a raw wastes whenever storm runoff
overloads its combined storm and sanitary sewer system and causes it to
overflow. Where major efforts have been made, as at the Upper Potomac
River Commission's Westernport plant below the big Luke, Maryland, pulp
and paper mill, the wastes are so voluminous and complex that some of
them still have to be dumped, and the effluent from even highly
efficient treatment further degrades the river.

Fortunately, the North Branch, acid above, deprived of oxygen and
overenriched and septic below, is not typical of the flowing parts of
the Potomac river system, but it stands as a good grim example of what
pollution can mean, and as a foretaste of what may be expected to happen
elsewhere in the Basin if it is not stopped soon. Mine acid is not a
significant problem in any streams outside of that region, but untreated
or inadequately treated wastes are badly blighting many streams and
rivers or stretches of them. Some smaller watercourses, like historic
Antietam Creek below Hagerstown, Maryland, have deteriorated under the
influence of discharges from single or limited sources, while larger
ones suffer from a cumulative waste buildup in areas of concentrated
population or industry. Some twenty miles of both industrial and
municipal pollution in the South River Branch of the Shenandoah's South
Fork below Waynesboro, Virginia, have done much damage to that legended
river for a good distance downstream, a situation that is worsening with
the area's growth. On the North Fork of the Shenandoah similar effects
have been wrought by heavy organic loads from poultry processing and
other things. The list could be extended: aside from a few happy
exceptions like the prized Cacapon, draining rugged, forested, thinly
peopled hill country, nearly all the Basin's flowing streams of any size
receive damaging loads of waste from towns and industries.

[Illustration: WATER TREATMENT STEPS

(1) River water enters here

(2) Water chlorinated

(3) Water settles. Heavy particles sink

(4) Water pumped to Pretreatment Building

(5) Various chemicals (chlorine, alum, lime, carbon) added. Chemicals
and water stirred in rapid mixing basins

(6) Slow mixing to form "floc" (see Alum below)

(7) Water settles for 2-1/2 hours. "Floc" carries impurities to bottom

(8) Water filtered through 94 rapid sand beds

(9) Final chemical treatment (chlorine, lime, fluoride, phosphate)

PURPOSE OF CHEMICALS

CHLORINE: