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APPLICANT RESPONSE - ENGINEERING.pdfLANDT CHN L IES, INC wig laolf PLANNING o PERMITTING o ENGINEERING,_ MAKING A -WAY" OUT OF "NO WAY" Date: December 6, 2016 �9y Ica if ac�91F „ To: Jennifer Lambert City of Edmondsg°I Engineering Division 425. 771.0220 www.edmondswa.gov Project Name: Swerk Building Permit for Single Family Residence Application Number: BLD20161004 Review Completion Date: 4 November 2016 Project Address: 18816 Olympic View Dr., Edmonds, WA 98026 The following pages are the responses to the Swerk Building Permit review comments of 4 November 2016. City comments are presented with numbering as provided in the review letter but are prefaced by the letter "C". Responses follow each comment and are numbered to match the response but are prefaced by the letter "R". Supplemental images or graphics are provided and are appended to the letter responses and noted by figure numbers that include comment number. Respectfully, Paolo Musante, MS, PE 360-653-2700 aolocedarcomm,com ,21 -Nov z016 18820 3rd Ave NE - Arlington, WA. 98223 (360) 652-9727 Fax (360) 652-5374 Responses to Review Comments GENERAL Cl) Please revise the title "Stormwater management site plan" to "Stormwater/utility site plan". R1. Plan has been retitled. C2) Clearly distinguish what will be installed with this project and what is currently installed (i.e. different line types, bolding, etc.). R2. All existing entities were/are drawn with grey color and various format of dashed lines. All labels for existing entities was/are presented with italics style of font. Legend has been expanded to include all standardized as displayed line styles. C3) The plans do not scale as stated. Please revise the plans accordingly. Provided PDF file of plan set provided was correctly scaled. Steps taken to ensure re -submittal plan is plotted correctly at 1:1 plot scale. General Notes Cl) Note #13 — Please revise the note to include that all pipe shall have a minimum of 2' of cover under drivable surfaces. R1. Note has been revised. Gill!i=- Cl) Note #1 — Please change `street use' to 'right-of-way permit'. R1. Note has been revised. C2) Add the following note —'If rim to invert exceeds 5' (ft.) a type II manhole must be installed.' R2. Note has been added. Swerk Building Permit Response to Comments 6 December 2016 Page 2 of 2 Swerk Building Permit Response to Comments 6 December 2016 Page 3 of 3 WATER Cl) It appears that a fire sprinkler system is required for this property. The applicant will be required to pay for the new tap on the main and the new meter. This fee is $2970.00. 1. To be addressedr (I Ben Swerk understand that this is required) a. Please add a note that a 1" meter is to be installed. R1a. Note has been added. C1 b. Please show a 1-1/2" line to be installed from the back of the meter to the house (as required for a combination fire and domestic service line). Rib. Note has been added. C1 c. Please label the pipe material and note tracer wire to be installed on the water service line. R1. Notes added to pipe label. C2) Show that there is a minimum of 3' of horizontal separation between the water and the dry utilities (i.e. power, phone, gas, cable, etc.). R2. Separation note added. C3) Please keep in mind that there is a requirement that there is a minimum of 10' of horizontal separation between the water and the sewer lines. R3. Separation note added. Swerk Building Permit Response to Comments 6 December 2016 Page 4 of 4 SEWER Cl) Please label the sewer easement as private. R1. The text "Private' added to label. C2) Show a cleanout at the edge of easement and within 2' of the structure. R2. Cleanouts & labeling added. C3) Please show the invert elevations at the stub and the house so that slope (minimum of 2%) and coverage (minimum 2') can be verified. If the slope of the pipe exceeds 20% the pipe will need to be anchored. R3. Invert elevations added. C4) Label the pipe material and size. R4. Labeled new sewer pipe size and material. Swerk Building Permit Response to Comments 6 December 2016 Page 5 of 5 STORM Cl) There appears to be inconsistencies between the Civils and the Landscape Plan regarding impervious areas. Changes have been coordinated for all sheets. C1 a. What is the material for the play area? R1a. Material description added to Sheet C1 C1 b. If there are any areas where crushed rock can be driven on, the area will be considered imperious. Rib. Although not used for Swerk permit, recognize that crushed rock on properly prepared subsurface (geogrid generally also used) can function as porous pavement as pore volume in bed can be sized to meet reservoir needs for full infiltration. We label these as private porous gravel driveways or parking, so please use caution with blanket definitions. C1 c. The patio (stamped concrete) to the west of the garage is not shown on the Civils. Ric. Patio area and surfacing label has been added to plan. C1 d. Please revise the plans to be consistent and revise the imperious surface calculations accordingly. Rid. All storm plan data and drainage calculations have been updated to the finalized layout, C2) Show where the footing drains will discharge to. If the footing drains are to discharge to the onsite stormwater management system, please address the allowance for the footing drains in the design calculations. R2. The downspout / footing drain note has been expanded to explicitly specify the connection to infiltration facility. Realize that by use of the HSPF model analysis via the WWHM software interface, all surface and interflow waters intercepted by any footing and/or wall drains are automatically a component of the hydrologic analysis, thus are addressed. Only when true aquifer or'groundwater' is intercepted by a footing drain is additional and more complicated modeling required. C3) All pipes shall discharge to a catch basin prior to discharge to any stormwater management facilities. Please revise the plans accordingly. R3. Per the plans, other than footing, which do not need/require CB interception, all yard drain pipes from roof and driveway have yard catch basins with filters specified prior to entry to the infiltration facility. Swerk Building Permit Response to Comments 6 December 2016 Page 6 of 6 C4) Show the overflow path for the proposed stormwater management facility and clearly indicate/show that it will not negatively impact downstream properties. R4. An probable flow line path for overflow release has been added to plans. Overflow is addressed in the report which demonstrates no negative impacts per code. C5) Please provide a cross section detail of the driveway between lot 1 and lot 2's driveway so that it is clear how the berm will be constructed to prevent runoff from lot 1 enter the stormwater management system for lot 2. If it is not possible to prevent the runoff, the system could be designed to account for the additional impervious area. R5. An extrinsic berm detail is provided. The berm was requested per the earlier city comments to prevent additional runoff to new driveway and a 'berm' exists there now. Meticulous analysis shows that about of 160-sf of currently compacted soil will be replaced with pavement on Lot-1 that this berm is intended to re -direct the runoff from. Technically, the berm is not required as this flow should be considered existing upstream bypass flow. Redirected runoff ultimately will be picked up by wall drains and routed to the proposed drywell. [***] 6) Please show the side sewer on the segmental wall detail. The detail should show that there is no point loading on the sewer pipe. R6. Sanitary sewer protective sleeve added to detail. Swerk Building Permit Response to Comments 6 December 2016 Page 7 of 7 The following comments are from the City of Edmonds stormwater consultant. Cl) The letter report (7/22/16) states that a treatment facility must be provided since the total impervious area exceeds the 5,000 sf threshold; however, the total pollution -generating impervious surface (PGIS) does not exceed the 5,000 sf threshold for Small Site Minimum Requirement #6, so treatment is not required. R1. A welcome comment. A common misinterpretation for MR#6 is that if project exceeds 5,000-sf impervious, a treatment BMP or facility is required, if PGIS is part of total, thus treatment was included. This also addressed potential request by city to include and account for entire driveway area from road. Treatment facility removed. C2) The letter report (7/22/16) and plan set (8/2/16) describe a stormwater facility that appears to be a rain garden stacked on top of an infiltration trench, which is not an approved BMP in the 2005 Stormwater Management Manual for Western Washington (SWMMWW). Since treatment is not required, it is recommended to simplify this design to either a rain garden or an infiltration trench or to show the facilities in series, but not stacked on top of each other. The letter report states that "This assemblage is commonly referred to as a rain garden, through there will be no requirement for the intensive landscaping typical of such a facility, this being simply a BMP and used primarily for percolation treatment of the driveway runoff." This statement is incorrect and appears to be mixing aspects of infiltration trenches and rain gardens. If a rain garden is selected, vegetation would be required per the guidance in the 2005 SWMMWW. R2. For new design without treatment facility, this comment is moot. That said, I feel it best to point out that this assessment is in error and why. A treatment facility can precede an infiltration facility and is typically required. The flow from the treatment facility is to be routed to the infiltration facility. This is THE approved format. For a bioswale (a.k.a. rain garden), the outlet for the treated water (91% of total flow volume) is that which percolates through the soils. This is the Outlet 2 in the WWHM module. A standpipe or weir is the surface outlet for overflow, which should be only for water that does not require treatment of is in the remaining 9% of the total runoff volume and is the Outlet-1 in the WWHM module. In the reviewed design, the treated water flows (i.e. falls) from the treatment facility into the infiltration facility. This is perfectly acceptable and a very compact layout for the facilities. This arrangement should be encouraged in urban areas as it helps the City stay in compliance with the GMA. The important aspect is to understand that all required treatment waters percolate through the 'swale' soils and are allowed to'fall' - hence the easy to conceptualize100-in/hr infiltration rate is used for the '2"d outlet' of the facility. This rate could be as high as 2,400-in/hr for flow through the gravel bed. Annotated image provided to illustrate design and approvability. Basically, if a layout can be schematically mapped in the WWHM software, it should be legitimate. Swerk Building Permit Response to Comments 6 December 2016 Page 8 of 8 The rain -garden reference, while not 100% accurate, as noted, due to lack of specific plantings, was presented for aid for understanding function. Common misperception for true bio-swales, in the 'classic sense', expects that water flows in one end and out the other. 'Bio-swale' design can be such that all received runoff will percolate through the soils. When this happens, a gravel trench under -drain pipe is used to route the water to the next facility. In this case, there is no underdrain. The pipe showed in the rock -bed is the feed from the roof runoff to the infiltration trench. The landscape requirements for 'rain gardens' add not just treatment, but to add extra transpo- evaporation, which is not required or considered extremely minimal in this situation. The plantings for bio-swales fits the situation. Swerk Building Permit Response to Comments 6 December 2016 Page 9 of 9 C3) The plan set (8/2/16) describes a bioswale in detail 300 and in the seeding mix specified in detail 120. A bioswale (or biofiltration swale) is designed to be a flow -through water quality treatment BMP, not an infiltration BMP. R3. The bioswale IS (was) the treatment facility. See previous response. The infiltration facility hydraulically follows the treatment facility, which is beneath the treatment in this case. C4) The perforated pipe included in the rock bed in detail 300 on Sheet C2 of the plan set (8/2/16) was not included in the WWHM modeling and can clog easily. Due to the infiltration rates, an underdrain pipe is not necessary. If it is included in the design, it should be slotted PVC pipe and included in the WWHM modeling inputs. R4. The pipe is not an underdrain. See response-2. This is the infiltration facility distribution pipe. It is protected by a downspout sediment and floatables filter as is called out per Detail 302 on the sheet c2. Cleanout are also specified for each end of the pipe across the perforation area. This will not clog easily. C5) The letter report (7/22/16) and plan set (8/2/16) describes the compost -amended soils requirement (BMP T5.13) instead of the bioretention soil mix required for bioretention installations. The WWHM output report (7/13/16) also uses the "SMMWW 12 in/hr" material type which is linked to the bioretention soil mix specifications, not BMP T5.13. R5. There is no longer a treatment facility required, hence no treatment soils need be specified and nothing to address. C6) All disturbed pervious surface areas (areas that are not covered with an impervious area or a stormwater BMP) shall be amended per BMP T5.13 (Post -Construction Soil Quality and Depth). Please add a note to the plan set regarding this requirement R6. Extra soils note added to sheet C1. C7) The WWHM output report (7/13/16) contains the following errors/discrepancies: C7a. The Everett Rain Gage with a Precip Scale of 0.80 is used for sizing; however, the Edmonds Stormwater Supplement requires the use of the Puget East 36 rain gage which can be selected by checking "Use WS-DOT data" on the "Map Information" tab in WWHM. 117a. The analysis has been re -run with the WSDOT precipitation / evaporation series and report updated. C7b. The pervious area is 0.08090 acres (3,524 sf) which is inconsistent with the 1,620sf included in the letter report. Swerk Building Permit Response to Comments 6 December 2016 Page 10 of 10 R7a. While this typo discrepancy is now irrelevant since there is no surface water draining to a bioswale, the larger pervious area value modeled shows the healthy design and capacity of the previous SWM facility proposed. C7c. The infiltration rate is 100. 117c. Comment now irrelevant since bioswale has been removed. Rate presented was appropriated. See response to C2. C7d. The riser height for the swale is 0.75 feet; however, the letter report specifies a 6-inch ponding depth R7d. Comment now irrelevant since bioswale has been removed. It is worth noting that the riser height in the WWMH report should have read 0.5 ft to be consistent with design though review of hydraulic table shows that any value above 0.5 ft is inconsequential as there is no surface release and no modeled water level reached even 0.5 ft. C7e. The geotechnical site evaluation identifies the site soils as Class A soils; however, Class C (till) soils are specified in the WWHM output report. R7e. Not quite a correct observation. The geotechnical assessment and the NRCS mapping shows the surface soils as hydrologic group C soils though the geotechnical site exploration shows that these lower permeability soils reside above a thick layer of higher permeability advance outwash soils, more of a Group A soil (as explained in the report's soils section). This is why the infiltration facility requires a minimum depth of 5 ft located near the base of the slope to ensure contact with the higher permeability soils. C7f. The pervious areas are modeled as pasture. If these areas will be standard lawn/landscaping, they should be modeled as lawn. ***An alternative to the WWHM modeling approach is to use the City's simplified sizing (Handout #E7213) to size either an infiltration trench or a bioretention cell.*** R7f. Note that per the DOE guidelines, areas restored per BMP 5.13 gain credit and safely can be modeled as pasture in the continuous modeling. This is no longer an issue as there is no longer surface runoff to the facility and the remaining pervious area has effectively a net reduction change in runoff characteristic from LAWN to PASTURE. This requires no flow control per the small project requirements. C8) WWHM2012 is the most recent and up-to-date version of the Western Washington Hydrologic Model. Although not required, it is recommended for use over WWHM4 since it contains the latest updates from the model developer. R8. The WWHM4 pro software is the identical to the WWHM-2012 for analysis (it is the same program). The pro version simply is provided with additional 'Pro Element' analysis modules Swerk Building Permit Response to Comments 6 December 2016 Page 11 of 11 and other support back -ground tools like time series analysis and processing. The analysis has been re -run with the public 2012 version for review simplicity and to avoid complication. C9) The infiltration testing conducted at TP-1 and TP-3 are too variable to support 2 inches/hour at the site of the proposed infiltration facility. The geotechnical report (5/16/13) states that an infiltration trench installed along the west side of the west lot at and around TP-3 may be designed with an infiltration rate of 2.5 inches/hour, but anywhere else on the lot should be designed for an infiltration rate no more than 0.24 inches/hour. R9. Please re -read the report Section 1.3.1, Expanded Soils Evaluation (now Section 1.2.5 in the resubmitted report). I respectfully disagree with this comment and feel that use of a 2.0 in/hr rate is well supported per the drainage manuals and industry standard guidelines. Further note that the facility is sited in the location of the TP-3 where the favorable sandy soils sample was taken and analyzed. C10) The letter report (7/22/16) states that the project is located in the Fruitdale drainage basin and the plan set (8/2/16) states that the project is located in the Puget Sound drainage basin. Please confirm correct drainage basin and update for consistency. R10. The report is accurate as written. All of Edmonds drains to the Puget Sound Watershed. I use the DOE definitions so that the larger area defined by the natural topography and drains to a point (river or water body) is the watershed. Local basins or sub -basins fall within the watershed. The local sub -basin (a.k.a watershed per city map) is named Fruitdale and is accurate per the Edmonds April 2010 "STORMWATER CODE SUPPLEMENT TO EDMONDS COMMUNITY DEVELOPMENT CODE CHAPTER 18.30", EXHIBIT A. Map extract follows: Swerk Building Permit Response to Comments 6 December 2016 Page 12 of 12 ii FIGURE B-1 CITY OF EDMONDS WATERSHEDS _. Deer Creek F. Perrinville fEdmonds Marsh, Puget Sound Edmonds way Puget Sound Piped Prultdale llllill!/ll/r Shen Creek Good Hope Pond Shellabarger Halls Creek Southwest Edmonds A Hindley Creek Southwest Edmonds B Lake Ballinger Stilthouse Creek V/11;I Lund'sGulch1� Talbot Park A Meadowdale A Talbot Park B Meadowdale B Terrace Creek Northstream Westgate Pond Outfall Creek Willow Creek 0 1,000 2,000 6.000 a lnuu r�ara 1 in = 2,000 ft No warranty of any soil, accompany this product March 30, 2010 Including acmracy, 0tners or mefchanlablllly .✓,.,,VIA ��W KiraYII y„ c ii � g"wVbp rv�#4 QI kilt ��r r . Y 1l %/ P, D� I �1 1 The sentence has been restructured to represent the hierarchal order for clarity. 11) The topographical contours are not labeled in the plan set (8/2/16). R11. Contour elevation numbers have been restored. &wLY��O N A No, Yi41k'1'h'�l' RMti mt 06146AW 12) The plan set (8/2/16) contains two details with the 302 callout (Infiltration Drywell on Sheet C1 and Downspout Filter for Infiltration Facility on Sheet C2). R12. To clarify, detail 302 on sheet C1 has been renumbered to 304. Swerk Building Permit Response to Comments 6 December 2016 Page 13 of 13 Cl) As changes are made, please revise this plan sheet as needed. R1. Changes have been coordinated for all changes in sheets. GENERAL C1) Show the filter fence and reference the Edmonds Standard Detail E1.1. R1. Filter fence linework and detail callout reference has been added to plan. C2) Add a note that the filter socks will be added to catch basins per Edmonds Standard Detail E1.3 as needed, downstream from the site and areas where debris may enter the City stormwater system from the construction/vehicles leaving the site. R2. Note added though there are no catch basins within 100 ft of the closest parcel corner downstream of the project. Any potential runoff would require travel across >100 ft of 1% to 2% lawn before reaching the any street or paved area. BMP call -out is not warranted. C3) Show the construction entrance and reference the Edmonds Standard Detail E1.2. R3. Note that existing entrance area is already paved and large paved staging area is available in Lot-1 as noted in CSWPPP. NTL, callout added. C4) Show protection fencing around any low impact stormwater facilities to prevent disturbance of the area during other site construction activities. R4. Updated design precludes need for such measures. C5) The plans do not scale as stated. Please revise the plans accordingly. R5. Apparent plotting error. Ben Swerk to confirm printing / plotting at 1:1 scale of provided PDF files. Permanent Stabilization Notes Cl) Note 1 — Please revise to state that seeding will occur as soon as disturbance of the soils have been completed. R1. Stabilization note have been updated. Swerk Building Permit Response to Comments 6 December 2016 Page 14 of 14 SHEET C4 OF C4(Grading 'Plans Cl) As changes are made, please revise this plan sheet as needed. R1. Changes in site grading and surface feature changes have been implemented. C2) Please add a note to the plans that the driveway shall not exceed a 14% slope. R2. Note has been added. Swerk Building Permit Response to Comments 6 December 2016 Page 15 of 15 LANDSCAPE PLAN Cl) The plans show trees and plants being installed over the existing private sewer system. Please note that this may make maintenance an issue in the future. RIBS - I understand. C2) There appears to be inconsistencies between the Civils and the Landscape Plan regarding impervious areas. RIBS — These have been resolved, if there is a discrepancy the Civil plan would rule. C2a. What is the material for the play area? RBS — We will have woodchips or pea gravel for the play area. C2b. If there are any areas where crushed rock can be driven on, the area will be considered impervious. RIBS — for that area west of the two -car garage we have included this as part of the impervious calculation just to be on the safe side. C2c. The patio (stamped concrete) to the west of the garage is not shown on the Civils. RBS — Now shown on all plans. C2d. Please revise the plans to be consistent and revise the imperious surface calculations accordingly. Changes have been coordinated for all changes in sheets. Swerk Building Permit Response to Comments 6 December 2016 Page 16 of 16