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Coppell Comm 1R3-CS040303 (2) d.~] JONES& CARTER, INC. Consulting Engineers 3030 LBJ Freeway, Suite 910 972/488-3880 Dallas,Texas 75234 Fax 972/488-3882 March 3, 2004 Mr. Keith R. Marvin, P.E. Civil Engineer City of Coppell 255 Parkway Coppell, Texas 750~19 Re: ~oyal Park, Coppell Commerce Center~ Lot 1R Block 3~ Construction Plan l~evlew comments Response Coppell, Texas Dear Mr. Marvin: Pursuant to your letter dated February 19, 2004, please accept this letter as a formal response to plan comments: General 1. The final plat has been included. 2. Plan sheets have had extra information removed. 3. Spelling errors have been corrected. Dimension Control Plan 1. All parking spaces located within interior of site are 9'x19'. All parking spaces adjacent to landscape areas are 9'x17' with an additional 2' of landscape area added for bumper overhang. 2. Additional maneuvering space has been added. Grading Plan 1. Plans have been reviewed and approved by Mr. Glenn Celerier, P.E. of ACT 21 in a design review meeting and have been submitted to DART to finalize the easement. Drainage Plan 1. All off site drainage areas that drain to the site are shown on the Drainage Plan. 2. In review of City of Coppell and DART record drawings, no information regarding the existing 27" RCP could be found. Also, no information could be found in a review of the adjacent development plans. Review of pre-development USGS maps indicated approximately 6.8 acres of undeveloped flow that was conveyed by this culvert. Jones & Carter performed a field survey of the culvert to determine the existing slope of the 27-inch RCP. We found the slope to be 0.37%. Using Manning's Equation, we determined that the normal flow conveyed by this pipe was 18.84 cfs. Utilizing a developed "C" of 0.70 for the adjacent development, we calculated the area to be 3.0 acres. The offsite drainage is being conveyed via a 4:1 vegetated swale. Mr. Keith R. Marvin, P.E. March 3, 2004 Page 2 The curb inlet has been shift to the east. The existing 24-inch through 42-inch storm sewer within Hammond Street (System A) was designed to accommodate the eastern 0.9-acres of the site at a 5-year event (I = 5.58) with developed conditions (C = 0.7). System A along with the drainage area map and the design calculations are shown in Exhibit A (see attached). This system was built in 1980. We evaluated the existing capacity of the system based on a 100-year water surface elevation of 511.58 feet at the system outfall to the G-1 tributary of Grapevine Creek. This water surface elevation of tributary G-1 was obtained from "The Southwest Coppell Storm Plan Update", prepared in 1999 by Halff Associates. Using the 511.58 starting water surface elevation, the acreages shown on Exhibit A, and developed conditions (C = 0.9), we calculated (Rational method) the allowable intensity that resulted in a hydraulic grade line at the gutter line. Table 1 - System A Intensity (see attached), shows the allowable intensity to be 2.90 inches per hour. Please note that at upstream stations 8+80 and 11+50 along Hammond Street, the hydraulic grade line does exceed the gutter. This is caused by the starting water surface elevation being higher than the existing paving. Based on an allowable intensity of 2.90-inches per hour, an area of 1.56 acres (0.9 acres from the site and 0.66 acres from the adjacent railroad right-of-way), and a runoff coefficient of 0.9, we calculated the allowable discharge to be 4.07 cfs for System A. Therefore, we designed the detention pond with a control release discharge of 4.07 cfs. 5. Profiles of Lines "A", "B" and "C" have been added. 6. Square storm sewer manholes have been shown. 7. Additional plan notes have been added to detail the removal and abandonment of the curb inlet and lateral. 8. All building downspouts have been shown. Utility Plan 1. Tapping sleeve and valves have been shown for connections to the existing system. 2. Double detector check vaults have been located in the center of water easement. 3. A sanitary sewer access device has been added at the point of connection. 4. Per landscape architect, the fire hydrants and transformer pad locations do not interfere with landscape requirements. Paving 1. 2. Plan Lime stabilization has been included in the paving specifications. Saw cuts have been revised to full depth. SWPPP 1. Additional silt fence has been added to the perimeter of the property. 2. TCEQ requirements will be followed. 3. The NOI will be provided to City of Coppell. 4. The location of the construction entrance has been revised. Mr. Keith R. Marvin, P.E. March 3, 2004 Page 3 Details 1. Only details that are not included in the City of Coppell Standards have been shown. 2. See note 7 under drainage plan. If you have any questions or wish to discuss these comments further, please call. Sincerely, "'Pleoj ect Manager JRE/je I:~Projects~l&CDallas~Pritchard Associates (D076)~002 Bums & Freeport~Letter\planrcsponse3-3-O4.DOC cc: Brett Ratliff, Pritchard Associates, Inc.