Encyclopedia of Environmental Science and Engineering, Volume I and II

ENVIRONMENTAL HEALTH 349

which a subsurface sewage disposal system is designed. Sand

fi lters, evapotranspiration beds, aeration systems, stabilization

ponds or lagoons, recirculating toilets and various types of

privies are used under certain conditions.

Large Sewage Works

The design of sewers and treatment plants should take into con-

sideration the broad principles of comprehensive community

planning discussed at the beginning of this chapter. Regional

and area-wide sewerage planning (preliminary) should take

place within the context of the general overall comprehensive

community plan. It recognizes the extent of present and future

service areas, the established water quality and effl uent stan-

dards, and the alternative solutions with their fi rst costs and

total annual costs. This information is needed to assist local

offi cials in making a decision to proceed with the design and

construction of a specifi c sewerage system and treatment plant.

1. Prechlorination


2. Pre-settling
   2 to 3 days, or


3. Storage, 30 to
   90 days or
   longer, or


4. Prefiltration
   (Where needed)


5. Aeration


6. Micro-straining


7. Screening
   
   
   1. Detention for
      20 to 45 min.
   
   
   2. Velocity 60 to
      150 ft. per min.
   
   
   3. Rapid mix30 sec.
      plus slow mix
      
      
      1. Detention for
         4 to 6 hr.
      
      
      2. Maximum
         velocity 0.5 ft.
         per min.
      
      
      3. Duplicate units
      
      
      4. Length twice
         to 3 x width
         or greater
      
      
      5. Overflow rate
         20,000 gpd/ft.
         weir
         
         
         1. Rate 2 gal. per
            sq. ft. per min.
         
         
         2. Sand depth
            24 in. Eff. size
            0.35–0.50 mm
            Unif. coef.
            15–20. For
            anthracite
            E.S. = 0.8–2.0 mm
            U.C. 1.7
         
         
         3. Rate controller
         
         
         4. Surface wash
            optional
            
            
            1. Capacity equal
               to average
               days demand
            
            
            2. Covered, if
               possible
            
            
            
            
         
         
         
         
      
      
      
      
   
   
   
   

Clear

well

Rapid sand

filters

Coagulation

basin and

sedimentation

Chemical

mix

Flow diagram

AA

B

C

D

X

A A A A

B

D D

F

F

E

C XX

C

X

Pretreatment

Raw water

Design

FIGURE 8 Rapid sand filter plant flow diagram. From Environmental Sanitation, Joseph A. Salvato, Jr., John Wiley & Sons,

Inc., New York, 1958.

WELL 100' min. FROM ANY TILE FIELD

WELL 50’ min. RADIUS FROMANY SEPTIC TANK

CLEANOUT

WASTELAUNDRY

GRADE 1/4" /FT.

SEPTIC TANK

10 'min.

10 'min.

DRILLED WELL HOUSE

STREET

10 ' FUTUREHOUSE SEWER

FUTUREWATER

SERVICE

GARAGE

SETBACK PROPERTY LINE

GROUND SLOPE

DISTRIBUTION BOX TIGHT JOINT PIPE

GRADE 1/6" /FT.

5 '

TILE FIELDGRADE 1/16’ /FT.LAID ON CONTOUR

NOTES:1. Watertight Footing Drain Within 25' Of Well

2. Tile Field To Be 50' Or More From Any Lake, Swamp, Ditch Or Watercourse & 10' Or More
   From Any Water Line Under Pressure


3. Coef from Pipe, Load Coated Joints Within 50' of Any Well


4. Discharge Footing, Roof And Celter Drainage Away Sewage system & Well

16 'min.

FIGURE 9 Private water supply and sewage disposal layout.

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