CHAPTER

FOUR

NONPOINT

SOURCE

POLLUTION

Nonpoint

source pollution

is a

general category

for

pollution which does

not

emanate

from

a

single location. This pollution

is

associated with

agriculture,

silviculture,

and

urban

runoff,

as

well

as

leaks

from

septic

tanks

and

waste

disposal

sites.

It

originates

from

contaminants collected

in

surface water

runoff,

discharges

from

boats

and

marinas,

and

atmospheric deposition. Included

in

nonpoint

source pollutants

are

pathogens, sediments,

nutrients,

toxicants,

and

oxygen

demanding substances. Most

of the

pollutants originate

on

land

and are

then picked

up by

rainwater which carries them into streams

and

rivers

that

empty

into

the

bay. Because Galveston

Bay

receives drainage

from

a

large land

area

as

well

as

discharges

from

boats

and

other water based sources,

it is

difficult

to

identify

the

numerous individual sources

of

pollution.

As

point source municipal

and

industrial

pollution

is

reduced, nonpoint source

pollution

plays

a

relatively

larger

role

in the

degradation

of the

nation's waters.

65

percent

of the

nation's waters

fail

to

meet water quality standards because

of

non-point

source pollution. Similarly,

28

percent

of the

nation's assessed coastal

areas, including lakes

and

estuaries,

fail

to

meet water quality standards because

of

urban

runoff

and

storm sewer discharges.

Tables

4-1

through

4-3

provide background information

on

nonpoint source

pollution

in the bay

area.

Table

4-1

illustrates

changing land use:

as

open land

declines

and the

proportion devoted

to

residential, commercial,

and

industrial

uses increases,

NPS

becomes more likely

and

more

difficult

to

control. GBNEP's

report

on

nonpoint source loadings provides

two

other estimates

of

land use.

Tables

4-2 and 4-3

provide estimates

of

NPS,

the

former

overall

and the

latter

by

land

use

category. Although Table

4-3

covers

only

a

limited study area (while

the

others

cover

the

entire

4-county

area)

it

illustrates

the

differing

kinds

of NPS

pollution

associated with

different

land uses. From

a

policy standpoint,

it

would

be

more

useful

to

normalize these data

on a per

acre

or

other appropriate basis.

This would

highlight

which kinds

of NPS are

most serious

for

each kind

of

land

use and

suggest priority approaches

to

NPS.

After

a

brief review

of the

general regulatory

framework

for

nonpoint source

pollution,

this

chapter considers several causes

of

nonpoint source pollution

in

Galveston

Bay: agriculture, stormwater

runoff,

and

septic tanks. Soil erosion,

another important kind

of

nonpoint source pollution,

is

considered

in

chapter

12.

Airborne

pollutants

that

precipitate

onto

the

water,

or

onto land

and

then wash

into

the

water,

may

affect

water quality

as

well.

The

extent

of

this

problem

is

unknown,

and it is not

treated here.

59