WALDEN, TOWN OF

Incident Narrative

ON AUGUST 31, 2022 THE WALDEN PIPELINE OPERATORS RECEIVED PHONE CALLS FROM THE CIG CONTROL CENTER, ABOUT CONCERNS FOR INCREASED GAS USAGE. ONLINE FLOW RECORDS SHOWED AN APPARENT 10X FLOW INCREASE AROUND AUGUST 23. CIG HAD CHECKED ITS DELIVERY METER AND FOUND NOTHING ABNORMAL. THE 50-MILE TRANSMISSION SYSTEM WAS SYSTEMATICALLY ISOLATED AND CHECKED BY SECTION, AND CIG NOTED AN ABRUPT DROP IN FLOW. THE LAST SECTION ISOLATED WAS THE HIGH-PRESSURE DISTRIBUTION SYSTEM IN COLORADO THAT FEEDS THE TOWN SYSTEMS IN COWDREY AND WALDEN.NEXT DAY WE PINPOINTED LOW PRESSURE ON THE 2-INCH SECTION THAT HELPS FEED WALDEN. THIS WAS THE ORIGINAL SUPPLY LINE TO WALDEN, BUILT CA 1958 OF COATED STEEL 2"" PIPE. WE HAD FOUND AND FIXED A CORROSION PINHOLE LEAK ON THIS SEGMENT EARLIER IN JULY, THE ONLY LEAK FOUND IN 20+ YEARS ON ANY PIPELINE IN COLORADO. THIS 17,000 FT SEGMENT WAS LOOPED CA 1979 WITH A 3"" COATED STEEL LINE, PARALLEL AND ABOUT 10 FT SOUTHEAST. THE 2"" SECTION WAS ISOLATED AND QUICKLY PRESSURED DOWN. LATER, GAS WAS REINTRODUCED AND A LEAK SURVEY DONE IN THE AREA AROUND THE PREVIOUS LEAK. THE NEWER LEAK WAS DETECTED ABOUT 180 FT SW OF THE PREVIOUS REPAIR, RUNNING ALONG A SHALLOW SAGEBRUSH WASH. WITH THIS SEGMENT SHUT DOWN AND THE 3"" LOOP CARRYING THE LOAD, WE EXCAVATED THE NEW LEAK AREA ON NOVEMBER 2, INTENDING A REPAIR. THE PIPE AND COATING LOOKED IDENTICAL TO THAT WITH THE NEARBY LEAK REPAIR, BUT WAS VERY SHALLOW. THE EXCAVATED MATERIAL WAS MOSTLY BLACK, SMELLY LEAK DIRT INDICATIVE OF A LONG-TERM GAS LEAK. THE EXCAVATOR STRIPPED OUT THE PIPE FOR 60 FT, AND WE INTRODUCED A SMALL AMOUNT OF GAS FROM THE NEARBY BLOCK VALVE. THE EXPOSED & CLEANED-OFF PIPELINE DIDN'T LEAK. BUT THE GAS DETECTOR PICKED UP GAS NEAR THE FRONT AND NORTH SIDE OF THE BACKHOE, WELL AWAY FROM THE EXPOSED 2"" AND THE SIDE AWAY FROM THE 3"" LOOP. AFTER FURTHER INVESTIGATION, DIGGING OUT MORE LEAK DIRT, WE EVENTUALLY FOUND A SECOND STRING OF 2"" PIPE RUNNING PARALLEL TO THE EXPOSED LINE, ABOUT 7 FT NW AND 3.5 FT DEEPER. WE STRIPPED OUT A 10-FT SECTION OF THIS NEWLY-DISCOVERED PIPE. THE COATING WAS A COLD-APPLIED YELLOW TAPE WITH THICK BLACK MASTIC, LIKELY HAND-APPLIED WITH GOOD OVERLAPS AND NO WRINKLES. WE COULD FIND NO OBVIOUS DEFECTS OR HOLES, UNTIL GAS WAS INTRODUCED. IN LESS THAN 5 SECONDS, THE SHORT SECTION APPEARED TO LEAK IN AT LEAST 4 PLACES, INCLUDING A PINKIE-SIZE HOLE IN THE TAPE AND THE PIPE ON THE BOTTOM. ALTHOUGH THE TAPE LOOKED GOOD ON FIRST INSPECTION, THERE WERE SEVERAL DEEP MARKS AND DENTS, ALTHOUGH THE SOIL WAS ROCK-FREE, MOIST CLAY. THE DEEP DENTS MAY HAVE BEEN MADE DURING INSTALLATION, WHEN THE PIPE WAS LOWERED IN WITH LOG CHAINS INSTEAD OF SOFTER PIPE SLINGS. THIS 3RD LINE IS NOT SHOWN ON ANY MAPS OR DESCRIBED IN ANY DOCUMENTS CONVEYED FROM THE ORIGINAL OWNER ROCKY MOUNTAIN NATURAL GAS TO THE TOWN IN 1995. WITH 5 CORROSION LEAKS (DESPITE GOOD CP READINGS) IN 200 FT IN A FEW MONTHS; AND WITH LITTLE HYDRAULIC VALUE, WE DECIDED TO PERMANENTLY ABANDON THE 2-INCH SEGMENT. WE CUT OUT AN 8-FT SECTION OF THE LEAKING PIPE, AND WELD-CAPPED BOTH ENDS OF THE 17,000 FT SEGMENT, WITH DOCUMENTATION THAT THIS SECTION CAN'T BE USED AGAIN. THIS LEAK WAS ABOUT 1.2 MILES FROM THE EDGE OF WALDEN. THE NEAREST PUBLIC ROAD IS THE COUNTY RODEO & FAIRGROUNDS ABOUT 1/2 MILE AWAY, AND 0.9 MILE TO THE NEAREST RESIDENCE. WE BELIEVE THIS LEAK HAS PERSISTED FOR DECADES. IT WAS NOT REPORTED BY THE PUBLIC, SINCE IT IS VERY REMOTE AND THE PREVAILING WIND GENERALLY BLOWS FROM THE SOUTHWEST, AWAY FROM ANY RESIDENCES OR ROADS. THE UTILITY HAD LEAK-SURVEYED THE 2 KNOWN PARALLEL LINES AS REQUIRED BY DOT PART 192. THE VEHICLE-MOUNTED RIG WAS ALWAYS DRIVEN BETWEEN THE 2 PIPELINES THAT ARE ONLY 8 FT APART. THE UNKNOWN LINE WAS ABOUT 12 FT OUTSIDE THE LEAK SURVEY PATH. WE BELIEVE OLD UNDETECTED PINHOLE LEAKS BLEW OUT WITH THE RE-PRESSURIZATION AFTER THE PREVIOUS REPAIR. NO INJURIES OR DEATHS RESULTED FROM THIS LEAK. THE ONLY DAMAGE WAS THE VALUE OF LOST GAS.