Watershed and Waterbody Characterization

This section presents a brief description of the impaired lakes, wetlands and streams addressed in this TMDL. Watersheds, land use, water quality conditions, and sources of chloride are discussed.

Lakes and Wetlands

The Impaired Lake and Wetland Characterization in the TCMA table presents the impaired lakes and wetlands and general characteristics of each waterbody and watershed, including watershed area, percent impervious, lake area, mean depth, and volume. Percent impervious was derived using the National Land Cover Database (NLCD) from 2011 and is discussed further in the Land Use section

Impaired Lake and Wetland Characterization in the TCMA
Link to this table

-* Source: 2011 NLCD -** Loring Pond receives runoff from the MnDOT I-35W tunnel on occasion due to surcharging.
Waterbody Name Watershed Area (ac) % Impervious (NLCD, 2011)* Lake Area (ac) Mean Depth (ft) Volume (ac-ft)
Battle Creek Lake 4,326 33% 93 4 372
Brownie Lake 452 53% 18 22 404
Carver Lake 2,242 31% 48 15 720
Como Lake 1,850 36% 69 6 414
Diamond Lake 744 45% 51 3 57
Kasota Pond North 10 45% 1.4 n/a n/a
Kasota Pond West 6 69% 0.9 n/a n/a
Kohlman Lake 7,533 33% 82 4 328
Little Johanna Lake 1,703 50% 17 10 170
Loring Pond (South Bay)** 34 17% 7 7.5 52.5
Mallard Marsh 16 43% 2.9 n/a n/a
Parkers Lake 1,064 41% 93 11 1,023
Peavey Lake 776 15% 9.7 n/a n/a
Pike Lake 5,735 43% 36 7 252
Powderhorn Lake 332 45% 12 4 73
Silver Lake 655 38% 71 6 426
South Long Lake 114,785 12% 186 16 2,976
Spring Lake 39 25% 3 9.5 28.5
Sweeney Lake 2,439 41% 69 12 828
Tanners Lake 1,732 31% 69 19 1,311
Thompson Lake 178 53% 7 8 56
Valentine Lake 2,404 32% 55 4 220
Wirth Lake 426 13% 37 11 407


Streams

The Impaired Stream Characterization in the TCMA table resents the impaired streams and watershed area and percent impervious cover of the watershed.

Impaired Stream Characterization in the TCMA
Link to this table

Waterbody Name Watershed Area (ac) % Impervious (2011)*
Bass Creek 5,434 30.9%
Bassett Creek 25,209 33.8%
Battle Creek 7,246 32.6%
Elm Creek 66,382 9.7%
Judicial Ditch 2 1,587 20.6%
Minnehaha Creek 109,151 14.4%
Raven Stream 42,750 2.0%
Raven Stream, East Branch 14,751 4.5%
Rush Creek, South Fork 13,844 4.7%
Sand Creek (includes AUIDs: 07020012-513 and 07020012-662) 175,578 2.0%
Unnamed creek (Headwaters to Medicine Lk) 6,447 37.6%
Unnamed creek (Unnamed ditch to wetland) 793 37.6%
Unnamed Stream (Unnamed lk 62-0205-00 to Little Lk Johanna) 1,627 51.6%

-* Source: 2011 NLCD



Subwatersheds=

Watershed maps for each impaired waterbody are included in Appendix A-1.

Land Use

The land use in the TCMA is largely urban in the core of Minneapolis and St. Paul with a transition to rural and agricultural moving outward through the suburbs. This land use pattern can be seen in Figure 2 which is based on the NLCD from 2011, the most recent national land cover product. This data is based on 2011 Landsat satellite data. Road densities by watershed are presented in Figure 3 based on road density information provided by the Minnesota Department of Transportation (MnDOT) and watershed catchments developed by Minnesota Department of Natural Resources (DNR). The NLCD also includes a layer for percent impervious (Xian et al., 2011). The impervious layer is comprised of 30m x 30m pixels each with a percent impervious value. The pixels for each drainage area are averaged to calculate a percent impervious for each impaired watershed. The percent impervious for the TCMA is shown in Figure 4 below. Similar to the land use pattern, both road densities and percent impervious are shown to decline moving outward from the TCMA core through the suburbs. The percent impervious for each impaired watershed is listed above in the Impaired Lake and Wetland Characterization in the TCMA table and the Impaired Stream Characterization in the TCMA table.

This image shows the land use in the TCMA
Land use in the TCMA


This image shows Chloride Impairments and Road Density in the TCMA
Chloride Impairments and Road Density in the TCMA
This image shows the percent Impervious in the TCMAf
Percent Impervious in the TCMA


Current and Historic Chloride Concentrations

Ambient chloride data for each impaired waterbody were compiled and assessed to understand current and historic water quality. A summary of the assessment is presented in Appendix A-1. As stated in Section 2, the chronic chloride standard of 230 mg/L has been applied as the numeric WQT for this TMDL. The impaired lakes, wetlands, and streams were compared in terms of the concentrations of chloride measured and ranked from highest concentrations to lowest. These rankings are presented in Figure 5 and Figure 6. These figures are not a direct reflection of the 303(d) listing assessment; rather they are intended to make a relative comparison of the extent of impairment across impaired waters. The values presented in these figures were calculated by first identifying the maximum chloride concentration measured in a waterbody on individual sampling days, and then averaging all the individual sampling day maximums that exceed the target of 230 mg/L for the period from 2003-2013. These figures indicate the variability in one waterbody or watershed to the next in terms of the severity of the impairment. This information may be used to target priority areas for reductions in chloride loads. Table 5 and Table 6 show the number of days with samples exceeding the chronic and acute standard within the last 10 years for lakes and streams, respectively. More information about the chloride trends in the TCMA can be found in section 2.3 of the TCMA Chloride Management Plan.


This graph shows a comparison of Impaired Lakes and Wetlands in the TCMA from 2003-2013
Comparison of Impaired Lakes and Wetlands in the TCMA from 2003-2013

Number of days with lake and wetland samples exceeding the chronic and acute criterion in the TCMA, 2003-2013
Link to this table

Lake Number of Individual Days with Samples Number of Days with Samples Exceeding 230 mg/L Chronic Criterion Number of Days with Samples Exceeding 860 mg/L Acute Criterion
Battle Creek Lake 81 4 0
Brownie Lake 27 21 5
Carver Lake 138 79 0
Como Lake 84 8 0
Diamond Lake 117 32 1
Kasota Pond North 91 70 8
Kasota Pond West 91 91 0
Kohlman Lake 80 6 1
Little Johanna Lake 9 9 5
Loring Pond (South Bay) 65 43 3
Mallard Marsh 122 122 0
Parkers Lake 30 19 0
Peavey Lake 20 17 0
Pike Lake 9 4 0
Powderhorn Lake 67 18 0
Silver Lake 78 11 0
South Long Lake 149 5 0
Spring Lake 32 32 20
Sweeney Lake 44 6 0
Tanners Lake 128 29 0
Thompson Lake 18 2 0
Valentine Lake 76 38 0
Wirth 68 17 0


This graph shows a Comparison of Impaired Streams in the TCMA 2003-2013
Comparison of Impaired Streams in the TCMA 2003-2013

Number of days with stream samples exceeding the chronic and acute criterion in the TCMA, 2003-2013
Link to this table

Stream Number of Individual Days with Samples Number of Days with Samples Exceeding 230 mg/L Chronic Criterion Number of Days with Samples Exceeding 860 mg/L Acute Criterion
Bass Creek 26 8 2
Bassett Creek 273 35 0
Battle Creek 366 39 10
Elm Creek 209 20 14
Judicial Ditch 2 45 9 0
Minnehaha Creek 1,281 242 12
Nine Mile Creek 304 40 1
Raven Stream 48 11 0
Raven Stream, East Branch 39 7 0
Rush Creek, South Fork 87 14 0
Sand Creek (includes AUIDs: 07020012-513 and 07020012-662) 389 19 0
Shingle Creek 330 66 15
Unnamed creek (Headwaters to Medicine Lk) 27 8 0
Unnamed creek (Unnamed ditch to wetland) 35 33 0
Unnamed Stream (Unnamed lk 62-0205-00 to Little Lk Johanna) 6 3 1



Chloride Source Summary

Chloride enters the TCMA lakes, streams, wetlands, and groundwater from a variety of sources. A conceptual model diagram of the primary anthropogenic sources is shown in Figure 7. A study of chloride fate and transport in the TCMA estimated that approximately 22%-30% of the chloride applied in the TCMA was exported out of the TCMA via streamflow in the Mississippi, Minnesota, and St. Croix Rivers (Stefan et al., 2008). Therefore, 70%-78% of the applied percentage retained in the TCMA suggests that chloride may continue to accumulate locally and eventually make its way to the deep aquifers. This implies that, on average, chloride concentrations in the TCMA waterbodies are increasing with time. If the chloride loading remains steady, the concentrations will level out when equilibrium develops between loadings and transport out of the TCMA. By the same token, if loadings are reduced sufficiently and persistently, the chloride concentrations in TCMA waterbodies will begin to decrease and will continue to decrease until a new equilibrium is reached. Each of the sources in Figure 7 is briefly described below.chloride was estimated to remain in the TCMA soils, lakes, wetlands, and groundwater. Since chloride does not break down, this potentially high


This image shows a Conceptual model of anthropogenic sources of chloride and pathways
Conceptual model of anthropogenic sources of chloride and pathways


Permitted Sources

Municipal Separate Storm Sewer System (MS4) Winter Maintenance Activities

Winter maintenance activities include snow and ice removal. Application of deicing and anti-icing chemicals, primarily salt, is common. Salt is applied to a variety of surfaces such as roads, parking lots, driveways, and sidewalks. The chemical properties of sodium chloride, most commonly salt, make it effective at melting ice, but these properties also result in chloride dissolving in water and being transported with snow melt and stormwater runoff to lakes, streams and wetlands. The dissolved chloride moves with the melted snow and ice, during melting events, and ends up in the local water resources. Because salt is typically applied on impervious surfaces during frozen ground conditions, the snow melt and stormwater runoff carrying the chloride has little opportunity to infiltrate and the majority will flow overland into local surface waters. However, chloride laden runoff that does infiltrate will enter shallow groundwater eventually and either flow via subsurface flow into local surface waters or into deep aquifers. Runoff from salt storage facilities is another potential source of salt. Chloride sources related to runoff from winter maintenance activities are largely covered under the MS4 permitting program. The St. Anthony Falls Laboratory at the University of Minnesota (UMN) developed an inventory of road salt uses in the TCMA for the MnDOT (Sander et al., 2007). The inventory estimated the total amount of road salt used for winter maintenance activities in the TCMA to be 349,000 tons per 17 year. Estimates of use by various entities included: cities ~ 33%; MnDOT ~ 23%; counties ~ 20%; commercial operators ~ 19%; and packaged ~ 5%.

Roads

The TCMA is estimated to have over 26,000 lane miles of roadways (Sander et al., 2007). Based on salt purchasing records and number of lane miles for the MnDOT, counties, and cities in the TCMA, the application rates range from 3 – 35 tons of road salt per lane mile per year (Wenck, 2009). These TCMA application rate estimates are consistent with national estimates of 10 to 30 tons per lane mile per winter season (Mullaney, 2009).

A survey of municipal winter maintenance professionals in the TCMA, found that typical application rates range from 100 to 600 lbs. of salt applied per lane mile per event, which is consistent with previous evaluations of road salt application rates (LimnoTech, 2013). However, rates can be much higher on hills, near intersections, and other ice problem areas. Higher speed roadways will typically have higher salt application rates. Some events may require multiple passes of salt application and increase the application rate per event.

A list of MS4 permittees within each impaired watershed area is included in Appendix A-2.

Parking Lots, Driveways, and Sidewalks

MS4s also provide winter maintenance on parking lots, driveways, and sidewalks. Estimates of application rates for this source are shown in more detail in Section 3.8.1.

Municipal and Industrial Wastewater Sources

Municipal wastewater, backwash from municipal water treatment facilities, and industrial facilities with waste streams may contain chloride. The concentration of chloride present in the waste stream will vary for every facility and is dependent on the source of chloride. The major source of chloride to municipal wastewater treatment plants (WWTP) is from residential water softeners (>90% in some municipalities). Industrial facilities may discharge directly to surface waters following treatment, or may discharge to a sanitary sewer system which transports the wastewater to a WWTP for further treatment prior to discharge to surface water. A range of industrial facilities discharge directly to waters impaired by chloride. These include food processing facilities, manufacturing, pipeline terminals, biofuel facilities, and groundwater treatment systems. Discharge of chloride from municipal and industrial wastewater sources are covered by individual or general permits. Monitoring data for theWWTP are not widely available at this point in time. However, chloride concentrations in the WWTP effluent for three WWTPs in the Sand Creek impaired watershed average from 521 mg/L to 618 mg/L.

A list of National Pollutant Discharge Elimination System (NPDES) wastewater dischargers and chloride allocations within each impaired watershed area is included in Appendix A-3 and Appendix A-4, respectively. They include both individual permits (denoted by NPDES permit numbers with an MN00 prefix) and general permits (denoted by an MNG prefix). The MNG25 general permit covers untreated noncontact cooling water discharges. The MNG255 general permit covers treated noncontact cooling water discharges. The MNG64 general permit covers water treatment facility filter backwash discharges. Individual industrial permits include discharges of noncontact cooling water, geothermal cooling water, reverse osmosis reject water, industrial process water and industrial stormwater.