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8.b2 Pittman Variance - CC Packet1 | P a g e
Date of Meeting: July 18, 2023
To: Members of the City Council
From: T.J. Hofer, Consultant City Planner
Trey Rouse, Consultant Planner
Re: Variance for PID 31.032.20.11.0032
Applicant: Craig and Beth Pittman Zoning: Rural Residential Neighborhood
Shoreland Management Overlay
Owner: Craig and Beth Pittman Future
Land Use: Rural Mixed Use
Location: PID 31.032.20.11.0032 Review
Deadline August 7, 2023
The applicant is requesting approval for a variance to allow the demolition of a current structure
located on the northwest part of the property to reconstruct an accessory structure and add an
accessory dwelling unit (ADU) above the structure. The ADU is not a part of the variance but
will be handled administratively through the city. The replacement would also rotate the
structure so that the overhead garage doors face Langley Avenue. This requires a variance
because of the setback from the property line and the structure is located on a legal non-
conforming lot within the RR-N – Rural Residential Neighborhood and Shoreland Overlay
District.
The Unified Development Code (UDC) permits either the alteration or replacement of an
accessory structure on a property that does not exceed 50% of the value of the structure and is
the minimal action required to address the structure.
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BACKGROUND
The existing site consists of a parcel zoned as Rural Residential Neighborhood (RR-N). The
parcel is distinguished as follows:
PID 31.032.20.11.0032
Lot Area (acres) 0.17
Zoning Rural Residential Neighborhood (RR-N)
Shoreland Management Overlay (SM-O)
The existing lot is legally nonconforming
as the existing zoning, Rural Residential
Neighborhood and Shoreland Ordinance
requires a minimum lot size of 2.5 acres.
The existing accessory structure does not
meet the rear yard setback.
The applicant met with staff before the
application was submitted to discuss the
process. Staff noted that the minimal action
needs to be addressed and that an alteration
could be the most minimal action to
alleviate the practical difficulties on the
property. The applicant detailed conditions
that establish why alteration was not a
feasible option based on the condition of
the structure. Staff concurred that replacement is a reasonable action in this case. No changes to
the lot are proposed.
The parcel is guided Rural Mixed Use on the 2040 Future Land Use map. The entirety of the site
is used for residential purposes. Big Marine Lake is located east of the parcel, but the parcel is
non riparian, and the existing structures conform with the setback required for the ordinary high
water level.
Adjacent parcels to the site are zoned RR-N – Rural Residential Neighborhood and are either
vacant or used for single family dwellings.
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EVALUATION OF REQUEST
Variance
Lot Standards
The dimensions of the lot compared to the RR-N dimensional standards are as follows:
Table 1: Zoning District Standards
RR-N Lot
Minimum Lot Size (ac.) 2 0.17
Minimum Lot Width (ft.) 150 50
Buildable Area One acre 0.047 acres
Setbacks (ft.)
Front 40 50
Side 10 9
Rear 50 20
Maximum Lot Coverage 25% 25%
The lot does not meet the dimensional standards for minimum lot size or rear yard setback for
the detached accessory structure, but otherwise conforms with the RR-N and SM-O standards.
Streets, Access, and Parking
Access on the site spans the entirety of the western lot line. No change will be made to the street
access that connects to the property.
The driveway will be altered to accommodate the reconstructed garage facing Langly Ave.
Landscaping
The current driveway will be remediated as a grass yard. The applicant will also be required to
install a rain garden to meet the requirements of the Carnelian-Marine-St. Croix Watershed
District.
Architectural Design Standards.
The proposed reconstructed garage and ADU must match or complement the main structure on
the property.
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Variance Standards
The variance would allow for the replacement of the detached garage (accessory structure in the
proposed site plan) along with the shifting of the location of the current driveway to match the
replacement of the detached garage. This variance is required due to the property being a legal
non-conforming lot and the existing structure being a legal nonconforming structure due to a rear
yard setback encroachment. The replacement of the detached garage will also include the
addition of an Accessory Dwelling Unit (ADU) above it. Every parcel within the City is allowed
one ADU.
The Rural Residential Neighborhood (RR-N) Base Zoning District is described as:
Lands zoned RR-N are the parcels adjoining, abutting, or a portion of which are within 1,000
feet of a lake with a public waters designation that were historically platted or divided into
smaller lots for seasonal use. The use of these lots has generally transitioned to permanent
year-round use with predominantly principal residential uses. Most parcels and lots in the
RR-N District are at least 50% contained within the Shoreland Management Overlay (SM-O)
District. In addition to the standards identified in this Section, the lots or parcels are subject
to the regulations contained within Chapters 155 of the City Code and the Washington
County St. Croix River District standards which are incorporated by reference here in. Land
zoned RR-N are guided Agricultural Core and General Rural in the Comprehensive Plan.
The proposed variance meets the description and purpose of the district. Meeting the purpose and
intent of the Zoning District is necessary for the variance to be approved.
The Shoreland Management Overlay District is described within the Shoreland Ordinance for
non-conforming lots and structures present on lots within this district. This lot is non-conforming
based on the standards of the Shoreland Management Overlay District to complete the proposed
detached garage construction must adhere to the following section(s) of the Shoreland
Management Ordinance:
3.72 All additions or expansions to the outside dimensions of an existing nonconforming
structure must meet the setback, height, and other requirements of Sections 5.0 to 8.0 of
this ordinance. Any deviation from these requirements must be authorized by a variance.
Criteria for the variance for the replacement of the detached garage must meet Chapter
153.500.110 of the Unified Development code for nonconforming buildings and structures
stating:
(A) Replacement. A lawful nonconforming structure which is removed, destroyed or altered
by any means to the extent that the cost of repair or replacement would exceed fifty
percent (50%) of the Assessed Value of the original structure shall not be replaced,
except in conformity with this Chapter. If a replacement structure cannot be placed on
the lot meeting all current standards, the variance procedure must be followed. For the
purposes of this Chapter, the term “Assessed Value” shall mean the market value of the
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property as determined by the current records of the City Assessor for the year in which
the damage was done.
Section 153.500.060 Subd. 1 (B) establishes the standards for when the City shall approve a
variance. The variance must be consistent with the Comprehensive Plan, must be in harmony
with the general purpose and intent of this Chapter, and when the strict enforcement of this
Chapter would result in practical difficulties with carrying out the strict letter of the Code.
Practical difficulties are established within the UDC and are listed below in italics. Staff’s
analysis of these is below each practical difficulty:
a. The applicant proposes to use the property in a reasonable manner not permitted by this
Chapter.
The proposed use is a reasonable use for the RR-N zoning district. A garage and
accessory dwelling unit are both permitted accessory uses within the RR-N District.
b. The plight of the landowner is due to circumstances unique to the property not created by
the landowner.
While the landowner is voluntarily replacing the detached accessory structure, the
existing structure has structural issues that alterations would not be able to address in
order for the landowner to achieve the reasonable use proposed. Additionally, no other
reasonable alternative exists. While the landowner could relocate the structure to be an
attached accessory structure, the structure would still be nonconforming as it would
encroach into the rear yard setback.
c. The variance, if granted, will not alter the essential character of the locality.
If the variance were granted, it would not alter the essential character of the locality .
d. Economic conditions alone shall not constitute practical difficulties.
The practical difficulties are not solely based on economic conditions.
e. May include, but is not limited to, inadequate access to direct sunlight for solar energy
systems.
The variance is not related to inadequate access to direct sunlight for solar energy
systems.
f. The proposed variance will not impair an adequate supply of light and air to adjacent
property, or substantially increase the congestion of the public streets, or increase the
danger of fire, or endanger the public safety, or substantially diminish or impair property
values within the neighborhood.
6 | P a g e
The proposed variance will not impair adequate supply of light and air to adjacent
property, or substantially increase the congestion of the public streets, or increase the
danger of fire, or endanger the public safety, or substantially diminish or impair property
values within the neighborhood.
g. The requested variance is the minimum action required to eliminate the practical
difficulty
Replacement of the structure is the minimal reasonable action required to eliminate the
practical difficulty. Other alternatives would result in nonconformities and the applicant
has established that structural issues exist that prevent alteration from being a viable
option.
ANALYSIS
Review Comments
The submittal was sent to city staff and other regulatory agencies for review and comment.
Carnelian-Marine-St. Croix Watershed District
The Carnelian-Marine-St. Croix Watershed District has provided comments and the comments
pertain to the following requirements:
1. Stormwater management for volume and rate control of all new/reconstructed
impervious surfaces. Total surfaces to be provided and shown in site plan.
2. Stormwater routing to management practice. Greater than 80% of new or reconstructed
surfaces must be captured. Routing to be clearly outlined in site plan.
3. Erosion and sediment control plans include construction sequencing, entrance, and
controls down gradient of all disturbed sediments. Locations shall be shown in the site
plan.
4. Site revegetation plans for all disturbed sediments. Must achieve 70% uniform
distribution. Site plan commenting required.
Engineering Department
The Engineering Department provided the following comments:
1. If the new detached garage is to be built on the same footprint as the previous, then the
setback from the lake must be maintained.
2. If a significant change is made then a grading permit will be needed, if on the same
footprint then this isn’t applicable.
3. No drainage issues were seen on the property.
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Public Works Department
The Public Works Director provided the following comments:
1. Applicant shall provide plans which include the connection to the existing septic tank on
the property.
2. Tank sizing shall be evaluated by the County to ensure proper sizing compared to the
total number of bedrooms: which includes the existing home and additional living space.
3. If tank size is determined to be undersized – new tank and pump installation will be
required at homeowner’s expense.
Washington Conservation District
Washington Conservation District provided no comment.
Washington County
Washington County provided no comment.
Fire Department
The Fire Chief had no comment.
Department of Natural Resources
The DNR Area Hydrologist provided no comment.
Planning Commission
The application was reviewed by the Planning Commission at their July 11, 2023 meeting. The
Planning Commission held a public hearing where one written comment was received in support
of the project. The Planning Commission then closed the public hearing.
The Planning Commission discussed the project and stated that the variance was a reasonable
action and that based on their site visit, the roof appeared to be a safety concern.
The Planning Commission moved to recommend approval of the variance. The motion was
approved with a vote of 5-0.
Staff Analysis
Staff finds that the proposed plan is generally consistent with the Comprehensive Plan and
Zoning Ordinance. Where the plan is not consistent, staff has included conditions to bring the
proposal into compliance.
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Staff believes that the proposal for the variance is generally in compliance with the requirements
outlined within the UDC. The variance is consistent with the future land use shown in the 2040
Comprehensive Plan and the proposed use meets the definition of the RR-N zoning district.
Staff has reviewed the plan for consistency with the applicant standards outlined in the
Comprehensive Plan, Zoning Ordinance, and Subdivision Ordinance. Staff noted in the staff
report the outstanding issues that must be addressed and have included conditions in the attached
resolution to address these issues. The City Council may recommend modifications to these
conditions.
COUNCIL ACTION
The City Council can do one of the following:
1. Approve the variance request, with or without conditions, of the attached ordinance and
resolutions.
2. Deny the variance request, with findings, of the attached ordinance and resolutions.
3. Table the request for further review/study.
RECOMMENDATION
The Planning Commission recommends that the City Council approve the request for variance
for the property noted as 18794 Layton Avenue N, Scandia, MN, 55047. Approval includes an
ordinance and resolution. The following findings are recommended:
1. The proposed use is a reasonable use for the RR-N zoning district. A garage and
accessory dwelling unit are both permitted accessory uses within the RR-N District.
2. While the landowner is voluntarily replacing the detached accessory structure, the
existing structure has structural issues that alterations would not be able to address in
order for the landowner to achieve the reasonable use proposed. Additionally, no
other reasonable alternative exists. While the landowner could relocate the structure
to be an attached accessory structure, the structure would still be nonconforming as it
would encroach into the rear yard setback.
3. If the variance were granted, it would not alter the essential character of the locality.
4. The practical difficulties are not solely based on economic conditions.
5. The variance is not related to inadequate access to direct sunlight for solar energy
systems.
6. The proposed variance will not impair adequate supply of light and air to adjacent
property, or substantially increase the congestion of the public streets, or increase the
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danger of fire, or endanger the public safety, or substantially diminish or impair
property values within the neighborhood.
7. Replacement of the structure is the minimal reasonable action required to eliminate
the practical difficulty. Other alternatives would result in nonconformities and the
applicant has established that structural issues exist that prevent alteration from being
a viable option.
The following conditions are recommended:
1. The reconstructed detached garage and accessory dwelling unit shall be in substantial
compliance with the site plan reviewed with this application, subject to conditions.
2. Prior to a building permit being issued:
a. Proof of recording must be provided for all relevant documents.
b. A site plan that shows the driveway relocated to comply with all required
setbacks, including side yard setback and wetland setback shall be submitted.
c. An administrative permit for the accessory dwelling unit must be acquired.
3. The applicant shall acquire any required permits from the Carnelian-Marine-St. Croix
Watershed District and comply with their requirements.
4. The applicant shall secure any other applicable Federal, State, County, and local
permits required for the project.
5. The applicant shall pay all fees and escrows associated with this application.
Attachments
1. Resolution No. 07-18-23-04
2. Zoning Map
3. Future Land Use Map
4. Application
5. Certificate of Survey (Proposed Conditions)
6. Site Plan
7. Building Plans
8. Stormwater Management Worksheet
9. Drainage Overview Map
CITY OF SCANDIA, MINNESOTA
RESOLUTION NO. 07-18-23-04
APPROVING A VARIANCE FOR A REPLACEMENT OF A NONCONFORMING
ACCESSORY STRUCUTRE LOCATED AT PARCEL ID 31.032.20.11.0032
WHEREAS, Craig and Beth Pittman (the “applicants”), have requested and made an application
for a variance from ordinary means to replace a legally nonconforming structure on a
nonconforming lot on property identified as 18794 Layton Avenue North, legally described as
follows:
SUBDIVISION NAME BLISS PLAT 2ND DIVISION LOT 14 BLOCK 3
SUBDIVISION CD 91101; and
WHEREAS, the Planning Commission reviewed the Variance request at a duly noticed Public
Hearing on July 11th, 2023, and recommended that the City Council approve the request;
NOW, THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF
SCANDIA, WASHINGTON COUNTY, MINNESOTA, that it should and hereby does approve
the requested variances, based on the following findings:
1. The proposed use is a reasonable use for the RR-N zoning district. A garage and
accessory dwelling unit are both permitted accessory uses within the RR-N District.
2. While the landowner is voluntarily replacing the detached accessory structure, the
existing structure has structural issues that alterations would not be able to address in
order for the landowner to achieve the reasonable use proposed. Additionally, no
other reasonable alternative exists. While the landowner could relocate the structure
to be an attached accessory structure, the structure would still be nonconforming as it
would encroach into the rear yard setback.
3. If the variance were granted, it would not alter the essential character of the locality.
4. The practical difficulties are not solely based on economic conditions.
5. The variance is not related to inadequate access to direct sunlight for solar energy
systems.
6. The proposed variance will not impair adequate supply of light and air to adjacent
property, or substantially increase the congestion of the public streets, or increase the
danger of fire, or endanger the public safety, or substantially diminish or impair
property values within the neighborhood.
7. Replacement of the structure is the minimal reasonable action required to eliminate
the practical difficulty. Other alternatives would result in nonconformities and the
applicant has established that structural issues exist that prevent alteration from being
a viable option.
FURTHER BE IT RESOLVED that the following conditions of approval shall be met:
1. The reconstructed detached garage and accessory dwelling unit shall be in substantial
compliance with the site plan reviewed with this application, subject to conditions.
2. Prior to a building permit being issued:
a. Proof of recording must be provided for all relevant documents.
b. A site plan that shows the driveway relocated to comply with all required
setbacks, including side yard setback and wetland setback shall be submitted.
c. An administrative permit for the accessory dwelling unit must be acquired.
3. The applicant shall acquire any required permits from the Carnelian-Marine-St. Croix
Watershed District and comply with their requirements.
4. The applicant shall secure any other applicable Federal, State, County, and local permits
required for the project.
5. The applicant shall pay all fees and escrows associated with this application
Whereupon, said Resolution is hereby declared adopted on this 18 day of July 2023.
Christine Maefsky, Mayor
ATTEST:
Kyle Morell, City Administrator
71.
4
Legend
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This drawing is neither a legally recorded map nor a
survey and is not intended to be used as one. This
drawing is a compilation of records, information, and data
located in various city, county, and state offices, and other
sources affecting the area shown, and is to be used for
reference purposes only. The City of Scandia is not
responsible for any inaccuracies herein contained.
Disclaimer:
© Bolton & Menk, Inc - Web GIS 6/9/2023 10:33 AM
City Limits
Parcels (4/1/2023)
Lot Lines
Parks
Scandia_2022.sid
Red: Band_1
Green: Band_2
Blue: Band_3
Pittman Variance
Location Map
28
5.7
Legend
0 200 Feet
This drawing is neither a legally recorded map nor a
survey and is not intended to be used as one. This
drawing is a compilation of records, information, and data
located in various city, county, and state offices, and other
sources affecting the area shown, and is to be used for
reference purposes only. The City of Scandia is not
responsible for any inaccuracies herein contained.
Disclaimer:
© Bolton & Menk, Inc - Web GIS 6/9/2023 10:35 AM
City Limits
Parcels (4/1/2023)
Lot Lines
Parks
Shoreland Overlay
PUD Overlay
Lakes
Mining Overlay
Saint Croix River District
Zoning
Agricultural Core
Agricultural Preserves
Rural Residential General
Village Neighborhood
Rural Commercial
Rural Residential Neighborhood
Village Historic Core
Village Center
Industrial Park
Scandia_2022.sid
Red: Band_1
Green: Band_2
Blue: Band_3
Pittman Variance
Zoning Map
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© 2023 WIDSETH SMITH NOLTING & ASSOCIATES, INC.
PROPERTY DESCRIPTION: (per Warranty Deed Doc. No. 1272123)
Lot 14, Block 3, BLISS PLAT SECOND DIVISION, Washington County, Minnesota.
AND
The Southerly One-Half of Lot 5, Block 1, HOLIDAY BEACH, Washington County, Minnesota.
0
SCALE ( IN FEET )
10 20
CONCRETE SURFACE
LEGEND
BOUNDARY LINE
OHE OVERHEAD ELECTRIC
ELEC POLE
LOT LINE
RIGHT OF WAY LINE
SURVEY NOTES:
1.Orientation of this bearing system is based on the Washington County Coordinate System NAD83 (1986 adj.)
2.The address of the property is 18794 Layton Avenue N., Scandia, MN, 55047
PID No. 3103220110032
3.Property zoned as GR - General Rural and Shoreland Overlay (per City of Scandia Zoning Map)
Building Setbacks (per City of Scandia Development Code )
Front yard:40 Feet
Side yard:20 Feet
Rear yard:50 Feet
Big Marine Lake - Recreational Development - DNR Public Waters ID No. 82-52P
The building setback lines are not shown on the survey.
4.Total Acreage: 7,368 Sq. Ft. or 0.17 Acres.
5.Vertical Control: MNDOT "MARINE MNDT AZ MK" ELEV.=986.74 NAVD88
6.The purposes of this Certificate of Survey drawing, only Lot 14, Block 3, BLISS PLAT SECOND ADDITION, was
surveyed.
NO
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EXISTING IMPERVIOUS CALCULATIONS:
Total Area= 7,368 Sq. Ft.
Existing House : 1,141 Sq. Ft.
Existing Garage : 540 Sq. Ft.
Existing Concrete Surfaces : 617 Sq. Ft.
Existing Gravel Surface : 28 Sq. Ft.
TOTAL IMPERVIOUS : 2,326 Sq. Ft.
PERCENT IMPERVIOUS : 31.6%SEPTIC CLEANOUT
SEPTIC TANK LIDS
BITUMINOUS SURFACE
SEPTIC ALARM POST
VINYL FENCE
DENOTES A FOUND 1/2" OPEN
IRON PIPE MONUMENT
UNLESS OTHERWISE SHOWN
GRAVEL SURFACE
E
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ELEC METER
GAS METER
FILE NUMBER:
CHECKED BY:
DATE:
SCALE:
DRAWN BY:
I HEREBY CERTIFY THAT THIS SURVEY, PLAN, OR REPORT WAS PREPARED BY
ME OR UNDER MY DIRECT SUPERVISION AND THAT I AM A DULY LICENSED
LAND SURVEYOR UNDER THE LAWS OF THE STATE OF
DATE:LIC. NO.
DATE AMENDMENTS PREPARED FOR:BY CRAIG PITTMAN
MINNESOTA.
Shawn M. Kupcho L.S.6/6/23 49021
June 6, 2023
AS SHOWN
JMM
SMK
2023-10727
CERTIFICATE OF SURVEY
BUILDING WALL HATCH
STORM SEWER
MAILBOX
TREE DECIDUOUS
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© 2023 WIDSETH SMITH NOLTING & ASSOCIATES, INC.J:\Craig Pittman-48170\2023-10727\CADD\Civil\2023-10727_Site Plan.dwg Plotted by:Frank Brodeen 7/5/2023 11:40:19 AM
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PROPOSED IMPERVIOUS CALCULATIONS:
Total Area: 7,368 Sq. Ft.
Proposed House : 1,141 Sq. Ft.
Proposed Garage:: 540 Sq. Ft.
Proposed Concrete Surfaces:: 203 Sq. Ft.
Total Impervious : 1,884 Sq. Ft.
Percent Impervious : 25.6%
LEGEND
PROPOSED CONTOUR LINE1000
BUILDING WALL HATCH
DRAINAGE ARROW
PROPOSED ELEVATION
PROPOSED CONCRETE
SURFACE
PROPOSED ROCK
CONSTRUCTION EXIT
PROPOSED BIOROLLBIOBIO PROPOSED NATIVE TURF
ESTABLISHMENT MIX
(SEE NOTES BELOW FOR
DETAILS)
TURF ESTABLISHMENT NOTES:
Turf establishment for the proposed rain garden from the bottom elevation to the top of berm as shown on this sheet shall
be as follows:
Seed Mix: MnDOT Native Seed Mix 35-221
Fertilizer: MnDOT Fertilizer Type 4
Stabilizing Cover: Rolled Erosion Prevention Product Category 10
All other disturbed areas can use a non-native seed mix and an appropriate stabilizing cover or sod.
DRAINAGE NOTES:
Storm runoff from proposed garage roof to be routed to proposed rain garden via gutters or other methods.
BOUNDARY LINE
OHE OVERHEAD ELECTRIC
ELEC POLE
LOT LINE
RIGHT OF WAY LINE
SEPTIC CLEANOUT
SEPTIC TANK LIDS
SEPTIC ALARM POST
VINYL FENCE
DENOTES A FOUND 1/2"
OPEN IRON PIPE
MONUMENT UNLESS
OTHERWISE SHOWN
E
G
ELEC METER
GAS METER
STORM SEWER
MAILBOX
TREE DECIDUOUS
STORM DRAIN INLET
PROTECTION
CONSTRUCTION LIMITS
PROPOSED GRAVEL
SURFACE
CARNELIAN – MARINE – ST. CROIX WATERSHED DISTRICT
Emmons and Olivier Resources, Inc -1 - Jan 2023
Small Residential Project Stormwater Worksheet
This worksheet assists with determining sizing requirements for compliance with District Rule 2.4.1 for residential projects.
This worksheet shall accompany a site plan that includes location and sufficient stormwater routing to treat the majority
(~80%) of the site's impervious surfaces. Multiple raingardens may be needed.
Date _____________________ Project Address _____________________________________
Determine Water Quality and Volume Control Standard
STEP 1: Determine all Impervious Surfaces.
(a)Existing Impervious:________SF
(b)Existing Impervious Disturbed: ________SF
(c)Total Impervious (Existing + Proposed): ________SF
(d)New & Reconstructed Impervious: ________SF
STEP 3: Will Proposed Activity Trigger the District’s Redevelopment Criteria? (Check One)
Yes. If (b) > (a) × 50%, then stormwater management is required for all impervious onsite.
Use (c) in STEP 4.
No. If (b) < (a) × 50%, then stormwater management is required for new & reconstructed
impervious. Use (d) in STEP 4.
STEP 4: Determine the Treatment Volume Requirement.
________ (STEP 2 c or d) × (2.0 inches)** × (0.9) / 12 = ________ cubic feet (e)
** Substitute 2.8-inches if the BMP is located in a buffer (Rule 4.5.2(dii); Substitute 4.2-inches if the BMP is tributary to a landlocked basin (Rule 2.4.1(b).
1 Treatment volume requirements may be waived for private drives on residential lots at least 10 acres in size if the drive is bordered downgradient by vegetated open space or a vegetated filter strip with a minimum width of 5 feet and runoff does not discharge directly
to wetland, groundwater-dependent natural resource, or public water.
STEP 2: Quantify the Impervious Surfaces1.
“Impervious surface” as defined by the District is a compacted surface, or a surface covered with material (i.e.,
gravel, asphalt, concrete, Class 5, etc.) that increases the depth of runoff compared to natural soils and land cover.
Including but not limited to roads, driveways1, parking areas, sidewalks and trails, patios, decks, courts, pools,
roofed structures, and other structures. Permeable hard surfaces are considered impervious surfaces but may
receive treatment volume credit if designed in accordance with District guidance.
Please ensure all existing and proposed Impervious Surfaces are shown in submitted site plans and
accounted for in Step 2.
If greater than 50% of the existing impervious surfaces are disturbed all exisitng and proposed impervious surfaces are
required to receive treatment. If less than 50%, only new & reconstructed impervious surfaces are required to receive
treatment.
18794 Layton Avenue N, Scandia, MN 55047 7/5/2023
3,363
1,630
X
1,237
1,237 186
CARNELIAN – MARINE – ST. CROIX WATERSHED DISTRICT
Emmons and Olivier Resources, Inc -2 - Jan 2023
STEP 6: Select the Appropriate BMP Design.
Select a Best Management Practice (BMP), then Utilize HSG identified in STEP 5 and enter into Table 2.
TABLE 1. BMP, Treatment Volume Credit Multiplier, and Primary Design Assumptions.
BMP
Treatment Volume Credit Multiplier
(CF/SF unless otherwise noted) Primary Design Assumptions*
Hydrologic Soil Group (HSG)
A B C D
Amended Soils with
Depressional Storage 0.4
•Shallow surface storage (3-inches)
•Compost-amended soil depth (6-inches)
•Bulk density testing required unless District staff
observes soil amendment process
Raingardens
(Bioretention &
Biofiltration)
2.1 1.8 1.5 1.5
•Surface ponding depth of 18-inches (HSG A, C & D)
•Surface ponding depth of 15-inches (HSG B)
•Perforated underdrain (HSG C & D)
Vegetated Swale with
Check Dams
600 CF
/ check
dam
500 CF
/ check
dam
400 CF
/ check
dam
400 CF
/ check
dam
•4-ft channel bottom with 3:1 side slopes
•2% channel slope with earthen check dam every 60
or 75-ft based on soil HSG
•Over-excavate 30 in and backfill with engineered
planting medium
•Perforated underdrain (HSG C & D)
Permeable Hard Surfaces
(e.g., Permeable Paver
Patio, Porous Concrete
Driveway)
0.6 0.6 0.4 0.4
•18-inches of rock storage
•18-inch sand layer required for HSG C and D soils
•Perforated underdrain (HSG C & D)
Infiltration Trench /
French Drain 1.2 1.2 0.8 0.8 •3-ft of rock storage
•4-ft wide
* See District Design Details for each practice for specific design criteria to receive treatment volume credit. The District can provide
detailed design cross sections. Treatment volume credit for BMPs is identified in Table 1 on a per unit surface area basis.
BMP Siting and Sizing Guidelines: Site BMPs downslope of impervious surfaces in most permeable soils. Site BMPs in HSG A and
B soils wherever feasible to maximize credit by providing infiltration of stormwater. Rooftop downspouts provide flexibility to
direct runoff to a variety of BMPs. In particular, raingardens must accept rooftop or driveway runoff, where feasible.
BMP Selection and Siting
STEP 5: Preliminary Identification of Onsite Soils.
Soil type is an important feature to infiltrating water. Sandy soils have greater infiltration capacity than organic, silt, or
clay soils. Identify the Hydrologic Soil Group (HSG) of onsite soils based on the Washington County Soil Survey
published by the Natural Resources Conservation Service available online at http://websoilsurvey.nrcs.usda.gov/app/
WebSoilSurvey.aspx or hosted on the District’s webmap at https://www.eorinc.io/maps/CMSCWD/. Soils review
determines applicable Credit Multiplier in Step 5.
(Circle) The HSG of onsite soils are predominantly: A B C D
CARNELIAN – MARINE – ST. CROIX WATERSHED DISTRICT
Emmons and Olivier Resources, Inc -3 - Jan 2023
Use TABLE 1 and the BMP siting and sizing guidelines above to fill in the proposed BMP design in TABLE 2 below. TOTAL Treatment Volume Credit (f) must meet or exceed the Treatment Volume Requirement (e) determined in Step 4.
TABLE 2. Proposed BMP’s Treatment Volume Credit.
COLUMN: A B C D E
BMP HSG
BMP Surface Area (SF)
or
No. of Check Dams (No.)
Credit Multiplier
from Table 1
(CF/SF or
CF/check dam)
Treatment Volume
Credit (CF)
[Column C x Column D]
Example:
Raingarden 1 B 200 SF BMP Surface Area 1.8 360 CF
TOTAL Treatment Volume Credit (CF) (f)
STEP 8: Onsite Soil Verification
Soil borings are recommended in the locations of proposed BMPs in order to assess the infiltration capacity of the soil as
characterized by the hydrologic soil group (HSG). Soil boring results guide the selection of the BMP(s) and helps to ensure the
BMP(s) will function properly. In lieu of borings, soil verification may be achieved by review of other applicable data (septic
system percolation tests/soil logs, test pits, etc.).
STEP 7: Calculating Proposed Treatment Credit
STEP 9: Ensuring Proposed Treatment meets or exceeds Required Treatment.
Proposed raingarden treatment volume credit must meet or exceed required volume to meet District Rules and
be considered for a permit.
Does STEP 7 (f) meet or exceed STEP 4 (e) ? Yes, proceed to STEP 10. No, repeat STEPS 6 & 7.
STEP 10: Ensuring Stormwater will be Routed to the BMP(s)
Proposed BMP location(s) must receive stormwater from the majority (~80%) of required impervious surfaces.
Do your submitted site plans clearly demonstrate stormwater routing from required impervious surfaces will be
directed into the BMP(s)?
Yes. Submit this worksheet and your site plans to the District for review.
No. Consider adding greater routing features (i.e. relocation, grading details, catch basins & piping,
swales, downspouts) to the proposed BMP(s). Repeat STEP 10.
No and routing alterations are not sufficient. Add an additional BMP and repeat STEPS 6 - 9.
PROPOSED
RAIN GARDEN A 89 SQ FT BMP Surface Area 2.1 187 CF
187 CF
X
X
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945
EOF:
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© 2023 WIDSETH SMITH NOLTING & ASSOCIATES, INC.J:\Craig Pittman-48170\2023-10727\CADD\Civil\2023-10727_Drainage Overview Map.dwg Plotted by:Frank Brodeen 7/5/2023 11:38:38 AM
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LEGEND
PROPOSED CONSTRUCTION LIMITS
IMPERVIOUS AREA TO RAIN GARDEN
PERVIOUS AREA TO RAIN GARDEN
LAND USE SUMMARY:
TOTAL PROJECT IMPERVIOUS = 1,237 SQ FT
(NEW AND RECONSTRUCTED)
TOTAL IMPERVIOUS TO RAIN GARDEN = 1,366 SQ FT
% IMPERVIOUS TO RAIN GARDEN = 110% > 80% MIN.
TOTAL DRAINAGE AREA TO RAIN GARDEN = 2,473 SQ FT
TOTAL ESTIMATED DISTURBED AREA = 3,089 SQ FT
Feet
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