1988 - Barge ACO-501

On November 24, 1988 the U.S. Coast Guard Marine Safety Office in St. Louis, U.S.A., received a report that a barge (ACO-501) loaded with sulphuric acid, was missing from the dock of a terminal facility in Herculaneum, Missouri on the Upper Mississippi River. The barge was a standard size river barge, about 60 metres in length and 11 metres wide with two cargo tanks, double bottoms and double sides (Figure 1). The barge had been loaded with approximately 1400 tons of 93% sulphuric acid on November 20. It was not absent from the dock on the morning of November 22, but the terminal facility personnel assumed that the barge had been picked up during the night by the tugboat as was scheduled. The towboat had arrived for the scheduled pickup that evening but, not seeing the barge, continued on its journey assuming that it had been picked up by another towboat. The discrepancy was only discovered after a representative from the barge line notified the facility that the scheduled pickup had not been made. Terminal personnel had checked at the mooring at their dock and there were no indications that the barge was there. Marine Safety Office personnel were dispatched to the scene and, using soundings with a steel rod, located the barge in 1.5 metres of water, several feet from its original mooring point. With this information, the U.S. Environment Protection Agency (EPA), the Missouri Department of Natural Resources and the Scientific Support Co-ordinator of the National Oceanic and Atmospheric Administration (NOAA) were notified whilst response personnel from other U.S. Coast Guard Offices were sent to the scene.

On November 24, 1988 the U.S. Coast Guard Marine Safety Office in St. Louis, U.S.A., received a report that a barge (ACO-501) loaded with sulphuric acid, was missing from the dock of a terminal facility in Herculaneum, Missouri on the Upper Mississippi River. The barge was a standard size river barge, about 60 metres in length and 11 metres wide with two cargo tanks, double bottoms and double sides (Figure 1). The barge had been loaded with approximately 1400 tons of 93% sulphuric acid on November 20. It was not absent from the dock on the morning of November 22, but the terminal facility personnel assumed that the barge had been picked up during the night by the tugboat as was scheduled. The towboat had arrived for the scheduled pickup that evening but, not seeing the barge, continued on its journey assuming that it had been picked up by another towboat. The discrepancy was only discovered after a representative from the barge line notified the facility that the scheduled pickup had not been made. Terminal personnel had checked at the mooring at their dock and there were no indications that the barge was there. Marine Safety Office personnel were dispatched to the scene and, using soundings with a steel rod, located the barge in 1.5 metres of water, several feet from its original mooring point. With this information, the U.S. Environment Protection Agency (EPA), the Missouri Department of Natural Resources and the Scientific Support Co-ordinator of the National Oceanic and Atmospheric Administration (NOAA) were notified whilst response personnel from other U.S. Coast Guard Offices were sent to the scene.

A visual inspection showed no signs that any chemical reactions had taken place due to release of acid into the river, nor were there any signs of acid in the river when pH readings were taken downstream. An initial evaluation showed that the low vapour pressure of the acid precluded any releases that would be harmful to nearby communities whilst any discharge into the water was predicted to be rapidly diluted and would not pose any significant threat to the environment. Although the potential for fish kills existed if acid entered the water, there were no stressed or dead fish observed in the vicinity of the barge or any reported downstream. A meeting was held between the Coast Guard and the barge owners to discuss the salvage operations whilst terminal personnel were tasked to perform hourly visual inspections and take pH readings to monitor the river water for the presence of acid.

A risk assessment indicated that if water entered the cargo tank, a large amount of heat and steam would be generated presenting the possibility of a rupture of the barge's hull and the creation of an acidic mist. Ships normally carry sulphuric acid in bulk at 98% to 93%. Below 65% to 70% acid concentration, mild steel corrodes rapidly and very high corrosion rates can take place at around 50% concentration. One of the problems faced by salvors who try to offload sulphuric acid diluted to 70% to 50% range may have trouble finding another ship or terminal willing to take the product.

The owners hoped to transfer the acid cargo from the sunken barge to an identical barge and then raise the barge. The lifting capacity of the salvage equipment did not have the capacity to raise the barge and the cargo. The barge would have to be either lightered or dewatered before any raising operations were to be undertaken.
A river survey was conducted to determine the depth of river over the barge and the slope of the riverbed under the barge. A diving survey was also conducted to see to the condition of the barge. The diver used a surface-supplied air system and wore a neoprene "dry-suit" that provided some protection against any acid that might be encountered. The survey indicated no significant hull damage although both cargo tanks had open ullage covers indicating that water had entered the tanks. pH readings indicated a water/acid mix-up to three feet below the cargo tank top with concentrated acid remaining in the rest of each tank. Due to the corrosive nature of the acid/water mix, the salvage plan was reassessed. Other considerations included potential damage to the environment and marine life.

Various options were considered: 1) underwater transfer of the acid from the cargo tanks as the barge lay on the riverbed to another container by either connecting into the onboard piping system or building a cofferdam over the deck of the barge to access the cargo tanks; 2) raising the barge with the cargo aboard by either dewatering the void spaces or lightering with "A-frame" floating cranes; 3) controlled discharge of the acid to the river to lighten the barge sufficiently to facilitate the salvage.

A number of technical and logistical problems were identified with option 1. The first was the availability of a suitable container which could also take the corrosive water/acid mix. Secondly, the volume involved was too large for the number of containers which could be made readily available. Thirdly, the question arose of whether pumps could be set up to transfer the product and whether these had the necessary pumping capacity to lift a product of a specific gravity of 1.83 and then to get the required suction to overcome the head of 16 metres to reach the road or rail line. Consideration was also given to a failure of the stainless steel transfer system (pumps and hoses) due to the corrosivity of the product. A final problem was the need to replace the cargo removed from the tank with air or water to avoid creating a vacuum in the tank spaces and to stabilize the barge on the bottom as the cargo was removed.

Although the construction of cofferdams was possible since the barge was only about 3 metres from the surface, technical difficulties such as the establishment of a tight seal on the barge's deck were not considered possible, probably due to the deck transverse framing and cargo piping. Furthermore, the cofferdams would have to be large enough to operate pumping systems, high enough to withstand changes in river water levels and would need to be strong enough to take currents of up to 4 knots. There would still be long hose runs with the potential for leaks.

A number of technical problems were identified with option 2. This option involved dewatering the voids using pumps or compressed air, using "A-frame" barges to lift the barge off the bottom. However, because there was no information as to why the barge sank and it was critical that the barge be dewatered evenly to minimize hull stresses due to the weight of its cargo, there was concern that a catastrophic hull failure and instantaneous release of the entire cargo would occur if the voids did not empty as planned. There was also concern that hull stress imposed by the lifting cables used by the "A-frames" at either end to lift the barge could break the barge if not positioned correctly or if the barge was not lifted evenly.

Option 3 involved using a pumping system to transfer the acid from the cargo tanks directly into the river. To do this, an airlift was to be placed into the cargo tank and operated to "lift" the heavier acid out of the tank. A "T" flange would be placed on the top of the airlift pipe to facilitate the mixing and diffusion of the acid in the water. With large volumes of water flowing past the barge, the acid would be quickly diluted.

Consideration was given to the violent reaction of water and acid and the production of an acidic mist once mixing takes place and the threat to the environment. Following consultation, it was determined that there were no significant resources in the area, with the exception of fish, whilst downstream water users were to be contacted and their water intakes monitored.

To evaluate the potential impact, a simulation model was run to estimate river pollution whilst river pH and air was to be closely monitored for sulphuric dioxide vapour by using colourimetric tubes.

Following consultations, controlled discharge of the acid to the river was opted for with a discharge monitoring criteria of pH 6 or greater set for 90 metres down river from the sunken barge. Air monitoring downwind was to be carried to evaluate potential exposure of personnel and the population. Levels of protection were specified for the various operations planned. The diver continued to wear the neoprene "dry suit". An alkaline solution was available to spray if necessary to neutralize any acid. All personnel had access to Escape Breathing Apparatus (EBA). Neoprene gloves were required for response personnel handling potentially contaminated equipment. Personnel performing air monitoring downwind from the barge were provided with level C protection and had access to EBA. Self Contained Breathing Apparatus (SCBA), first aid equipment, an emergency eyewash station and deluge shower were also set up at the scene. Contact was made with local police, fire department, ambulance and hospital to establish and confirm emergency procedures. A person was on the scene to handle the media coverage of the salvage operation.

Pumping operations continued from November 29 through December 3 using the airlift system (see Figure 2). Operations were suspended at night. On December 3, the cargo levels in tank 2 had been lowered as much as possible using the airlift system. The airlift pipe had to be replaced on December 3 due to corrosion. As attention was directed to tank 1, the barge shifted and the stern side became buoyant. As cargo discharge from tank 1 continued, the buoyant stern and reductions in river flow reduced the mixing and dilution effect of the river, lowering the pH reading downstream. A tug was brought in and its propeller wash used to increase the mixing of the discharged acid, however this was only partially effective. A reduction in discharge rate took place to maintain the pH at the desired level.

On December 7, the majority of the acid was emptied from tank 1 and permission was granted to begin lifting the barge using "A-frames" of a crane. Continuous sampling took place in the refloating operation.