05-0581 Review No. 1 050307
City of Yelm
Community Development Department
105 Yelm Avenue West
P.O. Box 479
Yelm, WA 98597
May 3, 2007
Olympic Engineering
300 Deschutes Way S.W. Suite 315
Tumwater, WA 98501
Re: Yelm Plaza – Site Construction Documents Review No.1, Corrections and Comments
City of Yelm Project Number - SUB-05-0581-YL
Mr. Chris M. Merritt, P.E.
The following need to be corrected on the Yelm Plaza construction plans, stormwater drainage report, storm drainage maintenance manual and erosion control report. Comments are as follows:
Storm Drainage Report:
Storm Drainage Report Section 1 – The DOE has only approved the Vortechs as pretreatment in advance of infiltration treatment. According to Section III-3.3 of the 1992 DOE Manual, an
infiltration treatment basin should have a maximum infiltration rate of 2.4 inches per hour in order to provide treatment. The proposed design infiltration rate is 20 inches per hour.
Therefore, the proposed application of the Vortechs system is not appropriate based on the current DOE approval. Further, the requirements for a water quality infiltration trench and
a streambank erosion infiltration trench differ. If the infiltration trench is also to be used for water quality treatment, it needs to meet those design criteria as well. Please revise
the treatment design.
Storm Drainage Report Section 6 – The site is within the Yelm Creek Drainage Basin according to the referenced Map. Please revise.
Storm Drainage Report Part III Maintenance Plan – Maintenance information for the StormTech Vortechs Filter and Chamber Systems shall be included.
Storm Drainage Report Appendix 1 – The basin information summary is for a total of 0.83 acres. However, this is a 1.23 acre site. It appears that there is existing development on a
portion of the site that may be part of a drainage system already in place. Please provide a discussion regarding the difference in site area versus the drainage area used for design.
If the existing drive aisle on the site is not part of an existing drainage system, drainage from it will need to be directed to the new drainage system on this parcel.
Storm Drainage Report Appendix 1 – Please update the water quality treatment calculations per comment #1. With the current design, sizing computations for the
infiltration system also need to be included in the water quality design. The infiltration basin shall be sized to infiltrate the 6 month storm within 24 hours. An alternative system
may not require this sizing calculation.
Storm Drainage Report Appendix 1 – With the current water quality design, the sizing computations are incorrect. As a Vortechs unit is pretreatment only, the infiltration basin also
provides treatment. Therefore, the roof runoff is being mixed with dirty runoff and should be included in sizing computations for the infiltration basin as discussed in comment #4.
An alternative system may not require this sizing calculation.
Storm Drainage Report Appendix 1 – Per Section III-3.6.5 of the 1992 DOE Manual, an infiltration trench shall infiltrate the 10 year storm in 24 hours. Please provide this calculation.
Storm Drainage Report Appendix 2 – Please provide a map showing the test pit locations with the geotechnical report.
Construction Plans:
All Sheets:
The following comments apply to all sheets:
Some minor redline comments have not been called out in the letter but need to be addressed in the revised plans.
Sheet 2 of 9:
What is the curb shown on the east side of the parking area? Is this existing and to be removed? If it is a proposed curb, what is its function? Please clarify.
Sheet 3 of 9:
Please extend the silt fence along the east property line as shown.
A construction entrance is needed to prevent sediment being tracked out of the site. Please show a construction entrance on the plan.
Sheet 4 of 9:
Add additional spot grades as shown around the handicapped stalls to ensure compliance with ADA requirements.
In addition to the spot grades, please show proposed contours.
It is unclear what is happening on the east side of the site around the curb that is discussed in comment #10. Several elevations are called out on this curb. If this curb is constructed,
water will be trapped between it and the curb a few feet to the east. It is assumed that this curb will not be constructed. Please remove.
The grade between the easternmost curb at the head of the parking and the existing drive aisle exceeds 2:1. As this appears to be a fill slope, please revise to be no steeper than 3:1.
These steep slope areas will be more evident with proposed contours.
There is an area of proposed grading that matches to the existing drive aisle that will be flat as proposed (see plan for location). This will cause the potential for ponding. Please
revise.
The pipe lengths, slope, and material need to be indicated on the plan. This can not be handled with a typical note as it varies per pipe.
Change note #13 to call out a Type III ramp only. This is the ramp that is shown.
The pipe between catch basin #3 and #2 has less than 1.5 feet of cover for a portion of its length and should be of ductile iron.
Note #2 calls out requirements for an isolator row for the StormTech Chamber System. The storm drainage report calculations for StormTech Chamber sizing indicate that an isolator row
is not provided. Please clarify. Use of an isolator row would be an acceptable method of providing additional treatment as discussed in comment #1. If an isolator row is proposed,
the layout of the StormTech Chamber System will need to be revised per the isolator row requirements.
What are the catch basins stationed from? Please show the stationing that these are referencing.
Sheet 6 of 9:
City of Yelm Standard details shall be used for items like the sidewalks and handicapped ramps.
Sheet 7 of 9:
What are the water and sewer structures stationed from? Please show the stationing that these are referencing.
For Building A, there appears to be conflicts between the roof drain system and the STEP tank and the roof drain system and the water service. Please ensure that there are not conflicts
and revise as required.
The STEP sewer main line needs to be profiled to ensure that minimum depth requirements are met.
A service box needs to be shown for the service connections to the main for Buildings B and C.
The STEP line for Buildings B and C is a main line. The connection to the existing STEP main is a main connection and not a service connection and should be called out accordingly.
Sheet 8 of 9:
Include details for the back flow prevention structures referenced on Sheet 7.
These comments are City of Yelm Community Development Engineering Review comments only. City of Yelm Community Development Planning, City of Yelm Water Department, Sewer Department
and Public Works Department comments will be addressed and sent to you as soon as we receive and review them.
Should you have any questions or comments, please contact me at (360) 458-8423 or e-mail me at steveh@ci.yelm.wa.us at your earliest convenience.
Respectfully,
Community Development Department
Steve Harrington
Civil Inspector
Copy: Jim Gibson, Development Review Engineer