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Summary Staff Report:
The most significant change in Chapter 2 is the
removal of the Northern Virginia BMP Handbook as
one of the design criteria. The Northern
Virginia BMP Handbook was originally adopted for
use by communities with drainage into the
Occoquan Reservoir. (These communities include
the Counties of Fairfax, Prince William and
Loudoun and the incorporated areas within.)
Since approximately 1/3 of Fauquier County
drains into the Occoquan, the decision was made
with the adoption of the stormwater management (SWM)
ordinance in 2002 to apply these standards to
the entire county. Thus, they were adopted in
conjunction with the Virginia Stormwater
Management Handbook (VSMH). With this change,
stormwater management ponds will only be
designed to the VSMH standards, consistent with
the majority of Virginia communities. This
eliminates the often confusing application of
two diverse sets of standards. In addition,
the elimination of the Northern Virginia BMP
Handbook standards will now allow the water
quality volume in a pond to be credited in the
calculation of the required quantity control
amount, thus reducing the size (and potential
oversizing) of SWM facilities.
In simplifying the DSM, duplicative state
standards were removed from Chapter 2, while
retaining references to the applicable state
standards. The VSMH Technical Bulletins have
also been deleted from this chapter. This
eliminates the need to coordinate the content of
this chapter with state revisions, thus saving
time and housekeeping effort in the future.
This change has condensed the chapter thereby
making it more user-friendly. (The deleted
Technical Bulletins, as well as deleted
checklists and worksheets associated with the
Northern Virginia BMP Handbook, were located in
the Appendix of the DSM and, for the sake of
clarity in the presentation of the changes, are
not shown as strikethrough pages in the amended
Chapter 2 document.)
Due to the large amount of soil having a high
water table characteristic in Fauquier County,
there is a need to design appropriate SWM
facilities when such facilities are located in
these soils. Over time, conflicts between
theoretical analytical practice and in-field
experience have arisen when dry facilities are
designed in wet soils. Standards for
determining a high water table and permeability
testing for SWM facilities using infiltration
have been included in the revisions. New section
A204.1(24) provides detailed procedures to be
followed for determining the seasonal high water
table and for the accurate testing for soil
permeability necessary for infiltration
facilities. This does not add an extra testing
requirement as a developer would normally
undertake this testing anyway. By outlining and
agreeing to an acceptable procedure, we minimize
potential interpretive conflicts (as well as
time and money for the developer) down the road
in the review process. These were added at the
encouragement of the DSM Committee to clarify
expectations and ensure predictability in the
review process.
There was considerable discussion with the DSM
Committee on how to prevent in the future the
significant drainage problems we are currently
experiencing in some subdivisions. As we did
not want the added requirement for on-lot
grading plans, the consensus was to increase the
overland relief standard from the 10-year storm
to the 100-year storm for areas located within
service districts. The DSM Committee felt this
was a valid health, safety, welfare and property
value concern. The revised standard is
consistent with surrounding areas including
Loudoun County, Prince William County, Stafford
County and Fairfax County.
To further simplify the DSM document, checklists
from the Appendix have been removed and placed
on the County website with references to them in
the Chapter. This will assist in keeping the
latest version of the checklist available to the
public and design community while reducing the
need for changes to the Design Standards
Manual. In addition, terminology used in the
chapter has been revised so that it is
consistent with the defined terms in the
Virginia Stormwater Management Handbook and
several new definitions have been added.
As most of the constructed stormwater management
ponds are currently maintained by homeowner’s
associations (unlike many of the surrounding
more developed, suburban communities that have
assumed public maintenance for these
facilities), standards reflecting generally
acceptable design practice have been
incorporated to help reduce future maintenance
problems of SWM/BMP ponds. Standards employed
include elimination of gabion weirs for SWM
forebays, providing a minimum orifice size for
outflow pipes and the inclusion of anti-clogging
devices. Having such minimum standards is
important because most homeowner’s associations
have very limited knowledge about the
maintenance of these structures, and the
potential for problems to arise due to a lack of
maintenance is high.
Other changes and refinements to Chapter 2
include:
-
Providing consistency in defining drainage
channels, as opposed to numerous terms such
as drainage swales, drainage ways, etc.,
that imply all depressions in the ground are
equal;
-
Providing flexibility in the location of
drainage easements on larger lots (currently
focused towards the edge of the property)
and consideration for lots less than ˝ acre
provided 75% of the available area for
building is contiguous and usable as
determined by the Zoning Administrator;
-
Deleting time lines for the review of SWM
plans as such plans are reviewed in
conjunction with the overall site plan or
construction plan and would follow the
defined time lines for those review
processes;
-
Eliminating the requirement for a SWM
concept plan (with engineering) for
rezonings;
-
Adding flexibility to the required 2%
minimum slope for newly graded areas – down
to 1% on commercial, business and industrial
sites and to follow accepted industry
standards for recreational sports fields and
conveyance channels;
-
Clarifying the appropriate use of high
density polyethylene (HDPE) pipe;
-
Requiring inspection and certification of
the correct installation of underground
stormwater management facilities;
-
Incorporating flexibility in the standards
for consideration of the use of innovative
new technologies for low impact development;
and
-
Reducing setbacks for ponds with smaller dam
embankments.
Revision Process
Between January 22, 2008 and April 21, 2009,
members of the DSM Committee met on a
semi-monthly basis to review the provisions of
the DSM drainage chapter. Clarifications were
proposed by both Community Development staff and
the DSM Committee members, often prompting
in-depth discussion of appropriate design
practices. The Committee expended numerous
hours in refining this ordinance and their
willingness, expertise, considered input and
patience through the process is greatly
appreciated.
The members of the Committee include several
private sector engineering and surveying design
firms, including: Chris Hritsik with Bohler
Engineering P.C.; Jim Carson, Rick Ashley and
Paul Bernard (formerly with Bury Partners) with
Carson-Ashley and Associates; Dave Hall and John
Orr with DRH Design Group, Inc.; Bruce Reese and
Mike Webb with The Engineering Group, Inc. and
Fred Ameen with Patton Harris Rust and
Associates, P.C. Also participating in the
Committee from Fauquier County were Kimberley
Fogle, Assistant Director of Community
Development; Christer Carshult, County Engineer
and Saundra O’Connell, Senior Planner. Jim
Sawyer, County Soil Scientist, provided
significant input into the sections dealing with
seasonal high water tables and soil testing.
Identify any other Departments, Organizations
or Individuals that would be affected by this
request:
Department of Economic Development
Development Community
Attachment:
Proposed Amendment to Chapter 2 of the Design
Standards Manual |