05-0345 Peer Review No. 1 042606 revltrMay 3, 2006
PMX# 247-1781-024 Willow Glenn III
Mr. Jim Gibson, P.E.
Development Review Engineer
City of Yelm Community Development Department
PO Box 479
Yelm, WA 98597
Re: Peer Review - Site Construction Documents
Dear Jim:
Per your request, Parametrix has performed a peer review of the Willow Green III construction plans and stormwater drainage report. Our comments are as follows:
Storm Drainage Report:
Storm Drainage Report Section 3 – Infiltration testing is required and shall be performed by a qualified geotechnical engineer. Soil testing should meet the criteria of the 1992 DOE
Manual.
Storm Drainage Report Section 9 Treatment – This section specifies that the filter strips and bioswales will be lined with a PVC liner. The construction plans do not show this liner.
Please revise plans.
Storm Drainage Report Section 9 Stormwater Basin, Basin A – the following comments are related to this section:
The description of the pond bottom area indicates that it will contain 1,175 square feet. The plans do not reflect this size and appear to be roughly one-third of the size indicated.
Further, the top area also does not appear to meet the indicated amount of 3,314 square feet. Please revise plans to reflect what is indicated in the report. Further, please indicate
the pond bottom and top elevations. This is not called out anywhere in the report or plan set.
The description of the open pond also indicates that the side slopes will vary from 6:1 to 4:1. The plans only indicate 4:1 slopes. Please revise the report or the plans for consistency.
The summary table of the required and provided volume appears to have an error. According to the Waterworks output, it would appear that the max stored volume is 4,287 cubic feet, not
the 3,505 cubic feet specified. Please correct.
Storm Drainage Report Section 9 Stormwater Basin, Basin B – the following comments relate to this section:
As Basin B has 2 different stormwater facilities, these should be modeled separately for accuracy. Further, since all of the information for the galleries and open ponds are lumped
together, it is impossible to ascertain how each pond is meeting the requirements. Separate discussions should be provided for each pond and gallery.
For both ponds, please provide information on top and bottom pond areas. Please ensure that these match what is shown on the plans.
The description of the open pond also indicates that the side slopes will vary from 6:1 to 4:1. The plans only indicate 4:1 slopes. Please revise the report or the plans for consistency.
The summary table of the required and provided volume appears to have an error. According to the Waterworks output, it would appear that the max stored volume is 11,047 cubic feet,
not the 10,939 cubic feet specified. Please correct.
Storm Drainage Report Section 9 Stormwater Basin, Basin C – The summary table of the required and provided volume appears to have an error. According to the Waterworks output, it would
appear that the max stored volume is 419 cubic feet, not the 434 cubic feet specified. Please correct.
Storm Drainage Report Section 9 – Generally, there needs to be a discussion provided regarding how the open ponds and infiltration galleries function together. Specifically, the concern
is how the catch basin will limit the ability of the system to function as designed. The catch basin that allows the stormwater to enter the infiltration gallery will be a limiting
factor that has not been adequately addressed. Please provide a discussion and calculations on how this will affect both water quality and quantity design.
Storm Drainage Report Section 12 – This section indicates that the plans will have a construction sequence with the TESC plan. This has not been provided. Please provide on the plans.
Appendix B Calculations and Computer Modeling – The following comments are related to this section:
The flow value used to compute the filter strip for Basin A is incorrect. A value of 0.37 cfs has been shown but the Waterworks output indicates a flow of 0.39 cfs. Please revise.
For all of the filter strips (Basin A, B1, B4, and C), the calculations are incomplete. The calculation of the T value is to establish the required filter strip width. A further calculation
also needs to be performed to calculate the required filter strip length. This required length is based on the requirement of a 20 minute residence time. Please refer to Section III-6.4
of the 1992 DOE Manual.
Section III-6.4 of the 1992 DOE Manual indicates that filter strips should not receive concentrated flow. Outflow from a pipe is concentrated flow. Please revise the design to address
this issue.
For all of the bioswales (Basin B2 and B3), insufficient information has been provided to assess the computation of the T value of the swale. The bioswale is not shown anywhere on the
plans and a description or cross section has not been provided. The computation of T is based on a V-ditch. Will the bioswale be a V-ditch? If so, please clarify on both the plans
and report. Further, it is unclear how the calculation of T relates to the swale being 6 feet wide. The computations appear to require much smaller swales. Please provide some
discussion that relates the computed T value to the swale selected. Also, please specify the cross section of the swale and the associated cross sectional area.
For all of the bioswales (Basin B2 and B3), the computation of the velocity is incorrect. The velocity is the flow divided by the cross sectional area of the bioswale.
For all of the bioswales (Basin B2 and B3), the minimum bioswale length is 200 feet. A shorter bioswale is allowed if a proportional increase in cross sectional area is provided. Therefore,
a 100 foot swale is acceptable only if the cross sectional area is increased. Please provide an analysis and computation of the cross sectional area to support a 100 foot bioswale.
Although it is unclear because the bioswales have not been shown on the plans or in the report, it appears that the bioswales may be in-line. As such, they need to be sized to pass
the 100 year storm and maintain minimum freeboard. Please provide these calculations.
Please provide additional computation and discussion of the water quantity facility design. At a minimum, please provide: how the basin discharges were calculated (using Darcy’s Law)
and the infiltration rate that was used, evidence that the required drawdown times have been met (1 day for 10 year storm and 2 days for 100 year storm), and a general discussion of
how the facilities were designed and laid out to meet the requirements of the manual. Please note, the computation of discharges using Darcy’s Law is dependent on area. Therefore,
the rate for the gallery should differ from the pond.
The Waterworks input information for the storage tables do not appear to match the plans. Further, there should be 2 storage basins for Basin B as there are two facilities. Please
revise.
The drainage sections have information that do not match the plans.
Appendix C Supporting Documentation – The information provided is insufficient. A geotechnical report performed by a qualified geotechnical engineer shall be provided to support the
design infiltration rate. Further, test holes should be within the boundaries of the proposed infiltration facilities. None of the test holes indicated are within the areas of these
facilities.
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 1:
Please provide the Hearing’s Examiner Conditions of Approval on the cover sheet.
Sheet 2:
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 clear how some areas will be graded. This is necessary to evaluate pond grading as well as tie ins and assessments
of pond setbacks.
The existing topography lines do not extend to the property boundaries. The existing topography map should include the entire property boundary. Further, please label all existing
and proposed contours.
Please show the limits of construction entrance on plans.
Please provide standard erosion control notes on this sheet or Sheet 3.
Inlet protection should be provided for all proposed and existing catch basins. Please provide and delineate on the plan.
The west and east property lines need bearings and distances.
At the entrance on Green Leaf Loop, it is unclear how the proposed sidewalk will tie to the existing. It is also unclear what will be removed as part of note 3. Please clarify this
area.
Sheet 5-9: The following comments are applicable to all of these sheets.
It is customary to put a vertical curve at any slope transition of 1% or greater. Please provide vertical curves at slope transitions of greater than 1%.
The right-of-way for the roads should be 56 feet per the local access road requirements. Please revise the roads to meet the requirements of Detail 4-7.
Please provide all of the applicable notes on the applicable sheets, no cross referencing. In most cases where cross referencing was used, it was incorrect.
All pipe call outs should indicate the pipe slope.
Sheet 5:
The sidewalk on the east side of Fir Ct. should be placed per Detail 4-7.
The handicap ramps should be the same for both sides of the street. Please revise.
The keynotes that are referenced do not match the items that are indicated. For instance, for call out 1, the referenced note is for a pipe and it is indicating a catch basin. Please
revise.
The catch basin spacing along the south side of the roadway exceeds 500 feet. Please add a catch basin.
Green Leaf Way should have a bulb out at the intersection with Green Leaf Loop per Detail 4-7 and 4-8B. Once the bulb out is added, please add flowline elevations to the bulb outs as
drainage tends to be a problem for road slopes of less than 1%.
Sheet 6:
The pipe within Green Leaf Way only has 1 foot of cover and should be ductile iron. This pipe also appears to be at zero percent slope. What is the purpose of this? All pipes should
be at a slope in order to provide adequate function.
The handicap ramp indicated along the south side of Green Leaf Way does not fit this application. Please revise.
The maximum allowable catch basin spacing is 500 feet. Catch basins need to be added to Green Leaf Way to meet this requirement.
According to the proposed road profile, the intersection of Birch Court and Green Leaf Way appears to be a low spot. Drainage structures need to be added or the profile revised.
Sheet 7:
Green Leaf Way should have a bulb out at the intersection with Grove Road per Detail 4-7 and 4-8B. Once the bulb out is added, please add flowline elevations to the bulbouts as drainage
tends to be a problem for road slopes of less than 1%. In addition, the handicap ramp along the south side of the roadway should be revised to match the other side of the road.
The proposed road profile should be extended to the limits of the frontage improvements. Currently, it shows connecting to an existing grade that will be revised with the frontage improvement
construction.
The handicap ramp indicated on the south side of the road at Oak Court does not fit this application. Please revise.
Sheet 8:
On both Birch Court and Fir Court, all of the catch basins are labeled as CB #4. Further, this is the only sheet with catch basin labels. Please revise the labels and add catch basin
labels to other sheets or remove to provide consistency throughout the plan set. For ease of construction, it is recommended that the catch basins be labeled to provide easy identification
in the field.
The pipe in Fir Court has only 1 foot of cover and should be ductile iron.
Birch Court should be revised per Detail 4-7 and 4-8B. This road has ample room for the roadway to flare back out and provide parking. Once the bulb out is added, please add flowline
elevations to the bulb outs as drainage tends to be a problem for road slopes of less than 1%.
The pipe in Birch Court has only 1 foot of cover and should be ductile iron. Further, this pipe also has zero percent slope. What is the function of this pipe? Flow should not be
transferred between basins as the stormwater facilities have only been sized for the associated drainage basin.
Sheet 9:
The spot grades shown in the vicinity of the catch basins within Oak Court do not work with the rim elevations indicated for the catch basins. Please revise.
Sheet 10:
Please provide the City of Yelm Standard Street Construction General Notes on this or another sheet.
A note should be added that indicates the driveway locations be identified prior to pouring the sidewalks or all sidewalks should be 6 inches.
The driveway placement detail should be revised to show a 6 foot planter.
Sheets 12-14: The following comments are applicable to all of these sheets.
Please provide invert elevations at all pipe outfalls into ponds. Further, an erosion control device such as a quarry spall pad should be indicated at all pipe outfalls.
Show the proposed footprints of the infiltration galleries under the ponds in the plan view.
Label all pond contours and show all associated grading including that outside of the pond.
For ponds with filter strips, please identify the limits of the proposed filter strips. As several ponds have more than one pipe entering the pond, please identify the location of the
filter strip for each outfall. Further, the storm report should be revised to discuss the multiple discharge point issue. Sizing discussions do not currently address multiple discharge
points.
On the pond sections, please identify the location of the pond high water including elevation.
On the plan view of the ponds, please indicate the pond bottom and top elevations.
Indicate PVC liners for the filter strips and bioswales as identified in the storm drain report.
The pond grading shown appears to be somewhat schematic and does not represent actual grading. The pond bottoms are generally sloped which is not reflected. For instance, the pond
at Grove Road (Sheet 14) appears to have a flat bottom but the bottom elevation appears to vary from elevation 345.32 to 344.77. Please revise pond grading to accurately reflect the
proposed elevations.
Sheet 12:
Please label the width of the infiltration gallery for the east pond.
Please label the pond setbacks for the east pond.
Sheet 13:
From the storm drainage report, it appears that this sheet should show two, 100-foot bioswales on either side of Birch Court. These do not show on the plans. Please show the bioswales
including required grading and provide a detail of the required cross sections. Further, a bioswale only provides adequate treatment if all flow enters at the beginning of the swale.
Please show how flow from the basin will be channelized to the beginning of these swales.
Sheet 14:
According to the storm drain report, the gallery at Fir Court should have a surface area of 3,314 square feet. It appears from the plans that only a 50 foot by 60 foot gallery is proposed.
Where is the other 314 square feet? Please revise.
The pond at Fir Court does not have the bottom and top area indicated in the storm report. Please revise so the report and plans are coordinated.
The profile of the pond at Fir Court appears to have an elevation error. Please see plans.
The pond at Grove Road does not appear to meet setback requirements.
Sheets 15-19: The following comments are applicable to all of these sheets.
For all sheets, please show the applicable lot numbers where water and sewer services are shown.
Please provide all details referenced in the notes.
Please provide all applicable notes on each sheet, no cross referencing. Most of the cross referencing information that has been provided is in error.
Label all proposed crossings.
Sheet 15:
There are several notes that do not appear to apply. Please remove.
Please provide the size of the existing STEP sewer line.
Sheet 16:
Add an adaptor to note #6.
There is a symbol shown in the profile view adjacent to the fittings associated with note 6. What is this? Please label or remove if not applicable.
Sheet 17:
The adaptors should be FL x MJ.
There is a symbol shown in the profile view adjacent to the fittings associated with note 4. What is this? Please label or remove if not applicable.
Provide the length of the water line in note 5.
Sheet 18:
The profile view of Fir Court calls out zero percent slopes on the water and sewer lines. Please remove these as it appears to be in error.
The end of the sewer lines should use end of line cleanouts per City of Yelm Detail 7-20. Please revise.
The blow-off assemblies and end of line cleanouts should be located in the planter strip. Please revise.
The City of Yelm does not allow pipe deflections. It would appear that deflection may be needed on Birch Court in order to provide the alignment shown. Please revise or provide commentary
if deflection will not be required.
Sheet 19:
The blow-off assemblies and end of line cleanouts should be located in the planter strip. Please revise.
The City of Yelm does not allow pipe deflections. It would appear that deflection may be needed on Oak Court in order to provide the alignment shown. Please revise or provide commentary
if deflection will not be required.
Sheet 20:
Provide a water system map.
Please update the water details. The details provided are out of date.
Sheet 21:
Please add Detail 6-9.
Sheet 22:
Please provide any details referenced in the plans that have not currently been included.
Please provide City of Yelm Details 7-18 and 7-19.
Sheet 24:
Please provide details of the frontage improvement including a cross section.
Tapers should be provided to transition the paving back to the existing edge of pavement. These shall be provided beyond the property limits.
The concrete sidewalk should extend to the property limits. The asphalt sidewalk would then be constructed beyond that. Please revise.
The curb across the entire property frontage should be raised curb. Please remove all references to depressed curb.
Please provide all applicable notes on this sheet, no cross referencing.
The sawcut should extend a minimum of 2 feet into the existing pavement.
The end of the sewer lines shall utilize end of line cleanouts per City of Yelm Detail 7-20.
The catch basins are too close to the proposed water line. As these are all new lines, adequate space should be provided. Please relocate the water line so it does not have such close
proximity to the storm structures.
There is a low spot indicated at Station 62+89.71 that does not have any drainage structures to prevent ponding. Either revise the profile to provide positive flow or provide for drainage.
The erosion control plans should include inlet protection for the proposed catch basins on the frontage. These can be shown on this sheet or on the erosion control sheet.
Should you have any questions or comments, please contact me at your earliest convenience.
Sincerely,
Parametrix, Inc.
Amy Head P.E.
Project Manager
Enclosure
P:\CAD\1781 - City of Yelm\247-1781-024 Yelm On-Call Civil Plan Review 2006\Phase 03 Willow Glen III\042606 reviewletter.ltr.doc