05-0343 Civil Review 1 from Parametrix 031306March 9, 2006
PMX# 247-1781-
Mr. Jim Gibson, P.E.
Development Review Engineer
City of Yelm Community Development Department
P.O. Box 479
Yelm, WA 98597
Re: Peer Review - Site Construction Documents
Vista Green Plan
Dear Jim:
Per your request, Parametrix has performed a peer review of the Vista Green Plat construction plans and stormwater drainage report. Our comments follow:
Storm Drainage Report:
Storm Drainage Report Section 1 Roof Runoff – Roof Drywells are to be designed using Section III-3.6.6 of the 1992 Department of Ecology (DOE) Stormwater Management Manual. Sizing indicated
is not per the manual requirements. Please reference the DOE manual.
Storm Drainage Report Section 3 – Infiltration Rates/Soils Report – Please provide a map demonstrating the locations of the test pits used for stormwater infiltration testing.
Erosion Control Section 1 – Please revise section on catch basin protection to match erosion control plan. Also, please indicate that the storm system is to be flushed upon completion
of construction.
Erosion Control Section 5 – Please add installation of catch basin filters for existing catch basins.
Maintenance Plan Section 1 – A section should be added for infiltration facilities.
Appendix 1 Design and Basin Information Summary – Please provide clarification on the non-tributary areas. Provide a description of the areas and where they will drain if not draining
to the pond. All site drainage should be directed to the stormwater facility with the exception of roof drainage.
Appendix 1 Sub Basin A Water Quality Calculations – The following are the comments related to this section:
According to the 1992 DOE manual, all wet ponds should be a minimum of two cells. Please revise pond to meet this requirement.
Please indicate length to width area provided for pond. A minimum of 3:1 is required.
Please provide more detail on the pond volume. A stage/storage table should be provided (including incremental areas) to aid in the evaluation of volume. According to the plan set,
the pond has a bottom area of 866 cubic feet. With only 3 feet of effective depth, it does not seem possible that a volume equal of 5,218 cubic feet is possible. Please clarify.
Appendix 1 Sub Basin A Water Quantity Calculations – The following are the comments related to this section:
Please clarify the stage/storage table provided. It appears that a volume of 3,737 cubic feet is required but a volume of 6,677 cubic feet is provided. However, when you add up the
volumes from the table, you only get 5,197 cubic feet. Please revised the stage/storage table to include the incremental areas as well as to clarify required versus provided. Again,
with a pond bottom area of 1,100 square feet and only 2 feet of effective depth, it does not seem possible that a volume of 5,197 or 6,677 cubic feet is possible. Please clarify
Please provide calculations on how Darcy’s Law was applied to establish the pond stage discharge rating curve. Typically, this value would increase with pond height unless only the
bottom area is used. Please clarify.
Construction Plans:
All Sheets:
Some minor redline comments have not been called out in the letter but need to be addressed in the revised plans.
Sheet C 1.1:
The plan should include lot dimensions for each lot.
Please provide information on the adjacent parcels including ownership, parcel number, and street address.
Label all easements including size and type.
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.
Provide rough grading of plat. Without an overall grading plan, it is not possible to evaluate whether the pond meets the setback requirements as well as locations of cut and fill.
It is also necessary to evaluate the cover on the pipe between the road and the ponds.
Please label all proposed contours
Per detail 4-7, local access roads require a bulb out at intersections. Please provide bulb outs at road B.
The length and slope of the pipe between catch basins 3 and 4 needs to be indicated somewhere on the plan sheet. In addition, this pipe has less than 2 feet of cover and should be ductile
iron.
The pipe between catch basin 1 and catch basin 2 has less than 2 1.5’ feet of cover in places and should be ductile iron.
At a minimum, the silt fence should be extended across the northern property boundary where indicated.
To meet minimum spacing requirements, a catch basin needs to be added between catch basin 4 and the intersection with Longmire Street on road A.
The bulb outs tend to be a problem for drainage if the roadway centerline is less than 1%. Please add flowline elevations to the bulb outs.
Please call out the type of handicap ramp to be used at the intersection with Longmire Street.
The handicap ramp called out in note 14 does not fit the situation. Please revise.
Please provide a road cross section.
Add catch basin protection to the existing catch basin in Longmire Street just east of the site.
Sheet C 1.2:
The roof drain drywell detail should be revised to call out the DOE requirements for sizing rather than the sizing criteria specified. In addition, the minimum acceptable pipe size
is 6 4” inches.
The overflow spillway needs to have a geotextile under the rock lining.
Label ponds to provide clarity. Revise ponds as required to address storm drain report comments.
The inlet protection notes do not match the detail provided.
The inlet pipe to the wetpond should be shown and proper erosion control for pipe outflow provided.
Please add COY detail 4-26.
Sheet C 2.1:
All tees should be called out to have thrust blocking.
Provide invert elevations of the storm drain crossings to aid in evaluation of crossing space. Only indicate a 6-inch sand cushion where needed. It would appear that it is unnecessary
on road B.
Note 6 calls out information that does not appear to apply. Please revise.
A water service has been called out for tract A. Please remove.
Sheet C 2.2:
Please provide a system map.
Per Hearing’s Examiner Condition # 13, please provide a detail of the hydrant lock.
Sheet C 3.1:
All tees should be called out to have thrust blocking.
Provide invert elevations of the storm drain crossings to aid in evaluation of crossing space.
Please remove note 2 where indicated.
Sheet C 3.2:
Please add City of Yelm details 7-4, 7-5, 7-6, 7-7, 7-9, 7-10, 7-16, 7-17, 7-18, and 7-19.
Should you have any questions or comments, please contact me at your earliest convenience.
Sincerely,
Parametrix, Inc.
Amy Head P.E.
Project Manager
Enclosure