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1. Motion Regarding Willows Storm Water Improvement Cost Sharing� � n City of Kalispell OFFICE OF THE CITY MANAGER MONTANA TO: Mayor Fisher and Kalispell City Council FROM: Doug Russell, City Manager DATE: October 10, 2012 SUBJECT: Willows Special Improvement District A Special Improvement District for the Willows subdivision has been discussed at several regular meetings and work sessions. The information from those meetings has been attached for reference purposes. At the latest work session, discussion occurred related to establishing a contribution from the City of Kalispell for the project. At the meeting, it was suggested to base the contribution from the City based on a contribution amount from the homeowners as though it represented a determined amount from a homeowners' association. The initial amount suggested was $20 a month. Talk was also held on a $15 a month contribution. Our financial advisor has provided sample bonding amounts based on these initial payments so the Council could review what the City's obligation would approximately be. It is important to note that these loan amounts are estimates as a change in any one variable changes the other numbers. It is also a challenge to demonstrate this information as the Special Improvement District (homeowners' portion) will be bonded. The term of the bond is typically decided at the time of issue and is dependent upon the respective interest rates and yield curves that provide the most advantages for the respective bond issue. Because of this, we looked at 15 and 20 year terms for a $20/month and $15/month homeowner assessment to provide Council an idea of what the City's contribution could look like. It is also important to note that these estimates are based on the preliminary engineering and construction estimates. These estimates also include estimates of the fees associated with the bond issuance. There are a number of ways a recommendation can be stated. Based on the Council discussion at the last work session, the recommendation is to decide upon an assessment amount for a specific time frame. This would identify the contribution amount and term from the Special Improvement District. The difference from that amount would be applied to the City's contribution. www.kalispell.com $20 a month 15 Year Term: City Contribution: $1.60,000 Bond Issue Size": $228,000 Estimated Assessment Rate: 3.50% Bond Rate + 50 basis points by State Law = 4.00% Estimated Annual Assessment: $238.73 = Estimated Monthly Assessment: $19.89 20 Year Term: City Contribution: $122,000 Bond Issue Size*: $271,000 Estimated Assessment Rate: 3.85% Bond Rate + 50 basis points by State Law = 4.35% Estimated Annual Assessment: $239.65 = Estimated Monthly Assessment: $19.97 $15 a month 1.5 Year Term: City Contribution: $210,000 Bond Issue Size*: $1.71,000 Estimated Assessment Rate: 3.50% Bond Rate + 50 basis points by State Law = 4.00% Estimated Annual Assessment: $14.92 20 Year Term: City Contribution: $1,82,000 Bond Issue Size*: $203,000 Estimated Assessment Rate: 3.85% Bond Rate + 50 basis points by State Law = 4.35% Estimated Annual Assessment: $14.96 Recommended motions: (Select one of the options below to complete the motion.) Move that upon creation of a Special Improvement District, the contribution from the homeowners in the Willows subdivision will be based upon: a) $20/month for 20 years. b) $20/month for 15 years. c) $15/month for 20 years. d) $15/month for 15 years. 20111"Avezzue East Kalispell, IVI 59903 Phone: 406-758-7720 - rax. 4,06-758-7831 Public Works Departmelit il1NT'Aj;%A _ www.katispell.com 1pubfic—works MEMORANDUM To: Doug Russell, City Manag_6 �j _ f"_ From: Susie 'Turner, P.E. Public Works Director/City Engineer , Date: 9/20/2012 Re: The Willows Subdivision Stormwater Council Inquiries The Willow SID approval and City participation contribution was discussed at the September 4, 2012 meeting. Below is Staff's response to the questions and additional information requested by Council. In an effort to stay consist with the material presented to Council, the following information will be presented using the four sub -delineated drainage basins as outlined in the September 4, 2012 meeting. 1. The Willows Drainage Basin (includes offsite vacant field to the north) 2. Muskrat Slough Drainage Basin 3. Leisure Heights 4. County Facility Impact Fees. Stormwater impact fees collected to date since the inception of Stormwater Impact fees in 2008 are listed below per drainage basin: Drainage Basin Impact Fee $ The Willows Drainage Basin 0.00 Muskrat Slough Drainage Basin 0.00 Leisure Heights Subdivision 7,760 County Facility 0.00 Total 7,760 Stormwater Assessments: Stormwater Assessments for FY 11/12 are provided in the table below. Retrieval of Stormwater Assessments collected back to 2001, when development first started in the Willows Subdivision, requires paper tracking for each property and staff did not have the time to collect this data prior to the Council meeting. If it is desired and provided more time, we can collect this remaining information, or estimates can be achieved by multiplying the FY 11/12 amount by the respective number of years. This would be a liberal estimate based upon lower fees and number of residences in the earlier years. Drainage Basin Stormwater Assessment FY 11/12 $ The Willows Drainage Basin 5,498.09 Muskrat Slough Drainage Basin 12,330.03 Leisure Heights Subdivision 3,919.80 County Facility 0.00 Total 21,747.91 Cost to Maintain Detention Facility: The annual cost to perform the maintenance for the Willow Detention Facility is estimated to be $ 2,656. This estimation includes semi-annual responsibilities to inspect, clean, and maintain the facility. A breakdown of the cost is provided in the Willow Detention Facility Maintenance Costs attachment. THE WILL- WS AREA STORM SEWER ASSESSMENT'S T-7 [\Alanths AcUan fterm Remove accumulated trash and debris Inspect outfall structure and clean if necessary Set rod outfall pipe if necessary Jet rod bypass pipe if necessary Number of Employees Number of Hours Employee Cost ($32.011hr) Equipment Cost (@$1951hr) Foreman's Time Scheduling (@$32.82) 2 4 $ 256.08 $ 780.00 $ 32.82 Toft"I cost $ 1,0600,90 12, NA a nn t h 5 1CUOn ftenns, Remove accumulated trash and debris Inspect outfall structure and clean if necessary Jet rod outfall pipe if necessary Jet rod bypass pipe if necessary Vac out sediment chamber Number of Employees Number of Hours Employee Cost (@$32.011hr) Equipment Cost (CcD$1951hr) Foreman's Time (@$32.82) 2 6 $ 384.12 $ 1,170.00 $ 32.82 Total cost 1,586.94 IAnnumf Mwintenance Cost $ 2,6555.84 -1 M lar Public Works Department MONTANA MEMORANDUM 201 P Avenue East PO Box 1997 Kalispell, MT 59903 Phone: 406-758-7720 Fax: 406-758-7831 www.kalispell.com /public works August 20, 2012 To: Doug Russell, City Manager' From: Susie Turner, P.E. Public Works Director/City Engineer l r Date: 8/29/2012 Re: The Willows Subdivision Stormwater Improvements Background: The Willows Subdivision experienced flooding in the spring of 2011 due to a plugged 12" discharge pipe from the Willows stormwater detention facility. The residents of the Willows approached the City and requested the City take over maintenance responsibilities for the detention facility and associated discharge piping. The City agreed to provide this service based on the stormwater detention facility and discharge system being updated to current City Standards. The improvements needed to meet current City Standards include re -development, upgrade, and installation of the following: • Detention facility sizing • Outlet structure • Side slopes • Offsite flows Water quality treatment Maintenance access The residents of the Willows came to a consensus the improvements would improve and enhance the subdivision and decided to proceed with the development of a Special Improvement District (SID). An engineer was hued to develop a preliminary engineering report which provides a cost estimate for the design and construction of the stormwater improvements. On August 13, 2012, City Council participated in a presentation outlining the Willows stormwater development and the proposed preliminary engineering report for the improvements. Questions arose concerning the offsite flows (bypass flows) in regards to who is responsible for that portion of the construction cost, and whether the City should participate in some of the offsite flows construction costs. Following discussion, Council requested options for consideration based upon potential participation in the offsite flows associated with the 18" pipe for this project. This report will outline the percentages of offsite flows associated with this project and offer several alternatives for participation and funding for the Council to consider. Preliminary Engineer Report and Offsite Flow Percentages: The Willows Detention Facility is located at the downstream end of a large drainage area. Flows from areas within the large drainage area can be broken into three sub -delineated drainage basins. 1. The Willows Drainage Basin (includes offsite vacant field to the north) 2. Muskrat Slough Drainage Basin 3. Leisure Heights 4. County Facility The flow contributions from each sub -delineated drainage basin are as follows: TABLE 1 Flow Contribution Drainage Basin Flow Contribution (cfs) Notes The Willows 13.3 Post Developed 100 year flows Muskrat Slough 2.53 Flows calculated from max allowable flows from pipe outfall structure at Willow Glen Drive Leisure Heights 6.39 Post Developed 100 year flows County Facility 9.16 77777ost Developed 100 year flows The preliminary engineering report outlined utilizing an 18" pipe to bypass the offsite flows from Muskrat Slough, Leisure Heights, and the County Facility. The flows from the Willows Subdivision were designed to discharge through the existing detention facility 12" discharge pipe and utilize some of the flow capacity of the bypass pipe. The table below summarizes the flows, capacities, and percentages of the pipes. The Willows will utilize the entire capacity of the 12" pipe and 36% of the bypass pipe. The remaining capacity of the bypass pipe will be utilized by the other sub - delineated drainage areas. TABLE 2 % Contribution to Bypass Pipe Drainage Areas Total Flow Contribution (cfs) 12" Pipe Contribution (cfs) Bypass Pipe Contribution (cfs) % Contribution to Bypass Pipe Willows 13.3 3 10.3 36% Muskrat Slough 2.53 0 2.53 9% Leisure Heights 6.39 0 6.39 23% County Facility 9.16 0 9.16 32% Total 31.38 28.38 Based on 12" pipe at 0.3% slope with 3 feet of head Please note, the figures used to calculate the % contribution were based on the preliminary engineering and are subject to change, however the same methodology will be used once the final design report is complete. The preliminary engineering report includes the estimated total costs for construction, engineering, and administration/financial, as shown in Table 3. Portions related to the bypass flows are highlighted. 2 TABLE 3 Cost Estimate — Phase 1 ITEM NO. DESCRIPTION EST. QTY UNIT UNIT PRICE EXTENSION 101 General Requirements 1 LS $10,300.00 $10,300.00 102 Mobitization/Demobilization 1 LS $8,200.00 $8,200.00 103 Taxes, Bonds, Insurance 1 LS $6,200.00 $6,200.00 104 Construct Pond Outlet Structure 1 EA $5,000.00 $5,000.00 105 Construct Diversion Structure I LS $15,000.00 $15,000.00 106 18" PVC Storm Pipe 1500 LF $25.00 $37,500.00 107 Construct new 18" overflow pipe 1500 LF $35.00 $52,500.00 108 Install manholes for overflow pipe 6 EA $2,000.00 $12,000.00 109 Replace existing discharge structure 1 EA $5,000.00 $5,000.00 110 Excavation to increase pond volume 1000 1 CY $10.00 $10,000.00 III Pond slope stabilization 3000 SF $5.00 $15,000.00 112 Construct pond access ramp I LS $10,000.00 $10,000.00 113 Construct pond access gate 1 EA $2,000.00 $2,000.00 114 Topsoil and reseed all disturbed areas 1 LS $2,000.00 $2,000.00 115 Rip -rap for outlet to river 200 TON $60.00 $12,000.00 116 Rip -rap for detention pond 50 TON $60.00 $3,000.00 117 Miscellaneous Work 1 LS $10,000.00 $10,000.00 Construction Sub -Total Contingency (20%) Construction Total $230,700.00 $46,200.00 $276,900.00 Engineering Design Construction Engineering Services Wetland Study Engineering Total $27,700.00 $27,700.00 $10,000.00 $65,400.00 Bond Counsel and Related Costs Revolving Funds Deposit (5%) District Reserve Fund Deposit (5%) Administrative/Financial Total $11,000.00 $19,628.00 $19,628.00 $50,256.00 Total Project Costs $392,556.00 The construction cost can be further broken down into items associated with the bypass flows pipe construction. Table 4 Proportional Cost Break Down, uses the percent contributions (calculated in Table 2) to produce a proportional cost estimated for the Willows and offsite flows associated with the three sub -delineated drainage basins. Table 4 summarizes, a total proportional construction cost of $41,374.21 is from the Willows Subdivision. The remaining construction costs associated with the offsite flow or bypass capacity is $87,625.79. Please note, the figures used to calculate the % contribution were based on the preliminary engineering and are subject to change, however the same methodology will be used once the final design report is complete. 3 TABLE 4 Proportional Cost Break Down The Muskrat Leisure County Total Off Site Flows ITEM NO. Construction Description Cost Willows Slough Heights Facility Cost Construct Diversion $15,000.00 0 $5,000.00 $5,000.00 $5,000.00 $15,000.00 105 Structure 106 18" PVC Storm Pie $37,500.00 $13,609.94 $3,343.02 $8,443.45 $12,103.59 $23,890.06 Construct new 18" $52,500.00 $19,053.91 $4,680.23 $11,820.82 $16,945.03 $33,446.09 107 overflow Pipe Install manholes for $12,000.00 $4,355.18 $1,069.77 $2,701,90 $3,873.15 $7,644.82 108 overflow pipe 115 Rip -rap for outlet to river $12,000.00 $4,355.18 $1,069.77 $2,701.90 $3,873.15 $7,644.82 Totals $129,000.00 $41,374.21 $87,625.79 Percent Cost Contribution 1 32% 68% Alternatives and Options: Alternative 1: Find that the offsite flows are representative of new development impacting the drainage system and fmance the facility upsizing with impact fees. Option 1 Elect to not participate in the funding of the improvements. Option 2 Elect to participate in 100% funding of the bypass improvements with impact fees covering the offsite flow percentage (68% per the example) and stormwater assessments for the remaining portion of the bypass project (18" pipe). Option 3 Elect to participate in the funding of the improvements with impact fees up to the percentage associated with off -site flows (68% per the example) for the bypass project (18" pipe) - Alternative 2: Find that the offsite flows represent historical quantities for the Willows Subdivision. Option A Elect to not participate in the funding of the improvements. Option B Elect to participate in in the funding of the improvements with storm sewer assessments up to the entire bypass project (18" pipe). Option C Elect to participate in the funding of the improvements with storm sewer assessments up to the percentage associated with off -site flows (68% per the example) for the bypass project (18" pipe). Alternative 3: Deny the petition to form the SID Alternative 4: As determined by Council M Funding Sources: Impact fees: The City's Stormwater Impact Fee Fund has $669,236, as outlined in the fiscal year 12/13 budget with two projects totaling $436,500 (though that is dependent upon new development occurring to encumber these appropriated funds.) Even with these projects, funding would be available in the Stormwater Impact Fee Fund. Stormwater Fund: Funding to support the construction for the bypass piping could be used from the budget line item Designated Capital Projects. Designated Capital Projects revenues are allocated from stormwater assessments at $50,000 per year. Ending cash in this line item for FY 12/13 is $465,844. With Council approval for use of either source, a new CIP would be created using the estimated bypass pipe construction cost with a follow up 12/13 budget amendment. Staff Recommendation: Discussion at the previous work session identified the offsite flows from neighboring development as having a negative impact upon the drainage system serviced by the Willows Subdivision. As such, it is recommend that Council approve the Resolution Authorizing the Willows Subdivision Special Improvement District and participate in funding the bypass project with impact fees up to the percentage associated with off -site flows (68% per the example) for the bypass project (18" pipe). 5 RESOLUTION NO.5590 A RESOLUTION RELATING TO SPECIAL IMPROVEMENT DISTRICT NO. 345; CREATING THE DISTRICT FOR THE PURPOSE OF UNDERTAKING CERTAIN LOCAL IMPROVEMENTS AND FINANCING THE COSTS THEREOF AND INCIDENTAL THERETO THROUGH THE ISSUANCE OF SPECIAL IMPROVE- MENT DISTRICT BONDS SECURED BY THE CITY'S SPECIAL IMPROVEMENT DISTRICT REVOLVING FUND. BE IT RESOLVED by the City Council (the "Council") of the City of Kalispell (the "City"), Montana, as follows: Section 1. Passage of Resolution of Intention. This Council, on June 18, 2012, adopted Resolution No. 5565 (the "Resolution of Intention"), pursuant to which this Council declared its intention to create a special improvement district, designated as Special Improvement District No. 345 of the City (the "District"), under Montana Code Annotated, Title 7, Chapter 12, Parts 41 and 42, as amended, for the purpose of financing the costs of certain local improvements described generally therein and consisting primarily of a storm water detention facility and outlet (the "Improvements") and paying costs incidental thereto, including costs associated with the sale and the security of special improvement district bonds drawn on the District (the "Bonds"), the creation and administration of the District, and the funding of a deposit to the City's Special Improvement District Revolving Fund (the "Revolving Fund") and to a District reserve account. Section 2. Notice and Public Hearing. Notice of passage of the Resolution of Intention was duly published and mailed in all respects in accordance with law, and on July 16, 2012, this Council conducted a public hearing to hear and pass upon protests against the proposed Improvements and the creation of the District. The public hearing was the first meeting of the Council following the expiration of the period ended 17 days after the first date of publication of the notice of passage of the Resolution of Intention (the "Protest Period"). Section 3. Protests. Within the Protest Period, three (3) protests were filed with the City Clerk by the owners of property in the District subject to assessment, representing 3.45% of the total estimated costs of the Improvements and costs incidental thereto to be assessed against the properties in the District, in accordance with the method or methods of assessment in the Resolution of Intention. Section 4. Creation of the District; Insufficiency of Protests. At the next regular meeting after the expiration of the Protest Period (i.e., the meeting on July 16, 2012), the Council heard and passed upon all protests and determined that the protests made by owners in the District to be assessed for the cost of the proposed Improvements and incidental costs to be financed with the Bonds is not more than 50% of all of such costs in the District. The Council found and hereby ratifies and confirms that the protests against the creation of the District or the making of the Improvements filed during the Protest Period are insufficient. The Council subsequently analyzed the Improvements in greater detail and determined that additional City contributions toward the costs of the Improvements may be warranted. The District is hereby created on the terms and conditions set forth in, and otherwise in accordance with, the Resolution of Intention, but taking into account any additional contributions by the City toward the costs of the SID #345 — Willows Subdivision Improvements, thereby, if made, reducing the special assessments against properties in the District. The findings and determinations made in the Resolution of Intention, including, without limitation, those relating to benefits conferred, funding the Revolving Fund and District reserve account and securing the Bonds thereby, and using the proceeds of the Bonds to pay or reimburse the City for all or a portion of the costs of the Improvements and costs incidental thereto are hereby ratified and confirmed. PASSED AND APPROVED BY THE CITY COUNCIL AND SIGNED BY THE MAYOR OF THE CITY OF KALISPELL, THIS 4TH DAY OF SEPTEMBER, 2012. ATTEST: Theresa White City Clerk Tammi Fisher Mayor SID #345 — Willows Subdivision 2 The Willows Stormwater Drainage Work Session Overview of Presentation • Stormwater Design- "The Basics" — Predeveiopment Drainage Patterns — Predeveiopment Drainage Analysis Developed Site Layout Developed Design and Calculation Detention Facilities — WQTreatment Facilities — Maintenance Responsibilities • The Willows Subdivision — Area Historic Drainage — Current Drainage Layout — Stormwater Development Progression • SID Improvements • Preliminary Plan and Cost • Completion to Date ® Next Steps Stormwater Design "The Basics" Predevelopment • Vacant land «� ez:+ iuytcn:N • Historic• drainage '; ••�� patterns ---------- • Assess ----------- - .- — offsite - F run-off — Down � y stream drainage patterns ----- ---------------- Stormwater Scenario, subdivision development of Lot 2. 1. Start with vacant vegetated lot 2. Assess Current drainage patterns • Site runoff • Offsite runoff ® Downstream drainage conveyance and pattern 3 Stormwater Design "The Basics" Predevelopment Drainage Analysis Calculate Predeveloped flowrate and volumes - Typically for 10 yr and 100 yr runoff events - Offsite run off flows - Downstream conveyance capacity at�m Hydrographs aW.. low �100 ear I OGO :aqq -�- -! - 38W 30 year I / uwi a Y d q 6 *C 2 14 e6 16 20 32 U 28 uw 1. Calculated pre -developed flow rate and volume for proposed development • 10 year and 100 year 24 hr storm events 2. Assess offsite runoff impacting proposed development • 10 year and 100 year 24 hr storm events 3. Assess down stream • Review current drainage status • Flood issues LI Stormwater Design "The Basic" Developed Site Layout � FhUf;MG i Layout Design Site Plan ..-. •.� _ -- • Stormwater ' Management :-.::: Conveyance ::.Ra,.,�n__:_::- y :� on•rt ,:•an and Facilities 3 1. Develop proposed site layout • Layout roads, sidewalks, lots • Include stormwater facilities 2. Use site layout to calculate: • Stormwater conveyance locations and size • Water quality treatment and size • Flood control facilities volume and size 5 Stormwater Design "The Basics" Developed Design and Calculations • Calculate Stormwater — Developed flowrate- 10 year peak — Flood control volumes — 10 and 100 year — WQvolumes- 1" storm event • Size Stormwater Facility • Perform Downstream Analysis — Ensure no effect on downstream properties Hydrographs 4,.*d., . . . . . . . . . . . . R Stormwater Design "The Basics" Detention Facilities • The detention pond temporarily stores stormwater runoff and slowly releases it through a specially designed outlet or control structure. IN all mn 1. Detention facilities area designed to store water from the new development and discharge at a flowrate matching the 10 pre -developed 2. Examples: DEQ facilities, Grandview Assisted Living Facility, MDT Ponds, Silverbrook, Mountain Vista YA Stormwater Design "The Basics" WQ Facilities • New Development Water Quality — Required to treat 1" rainfall event • Treatment Train • Combination — Treatment + Detention Water quality treatment facilities are designed to remove pollutants contained in stormwater runoff. The pollutants of concern include sand, silt, and other suspended solids; metals such as copper, lead, and zinc; nutrients such as nitrogen and phosphorus; certain bacteria and viruses; and organics such as petroleum hydrocarbons and pesticides. 1. Water Quality Treatment is required for new development projects • Required to treat 1" rainfall event 2. Treatment performed prior to detention facility or in conjunction with treatment facility P Stormwater Design "The Basics" Maintenance Responsibilities • Stormwater Facilities Standard Maintenance Policies — City Standards for Design and Construction, Nov 2009 — Resolution No. 5406, adopted Nov,16, 2009 • The City of Kalispell maintains the Stormwater system structures located within the public road right of way • The project owner shall provide for the perpetual maintenance of all elements of the stormwater system located outside the public right of way. — For privately maintained stormwater systems in residential neighborhoods, a homeowner's association shall be formed to maintain the facilities located outside of the public right of way. — For commercial/industrial and multi -family residential developments with joint stormwater systems and multiple owners, a property owners' association (POA) or similar entity such as a business shall be formed, or a reciprocal -use agreement executed. Proper maintenance of stormwater facilities leads to better performance and increases the life of the facility. Insufficient maintenance of stormwater control facilities can lead to poor performance, shortened life, increased maintenance and replacement costs, and property damage. The City of Kalispell maintains the stormwater system structures located within the public road right of way. Drainage parcels created by public projects will be maintained by the City of Kalispell. The project owner shall provide for the perpetual maintenance of all elements of the stormwater system located outside the public right of way. For privately maintained stormwater systems in residential neighborhoods, a homeowner's association shall be formed to maintain the facilities located outside of the public right of way. For commercial/industrial and multi -family residential developments with joint stormwater systems and multiple owners, a property owners' association (POA) or similar entity such as a business shall be formed, or a reciprocal -use agreement executed. Development examples: Silverbrook, Mountain View Estates, Spring Prairie Phase 3 E Overview Drainage Patterns 1. West of Willow Glen Drive- Drainage Area Pink 2. East of Willow Glen Drive —Drainage Area Red 3. The Willows Subdivision Location -Drainage Area Purple 10 The Willows Current Drainage Layout Current Drainage Layout- Full View West of Willow Glen -Pink Drainage area, same as 1997 11 The Willows Current Current Drainage Layout 1. East of Willow Glen Drive • County Facilities-swale to detention facility to river • Leisure Heights -detention facility - Willow Glen storm system - drainage swale to detention facility to river • North vegetated field- through the Willows storm system • Willows -detention facility to river 12 Drainage Swale Willows 13 Detention Facility 14 Detention Facility w The Willows Stormwater Development Progression April 1. 1997! County Commissioners approved preliminary plat with condition that Phases I & tl would be annexed into the City of Kalispell before final plat. • July 30,1997t City of Kalispell Preliminary Review of Infrastructure Improvements — Increase discharge pipe from 12' to 15' in anticipation of future flows from Greenacres Slough —City offered to pay the difference in cost of materials — Questioned how wetland area would be accessed for dredging/maintenance • January 12, 1998: DEQ approval of development plans including the stormwater and wetland treatment system. July 28,1998: Schwartz Engineering redesigned the stormwater conveyance system by eliminating the proposed wetlands stormwater treatment facility, original design by flilimayer included a constructed wetland treatment 10'X550`, 2:1 slopes, designed for 2-year 6-hour storm. New design included a settling swate to allow sediment removal, overflow into 15' pipe conveying water to the Stillwater River. August 26.1998: Revised drainagc plan proposed by Schwartz Engineering approved by City of Kalispell. November 30, 1998: Phase 1 complete -Request for annexation and initial zoning. • April 27. 1999 12" outfall was installed instead of the design size of 15". Letter form City stating 12" will have to be upsized to 15" prior to final plat of Phase if. • May 5,1999: Declaration of Condition, Covenants and Restrictions and signature, outlining responsibility of ownership and maintenance of stormwater drainage system. December 1, 2000: Letter from Schwartz to City of Kalispell requesting approval to Install 12" outfall pipe rather than. 15' outfall pipe. April 1, 1997: County Commissioners approved preliminary plat with condition that Phases I & II would be annexed into the City of Kalispell before final plat July 30, 1997: City of Kalispell Preliminary Review of Infrastructure Improvements • Increase discharge pipe from 12" to 15" in anticipation of future flows from Greenacres Slough City offered to pay the difference in cost of materials • Questioned how wetland area would be accessed for dredging/maintenance January 12, 1998: DEQ approval of development plans including the stormwater and wetland treatment system July 28, 1998: Schwartz Engineering redesigned the stormwater conveyance system by eliminating the proposed wetlands stormwater treatment facility. Original design by Billmayer included a constructed wetland treatment 10'X550', 2:1 slopes, designed for 2-year 6-hour storm. New design included a settling Swale to allow sediment removal, overflow into 15" pipe conveying water to the Stillwater River August 26, 1998: Revised drainage plan proposed by Schwartz Engineering approved by City of Kalispell November 30, 1998: Phase 1 complete -Request for annexation and initial zoning April 27, 1999: 12" outfall was installed instead of the design size of 15". Letter form City stating 12" will have to be upsized to 15" prior to final plat of Phase II May 51h 1999: Creation of CCR and signature, outlining responsibility of ownership and maintenance of stormwater Drainage system December 1, 2000: Letter from Schwartz to City of Kalispell requesting approval to install 12" outfall pipe rather than 15" outfall pipe 16 SID Improvements Improve Detention Facility and Discharge System to Current City Standards -- Detention facility sizing — Outlet structure — Side slopes — Offsite flow management — Water quality treatment — Maintenance access 1. Request from Willow Subdivision for the City to maintain operation of stormwater system 2. City agrees based on stormwater facility improvements 3. Improve Detention facility and discharge system to current City Standards •Detention facility sizing •Outlet structure •Side slopes •Offsite flows •Water quality treatment •Maintenance access 17 Preliminary Plan and Costs TABLE 9-1 COST ESTIMATE -PHASE s _ _ TABLE 64,CONT) rtueln. O'nSCRIpiroS ES a fRIIF COST ESTIMATE - PHASE i }O✓welRgwe`.Wwmx .____ -_`i �t5 f'6W1CG StOXOW . Gon�n✓rx,�IvLn.l]JYr f ^�—ivy Rit.1$ to3 I4N btin Wv�vnv N—W K.100. Im— S.6S,p Oppro ,a eeeeRe.lsena0— er._ O'DwooWoap IR1 Cvnepucl.+rcrlcn 9tnx!urnT LG 115 fol"10 S'5.& U 4pe.ne - ne tptl •]pp pl ir.e CemRv rw l`.'a.afbnr ,ni: if $FO.GO SUsto OD Fl..ame1%Sv,nv F::e;v%� S,3fM.� In�uvmlMiMn b 4rnnen 8 9R f3 [Op W II3.ppp W Re vc Jnep e1iln,cev,v U W 1 Op0 r'Nc UeWi S.akmsC?eO ,Mb, Sll.37AW to . a.am,9 IWO c. t,pW Ipmw Sub -Total Fy.. W.W iu�e a a im otiri M SF AO I Opp ,# ea am�m f�'O ncoza,anp is rro fpoW 9.c�roa:. m.n.nwe[w,eua s9r $IvpWW i C whvcl r.,ni r.+.w oMr -- Ea Um. S+WOW in MWNvnd rnnnep tlYRu,4d •erLa 9T. F3 Mar(:F.yReM.M Furq, C+ �6R- RI9 W P.i+�ep-rc vuMe1 ro IRx 7M I--- IS1 W 1". W R v 4 0eM I ]p TL1`! RMeNYnveua 14ai1 WR VI IXAW 5 14oL^ Cv Reunn AczuM mMl $,99W Ot Crne,rlRtbn9 - aai 33W. M. Tohl Coat wr see W ion9+,uctfan FM4 srs.9favv 77 Water Quality / Detention Facility - MT- -.. V 12" Pipe 18" Pipe 18" Pipe Bypass flows The existing stormwater treatment pond receives flow from a ditch that runs along the southern edge of the subdivision, outlet to Muskrat Slough, and flow from the Leisure Heights Subdivision. Because this ditch may receive continuous flow from the slough and Leisure Heights Subdivision, the pond cannot adequately treat stormwater runoff from the Willows. The solution is to bypass flow from the ditch around the pond so that the pond can function properly. Therefore, a diversion structure and pipe should be constructed as shown in the schematic below. The bypass pipe would be 18" in diameter and run under the pond. It would then connect to anew 18" overflow pipe that would parallel the existing 12" pipe to the river. In addition, the diversion structure would also allow flow to bypass over the top for larger storm events and/or a pipe clog. Construct a New Pond Outlet Structure Construct new outlet structure. According to the as -built drawings, the existing outlet structure is 2.5' x 4.0' x 3.0 feet tall. As designed, the inlet to the structure is at the same level as the bottom of the pond. This has led to clogging due to sediment and other debris in the inlet. In addition, this structure does not regulate flows leaving the detention pond and does not meet current City standards. The Stormwater Design Manual Provides a number of standard details for outlet structures ranging from 5 to 6 feet in diameter. These structures regulate the flows leaving the pond and would have an orifice sized to discharge the predevelopment flow rate. The structure would also bypass the orifice to safely pass larger storms through the system. Construct a New 18" Overflow Pine According to a note on the as -built drawings, the 12" storm drain pipe that remains in -place running from the pond outlet structure to the Stillwater River was to be replaced with a 15" pipe during Phase Hof the construction of the subdivision. However, the as-builts show a 12-inch pipe and field measurements confirm this. To safely pass flows generated from the subdivision, a new 18" pipe running from the new outlet structure to the Stillwater River is proposed to parallel the existing 12" pipe. The invert of this pipe would be located above the existing 12" pipe invert in the outlet structure and would act as an emergency bypass for larger storm events and would accept off -site flow from the ditch. Pond Slope Stabilization and Reconstruction While the existing slopes of the pond do not meet current City Standards of 4H:1 V, there is insufficient room at the site to meet this requirement. Existing residential yards are immediately adjacent to the pond to the north, and the county property is immediately adjacent to the pond on the south. Therefore, the existing slopes must be maintained. hi addition to the slope stabilization, the pond will have to be reconfigured with a second cell to meet water quality standards. This will allow the pond to essentially function as a wetpond as outlined in Section 6.3 of the Stormwater Design Manual. Construct an Access Gate and Maintenance Ramp The most logical point of access would be to place a gate on the fence to the Flathead County Shop Complex and negotiate an access easement with the County. In addition to the easement, an equipment ramp into the pond will have to be constructed to allow City crews to remove accumulated sediment and other debris. iR] Completed To Date • Preliminary Engineering Design — Provides baseline for cost to perform design and construction • SRF Funding — Preliminary Application has been submitted (need specific PER, EA documentation, and procurement of Engineer of Record) 19 Next Steps .. • Council Action — SID Approval or Denial • Approval — Proceed with SRF Funding — Engineer of record selection — Design and construction 20