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HomeMy WebLinkAboutTIS 2023-04-17 Item 2C - Update - Water Fund: Water Reservoir SitesCity of Tukwila Allan Ekberg, Mayor Public Works Department - Hari Ponnekanti, Director/City Engineer INFORMATIONAL MEMORANDUM TO: Transportation Infrastructure Committee FROM: Hari Ponnekanti, Public Works Director/City Engineer BY: Adib Altallal, Utilities Engineer CC: Mayor Allan Ekberg DATE: April 14, 2023 SUBJECT:Water Fund — Water Reservoir Sites Update Project No. 91240102 Information Only ISSUE Update on potential Water Reservoir sites. BACKGROUND During the City of Tukwila's 2015 Water Comprehensive Plan, the consultant identified that the continued growth within the City no longer meets the Department of Health's water storage requirements. As a result, the Water Reservoir and Pump Station was included in the Capital Improvement Program. During this year's Water Comprehensive Plan update, the City's water storage deficiencies were highlighted again. Further development throughout the City and especially in the Ryan Hill and Tukwila South areas are likely to be hindered or completely halted due to these water storage deficiencies. During subsequent January 2021 communications with the Transportation and Infrastructure Services Committee, four potential sites were identified. Two of those sites were in the Ryan Hill neighborhood and the other two in the North Hill neighborhood. Both of those neighborhoods have high topography that would reduce pumping costs. A new reservoir will need to be constructed regardless. ANALYSIS By constructing a second reservoir, the City would meet the Department of Health's water storage requirements. During the January 2021 update, a viable site in the Ryan Hill area was for sale and the plan was to construct the reservoir there and connect the neighborhood to the rest of the water system so everyone in the city benefits. That site, however, is no longer available. During the December 2021 update, a willing seller in the North Hill neighborhood was found. After further investigations, it was determined the prevalence of wetlands made the site a poor candidate. Since finding land that meets the City's criteria has been a difficult endeavor, the prospect of finding two suitable sites appears not to be viable. In the Summer of 2022, the site of the old Fire Station 52 was identified as a city -owned viable option. The construction of a new reservoir at this site would save the City's General Fund money by taking over the responsibilities of the demolition and mitigation of the old fire station 52 building. The project would greatly improve the condition of Hazelnut Park by expanding the area and adding recreational items for the residents' use. Further, the project would retain the old City Hall building and could potentially help improve that building as well. That will be sufficient if the Ryan Hill neighborhood is connected to the rest of the water system. The proposed site at the former Fire Station 52 would enable Ryan Hill to be connected via a pump station as opposed to a different reservoir entirely. The Committee of the Whole is scheduled to receive a briefing on the project at its April 24, 2023, meeting. FISCAL IMPACT The adopted 2023 Capital Improvement Program identified an estimated project budget of $16 million for the Water Reservoir and corresponding pump station. There would likely be increased staffing needs to operate and maintain the new reservoir as well. RECOMMENDATION Information only. 29 Reservoir Siting Conceptual Study 14475 59th Avenue S OVERVIEW I MARCH 2023 <<Car011 �,�Y �r�i� �"' .fir -pT. �_ - � '►. . - fr��'I ��'.6i�. T.\y • 311 Site Description CAROLLO Site Location h as s 137th 139th •,t< as to r Park S 13 0 141st 42nd I) co a) a) > Showalter L 11,1 S ▪ 00 1 a.. •--#. Foster t, ► ► Go f Links Tukwila Middle Foyer —� High Fool — School School 144th S S146t St 143rd 6 14�sr 144th S 148th S14•th 't Fort Dent Park/ Starfire Sports 152n oaf 518 S 1 56th St Crystal morn rt lnry'r CAROLLU 3 Existing Improvements • Hazelnut Park to remain/improve • Tukwila Heritage and Cultural Center to remain • Vacated fire station to be demolished and its site mitigated. Hazelnut Park Fire Station CAROLL. 4 Site Characteristics • Generally flat; ±10' grade change • Primarily impervious • Some trees • Improved frontages with curb, gutter and sidewalk • Water, sewer, storm, gas and power available Hazelnut Park Heritage Center Fire Station CAROLL331 5 Environmental Considerations • Mapped Class 2 (Moderate) and Class 3 (High) Landslide Areas onsite • Likely to encounter groundwater Shoring and dewatering will be significant portion of reservoir cost • Protect/Replace Trees "Protection of trees shall be a major factor in the location, design, construction and maintenance of streets and utilities." CAROLLU 6 Nearby Water Infrastructure • Large diameter existing pipes surrounding the site Most surrounding mains may not need to be upsized • Alternate location near existing reservoir was modeled last year Recommend site-specific modeling Diameter (in) 10 12 — 16 — 18 — 2 4 6 —g Other ror it 1518' CAROLL 6 Land Use CAROLLY 8 Zoning • Low Density Residential (LDR) • "Water Pump Station" & "Water Utility Reservoir and Related Facilities" are Unclassified Uses within LDR • Requires Unclassified Use Permit TMC 18.10.060 CAROLL .3; 9 Lot area, minimum 6,500 sq. ft. Average lot width (min. 20 ft. street frontage width), minimum 50 feet Development Area, maximum (only for single family development) 75% on lots less than 13,000 sq. ft. up to a maximum of 5,850 sq, ft, 45% on lots greater than or equal to 13,000 sq. ft. Setbacks to yards, minimum: • Front 20 feet • Front, decks or porches 15 feet • Second front 10 feet Sides 5 feet w Rear 10 feet Refer to TMC Chapter 18.52 "Landscape Requirements," Table A, for perimeter and parking lot landscaping requirements. Height, maximum 30 feet Off-street parking: Residential See TMC Chapter 18.56, Off-street Parking & Loading Regulations Accessory dwelling unit See TMC Section 18.50.220 • Other uses See TMC Chapter 18.56, Off-street Parking & Loading Regulations TMC 18.10.060 CAROLL .3; 9 Conceptual Layout CAROLLO I 10 Reservoir Site • Assumed boundary at south limits of Hazelnut Park • Park and Heritage Center to remain CAR0LLO40 11 Reservoir Site • Required yards for LDR zone based on assumed front (S 147th St), side, and rear • Rear setback from assumed subdivision line CAR0LL041 Reservoir Site • Approximate minimum buildable area with required yards Alternate layouts possible with reconfiguring of Hazelnut Park space • Minimum parking (including ADA accessible parking or access) required for park and/or Heritage center? • Restrictions on parcel due to park classification/funding? CAR0LL042 Site Layout • 2.5 MG reservoir desired • Conceptual footprint determined with assumed buildable area Circular: 112' diameter, 34' height Rectangular: 100' square, 33.5' height (Does not account for wall thickness or interior supports) • 40' x 50' footprint for pump station Pump Station CAR0LL043 Example Reservoir (Partially Below Grade) • 2.5 MG prestressed, partially buried concrete tank • 112' diameter, 28' height • Alpine, CA CAROLL044 15 Example Reservoir (Fully Below Grade) • Crestview Park, Tukwila Highline Water District reservoir (7.6 MG) • Seward Park, Seattle Seattle Public Utilities CSO storage facility (2.65 MG) CAROLL045 16 Key Assumptions & Considerations CAR0LL046 Key Assumptions & Limitations 1:1 Z 1 © 1 Hydraulic suitability Geotechnical & shoring 0 Buildable area Hazelnut Park and Heritage Center restrictions (eC:.3- r" • Survey Onsite stormwater facilities Site grading Classified Use Permit CAROLL047 18