Standards for drainage
within subdivisions are as follows:
(a)
Improvements. Drainage and
stormwater management facilities shall be provided, either on-site
or off-site, to reduce drainage flows, pollutants, and sediment
loading from the subdivision to levels in accordance with the
requirements of the Virginia Stormwater Management Regulations (4
VAC 3-20), as they may be amended from time to time, or to a lesser
level if deemed necessary to comply with other provisions of this
Code. The agent shall approve, or approve with modifications, only
those stormwater management facilities which comply with the
Virginia Stormwater Management Regulations and adopted overall
drainage plans and policies, if any. In this regard, the agent shall
not generally approve, except as a temporary measure, on-site
stormwater management facilities as an alternative to contributing
(in accordance with the provisions of paragraph (b) of this section)
to planned regional stormwater management systems. All management
facilities shall be designed and constructed in accordance with the
Erosion and Sediment Control Ordinance (chapter 10 of this Code) as
supplemented by the latest editions of the Virginia Erosion and
Sediment Control Handbook, Virginia Stormwater Management Handbook
and the Virginia Department of Trans-portation Drainage Manual as
well as those laws, ordinances, criteria, regulations, or policies
adopted by the Commonwealth or the county.
(b) Off-site drainage costs. The subdivider shall be
required to pay a pro rata share of the cost of providing reasonable and necessary
drainage improvements located outside of the property limits of land owned or controlled
by him whenever all of the following conditions exist:
(1) The county determines that such off-site improvements are
necessitated at least in part by the construction or improvement of the subdivision.
(2) The county or other appropriate authority has established a
general drainage improvement program for an area having related and common drainage
conditions.
(3) The subdivider's property is located within said designated
area covered by such program.
(4) The estimated cost of the total drainage improvement
program has been determined.
(5) The estimated storm water runoff has been established for
the designated area served by such program.
The subdivider's share of the above-estimated cost of
improvements shall be limited to the amount necessary to protect water
quality based upon the pollutant loading caused by the subdivision or
development or the proportion of such estimated cost which the volume
and velocity of storm water runoff to be caused by his subdivision bears to the total
estimated volume and velocity of runoff from such area in its fully developed state.
In calculating the pollutant loading caused by the subdivision or
development or volume and velocity of storm water runoff, the county
shall take into account the effect of all on-site water facilities or
best management practices constructed or required to be constructed by
the subdivider or developer and give appropriate credit therefor.
Any cash payment received by the county shall be expended only
for construction of those facilities identified in the established drainage facilities
improvement program and until so expended, shall be held in a separate account for the
individual improvement program.