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12.7 Selection of Best Management Practices 449
example of this methodology where the cost effectiveness drops dramatically as practices
are implemented to reduce lake standards exceedances to below 10 days per year.
The cost/benefit ratio approach, however, is limited by the number of cost/benefit
ratios that can be conveniently considered simultaneously. To represent the different ele-
ments of a complex issue better, where some benefits might be counterbalanced by some
detriments, multiple costs and benefits must be considered.

Matrix Comparison. Matrix comparison, a common decision-making method used in fa-
cilities planning and siting, is illustrated in Table 12.8. Environmental impacts in Table
12.8 can be divided into short-term construction-related impacts and long-term operational
impacts. The matrix comparison approach is also applicable to the assessment of urban
runoff control alternatives. This approach involves preparing a matrix that compares alter-
natives against selected decision factors, both quantitative and qualitative. Where possible,
numerical values are given to compare the alternatives and, for qualitative factors, subjec-
tive comparisons are used (such as poor, fair, good, and excellent).
Decision Factor Analysis. This is a matrix approach, which further quantifies the deci-
sion factors by using weighting methods. In this approach, quantitative factors are used to

Table 12.8 Example Matrix Comparison
Alternatives

Type of Impact #1 #2 #3 #4
Monetary Cost, $
Capital cost
Annual O&M cost
Cost per household unit
Environmental impact
Cultural resources 0
Floodplains and wetlands
Agricultural lands
Coastal zones
Wild and scenic rivers 0
Fish and wildlife
Endangered species
Air quality 0 0
Water quality and uses
Noise, odor, aesthetics
Land use 0
Energy requirements 0 0
Recreational opportunity
Reliability
Implementability

Legend:

Significant beneficial impact

Minimal beneficial impact
0
No impact

Minimal adverse impact

Significant adverse impact
Source: U.S. Environmental Protection Agency. Stormwater Best Management Practice Design Guide—Volume 1—
General Considerations (2004)