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Home My WebLink AboutNC0069841_Other Correspondence_20190320 • Union County Government Public Works 500 N Main St Union County Suite#400 Monroe, NC 28112 7:1\1 DWR T. 704.296.4210 ' 2 7 2019 EST. 1842 www.unioncountync.gov �;. .. ,t:1 poriYt1`%+4ourcea 9 Sectipq March 20, 2019 Deborah Gore, Supervisor Pretreatment, Emergency Response and Collection Systems Branch North Carolina Department of Environment Quality Division of Water Resources 1617 Mail Service Center Raleigh, NC 27699-1617 Subject: Twelve Mile WWTP (NC0085359) & Crooked Creek WWTP (NC0069841) Residential Flow Reduction Approval for Union County Currently North Carolina Department of Environmental Quality (NCDEQ) requires wastewater permitting and flow allocation in accordance with North Carolina Administrative Code (NCAC) as listed in 15A NCAC 02T .0114 Wastewater Design Flow Rates with the design daily wastewater flow rate for residential connections to be 120 gallons per day per bedroom. The minimum volume of sewage from each dwelling unit shall be 240 gallons per day and each additional bedroom above two bedrooms shall increase the volume by 120 gallons per day. Each bedroom or any other room or addition that can function as a bedroom shall be considered a bedroom for design purposes. In 15A NCAC 02T .0114(f), NCDEQ allows for this design flow to be adjusted if it can be demonstrated that the actual daily flows are less than the design flows. In July 2007, Union County requested a flow reduction to 270 gpd for an average of 3 bedrooms for residences in Union County served by Twelve Mile WWTP (NC0085359) and Crooked Creek WWTP (NC0069841) based on the analysis and data provided at that time. On July 19, 2007, NCDEQ issued an approval letter for Union County's use of 95 gpd per residential bedroom, with a minimum of 190 gpd for one and two bedroom units in all applicable non-discharge permit applications. In January 26, 2018, NCDEQ issued a Revised Residential Flow Reduction Approval to allow the estimating of bedrooms at 3 bedrooms for a total of 285 gpd per lot for permitting purposes with a requirement to modify the permit prior to completion if the bedrooms constructed were to exceed the specified total. Union County Public Works was thereby required to track the bedrooms installed with each engineering certification of completion submitted. The purpose of this memorandum is to demonstrate that the current adjusted flow rate of 95 gpd per bedroom or estimated 285 gpd per lot is no longer representative of the actual wastewater 14-66 410 - N�Qr Page 1 Zo9Ty '"- CPS flows in Union County. The following is an overview of the existing Union County wastewater system in addition to the procedure for calculating the adjusted residential design flow rate and the results of the calculations. Union County Existing Wastewater System Union County Public Works (UCPW) is charged with the management, operation and maintenance of the County's sanitary sewer system. The wastewater system is comprised of 5 active wastewater treatment plants (WWTP), 80 wastewater pumping stations, and over 685 miles of pipe with 36,244 connections. In addition to the 5 WWTPs which have a combined rated treatment capacity of 8.15 million gallons per day (MGD), the County, through contractual agreement, has 2.65 MGD and 3.0 MGD of purchased capacity at the City of Monroe WWTP and Charlotte's McAlpine Creek WWTP respectively. The Twelve Mile Creek WWTP serves western Union County including the towns of Wesley Chapel, Weddington, Mineral Springs and Waxhaw, along with portions of Stallings and Indian Trail. The Twelve Mile WWTP is currently rated at 6.0 MGD with an expansion currently under construction to expand to 7.5 MGD. The Crooked Creek WWTP serves the South Fork Crooked Creek basin in Union County which includes portions of Stallings, Indian Trail, Hemby Bridge, and Lake Park. The Crooked Creek WWTP is permitted to discharge 1.9MGD of treated wastewater. Wastewater Design Flow Rate Calculation Procedure Per the requirements of 15A NCAC 02T .0114(f), the following procedure was used to calculate the actual residential wastewater design flow rate for the Twelve Mile Creek/Crooked Creek WWTP service areas. 1. Gathered 12 consecutive months (December 2017 through November 2018) of daily wastewater flow readings for each WWTP and determined the highest average flow month for each WWTP. 2. Determined the minimum design daily sewage rate by averaging the highest 3 days of flow for the highest average flow month. 3. For the same 12-month period, the water meter billing date was collected for all customers with sewer connections. 4. The number of residential connections was determined for the month corresponding with the highest average wastewater flow month. (Note billing lags between actual water meter usage and billing data.) , O �eaz�Gtil 47 I Q 1 Page 2 CAR,' 5. For the same month, the average nonresidential flow was determined based on water meter records. It was assumed that 100 percent of the nonresidential water consumption was discharged to sewer, excluding irrigation meters. 6. A peaking factor was applied to the nonresidential wastewater flows based on the ratio of the average 3 day wastewater flow to the 2018 average wastewater flow. 7. The peak nonresidential wastewater flow was subtracted from the average 3-day flow for the highest average flow month. 8. The remaining flow was divided by the number of residential connections to determine the actual design daily flow rate for a residential connection. The daily wastewater flow data (as reported in the DMRs) and rainfall data for December 2017 through November 2018 for the Twelve Mile Creek and Crooked Creek WWTPs is presented in Tables 1 and 2, respectively. The highest average flow month is highlighted for each WWTP alongwith the topthree dailyreadings in this month. For both Twelve Mile WWTP and Crooked 9 Creek WWTP, the highest average flow month was November. The average of the three top daily flow readings for the highest flow months is also shown on each table. The water meter billing data for the highest flow months is also shown on each table. The water meter billing data for the Twelve Mile Creek and Crooked Creek WWTP service areas are attached in the Appendix A (CD) and includes a summary of the total water consumption, nonresidential water consumption and number of residential connections for the month that corresponds with the highest average wastewater flow. Table 3 then presents the calculations used for determining the actual wastewater design flow rate of 278 gpd for residential connections. Residential Average Bedroom Count When permitting sewer extensions, single family residential bedroom counts are difficult to predict and track as floor plans and layouts often change. Developers and engineers are tasked to predict the bedroom counts before the builders or homeowners buy the lots. Union County is the sewer provider to 13 municipalities located within Union County. Often the local zoning approvals do not require bedroom counts which also does not provide a means for bedroom estimating. Union County can only validate the bedroom count by the use of tax data collected, typically after the home is sold. The overall residential building data collected from Union County tax records from the past 5 years, as shown in Table 4, indicates the average number of bedrooms per residential dwelling unit is over 4 bedrooms per dwelling unit. Conclusions Based on the results of the residential wastewater design flow rate analysis, a reduced design flow rate can be requested for permitting future residential connections within the Twelve Mile "842 • y-0�__ Q Page 3 Creek WWTP and Crooked Creek WWTP service areas. For the Twelve Mile Creek and the Crooked Creek WWTP service area, a design flow rate of 278 gpd was calculated for an average residential connection which records indicate to have an average of 4 bedrooms. Union County requests the removal of tracking bedrooms in single family homes from the design flow rates and use 280 gpd (70 gpd per bedroom) per lot. We believe this requested design flow rate meets the requirements of the 15A NCAC 02T.0114 (f) and reflects an accurate representation of the actual wastewater flows per residential dwelling unit being constructed in Union County. Union County also requests to apply this adjusted flow rate of 280 gpd to all permitted residential connections that are not yet contributing flows to the wastewater system. If you have any questions or need any additional information, please feel free to contact me at 704-296-4239 or crystal.panico@unioncountync.gov. Sincerely, RECEIVED/D=NR DWR MAR 2 7 2019 /.71-261 �uGO Wa��r R�:�ource� PormiUng Section Crystal Outlaw Panico, PE New Development Program Manager Cc: Aubrey Lofton, Interim Public Works Administrator Scott Huneycutt, Engineering Director Kevin Moluf, Associate Engineer Chrystn Fertenbaugh, NCDEQ Environmental Engineer Corey Basinger, NCDEQ Environmental Regional Supervisor J�0NCazr(lud(i1 , o. . Q; Page 4 Spy C g°- 2017 2018 2018 2018 December January F October November Flow Flow FlovVow Flow (MGD) Rain(in) (MGD) Rain(in) (MGE1GD) Rain(in) (MGD) Rain(in) 1 3.51 - 3.44 - 4 3.39 - 3.37 0.0 2 3.26 0.2 3.21 - 4 2.97 - 3.58 0.3 3 2.96 0.1 3.45 - 4 2.90 - 3.23 - 4 3.26 - 3.37 - 6 3.42 - 3.69 0.1 5 3.68 1.5 3.28 - 5 3.34 - 5.85 2.0 6 3.69 0.3 3.23 - 4 3.25 - 4.33 0.1 7 3.36 - 3.38 - 4 3.22 - 3.59 0.2 8 3.37 - 3.37 - 4 3.26 - 3.65 0.1 9 3.57 - 3.44 - 4 3.34 0.0 4.14 1.3 10 4.32 - 3.53 - 4 3.45 0.8 3.91 - 11 3.66 - 3.89 0.1 4 6.66 3.8 3.66 _ - 12 2.90 - 3.70 1.4 4. 6.04 - 4.73 1.8 13 2.82 - 4.29 - 4. 3.53 - 8.32 0.4 14 3.27 - 3.75 - 4. 3.51 - 4.93 0.3 15 3.26 - 3.14 - 4. 3.68 - 7.67 1.9 16 3.02 - 3.41 - 4. 3.37 - 7.74 - 17 3.04 1.6 3.44 0.3 4. 2.62 - 4.98 - 18 3.55 - 3.18 0.1 3. 2.86 - 6.22 - 19 3.69 - 2.95 - 3. 3.23 - 3.63 - 20 4.91 - 3.29 - 3• 3.25 - 3.58 - 21 5.17 - 3.27 - 4. 3.05 - 3.66 - 22 5.16 - 3.35 - 1 3.17 - 4.18 - 23 4.94 - 4.17 1.3 3. 3.25 - 3.90 0.0 24 3.85 - 3.67 - 3• 3.12 - 5.13 0.6 25 3.44 - 4.06 - 3• 3.26 - 4.91 - 26 3.31 - 3.71 - 3• 4.33 2.2 3.97 - 27 3.33 - 3.73 - 3• 5.22 0.1 3.64 - 28 3.27 - 4.56 1.9 3. 4.30 - 3.58 - 29 3.21 - 7.79 0.1 3.36 - 3.55 - 30 3.28 - 4.69 - 3.67 - 3.71 0.0 31 3.35 - 4.13 - 3.39 - Monthly Avg.: Avg.(x) 3.59 0.12 3.74 0.17 4. 3.59 0.22 4.50 0.30 3.80 MGD Nonresidential Sewer Total 13.80 MG 13.33 MG 13. 17.34 MG 15.85 MG 16.20 MG Average , 445,150 GPD 430,143 GPD 493,9E13 409 GPO 528,361 GPD 532,829 GPD 2017 2018 2018 2018 Counts December January Ff October November (A)ct. 22572 22609 23457 23492 (R)es. 22142 22180 22992 23030 VA 159.20 GPD/Act. 165.29 GPD/Act. 186.053.18 GPD/Act. 191.60 GPD/Act. Standarized Peak: INovember I 23492 Accounts I 23030 Res.C 7.91 MGD IPF: 2.08344 Gross Peak: INovember I 23492 Accounts I 23030 Res.C 7.91 MGD IPF: 2.08344I r 2017 2018 2018 2018 December January F October November Flow Flow Flowlow Flow (MGD) Rain(in) (MGD) Rain(in) (MGDAGD) Rain(in) (MGD) Rain(in) 1 0.93 0.78 0• 0.78 - 1.01 - 2 0.91 - 0.81 - 1. 0.96 - 1.21 0.1 3 0.88 - 0.85 - 1• 0.88 - 1.40 1.0 4 1.06 - 0.92 - 0• 0.63 - 1.00 - 5 0.91 - 0.84 - 2• 1.16 - 1.56 1.5 6 1.09 0.0 0.90 - 1. 1.00 - 1.67 0.1 7 0.84 - 0.87 - 1. 0.79 - 1.63 - 8 0.92 - 0.87 - 1• 0.81 - 1.45 0.1 9 1.58 1.0 0.84 - 1. 0.78 0.1 1.09 0.1 10 1.22 - 0.99 - 1. 1.27 - 1.28 - 11 0.92 - 0.89 - 1. 1.47 1.4 1.28 0.4 12 0.95 - 0.93 0.2 0. 2.25 1.5 0.97 - 13 0.89 - 1.58 0.8 0. 1.47 - 2.27 2.0 14 0.95 1.08 0 1.47 2.27 0.1 RECEIVE /D NR/DWR 15 0.84 - 0.90 - 0. 1.05 - 1.63 1.8 16 0.83 - 0.94 - 0. 1.06 - 2.48 0.4 MAR 2 7 2019 17 0.83 - 0.91 - 0. 1.03 0.1 1.93, - Water Rp 18 0.80 - 1.06 - (3. 0.76 - 1.64 - P �oUfCe$ ermit;ing Section 19 0.90 - 0.92 - 0• 1.10 - 1.39 - 20 0.98 0.1 1.41 - 0• 0.93 - 1.24 - 21 1.92 1.0 0.60 - 0. 0.93 - 1.30 - 22 1.01 - 0.93 - 0. 0.79 - 1.18 - 23 1.09 - 1.17 1.4 0. 1.02 - 1.19 - 24 0.68 - 1.85 - 0. 1.11 - 1.43 - 25 0.77 - 1.18 - 0. 1.05 - 2.00 0.3 26 0.70 - 1.00 - 0. 0.97 0.5 1.54 0.5 27 0.83 - 0.89 - 0 1.12 1.20 0.1 28 0.85 - 0.92 - 0. 1.92 1.5 1.26 - 1 29 0.83 - 2.85 1.5 1.31 - 1.21 - 30 0.99 - 1.78 - 1.15 - 1.07 - 31 0.84 - 1.19 - 1.14 - Monthly Avg.: Avg.(x) 0.96 0.07 1.08 0.13 1. 1.10 0.16 1.46 0.28 1.09 MGD Nonresidential Sewer Total 13.50 MG 13.35 MG 14.£3.04 MG 13.53 MG 15.03 MG Average 435,562 GPD 430,665 GPD 529,6:1764 GPD 451,087 GPD 494,372 GPD 2017 2018 2018 2018 Counts December January F October November (A)ct. 6669 6667 6841 6833 (R)es. 5923 5918 6089 6081 z/A 143.85 GPD/Act. 162.72 GPD/Act. 155.51.03 GPD/Act. 213.55 GPD/Act. Standarized Peak: INovember I 6833 Accounts I 6081 Res.'2 34 MGD IPF: 2.141131 Gross Peak: 1 November I 6833 Accounts 1 6081 Res.'2.34 MGD IPF: 2.14113 TABLE 3 -Residential Sewer Flow Rate Item Service Area Calculation 12-Mile Creek Crooked Creek Combined Peak Month November November Monthly Avg. A 3,795,649 1,093,844 4,889,492 Wastewater Flow(gpd) Avg. Daily Sewer Flow for B 7,908,000 2,342,067 10,250,067 Highest 3 Days (gpd) Peaking Factor C Items B/A 2.083 2.141 2.096 (3 High. Avg./Annual Avg.) D Avg. Day Non Residential 532,829 494,372 1,027,200 Sewer Flow (gpd) E Peak Day Non Residential Items C*D 1,110,116 1,058,517 2,153,367 Sewer Flow (gpd) Calculated Peak Residential F Items B-E 6,797,884 1,283,550 8,096,700 Sewer Flow (gpd) #of residential sewer G 23,030 6,081 29,111 connections in peak month Calculated Res. Sewer Flow per Items F/G 278 Connection (gpd) Note: No difference in peak month whether using gross monthly average peak flow (MGD) or standardized monthy average peak flow (MGD per account) TABLE 4 - Union County Residential Tax Data YEAR BUILT DWELLING COUNT DWELLING AVG. NO. OF BEDROOMS 2018 1578 4.03 2017 1533 4.1 2016 1601 4.25 2015 1258 4.21 2014 1504 4.3 5 year average 1495 4.18