rOLLUTIOX OF THE I'<m>M.\c IllVEU :t4<i 



is therefore ])ecoming more iiutl more a matter of concern he- 

 cause of the fact that with the increase of popuhition in th«' I'o- 

 tomac ha.sin theartilicial imimrities will increase and the amount 

 of water to he taken out at Washington will also he greater, while' 

 the natural flow of the stream is practically unaflected. Ah hc- 

 fore stated, the impurities are of two kinds, natural and artilicial. 

 The natural im))urities consist mainly of the finely divided soil 

 washed from the agricultural lands of the valleys, this heing for 

 the most part the residual matter left hy solution of limestones. 

 It exists in such tine particles that while the water is in motion 

 it is not deposited and may remain in sus])ension for days, even 

 after the water sample has heeii put into a closed hottle. 



The proportion of this mud varies from time to time. Ix'ing 

 greatest during floods and least during periods of low water, 

 wlien the supply is received l)y percolation from underground 

 sources. At such times the water is clear and entin-ly unohjcc-* 

 tionahle as far as casual ohservation is concerned, hut the flow 

 in the river is greatly diniinislicd and the proitortion of sewage 

 must he notahly increased. 



While the natural imi)urities are usually so apparent and an- 

 noying to the eye through the dirty color and muddy sediment, 

 the artificial impurities, on the other hand, an- not so readily 

 noted. The heavier i)articles of the waste from the towns and 

 maiuifacturingestahlishmentsarewasheddown the stream slowly 

 and are gradually hurned up or oxidized or pass into solution in 

 the form of various organic compounds. These, as a rule, do n(»t 

 notahly discolor the water, and some of them may even aid in 

 giving a hright, sparkling eflect, so that very ililute sewage wlu-n 

 exposed to light and air for a few hours may he unohjectionalde 

 to the eye, although carrying with, it a great load of ohjectionahle 

 substances or minute animal or vegetahlc life. 



The pollution of the Washington water supply would he very 

 little if the hea<lwaters of the Potomac could l)e cut oil just hdow 

 Cumberland, and while the water is very had at that point, it 

 should l)e remembered that it is there a comparatively snnil I 

 stream, with a minimum discharge of less than (lO feet per second. 

 Avhile the minimum discharge at Point of Rocks, so far as oh. 

 served, is about 800 second-feet, and the .Monocacy and a number 

 of smaller tributaries reach the river between that point and the 

 intake of the waterworks at Great Falls. 



In times of low water, when, of course, these pollutions bear 

 the largest ratio to the total supj.ly. the Potomac nt CninlH.iland 



