Memorandum
To: City of
From: Randal Clark, Tony Davis, Barbara
Hoppe, Larry Magliola, and Jan Weaver
Date:
Re: Proposed Stormwater Performance
Standards for Ordinance 20-04
The impact on stream health
and integrity from increased stormwater runoff flows and volumes, which results
from impervious surfaces is one of the most difficult to control and perhaps
least understood impacts of urbanization.
Fortunately, a body of science already exists that can guide
As development progresses
into the sensitive watersheds of southern Boone County, especially the Little
Bonne Femme Creek, Gans Creek, Clear Creek, and Bonne Femme Creek Watersheds,
care and caution must be exercised in order to protect our valuable water
resources and Rock Bridge Memorial
State Park. These watersheds are recognized
by both the Federal and State Governments as being sensitive watersheds because
of their rich biological diversity, including more that 10 rare and endangered
species, and because they are heavily used for recreation in the area.
The proposed development of
the Philips Farm is a development to be concerned about. Its massive size and location in sensitive watersheds
will present challenges far exceeding anything previously faced by Council
and City staff. Done incorrectly, the
results will have long term devastating permanent impacts on these sensitive
streams. Done correctly, following
the course of other communities who are in the forefront on water quality
protection, these impacts may be minor to the point that stream health and
geomorphology can be reasonably maintained.
Stormwater
or Best Management Practices (BMPs) Performance Standards must
address
both hydrology and water quality.
These are separate issues and must be kept separate.
We have previously and consistently
asked for Performance Standards to be written into the ordinance approving
the zoning and annexation in order to clearly address hydrological issues
and water quality issues necessary for proper protection of the streams we
enjoy today. This is the time for such
Performance Standards to be defined and included in the ordinance, in fairness
to future developers and owners of the Philips Farm property, other land owners
in the watershed, and to the citizens of
Hydrology
(Peak Flow and Runoff Volume Standards)
There is little surface runoff
from the naturally forested portions of an area (presettlement),
because the rainfall is soaked up by soil, and is either used by the plants
or percolates into the groundwater, where it is slowly released to the streams.
But nearly all rain that falls on impervious surfaces becomes runoff.
Surface runoff occurs relatively rapidly in the urban watershed, since
storage and infiltration capacity have been reduced to practically zero. As urbanization increases in an area, more of
the total rainfall volume over time becomes runoff. This increase in the volume and flow rates (peak
flows) of water entering the streams causes floods and stream erosion and
is the root cause of aquatic
habitat degradation and property damage.
The proposed ordinance states
that “the developer shall design and construct improvements that will result
in peak
flows from the Philips Farm for
high frequency storms being lower than current levels and peak flows from
larger storms being no greater than current levels” (see Reference # 1).
The technology to protect
streams from peak flows and to limit flooding was developed in the 1970’s. In the 1980’s, it was determined that just
controlling peak flows was not working to protect the streams from the impact
of increased stormwater runoff. Beginning in the 1990’s many State and local
government agencies rewrote
their stormwater ordnances requiring stormwater protection systems to protect
streams from increased runoff volumes as well as peak flows
Hydrology
standards for the Philips Farm development must be volume based. This is not our opinion alone. It is the opinion of CH2MHill (see Reference
# 2) who stated such in their report commissioned by the City. Further,
From
the CH2MHill final report (see Reference # 1).
Page 10 “the hydrologic behavior should
be used as the basis for site planning and design”
This is volume based modeling.
Page 11 “the City should specify very
clear design criteria for this site for both construction and post- development”.
Respectfully, this recommendation is not being
followed.
Page 11 “The post- development BMP
design criteria should include runoff
volume (emphasis
by author), water quality, groundwater recharge, channel protection, and overbank flooding”. Volume based standards and requirements are not
contained in the amendments to Section17, Paragraph 1.
Page 12” Volume based hydrologic modeling
is recommended for site analysis and design.” “Peak flow based modeling should be performed
for hydraulic analysis and design but not as the only tool for evaluating
site performance.” Again
only
peak based standards are contained in Section 17.
Mid-America Regional Council
American and American Public Works Association’s “Manual of Best Management
Practices for Stormwater Quality” September
2003 (see Reference # 3).
APWA has established basic
goals for all developments to maintain predevelopment peak
flows, runoff volume, and water quality. In other words, developments
should not increase the velocity or quantity of runoff or the amounts of pollutants
leaving the site.
A review of “A Guidebook for
An important reference from
this document follows:
Page 2 “Since changes in water balance
and hydrology are the primary source of stormwater related impacts on watershed
health (Chapter 2) it is especially important to establish performance targets
for managing Runoff
Volume and Runoff rate”.
The language provided in Section
17 Paragraph 1 does
not include any reference to runoff volume based standards or requirements.
We recommend the following language be inserted in Paragraph 1 in lieu of
the last sentence currently contained therein and that the current last sentence
be stricken. This is not an extraordinary standard, other states are following
these standards and they are necessary to protect the streams from the impacts
of stormwater runoff and in fact form the very foundation of stream protection.
“The
developer shall design and construct stormwater improvements which will maintain
existing or current hydrological conditions in each watershed as follows:
1)
Maintain
the predevelopment (current) peak flow rates for runoff for larger storms( greater than 2 year return
interval)
2)
Reduce
to 50% of predevelopment (current) flow rates the runoff from the developed
site for the 2 year, 1 year and the water quality design storm.
3)
Maintain
the existing (current) volume of runoff for the runoff events up to a 5 year
return interval storm”.
We note that the language
in Section17 paragraph 1 seems to suggest that detention is only required
for the portion of the Philips Farm tributary to the lake when, in fact, stormwater devices including
retention/detention, and source control will be needed throughout the development
including those areas which are not tributary to the lake (Tracts 1, 2, 6,
7, and parts of 4).
The CH2MHill report also emphasized that this is needed. This language in Section 17, Paragraph 1 needs
to be revised accordingly.
Water Quality Standards
Water quality must be better
addressed in the proposed ordinance. Because maintaining designated uses in
the streams is expected and moreover is required by the State of Missouri,
the City of Columbia Council should establish a standard which allows no increase
in pollutants from the site (Philips Farm) after development than occurs now.
We ask for your consideration
in amending Section 17 Paragraph 1 by inserting the following bolded type
language in place of the next to last sentence.
Maintain or reduce pollutants
in the runoff from the developed site, on an average annual loading basis,
when compared to the current condition.
While there is presently little
good baseline data for pollutant loads for many of the streams in the area,
there
are pollutant loading models commonly used that can predict the expected level
of stormwater pollutants coming off a site (Source
Loading and Management Model (SLAMM) and others). The data used in these models
are based on a nationwide study of stormwater pollutants conducted by the
EPA. These models can be used to predict the amount
of pollutants coming off the Philips Farm even without having the current
baseline data. Then the information
from the models can be used to design each BMP on the Philips Farm so that
it may reduce the level of pollutants to the maximum amount possible.
Once the baseline data is available for the area, these data can be
used with the models to more accurately design or modify the BMPs. Establishing pollution load modeling does not
require any delay in development and will result in better designed BMPs.
For example, the residents
around
Another example, Austin, Texas
uses specific pollutant targets that results from baseline data collected
with USGS in 1990 (see Reference # 7). While
Water Quality Monitoring
Water quality monitoring is
vital to the success of any development in these watersheds. Jonathan Jones,
in his June 2003 report (see Reference # 8) on pages 34 and 35 Section 8.0
states: “Monitoring will be conducted
during both construction and post-construction
(fully developed) conditions.”
Mr. Jones goes on in some
detail about the monitoring (testing) program he will design for both the
construction phase and the post-development phase. If a monitoring program is
not designed, implemented and followed there will be no way to
determine, trace and solve stream health issues. Also there will be no way
to determine if the Stormwater Protection structures are working as designed,
and if they are not working to determine the best way to fix them. Not only is the developer’s engineer recommending
it, he is taking it for granted that a water quality monitoring program is
necessary. Also the City hired reviewer
CH2MHill says it is absolutely necessary. While recognizing costs associated with such
a program, it
is essential that a water quality and biological monitoring program be required. Needless to say, there will be more extensive
cost down the road if this is not done correctly. An ounce of protection is worth is a pound of
cure.
Every
stormwater protection
program that we have reviewed recognizes that water quality monitoring and
site monitoring is critical to the success of the program. They are some very good examples from Washington
state; Austin, Texas; and Littleton, Colorado.
The Cities of Austin, Texas
and
The residents around Bow Mar
Lake in Littleton, Colorado worked with the Grant Ranch developers (a residential
development) and Jonathan Jones to develop an on going water quality monitoring
program to protect their sensitive watershed from stormwater pollution (See
Reference # 6). The data is being used
to ensure that the BMPs at the Grant Ranch development
are working at design standards and have been used to modify existing BMP
structures to better control the amount of pollutants in the effluent.
SUMMARY
OF REQUESTED CHANGES TO THE ORDINANCE
Once again our Stormwater
Protection Performance Standards are:
The
developer shall design and construct stormwater improvements which will maintain
existing or current hydrological conditions in each watershed as follows:
1)
Maintain
the predevelopment peak flow rates for runoff for larger storms( greater than 2 year return
interval)
2)
Reduce
to 50% of predevelopment flow rates the runoff from the developed site for
the 2 year, 1 year and the water quality design storm.
3)
Maintain
the existing (current) volume of runoff for the runoff events
up to a 5 year return interval storm.
Maintain
or reduce pollutants in the runoff from the developed site, on an average
annual loading basis, when compared to the current condition.”
References and web sites of
additional details and information on what other states and communities require
are as follows:
Cited References
1.
Proposed
City Ordinance # 20-04.
2.
Final
Technical Memorandum by CH2MHill
3.
Mid-America Regional Council
American and American
Public Works Association’s “Manual
of Best Management Practices for Stormwater Quality”. September 2003. Section
3.1.1. Page 10.
4.
A
review by Randal
5.
“A
Guidebook for
http://wlapwww.gov.bc.ca/epd/epdpa/mpp/stormwater/stormwater.html
6.
“Grant Ranch Stormwater-Quality
Management Program”
in Stormwater Journal, January, 2004
http://www.forester.net/sw_0401_grant.html
7.
http://www.amlegal.com/nxt/gateway.dll?f=templates&fn=default.htm&vid=alp:austin_environment
Specific
requirements for
8.
Philips
Farm Conceptual Water Quality Protection Plan – Key Policies, Principles and
Criteria, June 2003 in Appendix B of
the Philips
Farm Water Resources Impact Assessment Report.
July 2003. Prepared
by Wright Water Engineers.
Additional
References
9.
Austin, Texas’s Land Development Code
http://www.ci.austin.tx.us/development/ldc1.htm
These are the specific codes
that
10.
http://www.tnrcc.state.tx.us/admin/topdoc/rg/348.pdf
11.
Review of
12.
Stormwater
Management Manual for
Chapter
2 Minimum Requirements for
New Developments and Redevelopment
http://www.ecy.wa.gov/programs/wq/stormwater/wwhm_training/index.html
One
of the best and most recent of the Stormwater Programs in the
13.
Review of Stormwater Management
Manuals for
12.
Putting the Pieces Together:
http://www.eli.org/pdf/nonpointstateenfmech.PDF
Very good review of how other
State’s and Local Government’s Stormwater Protection Programs works.
13.
North
This is the area includes
Dallas/Fort Worth and areas to the east.
They conducted with USGS a
watershed based stormwater monitoring program.
They are now on their own
going to conduct a study to look at impacts on the streams from stormwater.
Grab samples will be collected
and analyzed for E. coli, oil and grease, ph, BOD5, COD, TSS, TDS, AS, CD
Cr, Cu, Pb, Zn, dissolved and total phosphorus,
total nitrogen, and Diazinion.
14.
EPA Polluted Runoff Publications
List
http://www.epa.gov/owow/nps/pubs.html
15.
http://www.epa.gov/wqsdatabase/wqsreports.html
An
excellent source to compare water quality Standards across the
16.
EPA’s Urban Runoff Programs
for Small Municipalities
http://www.epa.gov/ORD/WebPubs/nctuw/Hays.pdf
A Model on how small towns
can develop their own stormwater protection system.
17.
EPA Nationwide Urban Runoff
Program (NURP) Database Downloads
http://www.eng.ua.edu/~awra/download.htm
Data
from a nationwide study of pollutants in stormwater. Data used with pollutant load models to design
better BMPs.
18.
Watershed Committee of the
Ozarks
http://www.watershedcommittee.org/default.htm
Information
on the stormwater program of