v>EPA
                        United States
                        Environmental Protection
                        Agency
                        Office of Water
                        Washington, D.C.
EPA 832-F-01-005
September 2001
Storm Water
Technology  Fact Sheet
On-Site Underground  Retention/Detention
DESCRIPTION

One of the  major components of storm water
management is flow control, particularly in newly-
developed areas  where buildings, parking lots,
roads, and other impervious surfaces replace open
space.  As imperviousness increases, there is less
area available for infiltration, and the amount of
runoff increases.  This may cause streams to  be
more prone to flash floods. Many municipalities
now require newly-developed areas to maintain pre-
development runoff conditions and to implement
measures to capture or control the increase in peak
runoff for a design storm event.

Several  different types  of storm  water  Best
Management  Practices   (BMPs),  including
retention/detention ponds,  storm water wetlands,
and underground storage structures, can provide
storm water volume control. These BMPs capture
flow and retain it until it infiltrates into the soil
(storm water retention) or release it slowly over
time, thereby decreasing peak flows and associated
flooding problems (storm water detention). Several
of these options,  including storm water wetlands
and large detention ponds, require relatively large
land areas, making them less of an option in areas
where land costs are high or where land availability
is a problem.  In many of these areas, such as
parking lots for malls or other developed sites in
highly urbanized areas,  storing  storm  water
underground on the site may be the best option.

Underground storm  water retention/detention
systems capture and store runoff in large pipes or
other subsurface structures (see Figure 1). Storm
water enters the  system  through  a riser pipe
connected to a catch basin or curb inlet and flows
into a series of chambers or compartments for
storage.  Captured runoff is retained throughout the
                      storm event, and can be released directly back into
                      surface waters through an outlet pipe. Outlet pipes
                      are  sized to  release  stored  runoff  at  pre-
                      development flow rates.  This ensures that there is
                      no net increase in peak runoff and that receiving
                      waters are not adversely impacted by high flows
                      from the site.  Some systems are also designed to
                      exfiltrate  stored runoff into the surrounding soil,
                      where it helps to recharge the groundwater table.

                      Underground retention/detention systems can be
                      constructed from  concrete,  steel,  or  plastic
                      materials.   Each material  has  advantages and
                      disadvantages and specific applicabilities, which
                      are discussed in the following sections.

                      APPLICABILITY

                      Underground  retention/detention  systems  are
                      primarily used in newly-developed areas where
                      land cost and/or availability  are major concerns.
                      They are not  usually  designed for retrofit
                      applications. Most systems are built under parking
                      lots  or  other  paved surfaces  in commercial,
                      industrial, and  residential  areas.   Perforated
                      underground retention systems that release stored
                      storm water into the subsoil are recommended only
                      for areas  with well-drained soils and where the
                      water table is low enough to permit recharge.  Some
                      pretreatment such as sediment traps or sand filters
                      may be necessary for infiltration to eliminate
                      sediment  and other  solids  that could  clog the
                      system.

                      On-site underground retention/detention systems
                      provide peak  runoff flow control  and can store
                      storm water  for future release  back  into  the
                      environment.  However, they are not designed

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                Riser inlet to catch
                basin or curb inlet
                                                                   Header
           Band
                  Barrels
                                                                f
                                                          Outlet pipe (sized
                                                          to control runoff)
  Source: Modified from Contech Construction Products, Inc., 2000.
       FIGURE 1 SCHEMATIC OF PIPE-BASED  UNDERGROUND STORM WATER
                                   DETENTION SYSTEM
specifically to enhance  water  quality; therefore,
other storm water BMPs may be required to provide
storm water treatment.  Underground retention/
detention  systems are  often used  in  "treatment
trains," which consist of a number of storm water
BMPs that provide both storm water treatment and
storage.  For example, storm water entering the
underground   detention   structure  in  Hauge
Homestead Park in Everett,  Washington, is first
collected from a parking area through a catch basin,
then flows through a series of vegetated swales,
then into a storm water pipe with a sump, all of
which filter out sediment and pollutants before the
runoff reaches the detention chambers. Runoff is
then released into a pond at a controlled rate, where
further pollutant removal occurs (City of Everett,
Washington, Department of Parks and Recreation,
2000).

ADVANTAGES AND DISADVANTAGES

This Section presents the overall advantages and
disadvantages   of  on-site   underground
retention/detention systems. The advantages and
disadvantages of specific designs and construction
materials (concrete, steel, plastic) for underground
retention/detention systems are discussed in the
Design section.

Advantages

•      The  primary advantage  of the  on-site
       underground  storm   water  retention/
       detention system  is that  it captures and
       stores  runoff,  thus  helping  meet the
       requirement  to maintain pre-development
       runoff conditions at newly-developed sites.

•      These  systems  are  ideal  for  highly
       urbanized areas, particularly in areas where
       land is  expensive or may not be available
       for ponds or wetlands.

•      These systems can be installed quickly. For
       example, construction and installation of a
       6'  by 4' by 156'  concrete  system  was
       installed  under  a  car   dealership  in
       Tennessee in  3  days (Sherman  Dixie
       Concrete Industries, Inc., 2000).

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•      These systems are very durable.  Once in
       the ground, most systems can last more than
       50 years.

•      Because these systems are underground,
       local residents are less likely to have access
       to them, making them safer than ponds or
       other aboveground storm water BMPs.

Disadvantages

•      The  primary disadvantage of the on-site
       underground  storm   water  detention
       structures is that they are not designed to
       provide  storm  water  quality  benefits.
       However,  if  they  are  included  in  a
       treatment-train type system, underground
       detention systems can be an important part
       of an  overall storm  water management
       process.

•      These systems may require more excavation
       than surface ponds or wetlands.

•      Recharge of the  groundwater  from  an
       underground retention unit may contribute
       to groundwater contamination if flow from
       the site  is  directly  discharged into the
       retention  system  before   pretreatment.
       Therefore, EPA does not recommend that
       percolation systems be designed for sites
       with coarse soils or  high groundwater
       tables.

•      These   systems   are  more  difficult  to
       maintain  and clean  than  aboveground
       systems.

DESIGN CRITERIA

On-site underground retention/detention systems
are designed to provide a predetermined amount of
storage volume within a specified area.  System
designs can range from  simple storage pipes or
chambers to  complex  systems  consisting  of
multiple pipes  or chambers,  with accompanying
joints, crossovers, multiple inlets and access points.
At a minimum, each system must have an inlet, an
outlet, and  a  structure  to  access the chamber
(Pacific Corrugated Pipe, 2000). All other design
elements are site, project, and material-specific, as
described below.

Among the most  important elements to consider
when designing underground retention/detention
systems  are  the  size,  shape,  and  physical
characteristics of available space available for the
system. These factors will influence how the system
is  constructed and what type  of construction
material  is chosen.  Depending on the  specific
application, design engineers have utilized different
materials, including concrete  pipes  and  other
concrete structures, steel pipes, and plastic pipes, in
designing   underground   retention/detention
structures. Each material has different advantages
and disadvantages under different scenarios.  The
type of material  to be used  in any individual
application should  be determined by  site and
application-specific conditions.

Site-specific considerations that may influence the
type of material used in an individual application
include:

•      The depth and area of allowable excavation
       space.   For  example,  to maintain  the
       structural integrity of corrugated steel and
       high  density  polyethylene pipe  systems,
       more fill is required below, between, and
       above the pipes than when using concrete.

•      The shape of the  area  available for  the
       system. For example, is the available space
       one continuous area where a large vault
       could be placed,  or  does it have angles
       which  might make a pipe system more
       appropriate?

•      The depth  of the water table. For example,
       there are some concerns that plastic pipes
       may float upward in areas with high water
       tables.

•      The construction costs (including material
       and labor costs) for different materials.

Table 1 summarizes the physical characteristics of
these materials. Additional considerations include
local ordinances,  which may preclude the use of
some types of materials for certain applications.
For example, Fairfax County,  Virginia,  does not

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   TABLE 1 COMPARISON OF DESIGN CONSIDERATIONS FOR CONSTRUCTION MATERIALS
            FOR UNDERGROUND STORM WATER RETENTION/DETENTION SYSTEMS
                                  Concrete
                         Construction Material

                                Plastic
                                (HOPE)
                         Steel and Aluminum
                                (CMP)
  Shapes


  Spatial Requirements


  Rigidity/Flexibility


  Fill Requirements


  Other Requirements
  Available Sizes
  Handling
   Rectangular vaults or
      circular pipes

Primarily continuous space
     with no angles

Very rigid, does not require
 fill to maintain rigidity; not
        flexible

   Requires minimum fill
     above structure
         None
 Multiple sizes that can be
 pre-cast or cast-in-place
     Circular pipes
 Can be fitted into irregular
   and angled spaces
   Rigid, requires fill for
   stability; not flexible
  Requires minimum fill
 between and above pipes

Requires minimum spacing
  between pipes. Water
 table must be below level
        of pipe
Multiple pipe diameters are
  available; all are pre-
     manufactured
Requires moving equipment    Can be moved by hand
Circular pipes, semi-circular
   pipe-arches, or other
     special shapes

 Can be fitted into irregular
    and angled spaces

   Rigid, requires fill for
  stability; can withstand
   some shifting without
   breaking or buckling

   Requires minimum fill
 between and above pipes
Requires minimum spacing
     between pipes
 12" to 144" diameters and
 pipe arches are available
  pre-assembled. Larger
  diameter pipe and pipe-
  arches are available for
    assembly on-site

    Requires moving
	equipment	
  Source: Compiled by Parsons Engineering Science, Inc., 2000.
allow plastic  pipes to be used  for underground
retention/detention systems for residential areas. In
contrast, plastic pipe has been the favored option
for systems built by the Department of Parks and
Recreation in Everett, Washington.

Once  appropriate  construction materials  are
determined for a specific application, design must
determine the amount of storage volume required
by the system.  As discussed above,  many areas
have adopted a policy of no net increase in runoff
for a design storm event for newly-developed areas.
Thus, the required storage volume is the difference
between pre and post-development runoff. In other
areas, local requirements dictate how much of a
given storm must be captured and treated, and the
required storage volume can be calculated using
this  value.   For  example, the  City  of Malibu,
California  requires  post-construction treatment
control  BMPs to treat the  first 0.75 inches of
rainfall  over a  24-hour period (City  of Malibu,
                         2000b).  In contrast, the Department of Public
                         Works in Everett, Washington, requires systems to
                         be designed for the 6-month, 24-hour storm (City of
                         Everett, Washington, Department of Public Works,
                         2000).

                         After  the  required storage  volume  has  been
                         determined, the design engineer can examine the
                         site to determine what configuration will maximize
                         storage while minimizing the size of the excavated
                         area.   Concrete structures, such as box culverts,
                         tend  to  provide  greater  storage  volume  per
                         excavated area because of their rectangular shape
                         (allowing more storage volume per cross-sectional
                         area)  and  the fact  that they can provide  one
                         continuous chamber.  Pipe systems, on the other
                         hand, tend to store less runoff per excavated area.
                         There  are several reasons  for  this. First,  round
                         pipes and pipe arches have less storage volume per
                         cross-sectional area than do square structures, such
                         as box culverts.   In addition, pipes are often laid

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parallel or at intersecting angles,  reducing  the
amount of storage per excavated area. Pipes also
require specific amounts of space for fill between
them.  While this promotes the structural integrity
of the pipes,  it reduces the amount of excavated
area available for storage.  These  requirements
make the largest diameter pipe that meets  the
minimum cover requirements the most economical.
For example, doubling the diameter of the pipe
usually doubles the cost of the pipe, but quadruples
the storage volume. In addition, the ability to angle
and arrange pipes in series of different lengths may
make them good choices when the space available
for  storage   is  not  continuous.    Several
manufacturers have produced CD-ROMs to aid in
the design and configuration of pipe systems.

PERFORMANCE

On-site runoff controls, such as underground storm
water retention/detention systems, are designed to
control  storm water quantity and they have little
impact on storm water quality.  Thus, underground
storm water retention/detention systems alone will
not satisfy most local storm water regulations. For
example, Fairfax County, Virginia, requires both
storm water management (i.e., storm water volume
control) and storm water BMPs (i.e., storm water
quality control) (Fairfax County, Virginia, 2000).
Therefore, most underground  retention/detention
systems are coupled with other water quality BMPs,
such as catch basins, curb inlets,  water quality
inlets, sand filters, or sumps. This "treatment train"
can help to improve the water quality of the overall
storm water control system, particularly during the
first part of a rain event when pollutants may be at
their highest concentrations. BMPs may be located
either   upstream  or  downstream   from   the
retention/detention system. Fairfax County, which
reviews storm water  plans for new development,
encourages planners to include sand filters or other
water quality control  devices upstream of an
underground detention system. The City of Malibu,
California, recommends a treatment train system
(City of Malibu, California, 2000b).  One system
that the city has looked at includes a sedimentation
basin, a detention basin, then a sand filter (City of
Malibu, California, 2000a).   A new project in
Hauge Homestead Park in Everett,  Washington,
includes storm water BMPs  both upstream and
downstream of the detention area.

When designing a treatment train, design engineers
must ensure that downstream BMPs are designed
for the appropriate flow from the underground
retention/detention system.  For example, the City
of Alexandria, Virginia, found that long drawdown
times   from  underground  retention/detention
systems  could result  in  continuous  flow  into
downstream sand filters, which could  cause the
resuspension of accumulated phosphorous (City of
Alexandria, VA, 2000). Therefore, Alexandria does
not recommend the use of sand filters downstream
from most retention/detention systems.

While underground storm water retention/detention
systems are  not specifically designed to provide
water quality benefits, they do often improve water
quality.  As storm water is retained before it is
released back into the  environment,  suspended
solids may settle out, thereby reducing the overall
pollutant load. For example, in the City of Everett,
Washington, local regulations require that at least
15 percent of the 6-month, 24-hour storm runoff be
retained above  ground, usually in a biofiltration
area. The remainder  of the runoff can  be stored
below ground, where suspended solids are allowed
to settle out before the water is released back into
the environment  (City of Everett,  Washington,
Department  of Public Works, 2000).  However,
unless the system is properly maintained, settled
solids may eventually fill the system.

OPERATION AND MAINTENANCE

Once underground storm water retention/detention
systems  are  installed, they  require very  little
maintenance.  They  have no moving parts and
remain intact for  many years. A major concern
with the use of corrugated steel or polyethylene
pipes has been that the pipes might crack or buckle
over time because of  the  weight of the  soil
surrounding them. However, a study of corrugated
steel pipe (CSP) underground storm water detention
structures in the Washington, D.C., metropolitan
area conducted by the National Corrugated Steel
Pipe Association (NCSPA)(NCSPA, 1999) found
that all of the systems  were performing well. None
of the pipe systems inspected, some of which had

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been in place for up to 25 years, showed signs of
buckling, cracking, or bending. In only one case
had the joints of pipe sections separated.

Underground  storm   water  retention/detention
structures must be cleaned periodically to remove
accumulated trash, grit, sediments, and other debris.
The installation of catch basins or grates at the inlet
will  reduce trash accumulation,  but  suspended
solids  will still be  carried  into the storage area,
where  they may settle  out and accumulate on the
bottom of the structure. The structures need to be
cleaned to remove this accumulated material, which
should be tested to determine if it contains any toxic
or hazardous materials, and then disposed according
to local regulations regarding storm water residuals.

In Fairfax County, Virginia, where there are over
300 underground storm water retention/detention
structures installed at commercial/industrial sites,
private owners of the structures are required to sign
a  maintenance contract with the County that
commits the  owner  to  maintain the structure
appropriately. Fairfax County also provides owners
with a  maintenance checklist and plans to inspect
these structures regularly (i.e., at least once every
five  years) to ensure  that they are  functioning
adequately.   If  an owner  fails to  maintain the
structures, the maintenance agreement allows the
County to perform the required maintenance at the
expense of the owner.

The City of Everett, Washington, takes ownership
of underground  storm water  detention  systems
constructed  in residential  developments under
existing rights-of-way, such as sidewalks or streets.
The  city conducts annual inspections of system
outlet structures and looks for  an accumulation of
sediment at the outlet as an indicator that the system
needs to be cleaned. Crews are then dispatched to
perform the clean-outs.  The  City also regularly
inspects private systems and issue notices to owners
when  sediment  accumulation is  noted (City  of
Everett, Washington, Department of Public Works,
2000).

COSTS

Costs    for  underground  storm   water
retention/detention structures are  highly variable
and depend primarily on the types of materials used
(concrete vaults, metal or plastic pipes) and the
amount of storage volume desired.  The type of
materials used will greatly affect construction and
installation costs, because they dictate the size of
the excavation required to achieve the necessary
storage volume.   As  discussed in the Design
section, to ensure their strength and rigidity, plastic
and  steel  pipes have  specific  requirements for
spacing, fill type and fill volume, all of which effect
the size of the excavation. Concrete structures do
not have  the  same level of fill requirements.
Another consideration is the  amount of  time
required to handle and assemble the various pieces
of the system.  Steel and plastic pipes tend to be
lighter and easier to handle than concrete vaults;
however,  large diameter pipes and "pipe arch"
structures  (which are delivered as separate sheets
and must be bolted in place) may increase handling
time requirements.

While  costs  for  specific types  of underground
detention systems can be highly variable, they can
be very economical,  especially compared  with
alternatives.    The primary alternative  to an
underground storm water detention structures is an
aboveground   wet  detention  pond.     While
construction costs for ponds are generally lower
than for underground storage units (ponds can cost
between $17.50 and $35 per cubic meter of storage
area [Center for Watershed Protection, 1998]), land
used for a surface pond cannot be used for any other
purpose.   This  is  not   true  for  underground
retention/detention systems, where the land above
can be utilized for parking lots or other purposes,
maximizing the economic potential of the land.  In
Everett,  Washington,   underground  detention
structures   are often used in conjunction  with
aboveground  ponds in  storm water management.
While  local  regulations  require  some  surface
treatment of storm water, the majority of runoff can
be stored  underground, minimizing the need for
large surface ponds that are both costly and require
economically-valuable   land.     Everett  also
encourages the use of concrete underground storage
systems, which  allows the  pond to actually be
placed directly on top of the underground storage
area, again making maximum use of the available
land (City of Everett, Washington, Department of
Public   Works,  2000).     Underground
retention/detention systems can also be economical

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when  compared to infiltration  trenches.    An
engineering estimate prepared for a commercial
installation in Glen Burnie, Maryland, showed that
a 150,000 cubic feet detention system consisting of
60" corrugated steel pipe covered by stone would
cost approximately $453,000 and occupy only 0.94
acres, while a stone infiltration trench that could
store the same volume would occupy 1.43 acres and
cost $576,000 (Contech, Inc., 2000).  The major
differences in cost between these two options were
that using only stone required a larger excavation,
and the stone fill and increased labor for placing the
stone fill was more costly than the cost of material
and labor for installing the pipe.

As discussed above, underground storm  water
retention/detention structures can vary greatly in
cost, depending  on the materials utilized,  the
excavation, construction, and installation costs, and
the storage  volume  required.    For example,
construction  of  the underground  storm  water
retention/detention segment of the Boneyard Creek
project in Champaign, Illinois, which consisted of
the installation of six 11-foot diameter corrugated
steel pipes (comprising 24,600 cubic meters  of
storage)  cost approximately  $9  million,  plus
contingencies (City of Champaign, Illinois, 2000).
When combined with a larger, aboveground storm
water  retention/detention   pond,  this  project
provides enough retention/detention for a 25-year
storm event,  preventing the perennial flooding of
Champaign's Campustown section and saving local
businesses from flood damage and lost business.

Engineer's  estimates for  installation  of CSP
systems in Arizona are approximately $84 per cubic
meter of storage (Pacific Corrugated Pipe  Co.,
2000).   For example, to capture the first inch of
runoff from a one acre plot, 72 feet of 96-inch CSP
would be installed at a cost of $8,650.  Costs are
scalable and increase proportionally to increases in
the amount of land served or the amount of runoff
stored.

High Density Polyethylene  (HDPE) pipe  was
utilized to construct an underground storm water
detention system at the T.F.  Green Airport  in
Providence, Rhode Island.   The parking lot was
created  when  an  existing neighborhood  was
demolished to create extra parking areas. The site
had a high water table and no runoff was allowed to
leave the  site.   The  contractor designed five
separate systems of 24-inch HDPE pipe, with the
largest systems consisting of approximately 2,500
linear feet of pipe each, to contain the runoff. The
total storage volume was 1,420 cubic  meters.
While the contractor determined that 36-inch pipe
was the most cost effective option, this would have
had required regrading  before installation while
maintaining three feet of soil between the pipe and
the groundwater as required by Rhode Island
regulations. The total project cost was $250,000,
which included 9,200 linear feet of 24-inch HDPE
pipe,  inspection ports,  filter fabric,  filter sand
bedding, nine inches of stone fill around each pipe,
and  almost three  feet of fill  over the  pipes
(D'Ambra  Construction Co., Inc.,   2000, and
Vanasse Hangen Brustlin, Inc., 2000).

There are trade-offs in  costs between pipes and
other systems, such as concrete vaults.  In some
cases, costs for concrete storage structures can be
lower than those for plastic  or  corrugated steel
pipes. Because they require less area to achieve the
same storage volume, less area  may  need to be
excavated for concrete  structures than  for pipe
systems. This may reduce excavation costs. Using
complete precast concrete sections can  decrease
assembly time, further  reducing costs. However,
these low costs may be offset by the higher costs of
handling concrete.  Installation of a 156-foot long
section of 6-foot by 4-foot concrete  precast box
culvert (106 cubic meters) at a car dealership in
Knoxville, Tennessee, was completed in 3 days and
cost  approximately $85,000 (Sherman  Dixie
Concrete Industries, Inc., 2000).

Case  Study: Hauge Homestead Park.   Everett.
Washington

The  City  of Everett, Washington,  undertook a
project to detain increased runoff generated from
new facilities (including a dock, a pier, restrooms,
and walkways) in Hauge Homestead Park on Silver
Lake.  Only 4 acres of land was  available for the
park,  some of which  was required for a wet
detention pond to capture runoff generated from the
facilities. However, because space was so limited,
the Parks  and Recreation Department wanted to
minimize the size of the pond while still providing

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the required treatment. The solution was to build
an  underground storm water retention/detention
system upstream of the pond to store excess runoff
until it was released at a controlled rate into the
pond.   Because the flow into the pond was
controlled, engineers could design a smaller pond
that still  achieved the  same pollutant removal
efficiency.  The underground retention/detention
system was composed of 350 feet of 36-inch HDPE
pipe, which provided 2,847 cubic feet (80.6 cubic
meters) of storage.  When added to the 804 cubic
feet of shallow pond and 1,869 cubic feet of deep
pond, the storage capacity exceeded the 5,130 cubic
feet required to handle a 25-year storm event. The
total cost for the underground detention system,
including materials and installation, was $28,190
(City of Everett, Washington, Department of Parks
and Recreation, 2000).

Case Study: Homestead Village Hotel Brookfield,
Wisconsin

In  order  to meet the requirements  for  no  net
increases in runoff volume from the construction of
the Homestead Village  Hotel  in  Brookfield,
Wisconsin,  engineers designed  an underground
retention/detention system consisting of 549 feet of
72-inch concrete pipe.  Many new development
projects in the suburban Milwaukee  area utilize
retention/detention ponds to control runoff because
land is usually available; however, in this case, the
hotel  was built into  the  side  of a  hill, and
construction of a pond required re-grading the site
and increased costs. Thus, the system was built in
a ring  around the hotel, with all roof and floor
drains  connected to the  system. The designers
chose concrete pipe for several reasons:

•      The large size requirement (72  inch pipe);

•      The owners wanted a 100-year plus product
       lifespan;

•      Multiple openings were required in the pipe
       for the drain inlets  and the designers felt
       that  concrete  pipe  would  maintain its
       strength under these conditions;

•      This pipe required a relatively small amount
       of fill.
•      Both HDPE pipe and CSP were eliminated
       as alternatives based on concerns that the
       soil conditions would corrode CSP pipe and
       seals required for HDPE pipe did not meet
       the State pressure-testing requirements.

The system storage capacity  is 120,000 gallons,
with outlets through 7-inch diffuser perforations
and also  through  a 12-inch  outlet pipe, which
eventually flows into a roadside ditch, then into a
nearby  stream.   Overall project  costs  were
approximately  $267,000, including sanitary and
storm sewers (APS Concrete Products, Inc., 2000,
and National Survey & Engineering, Inc., 2000).
Material costs  for the concrete pipe accounted for
approximately $75,000 of this total.

Case Study: Jordan Landing. West Jordan. Utah

Jordan Landing is a retail  mall in West Jordan,
Utah, covering 80 acres and  consisting of retail
stores and parking lots.  The  complex had  no
requirement to  detain runoff onsite. One option for
runoff generated by the site was to divert the runoff
to storm water structures downstream.  However,
these structures were not large enough to handle the
increased  flows, and the cost of constructing the
piping to convey the  runoff  downstream and
enlarging the downstream controls was deemed too
high. Therefore, the owners  opted to detain the
runoff onsite.

Because space was at a premium on the site, the
designers chose on underground retention/detention
as  the  best option to  control runoff.   They
considered several options for the detention system,
including  corrugated steel  pipe, aluminum pipe,
HDPE  pipe,  concrete vaults,  and  reinforced
concrete  boxes,  before deciding  that  48-inch
aluminum pipe was the best  option.  The other
options all had major drawbacks: CSP required an
expensive coating to  protect it  from  site soil
conditions, significantly increasing costs; costs for
HDPE pipe were high because the system design
required numerous expensive "T" fittings; the only
reinforced concrete boxes immediately  available
came in specific pre-manufactured sizes that did not
fit the site (in  some places on the site there was
only six feet of allowable excavation); and concrete
vaults were too large and expensive.

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The selected system utilized helical aluminum pipes
fastened with aluminum bands.  The system was
installed by first laying down the header pipes,
which were designed so that the barrel pipes could
be laid directly into them, saving costly fittings.
The barrels were then fitted into the header, and
bands were used to connect the pipes together.

Six separate  galleries  of aluminum pipe were
initially constructed.  A seventh was added later.
Altogether, the project utilized 20,000 feet of pipe
and achieved 7,120 cubic meters in storage volume.
The overall construction costs for the project were
$1.2 million (Nolte Associates, 2000).

A summary of comparative costing information for
on-site underground storm water retention/detention
systems is provided in Table 2.

REFERENCES

Other Related Fact Sheets

Handling and Disposal of Residuals
EPA832-F-99-015
September, 1999
Water Quality Inlets
EPA 832-F-99-029
September 1999

Wet Detention Ponds
EPA 832-F-99-048
September 1999
                            be  found at the
Other EPA  Fact Sheets can
following web address:
http ://www. epa. gov/o wrm'tnet/mtbfact.htm

1.    Advanced Drainage Systems, Inc., 1997.
      Technical Note  2.120 Re: Storm  Water
      Detention/Retention System Design.

2.    Advanced Drainage Systems, Inc., 2000.
      Materials provided to Parsons Engineering
      Science, Inc., by Steven Marsh, Advanced
      Drainage Systems, Inc.

3.    APS Concrete Products, Inc., 2000. Dennis
      Stevens,  APS  Concrete  Products, Inc.,
      personal  communication  with  Parsons
      Engineering Science, Inc.

4.    Center for  Watershed Protection,  1998.
      Costs and Benefits for Storm Water BMPs.
    TABLE 2 COMPARATIVE COST INFORMATION FOR ON-SITE UNDERGROUND STORM
                        WATER RETENTION/DETENTION PROJECTS

Material
Length of Pipe
(feet)
Diameter of
Pipe (inches)
Maximum
Instantaneous
Storage
Volume (cubic
meters)
Overall Cost
Boneyard
Creek,
Champaign,
IL
CSP
8,600
132
24,600
$9,000,000
Jordan
Landing
Mall, West
Jordan, UT
Aluminum
20,000
48
7,120
$1,200,000
T.F. Green
Airport,
Providence,
Rl
HOPE
12,500
24
1,420
$250,000
Hauge
Homestead
State Park,
Everett, WA
HOPE
350
36
81
$28,190
Homestead
Village
Hotel,
Brookfield,
Wl
Concrete
549
72
454
$267,000
Car
Dealership,
Knoxville,
TN
Concrete Box
Culvert
156
6' x 4' box
106
$85,000
Source: Compiled by Parsons Engineering Science, Inc., 2000.

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5.     City of Alexandria, VA, 2000.  Bill Hicks,
       Department  of Public  Works,  personal
       communication with Parsons Engineering
       Science, Inc.

6.     City of Champaign, IL, 2000.  Jeff Smith,
       Department  of Public  Works,  personal
       communication with Parsons Engineering
       Science, Inc.

7.     Contech Construction Products, Inc., 2000.
       Patrick Pusey and Dutch Van Schoonveld,
       Contech  Construction   Products,  Inc.,
       personal  communication with  Parsons
       Engineering Science, Inc.

8.     D'Ambra Construction  Co., Inc., 2000.
       John  Oliver, D'Ambra Construction Co.,
       Inc., personal communication with Parsons
       Engineering Science, Inc.

9.     Dewberry & Davis,  Inc., 2000.   George
       Kovats, Dewberry  & Davis, Inc., personal
       communication with Parsons Engineering
       Science, Inc.

10.     Everett, Washington, Department of Parks
       and Recreation, 2000. Ryan Sass, City of
       Everett, Washington, Department of Parks
       and Recreation, personal communication
       with Parsons Engineering Science, Inc.

11.     Everett, Washington, Department of Public
       Works, 2000.  Jane Zimmerman, City of
       Everett, Washington, Department of Public
       Works,  personal  communication  with
       Parsons Engineering Science, Inc.
12.     Fairfax County, Virginia, 2000.  Steve
       Aitcheson, Fairfax County Municipal Water
       Management, personal communication with
       Parsons Engineering Science, Inc.

13.     Malibu, California, 2000a. Rick  Morgan,
       City  of Malibu Department  of Public
       Works,  personal  communication  with
       Parsons Engineering Science, Inc.

14.     Malibu, California, 2000b. Rick  Morgan,
       City  of Malibu Department  of Public
       Works, memorandum to applicants for new
       development regarding New Development
       Standards  to  Reduce Water Pollution,
       March 3, 2000.

15.     National Corrugated Steel Pipe Association,
       1999.   "Condition Survey of Corrugated
       Steel Pipe Detention Systems."

16.     National Survey & Engineering, Inc., 2000.
       Fred  Spelshaus,  National   Survey  &
       Engineering, Inc., personal communication
       with Parsons Engineering Science, Inc.

17.     Nolte  Associates, 2000. Paul Hacunda,
       Nolte Associates, personal communication
       with Parsons Engineering Science, Inc.

18.     Pacific  Corrugated Pipe Company, 2000.
       Darwin Dizon,  Pacific Corrugated Pipe
       Company,  personal communication with
       Parsons Engineering Science, Inc.

19.     Sherman Dixie Concrete Industries, Inc.,
       2000. Al Hogan, Sherman Dixie Concrete
       Industries,  Inc., personal communication
       with Parsons Engineering Science, Inc.

20.     Thompson Culvert Company, 2000. Chris
       Hill, Thompson Culvert Company, personal
       communication with Parsons Engineering
       Science, Inc.

21.     Vanasse Hangen  Brustlin,   Inc.,  2000.
       Molly Rogers, Vanasse Hangen  Brustlin,
       Inc., personal communication with Parsons
       Engineering Science, Inc.

ADDITIONAL INFORMATION

American Concrete Pipe Association
Josh Beakley
222 West Las Colinas Boulevard, Suite 641
Irving, TX 75309

City of Champaign, Illinois
Jeff Smith
Department of Public Works
702 Edgebrook Drive
Champaign, IL 61820

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Contech Construction Products, Inc.
Phil Perry
P.O. Box 800
Middietown, OH 45044

Dewberry & Davis, Inc.
George Kovats
8401 Arlington Blvd.
Fairfax, VA 22301

Nolte Associates
Paul Hacunda
710Rimpau Ave.
Corona, CA 92879-5725

Pacific Corrugated Pipe Company
Darwin Dizon
P.O. Box 2450
Newport Beach, CA 92658

Vanasse Hangen Brastlin, Inc.
Molly Rogers
530 Broadway
Providence, RI 02909

Virginia Department of Conservation and
Recreation
Larry Gavan
203 Governor Street,  Suite 213
Richmond, VA 23219-2094

The  mention of  trade names or commercial
products  does  not  constitute endorsement or
recommendation for use by the U.S. Environmental
Protection Agency.
                                                       For more information contact:

                                                       Municipal Technology Branch
                                                       US EPA
                                                       1200 Pennsylvania Ave, NW
                                                       Mail Code 4204M
                                                       Washington, DC 20460
                                                       IMTB
                                                       Excellence in ^^ compliancethrough optimal technical solutions
                                                       MUNICIPAL TECHNOLOGY  B R A T

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