SEPTIC TANK STUDIES 7 



While the tanks were being operated the disposal lines were watched to observe 

 any evidence of excessive drainage from the tanks. None was observed from the 

 middle and south tanks but, mid-way through the October-to- December period 

 of 1944, the soil about the laterals of the north tank was definitely damp and re- 

 mained that way until the ground froze late in December. Around the end of 

 the lower lateral, water was visible on the surface of the ground, particularly at 

 the end of the line, and the ground was so soft that one stepping on it would 

 sink in the mud to his shoe tops. The ground water table at the season was not 

 unusually high. The situation during the second season (October to December, 

 1945) was similar except that the soil around the lower lateral from the north 

 tank was not quite so wet and no water appeared on the surface. 



Reference to the surveyor's notes indicated that the drop of the more distant 

 line of the north tank was somewhat sharper than it should have been; but, even 

 so, the results of these observations indicated that the flow from the tank with 

 the 8-hour retention period was too heavy to be taken care of satisfactorily by 

 the length of disposal line provided. If economy of size is sought in the con- 

 struction of rural septic-tank installations, it would seem advisable to economize 

 on the disposal line rather than on the tank, particularly if only a limited amount 

 of space is available for disposal. 



BACTERIOLOGICAL EXAMINATION OF EFFLUENTS FROM TANKS 



Samples of the effluents were collected from the wells on the disposal lines 

 previously described and shown in diagram I. The collection schedule is shown 

 in table 1. Samples were collected in sterile glass dippers which were pyrex 

 beakers of suitable size with long wire handles attached to permit them to be 

 dipped into the wells. A separate dipper was employed for each well, and samples 

 were collected into sterile, wide-mouth, glass-stoppered bottles with a capacity of 

 12 fluid ounces. Samples were taken directly to the laboratory, which was within 

 a few hundred yards of the tanks, and setting up of the bacteriological tests was 

 begun promptly and carried through as expeditiously as possible. In no instance 

 were the samples stored before they were examined. 



Table 1. — Dates of Collection of Sewage Effluents From Septic Tanks. 



Period I 



1944: October 17, 24, 30 



November 8, 14, 20, 29 

 1945; March 30 



April 12, 18, 24 

 Period II 



1945: October 5, 10, 17, 24 



November 1, 7, 13, 20, 28 

 December 3, 5, 11, 13, 17*, 19 



*Four samples were taken on December 17, at 9 and 11 a.m. and 1:30 and 3:30 

 p.m., to observe results through one day. 



Plate Counts 



Plate counts were made as directed in the Standard Methods of Water Analysis 

 (2). Dilutions were made in sterile distilled water, and one ml. quantities were 

 plated. Difco dehydrated nutrient agar was employed as the medium. In 

 trial tests to determine the best time and temperature for incubation, the best 



