Salt water from the well looked clear and 

 suitable for use following initial flushing; how- 

 ever, after the water was exposed to air, a 

 reddish-brown precipitate formed. Further 

 testing revealed that the well water contained 

 15 ppm of iron, apparently in the form of sol- 

 uble ferrous hydroxide, Fe(0H)2, which, upon 

 contact with the air, oxidized into insoluble 

 ferric hydroxide, Fe(0H)3. 



Iron precipitate was successfully removed 

 from the subsurface salt water by continuous 

 aereation as it was recirculated through a com- 

 mercial swimming-pool diatomaceous-earth fil- 

 ter. This filter contains seven 18- by 261/2-ir'ch 

 filter grids of polypropylene and stainless steel 

 with a total filtering surface of about 46 ft". 

 The filter material was commercial grade 

 diatomate. In less than 6 hr of recirculation, 

 the filter reduced the iron content of 500 gal 

 of salt water from 15 ppm to below 1 ppm. 

 Removal of the iron precipitate reduced the 

 hydrometer determined salinity from 29.7 %o, 

 its original value, to about 23.0 '<< . The dio- 

 tomaceous-earth filter grids required cleaning 



after they had filtered three or four 500-gal 

 batches of well water. 



A wedge of high-salinity water (30 %c plus) 

 was found to intrude along the bottom of the 

 40-ft deep Pascagoula River channel at the loca- 

 tion of the saltwater laboratory. This source 

 was also used to fill the recirculation system. 

 A suction hose lowered into the wedge conveys 

 this water into the laboratory where it is re- 

 circulated through the diatomaceous earth filter 

 before the water enters the system's reservoir. 



Figure 2 shows the floor plan of the labora- 

 tory. The combination experimental pool- 

 water reservoir, at the center of the laboratory, 

 is 18 ft in diameter and 41/2 ft deep, and holds 

 about 7,000 to 8,000 gal (the completely filled 

 system contains about 10,000 gal). The side 

 of the pool is of steel-reinforced concrete block 

 filled with poured concrete, and the bottom of 

 the pool is of poured concrete. A drain was 

 constructed in the center of the pool floor for 

 cleaning purposes. The pool was coated with 

 "Damtite", a concrete sealer, to ensure a water- 

 tight structure. 



WATER TABLE 



EQUIPMENT 

 TABLE 



EQUIP 

 TABLE 



EXPERIMENTAL TANK 



WELL 

 FILTER BOX 



AIR 

 COND 



Figrure 2. — Floor plan of the seawater laboratory at the Exploratory Fishing and Gear 



Research Base, Pascagoula, Miss. 



