Poplar River Turbidity Total Maximum Daily Load Evaluation of Existing Data

Transcription

1 Poplar River Turbidity Total Maximum Daily Load Evaluation of Existing Data Task Order No Prepared for: U.S. Environmental Protection Agency Region 5 77 West Jackson Boulevard Chicago, IL Prepared by: RTI International 3040 Cornwallis Road Research Triangle Park, NC USEPA Contract Number 68-C August 16, 2007

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3 Poplar River Turbidity TMDL Evaluation of Existing Data Page i of 63 Table of Contents List of Tables... ii List of Figures...iii List of Acronyms...v 1 Executive Summary Introduction Assessment of Impairment Description of Watershed Characteristics Data and Information Sources Evaluation of Existing Data Streamflow Assessment Snowmelt and Snow Pack Water Quality Monitoring US Forest Service Monitoring ( ) LakeSuperiorStream Project Sonde Data (2006) MPCA Ambient Monitoring Program ( ) North Shore Load Project ( ) Turbidity-Total Suspended Solids Relationship Turbidity Methods Sediment Loading Analysis Upstream (S ) Downstream (S ) Load Duration Curve Total Suspended Solids Loading from Point Sources Discussion and Conclusions References Appendices List of Appendices Appendix A... A-1 Appendix B... B-1

4 Poplar River Turbidity TMDL Evaluation of Existing Data Page ii of 63 List of Tables Table 1 Poplar River impaired segment and turbidity listing in Minnesota s (d) List...5 Table 2 Data and information sources identified in the Summary of Existing Water Quality Data and Information Task...9 Table 3 Stream flow Stations in the Poplar River and nearby Baptism, Knife, and Pigeon Rivers Table 4 Streamflow correlation coefficients at stations in the Poplar, Pigeon, Knife, and Baptism Rivers Table 5 Streamflow Statistics for daily data at the Poplar River (USGS and DNR/MPCA), and Pigeon River (USGS)...14 Table 6 Last Day of Snow Pack Data from Grand Marais (213282) and Lutsen (214918)...18 Table 7 Sample statistics for two monitoring locations in the Poplar River watershed Table 8 Monthly summary statistics for turbidity at the upstream location for years , downstream location for years , and downstream location for years Table 9 Correlation coefficients for turbidity at the upstream and downstream locations using data collected during Table 10 Turbidity analytical methods employed by MPCA during Table 11 Monthly summary statistics for TSS at the upstream location for years , downstream location for years , and downstream location for years Table 12 Winter (November March) summary statistics for TSS at the downstream location for years No data is available for winter months at the upstream station...32 Table 13 Flow weighted TSS concentrations for all stratification periods for upstream station (S ) Table 14 Estimated annual loads at the upstream station (S ) Table 15 Estimated average monthly load at the upstream station (S )...34 Table 16 Estimated annual loads at the downstream station (S ) Table 17 Estimated average monthly load at the downstream station (S ) for Table 18 Comparison of annual loads at both sampling stations...37 Table 19 Comparison of estimated average monthly loads at the upstream and downstream station for the Table 20 Comparison of loads calculated at the downstream station (S ) using two different methods. Loads are for summer months (April through October)...38

5 Poplar River Turbidity TMDL Evaluation of Existing Data Page iii of 63 Table 21 Summary of turbidity samples and the number of samples above 10 NTU within each flow range of the LDC. This table includes measured turbidity values collected during Table 22 NPDES permitted facilities in the Poplar River watershed Table 23 Caribou Highlands Lodge (MN ) permit limits for flow and TSS during Table 24 Monthly and annual TSS loads from the Caribou Highlands Lodge wastewater treatment facility for List of Figures Figure 1 Poplar River and its major tributaries. GIS information obtained from the DNR Data Deli online at Figure 2 Lower Poplar River watershed showing 2.73-mile impaired stream length and water quality and streamflow station locations. GIS information obtained from the DNR Data Deli online at Figure 3 Locations of three potential reference USGS stations in proximity to the Poplar River near the Lutsen, MN station. GIS information obtained from the DNR Data Deli online at Figure 4 Linear regression of mean daily flow measured during at the Poplar River near Lutsen station (MPCA data) and the Pigeon River at Middle Falls near Grand Portage, MN (USGS data) Figure 5 Measured and estimated flow at the Poplar River near Lutsen station based on DNR/MPCA-measured flow and USGS flow at Pigeon River at Middle Falls near Grand Portage...15 Figure 6 Histogram of flow at the Poplar River near Lutsen station ( ) during (excluding winter months when flow was not measured).16 Figure 7 Histogram of flow at the Poplar River station based on 30 years of estimated data using Pigeon River data ( )...16 Figure 8 Turbidity collected at station S using ambient monitoring program data Figure 9 Turbidity and streamflow relationship at station S (upstream site) using lab turbidity data (NTRU only) collected during , and streamflow measured at the Poplar River downstream site Figure 10 Turbidity and streamflow relationship at station S (downstream site) using lab turbidity data (NTRU only) collected during , and streamflow measured at the Poplar River downstream site Figure 11 Average monthly turbidity results at the upstream and downstream locations based on data. Sampling frequency varies significantly between months (see Table 8) and should be consulted when interpreting averages....25

6 Poplar River Turbidity TMDL Evaluation of Existing Data Page iv of 63 Figure 12 Turbidity-TSS correlation using all available data at the downstream site (S ) using log-transformed data collected during Figure 13 Turbidity-TSS correlation using only values less than or equal to 40 NTU at the downstream site (S ) using log-transformed data collected during Figure 14 Turbidity-TSS correlation using all available data collected at the upstream site (S ) using log-transformed data collected during Figure 15 Observed TSS concentrations at various flow rates for the upstream monitoring site (Station S )...33 Figure 16 Observed TSS concentrations at various flow rates for the downstream monitoring site (Station S )...35 Figure 17 Log flow-log concentration relationship at downstream location (S ) for April through October (r2 = 0.21) Figure 18 Concentration duration curve for measured and estimated TSS at the downstream location Figure 19 Load duration curve including measured and estimated TSS, and measured TSS at the downstream location...41 Figure 20 Load duration curve including measured and estimated TSS presented by year in which the measurement was acquired...42

7 Poplar River Turbidity TMDL Evaluation of Existing Data Page v of 63 List of Acronyms CFS CWA DNR EDA FTU GIS MPCA NRRI NTU NTRU NWIS QA/QC QAPP RTI TMDL TSS USGS USFS WEPP Cubic Feet per Second Clean Water Act Minnesota Department of Natural Resources Environmental Data Access Formazin Turbidity Unit Geographic Information Systems Minnesota Pollution Control Agency Natural Resources Research Institute Nephelometric Turbidity Unit Nephelometric Turbidity Ratio Unit National Water Information System Quality Assurance/Quality Control Quality Assurance Project Plan Research Triangle Institute Total Maximum Daily Load Total Suspended Solids United States Geologic Survey United States Forest Service Water Erosion Prediction Project

8 Poplar River Turbidity TMDL Evaluation of Existing Data Page 1 of 63 1 Executive Summary The Poplar River watershed is located in the Lake Superior Basin (Northeast Minnesota) near Lutsen, MN. The entire watershed covers an area of approximately 114 square miles - with a river distance of approximately 25.5 miles (Figure 1). Minnesota s 2004 Clean Water Act (CWA) Section 303(d) List identified the most downstream 2.73-mile segment of Poplar River, between Superior Hiking Trail Bridge and the outlet to Lake Superior (AUID ), as not meeting its intended use (aquatic life) based on turbidity violations (Figure 2). Section 303(d) of the Clean Water Act and Chapter 40 of the Code of Federal Regulations Part 130 require states to develop Total Maximum Daily Loads (TMDLs) for waters not meeting designated uses under technology-based controls for pollution. The TMDL process quantitatively assesses the impairment factors so that states can establish waterquality based controls to reduce pollution from both point and nonpoint sources, and to restore and protect the quality of their water resources. This report supports the development of a TMDL for turbidity in the Poplar River, Minnesota, by providing a summary and analysis of the existing data on water quality, streamflow, and snowfall/snow pack within the Poplar watershed with a focus on turbidity and total suspended solids (TSS). Water quality and streamflow monitoring in the Poplar River watershed have been ongoing since The watershed has been the site for a number of sampling programs and water quality studies, including, the Minnesota Milestone River Monitoring Program, the ambient monitoring program, the Cook County Water Program Lakes and River Monitoring Program, and, most recently, the North Shore Load Project. Ambient monitoring, which has been ongoing at the S station since 1973 provides an extensive dataset of water quality under various flow conditions. Between 2001 and 2007, as part of the North Shore Load Project, two water quality stations in the Poplar have been sampled with an emphasis on event flow conditions in an effort to understand and characterize sediment loading in the watershed. Combined, these monitoring programs provide valuable information into the nature, variability, and sources of turbidity impairment in the watershed. The following sections outline our approach in evaluating the data and our primary findings. Streamflow Assessment Streamflow data were used in this report to assess flow conditions under which turbidity exceedances occur, identify potential TSS and turbidity sources, develop sediment loading analyses, and develop the load duration curve which will be used as the basis for the TMDL. Historic and recent streamflow data in the lower Poplar River are available through the USGS National Water Information System (NWIS) and Minnesota Department of

9 Poplar River Turbidity TMDL Evaluation of Existing Data Page 2 of 63 Natural Resources (DNR)/Minnesota Pollution Control Agency (MPCA) Cooperative Stream Gaging websites. Daily data are available between and Because streamflow is an important component in assessing sediment loading and turbidity impairment and developing the load duration curve, the RTI Team took steps to estimate flows for the period missing from the flow record. Three USGS stations, each located in close proximity to the Poplar River station, were analyzed by the RTI Team as potential reference stations for the Poplar River. Based on the use of correlation coefficients and linear regressions, the Pigeon River at Middle Falls, Minnesota, was found to be the best source for estimating flow during periods when flow data are not available at the Poplar River near Lutsen station. To confirm the use of the Pigeon River data in estimating flow in the Poplar River, cumulative frequency histograms were developed based on measured flow at the Poplar River and 30 years ( ) of estimated flow at the Poplar River. These histograms revealed similar trends in flow frequency and cumulative flow between measured flows and estimated flows and confirm the decision to use the Pigeon River data. Snowmelt and Snow Pack Issues Several sources of information were consulted in an effort to determine when snow pack is no longer present within the watershed. This information is useful for assessing potential sources of sediment because melting snow may detach and transport soil to the Poplar River and the lack of vegetative cover typical for this time period will allow greater soil detachment and transport from rainfall. The sources of information reviewed include Lutsen Mountain marketing literature, an e-newsletter from the Minnesota Climatology Office, and Lutsen and Grand Marais weather gage snow pack information. Our analysis included years 1980 through All three information sources indicate that the snow pack typically is gone by the end of April. Lutsen Mountain marketing literature indicates that the ski resort likely has greater snow pack for a longer period of time than the rest of the watershed due to snow making. DNR water usage permit data were reviewed and used to calculate the hydrologic loading to ski slopes due to snowmaking. The calculations indicated that on average 3.9 feet of water is applied to the 60 acres of ski runs during the winter months. Water Quality Monitoring Turbidity and TSS are the primary water quality constituents of concern in this project. Data are available at three locations in the Poplar River watershed (station S , LakeSuperiorStream project sonde located upstream of the State Highway 61 overpass, and station S ) through the United States Forest Service (USFS) Region 9, Natural Resources Research Institute s (NRRI) LakeSuperiorStreams project, and MPCA monitoring programs. Sampling frequency, methods, goals, and results for each of the sampling programs are discussed in this report.

10 Poplar River Turbidity TMDL Evaluation of Existing Data Page 3 of 63 The primary source of turbidity and TSS data in the Poplar are data collected by the MPCA at stations S and S through the Minnesota Milestone River Monitoring Program and North Shore Load Project. The Minnesota Milestone River Monitoring Program is MPCA s ambient water quality program. This program is a long term monitoring program with the goal of understanding the overall trend of water health in Minnesota. Water quality data collected in the Poplar River as part of the ambient program were collected periodically between 1973 and 1999 at station S The purpose of the North Shore Load Project is to assess current water quality conditions using state of the art monitoring techniques, provide baseline information for detection of water quality trends over time, and assist in the development of stream protection and remediation management options for public, private, and commercial interests. Turbidity-Total Suspended Solids Relationship This section provides an evaluation of the relationship between turbidity and other water quality parameters (such as TSS and sediment), and a discussion on field and laboratory analytical methods used to measure turbidity between 1973 and 2006 in the Poplar River. Because turbidity is measured in NTU, and not as a concentration, another parameter that is measured as a concentration must be used to represent turbidity for the calculation of loadings in the watershed. Correlation coefficients used to identify this surrogate parameter showed total solids and total suspended solids (TSS) to have a highest correlation with turbidity. Based on the availability of a large TSS dataset, TSS was selected as an indicator for turbidity impairment and as a surrogate for developing load estimates. A more detailed assessment of nonpoint sediment sources will be provided as part of the Physical Channel Assessment (Task 6) and Source Identification Summary (Task 5) conducted in the spring and summer of Sediment Loading Analysis TSS loads were estimated at the upstream (S ) and downstream (S ) sampling locations using the U.S. Army Corps of Engineers computer program FLUX. At the upstream location, all observed TSS concentrations were less than 12 mg/l when flows were under 400 cfs. Above 400 cfs TSS concentrations exhibited greater variability, though, in general, were higher than TSS values collected during flows below 400 cfs. At the downstream location high TSS concentrations were found under all flows. Comparing the annual and monthly load estimates for the upstream and downstream sites provided an estimate of the contribution of sediment that the lower Poplar River watershed delivers to the river. Based on the FLUX modeling, during , loads from the upper Poplar River watershed ranged from 282 tons to 1055 tons and varied from 15% to 32% of the total load estimated at the downstream sampling station (S ). Sediment loads originating from the lower Poplar River ranged from 994 tons to 2,194 tons annually

11 Poplar River Turbidity TMDL Evaluation of Existing Data Page 4 of 63 between 2001 and A seasonal analysis of loads demonstrated that most of the load is delivered between April and June of each year. A load duration curve analysis, used to visualize TSS loading as a function of flow frequency, revealed exceedances to the turbidity standard occur under most flow conditions. In general, few exceedances were observed under low flow conditions. Under conditions where flows were at or above 60 cubic feet per second (cfs), the number of exceedances increased. Most turbidity violations occurred under high flow conditions. USEPA s water discharge permits website ( was consulted to obtain information on permitted facilities in the Poplar River watershed. Of the permitted facilities present, only one requires monthly monitoring for turbidity and flow. The Caribou Highlands Lodge (MN ) wastewater treatment facility maintains a treatment lagoon that periodically discharges to the Poplar River. Effluent data for MN during the period were provided through MPCA. Annual and monthly TSS loads from the Caribou Highlands discharge were calculated for the period. Results of this analysis suggest that the Caribou Highlands discharge contributes very little (<1%) to the overall TSS load in the river.

12 Poplar River Turbidity TMDL Evaluation of Existing Data Page 5 of 63 2 Introduction As stated in the Poplar River TMDL Quality Assurance Project Plan (QAPP) (RTI, 2007a), data and information identified in Task 1 (RTI, 2007b) serve as a foundation for developing the Poplar River TMDL. The MPCA has provided guidance, in the form of three questions, for the review and evaluation of turbidity data for TMDL development (MPCA, 2006): 1. What are the prominent data gaps? 2. Can the key stressors affecting turbidity be identified? 3. Are there critical conditions for the impairment analysis? If so, what are they? In addition to addressing these three questions, this report will evaluate any identifiable temporal or spatial trends in water quality in the Poplar River. In Task 1 of this project, the RTI team compiled a list of existing data and information, including parameters analyzed, period of record, and the availability of results (RTI, 2006b). The information included in these data sources will be used in this task to analyze potential sources of turbidity, the magnitude and frequency of turbidity criteria exceedances, the magnitude and frequency of discharges from sources, and the geographic extent of water quality issues. This report will provide an overview of data within the entire Poplar River watershed; however, most of the detailed analysis will focus on the lower 2.73-mile portion of the Poplar River located between the Superior Hiking Trail Bridge (upstream station) and the confluence of the Poplar River with Lake Superior. 2.1 Assessment of Impairment The Minnesota Rules, Chapter , identify classifications for waters in major surface water drainage basins, including those applicable in the Poplar River. Per Chapter , the Poplar River is classified as a Class 2A water, and, as such, the applicable water quality standard for turbidity in the Poplar River is 10 Nephelometric Turbidity Units (NTU). In 2004, a portion of the Poplar River in the Lake Superior Basin was listed on Minnesota s 303(d) list of impaired water bodies. The impaired segment, Assessment Unit ID: , includes a 2.73-mile segment of the Poplar River from Superior Hiking Trail Bridge to Lake Superior. A summary of information included for the Poplar River turbidity listing is provided in Table 1. Reach Table 1 Poplar River Poplar River impaired segment and turbidity listing in Minnesota s (d) List. Years Pollutant/ Description Listed River ID# Affected Uses Stressor Superior Hiking Trail Bridge to Lake Superior 2004, Aquatic life Turbidity

13 Poplar River Turbidity TMDL Evaluation of Existing Data Page 6 of Description of Watershed Characteristics The Poplar River watershed is located in the Lake Superior Basin in northeast Minnesota near Lutsen, Minnesota (Figure 1). The entire watershed covers an area of approximately 114 square miles with a river distance of approximately 25.5 miles. The Poplar River originates at the Boundary Waters Canoe Area, Hilly Lake area, and ends at the river s confluence with Lake Superior. The Poplar River watershed includes Tait Lake/Tait River, Pike Lake, and Caribou Lake (MPCA, 2002). The watershed in the Poplar River headwaters area is characterized as having low-gradient slopes and a significant wetland area. Downstream of the headwaters area, the watershed narrows considerably as it flows over the escarpment, where the gradient increases greatly and the channel is defined by bedrock, lacustrine beach, and glacial deposits. These most downstream portions of the Poplar River and watershed are characterized by significant drops in elevation including sloping cascades and waterfalls, with an average gradient of nearly 41 feet per mile, and by both forested and cleared steep slopes. 2.3 Data and Information Sources Data and information to be used in evaluating turbidity impairment in the Poplar River were placed in hierarchical categories based on the documented quality assurance and quality control processes (RTI, 2007a). Data evaluated in this report include water quality data, streamflow and discharge data, climate data, GIS data, and soil survey reports. This information was evaluated, categorized as high, moderate, or low quality, and used to assess turbidity impairment in the Poplar River. Data and information available for use in developing the Poplar River TMDL were identified in Task 1 (Summary of Existing Water Quality Data and Information) and are provided in Table 2. Table 2 lists two additional information sources that were not available at the time of Task 1 completion (see Table footnote). Based on the guidelines set forth in the Poplar River QAPP, water quality data collected by MPCA, streamflow data collected by the USGS and DNR/MPCA, climate data collected by the Climatology Working Group, and water quality collected by MPCA (available through the MPCA Environmental Data Access database) are categorized as high-quality data. Existing Water Erosion Prediction Project (WEPP) modeling is considered low-quality data because quality assurance and quality control documents do not exist, and no QAPP or QA/QC plan for the WEPP application exists detailing the computer modeling process.

14 Poplar River Turbidity TMDL Evaluation of Existing Data Page 7 of 63 Figure 1 Poplar River and its major tributaries. GIS information obtained from the DNR Data Deli online at

15 Poplar River Turbidity TMDL Evaluation of Existing Data Page 8 of 63 Figure 2 Lower Poplar River watershed showing 2.73-mile impaired stream length and water quality and streamflow station locations. GIS information obtained from the DNR Data Deli online at

16 Poplar River Turbidity TMDL Evaluation of Existing Data Page 9 of 63 Table 2 Data and information sources identified in the Summary of Existing Water Quality Data and Information Task. QAPP designations are provided only for raw water quality data, flow data, modeling data/results, and meteorological data. QAPP Documentation Source Description Designation Recommended Use in Developing TMDL MPCA Environmental Data Access database MPCA Water quality data High Load duration curve, seasonal trends, TSSturbidity relationship, identify critical conditions, source assessment USGS Water Data for Poplar River at Lutsen Mountain USGS Streamflow data High Identify critical conditions, source assessment Climatology Working Group Climatology Working Meteorological High Seasonal trends Group, Univ. of MN data Soil Survey of North Shore of Lake Superior Coastal MPCA Soil Survey High Source assessment Zone Management Area Information Poplar River flow MPCA 2 Streamflow data High Identify critical conditions, source assessment Poplar River flow, stage, turbidity data, and maps that MPCA 2 Water quality High Identify critical conditions, source assessment are processed and no longer provisional status North American Wetland Engineering and SE Group, Environmental Report for Lutsen Mountain, Cook County, Minnesota, Report for Lutsen Mountain Resort developed by SE Group Cook County Planning and Zoning Department data Report and Model Results Low Qualitative assessment and source identification Lower Poplar River Watershed Alternative Urban Area-Wide Review (AUAR) Report (qualitative) Not Applicable Qualitative assessment and source identification An Assessment of Representative Lake Superior Basin MPCA Report Not Applicable Qualitative assessment and source identification Tributaries 2002 Lake Superior Basin Plan MPCA Report Not Applicable Qualitative assessment and source identification SE Group memorandum regarding the Preliminary Summary report for Lutsen Report Not Applicable Qualitative assessment and source identification Summary, Poplar River Impairment Study, October 13, Mountain Resort 2006 Selected Water Quality Characteristics of Minimally Impacted Streams from Minnesota s Seven Ecoregions, 1993 MPCA Report and Data Not Applicable Qualitative assessment and source identification 2006 Integrated Surface Water Quality Report MPCA Report Not Applicable Not Applicable Comprehensive Plan: Cook County Soil and Water Cook County SWCD Report Not Applicable Qualitative assessment and source identification Conservation District Guide to Stormwater Best Management Practices for Cook County SWCD Report Not Applicable Qualitative assessment and source identification Lutsen and Poplar River Watersheds Cook County Local Water Management Plan Cook County Planning Report Not Applicable Qualitative assessment and source identification Department Slope Stabilization Work Plan North American Wetland Report Not Applicable Qualitative assessment and source identification For Poplar River Management Board 1 Engineering, LLC Poplar River, MN (Cook County) 2006 Automated, in Center for Water & the Report and Not Applicable Qualitative assessment and source identification situ, Water Quality Data: Preliminary Analysis 1 Environment, NRRI Statistics Turbidity TMDL Protocols and Submittal Requirements 1 MPCA Report Not Applicable Guidance document for developing the TMDL report 1 Report obtained after completion of Task 1: Summary of Existing Water Quality Data and Information, prepared for USEPA Region 5 on December 22, Correspondence with Jesse Anderson, MPCA on April 16, 2007.

17 Poplar River Turbidity TMDL Evaluation of Existing Data Page 10 of 63 3 Evaluation of Existing Data This section provides an evaluation of existing streamflow data, snowmelt and snow pack issues, and water quality monitoring. 3.1 Streamflow Assessment For this project, streamflow data will be used to assess flow conditions under which turbidity exceedances occur, identify potential TSS and turbidity sources, develop sediment loading analyses, and develop the load duration curve which will be used as the basis for the TMDL. A number of recent studies conducted within the Poplar River watershed and Lake Superior region have highlighted the importance of hydrology in understanding turbidity impairment (NAWE, 2007; NAWE, 2005; and, Axler, et. al, 2007). Hydromodification can result in increased stream bank erosion because of increased intensity and frequency of streamflows, which in turn can result in an increase in sediment loading and turbidity. This section provides an analysis of streamflow data available in the Poplar River and neighboring rivers and documents the methods used to estimate flow data that will be used to develop the TMDL. Historic and recent streamflow data in the lower Poplar River are available through the USGS National Water Information System (NWIS) and Minnesota Department of Natural Resources (DNR)/MPCA Cooperative Stream Gaging websites. Between 1912 and 1961, the USGS maintained station , Poplar River at Lutsen, MN. This station was located approximately 100 yards upstream of the MN State Highway 61 overpass near Lutsen, MN (Figure 2). Average daily streamflow data, collected during at this station, are available through the USGS NWIS website ( In recent years, the Minnesota DNR and MPCA have teamed to collect additional flow data in the lower Poplar River. Through this partnership, daily data are available online through the DNR/MPCA s Cooperative Stream Gaging Network website ( for the period The DNR/MPCA station, , is located approximately 200 yards upstream of the Highway 61 overpass near Lutsen, MN (100 yards upstream of the USGS station). Provisional, real-time flow data in the Poplar River near Lutsen, collected at thirty-minute intervals, is provided on the LakeSuperiorStreams.org website ( Provisional data are currently available for data collected during 2006 and Prior to the release of daily streamflow data on the DNR/MPCA s Cooperative Stream Gaging Network website rigorous quality assurance and quality control procedures are followed to be sure data are accurately presented. Quality assurance and quality control procedures used by DNR/MPCA staff are provided online at

18 Poplar River Turbidity TMDL Evaluation of Existing Data Page 11 of 63 The USGS and DNR/MPCA datasets provide daily streamflow data during and , respectively. Because streamflow is an important component in assessing sediment loading and turbidity impairment and developing the load duration curve, the RTI Team took steps to estimate flows for the missing period prior to To generate the flow duration curve and loading analyses it is preferable to use a data set with several years of data (ideally 30 years) collected at or near the water quality station. Several approaches to estimating flow in streams have been used by USGS and others. In streams where limited gage data are available, one common approach involves the use of weighted flow measurements from nearby reference stream(s) in which data are available for both the period of missing data and available data. Three USGS stations, each located in close proximity to the Poplar River station, were selected by the RTI Team as potential reference stations for the Poplar River. Table 3 provides a summary of the Poplar River stations and these three potential reference stations at which streamflow data were obtained and reviewed for this task. These stations are also identified in Figure 3. Table 3 Stream flow Stations in the Poplar River and nearby Baptism, Knife, and Pigeon Rivers. River/Station Name Data Source Station Number Distance from Poplar River (mi) Drainage Area (mi 2 ) Discharge Period of Record Latitude/ Longitude Poplar River near Lutsen, MN DNR/ MPCA '24", 90 42'38" Poplar River at Lutsen, MN USGS '23", 90 42'31" Baptism River near Beaver Bay, MN USGS miles southwest '15", 91 12'02" Knife River near Two Harbors, MN USGS miles southwest '49", 91 47'32" Pigeon River at Middle Falls near Grand Portage, MN USGS miles northeast '44", 89 36'58" The flow record for the Poplar River and the surrounding watersheds was analyzed and compared to develop a better understanding of the flow regimes in Minnesota s North Shore and develop a long term loading analysis. Typical streamflow characteristics for the lower Poplar River are provided in the Streamflow Summary Statistics section and the estimated flows using the surrogate flow station were used to develop the load duration curve, annual sediment loads, and monthly sediment loads.

19 Poplar River Turbidity TMDL Evaluation of Existing Data Page 12 of 63 Figure 3 Locations of three potential reference USGS stations in proximity to the Poplar River near the Lutsen, MN station. GIS information obtained from the DNR Data Deli online at

20 Poplar River Turbidity TMDL Evaluation of Existing Data Page 13 of 63 Examination of the three potential reference stations included review of the following: 1. Availability of recent flow data (ideally 30 years) 2. Close in proximity to Poplar River near Lutsen, MN station 3. Correlation coefficient derived between flows at the reference station and flows at Poplar River USGS and DNR/MPCA stations. Of the three reference stations listed in Table 3, both the Pigeon River and Knife River stations have 30 years of recent flow data and are situated close to the Poplar River. The Baptism River station, although close in proximity to the Poplar River, does not have data available after Correlation coefficients used to evaluate flow relationships are shown in Table 4. Of the three reference stations, the Pigeon River at Middle Falls, Minnesota, was found to have the highest correlation with USGS flow data and DNR/MPCA flow data in the Poplar River (0.88 and 0.89 respectively). A comparison of Knife River flow with DNR/MPCA flow resulted in a much lower correlation of Data from the Baptism River and the USGS record in the Poplar River were based on flows recorded during the period and resulted in a correlation of Based on these findings, the Pigeon River at Middle Falls, Minnesota, was found to be the best source for estimating flow during periods when flow data are not available at the Poplar River near Lutsen station. Table 4 Streamflow correlation coefficients at stations in the Poplar, Pigeon, Knife, and Baptism Rivers. Poplar River Station Reference Station Period of Comparison Correlation Poplar River at Lutsen, Baptism River near Beaver Bay, MN (USGS) MN (USGS) Poplar River nr Lutsen, Knife River near Two Harbors, MN (DNR/MPCA) MN (USGS) Poplar River at Lutsen, Pigeon River at Middle Falls near MN (USGS) Grand Portage, MN (USGS) Poplar River nr Lutsen, Pigeon River at Middle Falls near MN (DNR/MPCA) Grand Portage, MN (USGS) A linear regression developed using average daily flows at the Poplar River near Lutsen, MN station and the Pigeon River at Middle Falls near Grand Portage, MN station reveals that the flow relationship between these two stations is good under most flow conditions. The relationship is less strong under high flows, specifically when flows are above 700 cfs in the Poplar River. This weak relationship under high flows is, in part, due to the lack of available data above 700 cfs. Only five measurements above 700 cfs are available during In addition, the distance between the watersheds (approximately 57 miles between stations), and the difference in drainage area may contribute to the change in relationship under high flows. Most notable, however, is that since flows above 700 cfs in the Poplar River occur approximately 1% or less of the time the importance of the relationship above 700 cfs has a relatively small impact on the

21 Poplar River Turbidity TMDL Evaluation of Existing Data Page 14 of 63 TMDL. Based on the regression presented in Figure 4, the following relationship between these stations was established: Poplar River at Lutsen, MN, flow = (Pigeon River at Middle Falls flow/4.5544) This equation was used to estimate flow at the Poplar River station for the period , which will be the basis for the flow duration curve and load duration curve Streamflow Linear (Streamflow) Pigeon River Streamflow, (cfs) y = x R 2 = MPCA Poplar River near Lutsen Streamflow, (cfs) Figure 4 Linear regression of mean daily flow measured during at the Poplar River near Lutsen station (MPCA data) and the Pigeon River at Middle Falls near Grand Portage, MN (USGS data). Streamflow statistics for the Poplar River and Pigeon River flow datasets are provided in Table 5. Flow data in the Pigeon River was found to be, on average, approximately five times higher than flows at the Poplar River. The Pigeon River drainage area, including Canadian portions, is approximately five and one-half times larger than the Poplar River drainage area (USGS summary statistics for station). Table 5 Streamflow Statistics for daily data at the Poplar River (USGS and DNR/MPCA), and Pigeon River (USGS). Poplar River data between 2002 and 2006 excludes 0 values where flows were not recorded by DNR/MPCA. Station/Data Source Flow Record Count (days) Minimum (cfs) Maximum (cfs) Average (cfs) Median (cfs) Poplar River at Lutsen, MN (USGS) Poplar River near Lutsen, MN (DNR/MPCA) Pigeon River at Middle Falls nr Grand Portage, MN (USGS)

22 Poplar River Turbidity TMDL Evaluation of Existing Data Page 15 of 63 Figure 5 provides a comparison of measured and estimated flow during the period at the Poplar River station. Estimated flow corresponds well to actual flow during the period, with the exception of some high flow events in the measured data set during the spring of 2003 and 2004 and fall of 2002 and Based on the linear regression equation selected for estimation of Poplar River flows from Pigeon River flows higher flows will be overestimated. This may result in an overestimate of annual and monthly loadings during periods with flow greater than approximately 700 cfs Poplar Measured (MPCA) Poplar Estimated (Pigeon River USGS Flow) Annual Rainfall for Calendar Year 30 year Annual Rainfall Average = inches ( ) Streamflow (ft 3 /sec) Annual Rainfall (inches) Year 0 Figure 5 Measured and estimated flow at the Poplar River near Lutsen station based on DNR/MPCA-measured flow and USGS flow at Pigeon River at Middle Falls near Grand Portage. Annual rainfall and 30-year average annual rainfall obtained through the Minnesota Climatology Working Group ( A cumulative frequency histogram based measured flow at the Poplar River is presented in Figure 6. A similar histogram for 30 years ( ) of estimated flow at the Poplar River is presented in Figure 7. Figures 6 and 7 reveal similar trends in flow frequency and cumulative flow between measured flows and estimated flows, with increased frequency of flows occurring between cfs and cfs. Annual histograms (flow frequency and cumulative % values) for were also developed for daily flow data available through the DNR/MPCA and are provided in Appendix A.

23 Poplar River Turbidity TMDL Evaluation of Existing Data Page 16 of 63 Frequency Frequency Cumulative % 120% 100% 80% 60% 40% 20% Flow Ranges (ft 3 /sec) 0% Figure 6 Histogram of flow at the Poplar River near Lutsen station ( ) during (excluding winter months when flow was not measured). Frequency Frequency Cumulative % 120% 100% 80% 60% 40% 20% % Flow Ranges (ft 3 /sec) Figure 7 Histogram of flow at the Poplar River station based on 30 years of estimated data using Pigeon River data ( ).

24 Poplar River Turbidity TMDL Evaluation of Existing Data Page 17 of Snowmelt and Snow Pack Melting snow contributes to the peak flows observed in April of each year. The melting snow may detach and carry sediment, contributing to the turbidity problem. This section assesses when the snow pack typically melts. Results of the analysis will contribute to the understanding of the hydrologic process and inform the analysis of seasonal turbidity levels and sediment loads. Several sources of information were consulted in an effort to determine when snow pack is no longer present within the watershed. This information is useful for assessing potential sources of sediment because melting snow may detach and transport soil to the Poplar River and the lack of vegetative cover typical for this time period will allow greater soil detachment and transport from rainfall. The sources of information reviewed include Lutsen Mountain marketing literature, an e- newsletter from the Minnesota Climatology Office, and Lutsen and Grand Marais weather gage snow pack information. The information provided by each source follows. Lutsen Mountain Resort website on April 19, 2007 Lutsen Mountain Resorts uses snowmaking equipment to supplement natural snow. This capability has allowed Lutsen Mountain to stay open until mid-april for the past 18 years (Lutsen Mountain, 2007). E-newsletter of the Minnesota Climatology Office The average date of the last occurrence of three or more inches of snow depth is on or after April 10 for most north-central and northeastern Minnesota communities. The average date of the final day of snow cover along the North Shore highlands is April 20 ( Station Lutsen-Cook An analysis of snow pack data retrieved from the Minnesota High Density Network, (Lutsen and Grand Marais stations) indicate that snow pack is present on average until the first week of April. This analysis included years 1980 through The criteria used to determine the last day of snow pack are as follows: 1. Last day of continuous snow pack was used (e.g., at least the previous 3 days had recorded snow pack). 2. Early spring snow falls that did not result in snow lasting more than 2 days, were ignored. 3. Trace amount of snow pack was considered no snow pack (e.g., last day with measurable amount of snow pack was used).

25 Poplar River Turbidity TMDL Evaluation of Existing Data Page 18 of 63 Table 6 reports the last date, the week, and the Julian day of snow pack recorded at Lutsen or Grand Marais. Grand Marais data were used to fill in periods of data missing from the Lutsen record. Table 6 Last Day of Snow Pack Data from Grand Marais (213282) and Lutsen (214918) Year Last Day of Snow Pack Calendar week Julian Day Station /16/ /07/ /21/ /23/ /11/ /18/ /08/ /01/ /31/ /20/ /30/ /07/ /06/ /31/ /12/ /06/ /01/ /16/ /31/ /30/ /06/ /28/ /25/ /09/ /03/ /31/ Average= (~ 1 st week of April) Water Appropriations Permit The Minnesota DNR has records for 3 water appropriations permits for Lutsen Mountain Resorts (permit numbers , , P3). Snowmaking may have occurred prior to 2001; however, data exists for seasons. The DNR records annual withdrawals in millions of gallons per year. Total withdrawals for each year are reported as: 60 MG used in 2001; 88 MG used in 2002; 67 MG used in 2003;

26 Poplar River Turbidity TMDL Evaluation of Existing Data Page 19 of MG used in 2004; and, 93 MG used in This results in an average withdrawal of 76.2 MG per year. This water is used for snow making on the approximately 60 acres of ski runs that exist on resort property (NAWE, 2005). This hydrologic loading would result in 3.9 feet of water available for runoff in addition to the natural precipitation that occurs during the winter and spring months. The additional hydrologic loading to the slopes near the Poplar River may contribute to the increased sediment loading during spring snow melt periods. All four information sources indicate that the snow pack typically is gone by the end of April. Lutsen Mountain marketing literature indicates that the ski resort likely has greater snow pack for a longer period of time than the rest of the watershed due to snow making, and DNR permit data support this claim by demonstrating that sufficient water is used to augment natural precipitation with 3.9 feet of water on the ski run area. 3.3 Water Quality Monitoring Turbidity and TSS data are available at three locations in the Poplar River watershed through the United States Forest Service (USFS) Region 9, Natural Resources Research Institute s (NRRI) LakeSuperiorStream project, and MPCA monitoring programs US Forest Service Monitoring ( ) The USFS (Poplar River 0.9 miles east of Tofte Mountain) dataset includes monitoring from 1975 through 1983 (available online at During this time period, sixty turbidity samples were collected at Station Of the sixty measurements, values ranged between 0.4 and 30 Formazin Turbidity Units (FTU) and averaged 3.3 FTU. Two of the sixty USFS samples were above 10 FTU. This data, will be used to provide a qualitative assessment of historic water quality conditions in the Poplar River, but will not be used in developing the TMDL given the time period in which the data were collected and because QAPP and QA/QC information for the data collection are not currently available LakeSuperiorStream Project Sonde Data (2006) In 2006, water quality data were collected by NRRI in collaboration with the MPCA and USGS for the LakeSuperiorStreams project ( A preliminary report on water quality data collected in the Poplar River during 2006 was provided by NRRI in February 2007 (Axler, 2007). The report provides a summary of the in situ sensor turbidity data for 2006, describes the basis for sampling locations, quality assurance protocols, and field and laboratory methods used for turbidity analysis. For this project, a sonde device was placed in the Poplar River in close proximity to the current MPCA stage/flow gauging station being used by MPCA, approximately 200

27 Poplar River Turbidity TMDL Evaluation of Existing Data Page 20 of 63 meters upstream of the MN highway 61 overpass. During the periods March 28 th May 3 rd and August 24 th November 27 th, a variety of water quality parameters, including turbidity, were collected at 30-minute intervals. Analysis of the sonde turbidity results for 2006 are provided by Axler (2007). A linear regression between sonde turbidity and TSS grab samples yielded a good fit, however sonde turbidity values were found to be, uniformly, more than three times higher than laboratory turbidity measurements which were taken a short distance downstream of the sonde. Sonde turbidity data also displayed high variability (i.e. noisy ) from sample to sample. The report provides analysis of these discrepancies and suggestions on options for addressing these issues when deploying the sonde in For the reasons outlined in Axler (2007), the sonde data will be used to qualitatively understand turbidity and sediment loading in the Poplar River, but will not be used to develop a relationship between TSS-turbidity or be used directly in developing the TMDL MPCA Ambient Monitoring Program ( ) The MPCA ambient monitoring program, now known as the Minnesota Milestone River Monitoring Program, is a long term monitoring program with the goal of understanding the overall trend of water health in Minnesota. Water quality data collected in the Poplar River as part of the ambient program were collected periodically between 1973 and 2006 at station S This station is located downstream of the Highway 61 overpass, adjacent to Lake Superior at a walking bridge at Lutsen Resort (Figure 2). Data for this station is available on the MPCA Environmental Data Access website ( and are summarized in Table 7 and shown in Figure 8. Of the sixty-nine samples collected at this station, four measurements were above the 10 NTU standard. Trend lines were developed for the entire dataset (excluding one measurement on 9/19/2005 where turbidity = 67 NTRU) and for data collected since 1994 (excluding the same measurement on 9/19/2005). No strong trend, either positive or negative is present in either of these two trend lines; however, there is a slight trend in increasing turbidity values when analyzing data. This upward trend increases dramatically with the inclusion of the measurement taken on 9/19/2005 in which turbidity equaled 67 NTRU. Despite this increase, in 2006, the regression line remains well below the 10 NTU standard.