__________________________________________________________________________________________

MINNESOTA IOWA WISCONSIN

Karst Evaluation:

Proposed Lake Zumbro Dredge Disposal Site T108N R13W Section 7 SW ¼ Farmington Township, Olmsted County, Minnesota

Prepared for: Mr. Nathan Anderson, P.E. WHKS & Co.

March 2, 2018 12074.17.MNR

Chosen Valley Testing

C

V T

______________________________________________________________________________________________________ Minnesota Iowa Wisconsin

Chosen Valley Testing, Inc. Geotechnical Engineering and Testing • 1410 7th Street N.W. • Rochester, MN 55904 • Telephone (507) 281-0968 • Email rochester@cvtesting.com Mr. Nathan Anderson, P.E. March 2, 2018 WHKS & Co. 2905 South Broadway Rochester, MN 55904 nanderson@whks.com Re: Karst Evaluation Proposed Lake Zumbro Dredge Disposal Site T108N R13W Section 7 SW ¼ Farmington Township, Olmsted County, Minnesota CVT Project Number: 12074.17.MNR Dear Mr. Anderson, As authorized, a karst survey has been performed around the Lake Zumbro Dredge Disposal Site near Rochester, Minnesota. The karst walk survey was performed on December 19, 2017. This brief letter, along with the attached karst survey sheets, describes our findings. Background and Scope

The proposed project consists of the construction of two sediment basins on the property in Farmington Township, Olmsted County, Minnesota. Our scope consisted of reviewing available geologic data and performing a walk-over survey of the site to investigate for potential karst features. Chosen Valley Testing performed fourteen standard penetration test borings at the site on January 9 and 10, 2018 to investigate subsurface soil and rock conditions across the site. The borings generally encountered about 1 to 7½ feet of topsoil over loessial clays and silts to approximately 4 to 17 ½, followed by glacial clays to around 10 ½ to 21 feet, until coming across and terminating within weathered dolomite and sandstone roughly 11 to 21 ½ feet below the surface with a few exceptions. A couple of berm area borings on the east side of sediment basin #2 met gravel and residual/weathered dolomite and sandstone following about 1 to 2 feet of topsoil, until terminating due to auger refusal around 4 to 6 feet. Another sediment basin #2 pool area boring met loessial clay to about 16 ½ feet over residual sandstone to approximately 19 feet where the boring was terminated due to auger refusal, presumably on bedrock. A boring in sediment basin #1 terminated in glacial clay around a planned depth of 31 feet below the surface. Area of Investigation

The karst investigation was performed around the proposed Lake Zumbro Dredge Disposal Site located in T108N, R13W, Section 7, SW ¼. This is located in Farmington Township, Olmsted County, Minnesota.

Lake Zumbro Dredge Disposal Site March 2, 2018 Project#: 12074.17.MNR Page 2

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Summary of Desktop Findings

Available aerial imagery, topographic data, geologic data, and soil survey data were reviewed. Based on the Olmsted County Surficial Geology Map, the dominant soil types in the area consist of loessial (wind deposited) clays and silts overlying glacial till deposited mixtures of clay, silt, and sand. Based on the County Bedrock Geology Map the underlying bedrock consists primarily of dolomite and sandstone with minor amounts of shale of the Prairie Du Chien Group. The geological information is illustrated in the attached “Surficial Geology Sketch” and “Bedrock Geology Sketch”. The attachment labeled “Sinkhole Probability Sketch” shows the location of the site, approximate area of the sediment basins, and the published karst features. As shown on this sketch, the site is located within a low-moderate sinkhole probability area and with a portion of the north end of the site being considered a low sinkhole probability area. The closest published karst features are sinkholes about 1 mile north, east, and west of the site. Summary of Site Findings

The karst walk survey was performed on December 19, 2017. The area investigated consisted of the east ½ of the southwest ¼ of Section 7 in Farmington Township, Olmsted County, Minnesota. The site primarily consisted of farm fields with harvested corn stalks on the order of 1-foot tall or less. A grass covered waterway runs southwest to northeast through the south-central part of the site. The grass was mostly on the order of 1 to 2 feet tall. A large granite boulder was found along this water way along with a few trees. Trees also existing along the east tree line and along a few steep slopes in the central and northern parts of the site. Granite cobbles were also observed along the fence lines and in the wooded areas, which appear to be the remnants of glacial deposits. However, some dolomite cobbles and rocks were observed along the edge of the small woodland in the northeast part of the site, indicating bedrock was likely very shallow is this area. The weather weeks prior to the site visit had consisted of seasonally warm temperatures at the beginning of the month and then seasonal temperatures around freezing the week leading up to the site visit. Precipitation totals were below average with a couple light rain falls and one snow flurry in the two to three weeks prior to the site visit. During our karst walk no obvious karst feature characteristics (i.e. depressions, disappearing streams/stream sinks, blind valleys, karst windows, or caves) were observed on site. As previously mentioned, dolomite cobbles were observed along the edge of the small woodland area in the northeast portion of the site where the north Sediment Basin No. 2 berm is planned to be constructed over, indicating the site is in karst terrain. This is further supported by the majority of soil borings which terminated on shallow bedrock. Analysis

Based on the results of our desktop study and our subsequent reconnaissance of the site, no obvious karst features were observed on site and no published karst features are known to exist within a ½ mile radius of the site. The property is located within karst terrain but published sinkhole probability maps label the site as to being within low-moderate sinkhole probability area and with a portion of the north end of the site being considered a low sinkhole probability area. The lack of karst features within the planned project area can also be attributed to surficial geology, which includes a protective layer of glacial clay deposits over most of

Lake Zumbro Dredge Disposal Site March 2, 2018 Project#: 12074.17.MNR Page 2

______________________________________________________________________________________________________ Minnesota Iowa Wisconsin

the area, protecting the underlying rock from surface water. The impoundment of water is understood to be temporary and the filling operation is expected to result in the addition of deeper protective sediments throughout the process. Level of Care

The services provided for this project have been conducted in a manner consistent with that level of care and skill ordinarily exercised by members of the profession currently practicing in this area, under similar budget and time constraints. This is our professional responsibility. No other warranty, expressed or implied, is made. Remarks

CVT appreciates the opportunity to serve you. If you have any questions about our findings, please feel free to contact us at (507) 281-0968.

Sincerely, Chosen Valley Testing, Inc.

Devin M. Ehler, PE Geotechnical Engineer

Colby T. Verdegan, PE Sr. Geotechnical/Materials Engineer

Karst Features Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

1. Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA,

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Lidar Sketch

¯0 1,000 2,000500 Feet

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. DEM03HS - Hillshade of DEM03, November 18-24, 2008;Minnesota Geospatial Information Office;http://www.mngeo.state.mn.us/chouse/metadata/lidar_semn2008.html2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Surficial Geology Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Hobbs, Howard C. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A,Plate 3 - Surficial Geology.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Surficial Geology

Project Location

Bedrock Geology Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Olsen, Bruce M. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A, Plate 2 - Bedrock Geology.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Bedrock Geology

Project Location

Sinkhole Probability Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Alexander Jr., E. Calvin and Maki, Geri L. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A, Plate 7 - Sinkhole Probability.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Sinkole Probability

Project Location

__________________________________________________________________________________________

MINNESOTA IOWA WISCONSIN

Supplemental Karst Evaluation:

Proposed Lake Zumbro Dredge Disposal Site T108N R13W Section 7 SW ¼ Farmington Township, Olmsted County, Minnesota

Prepared for: Mr. Nathan Anderson, P.E. WHKS & Co.

May 18, 2018 12074.17.MNR

Chosen Valley Testing

C

V T

______________________________________________________________________________________________________ Minnesota Iowa Wisconsin

Chosen Valley Testing, Inc. Geotechnical Engineering and Testing • 1410 7th Street N.W. • Rochester, MN 55904 • Telephone (507) 281-0968 • Email rochester@cvtesting.com Mr. Nathan Anderson, P.E. May 18, 2018 WHKS & Co. 2905 South Broadway Rochester, MN 55904 nanderson@whks.com Re: Supplemental Karst Evaluation Proposed Lake Zumbro Dredge Disposal Site T108N R13W Section 7 SW ¼ Farmington Township, Olmsted County, Minnesota CVT Project Number: 12074.17.MNR Dear Mr. Anderson, As authorized, a supplemental karst survey has been performed around the Lake Zumbro Dredge Disposal Site near Rochester, Minnesota. The initial karst walk survey was performed on December 19, 2017 and the supplemental karst walk survey was performed on May 3, 2018. This brief letter, along with the attached karst survey sheets, describes our findings. Background and Scope

The proposed project consists of the construction of two sediment basins on the property in Farmington Township, Olmsted County, Minnesota. Our scope consisted of reviewing available geologic data and performing a walk-over survey of the site to investigate for potential karst features. During a meeting with the Minnesota Department of Natural Resources (MN DNR) and WHKS on May 1, 2018, we were informed that Mr. Jeff Green of the MN DNR review of LIDAR mapping suggested the possible existence of a terminal sinkhole on the south end of the property, about 150 feet north of the culvert crossing White Bridge Road NE. It was requested that this location and the tree/vegetative covered hillside at the primary spillway/berm for sediment basin #2 be revisited. It was also requested that additional borings be performed at the north berm of sediment basin #2 as data was lacking in that location. Chosen Valley Testing performed fourteen standard penetration test borings at the site on January 9 and 10, 2018 to investigate subsurface soil and rock conditions across the site. Four additional borings were performed on May 3, 2018 to supplemental exploration with two of the borings along the north berm of the sediment basin #2, on in the northern pool area of sediment basin #2, and the last boring drilled at the location of the possible terminal sink. The borings generally encountered about 1 to 7½ feet of topsoil over loessial clays and silts to approximately 4 to 17 ½, followed by glacial clays to around 10 ½ to 21 feet, until coming across and terminating within weathered dolomite and sandstone roughly 11 to 21 ½ feet below the surface with a few exceptions. Three of the berm area borings on the east and northeast side of sediment

Lake Zumbro Dredge Disposal Site May 18, 2018 Project#: 12074.17.MNR Page 2

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basin #2 met gravel and residual/weathered dolomite and sandstone following about 1 to 2 feet of topsoil, until terminating due to auger refusal around 4 to 6 feet. Another sediment basin #2 east berm area boring met loessial clay to about 16 ½ feet over residual sandstone to approximately 19 feet where the boring was terminated due to auger refusal, presumably on bedrock. A boring in sediment basin #1 terminated in glacial clay around a planned depth of 31 feet below the surface. The terminal sink additional boring encountered about 1 ½ feet of topsoil over loessial clay to an approximate depth of 6 ½ feet over alluvial clay with sand to roughly 10 ½ feet, where silty sand with gravel was met to around 11 feet when weathered dolomite was met. Area of Investigation

The karst investigation was performed around the proposed Lake Zumbro Dredge Disposal Site located in T108N, R13W, Section 7, SW ¼. This is located in Farmington Township, Olmsted County, Minnesota. Summary of Desktop Findings

Available aerial imagery, topographic data, geologic data, and soil survey data were reviewed. Based on the Olmsted County Surficial Geology Map, the dominant soil types in the area consist of loessial (wind deposited) clays and silts overlying glacial till deposited mixtures of clay, silt, and sand. Based on the County Bedrock Geology Map the underlying bedrock consists primarily of dolomite and sandstone with minor amounts of shale of the Prairie Du Chien Group. The geological information is illustrated in the attached “Surficial Geology Sketch” and “Bedrock Geology Sketch”. The attachment labeled “Sinkhole Probability Sketch” shows the location of the site, approximate area of the sediment basins, and the published karst features. As shown on this sketch, the site is located within a low-moderate sinkhole probability area and with a portion of the north end of the site being considered a low sinkhole probability area. The closest published karst features are sinkholes about 1 mile north, east, and west of the site. Summary of Site Findings

The initial karst walk survey was performed on December 19, 2017 and a supplemental karst walk of the entire site was re-performed on May 3, 2018. The area investigated during the initial and supplemental site visits consisted of the east ½ of the southwest ¼ of Section 7 in Farmington Township, Olmsted County, Minnesota. The site primarily consisted of farm fields with harvested corn stalks on the order of 1-foot tall or less. A grass covered waterway runs southwest to northeast through the south-central part of the site. The grass was mostly on the order of 1 to 2 feet tall. A large granite boulder was found along this water way along with a few trees. Trees also existing along the east tree line and along a few steep slopes in the central and northern parts of the site. Granite cobbles were also observed along the fence lines and in the wooded areas, which appear to be the remnants of glacial deposits. However, some dolomite cobbles and rocks were observed along the edge of the small tree and vegetative “island” in the northeast part of the site, indicating bedrock was likely very shallow is this area. The possible terminal sink location was revisited and water was seen flowing from the culvert through the scoured waterway which was approximately ½-foot deeper than the surrounding ground surface until coming to a shallow field crossing where water was somewhat ponding in front of and cutting off the scoured drainage path. The run-off water passing the field crossing dissipated into the grass about 10 to 20 feet further to the north until becoming visible again where draintiles were outletting into the waterway. No

Lake Zumbro Dredge Disposal Site May 18, 2018 Project#: 12074.17.MNR Page 2

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depressions, cavities, caves, sinkholes, or disappearing streams were observed. As a consequence of the closer review, the feature is not considered to be a terminal sink or other karst feature. The tree covered hillside on the northeast portion of the site which the DNR is concerned about was re-visited. As observed during our initial and supplement site visits, piles of granite and dolomite rocks were observed towards the edges of this wooded area but no rock outcrops, depressions, groundwater seepage, cavities, or caves were observed. The rock piles appear to be man-made and likely the result of farmers picking rocks out of their fields. The weather weeks prior to the initial site visit had consisted of seasonally warm temperatures at the beginning of December and then seasonal temperatures around freezing the week leading up to the site visit. Precipitation totals were below average with a couple light rain falls and one snow flurry in the two to three weeks prior to the site visit. The weather weeks prior to the supplemental site visit consisted of wetter than normal weather with frequent rain storms and seasonal temperatures. The day of the site visit was mostly sunny and temperatures in the upper 60 to lower 70 degrees Fahrenheit. During our karst walk no obvious depressions, disappearing streams/stream sinks, blind valleys, karst windows, or caves (i.e. karst feature characteristics) were observed on site. The site is however located within karst terrain as soluble bedrock was found within 50 feet of the surface in our boring explorations and the rock formations on site are known to be fractured and associated with sinkholes in other areas. As previously mentioned, dolomite cobbles were observed along the edge of the small woodland area in the northeast portion of the site where the north Sediment Basin No. 2 berm is planned to be constructed over, indicating the site is in karst terrain. This is further supported by the majority of soil borings which terminated in soluble bedrock within 50 feet of the surface and the rock formations on site are known to be fractured and associated with sinkholes in other areas. Analysis

Based on the results of our desktop study and our subsequent reconnaissance of the site, no obvious depressions, disappearing streams/stream sinks, blind valleys, karst windows, or caves (i.e. karst feature characteristics) were observed on site and no published karst features are known to exist within a ½ mile radius of the site. The property is located within karst terrain but published sinkhole probability maps label the site as to being within low-moderate sinkhole probability area and with a portion of the north end of the site being considered a low sinkhole probability area. The lack of karst features within the planned project area can also be attributed to surficial geology, which includes a protective layer of glacial clay deposits over most of the area, protecting the underlying rock from surface water. The impoundment of water during the dredging settlement process is understood to be only over the period of months and that the filling operation is expected to result in the addition of sediment over the bedrock increasing the drainage path required to reach and dissolve the karst susceptible bedrock on site. A clay liner is further recommended in our geotechnical report to increase protection from seepage water reaching the bedrock.

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Level of Care

The services provided for this project have been conducted in a manner consistent with that level of care and skill ordinarily exercised by members of the profession currently practicing in this area, under similar budget and time constraints. This is our professional responsibility. No other warranty, expressed or implied, is made. Remarks

CVT appreciates the opportunity to serve you. If you have any questions about our findings, please feel free to contact us at (507) 281-0968.

Sincerely, Chosen Valley Testing, Inc.

Devin M. Ehler, PE Geotechnical Engineer

Colby T. Verdegan, PE Sr. Geotechnical/Materials Engineer

Karst Features Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

1. Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA,

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Lidar Sketch

¯0 1,000 2,000500 Feet

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. DEM03HS - Hillshade of DEM03, November 18-24, 2008;Minnesota Geospatial Information Office;http://www.mngeo.state.mn.us/chouse/metadata/lidar_semn2008.html2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Surficial Geology Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Hobbs, Howard C. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A,Plate 3 - Surficial Geology.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Surficial Geology

Project Location

Bedrock Geology Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Olsen, Bruce M. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A, Plate 2 - Bedrock Geology.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Bedrock Geology

Project Location

Sinkhole Probability Sketch

¯0 10.5 Miles

Legend

Sediment Basin Areas

300 ft Radius of Basins

1,000 ft Radius of Basins

1/2 Mile Radius of Basins

# Published Sinkhole

Y Published Stream sink/sieve

A

Published Spring

A

Published Spring - not field checked

C Chosen Valley Testing, Inc.

V T

1. Alexander Jr., E. Calvin and Maki, Geri L. (1988). University of MinnesotaGeological Survey, County Atlas Series, Altas C-3, Part A, Plate 7 - Sinkhole Probability.2. University of Minnesota, Department of Geology and Geophysics; Minnesota DNR - Division of Waters: Karst FeatureInventory Data Points - http://deli.dnr.state.mn.us/

Proposed Lake Zumbro Dredge Disposal SiteT108N R13W Section 7 SW ¼

Farmington Twp, Olmsted Co, Minnesota12074.17.MNR

Sinkole Probability

Project Location