Environmental Engineering FOURTH EDITION

170 ENVIRONMENTAL ENGINEERING

House

~

v--’

-----------

PLAN VIEW Gravel

trench

Septic tank ELEVATION

Figure 9-2. Septic tank and tile field used for on-site wastewater disposal.

Table 9-2. Adsorption Area Requirements for

Private Residents

Percolation rate

(in./min)

Required adsorption

field area,

per bedroom (e)

~~~ ~ ~

Greater than 1 70

Between 1 and 0.5 85

Between 0.5 and 0.2 125

Between 0.2 and 0.07 190

Between 0.07 and 0.03 250

Less than 0.03 Unsuitable ground

The U.S. Public Health Service and all county and local departments of health
have established guidelines for sizing the tile fields or seepage pits. vpical standards
are shown in Table 9-2. Many areas in the United States have soils that percolate
poorly, and septic tank/tile fields are not appropriate. Several other options are available
for on-site wastewater disposal, one of which is shown in Fig. 9-3.
In urbanized areas, it has been several centuries since there was enough land avail-
able for on-site treatment and percolation. Up until the nineteenth century, this problem
was solved by constructing large cesspools or holding basins for the wastewater; these
holding basins needed periodic pumping as they filled up. The holding basins also
created considerable public health problems, as in the Broad Street pump incident dis-
cussed in Chap. 4. A better way to move human waste out of a congested community
was to use water as a carrier.
The water closet, as it is still known in Europe, has thus become a standard fixture
of modern urban society. Some authors (Kirby ef al. 1956) credit John Bramah with