ls. Public education and wiser restrictive
legislation may help, but the only real hope in terms of these poisons
appears to be that more selective and less indestructible substitutes
will be found, and all promising means of biological pest control
explored. Continuing programs are focused on the problem, but it
continues to be serious.

Pollutive runoff from urban areas merges with the whole question of
urban sewer systems, for most of it gets to the river through storm
sewers. We have seen that the old-style combined sewers of the District
of Columbia and Alexandria cause gross pollution when storms force open
their overflow gates, and we have seen too why the approach to this
problem that formerly prevailed--the arduous, hugely expensive digging
up of sewers and their replacement with dual pipes to carry storm runoff
and sewage separately--is no longer considered satisfactory. For the
more modern dual systems also contribute much trouble through the filthy
rainwater that pours out into streams from the storm system and through
the accidental or illegal channeling of sanitary wastes into storm
sewers.

A wholly satisfactory answer would allow runoff water as well as all
sanitary wastes to be held for full treatment at a standard plant. But
when we consider that at the Washington metropolis the dirty local
runoff from a single storm may amount to billions of gallons, the
question of where to hold it grows a bit complex, and is leading toward
experimentation with such ideas as vast subterranean networks of tunnels
for storage. Partial answers might come from subjecting storm and mixed
flows to different and lesser kinds of treatment by micro-screens at
sewer outfalls, detention and settling tanks, and filtration beds. These
possibilities and others need much investigation and testing.

Then there are the multitude of nasty mysterious dribbles that help to
degrade Rock Creek and can undoubtedly be found in even more profusion
along every other metropolitan watercourse. Such of them as issue from
storm sewers will be eliminated when a solution turns up for the problem
of runoff water. The others, and they are numerous, will not. Even if
the bureaucratic and political tangles that help to perpetuate
them--which will be mentioned again--are dealt with, the sheer
mathematics of possibility in a great city, plus the frequent difficulty
of fixing responsibility, make the overall problem of these
miscellaneous leaks and dri