Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 421

Quantitative Assessment

Quantitative assessment methods are typically used for evaluating physical-chemical
changes, for example, modelling of airborne pollutants. A wide range of models exists to
quantify physical-chemical project impacts. These can range from relatively simple mod-
els, considering only one aspect of the environment, to complex models, predicting natural
system responses. Although physical or analogue models do exist, mathematical models
are normally used in the context of environmental impact assessment.

Mathematical Models

Mathematical models lend themselves to the spatial and temporal analysis of selected envi-
ronmental aspects such as air and water quality, water volume and l ows, noise levels or
airborne deposition on soils and vegetation. Analytical models often provide a i rst esti-
mate of the magnitude of the impact. Numerical models are applied if higher accuracy is
required, but developing numerical models is generally demanding in terms of cost, exper-
tise, time, and input data requirements. The use of proven numerical models accepted by
regulatory authorities is preferable. For competent references to available mathemati-
cal models see Spitz and Moreno (1996) (groundwater), Chapra (1997) (surface water),
USEPA (2005) (air), Canter (1996), and Canter and Sadler (1997). These provide excellent
overviews of prediction techniques, based on US experience ( Table 9.7 ) .
Mathematical models approximate geographical and cross-media pathways from the
source of the impact to its effect as shown in Figure 9.10 . Using mathematical approxima-
tions they link inputs (x, say in terms of source and concentration) with outputs (y, say in
terms of pollution concentration at the receptor). In general, the output variable (y) is a
function of one or more input variables (X):

The use of proven numerical
models accepted by regulatory
authorities is preferable.

Y f(X ), i 1, n

(9.1)

i

Mathematical models range from simple analytical equations to complex numerical mod-
els. Impact evaluation can be based on one model or a combination of numerous models
( Figure 9.11 ). However, evidence from case studies suggests that the use of simple models
is the rule rather than the exception in most EIAs. Simple models include:
●

Steady-state, single source, Gaussian plume dispersion model for air quality;

●

Simple runoff model based on watershed area and rainfall;

●

Water balance involving rainfall, evaporation, runoff, ini ltration, and storage in a
watershed or other hydrologic system;

●

Steady-state dispersion model for water quality;

●

Universal soil loss equation predicting erosion rates from knowledge about rainfall,
slope, soil structure, vegetative cover, and management practices;

●

Population dynamics, predicting the rise and fall of biological organisms and commu-
nities from knowledge of lifecycles, predator-prey relationships, food webs, and other
factors affecting the lives of various species; and

●

Inventory approaches for direct and higher-order effects on receptors.

Complex modelling demands
accurate input data, often not
available at the early stage of
mine development.

Although impact evaluations based on simple models are approximates, the quality of results
will depend on the particular problem and circumstances for which the model is applied.
Two main factors restrict the application of complex models. First, complex modelling
demands accurate input data, often not available at the early stage of mine development;