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HomeMy WebLinkAbout03-00500176- 00076225 03- t ,�� CITY OF COLLEGE STATION `f DEVELOPMENT SERVICES 1101 Texas Avenue South, PO Box 9960 COLLEGE STATION College Station, Texas 77842 Phone (979)764 -3570 / Fax (979)764 -3496 MEMORANDUM 4/11/2003 TO: Kent Laza, P.E., Via fax 693 -2554 FROM: Spencer Thompson, Development Services Engineering SUBJECT: Edelweiss Gartens Phase 5 - Sewer OP Request City Staff has evaluated your request for OP as outlined in your letters dated 03/12/03 and 03/21/03. The following comments are being returned to you: • The request for OP by the Westfield Development for increased line size from an 8" line to a 15" line (FF -EE) appears to be in compliance with ordinance. • The request for OP by the Westfield Development for increased line size from an 8" line to a 12" line (EE- Victoria) appears to be in compliance with ordinance. • The request for OP by the Edelweiss Gartens Development for increased line size from an 8" line to a 12" line (Victoria to creek channel) appears to be in compliance with ordinance. The node labeled BB should be moved east to the creek channel. • The request to consider the area labeled AA as commercial can not be considered at this time. The Land Use Plan distinctly shows this area as residential. The City can not support payment to the Edelweiss Gartens Development for increased line size that the Westfield Development is responsible for. If you have any questions, please contact me at 764 -3570. Home of Texas A &M University Westfield Village Phase 6 Engineering Review Comment Response The following is a reply to the engineering review of the construction plans for phase 6 of the Westfield Village Subdivision dated August 14, 2003. 1. All public utility construction must be in a dedicated PUE. The PUE must be submitted to the City prior to plan approval. A PUE for all utilities not in the ROW is being prepared and will be submitted to the City. 2. Sheet 2: Sidewalk required with street. Extend to end of street construction. The sidewalk is being extended to the end of the boundary of Phase 6 as required. The additional portion of Victoria is being constructed as a temporary turn- around as required by the city. A street is currently being planned to intersect Victoria at Station 49 +78.81 in conjunction with a future section of Edelweiss Gartens. We have left the sidewalk off intentionally to avoid its removal when this street is built. 3. Sheet 3: Remove "Typical 40' Subgrade Section" f,4 There are no prohibitions for this type of work in the city regulations and we believe the diagram is necessary on this project. The soil being excavated from Mountain Breeze Way is being used as fill on other portions of the it- J e-i - subdivision. This diagram is the only information the contractor will have for the earthwork along Mountain Breeze Way. 4. Sheet 3: Section A -A should show 7" flex base. Sidewalk is required with street construction. Since a turn - around is being required on Victoria, we have attempted to design a facility that will serve that purpose, but can still be used with the future extension of Victoria Avenue. Our concern is that any turning movements by heavy vehicles will damage the surface course and it will become necessary to replace the asphalt before the city will accept it in the future. We have designed the temporary turn- around with 5.5 " of base and 1.5 " of HMAC. As you can see in the detail, the asphalt is being left 1.5 " below the lip of the gutter. An additional 1.5 " of HMAC will be added to this portion of the street with future construction of Mountain Breeze Way. We believe 3 " of HMAC on 5.5 " of base is a superior section to 7 " of base and 1.5" of HMAC. The sidewalk is addressed in #2 above. 5. Sheet 4: Curved storm sewer along Night Rain Drive not in accordance with Drainage Policy and Design Standards (DPDS). The use of curved storm sewers was approved by the Director of Public Works 0 for Phase 1 of this subdivision so long as the joint deflections fall within the manufacturer's guidelines. We are unaware of a change in this policy. 6. Sheet 5: Outlets for Storm Drain A and B. Riprap in channel as shown constitutes modification to natural watercourse. When placing riprap in lieu of energy dissipation structure, you must show that velocities are reduced before entering natural channel. To our knowledge, there is no prohibition to the modification of an ephemeral stream through the placement of rip -rap. We are simply installing an outfall from a development into a natural watercourse (Lick Creek Tributary A) as done on many other public and private projects. The rip -rap is intended to provide a short section of lined channel where the velocity in the pipe slows to the velocity in the receiving stream. Energy dissipation occurs in the swirls and eddies that form at that point. If the streambed is not lined in this area, it is subject to washouts immediately below the pipe headwall. Rip -rap has proven to effectively reduce these washouts on previous projects. It has been accepted by all of the area governments, including College Station, and it is unclear why this application is any different than those previous installations. Formal studies of Lick Creek Tributary A were conducted in the drainage reports from Alexandria Subdivision and Westfield Subdivision. Those reports included computer models of the stream in the area where this outfall is being proposed. The maximum water velocity for both the 100-yr and 25-yr storm events is 3 fps, which is less than the maximum allowable for grass - lined waterways in the College Station DPDS. Any runoff coming from outfalls like the one being proposed will immediately slow to the velocity in the natural watercourse. With the exception of some eddies in the stream, there are no erosive velocities to consider. Energy dissipaters at the base of the outfall will be completely ineffective because they will be submerged by water in the stream. In our opinion, this is not an appropriate application of energy dissipation devices as described in the College Station DPDS. The water velocity in the receiving stream will not be significantly changed by such devices if installed at this location. 7. Sheet 6: Manhole required at end of S -2 per TNRCC 317. The plans have been changed to show this revision. �8. Remove references to "existing" sewer where sewer does not exist. The plans have been changed to show this revision. 9. Sheet 7: Inset B. Cross not permitted as shown. Install additional valve or replace cross with tee. The cross is designed correctly with valves on three of the four legs. As indicated previously, a street is being planned at the Victoria /Mountain Breeze Way associated with a future phase of Edelweiss Gartens. The water line extension shown here is intended to serve that future development. 10. 2" sand cushion required on sidewalk/pathway detail. The plans have been changed to show this revision. Edelweiss Gartens, Phase 5 Engineering Review Comment Response The following is a reply to the engineering review of the construction plans for phase 5 of the Edelweiss Gartens Subdivision dated August 14, 2003. 1. All public Utility construction must be in a dedicated PUE. The PUE must be submitted to the City prior to plan approval. A PUE for all utilities not in the ROW is being prepared and will be submitted to the City. 2. Sheet 7: Storm Drain Sta. 20 +90.19 does not meet Drainage Policy and Design Standards (DPDS) § VI, B, 3. The bend has been removed from the plans. 3. Sheet 7: SD -J and SD -I. Riprap in channel as shown constitutes modification to natural watercourse. When placing riprap in lieu of energy dissipation structure, you must show that velocities are reduced before entering natural channel. To our knowledge, there is no prohibition to the modification of an ephemeral stream through the placement of rip -rap. We are simply installing an outfall from a development into a natural watercourse (Lick Creek Tributary A) as done on many other public and private projects. The rip -rap is intended to provide a short section of lined channel where the velocity in the pipe slows to the velocity in the receiving stream. Energy dissipation occurs in the swirls and eddies that form at that point. If the streambed is not lined in this area, it is subject to washouts immediately below the pipe headwall. Rip -rap has proven to effectively reduce these washouts on previous projects. It has been accepted by all of the area governments, including College Station, and it is unclear why this application is any different than those previous installations. Formal studies of Lick Creek Tributary A were conducted in the drainage reports from Alexandria Subdivision and Westfield Subdivision. Those reports included computer models of the stream in the area where this outfall is being proposed. The maximum water velocity for both the 100-yr and 25-yr storm events is 4 fps, which is less than the maximum allowable for grass - lined waterways in the College Station DPDS. Any runoff coming from outfalls like the one being proposed will immediately slow to the velocity in the natural watercourse. With the exception of some eddies in the stream, there are no erosive velocities to consider. Energy dissipaters at the base of the outfall will be completely ineffective because they will be submerged by water in the stream. In our opinion, this is not an appropriate application of energy dissipation devices as described in the College Station DPDS. The water velocity in the receiving stream will not be significantly changed by such devices if installed at this location. 4. Sheet 10: Manholes required at end of sewer line per TNRCC 317. The plans have been changed to show this revision. 5. Sheet 10: Remove 6" stub at MH 5. We would prefer to install this stub -out with this phase of construction. The v current developer now owns the property to the south and plans to develop it in the near future. By installing the 20 ft. stub out now, it eliminates the need to break into the manhole when the future line is constructed. This stub out will be privately owned and maintained until the adjoining land is developed. 6. Sheet 11: Manhole 9 is in handicap ramp slope area. The manhole cover is actually located in the landing at the top of the ramp and does not infringe into the sloped sections of the ramp. (The ring and cover are smaller than the circle shown in the plans) 7. Sheet 11: 12" Sewer line is less than required 42" burial depth. The plans have been revised to provide 3" of additional cover under the stream. 8. Sheet 12: Manhole 13 is in handicap ramp slope area. The manhole cover is actually located in the landing at the top of the ramp and does not infringe into the sloped sections of the ramp. (The ring and cover are smaller than the circle shown in the plans) 9. Sheet 13: Manhole 18 does not comply with TNRCC 317. Tops of different size pipes must be aligned. The plans have been changed to show this revision. 10. Sheet 14: End of sewer line does not meet TNRCC 317. A manhole has been added to the end of the sewer line. 11. Sheet 14: 3 -36" culverts do not appear anywhere else in plan set. Remove. The plans have been changed to show this revision. 12. Sheet 17: Inset A. Change to 6 "x8" tee and 8" valve. We believe the connection is designed correctly. There is no 6 "x 8" Tee. There is only 8 "x 6" Tees and 6 "x 6" Tees. The first number represents the "through " portion of the tee. Since the lines coming to the "through " portion of the tee are both 6" lines, it is logical to install a 6 "x 6" Tee. The minor head losses through the fittings are insignificant to the overall system operation. 13. Sheet 19. Remove "Future Reinforced Concrete Flume ". This drawing is provided for informational purposes about the drainage system being considered as an outfall for SH 40. It is intended to help the developer, TxDOT, and the city understand how drainage will be handled through this area and where it is located in relation to the subdivision boundaries. It is not being proposed for construction at this time, but it could be submitted in the near future when SH 40 is built. Discussions about this system are currently underway. Even though the drawing has no bearing on the construction of Edelweiss Gartens, Phase 5, we believe it is necessary to leave it in the plans for future reference. 14. Sheet S 1: 2" sand cushion required on sidewalk detail. The plans have been changed to show this revision. Edelweiss Gartens, Phase 5 Engineering Review Comment Response September 2, 2003 The following is a reply to the engineering review of the construction plans for phase 5 of the Edelweiss Gartens Subdivision dated August 14, 2003. 1. All public Utility construction must be in a dedicated PUE. The PUE must be submitted to the City prior to plan approval. A PUE for all utilities not in the ROW is being prepared and will be submitted to the City. 2. Sheet 7: Storm Drain Sta. 20 +90.19 does not meet Drainage Policy and Design Standards (DPDS) § VI, B, 3. The bend has been removed from the plans. 3. Sheet 7: SD -J and SD -I. Riprap in channel as shown constitutes modification to natural watercourse. When placing riprap in lieu of energy dissipation structure, you must show that velocities are reduced before entering natural channel. The outfall structures have been pulled back 10-15 ft. from the natural watercourse and a small, lined channel is provided to carry water the rest of the way. No new rip -rap will be placed in the natural watercourse. Note that the water line stub out shown in Inset A of Sheet 18 has been altered slightly to provide sufficient cover where it parallels one of these new channels. 4. Sheet 10: Manholes required at end of sewer line per TNRCC 317. The plans have been changed to show this revision. 5. Sheet 10: Remove 6" stub at MH 5. As noted in "Other Changes" below, the alignment of the sewer line has changed The stub out has been shortened, but it remains on the plans for future extension as discussed in our meeting of 8/28. 6. Sheet 11: Manhole 9 is in handicap ramp slope area. The manhole cover is actually located in the landing at the top of the ramp and does not infringe into the sloped sections of the ramp. (The ring and cover are smaller than the circle shown in the plans) 7. Sheet 11: 12" Sewer line is less than required 42" burial depth. The plans have been revised to provide 3" of additional cover under the stream. 8. Sheet 12: Manhole 13 is in handicap ramp slope area. The manhole cover is actually located in the landing at the top of the ramp and does not infringe into the sloped sections of the ramp. (The ring and cover are smaller than the circle shown in the plans) 9. Sheet 13: Manhole 18 does not comply with TNRCC 317. Tops of different size pipes must be aligned. The plans have been changed to show this revision. 10. Sheet 14: End of sewer line does not meet TNRCC 317. A manhole has been added to the end of the sewer line. 11. Sheet 14: 3 -36" culverts do not appear anywhere else in plan set. Remove. The plans have been changed to show this revision. 12. Sheet 17: Inset A. Change to 6 "x 8" tee and 8" valve. We believe the connection is designed correctly. The minor head losses through the fittings are insignificant to the overall system operation regardless of how it is plumbed The water system analysis indicates that the system works well as is designed, with all pressures well above the minimum required by TCEQ and the City of College Station. 13. Sheet 19. Remove "Future Reinforced Concrete Flume ". The detail has been removed. 14. Sheet S 1: 2" sand cushion required on sidewalk detail. The plans have been changed to show this revision. OTHER CHANGES A. Sheet 1 — The southern boundary line of Phase 5 has been moved 10 feet to match the boundary of the preliminary plat. Associated changes to Brandenberg Street and the utility lines are included on various sheets in the plan set. B. Sheet 10 — The 10" sewer line that extends off -site has been moved to the opposite side of the future 30' drainage ROW to avoid a power pole and a transformer that was installed with Phase 4. An easement will be provided to cover the new alignment. C. Sheet 12 and 13 — Sewer stub -outs from manholes have been shortened to 20 feet or less as discussed in our meeting of 8/28.