Peer Review Letter 001HEA
ARR~EWELL~~~
September 5, 2007
Mr. ]im Gibson, P.E.
Development Review Engineer
City of Yelm Community Development Department
P.O. Box 479
Yelm, WA 95597
Re: Peer Review -Site Construction Documents
Samantha Ridge
Dear Jim:
Per you request, Shea, Carr & Jewell, Inc. has performed a peer review of the Samantha
Ridge construction plans and stormwater drainage report. Our comments are as follows:
Storm Drainage Report:
1. Storm Drainage Report Section 9 -According to this section, on-site soils were
categorized as Group C soils. The geotechnical report does not support this
classification. According to the report, the underlying soils are Spanaway recessional
outwash sand and gravel, Spanaway soils are typically a Group A or B soil with good
infiltration. Please revise this section as well as any computations based on this
grouping.
2. Storm Drainage Report Appendix B -The stormwater calculations require revision per
the requirements of an infiltration facility, not a detention facility (see subsequent
comments regarding infiltration). Infiltration is the preferred method of handling
stormwater runoff and is required per Hearing's Examiner Condition #9. It is clear,
based on the hyd rogeologic assessment, that infiltration should not be proposed in the
southwest area of the site. The geotechnical report, however, indicates that
groundwater is much deeper in other areas of the site and infiltration is possible.
Therefore, an infiltration facility located away from the area of groundwater concerns
should be proposed. Please revise the stormwater design to provide infiltration rather
than detention. As the hydrogeologic assessment assumed no infiltration, please update
to include an evaluation of the site design given infiltration is proposed.
Storm Drainage Report Appendix B -Please provide at minimum: elevation/area/volume
computations for the proposed stormwater facility compared to volume required; sizing
computation showing treatment flow required versus flow provided by Vortechs;
discussion regarding maximum allowable flow through Vortechs versus maximum
expected flow and whether a bypass will be required; information on infiltration
drawdown requirements. The modeling output is back up to support calculations
provided demonstrating that the requirements of the 1992 DOE Manual have been met.
Simply providing the model information is insufficient for review. In addition, on the
model information, please provide marginal comments identifying the purpose of each
printout and what it is showing. It is simply not possible to determine what has been
done from over 20 pages of modeling output with no accompanying information.
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~HEA
ARR~EWELL
Mr. Jim Gibson, P.E.
September 5, 2007
Page 2 of 6
4. Storm Drainage Report -The geotechnical report should be provided as an appendix to
the stormwater report as the determination of infiltration rates are based upon this
report. On future submittals, please include.
5. Storm Drainage Report -The geotechnical report appears to have based the calculation
for the infiltration rate of the on-site soils on the current DOE manual which is more
restrictive than what the City of Yelm allows. The City of Yelm uses the 1992 DOE
Manual and soil analysis may be based on this manual. Typically, soil infiltration rates of
SO inches to 20 inches per hour are used for design on a site with soils similar to those
on-site. Please have the geotechnical engineer revise the soils report. Based on the
final location of the infiltration facility, additional soil testing may be required.
6. Storm Drainage Report -Please provide a drainage basin map showing areas included
within drainage calculations. Please note, only undisturbed areas maybe excluded from
the drainage area. The drainage area should include all areas that are disturbed.
7. Storm Drainage Report -Once the infiltration facility is designed, please demonstrate
adequate drawdown is provided. The 1992 DOE Manual requires that an infiltration
facility be shown to completely drain the stored runoff from the SO-year, 24-hour design
storm within one day and the 100-year, 24-hour design storm within two days. Please
provide calculations demonstrating this condition has been met.
8. Storm Drainage Report -Roof runoff shall be directed to on-site roof drain drywells
(Hearing's Examiner Condition #9). Please revised design and provide sizing guidelines
for the roof drain drywells. Guidelines need to be per the requirements of the 1992 DOE
Drainage Manual. Drywells for homes in the area of groundwater concerns may require
alternative locations such as under the private roadway. The drywell locations and
designs should also be coordinated with the geologist.
9. Storm Drainage Report -Please include a copy of the FEMA map that shows the
elevation of the 100 year floodplain.
l O.Operation and Maintenance Plan -The description for the on-site storm systems does
not match what is currently proposed. Further, this plan will require revision with the
design modifications.
Construction Plans:
All Sheets:
The following comments apply to all sheets:
11. Some minor redline comments have not been called out in the letter but need to be
addressed in the revised plans.
12. The plans as currently provided are not stakable. The road stationing needs to be tied
down to some type of marker such as a monument or a benchmark.
Mr. lim Gibson, P.E.
,SHEA September 5, 2007
I.ARR~EWELL.. Page 3 of 6
Sheet 1 of 17:
13. The conditions of approval shall be shown on the cover sheet.
14.The 100 year floodplain line does not appear to match what is indicated in the drainage
report or on the FEMA flood maps. According to these documents, the floodplain is at
elevation 330 feet. The floodplain line shown appears to vary from 329 to 330. It is
understood that the line is being modified by the proposed development and the line
shown is likely the revised line. For clarity, please provide the original floodplain line as
well as the modified line and label accordingly.
Sheet 3 of 17:
15. The construction sequence should be modified to indicate when construction entrance,
filter fabric fence, interceptor dike, check dams, and sediment pond will be installed.
Sheet 5 of 17:
16. This sheet shall be revised to provide an infiltration facility rather than a detention
facility.
17. The proposed grades are very difficult to read as they are they have a broken line type
which is the same as the existing. Please revise the proposed grade lines to have a
different line type that is easier to differentiate.
18.There is a proposed contour on the south side of the site that is labeled as both a 338
and a 336 contour. Please clarify. If this is 338 feet in that area, it appears that there
would be some missing grades between the 2 buildings.
19. At the entry drive on Crystal Springs Road, there is a missing 340 contour between 341
and 339.
20. Indicate the elevation out the outflow pipe in to the stormwater facility. The outflow
pipe needs to have an erosion control pad added.
21.The maximum height of a Type 1 Catch Basin is 5 feet. Catch Basins 1 and 2 shall be
revised to Type 2 structures.
22. Please provide information on the grading of the 2 parking stalls on the southwest
corner of the private road. Unless these stalls are at grade, there appears to be some
missing grading information.
23. There is missing grading information between the two buildings immediately south of the
entrance on to Crystal Springs Road. It appears that the west side of these buildings
are at elevations 344 to 341 or so (please note that this is hard to discern so please
label these contours where indicated). The buildings are at elevations 338 and 337
respectively. It is understood that the buildings are acting as retaining structures.
However, what happens between the buildings? I[ appears that proposed grading is
missing between these structures.
24. Please add spot grades where indicated to add clarity to the proposed grading.
~SHEA
ARR~EWELL..
Mr. ]im Gibson, P.E.
September 5, 2007
Page 4 of 6
25. The driveway grades are all labeled at 2%. However, spot checks of grades show that
the driveway grades vary and are typically much higher. Random checking did not yield
one driveway at 2% (please note all driveways were not checked). If this is a minimum
allowed grade, this would be better handled with a notation. If graded as shown, there
will be a disconnect between roadway and driveway grades.
26. How do these units function? There are many units that have finished floors of, for
example, 336 feet but show 335 foot contours tying in at the front of the structure. Are
steps proposed? Please clarify.
27. Please remove all references to Pierce County from the standard notes.
28. The current plan shows fill within the floodplain. If fill is proposed, compensation
volume must be provided. Please revise.
29.The pond slopes shown are 2: 1. Maximum allowed pond slopes are 3: 1.
Sheet 6 of 17:
30.In order to evaluate crossings, the water and sewer should appear in the background on
the plan view.
31. Please provide curve data for the horizontal curves.
Sheet 7 of 17:
32. Drainage from proposed frontage improvements needs to be collected and conveyed to
the on-site drainage facility as much as is feasible. This can be accomplished by
breaking up the drainage and providing separate on-site facilities or collecting drainage
and directing it to the main on-site facility.
33. Please provide existing topography for the ditch in the vicinity of the discharge point.
34. The maximum depth of a Type 1 Catch Basin is 5 feet. Catch basins 9 through 11 all
exceed 5 feet and shall be type 2.
35. Please provide information on the type of handicap ramps proposed at the entrance on
to Crystal Springs Road. Please include a detail of the ramp type.
Sheet 8 of 17:
36. According to the City of Yelm minimum street standards, a private roadway should
follow the requirements of a local access residential roadway. Please revise.
37. The slopes across the handicapped ramps along Crystal Springs Road exceed 2%.
Please revise.
38. The spot grades noted at the intersection of the internal roadways don't seem to match
the grading plan which calls out this road at 1 percent grade. Please review and revise if
necessary.
rSHEA
l ARR~EWELL.
Sheet 9 of 17:
Mr. ]im Gibson, P.E.
September 5, 2007
Page 5 of 6
39. It is unclear why the street lighting construction notes would be on this plan. Please
relocate to a more appropriate location.
40.The pond detail does not show the proposed access road. The access cannot be
constructed on a 2:1 slope. Please revise.
Sheet 10 of 17:
41. It is unclear when a cement concrete approach would be used. This is not required with
rolled curb and this detail should be removed.
Sheet 11 of 17:
42. Due to poor copy quality, it is unclear if there is an existing force main in Crystal Springs
Road. If a main is present, please label and make the line darker so it is visible. If not,
as part of the proposed frontage improvements, utilities should be provided within the
entire frontage regardless of whether there is an existing utility to connect to at present.
43. Please label where all connections to the existing system is to occur as well as any kind
of fittings or modifications that may need to be made to provide an extension. It
appears 2 connections are proposed but only one reference is made.
44. Please provide 2 gate valves at each tee.
46. Please revise the pig port at station 4+61.26 to be an end of line cleanout.
46. [s the existing 10 inch force main between the 2 proposed connections to remain? If it
is to be removed, please note on the plans. If it is to remain, there is not adequate
separation between the sewer and the proposed water.
47. The STEP and forcemain mainlines and services will need to be within an easement to be
dedicated to the City. Please show this on the plans and label.
48. Please show the proposed water lines in the background of the plan and indicate the
separation between water and sewer. A minimum of 10 feet is required.
Sheet 12 of 17:
49. It appears deflection is proposed for the construction of the STEP mainline. The City of
Yelm does not allow pipe deflection, please revise.
SO.The labels on the length of the 10 inch force main are inconsistent between this sheet
and Sheet 11.
Sheet 14 of 17:
51. Due to poor copy quality, iI is unclear if there is an existing water line in Crystal Springs
Road across the entire property frontage. If a main is present, please label and make
the line darker so it is visible. If not, as part of the proposed frontage improvements,
,.SHEA
`ARR~EW ELL
Mr. Jim Gibson, P.E.
September 5, 2007
Page 6 of 6
utilities should be provided within the entire frontage regardless of whether there is an
existing utility to connect to at present.
52. Please provide 2 gate valves at each tee.
53. IS the existing water line between the 2 proposed connections to remain? If it is to be
removed, please note on the plans.
54. The water mainlines and services will need to be within an easement to be dedicated to
the City. Please show this on the plans and label.
S5. Please show the proposed sewer lines in the background of the plan and indicate the
separation between water and sewer. A minimum of 10 feet is required.
56. Please note the location of the irrigation meter(s) and note the appropriate backflow
prevention.
57. Please indicate the connection type for all fittings - FL, FLxMJ, etc.
Sheet 15 of 17:
58. It appears deflection is proposed for the construction of the water mainline. The City of
Yelm does not allow pipe deflection, please revise.
59. It appears that there may not be 6 inches of minimum separation between storm and
water at approximately station 3+40. Please revise.
60. Water lines require a minimum of 42 inches of cover. It appears that only about 24
inches has been provided. Please revise.
Should you have any questions or comments, please contact me at (360)352-1465 at your
earliest convenience.
Sincerely,
a,f(Carr & Jewell, nc.
y M~ e
Proje~ ~anager
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