November 28, Dear Mr. Bechtold:

Transcription

1 4000 Hollywood Boulevard Seventh Floor, North Tower Hollywood, Florida (954) Fax: (954) November 28, 2012 Wastewater Compliance and Enforcement Section FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION Southeast District Office 400 North Congress Ave, Suite 200 West Palm Beach, Florida, City of Hollywood Southern Regional Wastewater Treatment Plant FDEP Facility Permit No. FL Influent Flow Monitoring Accuracy Report Dear Mr. Bechtold: The purpose of this report is to fulfill the requirements of Section VI.2 of the Florida Department of Environmental Protection (FDEP) Facility Permit Number FL , which incorporates by reference Administrative Order No. AO DW-06 SED. Recently, FDEP questioned the accuracy of measured influent flows at the Southern Regional Wastewater Treatment Plant (SRWWTP) and, as a condition of the facility permit mandated that the City of Hollywood (City) perform an influent flow accuracy study to demonstrate the accuracy of flow metering at the SRWWTP, provide conclusions regarding the viability of the existing flow monitoring methods, and provide recommendations for follow-up work, as justified. Historical influent and effluent flow data for the 5-year period between January 2007 and December 2011 were used in the evaluation. The City owns and operates the SRWWTP which was originally constructed prior to Additionally, the City owns and maintains an extensive network of wastewater pipelines, pump stations and force mains that collect and transport wastewater from various sources to the SRWWTP for treatment and disposal. Wastewater transported to the plant for treatment and disposal includes flows from retail customers within the City limits and from six Large Users, including: Broward County City of Dania Beach City of Hallandale Beach City of Miramar Town of Pembroke Park City of Pembroke Pines Page 1 of Influent Flow Study

2 Francois Domond, P.E. November 28, 2012 Wastewater transported to the SRWWTP only for disposal includes secondary treated effluent from the Town of Davie and from the City of Cooper City wastewater treatment plants, as well as concentrate from the City of Hollywood s Water Treatment Plant (WTP). Treated effluent disposal at the plant is achieved through three separate systems: a deep injection well system, an open ocean outfall discharge system, and a reclaimed water system. The deep injection well system is the primary means of effluent disposal at the SRWWTP. The open ocean outfall discharge system is used to supplement the deep injection well system for disposal of the remainder of SRWWTP treated secondary effluent. Outfall effluent disposal also includes Davie and Cooper City secondary treated effluent and Hollywood WTP concentrate. The reclaimed water system consists of a public access land application (off-site reuse) system and an industrial reuse (site plant non-potable water, (NPW)) system. The water treated for offsite reuse (golf courses) is low saline treated secondary effluent supplied by the Town of Davie and the City of Cooper City. Davie/Cooper City low saline effluent not utilized by the public access land application system is preferentially used by the industrial reuse system with unmet NPW needs satisfied by SRWWTP effluent. NPW uses consist primarily of process foam control, pump seal water, process make-up water, odor control scrubbers and equipment washdown. In accordance with Florida Administrative Code (FAC) Rule (1) and Rule (6), the City monitors flow at the SRWWTP utilizing electromagnetic flow meters with converters. Magnetic flow metering is a proven technology for wastewater and is considered the best available technology for producing high quality and reliable data. In accordance with permit requirements, the SRWWTP continuously monitors and reports flows to FDEP. Historically, flow metering at the SRWWTP has been very reliable and in compliance with all regulatory permitting requirements. Additionally, as required by permit, all flow meters are calibrated annually. Regular meter calibration ensures that meters continue to perform accurately and that quality and reliable data is produced. Figure 1 presents an overview of major treatment unit flows and corresponding flow meter locations at the SRWWTP. Influent Flows Large User flows enter the City s collection system and combine with flows generated from the City s retail customers. Combined flows enter the SRWWTP at the bar screen building through several pipelines. A list including a brief description is as follows: Page 2 of Influent Flow Study

3 R1.cdr Figure 1 Southern Regional Wastewater Treatment Plant Flow Path and Flow Meter Locations Influent Flow Monitoring Accuracy Report

4 Francois Domond, P.E. November 28, inch diameter force main from: City of Dania Beach, City of Hollywood 60-inch diameter gravity sewer from: City of Pembroke Pines, City of Miramar, City of Hallandale Beach and City of Hollywood 66-inch diameter gravity sewer from (under construction): City of Pembroke Pines, City of Miramar, City of Hallandale Beach and City of Hollywood 48-inch diameter gravity sewer from: City of Hallandale Beach, City of Hollywood 48-inch diameter gravity sewer from: City of Hallandale Beach, City of Hollywood 30-inch diameter force main from: City of Hollywood These flows enter the bar screen inlet box at elevation (-)12.50 NGVD which is approximately 20 feet below grade. Due to the numerous raw wastewater sources entering the SRWWTP under gravity, the depth of the gravity mains entering the plant, as well as, the significant variation of water surface elevations resulting in full pipe flow and less than full pipe flow (open channel) during each diurnal period, metering of the influent flow streams before or after the bar screens is not feasible. Therefore, influent flows at the SRWWTP are calculated and reported to FDEP based on effluent flow metering. The SRWWTP treated effluent flows (influent flows) are determined by calculating the difference between the sum of metered flows to the ocean outfall (FLW01), the deep injection wells nos. 1 and 2 (FLW03, FLW04) and the off-site reuse disposal (FLW05) systems and the sum of metered flows from the Town of Davie (FLW11), the City of Cooper City (FLW12) and the Hollywood WTP (FLW02). Effluent Flows In 2003, the City replaced the existing outfall insertion magnetic flow meter with a new large diameter magnetic flow meter at a cost of approximately $2,000,000. The large diameter magnetic flow meter was selected after an extensive evaluation of meter options, including input from major meter manufacturers and was determined to be the best suited for the application. Electromagnetic meter technology is also used for the deep injection well and reclaimed water systems. Inaccuracy is inherent in any flow meter and will contribute to differences between readings. Typical electromagnetic flow meter accuracy as reported by the manufacturers varies and is dependent upon the type of fluid, fluid velocity through the meter, and the proximity of the meter installation to pipe fittings. However, electromagnetic flow metering is among the most accurate technology for full pipe flow measurement and it is estimated that at flow velocities greater than or equal to 0.5 ft/s the expected meter measurement error will be less ±0.2% of measured flow. Slightly greater inaccuracies exist in the electromagnetic flow meter converter. Flow meter calibrations as discussed herein indicate converter errors of ±0.5%. Table 1 summarizes Page 3 of Influent Flow Study

5 Francois Domond, P.E. November 28, 2012 information on the flow meters located at the deep injection well, ocean outfall and reclaimed water effluent disposal systems. Calibrations are regularly performed by an independent testing company. Location Table 1 City of Hollywood SRWWTP Existing Effluent Disposal System Flow Meters Meter Size (Inches) Type Last Calibrated Deep Injection Well No Electromagnetic 07/26/2012 Deep Injection Well No Electromagnetic 07/26/2012 Ocean Outfall System 60 Electromagnetic 10/10/2012 Off-Site Reuse 16 Electromagnetic 07/26/2012 Table 2 summarizes information on the existing City of Cooper City, Town of Davie and Hollywood WTP flow meters. Calibrations are regularly performed by an independent testing company. Location Table 2 City of Hollywood SRWWTP Additional Flow to Effluent Disposal System Flow Meter Meter Size (Inches) Type Last Calibrated City of Cooper City 12 Electromagnetic 01/25/2012 Town of Davie 12 Electromagnetic 10/10/2012 Hollywood WTP 16 Electromagnetic 11/15/2012 The recorded historical annual average flows to the deep injection well system, the ocean outfall system and the off-site reuse system are summarized in Table 3. Table 3 also includes the recorded historical annual average treated secondary effluent flows from the City of Cooper City and the Town of Davie and the concentrate from the Hollywood WTP. Additional monthly flow data are presented in the Appendix. Page 4 of Influent Flow Study

6 Francois Domond, P.E. November 28, 2012 Year IW-1 (FLW03) Table 3 City of Hollywood SRWWTP Annual Average Effluent Disposal Flows (mgd) IW-2 (FLW04) Ocean Outfall (FLW01) Off-Site Reuse (FLW05) Cooper City (FLW12) Town of Davie (FLW11) WTP Concentrate (FLW02) The data shows that in 2007 and 2008 effluent disposal was primarily through the ocean outfall system. Due to recent regulations, effluent disposal through the ocean outfall system has been reduced resulting in a subsequent increase in flows through the injection well system. Despite the change in flow allocation through each system, the combined annual average flow through the deep injection well system and the ocean outfall system consistently averaged approximately 45 mgd. Similarly, recorded flows to the off-site reuse system, and flows transported to the SRWWTP s effluent disposal system from the City of Cooper City, the Town of Davie and the Hollywood WTP, remained fairly consistent over the five year period. Process Flow Verification The SRWWTP operates a conventional activated sludge process. To maintain proper operation and control of the activated sludge process, meters located at oxygenation trains 1 through 5 continuously record incoming wastewater flow rates. Oxygenation train metering is necessary to ensure that the Return Activated Sludge (RAS) flow rate is adjusted appropriately since, the RAS flow rate is paced with the wastewater feed to each oxygenation train. It should be noted that at the SRWWTP, oxygenation train flow rates are used strictly for RAS adjustment and not for permitted influent flow monitoring. Due to the inclusion of miscellaneous and intermittent unmetered recycle flows discharged upstream of the oxygenation train meters, they cannot be used to determine definitive influent flow volumes at the SRWWTP. Readings recorded by the flow meters located at oxygenation trains 1 through 5 are expected to overestimate influent plant flow for this reason. However, although the volumes between the oxygenation train and treated effluent meters should differ as a result of the recycle flows, flow rates can be expected to vary directly. Fluctuations in intermittent recycle flows can be dampened by analyzing data utilizing an increased time scale. To this end, monthly data was used in the analysis. Table 4 summarizes information on the existing oxygenation train flow meters. Similarly to the previously described meters, calibrations are regularly performed by an independent testing company. Page 5 of Influent Flow Study

7 Francois Domond, P.E. November 28, 2012 Table 4 City of Hollywood SRWWTP Oxygenation Train Flow Meter Meter Size (Inches) Last Calibrated Locations Type Oxygenation Train 1 54 Electromagnetic 11/14/2012 Oxygenation Train 2 54 Electromagnetic 11/14/2012 Oxygenation Train 3 36 Electromagnetic 11/14/2012 Oxygenation Train 4 36 Electromagnetic 11/14/2012 Oxygenation Train 5 36 Electromagnetic 11/07/2012 The most recent meter calibration results for the flow meters summarized in Tables 1, 2 and 4 show that all the flow meters are operating within an acceptable accuracy range. The recorded historical annual average flows to oxygenation trains 1 through 5 are summarized in Table 5. Additional monthly flow data are presented in the Appendix. The combined annual average flows remained fairly consistent over the five year period, despite variation in flows between each oxygenation train. Oxygenation Train 1 (FLW06) Table 5 City of Hollywood SRWWTP Annual Average Oxygenation Train Flows (mgd) Oxygenation Train 2 (FLW07) Oxygenation Train 3 (FLW08) Oxygenation Train 4 (FLW09) Oxygenation Train 5 (FLW10) Combined (Train 1 5) Year Recycle Flows Some recycle flows are transported through the central plant drain (CPD) system and discharged back to the head of the plant for re-treatment and ultimate disposal. To determine the potential for comprehensive measurement of recycle flows, an inventory of recycle sources discharging upstream of the oxygenation flow meters was developed and a brief review of the recycle systems was performed. The major sources contributing to recycle flows at the SRWWTP include, non-potable spray water used for foam control, equipment washdown, pump seal water system, odor control scrubber and process make-up water, clarifier scum manholes, effluent filter backwash water, Page 6 of Influent Flow Study

8 Francois Domond, P.E. November 28, 2012 deep injection well strainer backwash, NPW and off-site reuse system strainer backwash, filtrate liquid from the biosolids dewatering building and the vacuum truck sump area. The CPD system discharges to the head of the plant at two locations via three separate piping systems, including: 48-inch diameter CPD gravity pipe that collects recycle flows from the plant site north of the influent pump station and transports it into junction box C located at Grit Chamber No.3 15-inch force main that transports flows from the CPD pump station and discharges to the influent flow diversion 15-inch diameter CPD gravity pipe, part of a small CPD gravity system east of the south electric service center that discharges to the influent flow diversion box Figure 2 and 3 present the layout of the SRWWTP CPD system. Because of the intermittent and relatively low flows (small diameter pipe), it was determined that measurement of the recycle flows was not practical. Evaluation The SRWWTP treated effluent flow volumes are determined by calculating the difference between the sum of flows to the ocean outfall, deep injection well nos. 1 and 2 and off-site reuse disposal systems and the sum of Davie/Cooper City treated secondary effluent and Hollywood WTP concentrate flows. The relationship is presented in the current facility permit as follows: SRWWTP Treated Effluent = (FLW01+FLW03+FLW04+FLW05) (FLW11+FLW12+FLW02) As a check on flow accuracy, the calculated treated SRWWTP effluent flow was trended against the flow measured at oxygenation trains 1 through 5 on a monthly basis for the five year period. Oxygenation Train Flow = FLW06 + FLW07 + FLW08 + FLW09 + FLW10 Table 6 presents the calculated recycle flow rate on an annual average basis. Additional monthly averages are presented in the Appendix. Page 7 of Influent Flow Study

9 R1.cdr Figure 2 Southern Regional Wastewater Treatment Plant Central Plant Drain System Influent Flow Monitoring Accuracy Report

10 R1.cdr Figure 3 Southern Regional Wastewater Treatment Plant Central Plant Drain System Influent Flow Monitoring Accuracy Report

11 Francois Domond, P.E. November 28, 2012 Table 6 City of Hollywood SRWWTP Summary of Annual Average Effluent, Oxygenation Train and Recycle Flows (mgd) Year Oxygenation System Flow 1 (mgd) SRWWTP Treated Effluent Flow 2 (mgd) Recycle Flow 3 (mgd) Year Average FLW06 + FLW07 + FLW08 + FLW09 + FLW10 2 FLW01 + FLW03 + FLW04 + FLW05 FLW11 FLW12 FLW02 3 Oxygenation Train Flow SRWWTP Treated Effluent Flow The possibility of a direct variation between two data sets can be determined by the Pearson correlation as it accounts for both the covariance and standard deviation of the two variables. The Pearson coefficient was calculated and found to be As this correlation is close to 1, the data exhibit a strong positive correlation. Regression analysis found the variation to be 0.88, meaning that when influent flow varies by 1 mgd, the effluent flow varies directly by 0.88 mgd. For graphical purposes, the influence of the recycle flows can be removed through normalization of each data set. Figure 4 presents the normalized monthly treated effluent flow rate and the oxygenation train influent flow rate for the period January 2007 through December Normalization of the data was achieved by dividing the monthly average treated effluent flow rate and the oxygenation train flow rate by the respective five year averages. As determined through statistical verification and exhibited in Figure 4, the two metered sources track closely. Therefore, the two flow metering approaches are equivalent for the measured flows, however only the effluent flow measurement accurately reflects treated plant flow as a result of the inclusion of unmetered recycle flows in the oxygenation train meter readings. Conclusion Due to its status as a regional facility, the SRWWTP accepts flows from numerous large users and has required several expansions over its history. As such, it has a complicated system of influent flows and disposal discharges. Flow meters are used to control the treatment process and for Large User billing purposes. Due to the numerous raw wastewater sources entering the SRWWTP from differing directions under gravity at the bar screen inlet box, metering of the Page 8 of Influent Flow Study

12 R2.cdr SRWWTP Treated Effluent Flows Oxygenation Train Flows 1.3 Influent Flow Monitoring Accuracy Report Flow Rate / Average Flow Rate Jan-07 May-07 Oct-07 Mar-08 Aug-08 Jan-09 Jun-09 Nov-09 Apr-10 Sep-10 Feb-11 Jul-11 Dec-11 Figure 4 City of Hollywood SRWWTP - Normalized Monthly Average Influent and Effluent Flow Rates January 2007 to December 2011 Date

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14 APPENDIX SRWWTP FLOW DATA ANALYSIS

15 City of Hollywood SRWWTP Average Monthly Disposal System Flows (mgd) Cooper City WWTP Effluent Year Month IW-1 IW-2 Ocean Outfall Off-Site Reuse Davie WWTP Effluent 2007 Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug WTP Concentrate

16 City of Hollywood SRWWTP Average Monthly Disposal System Flows (mgd) Cooper City WWTP Effluent Year Month IW-1 IW-2 Ocean Outfall Off-Site Reuse Davie WWTP Effluent 2010 Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec WTP Concentrate

17 City of Hollywood SRWWTP Average Monthly Oxygenation Train Flows (mgd) Oxygenation Oxygenation Oxygenation Train 2 Train 3 Train 4 (FLW07) (FLW08) (FLW09) Oxygenation Train 1 (FLW06) Oxygenation Train 5 (FLW10) Year Month 2007 Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug

18 City of Hollywood SRWWTP Average Monthly Oxygenation Train Flows (mgd) Oxygenation Oxygenation Oxygenation Train 2 Train 3 Train 4 (FLW07) (FLW08) (FLW09) Oxygenation Train 1 (FLW06) Oxygenation Train 5 (FLW10) Year Month 2010 Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec

19 City of Hollywood SRWWTP Average Monthly Effluent, Oxygenation Train and Recycle Flows (mgd) SRWWTP Treated Oxygenation Train Effluent Flow 2 Recycle Flow 3 (mgd) Year Month Flow 1 (mgd) (mgd) 2007 Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug

20 City of Hollywood SRWWTP Average Monthly Effluent, Oxygenation Train and Recycle Flows (mgd) SRWWTP Treated Oxygenation Train Effluent Flow 2 Recycle Flow 3 (mgd) Year Month Flow 1 (mgd) (mgd) 2010 Sep Oct Nov Dec Jan Feb Mar April May June Jul Aug Sep Oct Nov Dec FLW06 + FLW07 + FLW08 + FLW09 + FLW10 2 FLW01 + FLW03 + FLW04 + FLW05 FLW11 FLW12 FLW02 3 Oxygenation Train Flow SRWWTP Treated Effluent Flow