Lee's Summit

Please refer to comment #6 of the applicant letter dated Sept. 28, 2017. The City does not desire a pedestrian guardrail since it does not appear a pedestrian guardrail is warranted. If you are not in agreement with this, please submit justification for a guardrail. According to our review, it is not necessary and therefore, undesired.

The rip rap section shown at the end of the storm line crossing at 16th St. shows what appears to be a 1.5 foot increase in height at the end of the rip rap in relation to the flow line elevation of the pipes at the discharge point. This will likely lead to silting-in of the pipes. What is the justification for this design?

As of this date, we do not appear to have a final stormwater detention study in our possession. The latest version in our posession is dated April 21, 2017. This version contains contradictions in the design of the outlet structure. In particular, a 13.5 inch opening is shown at the permanent pool elevation, but the plans show a 10 inch opening at the permanent pool elevation. Other issues with the report include the following: 1) discussion of a 7' by 5' rectanglular concrete box culvert to handle anticipated flows for the retention basin, 2) no discussion of the fact that this 84 acre site exceeds the allowable peak flow rate using simple multiplication of the area times the allowable release rate per acre (are there off-site contributions to stormwater flow that need to be discussed?), 3) an appendix with no definition of the various nodes, either graphically or by text, rendering the review of the appendix difficult. Please submit a final stormwater detention study which addresses these issues.

It appears the Engineer's Estimate of Probable Construction Costs was missing the following items: 1) street repair at 16th St., 2) water valves, 3) water main encasement, and 4) thrust blocks.

The plans call for the grading in the "cut-off" channel to be shown on separate plans for 16th Street Improvements. In our opinion, this is not a logical placement of the plans for regrading and providing adequate drainage (i.e., within the 16th Street Improvements Project). The 16th Street Improvement Project is related to the widening of 16th Street, and not re-grading outside the right of way. In addition, we are still awaiting a resubmittal of the 16th Street Improvement Plans, and these plans do not currently include any plans for managing the drainage within the "cut-off" channel. Please include the grading and drainage plans for the "cut-off" channel within the Mass Grading and Stormwater Plans.

Sheet C5.2: The profile view of the storm lines show what appear to be a single 42" PPP. Isn't the pipe system going to consist of three (3) 42" pipes? If so, please specify.

Sheet C5.2: The plan view still calls-out the installation of an RCB rather than three (3) 42" PPPs. Please review these errors, and correct as appropriate.

Sheet C5.2: "Refer to 16th Street Improvement Plans for Blockout Elevation from East and West". Please see previous comment related to this note. In our opinion, these plans should incorporate this design, since it is integral to the design of the junction boxes.

Sheet C5.2: Please call-out the retention pond outlet structure as "private", extending to the downstream junction box. The junction box shall be considered public, and all other aspects of the system upstream of this point shall be considered "private".

Sheet C7.2: Pedestrian guardrail is shown. Why is there a need for a pedestrian guardrail at this crossing? We do not see the necessity of providing this guardrail. It should also be noted that this particular design does not appear to meet City design standards for guardrail.

Sheet C7.2: Pavement trench repair detail appears to shown two (2) 48" pipes, and one (1) 42" pipe. Please reconcile with the other sheets, which appear to shown three (3) 42" PPPs.

A profile view of the relocated water line is required. The profile view should show the water line being DIP with restrained joints at the stream crossing, a minimum of 42" below the natural streambed, extending twenty (20) feet beyond the streambank, utlity crossings such as sanitary sewer, and concrete encasement within the stream crossing. Gate valves shall be provided at each end of the stream crossing, so the section can be isolated for repair. The valves shall be easily accessible and not prone to flooding.

Sheet C7.2: The pavement trench repair detail should be revised to reflect our collector street standard for pavement replacement. This will require the use of geogrid or subgrade stabilization on to of 95% compacted subgrade, granular base, and a base and surface course of asphatlic concrete. If KCMMB concrete mix is used in lieu of asphalt, then please see the collector street standards listed in the Design and Construction Manual, Table LS-3.

Sheet C7.3: A permanent asphalt section is shown, but it is not clear where this is used. In general, this detail is not sufficient because it only shows a 2" surface course over a granular sub-base.

Sheet 7.4: Calculations should be provided for the energy dissipation (rip rap) proposed for the project. These calculations should be based on a recognized system for the design of the rip rap. The resulting dimensions for the rip rap should be based on these methods.

A revised cost estimate should be prepared for the work necessary to complete the project.

All necessary easements should be prepared and executed prior to approval of these plans. The easements should be on forms provided by the City. An exhibit is required for each easement. Prior to execution of the easement(s), please provide the City with a courtesy review copy. Following a short review (typically a day), you will be responsible for executing the easement, and recordation at the Jackson County Recorder of Deeds.

The reinforced concrete box (RCB) size has changed since the last submittal. It appears to be a 6' x 3', with other references showing 6' x 3.5'. The previous submittal showed a 5' x 7' RCB. The minimum height for the box should be 5 feet. This is needed to maintain the box culvert by Operations personnel.

The hydraulic grade line for the 100 year event within the box culvert is well above the top of the box culvert. The City made an allowance for the assumption of upstream detention rather than using maximum C values in the design of the culvert, but we cannot allow the 100 year water surface elevation to be above the top of the RCB.

Sheet C4.1: The 100 year water surface elevation within the retention basin does not appear to match what is shown in the stormwater report.

A revised Engineer's Estimate of Probable Construction Costs should be submitted. This revised estimate should include the correct size RCB.

Sheet C4.1: Please check the slope on the north side of the Lot 2 development. Please see comments on the Final Development Plan for detailed comments concerning the slope in this area. It appears that several options are available to achieve a minimum of 3:1 (or better) slope.

Sheet C4.1: Please show the permanent pool elevation, and the 100 year water surface elevation within the retention pond. Please consider labeling this as "Retention Basin" due to the fact this has a permanent pool.

As a basin with a permanent pool, there are several requirements applicable to this situation. The first requirement is that a non-clogging outlet be installed, typically with a reverse slope, as per Section 5608.4(E)(5). Also, an emergency spillway in accordance with Section 5608.4(F). A method for emergency drawdown should be designed in accordance with Section 5608.4(G). Usually, we have seen a siphon installed to eliminate the potential for piping, with a 8" PVC pipe installed over the top of the dam. Finally, the dam and associated structures must be designed in accordance with SCS Technical Release 60, "Earth Dams and Reservoirs", as a Class C structure.

All Stormwater Profile View Sheets: Show the hydraulic grade line of the design storm. It would appear the 1% storm must be used as the criteria for design in the case of the RCB.

Sheet C5.2: A box should be installed downstream of the retention basin outlet structure to denote the end of the public stormwater system. This box should be installed within the limits of a drainage easement. The retention basin outlet structure must be installed outside the limits of the drainage easement.

General Comment: A stormwater calculation sheet was not provided. Please provide a separate sheet for all stormwater calculations, including design storm. Ensure that velocities are shown in the calculations along with all other normal calculations.

Sheet C5.2: The slope of the RCB between the last RCB bend at station 2+86, and the flared end section appears too high. Without velocity calculations, it is difficult to determine if the maximum velocity of 20 ft/sec will be exceeded during the 1% design storm. Please provide calculations, and consider flattening the slope in this section.

Sheet C5.2: Please provide sufficient notes at the end of the flared end section which reference the specific detail for the energy dissipation measures to be installed.

Sheet C5.2: Where are the finish grades on the profile view? They appear to be missing. Please show the road (i.e., 16th St.) in the profile view.

Sheet C6.1: CSB is called-out with no definition. Please define CSB.

Sheet C6.1: Please provide a typical section view of the temporary shoo-fly.

Sheet C6.2: The pavement trench detail is lacking sufficient detail. Please provide the thickness of the KCMMB concrete patch (i.e., 8"), extending a minimum of one (1) foot on either side of undisturbed native subgrade, and a final 2" layer of asphaltic concrete. In addition, the detail calls-out note #8 for compacted soil, but it does not appear this note is included. If this note is included on a separate sheet, then reference the sheet number where the note is located.

The RCB is a single box culvert without a low-flow channel. At a minimum, a low-flow channel should installed within this single box culvert. This requirement would be in addition to any United States Army Corps of Engineers (USACE) requirements concerning the 404 permit.

It did not appear that any RCB bend details were provided.

Sheet C6.3: The City does not want the water line to be installed beneath the RCB. An alternate route should be established either to the south of the RCB, or on top of the RCB. Without proposed grades (see previous comment), it is difficult to determine the best course of action.

Standard details appeared to be missing for junction boxes, and manhole frame and covers (including standard City of Lee's Summit lettering for the covers).

Details for the two RCBs used on the project appear to be lacking. Please provide details of these boxes. Provide notes stating that the City shall review, but the engineer shall ultimately approve, the shop drawings for the public RCB (i.e., the long RCB installed beneath 16th St.). It must meet the requirements of Section 5700 of the City of Lee's Summit Design and Construction Manual (i.e., KCAPWA incorporated by reference). Please be aware of the specific design details required under Section 5711 of the Design and Construction Manual.