05-0601 City Review letter No. 2 020207(360) 458-8438 (360) 458-3144 FAX www.ci.yelm.wa.us City of Yelm Community Development Department 105 Yelm Avenue West P.O. Box 479 Yelm, WA 98597 February 2, 2007 Robert Connolly Skillings
Connolly Inc 5016 Lacey Blvd. SE Lacey, WA 98503 RE: The Hutch Subdivision – SUB-05-0601-YL Second Review of Civil – Site Construction Documents Mr. Connolly: The City of Yelm has completed
the initial review of the proposed subdivision. Your application included: ?? Construction Plans dated 12/14/06 ?? Stormwater Report dated 12/14//06 ?? Landscape Plans not included We
have reviewed the plans for compliance with the City of Yelm Development Guidelines, the DOE Stormwater Manual and general standards of civil engineering practice. In an effort to expedite
the review of this project we have sent this project out for Peer Review. The following comments need to be addressed before the plans may be approved for construction. The comments
are summarized below: Peer Review Comments from Shea and Carr: Storm Drainage Report: 1.????? Storm Drainage Report Section 1 – Proposed Project Description – The paragraph on Mountain
View road indicates that an addendum to the storm drainage report will be issued at a later date. Please remove this language. 2. Storm Drainage Report Section 3 – The infiltration rates
provided are for Basins A and B only. An assessment of the infiltrative capability of Basins C and D also need to be provided. These rates should be used for calculation of required
volumes. 3. Storm Drainage Report Section 9 – Please provide a stage/storage relationship for the stormwater ponds in Basins C and D in order to assess the volume provided. 4. Erosion
Control Report Section 5 – Inspection Sequence – The inspection sequence should include further sequencing information. For instance, inspections should occur after installation of erosion
control measures, after installation of permanent stormwater features, and after installation of permanent site restoration.
February 2, 2007 5. Erosion Control Report Section 6 – Control of Pollutants Other Than Sediment – Please include a requirement for a designated wash down area for equipment and concrete
trucks. 6. Storm Drainage Report Appendix B – Please provide calculations on how the discharge rates of 1.897 cfs and 1.009 cfs were computed for discharge nodes D1 and D2 respectively.
I assume this was calculated using the infiltration rate times the bottom area of the gallery but do not see any computations. Please note, this will also need to be provided once the
modeling for Basins C and D are provided. 7. Storm Drainage Report Appendix B – Please provide calculations on how the 6 month storm event flow was determined for Basins C and D. Also
provide calculations on how the required retention volumes for the stormwater ponds were calculated. This information has been provided for Basins A and B only. 8. Storm Drainage Report
Appendix B – In order to maintain sheet flow across the filter strip, a y value of ½ inch should be used. Please revise the y value to reflect this in the biofiltration filter strip
calculations. Please refer to Section III-6.4 of the 1992 DOE Manual. 9. Storm Drainage Report Appendix B – According to Appendix III-6.1 Design Step D-2, the manning’s n for dense grass
should be about 0.07. Table III-2.8 in Chapter III-2 also supports the use of much lower values than 0.24. Please revise the manning’s n used in the computation of the biolfiltration
strip design for Basins C and D. 10. Storm Drainage Report Appendix B – According to Section III-6.4, the length of a filter strip should normally be 100 to 200 feet in length. However,
given the cross sectional area has been greatly increased, the 22 feet of length provided is acceptable if it can be shown that the level spreader will spread the flow across the entire
100 feet of width. As currently shown, the level spreader is not expected to provide this (see comments on Sheets 28). 11. Storm Drainage Report Appendix B – In order for the biofiltration
strips to function, sheet flow must be maintained for the entire 6 month storm volume. Therefore, demonstrate that the lower cell of the pond bottoms for both Basins C and D can hold
the 6 month volume. If they cannot, ponding will occur on the filtration strip and will negate its treatment effects. 12. Storm Drainage Report Appendix C – The geotechnical report provided
does not contain infiltration information for Basins C and D. An evaluation of the expected infiltration rates needs to be provided for these basins. 13. Storm Drainage Report Appendix
B – Please provide pipe sizing calculations. Although you have indicated that the largest drainage area is 5.45 acres and it has a flow of 2.17 cfs and the pipe capacity is actually
2.73 cfs for a 12 inch pipe at 0.5% slope, no computations have been provided to support these numbers. A computation of the drainage area, flow for the drainage area, and pipe capacity
should be shown for each pipe. This should take in to account the cumulative effect of the flow to the the pipes. In other words, the cumulative drainage area may be 5.45 acres for the
pipe, but the cumulative flow is computed based on the individual drainage areas and associated times of concentration. Even if all pipes are adequately sized, calculations demonstrating
this need to be provided? As the City will take
February 2, 2007 over the maintenance of this drainage system, it shall be demonstrated that the pipes can handle expected flows. Please note, a 25 year event can be used for pipe sizing.
Construction Plans: All Sheets: The following comments apply to all sheets: 14. Some minor redline comments have not been called out in the letter but need to be addressed in the revised
plans. Sheet 3 of 29: 15. The construction plans provided do not provide any additional erosion control measures beyond the addition of the silt fencing. Please provide additional measures
as originally specified. Sheet 5 of 29: 16. The eastern intersection of Road B and Road A, still has contours that seem to indicate a possible low or high spot in the middle of the road.
Does this correspond with the bulbouts? 17. Several contours on Road D seem to disappear. Will a retaining wall be used? What happens to these contours? Sheet 6 of 29: 18. The cross
sections for Mountain View Road and the plan view on Sheet 28 do not seem to match. Please revise the cross section to show the complete limits of existing pavement. Also, please indicate
if pavement removal will occur. The current cross section shows proposed paving for the entire cross section. If existing pavement is to remain, please show as different line types to
signify what is proposed and what is existing. Further, from the plan view on Sheet 28, it appears that the existing paving extends beyond the proposed curb line in to the planter area.
Please show these limits on the cross section and label as being removed. 19. On Mountain View Road, the area from Yelm Highway to Station 307+59 is not adequately covered by a single
cross section. There are areas where the existing pavement extends further out and existing curb will be used on the west side of the road. There is also an area that has wider pavement
to accommodate what appears to be a turn lane. Please provide additional cross sections to cover these areas. Sheet 7 of 29: 20. The profile of Road D has incomplete information. See
plans. 21. Typically, an angle point is only used when the change in grade is 1% or less. Where Road D matches to Mountain View Road, the transition from the 2% crown slope of Mountain
View Road to the 3.68% slope of Road D is achieved with an angle point. A vertical curve should be used. Please revise. 22. Comment #21 also applies to the transition from Road D to
Road A. A vertical curve should be used. 23. It appears that less than 6 inches of clearance is provided between the storm line in Road D and the water line. Please provide a minimum
of 6 inches. Sheet 8 of 29:
February 2, 2007 24. According to the response letter, a catch basin was added on the north side of Road A as requested. No catch basins have been added on the north side of the road.
The spacing requirement of 500 feet is still exceeded between CB #4 and CB #10. Sheet 10 of 29: 25. Invert information has been changed on catch basins #31 and #23. However, the flow
problem has not been fixed. Further, information has now been changed on CB #39 that has created a gravity flow problem from this CB to CB #31. The direction of flow is from CB #39 to
CB #31 to CB #23. The respective inverts for these CB’s are 335.27, 335.45, and 336.84. Please revise including the slope information on the pipe connecting these catch basins. Sheet
18 of 29: 26. There does not appear to be any revision addressing how the sewer service for lots 46 and 47 will connect. Please see comment #64 from previous letter. 27. There does not
appear to be any revision addressing how the water services for lots 41-44 will connect. Please see comment #65 from the previous letter. 28. It appears that there is less than 6 inches
of clearance between water and storm lines in the profile for Road D. Please revise. 29. Please show the approximate locations of the other underground utilities in Mountain View Road
on the profile for Road D – gas, telephone, etc. Sheet 20 of 29: 30. The profile for Road E should show approximate locations for crossings of existing underground utilities such as
the buried telephone line shown in plan view. An approximate depth should be available from the phone company. 31. Please add a note to the plans that the water and sewer stubs shown
from Killion Road are not existing, but are part of the proposed Killion Road improvement project. Please also note that, if these stubs are not in place at the time of construction,
contractor to contact engineer regarding design revisions. Sheet 28 of 29: 32. Please provide flow arrows on all storm pipes. 33. The pipe between CB from note #5 and the CB from note
#7 has been designed to be full of water. The CB from note #7 shall be made deeper to provide positive flow from the CB from note #5. (Please note, comments would be made easier if the
catch basins were numbered as on other sheets). 34. As the Neenah Foundary catch basin is not a standard structure, please provide a detail. 35. It is not clear from the cross sections
on Sheet 6 or this sheet where the limits of the existing pavement are and what is occurring with the existing pavement. Will it all be removed and replaced? 36. Please call out the
invert elevation of the pipe in to the ponds within the pond details rather than on the pipe call out. The elevations noted do not seem to correspond to what is shown on the detail.
The details show a pipe at the pond bottom elevation. The noted elevations appear to have the pipe further up the slope. 37. Please provide a detail of the level spreader. Please also
provide further detail of its relationship to the incoming pipe. As shown in the pond sections, the outflow from the pipe would simply flow over the level spreader and flow in to the
pond as concentrated flow.
February 2, 2007 Concentrated flow is not allowed with a biofiltration strip. A dispersal trench may be a better application to achieve sheet flow down slope from a pipe. 38. Please
indicate the maximum water elevation in the pond cross sections. 39. Construction Note #2 is called out a couple of times on Mountain View Road where the notation doesn’t make sense.
Please clarify. 40. It is unclear from the profile whether the pipe connecting the CB from note #1 to the CB from note #7 has adequate clearance from the existing water and sewer mains.
A note on the pipe call out states that the contractor to field verify. However, this information should be available from the City by requesting as-built drawings. The pipe design should
be checked against the as-builts in addition to the notation for the contractor to also field verify. 41. Please call out the existing water line on the profile. Sheet 29 of 29: 42.
On CB’s that have multiple pipes, please indicate inverts of all pipes as was done on all previous sheets.. 43. The CB from note #5 has a higher invert than the CB from note #7. Please
revise. 44.Remove the storm pipe from the planter strips. In order to achieve proper distance from existing utilities, the storm main line could run along the west side of Mountain View
Road. 45. It is unclear from the profile whether the pipe connecting the CB from note #1 to the CB from note #7 and the pipe connecting the CB from note #11 to note #13 have adequate
clearance from the existing water and sewer mains. A note on the pipe call out states that the contractor to field verify. However, this information should be available from the City
by requesting as-built drawings. The pipe design should be checked against the as-builts in addition to the notation for the contractor to also field verify. If the profile of the existing
water is correct, it appears that there may be a conflict with the pipe connecting the CB from note #1 to the CB from note #7. This conflict should be corrected. 46. Construction note
#2 is called out several times where it does not make sense. Please clarify. 47. There are a couple of existing elements that are not identified that may require adjustment or relocation.
Please identify. Sewer Departments Review: Completed By Jon Yanasak 1. All fittings used for the sewer installation need to be PVC. No Ductile iron fittings! 2. The “encasement note”
shown on sheet 20 does not apply to Sewer pipe sleaving. 3. Mountain View Road stormwater catchbasins are shown over the existing sewer system. Please resubmit a design that does not
have this conflict. Water Department Review: Completed By Edward Smith: 1. Can the water meter for lot 106 be moved to /with lot 107 to make it a double and to get away from the sewer
box? 2. Can the water meter for lot 105 be moved to /with lot 104 to make it a double and to get away from the sewer box? 3. Sheet 20 Notes 9 and 10. The water main is not stubbed out
in this area. This needs to be hot tapped. 4. The air/release need to exit thru the side or back of the box. (Not the lid) 5. Any Pocket Parks, street frontage on Killion Road and Mountain
View Road with irrigation meters and double check valve assemblies 6. All the fire hydrant need to have a six inch gate valve for the fire hydrants at the main.
February 2, 2007 Please review and revise the plans to address the above referenced comments. When the project is resubmitted you will need to submit 4 sets of plans, 2 stormwater reports.
The project engineer is required to include a written response with the resubmittal, indicating how all the review comments above have been addressed or responded to. This will significantly
expedite our review of the project. Please do not resubmit the construction plans unless the landscape plans are included. The City will no longer accept partial resubmittals. If you
have any additional questions or comments please do not hesitate to call or contact me at jimg@ci.yelm.wa.us. Community Development Department Respectfully, Jim Gibson P.E. Development
Review Engineer