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Home My WebLink About016 DEQ Exemption Request Package 16 - DEQ Exemptions Request An exemption request has been submitted to the DEQ for this 7-lot Subsequent Minor Subdivision. Please see a copy of the letter included in this submittal. Gran Cielo I Block 4 Minor Subdivision Preliminary Plat Application M NOW A PART OF MADISON /. ENGINEERING '^^WWC ENGINEERING 895 TECHNOLOGY BOULEVARD,SUITE 203,BOZEMAN,MT 59718 1 406.586.0262 March 24,2025 Department of Environmental Quality Permitting&Compliance Division Water Quality Division P.O. Box 200901 Helena,MT 59620-0901 RE: Gran Cielo I Block 4 Subsequent Minor Subdivision—Preliminary Plat Application Exemption Request Dear Reviewer, WWC Engineering/Madison is requesting an exemption for infrastructure plan and specification review regarding the proposed 2 lot subsequent minor subdivision legally described S23, T02 S, R05 E, BLOCK 4,Lot 1-7 located in Bozeman,MT. The zoning of these lots are R-3,Residential medium-density district. The current Block 4 has 5 parcels, and the subsequent minor proposed will add 2 parcels within Block 4. The property lines will be divided into 7 lots, all lots lay on undeveloped existing platted parcels. There is no planned construction with this subdivision other than the abandonment and installation of utility stubs for the new parcels. There is an existing 8"ductile iron water main and an 8"PVC sewer main that both run north-south on 31 st Ave that will service these newly created lots. Therefore, there is no proposed water main or sewer main installation associated with this preliminaa plat. Currently service stubs exist that serve the five platted lots. SS service stubs will need to be added to the two additional lots(lots 3 and 6).Additionally,due to the relocation of property lines,water service stubs for lots 3,4&5 will need to be installed,while the existing service in lot 4 will need to be abandoned. No additional utilities are proposed to be installed with this minor subdivision. Enclosed,please find a memo that identifies the existing stormwater retention pond has the ability to handle two additional lots. Enclosed, also find a copy of the block 4 layout with service changes for your reference. Please respond at your earliest convenience with any comments or questions to the address provided below,or feel free to contact me directly at 406-586-0262 or email at erin sg ak(cr�,wwcen in�g com Thank you for your consideration. Sincerely, WWC Engineering,Inc. a A- kx:n4�% Erik Ringsak,PE enc: Previously approved Stormwater Drainage Plan&Memo Proposed Subdivision Services& Site Layout 895 Technology Blvd, Ste 203 ♦ Bozeman,MT 59718 ♦ (406)586-0262 K:\Bozeman\Bozeman Haus LLC\2024500 Gran Cielo 1-Block 4 Subdivision\05CAD\Sheets\Services&Site Layout.dwg TEST PIT 3/24/2025 11:55:50 AM Cn —S ALLEY O SS `� SS LOT 1 4047 SQ. FT. LOT 10 MIKAEL AERON LOT 5 MOORE BOZEMAN HAUS,LLC o— SM WS PROPOSED LOT LINES PREVIOUS LOT LINES LOT 2 ws 4048 SQ. FT. LOT 9 JOSEPH M. ANDERSON SS SS LOT 6 BOZEMAN HAUS,LLC sM SEWER SERVICE TO BE INSTALLED SS LOT 3 ws 4046 SQ. FT. W WATER SERVICE TO BE INSTALLED 0 LOT 8 Q ws Op BOZEMAN HAUS,LLC EXISTING WATER SERVICE TO BE ABANDONED 7� SS SS LOT 4 w O LOT 7 SM ws 4049 SQ.FT. J �^ BOZEMAN HAUS,LLC WATER SERVICE TO BE INSTALLED Q V, o LLI Q W WATER SERVICE TO BE INSTALLED LOT 5 ws —Z4050 SQ.FT. O SS LOT 7 J ?� SS — BOZEMAN HAUS,LLC W o U LOT 8 SM z BOZEMAN HAUS,LLC ws SEWER SERVICE TO BE INSTALLED LOT 6 SS — 4050 SQ.FT. fL.L V PREVIOUS LOT LINES o SS SS PROPOSED LOT LINES LOT 7 LOT 6 LOT 9 C AA ws 5862 SQ.FT. BOZEMAN HAUS,LLC BOZEMAN HAUS,LLC J�Y� >-1 X wv N w w w w w w w CIELO WAY I- 0 15' 30' V! SCALE: 1"=30' o 0 o o BOZEMAN HAUS LLC PREPARED BY NO. REVISION BY DATE 1 m D y m z Z GRAN CIELO I BLOCK 4 SUBDIVISION -,^^^W C ENGINEERING= e mo m j < m 895 TECHNOLOGY BLVD.,SUITE 203 i SERVICE & SITE LAYOUT BOZEMAN,MT 59718 nn p p (406)624-3910 u A GALLATIN COUNTY, MT www•wwcengineering.com Now A PART OF MADISON /► ENGINEERING �-^-'WWC -� ENGINEERING 895 Technology Boulevard, Suite 203, Bozeman, MT 59718 1406.586.0262 March 24th, 2025 DEQ Stormwater Memo Stormwater With the addition of two lots, there will be two additional single family detached households. Our calculations were based off the conservative assumptions that Block 4 would be 60% impervious with 5 lots and 80% Impervious 7 lots. The increase of impervious area would come with the addition of two new buildings, driveways, and walkways. A 20% increase is a conservative estimate, and was used to demonstrate there would still be adequate stormwater runoff capacity. It should be noted that this subsequent minor subdivision is a part of a greater subdivision that has been previously approved. Refer to Appendix A for existing stormwater plan and layout for Gran Cielo I. Table 1 below shows the previously accepted required volume for the stormwater Pond 1. Block 4 is a part of Basin 13, and all runoff contributes to Pond 1. Page 2 in that report identifies that the required volume for Pond 1 is 12,105 cubic feet. The Basins approximate size is 14,427 cubic feet, meaning Pond 1 could support an additional 2,322 cubic feet of stormwater runoff. TABLE 1 DETENTION POND VOLUMES 10-yr,2-hr Post Approx. Required Contributing Development Proposed Pond ID Basins* Peak Runoff Volume Volume cis (C.F.) C.F. f 1 6,7,8,9,13 8.30 12,105 14,427 uture base) 2 3,4,5,14,15 6.39 8,753 13,385 3 2,12,16,17,18 4.14 7,842 7,846 lure base Infiltration Basin 3 1 0.72 487 533 (fieumphase) 4(Meadow I 1 0.54 450 1,505 Creek Phase 1 •See Sheet SD1.0 Storm Drainage Basins Our calculations estimated that the addition of two lots would create an increase of 286 cubic feet. Block 4 would contribute 1,267 cubic feet of stormwater runoff with 5 lots and 1,553 cubic feet with the addition of 2 lots. This is a negligible increase compared to the Pond I's potential capacity. Refer to appendix B for calculations Attached: Appendix A Gran Cielo Subdivision Drainage Basin Appendix B Gran Cielo Subdivision Drainage Basin Calculations WWC/Madison Engineering Ru Erik Ringsak,PE 895 Technology Blvd Suite 203 ♦ Bozeman,MT 59718 ♦ (406) 586-0262 Project: Gran Cielo Block 4 Subdivision APPENDIX A Gran Cielo Subdivision Drainage Basin 895 Technology Blvd Suite 203 Bozeman,MT 59718 (406)586-0262 R UJ Dltit`E — ---- I Z mZ� cm m < o I I mmo �z z mD z �. z mZ t cz o «��w 'Z� « mho rno o -W -O.,i I �i m-mi j or I I oZ r Cow I I II � - m I II m o c I �pZ z I y �I Woz00 I �I mmn� � --sBENN1:I'T BLVD�--�-= _ Iltm I . I Imo, ( Zn Z�C C I I! Iwl =Z <o <p ;u ;u i O C I �I Nzm, m I -imz xNmm r~ x mK f y �z vDi o ocm ✓>---�II!C�I�I �0O I m I zmi m m cn -z ti ` -na,Z lid zoD vm+ ' c � �- y m m� li lid J L \ \ m � mD .Tl t I - — — — — i ' t \ U) n-� r.: D� 11..I �� Tl� \ �cDi) �: j � I L . _�Z� .� I �' �nZ I o Z 1 r''�� I CIF.Lo znD III Zx ZZ I� rZ �Z I f I y I i m m I m zz > m tr r Z L a r D I � Z mOD I - I Zzm i rlrxlz�I:uv z D — J \.. BASIN 10 GR_\F STREET BASIN 12 rrl r� CO m0X m� om � T om o� c� <o� �c)c r� n0 cm r,im °° �m mm z mz NZ r �1 m� M �z z N- J n z o v v T ':/\ -:{I C JrY�L.l4nwii4u-n:n'an G euyv Ycau.J' p cn MADISON ENGINEERING GRAN CIELO SUBDIVISION "° ^51� ro 895 TECHNOLOGY BLVD,SUITE 203 STORM DRAINAGE BASINS B 8 0 o BOZEMAN,MT 59718 (406)586-0262 (406)586-57+0 FAX BOZEMAN,MT 2 P LL m o Project: Gran Cielo Block 4 Subdivision APPENDIX B Gran Cielo Subdivision Drainage Basin Calculations 895 Technology Blvd Suite 203 Bozeman,MT 59718 (406)586-0262 Gran Cielo I Block 4 Minor Sub Stormwater Detention/Retention Calculations Detention Pond 1 Calculation of Required Volume for Storm Water Retention&Infitration System Design Rainfall Freq. 10 10 Year-2 Hour event OF coefficient a 0.64 OF coefficient b OF coefficient n 0.65 5 Lot Calculations: Total Basin Area: 30,152 sf C Areas (ft2): Impervious 18,091 0.90 Landscaped 12,061 0.20 Total: 30,152 0.62 Retention Basin Calculation: Q= CIA C= 0.62 (post-development) I = 0.41 in/hr(10-yr, 2-hr storm) A= 0.69 acres QPost= 0.18 cfs Required retention storage(ft3)= 1,267 ft3 (10-yr, 2-hr storm) 7 Lot Calculations: Total Basin Area: 30,152 sf C Areas (ft2): Impervious 24,122 0.90 Landscaped 6,030 0.20 Total: 30,152 0.76 Retention Basin Calculation: Q= CIA C= 0.76 (post-development) I = 0.41 in/hr(10-yr, 2-hr storm) A= 0.69 acres QPos,= 0.22 cfs Required retention storage(ft3)= 1,553 W Additional Storage required with the addition of 2 Lots: 286 ft Additional Storage available for Pond I: 2,322 ft Detention Pond Requirements.xlsx