Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 318

Figure 10.1 Groundwater contamination from a surface point source.
Point source pollutants in surface water and groundwater are usually found in the
form of a plume that has the highest pollutant concentrations nearest the source and
diminishing concentrations farther away from the source (Figure 10.1). It is typical of
underground plumes that the interactions with the solid phase and the soil microbiota
are restricted to the plume's surface region, mainly the head region. Biodegrada-
tion occurs solely here, the inner part of the plume is more or less inactive without
biodegradation or any other physico-chemical attenuation taking place.
The same pollutants may be sorbed on the solid particulate matter in a three-phase
soil (above the groundwater level) or solubilized in the water phase depending on the
contaminants' affinity to water. It is worth distinguishing between the ways the con-
taminants may enter the “soil''. If contaminants enter directly the groundwater, the
solid phase will be contaminated by sorption from the water. Due to several orders of
magnitude difference in the equilibrium state between the amounts dissolved in water
and sorbed on the solid, the soil's filtering capacity is the dominating factor. Another
way contaminants can enter the three-phase soil is through primary sorption to the
solid phase: in this case they contaminate the water through desorption. Such solid-
bound contaminants may contaminate water volumes 10 3 -10 5 -times the contaminated
soil's volume. The partition coefficient quantifies the ratio of the concentration of a
chemical contaminant between soil solid phase and pore water in an equilibrium case:
Kp soil - water =C soil /C water . Contaminants entering the soil's solid phase and groundwater
approach equilibrium from two opposite sites. As equilibrium is not typical in the envi-
ronment, caution should be used when applying equilibrium partitioning in transport
modeling.
Point sources of air pollution include stationary sources such as power plants,
smelters, industrial and commercial boilers, wood and pulp processors, paper mills,
industrial surface coating facilities, refinery and chemical processing operations, or
petroleum storage tanks (Pollution Issues, 2013).
Point source pollution enters a water body at a specific site and is generally readily
identified. Potential point sources of water pollution include production and use of
chemical substances, industrial sites, power stations, fish farms, effluent discharges