07-0276 Shea Carr 060308
June 6, 2008
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
Yelm RV/Boat and Mini-Storage
Dear Jim:
Per your request, Shea, Carr & Jewell, Inc. has performed a peer review of the Yelm RV/Boat and Mini-Storage engineering construction plans and stormwater drainage report. Our comments
are as follows:
Storm Drainage Report:
Storm Drainage Report Section 2 – The minimum requirements listed do not appear to follow the requirements per the 1992 DOE Manual Section I-2.4 New Development and Redevelopment – Application
of Minimum Standards. Most of the main points have been identified but not in the same order or same title. It would appear, perhaps, another manual may have been used to identify
the minimum requirements.
Storm Drainage Report Section 2 – It is stated that Construction Stormwater Pollution Prevention is not required because all runoff is infiltrated. It is correct that the DOE would
not require a NPDES General Stormwater Permit for sites with 100% infiltration and, therefore, a SWPPP would not be required. However, construction stormwater pollution prevention is
always applicable despite the method of runoff disposal. Each site will still require construction entrances to prevent soil track out, silt fences to contain and filter drainage, inlet
protection to prevent sediment from clogging the conveyance systems, etc. Please revise the drainage report to include a brief section on erosion control requirements.
Storm Drainage Report Section 2 – It is stated that source control pollution controls are not required. Source control is typically always required. Trucks and/or construction equipment
could have oil leaks while on-site, building construction typically will require storage of products such as paint and solvents, etc. Please revise to include a brief section on requirements
for source control prevention during construction.
Stormwater Drainage Report Section 2 – The operation and maintenance information is required to be part of the drainage report. Please include.
Storm Drainage Report Section 4 – Please provide more discussion of how the drainage system design provides the required amount of water quality and quantity control. Please relate
the manual requirements to what has been provided. Absolutely no information has been provided to allow evaluation of the design and how it meets the requirements of the stormwater
manual. At minimum, please provide:
The assumed rainfall depth for each storm event.
A discussion about the water quality system proposed including how sizing was established and relate sizing back to manual requirements.
Calculations of the 6 month design flow and/or volume used to size required water quality systems.
Sizing calculations for water quality system.
A discussion about the streambank erosion control system proposed including how sizing was established and relate sizing back to manual requirements.
Calculations demonstrating the required size and provided size of streambank erosion facilities.
Storm Drainage Report Section 4 – Please provide all of the stormwater model input and output information demonstrating that the manual requirements have been met. It is not possible
to evaluate the storm drainage design of the porous asphalt without this information.
Storm Drainage Report Section 4 – What portion of the asphalt section is providing treatment? Please indicate where treatment is occurring and provide computations indicating the volume
provided within this area. Further, please provide information on the required volume for the treatment portion of the section. A summary of these calculations including model information
needs to be provided.
Storm Drainage Report Section 4 – No computations have been shown indicating the volume provided within the pervious asphalt base course. Further, no information has been provided on
the required volume for the pervious asphalt base course. A summary of these calculations including model information needs to be provided.
Storm Drainage Report Section 4 – Per Section III-3.6.8 of the 1992 DOE Manual, the porous asphalt system shall infiltrate the 10 year storm in 24 hours and the 100 year storm in 48
hours. Please provide calculations demonstrating the required drawdown has been provided..
Storm Drainage Report Section 4 – Per Section III-3.6.7 of the 1992 DOE Manual, the porous asphalt system shall infiltrate the 6 month storm in 24 hours. Please provide the calculations
demonstrating this drawdown has been provided.
Storm Drainage Report Section 4 – It is indicated that the pervious asphalt alone will provide the required water quality treatment. However, according to Section III-3.6.7 of the 1992
DOE Manual, a pretreatment BMP must precede the pervious asphalt. Please review this section and revise the design to meet all of the requirements.
Storm Drainage Report - Excessively drained soils are not appropriate for use as a water quality treatment BMP (see Section III-3.3.3 of the 1992 DOE Manual). Typically, if an infiltration
system is appropriate for use as a water quality system, it is not appropriate for use as the streambank erosion control system. Please review this section and revise the design to
meet all of the requirements. The geotech report recommends 20 inches
per hour for design which is in excess of what is recommended by the Manual for water quality infiltration.
Storm Drainage Report Section 4 – Per Section III-3.6.7 of the 1992 DOE Manual, porous asphalt is typically only recommended for certain traffic loading conditions. Given the nature
of the site, it is expected that large, heavy vehicles will be traversing the pavement section (RV’s, moving trucks, large trucks pulling boat trailers with boats, etc.). Please provide
a geotechnical report supporting the use of pervious asphalt for this application and that provides a recommended minimum thickness for vehicle support.
Storm Drainage Report Section 4 – This section should include a summary of the infiltration rate that has been used for stormwater sizing. It should also include an estimate of the
high groundwater elevation as provided by a hydogeologic report. The bottom of the infiltration systems shall be a minimum of 6 feet from the estimate high groundwater elevation per
the SEPA conditions. If this cannot be provided, please include a discussion summarizing the results of the groundwater mounding analysis.
Storm Drainage Report Section 4 – Please address the drainage path runoff will take if the pervious asphalt were to clog. It appears likely the buildings may flood if this were to occur.
Storm Drainage Report Section 5 – Please provide a discussion on required erosion control measures including requirements for installation and inspection.
Storm Drainage Report Section 6 – It is not clear why a groundwater mounding analysis has been provided. Is the bottom of the infiltration facility less than 6 feet from the estimated
high groundwater depth? If so, please include a discussion regarding this within the groundwater mounding analysis report. In addition, the 1992 DOE Manual does not provide guidance
on groundwater mounding. Therefore, groundwater mounding analyses should follow the methodology currently recommended by DOE, not criteria of Thurston County.
Storm Drainage Report Section 6 – The mounding analysis that has been provided is incomplete. The appendices shall also be included.
Storm Drainage Report Section 7 – Please provide operation and maintenance information for the proposed stormwater facilities.
Please note, the drainage report that was provided was incomplete and difficult to follow. Absolutely no calculations were provided to indicate that the proposed stormwater facilities
meet the requirements of the 1992 DOE Stormwater Manual. What little information has been shown clearly indicates that the stormwater design proposed is unacceptable with regards to
water quality. Further, a groundwater mounding analysis has been provided but with no explanation. The drainage report should discuss why there was a need for mounding as the mounding
analysis does not provide this information. In addition, the groundwater mounding analysis itself is incomplete (appendices not included) and difficult to follow. It is based on a
Thurston County Drainage Manual requirement rather than a DOE requirement. All stormwater design in the City of Yelm shall be based on the 1992 DOE Manual. If that manual does not
address an issue, then the current DOE Drainage Manual
shall be followed. Overall, it would seem that the drainage system proposed will not work for the site conditions and shall be revised. Please ensure that all future drainage reports
that are submitted are complete and contain all required information to adequately review the proposed drainage systems.
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.
Please revise the approval block to read Development Services Engineer instead of Director of Public Works.
The plans as currently shown are not stakable. Structure location information needs to be tied to something such as a benchmark.
Sheet 1 of 7:
The site plan review conditions of approval need to be on the cover sheet. Please revise to include the SPR conditions in addition to the SEPA conditions.
The existing legend shows the same line type for several existing facilities. It appears that a layer may have been turned off with a letter for each type of facility. Please revise.
Sheet 2 of 7:
An existing sanitary sewer line is indicated but the line shown is unclear. Also, please indicate the size of the existing sewer line.
Please indicate the size of the existing water main shown.
The construction entrance needs to be a minimum of 100 feet long. Please revise the plan and corresponding notes.
Sheet 3 of 7:
Revise the construction entrance detail to indicate a minimum 100 foot length.
One of the main causes of failure of pervious paving systems is clogging. They are especially susceptible to clogging during construction. Please include notations regarding prevention
of sedimentation onto the pervious asphalt section once installed. Also, includes notes regarding required cleaning if sedimentation or spills occur.
An inlet protection detail and notes are provided but no inlet protection is shown on the plans. Is inlet protection to be provided? If so, please indicate the location.
Sheet 4 of 17:
Please provide proposed contours in addition to spot grades. Although the site is fairly flat, it is necessary to show the contours to demonstrate how proposed grading will tie back
to existing contours. It will also demonstrate areas of steep grading. Steep grading is of concern along Rhoton Road. It appears that a fill slope in excess of 3:1 will be required
between the building (FFE 332) and the new right of way line (elevation 329).
The pervious asphalt is shown to be directly adjacent to the buildings. According to Section III-3.6.7 of the DOE Manual, pervious asphalt shall be 20 down slope of any building. Please
revise.
The proposed asphalt paving section shows a sand base to act as the water quality treatment layer. This suggests that the proposed pervious asphalt section proposed may be based on
the requirements specified in the LID Technical Guidance Manual for Puget Sound. If the design criteria of that manual are proposed, then the sizing methodologies must also be followed
including using a continuous simulation model for sizing. The storm drainage report must address all of the criteria specified in this manual for both the water quality and water quantity
sizing. The criteria for the 1992 DOE Manual may not be mixed with the criteria for the LID Manual. Please select one design criteria and follow all of the requirements including
sizing calculations etc.
Infiltration facilities may not be located within the 100 foot well protective radius. The pervious asphalt is within this radius area. Please revise.
The driveway entrances are shown as pervious asphalt. Will these be pervious or standard? Given the slopes that are shown, it would seem that standard asphalt would be more appropriate.
Please show proposed re-grading of existing ditch including proposed contours and required cross section.
With the grades shown at the entrances, the proposed culverts will either be within inches of the top of asphalt or will be a speed bump within the driveway. Further, the pipe would
also be within the paving section for either the pervious or standard paving section. Please revise the proposed grading to accommodate the culverts. Be sure to also accommodate the
proposed pavement section.
Please provide a detail of the roof drain splash blocks proposed. Currently, the drive aisles between buildings are about 25 feet wide. The splash blocks will presumably encroach into
this width. Please show that the splash blocks will not impede traffic flow between buildings.
How will solid waste be handled on-site? According to SPR Condition of Approval #10, a refuse collection area is required. Please revise the plan to include an area for refuse collection
per the SPR condition.
The sidewalk ramp adjacent to the handicap parking stall requires a minimum 5 foot landing beyond the ramp. The ramp shown only has a 3 foot landing. Please revise.
Please provide a detail of the proposed handicapped ramp at the handicapped parking stall.
Per the spot grades and slope arrows shown, it appears that the low spot on the south end of the site is at the joint between the standard pavement section and the pervious paving section.
As such, the runoff from the standard paving section will sheet flow to the low spot and will then have to pond before it will reach the pervious asphalt area. Please revise.
There are conflicting slopes in the parking area adjacent to the office. On one side of the drive aisle, the slope is to the east. On the other side it is to the west. Therefore the
cross slope of the drive aisle will vary which may be awkward for drivers.
There are a few parking stalls in the area of the standard paving section that appear substandard. Please review the City of Yelm requirements for angled parking stall dimension requirements
and revise.
Sheet 5 of 10:
Water
As a note, the City of Yelm allows PVC pipe for water mains of 8 inches. Please consult the City of Yelm Development Guidelines for specific requirements.
Per City of Yelm Standard Detail Number 6-7, the 6 inch gate valve for fire hydrant assemblies shall be FLxMJ. Please revise all notations indicating the gate valve shall be FLxRJ to
FLxMJ. Further, the hydrant notations also indicate that the 6 inch pipe shall be RJ. RJ is a joint reference and would not be applicable on a pipe notation. Please revise.
A gate valve on the main line is not required for fire hydrant connections. The 8 inch gate valves referenced can be removed.
The minimum required width for the water line easement is 15 feet, please revise.
A water service connection is not shown for the office building. Please show the domestic water service, the water meter, and the required backflow prevention device. Also please include
appropriate details for these items on the detail sheet.
Is irrigation proposed for landscaping? If so, please show the required irrigation meter and appropriate backflow prevention device.
The water line stationing needs to be tied to something such as a monument in order to be stakable.
Fire hydrants are proposed directly adjacent to the buildings. Typically they should be located away from the building to allow safe access should that building be on fire. Please
consult the applicable fire code for hydrant placement.
Sewer
Please provide station information for all structures from the STEP tank to the mainline. (Note – stations shall be tied to something such as a monument.)
Please indicate the STEP tank size on this sheet.
It would appear from the invert elevation provided that the proposed STEP tank will be within the proposed pervious asphalt paving section. Please revise so the top of the STEP tank
does not extend within the proposed stormwater management area. Please note that the maximum allowable depth is 5 feet from invert to finished grade.
The 2 inch STEP force main pipe shall be PVC IPS 1120 SDR 21 Class 200 pipe. Please revise.
A hose bib must be installed within 50 feet of the proposed STEP tank. This can be on the building. Please indicate the location of the hose bib.
Please show the location of the Carson box to be installed for the new service line.
Sheet 6 of 7:
Please provide the following standard City of Yelm details in addition to those already included: 6-3 (or applicable detail for required water meter size), 6-6, 6-13, and 6-14.
Please provide a water system map.
Sheet 7 of 7:
Please provide the appropriate standard City of Yelm detail for float level.
Should you have any questions or comments, please contact me at (360) 352-1465 at your earliest convenience.
Sincerely,
Shea, Carr & Jewell, Inc.
Amy M. Head, P.E.
Project Manager
N:\Projects\605 City of Yelm\605-05 Civil Plan Reviews\Phase 20- Yelm RV-Boat & Mini-Storage\Correspondence\060308firstreviewcommentltr.doc