TCMA Chloride TMDL - Watershed and Waterbody Characterization Revision as of 16:42, 16 May 2016 by PLeegar (talk | contribs)(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff) TCMA Chloride TMDL - Watershed and Waterbody Characterization

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.

Land use in the TCMA

Chloride Impairments and Road Density in the TCMA

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.

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

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

Conceptual model of anthropogenic sources of chloride and pathways