Appendix 4-29 Technical Memorandum WW-1 on Existing WWTF and Vent Evaluation

Appendix 4-29 Technical Memorandum WW-1 on Existing WWTF and Vent Evaluation TECHNICAL MEMORANDUM WW-1 March 8, 2013 To Town of Falmouth, MA Copy to File; Project Team From Marc R. Drainville PE, BCEE, LEED AP Tel 774-470-1634 J. Jefferson Gregg, PE, BCEE 774-470-1640 Wastewater and Nutrient Management Services Subject Job No. 8615097 Existing WWTF and Vent Evaluation 1 INTRODUCTION The purpose of the memo is to evaluate the existing Falmouth Wastewater Treatment Facility and service vent in order to determine the treatment capacity of the facility and also identify operational limitations. The evaluation consists of the following tasks: x An assessment of treatment capacity and capacity limitations on all unit processes. x An assessment of the equipment and structures at the facility determining the physical state of the equipment and structures. x A detailed assessment of all processes and groups of equipment to compare them to current standards. x A review of plant operations. The facility was evaluated against the following design standard: x TR-16 Guides for the Design of Wastewater Treatment Works; New England Interstate Water Pollution Control Commission, 2011 Edition. This document was used because it is a New England design standard and is comprised of industry standard documents such as NFPA 820 and Water Environment Federation (WEF) Manual of Practice textbooks. This is the document that DEP uses in its approval process for new and modified wastewater infrastructure. It should be noted that an earlier version of the document would have been used to design this facility. The current version was used in this evaluation as a reference document because any updates made to the facility will need to comply with the most current version available. 2 BACKGROUND The Falmouth Wastewater Treatment Facility was originally constructed in 1986. At that time, the facility consisted mainly of a lagoon treatment system, and had a single process and control building. Effluent disposal was accomplished by open sand beds and spray irrigation. In 2005, the main treatment process of the facility was changed from lagoon treatment to Sequencing Batch Reactors (SBR) followed by denitrification filters. This facility’s design targets were an effluent Biochemical Oxygen Demand (BOD) of 30 mg/L and an annual average effluent Total Nitrogen (TN) of 3 mg/L, based on the influent load conditions in the performance guarantee for the SBR. TM WW-1 In 2011, a new groundwater discharge permit was issued to the Town. Both the Town and the Buzzards Bay Coalition appealed this permit, which, among other restrictions, included an average annual total nitrogen effluent limit of 3.0 mg/L. The appeal was settled and the final permit took effect June 29, 2012. The final permit is shown in Appendix WW-1-A. It should be noted that this memo reviews the ability of the existing facilities to treat additional flow (as stated in Section 1 above) on a hydraulic and treatment capacity only. The current permit significantly restricts the flow of the facility below the design capacity of the plant to 800,000 gpd or less. The permit is the subject of a companion project. The scope of this work is as defined in GHD’s proposal dated September 5, 2012. 3 FLOWS AND LOADS 3.1 Existing Flows and Loads This section will review historical data with respect to plant flows and loads, and comment on the approximate capacity of the facility. Over the years, operational changes have been made and process upsets have been minimized. As a result of this, and possibly other factors, performance within the past two years in particular has been very good. As a result, data will be presented both for the entire period the plant was in service as well as within the past two years. The performance of the facility over time is shown in the following tables. Table 3-1 shows the composite performance since the upgraded plant was put into service. The performance of the facility, in relationship to the permit in effect at the time, is the subject of the Nitrogen Optimization Plan (currently in development). Table 3-1 Effluent Concentrations January 2006—November 2012 Average (mg/L) Max 30 Day Avg (mg/L) Max Day (mg/L) Effluent BOD 3 51 91 Effluent TSS 3 34 38 Effluent TN 5 20 22 Effluent NO2 0 0 0 Effluent NO3 1 7 8 Effluent TKN 3 19 22 Plant operations have been fine-tuned over the years, and some operational changes have been made in recent years to enhance performance. As a result of a combination of factors, performance within the past two years has been very good as demonstrated in Table 3-2. 2 TM WW-1 Table 3-2 Effluent Concentrations November 2010—November 2012 Average (mg/L) Max 30 Day Avg (mg/L) Max Day (mg/L) Effluent BOD 2 15 58 Effluent TSS 3 7 9 Effluent TN 3 5 8 Effluent NO2 0 0 0 Effluent NO3 1 2 6 Effluent TKN 2 5 5 3.1.1 Existing Flows Table 3-3 summarizes the influent flows seen at the WWTF during the two-year period of November 2010 to November 2012. Flow measurement analysis at the Falmouth WWTF is summarized in the ‘Flow Measurement Evaluation’ compiled by GHD in 2012 (currently in draft form and under review by the Town). It should be noted that the intent of the Flow Measurement Evaluation is to improve flow measurement at the plant as the accuracy of some measurements have been questioned. Table 3-3 Influent Wet Well Measured Flows November 2010—November 2012 Average (mgd) Max 30 Day Avg (mgd) Max Day (mgd) Influent Wet Well 0.43 0.62 0.92 3.1.2 Existing Loads A summary of plant influent loads and concentrations are shown below in Tables 3-4 and 3-5. Table 3-4 Influent Concentrations January 2006—November 2012 Average (mg/L) Max 30 Day Avg (mg/L) Max Day (mg/L) Influent BOD 178 465 488 Influent TSS 186 895 895 Influent Ammonia 16 30 48 Influent TKN 28 56 89 Influent TN 29 56 89 3 TM WW-1 Table 3-5 Influent Loads January 2006—November 2012 Average (lb/d) Max 30 Day Avg (lb/d) Max Day (lb/d) Influent BOD 618 1717 2479 Influent TSS 643 2534 3914 Influent Ammonia 52 133 200 Influent TKN 89 218 332 Influent TN 89 218 332 These summaries of plant data will be examined more closely in Section 3.2 to help determine current capacities. The influent BOD Data from January 2006 to September 2012 is graphically presented in Figure 3-1. Figure 3-1 Influent BOD (mg/L) vs. Time As can be seen in Figure 3-1 the data set contains a measurement on 6/12/2008 of 1,007 mg/L, which is at least twice any other concentration seen during the data collection period. Because of this, the value was determined to be an outlier. 4 TM WW-1 Figure 3-2 shows the same data set without the outlier and also includes a trend line of the revised data set. Figure 3-2 Influent BOD (mg/L) vs. Time This figure shows a downward trend in the BOD concentration over time, and this decrease in the concentration has occurred while plant flows have remained steady (actually flows have increased slightly over this time period). Table 3-6 shows the clear decrease in the loading. Table 3-6 Influent Average Loading Loading Since Startup (2006—2012) 2006—2010 Nov 2010—Nov 2012 Influent BOD (lb/d) 619 722 247 5 TM WW-1 3.1.3 Existing Capacity The Falmouth WWTF was designed to receive an average flow of 1.2 million gallons per day (mgd). The concentrations and loadings which the facility was designed for are detailed in the draft Falmouth WWTF Operations & Maintenance Manual (See Appendix WW-1-B). The data outlined in the previous section can be compared to the design loading conditions for the facility to determine if the SBR is adequately sized for its current operation. The process guarantee from AquaAerobics is included as Appendix WW-1-E. Because the current permit requires the facility to meet a monthly permit for all parameters, including nitrogen, existing maximum 30 day influent loading conditions were determined. Although it is understood that the current permit in Appendix WW-1-A does not have a true limit for Nitrogen, our analysis was based on the assumption that a future permit may contain a monthly limit of total nitrogen as low as 3 mg/L. As shown previously, influent BOD loads trended downward over the past several years. In order to account for this apparent load reduction, more recent data was considered. In addition, plant performance has been steady over the past two years and process upsets have been minimized. As a result of both of these factors, the past two years of plant data seemed to be representative of current conditions. Table 3-7 Design and November 2010 to September 2012 Loading for Sequencing Batch Reactors (lb/d) Design Loading (stated as SBR Design “average” in Loading Influent performance Max 30 Day Avg Capacity Concentration guarantee) Loading Currently Used BOD5 250 2502 1372 55% TSS 180 1801.4 1259 70% TKN 30 300.2 218 73% Total N 36 360.3 218 61% From this analysis, it would appear that the facility is at approximately 60-70% capacity. 3.1.4 Recycle Loads Because of the location of the influent sampler, composite influent wet well samples do not include recycle flows even though the recycle flows enter the wet well.

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