PROJ00032 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I SECTION 4 PIPELINE EVALUATION Evaluation of the pipeline consists of a review of the existing pipeline capacity and condition, along with consideration of the size, material, and alignment of a new pipeline which will replace the existing line. Existing pipeline Characteristics The existing raw water supply pipeline was constructed in 1949, and is made up of 9,500 feet of 14-inch diameter steel pipe, 6,500 feet of 12-inch diameter steel pipe, and 180-feet of 24-inch diameter ductile iron pipe. The present pipeline capacity is estimated to be in the range of 4 to 5 mgd (6.0 to 7.7 cfs). The existing steel pipeline is coated, lined, and joined with Dresser joints. Records maintained by the City of Cortez Public Works Department indicate that repair work has been performed on this line annually since 1975. Repairs generally consist of banding large leaks, replacement of small sections of line, and plugging small leaks with redwood pegs. No construction drawings, as-built drawings or project records are available for the original pipeline, so the location, number, type, and size of any fittings such as isolation valves, couplings, air-release valves or service taps is not known with any degree of confidence. A field inspection performed in December 1985 identified leaks in several locations. This field inspection consisted of walking the alignment of the existing raw water supply line and visual inspection of several sections of pipe which had been replaced. At more than one location, water was surfacing at a noticeable rate (1 to 2 gpm estimate) from directly above the pipeline. This is a typical indicator to City maintenance crews of leaks in the line. The sections of removed pipe showed several holes up to I inch in diameter, worn completely through the pipe wall. The pipeline will still deliver raw water to the Cortez Water Treatment plant for some months to come; however, in view of the constant maintenance attention the line receives, and after inspection of the condition of sections of removed pipe, the pipeline has reached the end of its useful life. The potential for a serious failure of this line is high and significant disruption of raw water supply to the plant would result. City maintenance activities are directed towards patching and replacing individual leaks as they are discovered. There is no value in attempting to rehabilitate this BROWN AND CALDWELL C CONSULTING ENGINEERS