Chapter IV: Biofouling And Corrosion Study
(continued)

Water Quality and Biofouling in Interior Spaces

Methods

Examination of biofouling and sediment coverage of walls and floors was done in some interior spaces where the presence of open portholes enabled observation. Divers simply inserted a flashlight at arm's length through portholes and visually scanned surfaces. Visibility was usually restricted to about 15 feet by the low intensity of the light used and by the small viewing openings provided by the portholes, which commonly had nearly 50 percent of their open area occluded by hard fouling.

Water motion and the flushing rate in interior spaces of the ship's hull are probably low, due to the scarcity of large openings connecting those spaces with ambient harbor water. It was also assumed that "stagnant" water trapped in interior spaces would exhibit oxygen and pH levels considerably lower than typical harbor water, primarily due to the effects of oxygen consumption by microbes and heterotrophic organisms. Under conditions of lowered oxygen, pH and water motion/flushing, it would be expected that abundance of fouling communities would diminish because of reduced availability of oxygen and water-borne food. On the other hand, corrosion rate of steel would be lessened by those very conditions of low oxygen and low water motion, but would be accelerated by the presence of low pH and sparse fouling coverage (ref. 2).

To assist in defining the chemical and biological conditions inside the ship, water quality was measured in water pumped directly from selected interior spaces. The pumping apparatus consisted of a 15-foot-long piece of 3/4-inch-diameter PVC pipe connected by 30 feet of 1-inch-diameter vinyl hose to a 12-volt water pump that was situated in a small boat. From the pump, water was delivered to a wet-well manifold on the boat that contained sensor probes for oxygen, pH and temperature measurements. A technician on the boat recorded data from the instruments (Yellow Springs Instruments Co. model 57 dissolved oxygen and temperature meter, and Beckman Co. model 1009 pH meter) when appropriate signals were received from the divers below.

Water-quality measurements were accomplished in six interior spaces (Figure 4.9). In the course of a typical measurement run, divers first held the pipe/hose intake about 2 feet away from the opening that accessed the space to be sampled. After the outside (ambient) water data had been recorded, the divers inserted the pipe into the opening to the full length of the pipe (15 feet) or until an obstruction was encountered. Water-quality measurements were taken at maximum insertion and, in three cases, also at 8 to 9 feet of insertion. After withdrawal of the pipe, a second set of ambient measurements were taken.

Figure 4.9. Locations of points of entry for water-quality measurements made in interior spaces in the USS ARIZONA.

When water was being pumped at maximum pipe insertions, water samples were collected from the topside manifold port. Those samples were chilled and checked at the end of the sampling run for odors indicative of hydrocarbons or sulfides. Also, notes were made on the presence of visible sediment and hydrocarbons that appear in the pumped water.

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