Environmental Engineering FOURTH EDITION

Nonpoint Source Water Pollution 241

Table 11-4. P Values for Erosion Control Practices on Croplanda

Type of control practice

Cross-slope Cross-slope Contour

Slope downhill strips farming strips cropping

Up- and fanning without Contour farming with strip-

2.0-7 1 .o 0.78 0.50 0.37 0.25
7.1-12 1 .o 0.80 0.60 0.45 0.30
12.1-18 1 .o 0.90 0.80 0.60 0.40
18.1-24 1 .o 0.95 0.90 0.67 0.45

aSource: USEPA (1976), p. 64.

into a watershed-level hydrologic model or landscape-level GIs model (e.g., HSPF),
the RUSLE can be used to estimate sediment erosion and loading on a much larger
scale.

PREVENTION AND MITIGATION OF NONPOINT SOURCE POLLUTION

There has been a growing emphasis on prevention and mitigation of nonpoint source
pollution during the past decade. Many counties now require agricultural “farm plans”
that provide site-specific guidance for minimizing agricultural nonpoint source pollu-
tion. Similarly, many cities are now required to have discharge permits for storm drains
that empty into natural water bodies. The following section will describe current prac-
tices for preventing and mitigating nonpoint source pollution from three types of human
activities: agricultural practices, construction, and urban storm water runoff. As indi-
cated in Table 11-1, these three sources are associated with a wide range of pollutants,
including suspended solids, nutrients, toxic metals, pesticides, human pathogens, and
organics.

Agricultural Nonpoint Source Pollution

Runoff from agricultural areas may contain high concentrations of suspended sedi-
ments, dissolved and suspended nutrients (phosphorus and nitrogen), biodegradable
organic matter, pesticides (herbicides, insecticides, fungicides), and pathogens from
animal waste. If biosolids from municipal wastewater treatment facilities have been
used as a soil conditioner or fertilizer, the runoff may also contain traces of toxic metals
and other residues associated with municipal sludges (see Chap. lo).
Pollution control in agricultural areas is aimed at preventing or reducing sedi-
ment erosion; controlling pesticide runoff; improving the efficiency of fertilizer and
irrigation water use, and reducing the amount lost to groundwater seepage and surface
water runoff; improving riparian and conservation buffers; restricting animal access
to streams; and improving manure management techniques. The U.S. Environmental