Loading...
ST9302-CS000906 (2)FAX (214) 352-3201 TELEPHONE (214) 358-6581 ED BELL CONSTRUCTION COMPANY POST OFFICE BOX 540787 10605 HARRY HINES DALLAS, TEXAS 75354-0787 DALLAS, TEXAS 75220 September 6, 2000 Mr. Kenneth M. Griffin, P.E. Director of Engineering/Public Works City of Coppell 255 Parkway Blvd. Coppell, Texas 75019-4409 Re: Sandy Lake Road Reconstruction Coppell Project ~: ST 93-02 Kimley-Horn Project #: 06940600 DWU Project #: 98-311F Dear Mr. Griffin: Per your request in your letter dated August 31, 2000 please find the attached report from our subcontractor, M-Co Construction, Inc., regarding the procedures that were followed prior to the placing in service of the 30" water line on the above referenced project. Please contact our office at your convenience if you desire to have a meeting to discuss this issue. Sincerely,, ED BE~ ~5~STRUCTION COMPANY Steven Pr, j~ly, P.E. President(/ AN EQUAL OPPORTUNITY EMPLOYER FROM :'M-CO CONSTRUCTION INC. PHONE NO. : 817 589 9155 S~p. 05 2000 10:51AM P2 M-Co Construction, Inc., 6816 Harmonson N. Richland Hills, Texas, 76180 OFFICE: Metro (817) 589-7601 FAX: I~/letm (817) 589-9155 September 5, 2000 Steven Pridy Ed Bell Construction, Inc. 10605 Harry Hines Blvd. Dallas, Texas 75354-0787 RE: The placing in service of the final section of the Ceppell 30" water main east of Mac. Author Blvd. on Sandylake Road. Dear Steven, Enclosed is a report showing our findings of what happened on August 30, 2000. Please review this report and let me know if them is ar~ything that is not clear or needs further explanation. Estimator M-CO Constructior~. Inc. 'FROM :' M-CO CONSTRUCTION INC. PHONE NO. : 817 58g g155 Smp. 05 2000 10:SLAM P3 Report on Sediment that disrupted city water system on August 30, 2000 Problem - When the new water main was placed in service the water turned brown and made the water cloudy in appearance. What happened on the project Just prior to water tuminf; colors - Glen Holloweil called our foreman (Slim) and said that the bacteda test had passed and he would have a valve crew come out after lunch and open the valves. About 1:00 P. M. Marshall and his helper' (The valve crew) came out to the project and said that Glenn had sent them out there. Marshall asked Garreth Campl~.,ll (project construction inspector) which valves needed to be turned on. Mr. Campbell told him the two 30" valves. Before turning on the 30" valves Mr. Campbell, Marshall, and Slim went over an¢ opened the 2" blowoff once more to visually inspect the water. After letting the water mn for ,.about five minutes they shut off the two inch. They said it looked good and Slim agreed. At that tim,~ Marshall, his helper, and some of our employees went up to the 30" valve at the Kimball Kourt pu~rnp station and opened it. After it was opened they came down to the valve at the Kroger Store anti started opening it. Marshall and Slim then left and went down the line to open a fire hydrant. When they returned to the valve it was open. So Slim and our crew went back to work. What happened after the brown water started running ~ut of the Are hydrant - About 15 minutes later Slim returned to the fire =.~drent and brown dirty water was running from it. He asked Marshall if he wanted him to open mom hydrants and he said that they would flush them one at: a time. At that time Marshall decided to close the 30" line by closing the valve at Moore Road. Slim and Mike Reed helped by sbJffing the t 6" valve that ties into the 30' line. Marshall and his helper continued to flush fire ~rdrants. We did not hear anything else about the problem until the next day. Two possible causes to the problem - (1) The 30" waterline was installed to provide more pressure from the east side of town to the west. The pressure at the Kimble Kourt Pump Station was 100 psi when we connected to it. When we tested the sections that were placed in service ,:luring the last year on the west end of the project the pressure was 50 psi. and below. When the t,wo 30" valves were opened (as described above) the water surged through the 10,000 feet of 30" pipe picking up and mixing the sediment that has been collecting over the last year. There is over two miles of 30' Water line that is. in service for about a year collecting sediment from the existing city lines. This is a 30" pipe that is being fed by smaller existing lines. When the water from a smaller line enters the larger line the wa:[er slows and allows material to settle to the bottom of the larger line. Over time this sediment will brJild up. (2)The city specific~ion require that flushing of the main be used to purge the new pipe of unwanted material. This is a standard procedure used to ~emove excess dirt/material from the lines but it does not remove all of it. Some of the material settles to the bottom of the pipe due to lack of flow and fom.~ needed to move it to the blowoff, This sediment i= no~ harmful after being disinfected and is acceptable under water purification standards. Improper purging of the system wOuld leave ex~ive rnaterial in the line. 'FROM :'M-CO CONSTRUCTION INC. PHONE NO. : 817 589 9155 S~p. 05 2000 10:52AM P4 Who's responsible - The contractor is responsible for keeping the pipe free of dirt and trash, ff dirt or trash enter the pipe at anytime during the pipe laying process it is to be removed immediately. I have not heard of one instance where this happened and was not corrected. If some dirt had been accidentally left in the line, that is why the specitlcations require the line be purged. Pfeifer purging would have revealed it and would have corrected the problem. The city's personnel perform the actual purging, sterilization, and bacterial testing of the line. The purging process either fluahing or pigging is selected by fhe city. Copy of NCTCOG specification item 6.7,3.(s) enclosed. The contractor is not allowed to operate any valve that is connected to the city water system that is in service unless we are under the direct .supervision of city personnel. The contractor's personnel are only to assist the valve crew as d~rected. Field Procedures that wouRI have prevented the problem - If the city valve crew had open either of the two valves 1/4 open instead of full open. The water should have equalized the pressure betwee~ the two sides over night. After the pressure equalized the valves could have been fully opened with little disturbance to the sediment in the pipes. Solution and Prevention - There are several cities in the metroplex that use a pigging program that removes sediment from a line at the time of installation, This program is more costly but it does reduce the sediment in the system so that when thers is a surge in pre,,;sure the disturbance in the system is minimized, (Pigging - a foam bullet is placed in the line at one end and when the water is turned on, it pushes possible sediment out the other end.) Closing - We did not pick or design the purging system u:sed on this project. If there was any excess dirt in the new line being placed in service the proper purging of the line would have prevented it from entering the system. Our investigation of what happened concJudes lhat the two miles of 30" that was already in service acted as a sediment trap for this last year. When the 30" valves by the pump station were open, the sudden flow increase picked up and mixed the sediment in the 3(7' pipe and the sediment in the existing city system causing the; entire system to become cloudy and dirty in appearance. 'FROM' :' M-CO CONSTRUCTION INC. PHONE NO. : 817 589 9155 Sep. 05 2000 1B:5PRM P5 J ~'"') 0 ~'~ ..... ( ...... ',~'""" "" '(-'"") .......... . x ....... . ,J L,. .~ ,.. , ~ROM~ :' M-CO CONSTRUCTION INC. PHONE NO. : 817 589 9155 Sep. 05 2000 10:53AM P6 c v=- o.,~>'- e~ ~ m~ ~ G~ ~ -~ ~ ~ ';~ ~-ROM':'M-CO CONSTRUCTION INC. PHONE NO. : 817 589 9155 Sep. 05 2000 10:S4AM P7