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5.b Pittman Variance - PC Packet1 | P a g e Date of Meeting: July 11, 2023 To: Chair Loeffler and Members of the Planning Commission 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. This site plan approval procedure requires the approval of the Planning and Zoning Commission and the City Council. 2 | P a g e 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 a legally nonconforming as the existing zoning, Rural Residential Neighborhood and Shoreland Ordinance requires a minimum lot size of 2.5 acres. In addition to this the existing accessory structure does not meet the rear yard setback from the lot line. 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 impact on the property. After discussion, replacement was described to be needed by the applicant due to structural issues within the interior of the current structure. Staff concurred that replacement is a reasonable action in this case. As shown, the parcel will continue to be a legal non-conforming lot after replacement of the proposed structure. More details on the lot will be discussed further in this report. The parcel is currently 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. Parcels that surround the parcel with the proposed replacement are zoned RR-N – Rural Residential Neighborhood and are either vacant or used for single family dwellings. 3 | P a g e 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% For the Shoreland Overlay District, although the lot does not meet the minimum lot size or rear yard setback for the detached accessory structure, it does meet the remaining requirements of the district through Sections 5 through 8 of the Shoreland Ordinance and the dimensional standards of the RR-N zoning district. 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 and changed to accommodate the reconstructed garage facing Langly Ave. As long as the driveway meets the impervious surface requirements and other requirements laid out in the Scandia City Code, there are no outstanding issues. 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. 4 | P a g e Architectural Design Standards. The proposed reconstructed garage and ADU must match or complement the main structure on the property. 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 RR-N District is allowed one ADU on the parcel, this follows the guidelines of the district. 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 as detailed within the Scandia City Code and written above. Meeting the purpose and intent of the Zoning District is necessary for this variance. The Shoreland Overlay District is described within the Shoreland Ordinance for non-conforming lots and structures present on lots within this district. This lot is considered a non-conforming lot within the district and to complete the proposed detached garage construction must adhere to the following section(s) of the Shoreland Overlay District code: 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: 5 | P a g e (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 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. Economic conditions are not a factor in the variance. 6 | P a g e 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. 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. 7 | P a g e 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. 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. 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. 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. 8 | P a g e 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 draft resolutions to address these issues. The Planning Commission may recommend modifications to these conditions. COMMISSION ACTION The Planning Commission can do one of the following: 1. Recommend approval, with or without conditions, of the attached ordinance and resolutions. 2. Recommend denial, with findings, of the attached ordinance and resolutions. 3. Table the request for further review/study. Staff recommends that the Planning Commission recommend approval of 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. Economic conditions are not a factor in the variance. 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. 9 | P a g e 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. 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. STAFF RECOMMENDATIONS Staff recommends the Planning Commission recommend approval of the attached variance with conditions as described above. Attachments 1. Draft Resolution 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-XX 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. Economic conditions are not a factor in the variance. 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. 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 0 50 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 10:33 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 m i n n e s o t a RL Ate' m 1IqmIp E: y n _ 95 4 kz/1 Mfg i i / Z"] / iii - 1 _ OH E OH E OH E OH E OH E OH E OH E OH E OH E OH E OH E S S S S S AC G OHEOHEOHEOHEOHEOHEOHEOHEOHE OH E OH E OH E OH E OH E OH E OH E LA Y T O N A V E N U E N . LA N G L Y A V E N U E N . 3 E 14 OH E OH E OH E OH E OH E OH E OH E OH E OH E 9 4 5 945 944 9 4 3 944 94 4 9 4 5 945 945 9 4 5 94 5 944 94 4 94 4 94 3 943 9 4 4 945 94 5 944.3 944 94 4 943 942.8 94 4 . 3 944945 945 EOF: 944.3 BIO BIO BIO BIO BIO BIO BIO BIO BIO BIO BIO BIO BI O BI O BI O BI O BIO BI O BI O BI O BIO BIO BIO BIO BIO BIO BIO BIO BIO BI O BI O BI O DR A F T - N O T F O R C O N S T R U C T I O N © 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 SHEET NO. JO B N U M B E R : CH E C K E D B Y : DA T E : SC A L E : DR A W N B Y : DA T E RE V I S I O N S D E S C R I P T I O N RE V # BY LI C . N O . DA T E : PI T T M A N R E S I D E N C E - G A R A G E C O N S T R U C T I O N SC A N D I A , M N WA S H I N G T O N C O U N T Y PR O P O S E D S I T E P L A N FIG. 1 JU L Y 2 0 2 3 AS S H O W N FE B SM K 20 2 3 - 1 0 7 2 7 20 . 0 0 ' 24 . 3 3 ' 22.18' Feet 0 10 20 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 OH E OH E OH E OH E OH E OH E OH E OH E OH E OH E OH E S79°30'1 7 " E 1 4 8 . 0 3 S79°17'5 3 " E 1 4 9 . 0 9 S S S S S AC G OHEOHEOHEOHEOHEOHEOHEOHEOHE OH E OH E OH E OH E OH E OH E OH E LA Y T O N A V E N U E N . LA N G L Y A V E N U E N . 3 E S1 1 ° 3 2 ' 3 0 " W 4 9 . 3 3 S1 0 ° 1 8 ' 3 9 " W 4 9 . 8 6 14 OH E OH E OH E OH E OH E OH E OH E OH E OH E OH E 9 4 5 945 944 9 4 3 944 94 4 9 4 5 945 945 9 4 5 94 5 944 94 4 94 4 94 3 943 9 4 4 © 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 R T H 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 G 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 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 AC LA N G L Y A V E N U E N . 9 4 5 945 944 944 9 4 5 945 945 9 4 5 94 5 944 945 94 5 944.3 944 94 4 943 942.8 94 4 . 3 944945 945 EOF: 944.3 DR A F T - N O T F O R C O N S T R U C T I O N © 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 SHEET NO. JO B N U M B E R : CH E C K E D B Y : DA T E : SC A L E : DR A W N B Y : DA T E RE V I S I O N S D E S C R I P T I O N RE V # BY LI C . N O . DA T E : PI T T M A N R E S I D E N C E - G A R A G E C O N S T R U C T I O N SC A N D I A , M N WA S H I N G T O N C O U N T Y DR A I N A G E O V E R V I E W M A P FIG. 2 JU L Y 2 0 2 3 AS S H O W N FE B SM K 20 2 3 - 1 0 7 2 7 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 0 5 10 20 . 0 0 ' 22.18' 24 . 3 3 '