs throughout the City with emphasis towards the Gulpha basin. Figure 2 illustrates the location of the rain gauges. SSO AND RAINFALL EVALUATION Although the rain gauges were active for over six months, the 2-year/24-hour rainfall event never occurred, so evaluations of recorded SSOs have been compared to the three largest rainfall events that occurred during the rainfall monitoring period. A summary of these rainfall events is given in Table 1. To determine the recurrence interval of these three rainfall events, RJN used an inhouse software that plots rainfall data on a depth/duration/frequency chart (DDF Chart). The DDF chart also plots the 1, 2, 5 and 10-year rainfall eventsfor Hot Springs using data from NOAA Atlas 14. Table 1 Summary of Rainfall Events Date Rain Gauge Total Rainfall (in) Duration (hr) 2/18/2020 HS3 3.31 12 4/12/2020 HS3 2.78 24 5/17/2020 HS1 3.24 22 February 18, 2020 Event The February 18th rainfall event had a total rainfall depth of 3.31 inches over 12 hours. This was the largest rainfall event recorded during the monitoring period and reached a recurrence interval of one-year after 6 hours. Figure 3 depicts the DDF curve for this rainfall event. The City of Hot Springs recorded 14 SSOs resulting from this rainfall event. Table 2 summarizes the SSOs from the February 18th rainfall event. Figure 4 on page 5 shows the locations of the February 18th SSOs. Figure 2 - Location of Rain Gauges
4 | Page Table 2 February 18, 2020 SSO Summary SSO Manhole Address MH# 1750 117 Catherine Heights Rd. MH# 5259 857 Carpenter Dam Rd MH# 5260 816 Carpenter Dam Rd. MH# 1865 352 Fontatna Rd. MH# 1866 362 Fontana Rd. MH# 1684 104 Forest View Ct. MH# 12242 106 Forest View Ct. MH# 1755 954 Ridgeway St. MH# 4118 1539 Spring St. MH# 4117 1539 Spring St. MH# 10578 611 East Grand Ave MH# 13484 2460 Marion Anderson Rd. MH# 13483 2460 Marion Anderson Rd. MH# 9250 118 Ridge Pt. Figure 3 - February 18, 2020 DDF Chart
5 | Page Hot Springs sewer system operates roughly 2,350,000 feet of gravity main sewer or 445 miles. Standardizing the 14 SSOs from the February 18th rainfall event per 100 miles yields a value of 3.15 SSOs per 100 miles. The number of SSOs is likely affected by antecedent moisture conditions resulting from 2.5 inches of rain the prior seven days. April 12, 2020 Event The April 12th rainfall event had a total rainfall depth of 2.78 inches over 24 hours. This was the third largest rainfall event recorded during the monitoring period and had a recurrence interval of under oneyear. Figure 5 on page 6 depicts the DDF curve for this rainfall event. From this rainfall event the City of Hot Springs recorded 10 SSOs. Table 3 summarizes the SSOs from the April 12th rainfall event. Figure 6 on page 7 shows the locations of the April 12th SSO. Figure 4 - Location of February 18, 2020 SSO
6 | Page Table 3 April 12, 2020 SSO Summary SSO Manhole Address MH# 1750 117 Catherine Heights Rd. MH# 5259 857 Carpenter Dam Rd MH# 1754 962 Ridgeway Rd. MH# 4118 1539 Springs St. MH# 4117 1539 Springs St. MH# 5260 816 Carpenter Dam Rd. MH# 12242 106 Forest View Ct. MH# 13484 2460 Marion Anderson Rd. MH# 13483 2460 Marion Anderson Rd. MH# 9250 118 Ridge Pt. Figure 5 - April 12, 2020 DDF Chart
7 | Page Standardizing the 10 SSOs from the April 12th rainfall event per 100 miles yields a value of 2.25 SSO per 100 miles. May 17, 2020 Event The May 17th rainfall event had a total rainfall depth of 3.24 inches over 22 hours. This was second largest rainfall event recorded during the monitoring period and had a recurrence interval of under one-year. Figure 7 on page 8 depicts the DDF curve for this rainfall event. From this rainfall event the City of Hot Springs recorded two SSOs. Table 4 summarizes the SSOs from the May 17th rainfall event. Figure 8 on page 9 shows the locations of the May 17th SSO. Figure 6 - Location of April 12, 2020 SSO
8 | Page Table 4 May 17, 2020 SSO Summary SSO Manhole Address MH# 1750 117 Catherine Heights Rd. MH# 5259 857 Carpenter Dam Rd. Figure 7 – May 17, 2020 DDF Chart
9 | Page Standardizing the two SSOs from the May 17th rainfall event per 100 miles yields a value of 0.45 SSOs per 100 miles. CONCLUSION From 2004 to 2008, SSOs occurred at an average rate of 18 overflows per 100 miles of gravity sewer for larger rainfall events. The City pledged to reduce inflow and infiltration throughout the system by implementing extensive flow monitoring, a comprehensive sanitary evaluation study and targeted infrastructure rehabilitation. Post flow monitoring outlined that over 20% of peak inflows had been removed through these efforts, impacting peak flow management significantly. Additionally, a full system hydraulic model was constructed and calibrated with the flow monitoring data collected. Results from the computer simulations of the 2-year storm event outlined that even with reduced peak wet-weather flows, several large-scale capacity enhancements were necessary to contain those peak flows and alleviate SSOs. The City undertook these projects along with upgrading the headworks at Davison treatment plant to handle the additional contained flows. Since completing the evaluation of six months of rainfall data and SSO reporting and making the resulting corrections as detailed in the CAO, the City has gone from 18 SSOs per 100 miles of gravity sewer to less than 3.5 per 100 miles of gravity sewer. Figure 8 - Location of May 17, 2020 SSO
APPENDIX 16 Tech Memo – System Wide Flow Monitoring, Model Calibration, and Model Update
March 3, 2022 Daniel Jackson, P.E. Mac Compton, P.E. 501.224.2248 www.rjn.com March 2022 System Wide Flow Monitoring, Model Calibration, and Model Update RJN | Crist | Hot Springs City of Hot Springs Final Report
www.rjn.com March 3, 2022 Craig Johnson, P.E. Crist Engineers Inc. 205 Executive Ct. Little Rock, AR 72205 Subject: Hot Springs System Wide Flow Monitoring, Model Calibration, and Model Update Dear Mr. Johnson: In accordance with the February 2021 Subconsultant Agreement with Crist Engineers, RJN Group, Inc. (RJN) is pleased to submit the Hot Springs System Wide Flow Monitoring, Model Calibration, and Model Update final report. The activities included installation of 44 flow monitors and 10 rain gauges that recorded data from March 18, 2021 to May 24, 2021, updates to the hydraulic model with edits made to the current population, water consumption data, sewer main additions, and recalibration of the hydraulic model to dry and wet-weather flows. Capacity analysis and recommendations to eliminate the 20 wet-weather SSOs recorded throughout 2020 and 2021 are also included in this report. A separate Technical Memorandum has been submitted and is attached to this report for the Gulpha Basin Alternative Evaluations. We appreciate the opportunity to work with Crist Engineers and Hot Springs and the excellent cooperation throughout the project. Should you have any questions, please do not hesitate to reach out. Respectfully Submitted, RJN Group, Inc. Mac Compton, P.E. Senior Project Manager Colton Bryant, E.I. Project Engineer MC/CB/18-3665-00 Enclosure
TABLE OF CONTENTS Page i Executive Summary Summary ................................................................................................................ ES-1 Background ............................................................................................................ ES-1 Objectives............................................................................................................... ES-1 Collection System and Study Area ........................................................................ ES-1 Flow/Rainfall Monitoring ....................................................................................... ES-1 Hydraulic Model Update and Calibration ............................................................. ES-2 Hydraulic Model Capacity Analysis ....................................................................... ES-3 1. Introduction Summary .................................................................................................................. 1-1 Background .............................................................................................................. 1-1 Scope of Development ............................................................................................ 1-2 Project Administration and Management........................................................ 1-2 Flow Monitoring ................................................................................................. 1-2 Hydraulic Model Software ................................................................................ 1-2 Hydraulic Model Updates ................................................................................. 1-3 Hydraulic Model Re-Calibration ........................................................................ 1-4 Hydraulic Model Capacity Analysis .................................................................. 1-4 Reporting ........................................................................................................... 1-4 Terminology/Definitions/Acronyms ........................................................................ 1-5 2. Flow Monitoring Summary .................................................................................................................. 2-1 Site Selection ........................................................................................................... 2-1 Flow Meter Type Information .................................................................................. 2-1 Meter Principles ................................................................................................ 2-2 Calibration and Installation .............................................................................. 2-2 Telemetry Equipment .............................................................................................. 2-2 Meter Maintenance ................................................................................................. 2-3 Rainfall Monitoring .................................................................................................. 2-3 Rainfall Results ................................................................................................. 2-3 Determination of Average Daily Dry-Weather Flow................................................ 2-6 Average Daily Dry-Weather Flow Peaking Factor ................................................... 2-6 Wet-Weather Flow Peaking Factors ........................................................................ 2-6 3. Model Development and Calibration Summary .................................................................................................................. 3-1 Model Description ................................................................................................... 3-1 Model Update .......................................................................................................... 3-1 Collection System Updates from GIS ............................................................... 3-1 Record Drawings ............................................................................................... 3-2
TABLE OF CONTENTS Page ii Sub-Catchments ................................................................................................ 3-3 Residential Flow Updates ................................................................................. 3-3 Commercial/Institutional/Industrial Loading .................................................. 3-4 Model Testing .................................................................................................... 3-4 Model Calibration .................................................................................................... 3-4 Process .............................................................................................................. 3-4 Dry-Weather Period ........................................................................................... 3-4 Wet-Weather Calibration .................................................................................. 3-8 4. Capacity Analysis Summary .................................................................................................................. 4-1 Existing System Performance ................................................................................. 4-1 Dry-Weather Flow System Performance .......................................................... 4-1 Inflow and Infiltration ........................................................................................ 4-1 Operational Assumptions ................................................................................. 4-2 Existing System Analysis ......................................................................................... 4-2 Design Storm ..................................................................................................... 4-2 Design Storm Results ....................................................................................... 4-2 Determination of Required CIP Projects ................................................................ 4-3 Hot Springs Creek (HSC) Tributary ................................................................... 4-3 Southwest Wastewater Treatment Plant (SWWWTP)/Mazarn Tributary ....... 4-6 Stokes Pump Station Tributary ...................................................................... 4-10 Gulpha Tributary .............................................................................................. 4-10 Conclusion ............................................................................................................. 4-11
TABLE OF CONTENTS Page iii List of Figures 1.1 Wet-Weather SSOs 2020/2021 ................................................................ 1-1 1.2 Summary of Recorded SSOs ...................................................................... 1-2 1.3 Hot Springs Sanitary Sewer System .......................................................... 1-3 1.4 Design Storm Hydrograph .......................................................................... 1-4 2.1 FlowShark ................................................................................................... 2-2 2.2 Continuity Equation .................................................................................... 2-2 2.3 Typical Meter Installation ........................................................................... 2-3 2.4 Basin Flow Diagram.................................................................................... 2-4 3.1 Sewer Added from CHS GIS ....................................................................... 3-2 3.2 Residential Profile ...................................................................................... 3-5 3.3 Commercial and Industrial Profile …………. ............................................... 3-6 3.4 Dry-Weather Calibration Graph ……….... .................................................... 3-7 3.5 Wet-Weather Calibration Graph ................................................................. 3-9 4.1 Wet-Weather Hydrograph ........................................................................... 4-1 4.2 Lakeside Pump Station Tributary CIP Recommendations ....................... 4-4 4.3 Area Services by 27-inch Interceptor in HSC Tributary ............................ 4-5 4.4 Current Routing of Flow Through the Mazarn Tributary ........................... 4-7 4.5 Mazarn Tributary SSO Locations ............................................................... 4-7 4.6 Proposed Routing in the Mazarn Tributary ............................................... 4-8 4.7 Proposed 12-inch Common Force Main ................................................... 4-9 4.8 Stokes Pump Station Tributary SSO Locations ....................................... 4-10 List of Tables 2-A Rainfall Summary ....................................................................................... 2-5 2-B Treatment Plant Influent Flows ................................................................. 2-7 2-C Dry-Weather Peaking Factor ...................................................................... 2-8 2-D Wet-Weather Peaking Factor ..................................................................... 2-9 3-A Pipeline Characteristics ............................................................................. 3-3 4-A Wet-Weather SSOs 2020-2021 ................................................................ 4-3 4-B Cost Summary of Lakeside Pump Station Proposed CIP ......................... 4-4 4-C Cost Summary of Mazarn Tributary Options ............................................. 4-9 4-D Summary of Recommended Plan ............................................................ 4-11 Appendices APPENDIX A– Flow Meter Site Sheets APPENDIX B– Rain Gauge Site Sheets APPENDIX C– Dry vs Wet Flow Hydrographs List of Exhibits EXHIBIT A – Flow Meter Sites EXHIBIT B – Rain Gauge Sites
EXECUTIVE SUMMARY Page ES-1 [Type here] Summary This Executive Summary presents the results of the Hot Springs System Wide flow monitoring and model analysis developed for Crist Engineers and the City of Hot Springs (CHS) by RJN Group, Inc. (RJN). The purpose of this study is to update the hydraulic model, recalibrate the model to dry and wetweather flows recorded during the flow monitoring survey period, and assess the required capacity improvements to eliminate the 20 wet-weather Sanitary Sewer Overflows (SSOs) that were recorded throughout 2020 and 2021. Background Since 2009, RJN has been assisting CHS in eliminating SSOs throughout the Hot Springs, AR sewer system. RJN performed a flow monitoring program of the entire sanitary sewer system along with subsequent Sanitary Sewer Evaluation Studies (SSES) from 2009 to 2010, after which, the 2010 SECAP report was delivered. A hydraulic model of the sanitary sewer system was also constructed during this time to assist in recommendations of capital improvement projects. In 2015, A hydraulic model update and recalibration was performed, which focused on those areas that were about to undergo capacity improvements, such as the Stokes Pump Station tributary area. The purpose of this study is to update and recalibrate the hydraulic model and refine the capacity improvements recommended in the 2010 SECAP report that have not been constructed. Objectives The study consisted of the following tasks: Flow/Rainfall Monitoring: 44 temporary flow meters and 10 temporary rain gauges for 67 days Update and recalibrate the existing hydraulic model to reflect current constructed geometry and flow conditions Simulate the design storm on the updated model Verify Recorded Overflows Assess and refine the remaining SECAP improvement projects recommended in 2010 against current flow conditions Prepare and submit a Technical Memorandum summarizing findings and recommendations for the Gulpha basin Collection System and Study Area The existing wastewater collection system for Hot Springs, AR contains 2,336,393 LF of gravity sanitary sewer line, 12,591 manholes, and 1,332,595 LF of force main, which are owned and maintained by CHS. The majority of the system flows to the Davidson Wastewater Treatment Plant (DWWTP) and a smaller section of the sewer system flows to the Southwest Wastewater Treatment Plant (SWWWTP). The Hot Springs sanitary sewer system experienced SSOs at 20 different locations throughout 2020 and 2021.
EXECUTIVE SUMMARY Page ES-2 [Type here] Flow/Rainfall Monitoring Flow monitoring was conducted for a 67-day period from March 18, 2021 to May 24, 2021, to collect both dry and wet-weather flows. A total of 44 temporary flow meters and 10 temporary rain gauges were included in the scope for the evaluation of the Hot Springs sanitary sewer system. Total average daily dry-weather flow for the study area was calculated to be 11.989-MGD. Total average daily dryweather flow for basins discharging to the Davidson WWTP was calculated to be 11.764-MGD. Total average daily dry-weather flow for basins discharging to the SWWWTP was calculated to be 0.225- MGD. The data indicated that several of the flow monitoring basins have a significant response to wetweather events. Wet-weather peaking factors were calculated to be above the standard value of five at 32 flow monitoring locations. Hydraulic Model Update and Calibration As part of the 2015 SECAP Update Project, RJN updated and calibrated a hydraulic model originally built in 2010.The 2015 hydraulic model was used as the start point for the Hot Springs System Wide Model Update and Model Calibration study and has been comprehensively updated and extended. InfoWorks ICM hydraulic modeling software by Innovyze was the platform used for the model update. InfoWorks ICM is a fully dynamic hydraulic-modeling software capable of analyzing large, complex sewer systems. The following model update tasks have been completed as part of this study: Model updated to include all sanitary sewers from CHS’s GIS which had not previously been included in the model, providing a one-to-one relationship between the GIS and model Model updated to include all recently constructed sanitary sewer infrastructure All sewer relining/relaying projects completed since 2015 updated into the model The model updated with pipe and MH data from “Record” drawings obtained from CHS where issues were identified Post 2015 new development incorporated into the model Non-residential dry-weather flows updated using 2020/21 water billing data provided by CHS Residential dry-weather flows updated using customer address point data provided by CHS and 2010 census data Incorporated pump curves for several “mid-major” and “major” pump stations Refined the dry and wet-weather operation of both the Stokes and Hot Springs Creek (HSC) pump station Operation of the South Rogers Diversion Box Updated the headworks of the Davison WWTP based on recent CIP Updated the modeling of the Davidson EQ Basin Validation tests were performed on the model to confirm logical network connectivity and consistent vertical alignments. With a few alterations, the model was able to run a 24-hour dry-weather simulation without any issues and model calibration could proceed. The hydraulic model calibration process comprised of the following tasks: Selection of a dry-weather period from the flow survey data. April 4, 2021 to April 11, 2021 was selected as the most representative dry-weather period for calibration purposes.
EXECUTIVE SUMMARY Page ES-3 [Type here] Development of residential dry-weather diurnal profiles based on the flow survey data. Calibration of the model to dry-weather conditions by modifying permanent groundwater infiltration rates, per capita flow rates/curves, and commercial/industrial flow rates/curves. Calibration of the model for wet-weather conditions as a continuous simulation for the full flow survey period, including modifications to reflect the operational performance of both the Stokes and HSC pump station. This enabled the model to accurately reflect the soil saturation conditions, the recession limb of each storm event and the inter event dry periods. Overall, the calibrated model provides a good representation of current flows and system hydraulics. Hydraulic Model Capacity Analysis The design storm analysis indicated a high correlation with the recorded overflows in the tributary area. The analysis also indicated that several projects recommended in the 2010 SECAP Update are still uncompleted and may have increased in size due to additional extraneous flow entering the system since the 2015 model calibration. The recommended projects include the Lakeside pump station tributary capacity improvements, the HSC Interceptor and pump station upgrade, and the Gulpha Interceptor and pump station upgrade projects. These projects are described in detail in Chapter 4 of this report. The current CIP program addresses the mandates of the Administrative Order and Capacity Constraints at a Capital Costs of $53,722,944 as well as potential I/I abatement studies/projects in the future to address extraneous flow in the HSC tributary and Stokes tributary. A breakdown by basin is outlined below. Immediate Priority Gulpha Tributary — Gulpha Gravity Interceptor: $28,936,832 — Gulpha Force Main: $10,368,400 — Gulpha Pump Station: $ 6,528,000 — Total: $45,832,832 Hot Springs Creek Tributary — LPS Gravity Main: $520,960 — LPS Force Main: $56,064 — LPS Pump Station: $896,000 — I/I Abatement Study/Projects: TBD — Total: $1,473,024 Near-Term Priority SWWWTP/Mazarn Tributary — Gravity Main: $418,034 — Force Main: $3,950,784 — Pump Station: $2,048,000 — Total: $6,417,088 Long-Term Priority Stokes Tributary — I/I Abatement Study/Projects: TBD — Total: TBD $29.9 $14.4 $9.5 Sanitary Sewer CIP (millions) Gravity Main Force Main Pump Station
INTRODUCTION Page 1-1 Figure 1.1 – Wet-Weather SSOs 2020/2021 Summary In February 2021, Crist Engineers contracted RJN Group, Inc. (RJN) to install 44 flow monitors and 10 rain gauges throughout the Hot Springs, AR sewer system with the purpose of recalibrating the existing hydraulic model. Along with recalibrating the model, updates to the 2015 hydraulic model were performed to bring the current population, water consumption data, and sewer main additions up to date. RJN, with assistance from Crist Engineers, was requested to evaluate storage and conveyance alternatives within the Gulpha sewer basin to eliminate the remaining five persistent Sanitary Sewer Overflows (SSOs). Additionally, Capital Improvement Projects (CIPs) are recommended for the remaining, wet-weather SSOs throughout the Hot Springs sewer system. The purpose of this report is to discuss the efforts mentioned above and their respective findings. Background Since 2009, RJN has been assisting the City of Hot Springs (CHS) in eliminating SSOs throughout the Hot Springs sewer system. RJN performed a flow monitoring program of the entire sanitary sewer system along with subsequent Sanitary Sewer Evaluation Studies (SSES) from 2009 to 2010, after which, the 2010 SECAP report was delivered. A hydraulic model of the sanitary sewer system was also constructed during this time to assist in recommendations of capital improvement projects. In 2015, A hydraulic model update and recalibration was performed, which focused on those areas that were to undergo capacity improvements, such as the Stokes tributary area. In 2018, two meters were placed upstream of the Gulpha pump station to evaluate the flows entering the station at that time. In response to the 2010 SECAP report, the City of Hot Springs rehabilitated over 4,200 manholes (MH), along with capacity improvements of multiple force mains, gravity mains, and pump station upgrades. This effort reduced a considerable amount of Inflow and Infiltration (I/I) and eliminated the majority of SSO’s, which were occurring across the city at that time. In 2020 and 2021, 20 wet-weather SSO locations were recorded, 11 of which occurred more than five times per year and are considered “chronic.” A chronic SSO is an SSO that occurs more than five times per year at one location. Figure 1.1 shows the locations of wet-weather SSOs occurring in 2020 and 2021. The graph on Figure 1.2 compares the frequency and volume of recorded SSOs since 2017.
INTRODUCTION Page 1-2 Figure 1.1 – Wet-Weather SSOs 2020/2021 Figure 1.2 – Summary of Recorded SSOs Scope of Development Project Administration and Management RJN coordinated with Crist Engineers and CHS staff on a regular basis during the study to update previous construction work, coordinate upcoming work, and receive any input from staff. General consultation was performed with Crist Engineers and CHS representatives regularly. Also, internal project control procedures including schedule and budget control, quality control review, and technical memorandums were performed. Existing information was attained from CHS that included maps, record drawings, pump curves, ArcView shape files and contours, SCADA system access, and water usage records by service address. Multiple meetings were conducted with Crist Engineers and CHS staff to provide updates on the project’s progress and to ensure concurrence with the proposed recommendations. Flow Monitoring Flow monitoring was conducted for a 67-day period from March 18, 2021 to May 24, 2021, to collect both dry and wet-weather flows. A total of 44 temporary flow meters and 10 temporary rain gauges were included in the scope for the evaluation of the Hot Springs sanitary sewer system. Hydraulic Model Software InfoWorks Integrated Catchment Modeling (ICM) software was used as the platform for developing an accurate representation of the CHS’s wastewater collection system. The software gave RJN the ability to create a single dynamic model that contains the pertinent features existing in the environment with
INTRODUCTION Page 1-3 Figure 1.3 – Hot Springs Sanitary Sewer System a single, unified hydrology. Additionally, Hot Springs has a complex integrated sewerage network of gravity and pressure systems, and ICM provides the best platform for this type of network. Hydraulic Model Updates As part of the 2015 SECAP Update Project, RJN updated and calibrated the hydraulic model originally constructed in 2010. The 2015 model update was specifically updated to evaluate several large capacity enhancement projects that the City was about to undertake to remove reoccurring SSO’s within the system. Therefore, the 2021 model update used a base network consisting of the original 2010 model, along with the updates that transpired within the 2015 update project. The following model update tasks have been completed as part of this study: Model updated to include all sanitary sewers from CHS’s GIS, which previously had not been included in the model, providing a one-to-one relationship between GIS and model. Model updated to include all recently constructed sanitary sewer infrastructure. All sewer relining/relaying projects completed since 2015 updated into the model. Model updated with pipe and MH data from record drawings obtained from CHS. All areas of new development since 2015 incorporated into the model. Non-residential, dry-weather flows updated using 2020/2021 water billing data provided by CHS. Residential dry-weather flows updated using customer address point data provided by CHS and 2010 census data. The extent of the Hot Springs sanitary sewer system is represented within Figure 1.3.
INTRODUCTION Page 1-4 Figure 1.4 – Design Storm Hydrograph Hydraulic Model Re-Calibration The following tasks were included in this phase of the project: 1. Selection of a dry-weather calibration period from the flow survey data. 2. Development of residential dry-weather diurnal profiles based on the flow survey data. 3. Calibration of the model to dry-weather conditions. 4. Calibration of the model for wet-weather conditions as a continuous simulation for the full flow survey period. This enabled the model to accurately reflect the soil saturation conditions, the recession limb (or peak infiltration) of each storm event and the inter event dry periods. Hydraulic Model Capacity Analysis The Hot Springs sanitary sewer system was analyzed under wet-weather conditions using the design storm event from the 2010 SECAP, which was reviewed and approved by the Environmental Quality Division of the Arkansas Department of Energy and Environment. Shown in Figure 1.4, the design storm event has since been updated with more accurate temporal distribution from NOAA’s Atlas 14 and is a theoretical storm event in which a total of 4.3-inches of rainfall falls over 24-hours and has a peak 1-hour intensity of 1.94-inches. Reporting Reporting included developing a Technical Memorandum to summarize the results of the Gulpha basin alternative evaluations, which is included in this report. The report describes work performed during various tasks, procedures, and methodologies used, then analyses findings and conclusions. Additionally, an electronic copy with flow monitoring hourly flows tabular data from March 18, 2021 to May 24, 2021 is provided with this report.
INTRODUCTION Page 1-5 Terminology/Definitions/Acronyms This section contains definitions and abbreviations commonly used throughout this report. Infiltration (as defined by USEPA) – The water entering a sewer system and service connections from the ground through such means as, but not limited to, defective pipes, pipe joints, service connections, service laterals, or manhole walls. Inflow (as defined by USEPA) – The water discharged into a sewer system, including service connections, from such sources as roof leaders; cellar, yard, and area drains; foundation drains; cooling water discharges; drains from springs and swampy areas; manhole covers; cross connections from storm sewers, combined sewers, or catch basins; storm waters; surface runoff; or drainage. Excessive infiltration and inflow (I/I) – The extraneous clean water that enters the sanitary sewer system that can be eliminated on a cost-effective basis. Base Flow – Wastewater flow exclusive of infiltration or inflow. Generally determined from water records during months when most of the water consumption is returned to the wastewater collection system. Permanent Infiltration – Extraneous flow that enters the sewer system through the ground during periods of dry-weather/low-groundwater. Generally determined by subtracting base flow during winter months from the average daily dry-weather monitored flow, or by taking the early AM flows and if 90 to 95-percent of the flow is infiltration and that there are no industries or large nighttime users. Peak Infiltration – The maximum extraneous flow that enters the wastewater collection system during high groundwater conditions after the inflow effects of a rain event have ended. Generally determined by subtracting dry-weather/low-groundwater flow (i.e., average daily dry weather monitored flow) from flow recorded during periods of high groundwater. Average Daily Dry-Weather Flow (ADWF) – Dry-weather/low-groundwater flow exclusive of dryweather/high-groundwater (peak infiltration) and wet weather (inflow) flow; includes base flow and permanent infiltration only. Average Daily Dry-Weather Flow Peaking Factor – The ratio between the peak hourly flow rate and the average daily flow. 1-Year/60-Minute Storm – A storm event that produces 1.63 inches of rain per hour and is expected to occur once in any given year. 5-Year/60-Minute Storm – A storm event that produces 2.24 inches of rain per hour and has a 20- percent probability of occurring each year. Design Storm Event – A storm event selected for purposes of analyzing its effect on the wastewater collection system. The Design Storm Event for the CHS system is a theoretical storm event in which a total of 4.3 inches of rainfall falls over 24 hours and has a peak 1-hour intensity of 1.94 inches. Gallons per Day (gpd) – Unit of measure for flow rate. Million Gallons per Day (mgd) – Unit of measure for flow rate.
INTRODUCTION Page 1-6 Inch-Diameter-Miles (idm) – The product of sewer pipe diameter in inches and length of sewer in feet divided by 5,280 feet. gpd/idm – Gallons per day per inch-diameter-mile. Surcharge Condition – When the sewer flow depth equals or exceeds the diameter of the discharging sewer lines. (WEF Manual of Practice FD-6) Inflow and Infiltration (I/I) – A combination of infiltration and inflow wastewater volume in sanitary sewer. Pump Station (PS) – Wastewater pump station used for pumping wastewater from a lower to higher elevation. Sanitary Sewer Overflow (SSO) – An event when surcharged sanitary sewer flow reaches a height above the top of a sanitary sewer structure and excess sanitary sewer flow is discharged out of the sanitary sewer system as bypass. Head – Pressure head of a fluid due to the pressure exerted on a pipe and measured in units of feet (1 foot head = 0.4335 ib/in2 or psi). Hydrograph – A graph showing depth, velocity, flow, and rain measurements with respect to time. InfoWorks Integrated Catchment Modeling (ICM) – An integrated modeling platform created by Innovyze and used for this project. Million Gallons (MG) – Unit of volume. Peak Hourly Wet-Weather Flow (PWWF) – The highest one-hour flow during a significant rain event. Rain-Derived Inflow/Infiltration (RDII) – A portion of rainfall that gets into a sewer system in the form of inflow and infiltration and becomes excess flow. Wet-Weather Flow (WWF) – The highest daily flow during and immediately after a significant storm event. It includes sanitary flow, infiltration, and inflow. Wastewater Treatment Plant (WWTP) – Biological, chemical, and physical process facility for removing contaminants from wastewater.
FLOW MONITORING Page 2-1 Summary Flow monitoring is one of the most critical steps when evaluating a wastewater collection system. It is typically performed during spring and fall seasons when the probabilities of rainfall are the highest. Flow monitoring data is used to examine the existing dry and wet-weather flows, the effects of rainfall on the wastewater collection system, and the extent of I/I entering the system. Temporary flow monitoring was performed for a period of 67-days from March 18, 2021 to May 24, 2021 in the Hot Springs sanitary sewer system. An area map denoting the locations of the flow monitors and rain gauges is included as Exhibits A and B, respectively at the end of this report. A basin flow diagram indicating direction of flow from one basin to another is shown in Figure 2.4 on page 2-4. Site Selection Once the preliminary location was identified, a site investigation was performed to determine if the site had good hydraulics for data collection. Generally, a preferred site has a straight channel where flow is free of turbulence or backwater effects. Below are other investigated considerations: Installation constraints Pipe dimensions Site accessibility Site specific concerns Manhole accessibility Silt deposition Maintainability Manhole configuration Flow depth range Velocity range Employee safety Surcharging evidence Telemetry constraints Sensor survival A copy of the Meter Site Installation Forms complete with photos for each meter location are provided in Appendix A. The photos of each meter site include the site location, inside the manhole, and the pipe before and after sensor placement. Flow Meter Type Information ADS meters were selected as the gravity flow meters to complete the flow monitoring program. The average accuracy of the meters for the depth measurement is ±0.15 inches and the average accuracy for velocity is ±0.04 fps. There were 44 locations where ADS FlowShark meters were installed. Additional information regarding the selected flow meter is on the following pages.
FLOW MONITORING Page 2-2 Meter Principles The ADS FlowShark (Model 5000), shown in Figure 2.1, is an open channel flow meter that utilizes Doppler ultrasound technology to sense the peak flow velocity, as well as a redundant depth sensor. The ADS FlowShark has five primary components: a logger unit that stores the collected data and houses the RTU; the ultrasonic, pressure, and velocity sensors; and the integrated wireless modem. The pressure depth sensor uses a pressure transducer that records the water level including full pipe and surcharge level. The ultrasonic sensor is a non-intrusive quad redundant transceiver sensor that will accurately record the depth to within one inch of the sensor’s face. The sensors emit signals and receive returned signals from the flow to capture the characteristics of the flow velocity and depth. During surcharged conditions, the ultrasonic depth sensors no longer function, and the level is recorded through the pressure sensor. Flows are calculated using the continuity equation, which is expressed as Q = AV, where Q is flow, A is the cross-sectional area, and V is the average velocity of the flow. Figure 2.2 illustrates the concepts of the continuity equation. The monitor records velocity and depth at five-minute intervals. Calibration and Installation ADS meters must be calibrated on site by entering physical offsets of the sensors and their positions in the meter as well as comparing the depth and velocity measurements recorded by the meter to manual measurements. Depth and velocity adjustments for the ADS meters are made directly to the meter as necessary. The meter housing was secured with an eyebolt on the wall of the manhole. A stainless steel, expandable band secured the depth/velocity probe to the channel. The probes were positioned in the flow of the incoming pipe to minimize the effects of flow turbulence and debris buildup that may exist in the manhole. Telemetry Equipment Each flow meter called into a central processing location during the project to perform a data dump for data collection and review. This process was performed through a Remote Transmission Unit (RTU) that collects data and sends the collected data by wireless telemetry to the central processing location. The data was then available for review on the website hosted by RJN. Each RTU initiated a call into the central location once every 24-hours. The RTUs transmit the five-minute data points recorded during that day. The antennas were typically located just outside the Figure 2.1 - FlowShark Figure 2.2 - Continuity Equation: Flow = Average Velocity x Area of Flow
FLOW MONITORING Page 2-3 manhole as cast-iron manhole covers block the wireless signals. The antennas were buried just below the existing surface and covered with traffic approved material. A typical installation is shown in Figure 2.3. Meter Maintenance During site visits, data stored in the meter was manually retrieved as a backup to the telemetry download and the meters were inspected to ensure proper operation. The meter depth and velocity readings were taken before and after maintenance/cleaning of the probes. Manual depth and velocity measurements were taken, silt deposit depths were recorded, and the batteries were changed, if necessary. Typically, six sixvolt batteries lasted an average of four weeks due to the RTU drawing power from the batteries. Offset adjustments were recorded in the site-specific meter maintenance log. Silt was observed at HS-13, HS-47, HS-54, and HS-60. The average silt depth was 1.1-inches, and the maximum recorded silt depth was 4.0-inches at meter site HS-47. Sensors were placed above the silt line to avoid disturbing the silt as it allows for accurate measurements of the sewer flow. The reduction in area and wetted perimeter caused by the silt were accounted for in the flow calculations. Rainfall Monitoring Ten temporary rain gauges maintained by RJN were used to monitor rainfall during the study period. Rainfall was recorded with a continuously recording rain gauge with an accuracy of 0.01-inches. The rain gauge was equipped with a separate RTU and called in once per day to relay data to the central database. A copy of the Rain Gauge Site Installation Forms is provided in Appendix B. Rainfall Results The rain gauges recorded seven rainfall events with greater than one inch of rainfall for a 24-hour period. The largest storm event occurred on April 24, 2021, where the average total rainfall was 2.13 inches, with an average peak 1-hour intensity of 0.81 inches-per-hour. The average total rainfall measured during the study period was approximately 14.49 inches. Rain gauge recorded totals and intensities are listed in Table 2-A on page 2-5. The five-minute electronic Excel data is provided with this report. Figure 2.3 - Typical Meter Installation
FLOW MONITORING Page 2-4 Figure 2.4 – Basin Flow Diagram
FLOW MONITORING Page 2- Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60 Minute Rainfall Intensity (in) (in/hr) (in) (in/hr) (in) (in/hr) (in) (in/hr) (in) (in/hr) 3/14/2021 0.39 0.11 0.40 0.17 0.45 0.17 0.47 0.27 0.59 0.32 3/17/2021 0.75 0.47 0.79 0.62 0.89 0.70 0.98 0.81 1.36 1.18 3/23/2021 1.06 0.46 1.12 0.56 1.07 0.52 1.18 0.74 1.22 0.76 3/25/2021 0.86 0.31 0.83 0.40 1.59 1.10 0.81 0.37 0.94 0.46 4/10/2021 0.20 0.15 0.17 0.13 0.15 0.14 0.19 0.14 0.16 0.14 4/14/2021 0.59 0.19 0.78 0.28 0.93 0.46 0.83 0.30 0.84 0.39 4/24/2021 2.34 0.83 2.03 0.84 1.71 0.55 2.04 0.77 1.94 0.76 4/29/2021 1.28 0.41 1.51 0.53 1.61 0.65 1.51 0.48 1.50 0.57 5/2/2021 0.36 0.23 0.41 0.24 0.33 0.22 0.39 0.27 0.36 0.23 5/4/2021 0.11 0.11 0.16 0.16 0.21 0.21 0.24 0.24 0.24 0.24 5/9/2021 0.24 0.22 0.56 0.56 0.03 0.03 0.58 0.58 0.37 0.37 5/10/2021 0.09 0.09 0.18 0.18 0.74 0.74 0.17 0.17 0.08 0.08 5/11/2021 0.76 0.18 1.00 0.47 1.05 0.52 1.22 0.64 1.18 0.60 5/17/2021 0.74 0.19 2.25 0.69 2.43 0.69 2.26 0.67 2.18 0.84 5/18/2021 1/ 1/ 0.93 0.60 1.49 1.21 0.46 0.27 0.94 0.58 5/19/2021 1/ 1/ 0.78 0.36 1.36 0.54 0.66 1/ 0.93 0.41 5/20/2021 1/ 1/ 0.83 0.76 0.11 0.08 0.38 0.31 1.06 0.99 Total 9.77 0.28 (Average) 14.73 0.44 (Average) 16.15 0.50 (Average) 14.37 0.44 (Average) 15.89 0.52 (Average 1/ error in recording rainfall Table 2 RAINFALL SU Date HSRG01 3904 Malvern Rd Hardman Lumber HSRG02 109 Airway Dr Goldens Paint & Body HSRG03 HSRG04 78 Fountain St 2070 Airport Rd Belvedere Golf Course Valero Gas Station HSRG05 125 Macon Terrace Pump Station
5 - e l y Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity Total Daily Rainfall Peak 60- Minute Rainfall Intensity (in) (in/hr) (in) (in/hr) (in) (in/hr) (in) (in/hr) (in) (in/hr) 0.50 0.17 0.46 0.21 0.40 0.21 0.48 0.18 0.54 0.21 0.51 0.23 0.89 0.61 0.63 0.42 0.83 0.65 0.76 0.51 1.05 0.68 1.00 0.50 0.94 0.46 1.09 0.57 1.21 0.65 0.81 0.33 1.66 1.04 1.27 0.81 1.20 0.71 1.74 1.07 0.29 0.22 0.18 0.14 0.34 0.25 0.20 0.14 0.19 0.16 0.57 0.20 0.74 0.25 0.67 0.24 0.85 0.34 0.77 0.27 2.62 0.97 2.14 0.87 2.32 0.93 2.00 0.80 2.13 0.77 1.35 0.50 2.21 0.71 1.32 0.39 1.57 0.50 1.66 0.57 0.22 0.12 0.45 0.28 0.37 0.25 0.34 0.22 0.35 0.24 0.16 0.16 0.12 0.12 0.11 0.11 0.14 0.14 0.14 0.14 0.44 0.44 0.74 0.74 0.34 0.34 0.31 0.31 0.39 0.39 0.12 0.12 0.14 0.14 0.17 0.17 0.10 0.10 0.29 0.29 1.08 0.51 1.27 0.62 1.23 0.58 1.07 0.46 1.05 0.43 1.56 0.65 3.26 1.29 2.66 1.08 2.35 0.73 1.12 0.71 0.44 0.22 0.86 0.67 0.43 0.19 0.35 0.24 0.01 0.01 0.55 0.19 2.31 1.36 0.95 0.37 1.36 0.79 1.17 0.84 0.03 0.02 0.41 0.30 0.69 0.61 0.29 0.21 1/ 1/ e) 12.30 0.34 (Average) 18.84 0.58 (Average) 14.84 0.44 (Average) 14.53 0.42 (Average) 13.52 0.45 (Average) 2-A MMARY HSRG06 e 1764 Shady Grove Rd Morning Star FD HSRG07 HSRG08 1676 Higdon Ferry Rd Amity Rd & Housley Pt Valero Gas Station Pump Station HSRG09 HSRG10 905 W Grand Ave 1534 Malvern Ave Area Agency on Aging Indiandale Center
FLOW MONITORING Page 2-6 Determination of Average Daily DryWeather Flow Flow data collected during dry-weather/low-groundwater periods were analyzed to determine the average daily dry-weather flow for each flow monitoring site. The dry period used for flow monitoring analysis is April 4, 2021 to April 11, 2021. Total average daily dry-weather flow for the study area was calculated to be 11.989-MGD. Total average daily dry-weather flow for basins discharging to the Davidson WWTP was calculated to be 11.764-MGD. Total average daily dry-weather flow for basins discharging to the SWWWTP was calculated to be 0.225-MGD. A treatment plant influent flow summary table is given in Table 2-B on page 2-7. A summary of average daily dry-weather flows by basin is given in Table 2-C on page 2-8. Dry vs. Wet Hydrographs for each basin are included in Appendix C. Average Daily Dry-Weather Flow Peaking Factor Wastewater flows during dry-weather periods will vary during the day in response to water consumption. By examining the diurnal curves for each flow monitoring site, a peaking factor was determined. The peaking factor is the ratio of the peak average daily flow rate and the average daily flow. Peaking factors varied from 1.211 to 2.542 with an average peaking factor of 1.547 and are shown on Table 2-C on page 2-8. Peaking factors between 1.5 and 2.5 are typically considered standard for dry-weather. Basin HS-01 was calculated to have a dry-weather peaking factor slightly above the standard range of 2.5 with a peaking factor of 2.542. Wet-Weather Flow Peaking Factors A wet-weather peaking factor is the ratio between the peak hourly flow during wet-weather and the average daily flow during dry-weather. A wet-weather peaking factor below five is standard. The wetweather peaking factor is calculated based on the peak hourly flow rate observed for the May 17, 2021 storm event, where the average total rainfall was 2.08-inches with an average peak one-hour intensity of 0.75 inches-per-hour. April 05, 2021 is used as a dry day for calculation to limit the differences in base flow due to water consumption. Wet-weather peaking factors were calculated to be above the standard value of five at 32 of the 44 flow monitoring locations. HS-50 had the highest wet-weather peaking factor which was calculated to be 18.046. The high peaking factor at HS-50 is mostly due to pump station influence from Stokes pump station. Surcharging was experienced at nine sites during the May 17, 2021 storm event. Table 2-D on page 2-9 summarizes the wet-weather peaking factors.
FLOW MONITORING Page 2-7 Table 2-B TREATMENT PLANT INFLUENT FLOWS Treatment Plant Average Daily Dry-Weather Flow1/ (mgd) Average Daily Average Flow (mgd) Peak Wet-Weather Flow2/ (mgd) Davidson3/ 11.764 12.294 33.966 Southwest 0.225 0.371 1.175 Total 11.989 12.665 35.141 1/ Average daily dry-weather flow based on dry week 2/ Peak flow based on May 17th, 2021 storm event 3/ Flow values are approximate due to split flows at Stokes Pump Station
FLOW MONITORING Page 2-8 Monitor Cumulative Average Daily Dry-Weather Flow (mgd) Discrete Average Daily Dry-Weather Flow (mgd) Peak Hourly Flow Rate (mgd) Dry-Weather Peaking Factor HS-01 0.083 0.083 0.211 2.542 HS-02 0.123 0.123 0.213 1.732 HS-03 0.142 0.019 0.256 1.803 HS-04 0.120 0.120 0.184 1.533 HS-05 0.063 0.063 0.102 1.619 HS-06 0.324 0.141 0.503 1.552 HS-083/ HS-08A 0.335 0.335 0.421 1.257 HS-09 0.035 0.035 0.070 2.000 HS-10 0.059 0.059 0.112 1.898 HS-11 1.066 0.972 1.980 1.857 HS-13 0.170 0.170 0.376 2.212 HS-14 0.074 0.074 0.161 2.176 HS-15 0.106 0.106 0.178 1.679 HS-17 0.215 0.215 0.340 1.581 HS-20 0.522 0.448 0.752 1.441 HS-22 0.136 0.136 0.201 1.478 HS-24 0.330 0.330 0.473 1.433 HS-25 0.564 0.234 0.688 1.220 HS-28 1.735 0.513 2.125 1.225 HS-29 0.167 0.167 0.211 1.263 HS-30 0.330 0.163 0.550 1.667 HS-33 1.060 0.739 1.299 1.225 HS-35 0.427 0.291 0.777 1.820 HS-38 0.312 0.138 0.427 1.369 HS-39 0.174 0.174 0.271 1.557 HS-41 0.440 0.440 0.562 1.277 HS-42 1.696 0.209 2.449 1.444 HS-43 2.548 0.852 3.175 1.246 HS-452/ 0.212 0.212 0.313 1.476 HS-46 0.221 0.221 0.345 1.561 HS-47 0.199 0.046 0.241 1.211 HS-48 0.153 0.153 0.222 1.451 HS-49C1/ 3.827 0.872 5.058 1.322 HS-501/ 0.460 0.460 0.772 1.678 HS-53 0.096 0.096 0.144 1.500 HS-53A 0.075 0.075 0.109 1.453 HS-541/ 2.131 0.894 2.927 1.374 HS-57 3.361 1.126 4.272 1.271 HS-60 0.098 0.098 0.145 1.480 HS-61 0.055 0.055 0.071 1.291 HS-62 0.135 0.135 0.195 1.444 HS-63 0.066 0.066 0.094 1.424 HS-64 0.137 0.071 0.223 1.628 HS-65 0.060 0.060 0.085 1.417 Total - 11.989 - 1.547 (Average) Table 2-C DRY-WEATHER PEAKING FACTOR 1/ Discrete values are approximate due to split flows at Stokes Pump Station 2/ Dry-weather calculated from 05/04/2021 - 05/08/2021 3/ HS-08 was moved downstream to HS-08A due to construction. The meter basins are identical.
FLOW MONITORING Page 2-9 Average Dry Flow 4/5/2021 5/17/2021 Wet-Weather (mgd) (mgd) Peaking Factor HS-01 0.080 0.412 5.150 HS-02 0.112 0.571 5.098 HS-031/ 0.139 0.763 5.489 HS-04 0.121 0.356 2.942 HS-05 0.066 0.755 11.439 HS-061/ 0.336 2.320 6.905 HS-083/ HS-08A 0.347 1.305 3.761 HS-091/ 0.031 0.256 8.258 HS-10 0.064 0.170 2.656 HS-11 1.066 3.816 3.580 HS-13 0.163 1.163 7.135 HS-14 0.082 0.644 7.854 HS-15 0.104 0.879 8.452 HS-17 0.206 1.537 7.461 HS-20 0.517 4.983 9.638 HS-221/ 0.141 0.841 5.965 HS-24 0.340 2.210 6.500 HS-25 0.578 2.510 4.343 HS-281/ 1.783 12.604 7.069 HS-29 0.177 0.645 3.644 HS-30 0.347 2.633 7.588 HS-33 1.048 6.252 5.966 HS-35 0.420 3.777 8.993 HS-38 0.316 2.608 8.253 HS-39 0.171 1.485 8.684 HS-41 0.440 2.473 5.620 HS-42 1.711 14.530 8.492 HS-43 2.513 14.930 5.941 HS-452/ 0.236 1.336 5.661 HS-461/ 0.211 1.471 6.972 HS-47 0.201 0.461 2.294 HS-48 0.156 0.402 2.577 HS-49C1/ 4.060 17.664 4.351 HS-50 0.437 7.886 18.046 HS-53 0.105 1.460 13.905 HS-53A 0.073 0.867 11.877 HS-541/ 2.153 13.337 6.195 HS-571/ 3.479 10.159 2.920 HS-60 0.100 0.252 2.520 HS-61 0.054 0.866 16.037 HS-62 0.134 1.478 11.030 HS-63 0.065 0.358 5.508 HS-64 0.138 1.479 10.717 HS-65 0.061 0.260 4.262 Average 6.994 Table 2-D WET-WEATHER PEAKING FACTOR Monitor Peak Hourly Wet Flow 2.08 in Rainfall 1/ Flow monitor experienced surcharging on wet-weather day 2/ Alternate dry-weather day used (05/10/2021) 3/ HS-08 was moved downstream to HS-08A due to construction. The meter basins are identical.
MODEL DEVELOPMENT Page 3-1 Summary This chapter provides a summary of the model update tasks and recalibration. Model Description As part of the 2015 SECAP Update Project, RJN updated and calibrated portions of the hydraulic model originally built in 2010. The 2010 and 2015 hydraulic model were used as the starting point for the Hot Springs System Wide Model Update and Model Calibration Study and has been comprehensively updated and extended. InfoWorks ICM hydraulic modeling software by Innovyze was the platform used for the model update. InfoWorks ICM is a fully dynamic hydraulic-modeling software capable of analyzing large, complex sewer systems. The following model update tasks have been completed as part of this study: Model updated to include all sanitary sewers from the City of Hot Spring’s (CHS’s) GIS, which had not previously been included in the model, providing a one-to-one relationship between the GIS and model. Model updated to include all recently constructed sanitary sewer infrastructure. All sewer relining/relaying projects completed since 2015 updated into the model. The model updated with pipe and manhole (MH) data from record drawings, obtained from CHS, where available. Post 2015 new development incorporated into the model. Non-residential dry-weather flows updated using 2020/21 water billing data provided by CHS. Residential dry-weather flows updated using customer address point data provided by CHS and 2010 census data. Incorporated pump curves for several “mid-major” and “major” pump stations. Refined the dry and wet-weather operation of the Stokes pump station. Operation of the South Rogers Diversion Box. Updated the headworks of the Davison WWTP based on recent CIP. Updated the modeling of the Davidson EQ Basin. Model Update Collection System Updates from GIS The first task was to update the model with additional infrastructure contained in CHS’s GIS. The 2015 model was overlaid onto the latest GIS sewer data provided by CHS. An additional 68,413 LF (13 miles) of pipe main has been added to the 2015 network, which equates to a 1.9-percent increase in the total pipe length in the model. The total pipe length now comprises nearly 3,668,998 LF (695 miles) of pipe main.
MODEL DEVELOPMENT Page 3-2 The majority of these additional sewers were six or eight-inch lines that had previously been omitted from the model or were new sewers constructed since 2015. Examples of additional sewers added to the model are depicted in red on Figure 3.1. The updated model was then verified for adequate slopes and connectivity using the validation tools built into InfoWorks. All data in the hydraulic model network was flagged to define its data source. More accurate information, such as Record Drawings or survey data was used in preference to GIS or interpolated data. Record Drawings CHS provided “Record Drawing” drawings for key locations in the sewer system as well as drawings of all sewer rehabilitation projects completed since 2015, which included relayed and rehabbed sewer mains. The drawings were used to update sewer elevations, pipe diameters, and MH ground elevations at critical locations such as major sewer junctions, flow meter locations, and reported/predicted SSOs. This exercise resulted in updates to an additional 289 sewer segments with a total pipe length of 114,130 LF (22 miles), which equates to approximately 3.1% of the network. (Note: some rehabilitated pipes from earlier periods have been incorporated into the “Record Drawing” statistics.) The updated Hot Springs sanitary sewer system model now contains 2,336,393 LF (442 miles) of gravity mains, and 1,332,595 LF (252 miles) of force mains. Table 3-A on page 3-3, contains the pipeline characteristics for the hydraulic model. Figure 3.1 – Sewer Added from CHS GIS