Re: South Regional Park Tributary: Minor Storm Event Outfall System Comments City of Thornton, Adams County, & UDFCD

Transcription

1 March 15, 2017 Tim Semones, PE Civil Engineer Development Engineering City of Thornton 9500 Civic Center Drive Thornton, CO Phone: (303) Fax: (303) Re: South Regional Park Tributary: Minor Storm Event Outfall System Comments City of Thornton, Adams County, & UDFCD Dear Tim Semones, This letter is in response to your 2 nd submittal comments to JR Engineering dated February 22, Responses by JR Engineering (in bold font). CITY OF THORNTON - ENGINEERING COMMENTS Tim Semones: Sheet 1 1. All sheets must be signed and stamped by a CO PE before the plans can be approved by the city. (Typical comment on all sheets) a. JR Response: Noted. Final submittal will be signed. Sheet 5 1. Who is Others? In order for these plans to be approved you will need to provide a reference to the set of construction plans for this outlet structure, or include a copy of the detail sheet by Others with this plan set for review and approval. All sheets, even those prepared by others must be stamped and signed by a Colorado PE. a. JR Response: The others reference is in regards to the Construction Plans Off-site School District 27J High School #3, Thornton, Colorado by JVA. We have added this reference to the plans. See Sheet CD4.3, which has also been included with this submittal for reference. The stamped comment is noted. 2. Per Section B of the Standards and Specifications, Manhole covers are not permitted within concrete areas such as sidewalks. Either the sidewalk or the manhole, or both will have to be modified to eliminate this conflict. a. JR Response: Per previous comment, the sidewalk in this area is realigned with a meandering sidewalk. The manhole has been depicted to show the manhole cone section rotated to keep the cover out of the sidewalk. An additional note has been added to the structure label for clarification. 1

2 3. Demo plan shows this storm sewer being removed and replaced, but not enough information is provided here to replace in kind. Need to show station and offset information (or coordinates), invert in, and invert out information. a. JR Response: Added station offset and inverts to plan. 4. Minimum required clearance is 18". Decrease drop through upstream manholes to 0.05' to increase clearance to 1.30' a. JR Response: Drops decreased from 0.10 to 0.05 to increase clearance to Show 100-year HGL line also. For 100-year storm event the pond at the upstream end of this storm sewer will have a higher WSEL than in the 5-year storm event, so unless flow into this pipe is limited by inlet control, a higher HGL line can be expected during the 100-year event. a. JR Response: Addressed. The 100-year event has been modeled in StormCAD and shown on the plans and added to the report. Sheet 6 1. Wing wall is in Adams County structure and any connection to this wing wall will need to be approved by Adams County. Urban Drainage will also need to review this as this is an outfall into and UDFCD maintenance eligible channel. These plans have been forwarded to these agencies for review and comment. a. JR Response: Adams County and Urban Drainage comments received and addressed in respective sections of this response letter. The pipe has been relocated to outfall upstream of the headwall. 2. Option 1: Requires pipe slope for pipes between MH-5 & MH-7 to be decreased. Invert out at MH-7 would be approximately and Invert would be approximately (please confirm calcs). So with a 0.10 drop at MH-6 pipe slopes could be as steep as 0.43%. a. JR Response: Addressed. Box based manholes and the use of dual elliptical pipe necessary to provide clearance between fiber optic lines and 21 sanitary sewer crossing. Minor regrading required to accommodate pipe cover. Less than 1 ft of fill will be necessary to accommodate acceptable cover. 3. See previous comment regarding 100-year HGL line. a. JR Response: 100-yr HGL is provided on the plans. 4. Option 1: Dual % a. JR Response: Addressed. The 100-year event has been modeled in StormCAD and shown on the plans and added to the report. 5. Minimum required clearance of 18" is still not provided. Minimum clearance could be provided in one of two ways. Option 1: Use dual 24" RCP 0.98% slope and go over sanitary sewer with the proper 18" clearance. Upstream two segments of pipe would need to be flattened to accommodate the higher upstream end of the dual 24" pipes, and box base manholes would need to be used at each end of the dual 24" pipes. 2

3 Option 2: Change pipe from 36" RCP to 29"x45" elliptical RCP and go under 21" sanitary sewer with the proper 18" clearance. Upstream and downstream MHs will need to increase in size to 7' diameter for pipe width increase. This option will require bypass flows in the 21" sanitary sewer during construction. Call if you would like to discuss. a. JR Response: The preferred option 1 has been provided and is reflected on the plan set. Sheet 7 1. As culvert and wingwalls were and Adams County project Adams County will need to approve this connection. a. JR Response: Adams County comments included in this response letter. Sheets See comments from Traffic Engineering review set. a. JR Response: Traffic comments received and addressed. 3. Sheet numbers are out of order for these sheets. a. JR Response: Sheets re-numbered. CITY OF THORNTON TRAFFIC ENGINEERING COMMENTS Tim Semones: Sheet 8 1. Sign legend is not showing up in pdf. a. JR Response: Addressed. Legend revised. 2. Color indicates phase 4, but note indicates phase 2. a. JR Response: Addressed. See phase 2 & 4 plans for details. 3. This is not showing in pdf. a. JR Response: Addressed. 4. It looks like a flagger will be needed in Phase 4. a. JR Response: Addressed. See phase 4 plans for more detail. 5. Phase 2 or Phase 4. a. JR Response: Addressed. Sheet 9 1. Should be and edge line, not a lane line. a. JR Response: Addressed. Revised. Sheet Should be and edge line, not a lane line. a. JR Response: Addressed. Revised. 2. Sheet 14 does not show a pedestrian detour. a. JR Response: Addressed. Revised. 3

4 CITY OF THORNTON DRAINAGE LETTER COMMENTS Tim Semones: 1. Page 2 How will this be accomplished? A higher depth at the entrance will cause a surcharged condition in the pipe, and some additional flow will be conveyed beyond what is stated in this document. You need to analyze what the split in flow is between the 36" RCP and the 48" RCP for the 5-year and 100-year Water Surface Elevations (WSELs) in the pond. For the 36" RCP: For WSELs between & flows into the 36" RCP appear to be inlet controlled. For the 48" RCP: (Per the proposed 27J Offsite Improvement Plans-Not Approved Yet) For WSELs between & the flow into the 48" RCP is controlled by the EURV plate on the outlet structure. For WSELs between & flow into the 48" RCP is controlled by a 13" wide by 12" tall rectangular orifice. For WSELs between to flow into the 48" RCP appears to be controlled by the pipe culvert configuration (not clear if inlet or outlet controlled). WSELs above will overtop Riverdale Road. a. JR Response: Please see JVA plans dated 06/21/2016. This shows the realignment of the road, in conjunction with the removal of the existing 48 pipe. This element of the design is conveyed on JVA plans and not a part of this submittal. A stage-release table for the 36 diversion has been added to the letter for reference showing the stage-discharge values requested on the sheet after this comment was made on. 2. Provide similar analysis for the 100-year wsel in the pond ( per the most recent submittal). a. JR Response: Stage/discharge values shown in table in first page of appendix material utilized per most recent materials provided by JVA. Adams County CONSTRUCTION DOCUMENTS COMMENTS Greg Labrie General 1. The portion of the 36 diameter RCP proposed to be installed beneath Riverdale Road will require an Adams County Permit. The contractor shall complete an Adams County Permit Application and submit the appropriate design drawings and fees to the Adams County One Stop Permit Center. a. JR Response: Noted. An application and plans was submitted to Adams County 11/29/16, comments were received from Matt Emmens 12/21/16, and the plans were resubmitted 2/2/17 including an FDP permit application. Permitting fees will be submitted upon plan approval and prior to start of construction. 4

5 2. Sheet 6 shows the new 36 diameter RCP pipe 10.3 below a sanitary sewer line. Development Engineering is requesting the applicant to add a note and/or drawing details, showing how to protect the sanitary sewer from damage during the installation of the 36 RCP. Development Engineering is also requesting a note and/or drawing details from the engineering consultant that will provide the contractor with specific action items required to complete if the sanitary sewer is damaged and leaking during construction. a. JR Response: Crossing revised with dual HERCP pipe to increase clearance to 1.50 above pipe. Notes added to construction drawing notes on storm plan and profile regarding construction activities. 3. The applicant must provide Adams County with an Operation and Maintenance Manual for the proposed detention pond located at the intersection of Riverdale Road and Yosemite. The O&M Manual is required to described who owns the pond and who has the ultimate responsibility to maintain the pond. A checklist of the minimum requirements for the O&M Manual is attached to this . If the O&M Manual for the pond was completed by another project, a copy of the manual is required to be submitted and/or referenced with this application. a. JR Response: The pond diversion area is not part of this plan set. JVA has plans currently under review for the new structures and associated major inflow/outflow pipes. These plans are Construction Plans Off-site School District 27J High School #3, Thornton, Colorado. See Sheet CD4.3, which has also been included with this submittal for reference. 4. An easement of outlot shall be created for the pond. a. JR Response: This pond diversion area is not part of this project. JVA has plans currently under review for the new structures and associated major inflow/outflow pipes. These plans are Construction Plans Off-site School District 27J High School #3, Thornton, Colorado. See Sheet CD4.3, which has also been included with this submittal for reference. URBAN DRAINAGE CONSTRUCTION DOCUMENTS COMMENTS DAVE SKUODAS General 5. The wingwall was not structurally designed to accommodate a 36 pipe penetration. a. JR Response: The outfall design has been reconfigured to occur upstream of the wing wall. 6. Coring through the wingwall would not be very easy and would likely damage the wingwall, certainly from an aesthetic standpoint but possibly from a structural standpoint as well. a. JR Response: Agreed. The original design on sheet 7 of 15 showed removing and reconstructing a structural section of wall around the 36 rcp. This pipe is now being relocated per your request. 7. The box culvert has been designed to potentially carry pedestrians through either the north or south cell at some point in the future if an underpass of Riverdale Road is 5

6 desired and after the downstream channel is lowered. Since we don t know which side the trail would be on, we don t want a pipe penetrating the wingwall because it would point right at people on the trail if the underpass went through the north cell. a. JR Response: Noted, design reconfigured. 8. I would suggest having the pipe daylight at the end of the wingwall into the existing riprap rundown we ve constructed, and I would require them to enlarge and improve the rundown to the creek from their new pipe outfall. a. JR Response: Existing grades in combination with the pipe depth/slope do not allow the pipe to daylight into the existing swale. Rather the pipe will need to pass under and discharge below this swale. The swale riprap protection will be removed and replaces as necessary to accommodate the slight adjustments in grade, +/- 1ft. 9. I would prefer the pipe outfall not be right up against the end of the wingwall but rather a good 10 + away from it (basically where the existing rundown is). a. JR Response: Existing grades in combination with the pipe depth/slope do not allow the pipe to be 10+ but rather 5 from the edge of existing wall. Protected properly this should ensure no damage to the existing wall. If you have any questions regarding the above comments, please do not hesitate to contact me at (303) Sincerely, JR Engineering, LLC Garrett Bales, P.E./CFM 6