Loading...
HomeMy WebLinkAbout17-0602 LUA17-000263 Civil Pre-App Comments DEPARTMENT OF COMMUNITY AND ECONOMIC DEVELOPMENT M E M O R A N D U M   DATE: June 2, 2017     TO: Matt Herrera, Senior Planner     FROM: Ian Fitz-James, Civil Plan Reviewer     SUBJECT: Utility and Transportation Comments for Cedar Ridge Short Plat LUA17-000263     I have reviewed the application for Cedar Ridge Short Plat located at 13609 156th Avenue SE and have the following comments: EXISTING CONDITIONS The site is approximately 1.69 acres in size and is rectangular in shape. The site contains two existing single family residences, a detached garage, a detached shed, and associated landscaping and lawn areas. The site is fronted by 156th Avenue SE to the east and SE 2nd Place to the north. WATER: Water service is provided by King County Water District 90. SEWER: The site is in the City of Renton sewer service area. There is an existing 10” PVC sewer running east to west in SE 2nd Place north of the site. Reference Project File WWP2703148 in COR Maps for record drawings. There is no existing sewer in 156th Avenue SE east of the site. The existing residences are served by private on-site septic systems. STORM DRAINGE: There is no stormwater conveyance system along the project’s 156th Avenue SE frontage. Runoff along the 156th SE frontage is conveyed south by a shallow ditch. The eastern portion of the SE 2nd Place frontage has no drainage improvements. Drainage from this frontage sheet flows southwest off the road into the site. Some drainage is intercepted by a Type 1 Catch Basin (COR Facility ID 117304) located on the southern frontage of SE 2nd Place across from the driveway to 6304 SE 2nd Place. Drainage from the western portion of the SE 2nd Place frontage also sheet flows southwest off the road into the site and 6301 SE 2nd Place. On-site drainage either infiltrates or sheet flows southwest. STREETS: 156th Avenue SE east of the site is classified as a minor arterial street. The 156th Avenue SE existing street section consists of a pavement width of approximately 45’ with an 11’ travel lane in the southbound direction, a 13’ travel lane in the northbound direction, an 11’ left turn lane for northbound 156th Avenue SE traffic, and a 10’ paved shoulder along the western frontage. A 0.5’ curb and a 4.5’ concrete sidewalk exist along the eastern frontage. The existing right of way width for 156th Avenue SE is approximately 60’ per the King County Assessor’s Map. SE 2nd Place north of the site is classified as a residential access street. The SE 2nd Place existing street section consists of a pavement width of approximately 38’ with a 15’ travel lane in the eastbound and westbound direction and a 4’ paved shoulder along each side of the roadway. There is no existing curb or sidewalk along either side of the roadway. The existing right of way width for SE 2nd Place is approximately 60’ per the King County Assessor’s Map. WATER COMMENTS Water service is provided by King County Water District 90. Please obtain a water availability certificate from the District and provide it to the City for review with the construction permit submittal. Review of the water plans will be conducted by King County Water District 90 and the Renton Regional Fire Authority. Plans approved by King County Water District 90 shall be routed to the City for final review prior to permit issuance. SEWER COMMENTS All new side sewers shall be 6”. All new side sewers shall flow by gravity to the main at a minimum slope of 2%. A grinder pump system internal to each home may be needed for a daylight basement. Each lot shall have its own side sewer. Sewer cleanouts should not be located in the new driveways. The preliminary utility plan submitted to the City by Pacific Engineering Design shows an individual side sewer for each lot connecting to the existing sewer main in SE 2nd Place. The site is served by a private on-site septic system. The septic system(s) shall be abandoned at the time of demolition of the existing homes in accordance with King County Department of Health regulations and Renton Municipal Code. Each lot is subject to a system development charge (SDC) for sewer service. The SDC for sewer service is based on the size of the domestic water service. The 2017 SDC for sewer service with a 3/4" or 1” water meter is $2,540.00. Sewer SDC fees are due at construction permit issuance. Each lot is subject to a Special Assessment District (SAD) fee. The site is located in the Central Plateau Interceptor SAD. The fee associated with this SAD is $351.95 plus interest per lot. SAD fees are due at construction permit issuance. STORM DRAINAGE COMMENTS A preliminary drainage plan and Technical Information Report (TIR) prepared by Pacific Engineering Design dated May 3, 2017 were submitted to the City as part of the site plan submittal. The site is located in the City’s Flow Control Duration Standard (Forested Site Conditions). The site is located in the Lower Cedar River drainage basin. The TIR was completed in accordance with the standards found in the 2017 Renton Surface Water Design Manual (RSWDM). All nine core and six special requirements were addressed. The site’s natural storm drainage discharge location is at the site’s southwest corner. The project is not proposing to discharge storm drainage at this location. Instead, the project is proposing to discharge storm drainage into the existing 12” pipe storm drainage system located north of the site in SE 2nd Place. Thus, the project is not in compliance with Core Requirement #1, Discharge at the Natural Location. A stormwater adjustment will need to be approved to use the proposed discharge location. The natural downstream flow path from the site flows southwest from the site through 278 Toledo Avenue SE and then south in the Toledo Avenue SE / 154th Avenue SE right of way to the end of the paved roadway where it is collected by a catch basin approximately 335’ south of 278 Toledo Avenue SE. From this point, drainage is conveyed south in a shallow open conveyance system south through the unimproved 154th Avenue SE right of way to the intersection of 154th Avenue SE and SE 142nd Street in unincorporated King County approximately 1,675’ south of 278 Toledo Avenue SE. From this point, the drainage path continues west in the SE 142nd Street right of way through a series of swales and unmapped culverts to a point where it discharges to an existing stream near the intersection of 150th Place SE and SE 142nd Street approximately 1330’ west of the intersection of 154th Avenue SE and SE 142nd Street. The proposed downstream flow path from the site has flows conveyed west from the site in an existing 12” piped conveyance system to the intersection of SE 2nd Place and Rosario Avenue SE approximately 875’ west of the site. The flows are then conveyed south through a water quality bioretention swale that was installed as part of the Highland Estates plat to a discharge point into an existing stream in King County park property. The discharge point is approximately 390’ south of the intersection of SE 2nd Place and Rosario Avenue SE. The flows are then conveyed southwest in the stream through King County park property for approximately 1,200’ to a piped King County conveyance system in 148th Place SE. Flows are conveyed in the piped system approximately 1,650’ south in 148th Place SE, 149th Place SE, and SE 142nd Street to the discharge point at the existing stream near the intersection of 150th Place SE and SE 142nd Street mentioned above. The final TIR needs to include a Level 1 offsite analysis for the proposed downstream drainage path to satisfy Core Requirement #2, Offsite Analysis. The offsite analysis in the preliminary TIR only accounts for the natural downstream drainage path. A detention vault is proposed to meet the flow control requirements to satisfy Core Requirement #3, Flow Control Facilities. The vault was sized using WWHM 2012. Vault sizing calculations used forested conditions for the existing conditions input into WWHM for the lot area after right of way dedication. Sizing calculations used the existing land cover for the existing conditions input into the WWHM for areas that will be disturbed along the 156th Avenue SE and SE 2nd Place frontages (including areas that will be dedicated as City right of way). Frontage areas that are disturbed as part of the project shall be modeled as forested conditions for the existing condition input into the WWHM model. Frontage areas that will drain to the site’s detention vault and that are not disturbed by the project may be modeled as their existing condition. Per the preliminary TIR, the vault is designed in accordance with the City’s Flood Problem Flow Control Standard (King County Level 3). Revised vault sizing calculations using WWHM should be provided with the construction permit submittal. Conveyance calculations were not provided in the preliminary TIR. Conveyance calculations shall be included in the final TIR to satisfy Core Requirement #4, Conveyance System. The conveyance calculations should include conveyance analysis of the flow through the existing bioretention swale water quality facility that was installed as part of Highland Estates and the stream through the King County park property. The bioretention swale shall continue to function as originally designed. Per the preliminary TIR, this project is exempt from Core Requirement #8, Water Quality Facilities as the project is proposing less than 5,000 square feet of new plus replaced pollution generating impervious surface. The project is proposing to use basic dispersion and restricted footprint to satisfy Core Requirement #9, On-Site BMPs. The combination of basic dispersion and restricted footprint provide at mitigation to at least 10% of the lot area. The TIR notes that full dispersion and full infiltration are infeasible BMPs due to site constraints and soil types. Limited infiltration is also infeasible due to the soils on site. Bioretention, rain gardens, and permeable pavement are infeasible as the site does not have infiltration rates of at least 0.3 inches per hour per the submitted geotechnical report. Prior to submittal for the civil construction permit, the applicant will shall apply and receive a decision for a storm drainage adjustment to not discharge at the site’s natural discharge location and divert the site’s stormwater to another drainage basin as shown on the submitted plans. The drainage adjustment is subject to review by the City Plan Reviewer and the Surface Water Utility Department. An adjustment request will only be considered if the vault is designed in accordance with the City’s Flood Problem Flow Control Standard (King County Level 3) to help mitigate for potential downstream issues. Thus, in addition to the Flow Control Duration Standard (Forested Site Conditions), the vault shall be designed to match the 100-year developed peak discharge rate to the pre-developed (forested) 100-year peak discharge rate. In addition, a Level 1 Downstream Analysis shall be completed for the downstream drainage path that flows will be diverted to. The downstream analysis should cover the entire flow path to the point where it rejoins with the natural flow path approximately 0.75 miles downstream of the site. The preliminary TIR only included a Level 1 Downstream Analysis for the site’s natural downstream flow path. The storm drainage adjustment application shall include a narrative describing the adjustment request and explanation of how the adjustment meets the two criteria for granting adjustments found in Section 1.4.2 of the 2017 RSWDM. The fee for the storm drainage adjustment is $566.50 ($550.00 +3 % technology fee). The preliminary drainage plan shows a piped stormwater conveyance system in the 156th Avenue SE and SE 2nd Place flowline that conforms to the City’s street standards. New storm drain shall be designed and sized in accordance with the standards found in Chapter 4 of the 2017 RSWDM. Storm drain with a minimum diameter of 12” is required in the public right of way. A geotechnical report evaluating site soil conditions was prepared by Cobalt Geosciences dated August 22, 2016 and updated April 24, 2017. The report notes that there was no evidence of earth movements, erosion, or indicator of future instability. Two small-scale pilot infiltration tests were performed within the property to evaluate infiltration potential of the site on April 21, 2017. The two areas were excavated to a depth of approximately 3’ below grade. Groundwater seepage was observed entering the excavations at a depth of approximately 2.5’ below grade. The report concludes that due to groundwater and the dense glacial till observed at the time, an infiltration rate of 0.3 inches per hour is not obtainable. Each new lot is subject to a stormwater system development charge. The 2017 SDC for stormwater is $1,608.00 per lot. A credit for two lots will be issued for the existing homes. Stormwater SDC fees are due at construction permit issuance. TRANSPORTATION/STREET COMMENTS Each new lot is subject to a transportation impact fee. The 2017 transportation impact fee is $5,430.85 per single family home. A credit for two lots will be issued for the existing homes. The transportation impact fee is due at the time of building permit issuance for each individual home. 156th Avenue SE is classified as a minor arterial. Per RMC 4-6-060, the minimum right of way width for a minor arterial with four lanes is 91’. The paved roadway section is 54’ consisting of 4 – 11’ travel lanes and 2 – 5’ bike lanes. A 0.5’ curb, 8’ planter, and 8’ sidewalk are required along each side of the roadway. The King County Assessor’s Map shows a current right of way width of approximately 60’ for 156th Avenue SE. A right of way dedication of approximately 15.5’ would be required along the project frontage. The City’s Transportation Department has established a corridor plan for this section of 156th Avenue SE. The corridor determined by the City’s Transportation Department requires a right of way width of 71’. The paved roadway section is 44’ consisting of 2 – 11’ travel lanes, 1 – 12’ center turn lane, and 2 – 5’ bike lanes. A 0.5’ curb, 8 planter, and 5’ sidewalk are required along each side of the roadway. The street section for 156th Avenue SE shown on the preliminary utility plan is consistent with the corridor plan described above. The applicant submitted a street modification request dated June 1, 2017 with the land use application. The street modification request is to conform to the City’s adopted corridor plan for the 156th Avenue SE frontage. City staff is recommending approval of the applicant’s modification request. Please see the Street Modification Criteria and Analysis for a complete summary of the request, staff analysis, and staff recommendation. SE 2nd Place is classified as a residential access street. Per RMC 4-6-060, the minimum right of way width for a residential access street is 53’. The minimum paved roadway width is 26’ which includes 2 – 10’ travel lanes and 1 – 6’ parking lane. A 0.5’ curb, 8’ planter, and 5’ sidewalk are required along each side of the roadway. The King County Assessor’s Map shows a current right of way width of approximately 60’ for SE 2nd Place. No right of way dedication would be required along the SE 2nd Place frontage. The street section for SE 2nd Place shown on the preliminary utility plan is consistent with the residential access street standards described above. Per RMC 4-6-060, a curb return of 35’ is required to meet City standards at the intersection of 156th Avenue SE and SE 2nd Place. The preliminary drainage plan shows a curb radius of 25’. This is not to City standards. Two perpendicular curb ramps per WSDOT standards are required at the corner of 156th Avenue SE and SE 2nd Place. Curb ramps shall be aligned to tie into the existing curb ramps on the opposite side of 156th Avenue SE and SE 2nd Place. Per RMC 4-4-080, the maximum width of a single loaded garage driveway is 9’ and the maximum width of a double loaded garage driveway is 16’. If a garage is not present, the maximum driveway width is 16’. Driveways shall not be closer than 5’ to any property line. Maximum slopes for driveways shall not exceed 15% provided that driveways exceeding 8% provide slotted drains at the lower end with positive drainage discharge to restrict runoff from entering the garage. Per RMC 4-6-060, street lighting is required as the project is larger than four residential units. A photometric study and street lighting plan per City standards shall be submitted with the construction permit submittal. The project does not require a Traffic Impact Analysis as the project produces less than 20 vehicles per hour in both the AM and PM peak periods. Paving and trench restoration within the City of Renton right of way shall comply with the City’s Restoration and Overlay requirements. GENERAL COMMENTS The fees listed are for 2017. The fees that are current at the time of the respective permit issuance will be levied. Please see the City of Renton website for the current fee schedule. Retaining walls that are 4’ or taller from bottom of footing and stormwater detention vaults will require a separate building permit. Structural calculations and plans prepared by a licensed engineer will be required as part of the building permit review. All civil plans shall conform to the current City of Renton survey and drafting standards. Current drafting standards can be found on the City of Renton website. A separate plan submittal will be required for a construction permit for utility work and street improvements. All plans shall be prepared by a licensed Civil Engineer in the State of Washington. Please see the City of Renton Development Engineering website for the Construction Permit Application and Construction Permit Process and Submittal Requirements. Please contact the City to schedule a construction permit intake meeting.