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ST9302-CS 990428Kimley-Horn and Associates, Inc. April 28, 1999 Mr. Ken Griffin, P.E. City of Coppell 255 Parkway Blvd. Coppell, Texas 75019-4409 Via Mail and Facsimile # (972) 304-3570 Re: Sandy Lake Road Reconstruction (ST 93-02) KI-IA No. 06108700 16" Water Line Lowering at Moore Rd. Dear Mr. Griffin: As you are aware, project delays have prompted the consideration of a change in the proposed 16" water linerelocation alignment at Moore Road. By allowing the COntractor to install the pipe above the 66' storm drain and the 16~I gas iine, which cross the water line at Stations 55+39 and 55+67 respectively, the proposed lowering at Moore Road can be accomplished before the Coppell water conservation program begins on May lYa. Under the original plan discussed in our April progress meeting, this new alignment would utilize a 24" - 26" steel casing to provide additional protection to the 16" PVC water pipe between Stations 54+75 and 55+75. Upon further review initiated by receipt of the contractor's request for additional COmpensation, we have determined that sufficient cover will exist and the casing will not be necessary. Without the casing, the water line would have a minimum of 3' of cover. Most of the section of pipe in question would have in excess of 3' of cover. Additional factors included in our evaluation include: · Manufacturer's Literature - The Installation Guide for CertainTeed 16" DR-18 AWWA C 905 PVC Water Transmission Main was consulted for recommendations on minimum depth of cover. The recommended minimum depth of cover for surface loading COnditions is 3'. Experience Record of Other Municipalities - Kimley-Horn & Associates has worked with other municipalities who have successfully utilized a depth of cover of 3' or less for PVC water mains. Avoiding the use of a steel casing is advantageous for several reasons. No additional cost will be added to the project if the casing is not utilized, the Potential for future maintenance problems resulting from use of the casing is avoided, and the connections of the existing 12" and 8" water lines to the 16" · TEL 817 335 6511 MET 817 654 4266 FAX 817 335 5070 · Suite 1100 801 Cherry Street Fort Worth, Texas 76102-6803 Kimley-Horn and Associates, Inc, Mr. Ken Griffin, P.E., April 28, 1999, Page 2 water line are simplified (the casing would extend beyond the location of the current connections and would require additional fittings to make the connections outside the limits of the casing). Another option for accomplishing the lowering without the casing would be to utilize 16' ductile iron pipe at the intersection crossing. This would provide additional strength in the area of relatively low depth of cover. The ductile iron pipe would cost considerably more than PVC, but should result in a lower cost than that requested by the contractor for the steel casing. One disadvantage of the ductile iron pipe is the lead time required to obtain it. We have contacted several suppliers in the area, and it would appear that the earliest that 16" ductile iron pipe would be available is Friday, May 7~. This would make it more difficult for the contractor to complete the lowering prior to May 15~. In our judgement, the 16" water line lowering should be accomplished without the casing, and with the PVC pipe already paid for and on site. The contractor should be able to begin this work immediately, enabling the lowering to be completed before May 15~. Please let Michael DeMotte know if this is acceptable, and he will prepare and deliver a revised exhibit for the 16" water line lowering at Moore Road. If you have any questions, please feel free to contact me. Respectfully submitted, KIMLEY-HORN AND ASSOCIATES, INC. Charles M. Staples, P.E. CMS/MGD:mgd KIML."~HOIk~ FT NORTH ~" P.1/2 03: 57PM Kimley. Hom Suite i I00 801 Cherry Street Fort Worth, TX 76102-~803 TEL 817 335 651I FAX 817 335 5070 mail: Yea:. No: Y- problems, please call 817/335-6511 and ask for: pages, including cover sheet: g, Fax No.:~ Job No.: This lac. simile is intended only for the addressee named herein and may contain information that is confidential, If you are not the intended recipient or the employee or allent responsible for delivery to the addressee, you are hereby notified that any review, disserntnation, disclosure, or copying of this communication is strictly prohibited, ff you have received this facsimile in error, please immediately notify us by telephone, and return the original facsimile to us at the address above via the U.S, Postal Sewice. Thank you.