| Wastewater | Deer Island, Boston Harbor - Page 22 |
For a topic that so much has been written about it is unfortunate that there is not a detailed account available of the actual construction of the new Deer Island treatment plant. Books have been written on the construction of famous dams, bridges, tunnels, buildings, and other major engineering accomplishments, but not one on the building of the country’s second largest wastewater treatment plant on an impossibly small, difficult to reach site. Then again maybe a book about constructing a sewage treatment plant just would not be a big seller.
There are mentions in the documents from the mid-1990s from the MWRA that list multiple internal and external newsletters that were produced during the project, but none appear to be still available today. The MWRA website, though it only went live in 1998, did list some of these publications, but they could be requested and were not available online. That many of the early MWRA documents are available online at all is thanks to a great part to the State Library of Massachusetts.
During the construction of the plant from 1989 to 1997 the MWRA published a series of four-to-eight-page documents each explaining how important components of sewage treatment plant and system will function. |
| Also available on the State site are selected annual MWRA capital improvement and current expense reports, though most are from after when the Deer Island project was completed. The ones available from the time of construction provide a detailed breakdown of cost and completion timetables for each of the 23 construction phases. Combined there were over 210 individual projects involved in building the plant and tunnels. Very informative, but really more of interest to an accountant. In contrast a 100 years earlier Howard Carson in his annual Report of the Chief Engineer for the Metropolitan Sewerage Commission provided a detailed chronicle annually of work performed and challenges faced while constructing the initial North Metropolitan system. Just while crossing Shirley Gut and reaching the outfall workers had to dig trenches through gravel so coarse that sea water flowed through it, drumlins so solid dynamite was needed, run pumps continuously to keep leaking coffer dams dry, and replace whole pipe sections carried away by ocean storms. All described in detail by Carson in annual reports. Of course, the two projects really can’t be compared. The complexity, the technology, and number of workers onsite was on a completely different scale during the construction of the modern treatment plant. Still, that the story of the construction is not available is frustrating. |
| During the peak construction phase of the Boston Harbor Project estimates of the numbers of workers on the Deer Island site at one time ranged from 2,000 up to 3,000, all in a very constricted area. While each of the many individual construction contractors had the primary responsibility to establish, implement and actively maintain effective safety programs, Kaiser Engineers as the construction manager was tasked with developing a project-wide safety program that all individual safety programs had to comply. There were mandatory safety orientation programs, procedures for emergency medical response and hazardous waste discovery and disposal, regular safety inspections, and for new hires a pre-employment drug test. The aggressive effort paid off with the overall project have a significantly lower loss time incidence rate compared to the average of other large-scale projects. |
| While a low loss time incidence rate might be impressive, it does not reflect the tragedy of the loss of five lives during the construction of the DITP. It was work in and around the tunnels that would prove to be most dangerous. Work on both the Outfall and Inter-Island tunnels started in 1991 meeting Judge Mazzone’s schedule for the project. Both were supposed to be completed in 1994. For the people of Quincy, the sooner better because completing the Inter-Island tunnel meant that that Nut Island treatment plant could be eliminated. For the people on Nahant and Cape Cod the 1994 date was a problem because it meant that the initial discharge of the Outfall tunnel would be effluent with only primary treatment. Construction of the secondary treatment portion of the new treatment plant was not scheduled to begin until 1995. The issue of discharge with only primary treatment would eventually become a moot point, but the controversy did serve to unite opposition to the Outfall in general. |
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For the Outfall tunnel contractors drilled over 50 test bores into Massachusetts Bay to determine what type of subsurface conditions would likely be encountered. For the Inter-Island tunnel, because the geology of the Boston Harbor had been studied for years, only 17 new test bores would be drilled. The geology of the harbor is complicated involving colliding continents, exotic terranes, mountain building, volcanoes, earthquakes, faulting, folding, weathering, erosion, deposition, and glaciers. The faults in the underlying rock of basin run generally east-northeast. Fortunately for the Outfall tunnel its path reaching into Massachusetts Bay ran roughly parallel to one of the faults. Unfortunately for Inter-Island tunnel its path ran north-south across a series of the faults. |
| While multiple test bores would give workers of both tunnels a general impression of what of type rock lies ahead, it could not identify the exact conditions they would encounter. One of problems the Outfall tunnel ran into was something called blocky rock, a term used to describe rock that has fractured into randomly sized blocks that are wedged together into a uniform mass. Nothing but their position holds the rocks together. Drilling through blocky rock can cause unsupported portions to collapse. An unusual feature the workers digging the Outfall tunnel encountered was a dry 25-foot-long, 35-foot-high cavern, two-hundred feet below the sea bottom, almost 400-feet below the ocean’s surface. The TBM needed to grip on a firm surface to move forward so 600 cubic yards of concrete was brought in. Also, the discovery of harder rock in the path of the tunnel than had been expected resulted in the need to replace rock cutter heads much more frequently. |
The path of the Inter-Island tunnel ran across five lithographic zones that, over a hundred years earlier, noted geologist William O. Crosby in his 1880 book “Conditions to the Geology of Eastern Massachusetts” described with almost delight as being “wonderfully contorted and folded; presenting anticlines and synclines of very variety, - large and small, open and closely folded, normal, inverted and faulted.” Wonderful for a geologist, a difficult challenge for the workers digging the tunnel. The initial straight path of the tunnel had to be modified when a depressed area of poor bedrock was discovered. The final path was slightly modified with a dogleg around the area.
While the Outfall tunnel would be lined with precast concrete segments, the Inter-Island tunnel used sprayed concrete as a liner. This would be applied directly on the face of rock in areas where the rock was self-supporting. In areas where the rock was not self-supporting steel ribs and matting would be first installed and then concrete sprayed as a liner. Workers ran into just such an area of crumbling rock in mid-1994 when it caved in on the TBM. That stretch of the tunnel had to be dug out by hand and then steel ribs installed. |
| Both tunnels had unexpected serious problems with water infiltration. Reports put inflow rates at times of 4,000 to 7,000 gallons of water a minute leaking into the tunnels. That would be enough water to fill an Olympic swimming pool in two hours. Far more than what had been predicted and it only increased the dangers posed by thousands of volts of electricity needed to operate the TBMs. But it would not be the dangers posed by the high voltages that would result in any of the loss of lives during the construction, and it would be neither the Outfall or Inter-Island tunnel where the first worker fatality took place. |
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Construction on the two side-by-side tunnels bringing the wastewater flow from North Main Pump Station to the new grit removal facility near the south end of the work site was just being completed in the early summer of 1992. One of the final steps was to install a 13-ton precast concrete collar supporting a manhole cover at the entrance of the tunnel. After that was completed, and most of the equipment moved to another job, it was discovered that a rubber gasket under the collar had not been installed. Another crane was brought in to lift the section and, in what was clearly a violation of safety practices, several workers applied the missing gasket with the heavy precast concrete just over their heads. The crane’s brake slipped, two workers seconds before moved back, but Michael R. Lee had not and was crushed. The timing of the accident near the very end of specific job would become a pattern for future fatal accidents. |
| Less than a month later the Deer Island Treatment Plant construction project experienced its second worker fatality, this one on an offshore drilling platform in Massachusetts Bay. It too occurred just as that portion of the project was being completed. Since the summer of 1991 work had been underway drilling the holes for the 55 riser pipes that would eventually be connected to the Outfall tunnel. The process first involved lowering a steel casing pipe to a predetermined location on the ocean floor. For the prior 54 holes that had been drilled, the 80-ton weight and varied amounts of driving, would push the pipe through a gravel base that had been deposited and into the soft top layer of sediment and clay on the ocean floor. Then the drill bit and an 80-ton device called the Bottom Hole Assembly (BHA) would be lowered into the casing and drilling begun. |
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On the morning of July 20, 1992, work had just begun with the lowering of the casing to the ocean floor settling only a few feet into the gravel base level. Without driving the casing through the soft sea floor, the drill bit and BHA was lowered on top. The addition of the 80-ton weight of the BHA caused the casing to drop suddenly 25 feet through the sediment layer. The sudden reduction of weight sprung open a door on the floor of the drilling platform. Two drill operators were knocked backwards and sustained minor injuries. Drilling foreman, Charles R. Spears, was knocked off a higher platform and fell 30 feet. He died the next day from his injuries. |
More than any other type of construction, an accident in a tunnel has the potential to put many workers at risk at one time. The MWRA narrowly avoided a tragedy that could have put the whole project at risk. On June 15, 1994, workers doing welding in shaft for the Inter-Island tunnel on Deer Island accidentally dropped a hot bolt onto the conveyor belt system that brought rock up to the surface. It caught fire blocking that exit for the forty-three workers in the tunnel at the time. The fire also cut power to the pumps that were keeping the tunnel dry and with water flowing in at 11,000 gallons a minute, it would not take long before the whole tunnel would flood. Fortunately, a decision had been made earlier that would permit all the tunnel workers to escape without injury.
Unlike the Outfall tunnel with only the ocean above, the path of the Inter-Island crossed under Long Island. To service the wastewater needs of Long Island the initial plan called for a 12-inch diameter drop shaft to the main tunnel. It would prove fortunate that the decision was made to increase its width to 4 feet. People might remember the 2010 rescue of thirty-three men from a Chilean mine. After a bore hole had been drilled, the workers two-at-time were brought to the surface in a torpedo-shaped escape capsule. News videos show workers being brought to surface on Long Island in a similar device. The tunnel itself would flood with water rising 50 feet. It would take months to repair and or replace the equipment in the tunnel. Fortunately, no one was injured.
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| Work in the tunnels would result in another tragedy on June 23, 1995. This time the accident occurred nine miles out at the head of the Outfall tunnel. In a tragic irony the victim had earlier identified the work area as being dangerous. In addition to the regular tunnel workers, employees from Stone & Webster as the primary Construction Manager for the Outfall tunnel portion of the project, and Kaiser Engineers as the CM for overall project, also regularly were in the tunnel inspecting the work and monitoring the safety. After being lowered down the shaft on Deer Island, personnel reached the working end of the tunnel by means of a locomotive towing what are called mantrip cars. Each mantrip car had four seating compartments with space for six people in each compartment. A single rail track ran the length of tunnel splitting into two just at the back of the 100-yard-long tunnel boring machine in an area called the trailing gear. |
| The Outfall tunnel being dug by the TBM was 30-foot in diameter. Machinery in the TBM installed concrete segments that lined the tunnel resulting in a final diameter of 24-feet. At the very end of the trailing gear was a two-level metal framework that on top had a conveyor belt carrying the material the cutting end of the TBM was removing. Below was a very congested area. Regular trips by railcars brought out the massive precast segments along with all the equipment needed to operate and supply the TBM. During a shift change the mantrip cars added to the congestion bringing out the new workers relieving the existing crew. |
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To ensure worker safety procedures required bells, horns, and lights be used to signal when it was safe for workers to disembark from the mantrip cars. Richard A. White, an employee of Kaiser Engineers, had filed two reports that identified the time during a shift change as being particularly dangerous primarily because not all the safety procedures were being consistently followed. On June 23, 1995, it was White who stepped off the mantrip car that had stopped without a signal and was fatally injured when the car moved forward trapping him between the car and metal framework of the trailing gear. |
| By the summer of 1997 the first of the three batteries for secondary sewage treatment of wastewater went online. The sequential construction plan for the new sewage treatment plant proposed by Richard Fox in May 1985 and approved by Judge Mazzone was beginning to produce results. By March of 1998 the second battery was completed (the third and final battery was completed in March of 2001). In October of 1998 the Inter-Island tunnel began operation and the Nut Island treatment plant torn down. |
| The drilling of the riser pipes for the Outfall tunnel had been completed in July 1992. Beginning in 1995, and before the Outfall tunnel had reached its full length, work had begun on digging the 55 side tunnels to connect to the riser pipes. The digging of the Outfall tunnel reached its full distance of 9.5 miles in September of 1996. Because the TBM was wider than the completed tunnel it was not possible to dismantle it. Instead, the tunnel was bored a short distance further and the TBM buried in concrete. |
| For the Outfall tunnel to function by gravity alone without pumps, the diameter of the tunnel had to be progressively reduced in the section with the risers. From a starting diameter of 24-feet, the tunnel had to choke down to five feet for the final three risers. To accomplish this a ramp was constructed to gradually reduce the overall diameter of the tunnel. To further reduce the diameter, seven-foot-high jersey barriers were placed progressively closer and closer together. For the final six-hundred feet concrete pipes with smaller and smaller diameters were used narrowing down to just five feet for the final three risers. |
A risk that had been identified very early on was what would happen, once the riser pipes began to be connected to the main tunnel, if any of the 55 diffuser caps on top of the risers was knocked off by, for example, a ship’s anchor. The tunnel would quickly flood, likely drowning all the workers. The solution was to install removeable caps at the top and bottom of the riser pipes was a good one and ensured the safety of the tunnel workers. What was not thought out was how to remove all 55 caps from the bottoms of the risers without exposing workers to the same risk of flooding once even the first cap was removed. The decision was made to finish the Outfall tunnel completely, remove all the construction equipment, and then send in a crew to remove the plugs at the bottom of the risers.
Work in the tunnel when it was under construction was only possible because extensive ducting brought in fresh air. Without it the crew removing the plugs would effectively be diving in an oxygen-free environment. The book, “Trapped under the sea - One engineering marvel, five men, and a disaster ten miles into the darkness,” by Neil Swidey, gives a detailed account of the tragedy that took place on July 21, 1999. Two men of the crew, Timothy Nordeen and William “Billy” Juse, died when their breathing equipment failed. In an unusual coincidence, the lead news on that day was the recovery of the bodies of John F. Kennedy Jr. and two others from the ocean off Martha’s Vineyard where his plane had crashed. Similar to the first two accidents on the DITP project, it was the final step of a specific task that proved the most dangerous. Though in this case it was the final step for the whole DITP project. |
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As with the other accidents there was an OSHA investigation. Penalties were levied and recommendations made for a safer work environment. Still the plugs had to be taken out and now OSHA was requiring that the tunnel be ventilated with fresh air before they were. Two alternatives were considered. One was to install temporary duct work to provide a workable environment. But that would be both costly and time-consuming. It would be an MWRA senior construction manager, Kenneth Chin, who would come up with the plan to remove the plugs efficiently and safely. A plan that in hindsight should have been the original plan. It called for a jack-up barge to be placed over one of the three risers that the earlier team had removed the lower plug. A caisson, basically a large metal pipe, was lowered onto the riser and the water inside pumped out. Then by means of a powerful fan on the barge breathable air was drawn in from the tunnel entrance on Deer Island. Starting on July 15, 2000, after testing to ensure that oxygen levels were adequate, a crew went in and removed all the plugs in five days.
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