Peer Review Comment LtrSCJ ALLIANCE
CONSULTING SERVICES
November 12, 2018
Tami Merriman, Associate Planner
City of Yelm Community and Economic Development Department
105 Yelm Avenue West
Yelm, WA 98597
Re: Peer Review —Yelm Auto Recycle (AKA NPR Recycling)
SCJ Project No. 0605.05 Task 41
Dear Tami:
The City has requested SCJ Alliance conduct a peer review of the above referenced project. We have
performed the review based on the City of Yelm Municipal Code, Development Guidelines and known
City policies. This review consisted of the following documents:
• Construction Plans — dated 9/16/2018 — Please note that the deferred improvements for the
road frontages, including related drainage improvements, were not reviewed. It is assumed
these will be resubmitted for permit when road frontage construction is required.
• Drainage Report - dated September 2018 — Please note that models and information for Basins 1
and 4 were not reviewed as these will be for deferred improvements. It is assumed these will be
resubmitted for permit when road frontage construction is required.
City of Yelm Notice of Site Plan Review Decision
Our comments and observations from the review are:
Construction Documents:
Sheet C0.1
1. Based on the topography shown on the west property line it appears that some off-site drainage
is directed to the site in the vicinity of the storm pond. Sufficient contour information is not
shown to determine the extent of this offsite flow. Please provide additional information to
determine if off-site flow is directed to the site. If it is, then this drainage will need to be
addressed.
Sheet C1.1
2. Note 8 indicates that a detail for the trash enclosure will be provided on sheet C1.2. A detail has
not been provided.
3. Driveway aprons are required to be concrete up to the ROW line.
4. Is curb proposed along the north side of the pavement? Grading proposed along this edge
seems to assume a curb would hold drainage from the yard area, but it does not appear a curb is
proposed. If flows are directed as shown and there is no structure to either hold the drainage
8730 Tallon Lane NE, Suite 200 • Lacey, WA 98516 • Office 360.352.1465 • Fax 360.352.1509 * scjalliance.com
November 12, 2018
Page 2
on the asphalt or direct flow through a channel, there will be erosion between the pavement
and the gravel. Please clarify.
Sheet C1.2
5. A detail is provided for wheel stops for compact stalls, but no compact stalls are indicated on
the site plan. Please clarify.
Sheet C2.1
6. There should be silt fence placed along the property border with Northern Pacific Road. Based
on the proposed grading, there is potential for silty water to get onto the adjacent road. Silt
fence should also be placed along the private road on the west as shown on the attached.
7. There needs to be silt fence along the north property line.
8. The silt fence symbol for the 1,640 feet of silt fence on the east property line is hard to read and
exact location cannot be determined. Based on the grading, the silt fence should be located
along the entire boundary adjacent to development.
9. As all of the drainage facilities are infiltration facilities, the infiltrative pond bottom surfaces
should be protected from silty water during construction. Please clarify how this will be
achieved. Usually inlet protection and silt fence are insufficient to provide sufficient protection.
Notes indicating that infiltrative surfaces be protected from silty waters can be sufficient.
Sheet C2.2
10. A detail for a grass lined channel has been included on this sheet but is not noted on Sheet
C2.1. Please clarify.
11. Under the TESC construction sequence, there are multiple references to pervious asphalt.
appears this sequence was written for a different project. Please revise.
Sheet C3.1
12. Is the intent for the yard storage area drainage to sheet flow directly into the V -ditches and
bioretention cells? Per the 2014 DOE Stormwater Management Manual for Western
Washington BMP T7.30, velocities of entering flows must be 1 ft/second or less to minimize
erosion potential of side slopes of the ditches and bioretention cells. Calculations of expected
velocities should be provided in the drainage report. If velocities exceed 1 ft/second, then a
design modification will be needed.
13. How are the roof drainage systems being connected to the site drainage system?
14. Provide more information on the v -ditch on the east side of the site (as noted on plan). In
addition, this ditch is proposing a 90 -degree turn. It is likely that this area will erode, and water
will escape the ditch. The v -ditch on the west side has a turn as well. Although this turn is less
severe, it should also be checked to see if velocities will cause flow to erode the ditch at this
turn. Per the 2014 DOE Stormwater Management Manual for Western Washington BMP C201,
sharp changes in alignment, bends or changes in grade should be avoided.
15. It appears that Basin #1 is for the future road frontage improvements as well as some currently
proposed landscaping. It also appears that Basin 4 is also for the future road improvements and
the landscaped areas. It is understood the road frontages will be deferred as well as related
drainage improvements. What will happen with the proposed landscape area drainage in the
interim? Basin 4 is an especially large area with no plan for drainage flow. It appears that the
Basin 1 drainage will flow onto the adjacent private road and the Basin 4 drainage will become
part of the Basin 3 drainage. Please address what will happen with Basin 1 and 4 drainage until
such time that the future facilities are constructed.
16. It is assumed CB #'s 13 and 14 will also be deferred. Please note on the structure table.
` November 12, 2018
Page 3
17. Per Chapter 5 of the Yelm Development Guidelines the only allowed polyethylene pipe is ADS N-
12 pipe. Please note this on the plans. Other allowed pipe types include PVC, plan and
reinforced concrete, and ductile iron.
18. There are several lines noted on the attached redlines. What are these? Is it some type of
drainage structure? These lines were not legible enough to understand. They show up on
multiple sheets, but they are never noted.
19. Please provide cross section and slope information for all proposed v -ditches. Please provide
ditch lengths as well.
Sheet C3.2
20. Provide an emergency overflow for the Basin 2 infiltration pond.
21. Outfall protection needs to be added where noted.
22. The note on this sheet for the gravel indicates that the gravel yard shall be fine -graded but no
grading information has been provided on this plan. Please clarify.
23. The note on this sheet for the gravel indicated that CSBC be added as needed. Given the highly
permeable nature of the native soils and the plan to store vehicles in this area, the gravel area
should be hardened sufficiently to prevent direct infiltration and promote runoff to the
bioretention cells. Therefore, the entire area should be compacted and covered with CSBC of a
uniform depth.
Sheet C3.3
24. The information for Section AA for Section 1 does not match information from Section 3 on
Sheet C3.3. The section on Sheet C3.3 shows that the top of the berm separating the
bioretention cell and the infiltration cell comes to a point and does not have a width. The detail
on Sheet C3.4 shows and 8 -foot wide berm. The overflow spillway will not work as designed if
the detail on Sheet C3.3 is correct. The grading plan on Sheet C3.2 seems to show a 3 -foot
width. Please provide consistency between the plan views and cross sections.
25. Same as previous comment for the other bioretention cell and infiltration cell internal spillway.
The information shown on the grading plan and various cross sections do not align. Please
correct.
26. Bioretention cells should be planted with more than grass. See the 2014 DOE Manual for
Western Washington for additional information on planting requirements.
Sheet C3.4
27. It is assumed that detail 6 is for the deferred stormwater facilities. If so, then it should be noted.
28. The berm widths noted in detail 1 and 2 do not match the widths noted on Sheet C3.3 details 3
and 4.
Sheet C4.1
29. The water pipe is closer than 10 feet to the STEP tank. Please revise.
30. There is a note 9 shown on the plan but no note 9 has been provided. Is this a sawcut?
31. Restoration of the road pavement where it will be affected for utility installation should be
noted on this sheet and details provided including required pavement depth per the road type.
32. Provide information regarding existing hydrants. Depending on amount and location of existing
hydrants, additional hydrant(s) may be required to provide sufficient fire protection.
General Comments
33. Lawn and landscaped areas shall be restored in accordance with BMP T5.13 — Post Construction
Soil Quality and Depth. Please add the applicable specifications, notes, details, etc. to the plans.
November 12, 2018
Page 4
Drainage Report:
34. Please provide an operation and maintenance plan and a SWPPP.
35. Please provide a summary of calculation results for pond sizing and conveyance sizing within the
main body of the report. Summary of conveyance results should include a comparison of the
actual flow to conveyance capacity.
36. Please provide conveyance calculations for all pipe sizes within each basin. For instance, only
the 12- inch pipe was calculated for Basin #2 but there is also 8 -inch pipe. All pipe sizes for all
basins must have conveyance calculations. This calculation can be limited to the worst-case
scenario for each pipe size.
37. Only one v -ditch conveyance calculation has been provided but there are additional v -ditches
proposed. Please provide calculations for all conveyance ditches.
38. The slope of the v -ditch for Basin #2 is identified as 2%. All information for the ditch is not
provided on the drawings but it appears to be roughly 500 feet long and have an elevation drop
of roughly 5 feet which would only be a 1% slope. Please either revise the ditch design to 2% or
correct the conveyance calculations.
39. Actual pond elevations instead of assumed elevations should be used in the MGS Flood model.
Using assumed elevations makes it difficult to assess and follow.
40. Please use actual pond dimensions instead of equivalent dimensions for all models.
41. Please provide a discussion about emergency overflow and what would happen with drainage
should it overflow out of both infiltration cells. A safe path of failure that does not cause the
threat of flooding for neighboring residences or businesses should be discussed.
42. Per the geotechnical report, test pits #1, #2 and #7 which are the pits within the footprint of the
stormwater facilities for the Basin #2 pond have evidence of high groundwater at elevations
about 8.5 feet below grade. The proposed infiltration pond bottom is at a depth of about 4 feet
below finished grade. Therefore, the separation between the pond bottom and the high
groundwater is only about 4.5 feet. Per the 2014 DOE Stormwater Management Manual for
Western Washington Section 111-3.3.7, SSC -5, the depth to groundwater must be greater or
equal to 5 feet. Lower separations down to 3 feet may be allowed but only with a groundwater
mounding analysis. Please either revise the design or provide a mounding analysis.
43. Per comment #1, it appears that off-site drainage is directed to the site. This needs to be
clarified and potentially addressed. This will potentially influence the design of the stormwater
facility along this property line.
Should you have any questions or comments, please contact me at (360)352-1465 at your earliest
convenience.
Principal
N:\Projects\0605 City of Yelm\605-05 Civil Plan Reviews\Phase 41 - NPR Recycling\Correspondence\To\Yelm\L-2018-1106 Review Letter.doc