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3.2.1.2.1 The storm water runoff rate from the site should
typically be held to its predeveloped rate, utilizing on-site
detention or retention facilities. Surface ponds or depressions
should be developed which are capable of storing, by detention
or retention, the required amount of water.
3.2.1.2.2 If the site to be developed has been acquired on the
commercial market and is part of a larger overall development
scheme, it may be part of a regional ponding system designed
for storage of the incremental increase in runoff from the overall
development. In such cases, the incremental runoff increase
from the site will be verified with the local water resources
regulatory agency to ensure that it is within the parameters of
the regional pond design.
3.2.1.2.3 Underground or subterranean storm water detention
facilities, or ponding in parking areas, are measures to be used
only if space is not available for the construction of surface
storage facilities.
3.2.1.2.4 One of the sustainable design considerations
recommends that the storm water plan adopted for the site
results in a 25% decrease in the rate and quantity of storm
water runoff, if the existing impervious area of the site is greater
than 50% of the site. This would require on-site retention, not
only detention, and may not be possible in all cases.
3.2.1.2.5 Another recommended sustainable design measure is
treatment systems for storm water quality to remove 80% of the
average annual post-development total suspended solids and
0% of the average annual post-development total phosphorus.
This is to be implemented by instituting Best Management
Practices (BMPs) as outlined in EPA's "Guidance Specifying
Management Measures for Sources of Non-point Pollution in
Coastal Waters" (EPA-840-B-92-002, 1143). The design
methodologies for determining percent removals are generally
highly empirical and no standard universal method has been
adopted for this purpose. Therefore, the local governing water
resources regulatory agency or water resources department of
the Government installation directorate of public works will be
consulted regarding acceptable design methodologies for
surface water quality treatment on developing sites. These
preferred local methodologies should be implemented for site
design. On some facilities, the site is not provided with a
positive overland drainage outlet and additional site area may be
required for development of infiltration ponds sized to
accommodate the incremental increase in site runoff.
UFC 4-171-05
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