Page 282 - Hydrogeology Principles and Practice

HYDC07 12/5/05 5:32 PM Page 265

Groundwater pollution remediation and protection 265

Fig. 7.9 Schematic illustration of source protection zones showing the relationship between Zones I, II and III and the groundwater
source in four idealized hydrogeological situations representing: (a) a low effective porosity limestone aquifer; (b) a high effective
porosity sandstone aquifer; (c) a confined aquifer; (d) a spring. In reality, the size, shape and relationship of the zones will vary significantly
depending on the soil, geology, amount of recharge and volume of water abstracted. See text for an explanation of the definitions of Zones
I, II and III. After Environment Agency (1998).

Zone I, or the inner source protection zone, is groundwater storage aquifers, such as sandstones,
located immediately adjacent to the groundwater it is necessary, in order to provide adequate attenu-
source, and is designed to protect against the impacts ation, to define further the outer protection zone to be
of human activity which might have an immediate the larger of either the 400-day travel time area or the
effect upon the source. The area is defined by a 50-day recharge catchment area calculated using 25% of the
travel time from any point below the water table long-term abstraction rate for the source.
to the source and as a minimum 50-metre radius Zone III, or the source catchment, is the remaining
from the source. This rule of thumb is used in other catchment area of a groundwater source, and is
countries and is based on the presumed time taken defined as the area needed to support an abstraction
for biological contaminants to decay in groundwater. from long-term annual groundwater recharge. For
The land immediately adjacent to the source and wells and boreholes, the source catchment area is
controlled by the operator of the source is included defined by the authorized abstraction rate while,
within this zone. for springs, it is defined by the best known value of
Zone II, or the outer protection zone, is the area average annual total discharge. In practice, the size
around the source defined by a 400-day travel time, of Zone III will vary from tens to a few thousands
and is based on the requirement to provide delay and of hectares depending on the volume of groundwater
attenuation of slowly degrading pollutants. In high abstraction and the amount of recharge. In areas