SEWAGE CONTAMINATION OF OYSTER BEDS. 205 



THE SOURCES OF SEWAGE POELUTION OF NAHKACANSETT BAY. 



The sewage of the city of Providence and immediate neighborhood 

 is collected at the sewage pumping station at Fields Point, about If 

 miles below the city, and is discharged into the river through a single 

 large main. The outlet of this drain is indicated on the map on page 

 203. Though it is covered by 25 feet of water at low tide, it may be 

 I'cadily located on a calm day by the greasy, turl)id stream of sew\age 

 which rises rapidly to the surface of the water at that point. 



In 1000 an average amount of nearly 14,000,000 gallons of sewage 

 was daily pumped into the river through the Fields Point sewer, and 

 at that time was thrown into the river in a "crude"" or "'untreated" 

 state; that is, it was simply passed through a screen to remove the 

 solid matters before being sent on to the outfall pipe. The screen con- 

 sisted of a rack or frame of parallel iron rods placed about an inch 

 apart, and was set at an angle of about 20 degrees from the perpen- 

 dicular. The stream of sewage was allowed to flow through this 

 apparatus, and whatever constituents w^ere too bulky to pass through 

 the grating were scraped off' Avith a rake and otherwise disposed of; 

 but, as might be expected, considerable amounts of solid matter slipped 

 through, and the beaches within half a mile of the outlet were strewn 

 with this refuse. 



Before these investigations were completed, however, the cit}^ put 

 in operation a sewage disposal plant at the Fields Point Station. 

 After screening, as already described, the sewage is su])jected to the 

 action of sulphate of iron and chloride of lime, which process causes 

 about 50 per cent of the total solids then in suspension to precipitate 

 out and sink to the bottoms of large reservoirs in which the sewage 

 is allowed to remain for twenty-four hours. The clearer fluid is then 

 dra-vyn off and turned into the river, while the" sludge" which remains 

 on the bottom of the basin is strewn over the land. Before this 

 method was employed the gray scum from this sewer could often be 

 traced on the surface of the water several miles below Fields Point, 

 where it had been carried b}^ tidal currents. The station has one other 

 large outlet, the "storm" sewer, which opens into the river from the 

 northern shore of the point. This sewer is a culvert built in the form 

 of an arch, which is entirely out of water at low tide. It is used only 

 in case of accident to the large main or during heavy rain storms, 

 when 20,000,000 and sometimes 25,000,000 gallons are discharged in 

 twenty-four hours. 



Two other small overflow sewers help to drain the east side of the 

 city, pipes discharging into the Seekonk River betv/een Red Bridge 

 and Washington Bridge. The sewage from these drains, together with 

 that of the city of Pawtucket, situated on this same stream 3 miles 

 above Providence, and the waste from the various mills along the banks 

 of the river pass down the Seekonk into the head of the Providence 



