Item 8B
AGENDA ITEM #3B
JUNE 26, 2006
CITY OF ATLANTIC BEACH
CITY COMMISSION MEETING
STAFF REPORT
AGENDA ITEM: Stormwater Storage (Public vs. Private) Cost Comparison
SUBMITTED BY: Rick Carper, P.E., Director of Public Works
DATE: June 13, 2006
BACKGROUND: In 2002, Atlantic Beach added a requirement for on-site storage of
increased stormwater runoff resulting from development or redevelopment
of individual lots to the Land Development Regulations. Although the
DEP and Water Management Districts have been regulating post
development runoff for commercial and larger residential projects for
many years, Atlantic Beach is the first city in Northeast Florida to invoke
~' this type of requirement all the way down to the single-family residential
level. A primary reason the requirement for on-site storage was added
was the limitations for handling increased runoff designed into the Old
"" Atlantic Beach (Core City) improvements. This $9 million dollar drainage
and infrastructure improvement project was designed to minimize damage
to trees in the right of way to maintain the canopy coverage that is so
~" much a part of the Old Atlantic Beach ambience. To minimize these
impacts, on many streets the drainage system was placed in the middle of
the street and pipe sizes were limited to that necessary to carry the
~" existing runoff volumes. (See attached City Manager letter for additional
details concerning stormwater collection system limitations).
Since the City started enforcing the requirement, there have been
many complaints from builders, developers and homeowners that control
of storm water was a municipal function and should not be required at the
lot level.
~, When the initial language for the on-site retention requirement was
drafted by the consultant preparing the 2002 Stormwater Master Plan
Update, they included an option fora `Stormwater Impact Fee' allowing
payment to the City for the eventual cost of building retention systems to
handle increasing runoff volumes as redevelopment increased impervious
areas. This option was not adopted, partly because of a belief that the
~, persons causing the problem should be responsible for the solution, but
also because of the problem of quantifying a cost for public development
of future facilities (as an example, the dramatic increase in land costs for
~, the Hopkins Creek Retention Pond since it was initially proposed in 1996).
This staff report is intended to provide a comparison of costs for
publicly financed stormwater retention systems to the cost for various
June 26, 2006 Regular Meeting
~"' AGENDA ITEM #3B
JUNE 26, 2006
~.
systems used by private homeowners /builders to meet the requirements
~. at the lot level. The attached cost comparison shows that private storage
is almost 50% less costly on a unit cost ($/CF) storage basis. ($6.65/CF
for Hopkins Creek vs. $4.52/CF for an in ground storage system already
~. constructed in Atlantic Beach. Private storage may also be accomplished
in many cases by surface swales or by perforated HDPE pipe in a gravel
envelope at even lower unit costs). Because of rapidly rising land values
at the beach, and limited areas in which to construct wet detention
facilities, the `Under Road' cost estimate ($11.50/CF) is a more likely
comparison point for future public vs. private costs. The 800 cubic foot
minimum was used as the approximate storage volume required for a
redeveloped 5000 SF lot in Old Atlantic Beach.
RECOMMENDATION: For Commission Information only
ATTACHMENTS: 1) Cost Comparison
2) Spec sheets of various storage options for individual lots
3) City Manager's Letter
BUDGET: No Budget Impact
REVIEWED BY CITY MANAG
~.
June 26, 2006 Regular Meeting
Cost for Public Retention {based on estimates for Hopkins Creek Pond volume and cost).
Stormwater Attenuation and Treatment Volume:
Wet Pond 8.4 Acre feet -Source CDM Technical Memorandum
Total Cost: Hopkins Creek Regional Detention Facility
`~" $2,425,000 Source - 2002 Stormwate Master Plan Update Appendix E,
with updated land acquisition cost.
Cost /Cubic Feet of storage -includes cost to purchase land
~"" $6.63
Under road (Atlantis System)
Atlantic Raintank System -modular tanks -system size can be tailored to need.
Volume per tank
4.2 Cubic Feet
Cost per Raintank (installed -assumes minimum 800 cubic feet)
$20.00 Per Module plus installation $8,000
Roadway Excavation /Repair
~"" 100 SY x $12/SY $1,200
Total Cost $9,200.00
Cost /Cubic Feet of storage
x11.50
Cost for Private (On~site) Retention
~„ Atlantic Raintank System -modular tanks -system size can be tailored to need.
Volume per tank
4.2 Cubic Feet
~. Cost per Raintank (installed -assumes minimum 800 cubic feet)
$20.00 Per Module Cubic Feet 449 Cubic Feet
Cost /Cubic Feet of storage
$4.76
Stonntech System -modular tanks -system size can be tailored to need (Actual values used).
Volume per tank 357
1612 Cubic Feet -total Volume Installed
Cost $15,800.00 Total as-built Cost
Cost /Cubic Feet of storage
$4.52
Stonntrap Precast Concrete Modular Detention System (Vaults)
Volume variable -custom built in height increments of 1 ", starting from 14" minimum
Estimated cost for residential applications -over $50 / CF
AGENDA ITEM #3B
JUNE 26, 2006
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ari~a-r~tat Vertical ~rair~~~
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AGENDA ITEM #8B
JUNE 26, 2006
The Atlantis philosophy is to resolve water management
at the source. That's the concept behind the Ecological
~* Road. This holistic system captures surface runoff from
roads and, instead of transporting itto a central storage
pond, provides short-term localized storage so that
stormwater can be either infiltrated to recharge
~' groundwater, released at a controlled rate, or recycled
for irrigation. RainTank provides benefits for everyone,
including the developer, the municipality, and the
~,,, community.
Benefits for the t3evelaper - Ecanarnic
. Less expensive than traditional techniques
. Replaces curb & gutter, inlet structures, -~ t'
drainage pipe, and stormwater ponds
,~
~'"' Frees up valuable space
~,
~,
~,,, Benefits far the Municipatify - Environrnentat
. Removes a variety of pollutants and nutrients
from hydrocarbons to phosphorous
. Encourages infiltration
. Reduces total runoff in detention applications
~w Benefits #a the Garrcmunity -Quality a# Life
. Eliminates breeding grounds for mosquitoes
and other vermin
. Completely maintenance-free
M ` '1~` Managing stormwater
close to the source.
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Economically sensible, environmentally friendly, and completely sustainable, the Ecological Road is a better way to
manage storm water.
~. E~~sic~r~ Uptians
Santa Monica, CA -Installation of 750cf of RainTanks installed
_'
There are many ways to incorporate the principles of the ecological road into a project design, as demonstrated by this project.
Excavation of the area. Placement o/ tanks. Backlill on top of structure. Completed job.
e'er, ~. j . `G.C:m."'tR"u?~ .. ! -:~ -,-- ...~.. .a a_.~ - ._
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Q#1~ntis t}imensic~ns
AGENDA ITEM #8B
JUNE 26, 2006
AAOdule WIdM Length LangM Height Height
(Units) Width (mm) (lrxllesj (mm) (inches] (mm) (inches)
Single (1) 408 16.06 fi95 26.97 450 17.72
Double (2) 408 78.06 665 26.97 860 34.65
Triple (3) 408 16.06 685 26.97 1310 57.57
Qued (4) 406 76.06 665 26.97 1740 68.50
Pent (5) 408 16.06 665 26.97 2170 85.43
ModtAe Tank Stink Weter Storage Weler Storage N of Larga Not Small
(Units) Volume(cf) Volume gal) Volums(cf) Volume (gal) Plates plates
Single (i) 4.44 33.22 4,<^2 31.56 4 4
Ooubte (2) 8.69 64.97 8.25 61.72 7 6
Trifle (3) 12.93 96.72 12.26 91.68 10 t2
Quad (4) 17.17 726.47 16.31 122.03 13 16
Pant (5) 21.42 160.21 20.35 152.19 7fi 20 '~.
Conversions 1 d = 7.4805195 galon
1 liter = 0.2641721 gallon
1 mm = 0.0393701 inches
1 d = 0.0263168 cm E
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18.06''_ ~~ ry6q'( 1806 ~ (4 B ) ~° 7
Single Module Double Module Triple Module
'f`e~rf I Crav+~l Ce11 SpeCificatie~n
1.18" Cell 2.f,5" Cell
Size
sw
Ultimate Load
Flow Rate
(H) 1.18" / 30mm (H) 2.05" / 52mm
(W} 15.94" / 405mm (W) 10.24" / 260mm
(L) 23.9" / 607mm (L) 18.9" / 480mm
*116.7 psi *166.0 psi
21.13 gals /min ($0 I /min) 37.51 gals 1 min (142 I min)
'Recommendetl maximum loading
~trep Filter PipeY'~ SpeCifrcati4n
size
Ultimate Load
Flow Rate
'Recommendetl maximum loading
v_ ,>~
The advanced design of StormTech's chambers allows stormwater
professionals to create more profitable, environmentally sound
installations. Compared with other subsurface systems, StormTech's
innovative chambers offer lower overall installed costs, superior
design flexibility and enhanced long-term performance.
StormTech chambers are ideal for commercial, municipal and res-
idential applications. One of the key advantages of the StormTech
chamber system is design flexibility. StormTech chambers can be
configured into beds or trenches, in centralized or decentralized
layouts to fit on nearly any site.
~,,, Typical Cross Section Detail (not to scale)
THE INSTALLED CHAMBER SYSTEM SHALL PROVIDE--.
THE SAFETY FACTORS SPECIFIED IN THE AASHTO LRFD `~~
BRIDGE DESIGN SPECIFICATIONS SECTION 12.12 FOR
EARTH AND LIVE LOADS, WITH CONSIDERATION FOR
,~ IMPACT AND MULTIPLE VEHICLE PRESENCES.
3/4-2' (20-50 mm) WASHED,
CRUSHED, ANGULAR STONE
ADS 601 GEOTEXTILE OR EOUAL
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AGENDA ITEM #8B
JUNE 26, 2006
The advanced features and innovative technology of StormTech
chambers streamline installations while lowering overall installed
costs. StormTech chambers offer these unique advantages:
Lightweight, two people can install chambers quickly and
easily, saving time and money
Extensive product research & development and rigorous
testing ensure long term reliability and performance
Versatile product design accommodates a wide range of site
constraints with cost-effective system designs
The chamber length can be cut in 6.5" (165 mm) increments -
reducing waste and optimizing the use of available space
Injection molded polypropylene ensures precise control of
wall thickness and product consistency
Isolator Row - a patent pending technique to inexpensively
enhance total suspended solids (TSS) removal and provide
easy access for inspection and maintenance
Corrugated Arch Design - a proven geometry for structural
integrity under H-20 live loads and deep burial loads, also
provides high storage capacity
CHAMBERS SHALL MEET ASTM F 2416-OS "STANDARD
SPECIFICATION FOR POLYPROPYLENE (PP) CORRUGATED
WALL STORMWATER COLLECTION CHAMBERS."
r -GRANULAR WELL GRADED SOIL/AGGREGATE
MIXTURES, <35% FINES. COMPACT IN 6' (150 mm)
LIFTS TO 95%STANDARD PROCTOR DENSITY. SEE
THE TABLE OF ACCEPTABLE FILL MATERIALS.
~ I PAVFMFAIT-----..
FOR UNPAVED INSTALLATION WHERE RUTTING
MAY OCCUR INCREASE COVER TO 24 (610 MM
~L ~~ ~~
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.ate _: ~ ...._ _
FR M VEHICLES ~]T ~.,
16" (460 mm) {2440 mm)
M N. MAX.
~, ...6' (i50---777mm) MIN. _.'
t, i _
30' (7160 mm) SC-740
16' (410 mm) SC-310
±:
.." DEPTH OF STONE
TO BE DETERMINED
_ _ .. I _ _ ,-- BY DESIGN ENGINEER'
s. ~ ~ i 1 ~ I ~ I .i~ ~ I~i I 'i I i i , -.:: _ _ i.. 6,. (150 mm) MIN.
i i
I- 1- ~ I _-i ~ __ - ...
DESIGN ENGINEER fS RESP I ~ ~ ~/ ~ ~ ~.:-~ ' , ~ 1 I' 1 '
'~1! ' ", ONSIBLE FOR ~- ----1
ENSVRING SUITABILITY OF SUBGRADE SOILS' ~ `---'6" (150 mm) MIN. ~-.---- 12' MIN. (305 mm) TYP.
THIS CROSS SECTION DETAILS THE REQUIREMENTS NECESSARY TO SATISFY THE SAFETY FACTORS SPECIFIED IN THE AASHTO LRFD BRIDGE
DESIGN SPECIFICATIONS SECTION 12.12 FQR EARTH AND LIVE LOADS USING STORMTECH CHAMBERS
2 Call StormTech at 888.892.2694 for technical and product information or visit www.stormtech.com
L to R: SC-310 chamber and SC-740 chamber
~.
AGENDA ITEM #8B
JUNE 26, 2006
The StormTech SC-740 chamber optimizes storage volumes in relatively small footprints by providing 2.2 ft'1ft2 (0.67 m'/m2) (minimum) of
storage. This can decrease excavation, backfill and associated costs. The StormTech SC-310 chamber is ideal for systems requiring low-rise
and wide-span solutions. The chamber allows the storage of large volumes, 1.3 ft3/ft2 (0.4 m3/m2) (minimum), at minimum depths.
StormTech SC-740 Chamber
(not to scale)
Nominal Chamber
Specifications
Size (L x W x H)
85.4"x51.0"x30.0"
(2170 x 1295 x 762 mm)
Chamber Storage
45.9 ft' (1.30 m')
Minimum Installed Storage
74.9 ft' (2.12 m')
- - _
Weight
74.0 Ibs (33.6 kg)
Shipping
30 chambers/pallet
60 end capslpallet
12 pallets/truck
StormTech SG-310 Chamber
~,. (not to scale)
Nominal Chamber
Specifications
"' Size (L x W x H)
85.4"x34.0°x16.0"
(2170 x 864 x 406 mm)
~ Chamber Storage
14.7 ft' (0.42 m'}
Minimum Installed Storage'
r. 31.0 ft' (0.88 m')
Weight
37.0 Ibs (16.8 kg)
---- _ _
Shi m
PP~ 9
41 chambers/pallet
108 end capslpallet
18 palletsltruck
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(203 mm) 24" (610 mm) DIA. MAX
SC-740 end cap
-- -
30.0
(762 mm)
I` }` ~~
(+ -51.0'(1295 mm)-----_. ~--
s. s r
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~" F '.
~-5-~ ~ 12" (305mm)
DIA. MAX
(150 mm)
SC-310 end cap
1 ~D / \\
(aos mm1 ~ \
_-~ . -
r-34.0° (864 mm)--~
- -ACCEPTS 4" (100 mm)
SCH 40 PIPE FOR OPTIONAL
INSPECTION PORT
(~In h !~~~ Fn-rn n`~ir 'r~ nF ~,. i" 'r~~lr
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s v, a ~! ~ ~ 1. ~/ v V _:~-
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~. _ __ - 90.T (2300 mm) -_ _ ~-+
~- - -- - - - - 85.4" (217D mm) INSTALLED -+--
rY I ~ ,j>{ Rn ~('; 4~ ~ 1 tm a t~~F v~ to t~l~
r ui 11 ,I ,
i ~~ f II' ~ i~ ,~~~~~ ~ I ), f:~~l ~ I~I~r~ ~ ~ ~, lql ( ~IGr,
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SC-740 chamber
-ACCEPTS 4" (100 mm)
SCH 40 PIPE FOR OPTIONAL
INSPECTION PORT
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~ _ _ _ - 90.7° (2300 mm) - - ~'t
-- - 85.4' (2170 mm) INSTALLED-
,~ ,r rp g~ r~i m, n an r-~ F 1 ~n i>s a: ~
t t r" t t r ~r t ~! t 3~ ;< eQT t o '~ r t-~ iii;
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L"-~:. ~ I~'N ~ ~ ~ i N '~ ~' !11 ~~ a~ 9~L X18 ~6 `~ ~ 1 ~ d ~' ~ ~ '~_ °~ 9i '~
SC-310 chamber
`This assumes a minimum of 6 inches (150 mm) of stone below, above and between chamber rows.
Call StormTech at 888.892.2694 for technical and product information or visit www.stormtech.com 3
_~
~"" AGENDA ITEM #3B
JUNE 26, 2006
Capacity of City of Atlantic Beach Storm Water System
,°, and Related Storm Water Regulations
April 5, 2006
There is no excess capacity in the City of Atlantic Beach storm water system. In recent
years, engineers working for Atlantic Beach have designed storm water improvements to prevent
street flooding during most major storms and flooding of homes during a 25 year storm. This
~. means a rainfall event that will occur on average once every 25 yeass. In Atlantic Beach, that
would equal 9.3 inches of rain over a 24 hour period. It has been many years since a storm of
that magnitude has been seen here.
The city recently spent over $9,000,000 in the old Atlantic Beach area making storm water and
other utility improvements. The fmal plan for these improvements was identified only after two
~. ,previous designs were rejected by the public because of their environmental impacts. Those
plans would have included converting major portions of two pazks into retention ponds, the
construction of lazge storm water lines and pumping systems and the removal of many street side
trees. Atlantic Beach is basically flat and getting storm water to move rapidly out of residential
neighborhoods is difficult.
Every additional square foot of impervious surface that is added in old Atlantic Beach will
increase the level of flooding in surrounding homes. For this reason, in 2001 the Mayor and
Commission adopted a 50% limit on the amount of impervious surface on any given lot and in
2003 adopted regulations requiring the on-site retention of additional storm water runoff
resulting from development. In spite of these regulations, the total impervious surface in
Atlantic Beach will grow in the future because most of the present lots have less than 50%
impervious azea, and they can legally expand under current regulations. The purpose of the
current regulations is to slow the increase of storm water into the city's system and thereby push
the need for additional and more invasive storm water solutions as faz into the future as possible.
Other areas of Atlantic Beach face the same problems. Some of those, like the area around
Aquatic Drive and Hopkins Creek, experience considerable flooding during major rainfall events
and will certainly experience hoose flooding luring a 25 yeaz ste,rm. Planning is underway for
improvements in those areas. In other neighborhoods such as Oceanwalk, little or no flooding
has been apparent even in the worst of storms. However, as the lots in Atlantic Beach are
redeveloped with larger homes, bigger driveways, new swimix-ing pools and other impervious
surfaces, more storm water will be put into the drainage systems which inevitably will cause
future flooding and the need for additional capital projects to bring that flooding under control.
Just because most of the city drainage system works now doesn't mean that we can be cazeless in
the design of new development.
For additional information on the status of the city's storm water system, consult the Atlantic
Beach Storm Water Master Plan dated February 1995 and the Master Plan Update dated August,
2002. Both are available in City Hall.