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Home My WebLink AboutNC0089630_Report_20080320lvao8" W Water Quality Modeling Report Long Creek Regional Wastewater Treatment Plant • CHARLOYFE. CHARLOTTE•MECKLENSURG UTILITIES Charlotte Mecklenburg Utilities Charlotte, NC City of Mount Holly Prepared by: Black & Veatch International Company 8520 Cliff Cameron Drive, Suite 210 Charlotte, NC 28269 (704)-510-8461 March 2008 MR M" No Table of Contents 1. Introduction.....................................................................................................................3 om 2. Background.....................................................................................................................4 3. Lake Wylie CE-QUAL-W2 Model.....................................................................................6 o, 4. Case Descriptions...........................................................................................................9 5. Model Inputs..................................................................................................................14 5.1 RIVER AND TRIBUTARY INPUTS.....................................................................................14 5.1.1 Inflow Volumes...................................................................................................14 5.1.2 Existing Condition Nonpoint Source Loadings....................................................15 5.1.3 Future Nonpoint Source Loadings......................................................................15 5.2 WWTP POINT SOURCE LOADINGS...............................................................................16 5.2.1 WWTP Inflow Volumes.......................................................................................17 5.2.2 WWTP Inflow Temperature................................................................................17 5.2.3 WWTP Inflow Water Quality...............................................................................17 S. Model Outputs...............................................................................................................21 7. Water Quality Impacts..................................................................................................23 7.1 DISSOLVED OXYGEN...................................................................................................23 7.2 TOTAL PHOSPHORUS...........................................24 ....................................................... 7.3 TOTAL NITROGEN........................................................................................................ 24 7.4 CHLOROPHYLL A.........................................................................................................25 7.5 FLOW AND NUTRIENT CONTRIBUTIONS.........................................................................25 8. Findings and Conclusions...........................................................................................27 FM 9. References.....................................................................................................................30 M F" MM em ow fm 2 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARI.OrrE. cxum�+®.xivain, 1. Introduction _ In 2006, CMU and the City of Mount Holly cooperated in a Feasibility and Preliminary Planning Study which evaluated the growing wastewater demands in both service areas and identified a number of alternatives that would meet future wastewater projections (Black & Veatch 2006). The proposed regional wastewater treatment plant was identified as the recommended alternative to meet the needs of a growing population in Mecklenburg County, the City of Charlotte and the Town of Mount Holly. Objectives for the Preliminary Planning Study included the following: • Evaluate population projections • Project wastewater flows that may be produced based on growth projections • Identify and evaluate wastewater treatment alternatives — both separate and regional solutions • Perform a detailed evaluation of environmental impacts associated with each alternative Alternatives identified in the study included a new regional WWTP adjacent to the existing Long Creek Pump Station in western Mecklenburg County as well as combinations of expansion and new construction on the Gaston County side of the Catawba River. Each of the six action alternatives as well as the No Action and Land Application alternatives considered for this project were presented in detail in Chapter 4 of this Environmental Impact Statement (EIS). The alternatives included: • Alternative 1: Operate separately with existing facilities • Alternative 2: Operate separately with additional and upgraded facilities .. • Alternative 3: Operate jointly at upgraded Mount Holly WWTP • Alternative 4: Operate jointly at new Mount Holly WWTP • Alternative 5: Operate jointly at new CMU WWTP ., • Alternative 6: Combination of new and existing facilities • No action 3 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report C HARLOTIM auiamrta®uea�m • Land application only As part of the evaluation of environmental impacts, a water quality modeling study of Lake Wylie was conducted to evaluate the potential impacts that increased wastewater discharge would have on the lake. Current conditions and many future scenarios were modeled to determine the potential water quality impacts from the proposed regional WWTP. The existing condition, which is similar to Alternative 1, was modeled assuming that the Mount Holly plant discharged at the current permitted flow of 4 mgd and at their existing nutrient concentrations. Currently, Mount Holly does not have permit limits for nutrients but is required to monitor for them on a monthly basis. From a modeling perspective, Alternatives 2 through 6 were the same assuming similar treatment levels at the combined or separate facilities. Alternatives 7 and 8 do not contribute additional discharges into Lake Wylie and therefore were not explicitly modeled. Nonpoint source inputs were included in the model as measured values from the monitored tributaries. Inputs from ungaged tributaries were estimated based on loads from nearby creeks and scaled by contributing watershed area. Anticipated changes in nonpoint sources loadings as a result of future population growth were also included in the model using an export coefficient approach. 2. Background A detailed water quality model was developed to estimate the potential environmental impacts associated with the construction of a new WWTP that would discharge to Lake Wylie. Assessment of current water quality conditions was a critical component in this effort. Surface water quality sampling in the project area and surrounding water bodies is conducted routinely by several governmental agencies, including US Geological Survey (USGS), NC Department of Water Quality (DWQ) and the Land Use and Environmental Services Agency (LUESA) of Mecklenburg County. As part of LUESA's monitoring program, five stations are sampled in Lake Wylie on a monthly basis. Determination of model requirements and preliminary discussions with DWQ staff members resulted in the addition of four mainstem sampling sites located adjacent to 4 0 Charlotte -Mecklenburg Utilities / City of Mount Holly wy �9UN� Water Quality Modeling Report samples currently being collected in the coves. Figure 1 shows the nine sampling locations, with the added sites designated with an "A" (e.g. LW4A). All sites were sampled on a monthly basis from May through December 2007; twice -monthly samples were collected July — September 2007. Samples were collected from the surface and near the lake bottom and analyzed for the following parameters: • Water temperature • Depth • Dissolved oxygen • Conductivity • pH • Total suspended solids, total solids, turbidity • Chlorophyll -a • Nutrients (total phosphorus, orthophosphate, total Keldahl nitrogen, nitrate -nitrogen, ammonia -nitrogen) • Fecal coliform Water quality modeling of Lake Wylie was performed to assist in the evaluation of water quality impacts from the proposed facility and to support the development of speculative NPDES limits by NC DWQ for the plant discharge into Lake Wylie. A CE-QUAL-W2 model of the lake (Lake Wylie Model) was previously developed by Duke Energy in support of the Federal Energy Regulatory Commission (FERC) relicensing process (Sawyer and Ruane, 2006). At that time, the Lake Wylie Model went through an extensive calibration process that included review and collaboration with several federal and state agencies. The calibration used flow and quality data from 1998 and 2002 which represented average and low flow years, respectively. Until 2007, 2002 represented the lowest flow year on record. Although additional data were collected during 2007, these data were not considered sufficient to warrant a recalibration of the model. Through discussions with the NC DWQ, it was agreed that the model would not be recalibrated as part of this project. The model would 5 M Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report r w� C HARLt M. �iJ iera imnee be run for the same two years used for calibration (1998 and 2002) and would incorporate changes that would occur with a new regional wastewater treatment plant. North South Carolina Mt Holly eIL WWTP� 9 " W F73 LWS LW4 LW4A LW7A LW2A Figure 1 LUESA monitoring stations on Lake Wylie. Additional mainstem stations added for this project are designated with an "A" (e.g. "LW4A"). 3. Lake Wylie CE-QUAL-W2 Model CE-QUAL-W2 is a two-dimensional, hydrodynamic and water quality model for reservoirs and rivers. It is assumed that lateral variations across a lake or reservoir can be ignored. Because of this assumption, the model is best suited to reservoirs that are relatively long and narrow like Lake Wylie. The hydrodynamic module predicts water surface elevations and velocities in the horizontal and vertical directions. The hydrodynamic module is directly 6 Charlotte -Mecklenburg Utilities / City of Mount Holly Lcsvc Water Quality Modeling Report CHARI.OY . linked to a water quality module that predicts time -varying concentration of water quality parameters. CE-QUAL-W2 model processes are described in detail in the User's manual for the model (Cole and Wells, 2002). The model uses a finite difference method to solve the laterally averaged equation of motion. The reservoir is represented by a grid consisting of a series of vertical segments and horizontal layers. The hydrodynamic calculations consider the effects of variable water density caused by differences in temperature and TDS. The model simulates the interactions of many biological and chemical factors that affect water quality. Specific processes simulated in the model include: ■ Temperature and salinity ■ The DO -carbon balance ■ The nitrogen cycle ■ The phosphorus cycle '■ ■ The silicon cycle ■ Phytoplankton ■ Bacteria ■ First order decay Required inputs include the bathymetry of the reservoir, initial conditions, inflow rates and concentration of water quality constituents, outflow rates, water surface elevations and kinetic rate coefficients. ■� The base CE-QUAL-W2 model was developed by the US Corps of Engineers (Cole and Wells, 2002) and the Lake Wylie application was developed by Resource Environmental Management Inc. at the request of Duke Energy. Information on the model application to Lake Wylie and the detailed calibration were provided by Ruane and Hauser (2006) and Sawyer and Ruane (2006). The bathymetry for the model was developed by dividing the reservoir into branches and then segmenting the branches longitudinally and vertically. The model configuration is shown on Figure 2. 7 ' Charlotte -Mecklenburg Utilities / City of Mount Holly �SC� Water Quality Modeling Report CIIARLOPI'F.. �.' sere" �„ The CE-QUAL-W2 model represents Lake Wylie as a single water body containing nine branches and ten tributaries. Branch 1 is the mainstem of the lake while the other branches are simulated arms of the lake. The ten tributaries enter the lake as point sources and include natural streams and discharges from WWTPs and power plants. The tributary inflows enter the lake at a specific location or segment within the model. A list of the branch and tributary inflows are shown in Table 3.1. As seen on the figure, segment lengths vary through the .. lake. Vertically, each layer is 1 meter thick. Table 3.1 Lake Wylie Model Inflows Input Branch Segments Segment Name 1 2-39 2 Mountain Island Dam Releases _ 2 42-47 12 South Fork Catawba River 3 50-53 14 Catawba Creek 4 56-58 15 Mill Creek 5 61-64 22 Crowder's Creek 6 67-70 27 Torrence Branch 7 73-80 29 Allison Creek 8 81-84 27 Unnamed 9 87-90 78 Little Allison Creek Input Tributary Segments Segment Name 1 n/a 2 Dutchman's Ck, Long Ck, and local inflow 2 n/a 7 Paw Creek 3-7 n/a 44 Allen Steam Plant 8 n/a 76 Catawba Nuclear Plant .. 9 n/a 2 Mount Holly WWTP 10 n/a 6 Belmont WWTP As described by Sawyer and Ruane (2006), the model was calibrated using data from 1998 and 2002. The primary calibration year was 2002 and was the driest year on record. During 2002, Duke Power conducted an intensive study of water quality and flows on the lake. In ' 1998, tributary inflows were relatively high during the first part of the year and low for the remainder of the year making it an average flow year overall. In addition, 1998 had a good database of measured flow and water quality constituents to use in the calibration process. The model was originally calibrated for 2002 conditions then model settings were then applied to 1998 conditions and the model performed well. 8 O AMffE- cxuvane�¢caEieuxo UI�1149 Neck/enburg Utilities Water Quality Modeb :ity of Mount HOG Report Figure 2. Model configuration for Lake Wylie 4. Case Descriptions The calibrated Lake Wylie model developed by Duke Energy was used to evaluate the effects of increased wastewater discharges to the upper section of Lake Wylie. Many scenarios were simulated to evaluate existing and potential future conditions. For both existing and future conditions both normal operating conditions and permit conditions were simulated. Increases in future nonpoint source (NPS) loads were also simulated. The specific cases modeled and presented in this report are summarized in Table 4-1. E �i Charlotte -Mecklenburg Utilities / City of Mount Holly tii+�� r Water Quality Modeling Report r ��/ CHARLOTTE. �. ieve'" 1 Normal plant operations for the existing condition were simulated using measured data as reported by the Mount Holly and Belmont WWTPs. Under this condition, flow and effluent quality vaned daily or monthly. Permit limits for the existing condition were simulated by assuming that these plants discharged at their maximum permitted flow every day. Because these plants do not have permit limits for nutrients, their actual measured values were used. Phosphorus concentrations for the Belmont WWTP were modified for the permit limit case by assuming that additional flow above the normal operating flow would come from residential uses and be typical of domestic wastewater. Concentrations measured at Mount .. Holly's WWTP were used to represent this domestic wastewater component. _ Normal plant operations for the future condition were simulated by assuming that the new regional plant would experience similar variations in flow and effluent quality that is _ currently measured at the McDowell WWTP. The procedures detailed in the "Technical Support Document for Water Quality -based Taxies Control" (EPA, 1991) were used to _ determine the maximum loads that could be discharged without exceeding permit limits. It was assumed that permit limits for the future flow rate of 25 mgd would be 1 mg/L total phosphorus (TP), 6 mg/L total nitrogen (TN) and 6 mg/L BOD. It was also assumed that the permit limits for nutrients would be given as loads and not concentrations and that interim flow rates would have the same load limits and therefore somewhat higher concentrations. The Technical Support Document presents equations that relate permit limits to long-term averages (LTA) of effluent quality using a coefficient of variation (CV). These equations are then used to calculate what the long-term average should be to meet permit limits. This ^ procedure was used to develop input files for effluent flow and quality for the proposed regional plant. An iterative procedure was used to calculate the input values using the following specific steps: ^ 1. Obtain the McDowell WWTP for 2007 and calculate the LTA and CV. The McDowell data set contained mostly daily values for flow, BOD, and nutrients. 2. Using the CVs calculated in step 1, calculate what the LTAs would be to achieve the assumed permit limits. 10 a Charlotte -Mecklenburg Utilities / City of Mount Holly �OU♦4'� Water Quality Modeling Report CHARLOrFE Mere ° Y 3. Increase the McDowell WWTP daily flows by a uniform factor until the LTA matches the one calculated in step 2. 4. Increase the McDowell WWTP BOD concentrations by a uniform factor until the LTA matches the one calculated in step 2. 5. Using the new flows, calculate the McDowell WWTP nutrient loads. Then increase the loads until the LTAs match the ones calculated in step 2. _ By following this procedure a simulated set of effluent data was produced that represented the largest loads that could be discharged while still meeting permit limits. Permit limits were expressed as weekly or monthly averages so, while the LTAs were less than the permit limits there were many days when the flow or loads exceeded the limits. For the future scenario of a 25 mgd permitted plant, the LTA for flow was 21.7 mgd but the flow ranged from 15.4 to 50.2 mgd throughout the year. The LTA for BOD was 4.0 mg/L and ranged from 3.3 to 15.2 mg/L; TP concentrations ranged from 0.4 to 7.4 mg/L with an average of 0.8 mg/L; TN concentrations ranged from 2.1 to 10.8 mg/L with an average of 5.8 mg/L. For scenarios using the permit limits, it was assumed that the WWTP discharged at the permit limits every day throughout the entire year. CHAffiATI'E. �WIOZR� Utilities / Water Quality Modeling Table 4.1 Lake Wylie Model — Case Descriptions of Case ID Case Description Dischar a Inouts Lake Inputs Mt Holly Belmont Long Creek Flow all Flow Quali Flow Quali Flow Quali EM2002 Existing Conditions, 2002 flow 2006 measured 2006 measured 2006 measured 2006 measured 2002 flow 2002 quality EM1998 Existing Conditions, 1998 flow 2006 measured 2006 measured 2006 measured 2006 measured 1998 flow 1998 quality EPMHB200 2 Permit Limits, 2002 flow 4 MGD 2006 measured 5 MGD 2006 adjusted 2002 flow 2002 quality EPMHB199 8 Existing Plants, 1998 flow 4 MGD 2006 measured 5 MGD 2006 adjusted 1998 flow 1998 quality FN172002 Future Normal Operations (17 2006 measured 2006 measured varies, typical for 17 MGD Based on other W WTP, consistent with 2002 flow 2002 quality MGD), Existing NPS Load, 2002 flow limit limits of TN = 8.82, TP = 1.47, BOD = 8.8 FN252002 Future Normal Operations (25 MGD), Existing NPS Load, 2002 flow 2006 measured 2006 measured varies, typical for 25MGD limit Based on other WWTP, consistent with limits of TN = 6.0, TP = 1.0, BOD = 6 2002 flow 2002 quality FN251998 Future Normal Operations(26 MGD), Existing NPS Load, 1998 flow 2006 measured 2006 measured varies, typical for 25MGD limit Based on other WWTP, consistent with limits of TN = 6.0, TP = 1.0, BOD = 6 1998 flow 1998 quality FN252002 NPS Future Normal Operations (25 MGD) Future NPS Load, 2002 flow Future Normal Operations (25 MGD), Future NPS Load, 1998 flow 2006 measured 2006 measured varies, typical for 25 MGD limit Based on other W WTP, consistent with limits of TN = 6.0, TP = 1.0, BOD = 6 2002 flow 2002 quality, adjusted for future NPS loads FN251998 NPS 2006 measured 2006 measured varies, typical for 25 MGD limit Based on other W WTP, consistent with limits of TN = 6.0, TP = 1.0, BOD = 6 1998 flow 1998 quality, adjusted for future NPS loads 12 utilities / City of Water Quality Modeling Dischar a Inputs Lake Inputs Mt Holly Belmont L ng Creek Case ID Case Description Flow Quality Flow Quality Flow Quality Flow Quality FP172002 Future at Permit 2006 2006 17 MGD TN = 8.82, TP = 1.47, 2002 flow 2002 quality Limits (17 MGD), measured measured BOD = 8.8 Belmont at Existing Loads, 2002 flow FP252002 Future at Permit 2006 2006 25 MGD TN = 6.0, TP =1.0, 2002 flow 2002 quality Limits (25 MGD), measured measured BOD = 6 Belmont at Existing Loads, 2002 flow FP251998 Future at Permit 2006 2006 25 MGD TN = 6.0, TP = 1.0, 1998 flow 1998 quality Limits (25 MGD), measured measured BOD = 6 Belmont at Existing Loads, 1998 flow FP252002 Future at Permit 5 MGD 2006 25 MGD TN = 6.0, TP = 1.0, 2002 flow 2002 quality Bel Limits (25 MGD), adjusted BOD = 6 Belmont at Permit Limits 2002 flow FP251998 Future at Permit 5 MGD 2006 25 MGD TN = 6.0, TP = 1.0, 1998 flow 1998 quality Bel Limits (25 MGD), adjusted BOD = 6 Belmont at Permit Limits, 1998 flow 13 Charlotte -Mecklenburg Utilities / City of Mount (�IAHLO'I'I'E. Water Quality Modeling Report 5. Model Inputs In an effort to determine the effects from the proposed Long Creek Regional W WTP, the CE- QUAL-W2 model developed by Duke Energy was modified to incorporate this new point source loading into Lake Wylie. Numerous existing, future, and permit limit scenarios were modeled using low and average river flows to help determine these effects (Table 4.1). The average flow year was represented using 1998 data while a low flow year was represented using 2002 flows. The model was modified to replace the Mount Holly WWTP discharge with a new point source representing the effluent from the proposed regional WWTP. All other model input parameters were not modified, with exception of the natural water quality inflow data associated with future non -point source (NPS) loading scenarios. Brief descriptions of the modified inputs are provided in the following sections. 5.1 River and Tributary inputs 5.1.1 Inflow Volumes The majority of the inflow to Lake Wylie comes from flow releases through the Mountain Island Dam with the remaining inflow primarily stemming from the South Fork Catawba River watershed (Sawyer and Ruane, 2006). These two inflows account for approximately 85 percent of the lake inflow. As stated previously the CE-QUAL-W2 model represents Lake Wylie as a single water body containing nine branches, two natural tributaries, and eight other tributaries that represent discharges from WWTPs or power plants. The model inflows are represented as branch, tributary, or distributed branch inflow. The tributary inflows enter the lake at a specific location or segment within the model. The distributed branch inflows enter the model along a branch and represent overland flow that enters the lake directly and is not included in the branch or tributary inflows. These distributed flows enter the lake at the surface. A list of the branch and tributary inflows was shown in Table 3.1. The majority of the natural inflows to Lake Wylie do not have associated flow monitoring stations. Flows for ungaged streams were estimated using data from a nearby gaging station and adjusted based on drainage area. 14 ^ CHARLOYM. LIUADRE.MctltEEl�llp 1110.RiE9 Neck/enburg Utilities / City of Mount Water Quality Modeling Report 5 1 2 Existing Condition Nonpoint Source Loadings Existing nonpoint source (NPS) loads entering Lake Wylie were included in the model by using measured flow and water quality of the tributaries to the lake. All inflows have associated temperature and water quality data. However, the majority of the natural inflows to Lake Wylie do not have water quality monitoring stations. To estimate inputs from these unmonitored inflows, data from nearby monitoring stations were used. 5.1.3 Future Nonpoint Source Loadings Nonpoint source loadings from the Lake Wylie watershed were estimated using an export coefficient approach based on current and anticipated future land uses. Export coefficients represent the average total load of a pollutant that enters into a water body and are expressed as the mass per unit area per year (e.g. kg ha I Y). This approach is generally used for calculating runoff pollutant loads from rural areas, although it has been successfully applied to more urban areas as well (reference). Since collecting site specific data for calculating these values is often cost -prohibitive, literature values from similar regions are often used. Due to specific climatological and physiographic characteristics of individual watersheds, land use export coefficients can exhibit a wide range of variability in nutrient export. By selecting values that were measured in watersheds with similar climate, topography and land use, these differences can be minimized (Beaulac and Reckhow 1982). Table 5.1 shows the export coefficients used for this project (Reckhow et al 1980, DWQ 1997, Black & Veatch, 1990). To estimate the relative increase in future NPS loads, current loads were first determined using existing land use data for the Lake Wylie watershed (USGS, 1996 LULC dataset). Loads were calculated by multiplying the total area for each land use type by the corresponding export coefficients listed in Table 5.1. ^ 15 Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report CHARLOTTE- Table 5.1 Export Coefficients for TN and TP Land Use (kghatY`) TN TP (kgha'Yl) Cultivated 16 4.5 Forest 2.2 0.2 High Intensity 10 1.9 Impervious surface 10 1.9 Low Intensity 7.4 1 Managed Herbaceous Cover 2.9 0.5 Shrubland 2.2 0.2 Unconsolidated Sediment 2.2 0.2 Unmanaged Herbaceous Cover -Upland 2.2 0.2 .. Water 0 0 Wetland 2.2 0.2 Future land use was determined by using population growth rates for each county. It was assumed that agricultural and forested land would be converted to low and high intensity development (residential and commercial land use types) to accommodate the increased population. Future NPS loads were calculated by multiplying the area in each future land use by the corresponding export coefficient. The difference between existing and future NPS loadings to the lake was calculated as a percentage for similar subbasins/counties within the Lake Wylie watershed. Increases in NPS loads were modeled within CE-QUAL-W2 by increasing the existing inflows (including branch, tributary, and distributed loads) water quality inflow concentrations into the lake. This was accomplished by increasing the existing TN and TP loadings for all inflows (branch, tributary, and distributed) draining to Lake Wylie by the percent differences between existing and future NPS loads. The percentage of increase was based on drainage area location. All TN and TP loadings were increased by an average of 22.2 percent in Mecklenburg County, 2.53 percent for drainage areas west of the lake, and 8.5 percent for Tributary 1 and its distributed inflow. 5.2 WWTP Point Source Loadings Wastewater treatment plant point sources to Lake Wylie included the Mount Holly WWTP and the Belmont WWTP. In the model, the Mount Holly WWTP and Belmont effluent data 16 Charlotte -Mecklenburg Utilities / City of Mount CHARLOTTE. Water Quality Modeling Report inputs were included in tributaries 9 and 10 which enter the model in segments 2 and 6 respectively. In the future scenarios, the Mount Holly WWTP data was replaced with the effluent data from the proposed regional facility. The effluent data consist of inflow volumes, temperature, and water quality constituents. These parameters are described in the following sections and are listed in Tables 5-2 and 5-3. 5.2.1 WWTP Inflow Volumes Inflows from the Mount Holly and Belmont WWTPs consist of 2006 measured data, to represent effluent flow volumes under the existing condition scenarios. The 2006 measured data consisted of average daily outflows from the Mount Holly facility and monthly average outflows from the Belmont facility. The permit limit flows assumed that the permit limit flow was constant for the entire modeling period. Two types of flow conditions were modeled for the future scenarios: normal operating conditions and constant permit limit conditions. Normal operating conditions simulated variations in flow and effluent quality that would be expected at a WWTP and were based on discharge data from the McDowell WWTP. The normal operating conditions used in the model represented the highest flows and loads that could be discharged while still meeting permit limits (see Chapter 4 for a detailed description of the calculation method). The permit limit conditions assumed that the permit limit flow was constant for the entire modeling period. 5.2.2 WWTP Inflow Temperature Daily average temperatures measured at the Mount Holly WWTP and monthly average temperatures at the Belmont WWTP in 2006 were used for the temperature of model inflow for each respective plant. Daily average temperatures measured at the McDowell WWTP in 2007 were used for the temperature of model inflow from the proposed regional facility. 5.2.3 WWTP Inflow Water Quality The water quality parameters that were simulated in the model include phosphorus, ammonia, nitrate, biochemical oxygen demand 5-day (BOD5), and dissolved oxygen (DO). 17 Charlotte -Mecklenburg Utilities / City of Mount Holly C� Water Quality Modeling Report ORAMrrt•,. For the existing condition, water quality concentrations in the discharge from the Mount Holly and Belmont WWTPs were based on measured data recorded in 2006 for each respective plant. For the permit limit operations at the Belmont WWTP, the phosphorus concentration was adjusted to more accurately represent this scenario. The measured flows from the Belmont WWTP include industrial loadings, therefore under the permit limit condition any additional flow was assumed to be domestic waste. Mount Holly nutrient concentrations were used to represent domestic wastewater for this additional flow. A mass balance approach was used to determine the adjusted phosphorus values, which ranged from -� 1.52 to 9.97 mg/L. �, Water quality concentrations for the proposed regional WWTP under normal operating conditions were derived using data measured at the McDowell WWTP in 2007 as described in Chapter 4. These concentrations represented the highest loads that could be discharged without exceeding any permit limits. Water quality concentrations for the proposed regional WWTP under permit limit conditions were calculated based on assumed permit limits for TN, TP, and BOD5 based on plant capacity. All calculated water quality constituents were assumed constant for the modeling period. Within the CE-QUAL-W2 model, BOD5 is represented using organic matter. Therefore, it was necessary to convert BOD5 to total organic matter. This was accomplished by calculating the maximum oxygen demand, assuming a ratio of ultimate BOD to BOD5 of 1.85, and calculating the total organic matter using typical cellular metabolism stoichiometry. The total organic matter was then distributed between labile dissolved organic matter (LDOM), refractory dissolved organic matter (RDOM), labile particulate organic matter (LPOM), and refractory particulate organic matter (RPOM) and input into the CE-QUAL- W2 model. 18 QIARLO'ITE. Water Quality Modeling Report Table 5.2 Innuts Values Used for F.ristina WWTP nicrharaac Constituent Mount olly Effluent Belmont Effluent 2006 Value Basis of Value 2006 Value Basis of Value 1.30 - 5.32 Average daily 1.10 - Average Flow mgd 2006 measured nigd . monthly 2006 data measured data Average daily Average Temperature 9.0 - 32.0 °C 2006 measured 8.8 - 24.6 °C monthly 2006 data measured data 0.98 - 5.80 Average monthly 1.85 - 30.00 Average Phosphorus* m� 2006 measured mg/L monthly monthly 2006 data data 0.50 - 4.42 Average monthly 0.16 - 0.72 Average Ammonia mg/L 2006 2006 measured mg/L monthly monthly 2006 data Calculated based Calculated Nitrate** 1.57 - 17.68* on 2006 measured 12.34 - 25.19 based on 2006 measured total mg/L total nitrogen and mg/L ammonia data nitrogen and ammonia data Calculated based Calculated LDOM 0.97 - 3.70 on 2006 measured 0.58 - 2.89 based on 2006 mg/ BOD5 data mg/L measured BOD5 data Calculated based Calculated BDOM 0.24 - 0.92 on 2006 measured 0.14 - 0.72 based on 2006 mg/L BOD5 data mg(L measured BOD5 data Calculated based Calculated LPOM 3.39 - 12.93 on 2006 measured 2.02 - 10.13 based on 2006 mg/ BOD5 data mg/L measured BODS data Calculated based Calculated BPOM 0.24 - 0.92 on 2006 measured 0.14 - 0.72 based on 2006 mg/L BOD5 data mg/L measured BODS data 4.59 - 7.75 Monthly averages 3.60 - 10.25 Average DO mg/L from 2002 daily m g/ monthly 2006 DMR data measured data T Assumes 1 r is equal to rU4 (no org P) ** Assumes no organic nitrogen in TN value 19 Utilities / City of Mount M M M CHARLOTTE. Water Quality Modeling Report Table 5.3 Inputs Values Used for Proposed Regional WWTP Effluent (Future Conditions) Normal Operating Conditions Permit Limits Constituent FN17 I FN25 I Basis of Value FP17 FP25 Basis of Value Calculated 10.5 - 15.40 - based on 2007 Flow 34.19 50.13 McDowell data - 17 mgd 25 mgd Plant capacity mgd mgd consistent with permit limits McDowell McDowell Temperature p 15.2 - °C 15.2 - °C WWTP average daily 15.2 - 15.2 - WWTP average daily 27.6 27.6 2007 measured 27.6 ,C 27.6 ,C 2007 measured data data Calculated 0.54 - 0.37 - based on 2007 Total Phosphorus 10.8 7.40 McDowell data - 1.47 mg/L 1.0 mg/L phosphorous mg/L mg/L consistent with permit limit ermit limits Calculated 3.3% of the 0.18 - 0.18 - based on 2007 TN permit Ammonia 4.14 4.14 McDowell 0.30 0.20 limit (Based on mg/L mg/L data - mg/L mg/L McDowell consistent with WWTP 2007 permit limits effluent data Calculated 82.8% of the 1.28 - 0.88 - based on 2007 TN permit Nitrate 15.36 10.56 McDowell 7.31 4.97 limit (Based on mg/L mg/L data - mg/L mg/L McDowell consistent with WWTP 2007 permit limits effluent data Calculated 1.28 - 0.89 - based on 2007 Calculated LDOM 5.87 3.96 McDowell 2.29 1.56 based on mg/L mg/L data - mg/L mg/L BOD5 permit consistent with limit permit limits Calculated 0.32 - 0.22 - based on 2007 Calculated RDOM 1.47 0.99 McDowell 0.57 0.39 based on mg/L mg/L data - mg/L mg/L BOD5 permit consistent with limit permit limits 4.47 - 3.01 - Calculated Calculated LPOM 20.56 13.84 based on 2007 8.03 5.47 based on mg/L mg/L McDowell mg/L mg/L BOD5 permit data - limit 20 Neck/enburg Utilities / City of Mount Water Quality Modeling Report Normal O eratin Conditions Permit Limits Constituent FN17 FN25 Basis of Value FP17 FP25 Basis of Value consistent with permit limits Calculated 0.32 - 0.22 - based on 2007 Calculated RPOM 1.47 0.99 McDowell 0.57 0.39 based on mg/L mg/L data - mgiL mgiL BOD5 permit consistent with limit ermit limits McDowell McDowell DO 7.2-10.1 7.2-10.1 WWTP average daily 7.2-10.1 7.2-10.1 WWTP average daily mg/L mg/L 2007 measured mg/L to 2007 measured data data & Model Outputs For each scenario simulated, the model outputs include estimated concentrations of each parameter at one meter depth intervals in each segment and for each day of the year. To _ summarize the model results and provide a method to compare scenarios, three types of plots were produced to graphically present the results of the modeling. These included vertical _ profiles, time series plots and contour plots of DO, TP, TN, and chlorophyll a. Vertical profiles illustrate how these parameters change with depth in the water column. The vertical profiles are shown at selected locations and for three days during the year to highlight seasonal and spatial differences. Time series plots were produced to show how concentrations at one location changed throughout the year. Time series plots were produced at two or three elevations and for several segments. Contour plots show a longitudinal and vertical slice through the lake. These were produced for three days for each scenario and for the four parameters. The graphical outputs included in this report are listed in Table 6-1. Selected graphs are included in Section 7. However, all of the outputs were presented in electronic format to DWQ staff in the Modeling and TMDL Unit. 21 Charlotte -Mecklenburg Utilities / City of Mount Holly a/ CFIARI.O'ITE. auau��cseixo Water Quality Modeling Report Table 6.1 Lake Wylie Model Graphical Outputs Vertical Profiles Segment Locations Parameters Dates (Julian day) 3 DS WWTP DO, TP, TN, Chia 141, 228, 269 4 DO, TP, TN, Chia 141, 228, 269 5 DO, TP, TN, Chia 141, 228, 269 6 Belmont DO, TP, TN, Chia 141, 228, 269 7 DO, TP, TN, Chia 141, 228, 269 8 DO, TP, TN, Chia 141, 228, 269 9 DO, TP, TN, Chia 141, 228, 269 _ 10 DO, TP, TN, Chia 141, 228, 269 11 US S. Fork DO, TP, TN, Chia 141, 228, 269 13 DS S. Fork DO, TP, TN, Chia 141, 228, 269 30 Dam DO, TP, TN, Chia 141, 228, 269 Time Series Segment Locations Parameters Depths Elevation 3 DS WWTP DO, TP, TN, Chia 2,6 170,166 4 DO, TP, TN, Chia 2,6 170,166 5 DO, TP, TN, Chia 2,6 170,166 6 Belmont DO, TP, TN, Chia 2,6 170,166 7 DO, TP, TN, Chia 2.6 170,166 8 DO, TP, TN, Chia 2,6 170,166 9 DO, TP, TN, Chia 2,6 170,166 10 DO, TP, TN, Chia 2,7 170,165 11 US S. Fork DO, TP, TN, Chia 2,8 170,164 13 DS S. Fork DO, TP, TN, Chia 2,8 170,164 30 Dam DO, TP, TN, Chia 2, 8, 14 170, 164, 158 Contour Plots Parameters Dates DO, TP, TN, Chia 141, 228, 269 Groups - for vertical and time series plots Normal Operating Conditions EM2002, FN172002, FN252002, FN252002NPS EM1998, FN251998, N251998NPS Permit Conditions EPMHB2002, FP172002, FP252002, FP252002Be1 .. EPMHB1998, FP251998, FP251998Bel Segment 3 includes the discharge for the Mt Holly/Long Creek WWTP Segment 6 is where Belmont WWTF is located Segment 11 is upstream of the South Fork Branch Segment 13 is downstream of the South Fork Branch Segment 30 is in the downstream portion of Lake Wylie 22 w�a Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report C,HARLOTM 7. Water Quality Impacts The fourteen scenarios simulated represent variations in effluent flow and quality as well as river conditions. These fourteen scenarios were arranged into four groups for comparison, including normal operating conditions at low and average river flows and permit limit conditions at low and average river flows. Results of the CE-QUAL-W2 model were extracted from the output files and plotted using Excel. Over one thousand plots were generated as listed in Section 6. Selected plots (Figures 3 through 50) are included at the end of this report for discussion. The discussion below focuses on the permit limits condition because that is considered by NC DWQ to be the critical condition. Vertical profiles of DO, TP, TN and chlorophyll a are presented at 2 to 4 important locations and for two days (August 16, 2002 and August 16, 1998). Time series plots are also presented at these same 2 to 4 important locations at one elevation. Time series for DO are presented at an elevation of 166 or 164 because this elevation is close to the thermocline and represents the location where low DO concentrations are typically experienced. Time series plots for TP, TN and chlorophyll a are presented at an elevation of 170 which is close to the surface. No contour plots are presented in this report but are included in the electronic files transmitted with the report. 7.1 Dissolved Oxygen Dissolved oxygen concentrations are affected by many chemical and biological processes in a reservoir. When evaluating wastewater discharges, the input of BOD is the primary factor affecting the DO concentration. As seen from the plots during a low flow year, DO concentrations under the future scenario of a new WWTP would not vary greatly from existing conditions (Figures 3 through 6 and 15 through 18). In the segment downstream of the Belmont discharge, DO concentrations would be slightly higher in the upper portion of the water column (Figure 4). In the area downstream of the junction with the South Fork Branch, the different scenarios exhibit virtually no differences in DO concentrations throughout the water column (Figure 5). In the lower portion of the lake, concentrations would be slightly reduced in the upper portions of the water column in the future scenarios (Figure 6). 23 0 ��r w Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOTTE_ ounm� saso The DO patterns for an average flow year are somewhat different. Downstream of the Belmont discharge, low DO concentrations would likely occur about 0.5 - 1 meter higher in the water column (Figure 28). Minor differences in DO concentrations are predicted to occur in the area downstream of the South Fork Branch (Figure 29 and 41) while virtually no differences are expected in the lower section of the lake (Figure 30 and 42). 7.2 Total Phosphorus Model results show that the predicted TP concentrations would be higher in the upper reaches of the lake under the future condition with a new WWTP discharge (Figures 7, 31, 19, and 43). The greatest differences between existing and future conditions would be observed in the segment downstream of the regional Long Creek WWTP during a low flow year (Figure 7). There were virtually no differences between existing and future conditions in the lower portion of the lake (Figures 8 and 22). Differences were further reduced during the average flow year (Figure 32). Total phosphorus concentrations in the South Carolina portion of the lake would be below the instream water quality criteria of 0.06 mg/L during the average flow year (Figures 45 and 46). During a low flow year, the model predicts that the criteria would be exceeded for a few days early in the year (Figure 21). Values exceeding the criteria would occur under all modeled scenarios for 2002 flows including the existing permit limits for the existing WWTPs. 7.3 Total Nitrogen Patterns of TN concentrations are similar to those predicted for phosphorus. Predicted TN concentrations would be higher in the upper reaches of the lake under the future conditions scenario (Figure 9, 23, 33, and 47). The difference between existing and future conditions would be greatest in the segment downstream of the regional Long Creek WWTP during a low flow year (Figure 9). There were virtually no differences in TN concentrations between existing and future conditions in the lower portion of the lake (Figure 10 and 24). Differences were further reduced during the average flow year (Figure 34 and 48). Total nitrogen concentrations in the South Carolina portion of the lake would be below the instream water quality criteria of 1.5 mg/L for all conditions modeled. �' 24 Charlotte -Mecklenburg Utilities / City of Mount Holly U Water Quality Modeling Report r R� CI11A}1tiorm. 7.4 Chlorophyll a Chlorophyll a concentrations were very low in the upper portion of the reservoir and generally increase in a downstream direction under both existing and future conditions scenarios (Figures 11 through 14). The differences between the existing and future conditions are greatest during a low flow year and in the segments at and immediately downstream of the Belmont WWTP. As shown in Figure 12, in Segment 7 (downstream of the Belmont WWTP) chlorophyll a concentrations would be about 3 µg/L higher due to the increased load from the Regional Long Creek plant and about 2.5 µg/L higher due to the increased load from the Belmont WWTP. Only minor differences between the scenarios were apparent downstream of the junction with the South Fork Branch (Figure 13 and 14). Virtually no differences in chlorophyll a concentrations were seen between scenarios run using average flow conditions (Figures 35 through 38). In all cases the predicted chlorophyll a concentrations were well below the water quality criteria of 40 µg/L. 7.5 Flow and Nutrient Contributions The contributions of flow and nutrient loads were calculated for the existing and future scenarios for flow conditions represented by 1998 and 2002. The major contributors included: • Mountain Island Lake • South Fork Branch, • Crowder's Creek, • Dutchman's Creek and Long Creek (which are combined in a single input in the model), • Mount Holly WWTP (existing) or Regional Long Creek WWTP (future), • Belmont WWTP • Combination of all other inflows, including distributed flows. For purposes of this analysis inflows from the power plants were not included in the load calculations. The specific scenarios compared were the existing conditions assuming that WWTPs were operating at their permit limits (EPMHB2002 and EPMHB1998) and the 25 see WON ., Ost nrs m so 04 on M h Charlotte -Mecklenburg Utilities/ City of Mount Holly tiS+�u♦�T (y �p Water Quality Modeling Report r}� CHARLOTTE. 5 "ieiu"Y uramrs future scenario assuming a new Regional Long Creek WWTP with a discharge of 25 mgd (FP252002Be1 and FP251998BEL). It was assumed that permit limits for TP and TN for the new regional facility were 1 mg/L and 6 mg/L, respectively. hi the future scenario, the Belmont plant was assumed to be operating at the current permit limits. The contributions of flow from the major inputs to Lake Wylie are shown in Figure 51. Even in a dry year, the combined flows from Mountain Island Lake and the South Fork Branch were estimated to contribute over 80 percent of the flows to the lake. Contributions of TP and TN are shown in Figures 52 and 53, respectively. Even though Mountain Island Lake was estimated to contribute more than half of the flow it was estimated that this source would contribute less than 15 percent of the TP and about 20 percent of the TN. The largest source of nutrients for both the existing and future cases was estimated to be the South Fork Branch. The Belmont WWTP was estimated to contribute about 26 percent of the TP loads under existing permit conditions; about double the load contributed by the Mount Holly WWTP. Under the future scenario, the new Regional Long Creek WWTP could contribute a slightly higher load than the Belmont WWTP although the flow would be five times greater. Similar patterns were shown in the comparison of TN load contributions. Flow Contributions - 2002 • Mt. Island ■ S. Fork D Crovder's D Dutchman ■ My WHY ■ Belmont ■ Others Flow Contributions -25 mgd - 2002 ■ Mt. Island ■ S. Fork ❑ Crovdees D Dutchman ■ Long CK WNTP ■ BeIrnont ■ Others Figure 51 Comparison of Flow Contributions for Existing and Future Scenarios OR 26 nn fee NeR M AeR eek wAr�. Charlotte -Mecklenburg Utilities / City of Mount Holly IS CHARIATI E Water Quality Modeling Report TP Contributions - Existing Limits .2002 ■ Mi. Island Is S. Fork ❑ Crowder's D Dutchman ■ My Fblly ■ Belmont 4R■ Others TP Contributions .25 mgd .2002 ■ Mt. Island ■ S, Fork ❑ Crovder's D Dutchman. ■ Long CK WATP ■ Belnnnt ■ Others Figure 52 Comparison of TP Contributions for Existing and Future Scenarios TN Contributions - Existing Limits - 2002 ■ Mt. Island ■ S. Fork ❑ Croxdees ❑ Dutchman ■ My Fblly ■ Belmont ■ Others TN Contributions .25 mgd -2002 ■ Mt. Island ■ S. Fork 0 Croxdees D Dutchman ■ Long CK WWTP ■ Belmont ■ Others Figure 53 Comparison of TN Contributions for Existing and Future Scenarios 8. Findings and Conclusions Water quality modeling of Lake Wylie was performed to assist in the evaluation of water quality impacts from the proposed facility and to support the development of speculative NPDES limits by NC DWQ for the plant discharge into Lake Wylie. The previously calibrated Lake Wylie model was used to evaluate the effects of increased wastewater discharges to the upper section of Lake Wylie. Many scenarios were simulated to evaluate existing and potential future conditions. For both existing and future conditions both normal operating conditions and permit conditions were simulated. Increases in future nonpoint source (NPS) loads were also simulated. Wastewater treatment plant point sources to Lake Wylie included the Mount Holly WWTP and the Belmont WWTP. Nel 27 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOTTE. The water quality parameters that were simulated in the model included phosphorus, ammonia, nitrate, BOD, and DO. For normal operating conditions, the concentrations used represented the highest loads that could be discharged without exceeding any permit limits. Water quality concentrations for the proposed regional WWTP under permit limit conditions were calculated based on assumed permit limits for TN, TP, and BODS based on plant capacity. The fourteen scenarios simulated represent variations in effluent flow and quality as well as river conditions. Model results indicated the following conditions would occur: ■ Dissolved oxygen concentrations under the future scenario of a new WWTP would not vary greatly from existing conditions. In the area downstream of the junction with the South Fork Branch, the different scenarios exhibited virtually no differences in DO concentrations throughout the water column. In the lower section of the lake, concentrations would be slightly reduced in the upper portions of the water column in the future scenarios. ■ During an average flow year, low DO concentrations would likely occur about 0.5 - 1 meter higher in the water column downstream of the Belmont WWTP. Only minor differences in DO concentrations were predicted to occur in the area downstream of the South Fork Branch while virtually no differences were expected in the lower section of the lake. ■ Predicted TP concentrations would be higher in the upper reaches of the lake under the future condition with a new WWTP discharge. ■ There were virtually no differences in TP concentrations between existing and future conditions in the lower section of the lake. Differences were further reduced during the average flow year. ■ Predicted TP concentrations in the South Carolina portion of the lake would be below the instream water quality criteria of 0.06 mg/L throughout the average flow year. '■ 28 ^ Charlotte -Mecklenburg Utilities / City of Mount Holly (r;Water Quality Modeling Report CHARLO7�IB However, during a dry flow year, under all existing and future conditions, it was estimated that the TP criteria would be exceeded for a few days early in the year. ■ Predicted TN concentrations would be higher in the upper reaches of the lake under the future conditions scenario. There were virtually no differences in TN concentrations between existing and future conditions in the lower section of the lake. Differences were further reduced during the average flow year. ■ Total nitrogen concentrations in the South Carolina portion of the lake would be below the instream water quality criteria of 1.5 mg/L for all conditions modeled. Chlorophyll a concentrations were very low in the upper section of the reservoir and generally increase in a downstream direction under both existing and future conditions scenarios. ■ Only minor differences between the scenarios were apparent downstream of the junction with the South Fork Branch. Virtually no differences in chlorophyll a concentrations were seen between scenarios run using average flow conditions. ■ In all cases the predicted chlorophyll a concentrations were well below the water quality criteria of 40 µg/L. ■ The largest source of nutrients for both the existing and future cases was estimated to be the South Fork Branch. ■ Under the future scenario, the new Regional Long Creek WWTP could contribute a slightly higher load than the Belmont WWTP although the flow would be five times greater. Similar patterns were shown in the comparison of TN load contributions. -■ Overall, the modeling shows that the effects of the new regional Long Creek WWTP would have minor impacts on water quality in Lake Wylie. Effects would be mostly confined to the upper reaches of the lake. Water quality criteria for TN and chlorophyll a would be met under all conditions. Criteria for TP could be exceeded for a few days during a low flow year under both existing and future conditions. 29 Charlotte -Mecklenburg Utilities / City of Mount Holly Q I�Lp E Water Quality Modeling Report �J( 9. References Beaulac, M. N. and K. H. Reckhow. 1982. "An examination of land use -nutrient export relationships". Water Resources Bulletin, 18(6), 1013-1024. Black & Veatch. 1990. "Water Quality and Quantity Studies to Support Randleman Lake Environmental Impact Statement". Prepared for Piedmont Triad Regional Water Authority. _ Cole, T. and S. Wells. 2002. "CE-QUAL-W2: A Two -Dimensional, Laterally Averaged, Hydrodynamic and Water Quality Model, Version 3.1 — User Manual' Instruction Report EL-2002-1; U.S. Army Engineering and research Development Center, Vicksburg, MS. NC Department of Environment and Natural Resources, Division of Water Quality (DWQ), _ 1997. "White Oak River Basinwide Water Quality Plan". Raleigh, NC. Reckhow, K. H., Beaulac, M. N. and J. T. Simpson. (1980). "Modeling phosphorus loading and lake response under uncertainty: A manual and compilation of export coefficients". U.S. EPA Report No. EPA-440/5-80-011, Office of Water Regulations, Criteria an Standards Division, U.S. Environmental Protection Agency, Washington, _ DC, Ruane, R.J. and G.E. Hauser. 2006. "Background document for Catawba-Wateree Water Quality Models". New License Application to FERC for the Catawba- Wateree Project No. 2232, Duke Energy, August. Sawyer, A. and R. J. Ruane. 2006. "Calibration of the CE-QUAL-W2 Model for Lake Wylie". Prepared for Duke Energy. July. US Environmental Protection Agency. 1991. "Technical Support Document for Water Quality -based Toxics Control'. EPA/505/2-90-001. US EPA Office of Water, Washington, DC. 30 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOTTE. cxum�aa¢namo Selected Figures for Permit Conditions, 2002 Flow Scenarios: EPMHB2002 — permit limits, existing plants FP172002 —future permit limits at 17 mgd FP252002 — future permit limits at 25 mgd, with Belmont at existing loads FP252002Bel — future permit limits at 25 mgd with Belmont at increased loads Vertical Plots — August 16, 2002 DO and Chlorophyll a at Segments 3, 7, 13 and 30 TP and TN at Segments 3 and 30 Time Series Plots — DO at Elevation 166 or 164 (near thermocline) at Segments 3, 7, 13 and 30 TP at Elevation 170 (near surface) at Segments 3, 7, 13, and 30 TN at Elevation 170 (near surface) at Segments 3 and 30 Chlorophyll a at Elevation 170 (near surface) at Segments 3 and 30 Segments 3 — downstream of Mount Holly/Long Creek Regional WWTP 7 — segment downstream of Belmont WWTP 13 — segment downstream of junction with South Fork Branch 30 — segment in lower portion of the lake near the dam 31 Charlotte -Mecklenburg Utilities / City of Mount Holly �S/+ Krn CIIARI.O"1'I'E. Water Quality Modeling Report s �. CMMIDRFYFCILLFI@Ilpt Vertical Profiles: Dissolved Oxygen Location: 3 Day: August 16 FIgUYC 3 120 170 E 165 —EPM WW2 —FP172002 —M520U —FP252002BM 155 150 0.00 1.50 3.00 4.50 6.00 7.50 9.00 10.60 12.00 13.50 15.00 Dissolved Oxygen (mg/1) Vertical Profiles: Dissolved Oxygen Location: 7 Day: August 16 Figure 4 175 — — 170 E 165 c O N 160 W 155 150 0.00 1.50 3.00 4.50 6.00 7.50 9.00 10.50 1200 13.50 15A0 Dissolved Oxygen (mg/1) -EPMHB2002 -FP172002 -FP252002 -FP252002BII 32 lam Charlotte -Mecklenburg Utilities / City of Mount CFIAI{LOTPE. Water Quality Modeling Report C "`-M£XBY0.4 V1M1E8 Vertical Profiles: Dissolved Oxygen Location: DS S. Fork Day: August 16 175 170 E 165 C O N W 160 Figure 5 —EPMH82002 —FP172002 —FP252002 —FP252002Be 155 150 0.00 1.50 3.00 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 Dissolved Oxygen (mg/l) Vertical Profiles: Dissolved Oxygen Location: Dam Day: August 16 Figure 6 175 170 E 165 155 150 —WMHB2002 —FP172002 —FP252002 —FP2520028el 0,00 1.50 100 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 Dissolved Oxygen (mg/1) 33 Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report } (' CHARLOTFE. Gv' c«unmle.uFa�xmn� IRMIE9 Vertical Profiles: Total Phosphorus Location: 3 Day: August 16 Figure 7 175 170 E 165 —EPMHB2002 —FP172002 —FP252002 —FP252002Be1 155 150 0.00 003 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30 Total Phosphorus (mg/l) Vertical Profiles: Total Phosphorus Location: Dam Day: August 16 Figure 8 175 1,0 E 165 155 150 —EPWMW2 —FP172002 —FP252002 —FP2520026e1 0.00 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30 Total Phosphorus (mg/1) 34 (h Charlotte -Mecklenburg Utilities / City of Mount Holly CFIARIA"ITE_ Water Quality Modeling Report rJ 1e7e �^ unnrtn Vertical Profiles: Total Nitrogen Location: 3 Day: August 16 Figure 9 170 E 165 C O N W 160 155 150 —EPMHB2002 —FP172002 —FP252002 —FP252002Be1 0.00 0.20 0.40 0,60 0.80 1.00 1.20 1.40 1.60 1.80 2c0 Total Nitrogen (mg/1) Vertical Profiles: Total Nitrogen Figure 10 Location: Dam Day: August 16 175_- 170 E 165 c Q 160 W 155 150 0.00 0.20 0.40 0.60 0.80 100 1.20 1.40 1.60 1.80 2.00 Total Nitrogen (mg/1) PMH B2002 —FP172002 P252002 —FP25200280 35 c(Th CRAi . M. Vertical Profiles: Chlorophyll a Location: 3 Day: August 16 I'D 170 E 165 155 150 Figure 11 —EPMHB2002 —FPn2002 —FP252002 —FP252002M 0.00 4100 8.00 12.00 16,00 20.00 24.00 28.00 32.00 36.00 40.00 Chlorophyll a (ugll) Vertical Profiles: Chlorophyll a Figure 12 Location: 7 Day: August16 175 170 E 165 C O N W 160 155 150 —EPMHB2002 —FP1>2002 —FP252002 —FPaW02Be1 0.00 4.00 8.W 12.00 16.00 2000 24.00 28.00 32.00 36,00 40.00 Chlorophyll a (ugll) NEO h Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARIA'ITE. UI.PFA Vertical Profiles: Chlorophyll a Location: DS S. Fork Day: August 16 17s 170 JII E 165 Figure 13 —EPMH82002 —FP172002 —FP252002 —FP252002Be1 155 150 0.00 4.00 8.00 12.00 16.00 2000 24.00 28.00 3200 36.00 40.00 Chlorophyll a (ug/1) Vertical Profiles: Chlorophyll a Fi ure 14 Location: Dam Day: August 16 g 175 170 1� E 1ss 155 150 —EPMHB2002 —FP172002 —FP252002 —FP2520026el 0.00 4.00 8.00 12.00 16.00 20M 24.00 28.00 32.00 36.00 40.00 Chlorophyll a (ug/1) 37 h Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARIA'I'I'E. CMIWDMME KLCWK UTu U Time Series Plot Location: DS WWTP Figure 15 Dissolved Oxygen Elevation: 166 15.0 -7- 12.0 9.0 rn a 6.0 3.0 00 — EPMHB2002 — FP172002 —FP252002 —FP25252002Bel 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: 7 Figure 16 Dissolved Oxygen Elevation: 166 15.0 12.0 c 9.0 rn 0 6.0 —EPMHB2002 — FP172002 —FP252002 — FP25252002Bel 3.0 0.0 0 50 100 150 200 250 300 350 Julian Day 9M h Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report r Rrr� o CHARLOTTE. uwaarrta¢cwexwrro NL. UfUIR9 Time Series Plot Location: DS S. Fork FIgUCC 17 Dissolved Oxygen Elevation: 164 15.0 12.0 c 9.0 rn E O 0 6.0 3.0 0.0 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: Dam Dissolved Oxygen Elevation: 164 15.0 12.0 c 9.0 rn E C3 6.0 3.0 0.0 E: 0 50 100 150 200 250 300 350 Julian Day —EPMHB2002 — FP172002 —FP252002 — FP25252002Bel Figure 18 — EPMHB2002 FP172002 — FP252002 —FP25252002Bel al CHARIA'IT8_ IIINE9 warer quarry moaeun Time Series Plot Location: DS WWTP Total Phosphorus Elevation: 170 0.08 V Illy 0.00 0 50 100 150 200 250 300 Julian Day Time Series Plot Location: 7 Total Phosphorus Elevation: 170 0.30 0.24 0.18 rn a 0,12 0.06 OM 0 50 100 150 200 250 300 350 Julian Day Figure 19 —EPMHB2002 —FP172002 —FP252002 —FP252520020el Figure 20 — EPMHB2002 — FPi 72002 — FP252002 — FP25252002Bel M Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOM. cxumltErcmFxe�wo Time Series Plot Location: DS S.Fork Total Phosphorus Elevation: 170 0.30 0.24 0.18 rn IL 0.12 o.e5 0.00 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: Dam Total Phosphorus Elevation: 170 0.30 0.24 0.08 0.00 0 50 100 150 200 250 300 350 Julian Day Figure 21 —EPMHB2002 — FP172002 — FP252002 —FP25252002Bel Figure 22 —EPMHB2002 — FP172002 — FP252002 — FP252520028el 41 Charlotte -Mecklenburg Utilities / City of Mount CHARI.O'ITE. Water Quality Modeling Report Time Series Plot Location: DS WWTP Total Nitrogen Elevation: 170 2.0 1.6 0.4 0.0 Figure 23 —EPMHB2002 —FP172002 —FP252002 —FP25252002Bel 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: Dam Figure 24 Total Nitrogen Elevation: 170 2.0 - - 16 F -- 0.4 0.0 0 50 100 150 200 250 300 350 Julian Day EPMHB2002 — FP172002 — FP252002 —FP25252002Bel 42 Charlotte -Mecklenburg Utilities / City of Mount CI WiLOTI'E_ Water Quality Modeling Report CIURIAiIE NECgE.M YRIf¢J Time Series Plot Location: DS WWTP Chlorophyll a Elevation: 170 40.0 - - — F. 32.0 24.0 = U 16.0 8.0 0.0 40.0 320 240 m 2 U 1&0 8.0 00 0 50 100 150 200 250 300 Julian Day Time Series Plot Location: Dam Chlorophyll a Elevation: 170 0 50 100 150 200 250 300 3 Julian Day Figure 25 —EPMHB2002 — FP172002 —FP252002 —FP25252002Bel Figure 26 —EPMHB2002 — FP172002 —FP252002 FP25252002Bel MCharlotte -Mecklenburg Utilities / City of Mount Holly la) Water Quality Modeling ReportCHARLOTTE. Selected Figures for Permit Limits Conditions, 1998 Flow Scenarios: EPMHB1998 — permit limits, existing plants FP251998 — future permit limits at 25 mgd, with Belmont at existing loads FP251998 — future permit limits at 25 mgd, with Belmont at increased loads Vertical Plots — August 16, 1998 DO and Chlorophyll a at Segments 3, 7, 13 and 30 TP and TN at Segments 3 and 30 Time Series Plots — DO at Elevation 166 or 164 (near thermocline) at Segments 3, 7, 13 and 30 TP at Elevation 170 (near surface) at Segments 3, 7, 13, and 30 — TP at Elevation 170 (near surface) at Segments 3 and 30 Chlorophyll a at Elevation 170 (near surface) at Segments 3 and 30 Segments — 3 — downstream of Mount Holly/Long Creek Regional WWTP 7 — segment downstream of Belmont WWTP 13 — segment downstream of junction with South Fork Branch 30 — segment in lower portion of the lake near the dam 44 Charlotte -Mecklenburg Utilities / City of Mount Holly CfIARIA'I'PE. Water Quality Modeling Report } CNBIAf1EA�CIBFMBBBO V• 11INE9 Vertical Profiles: Dissolved Oxygen Location: 3 Day: August 16 Figure 27 175 — — — 170 E 165 C O 7 6 -25H 1B08 FP151B88 FPISiBBGBBI N W 160 155 150 0.00 1.50 3.00 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 Dissolved Oxygen (mg/1) Vertical Profiles: Dissolved Oxygen Figure 28 Location: 7 Day: August 16 175 170 ✓= 165 C O N 160 W 155 150 -FN519H FP151BB0 fP1510988eI 0.00 1.50 3.00 450 6.00 7.50 9.00 10.50 12.W 1350 15.00 Dissolved Oxygen (mgll) 45 Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report CHARLOTTE.. 99N0 Vertical Profiles: Dissolved Oxygen Location: DS S. Fork Day: August 16 Figure 29 175 — 170 E 165 E wei 90 —FP251B95 —FP25199:Bel 155 150 0.00 1,50 3.00 4.50 6.00 7.50 9.00 10.50 12.00 13M 15.00 Dissolved Oxygen (mg/l) Vertical Profiles: Dissolved Oxygen Figure 30 Location: Dam Day: August 16 175 170 E 165 C 0 W 160 155 150 EPWB1998 —FP251998 —FP251998Be1 0.00 1.50 3.00 4.50 6.00 7.50 9.00 10.50 12.00 13.50 15.00 Dissolved Oxygen (mg/1) 46 Charlotte -Mecklenburg Utilities / City of Mount Holly Water Quality Modeling Report CFWRIA'ITE. �. ausnn5lo:nBBeum VIMlFB Vertical Profiles: Total Phosphorus Location: 3 Day: August 16 Figure 31 175 — — — 170 E 165 C O W 160 W 155 150 B MB18B8 —FP251008 —FP251BBBBel 0.00 003 006 0,09 0,12 0.15 0.18 0.21 0.24 0,27 0,30 Total Phosphorus (mg/1) Vertical Profiles: Total Phosphorus FiguY¢ 32 Location: Dam Day: August 16 175 170 E 165 155 150 E MHBIBBB —FP251BB8 —FP251BBBBe1 0.00 003 006 0.09 0.12 0.15 0.18 0,21 0.24 0.27 0.30 Total Phosphorus (mgll) 47 cmi Charlotte -Mecklenburg Utilities / City of Mount (SIARiA7TE. Water Quality Modeling Report PURDTIFY�ILLB,.M, 1lnrtes Vertical Profiles: Total Nitrogen Location: 3 Day: August 16 175 — - 170 165 C O N W 160 155 150 Figure 33 -FP25 on 0 K290 FP251900Be1 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 160 1.80 2.00 Total Nitrogen (mg/1) Vertical Profiles: Total Nitrogen Figure 34 Location: Dam Day: August 16 175 170 E 166 C O W 160 155 150 —EPMHB1080 —FP251888 —FP2518988el 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 L80 2.00 Total Nitrogen (mg/1) M Charlotte -Mecklenburg Utilities / City of Mount Holly K CHARI.O'ITEWater Quality Modeling Report r' . vnm[a Vertical Profiles: Chlorophyll a Location: 3 Day: August 16 Flgur¢ 35 175 170 E 165 E "819B5 —FP351998 —FP351B888e1 155 150 0.00 4.00 8.00 1200 16.00 20.00 24.00 28.00 32.00 36.00 40.00 Chlorophyll a (ugll) Vertical Profiles: Chlorophyll a Location: 7 Day: August16 FigurC 36 175 170 E 165 155 150 -PMM61BB8 F P 51BB8 FP351BBB9N 0.00 4.00 8.00 12,00 16.00 20.00 24.00 28.00 32.00 MOO 40.00 Chlorophyll a (ugll) 49 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOTTE. YfllF9 Vertical Profiles: Chlorophyll a Location: DS S. Fork Day: August 16 175 - - - - -- - -- 170 E 165 C O W ifiU Figure 37 EPMH815B8 -FM1698 -FP351BB86N 155 150 0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.W Chlorophyll a (ug/1) Vertical Profiles: Chlorophyll a FiguC¢ 38 Location: Dam Day: August 16 175 170 , E 165 a O Wd 160 155 150 EPMMBIBBB -FK] :98 -FP]5188BBBI 0.00 4.00 8.00 12.00 16.00 20.00 24.00 2&00 3200 36.00 40.00 Chlorophyll a (ug/I) 50 Charlotte -Mecklenburg Utilities / City of Mount Water Quality Modeling Report CHARLOrrE. Time Series Plot Location: DS WWTP Dissolved Oxygen Elevation: 166 15.0 12.0 Figure 39 — EPMHB1998 —FP251998 —FP251998Bel 3.0 0.0 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: 7 Figure 40 Dissolved Oxygen Elevation: 166 15.0 12.0 9.0 rn E O a 6.0 3.0 0.0 0 50 100 150 200 250 300 Julian Day —EPMHB1998 — FP251998 —FP251998Bel 51 Charlotte -Mecklenburg Utilities / City of Mount Holly h Water Quality Modeling Report CHAR OM. Time Series Plot Location: DS S. Fork Figure 41 Dissolved Oxygen Elevation: 164 15.0 12.0 9.0 O O 6.0 3.0 0.0 0 50 100 150 200 250 300 Julian Day Time Series Plot Location: Dam Dissolved Oxygen Elevation: 164 150 12.0 rn c 9.0 0 6.0 3.0 0.0 0 50 100 150 200 250 300 Julian Day —EPMHB1998 —FP251998 —FP251998Be1 Figure 42 —EPMHB1998 —FP251998 —FP2519988el 52 CHARLOTTE. uM� V.JV 0.24 0.06 0,00 Neck/enburg Utilities / City of Mount Water Quality Modeling Report Time Series Plot Location: DS WWTP Total Phosphorus Elevation: 170 —EPMHB1998 —FP251998 —FP251998Bel 0 50 100 150 200 250 300 350 Julian Day Time Series Plot Location: 7 Figure 44 Total Phosphorus Elevation: 170 0.30 0.24 0.18 m a �— 0.12 0.06 0.00 0 50 100 150 200 250 300 Julian Day — EPMHB1998 — FP251998 — FP251998Bel 53 qn Charlotte -Mecklenburg Utilities / City of Mount CFIARI.O'I'I'EWater Quality Modeling Report . Time Series Plot Location: DS S. Fork Total Phosphorus Elevation: 170 0.30 0.24 — 0.18 rn a. 0.12 0.06 0.00 0 50 100 150 200 250 300 Julian Day Time Series Plot Location: Dam Total Phosphorus Elevation: 170 0.30 0.24 0.18 rn a F- 0.12 0.0e 0.00 0 50 100 150 200 250 300 Julian Day Figure 45 —EPMHB1998 —FP251998 —FP251998BeI Figure 46 —EPMHB1998 —FP251998 —FP2519988el 54 Charlotte -Mecklenburg Utilities / City of Mount CHARI.O'I'I'E. Water Quality Modeling Report URR[8 Time Series Plot Location: DS WWTP Total Nitrogen Elevation: 170 20 1s� 1.2 rn 2 F- 0.8 o.a -.._...... �, . .. 0.0 0 50 100 150 200 250 300 350 Julian Day Figure 47 —EPMHB1998 — FP251998 — FP251998Bel Time Series Plot Location: Dam Figure 48 Total Nitrogen Elevation: 170 0a 0.0 0 50 100 150 200 250 300 Julian Day EPMH61998 — FP251998 — FP251998Bel 55 Charlotte -Mecklenburg Utilities / City of Mount Holly �U r Krn Water Quality Modeling Report CHARLOrFE. , na Time Series Plot Location: DS WWTP Figure 49 Chlorophyll a Elevation: 170 40 32.0 32.0 8.0 0.0 0 50 100 150 200 250 300 , Julian Day Time Series Plot Location: Dam Chlorophyll a Elevation: 170 40.0 32.0 24.0 U 16.0 8.0 0.0 0 50 100 150 200 250 300 Julian Day —EPMHB1998 —FP251998 —FP251998Bel Figure 50 —EPMHB1998 —FP251998 —FP251998Bel 56