20090083 Ver 1_Report_20000901

United States Office of Water EPA 832-F-00-023
Environmental Protection Washington, D.C. September 2000
Agency
EPA Wastewater
Technology Fact Sheet
Wetlands: Subsurface Flow
DESCRIPTION
Wetland systems are typically described in terms of
the position of the water surface and/or the type of
vegetation grown. Most natural wetlands are free
water surface systems where the water surface is
exposed to the atmosphere; these include bogs
(primary vegetation mosses), swamps (primary
vegetation trees), and marshes (primary vegetation
grasses and emergent macrophytes). A subsurface
flow (SF) wetland is specifically designed for the
treatment or polishing of some type of wastewater
and are typically constructed as a bed or channel
containing appropriate media. An example of a SF
wetland is shown in Figure 1. Coarse rock, gravel,
sand and other soils have all been used, but a gravel
medium is most common in the U.S. and Europe.
The medium is typically planted with the same types
of emergent vegetation present in marshes, and the
water surface is designed to remain below the top
surface of the medium. The main advantages of this
subsurface water level are prevention of mosquitoes
and odors, and elimination of the risk of public
contact with the partially treated wastewater. In
contrast, the water surface in natural marshes and
free water surface (FWS) constructed wetlands is
exposed to the atmosphere with the attendant risk of
mosquitoes and public access.
The water quality improvements in natural wetlands
had been observed by scientists and engineers for
many years and this led to the development of
constructed wetlands as an attempt to replicate the
water quality and the habitat benefits of the natural
wetland in a constructed ecosystem. Physical,
chemical, and biochemical reactions all contribute to
water quality improvement in these wetland
Optional Inlet 0 Vegetation
Manifold Warm O
Climates O 0
V --- ? Outlet Zone
Inlet Zone 2"to 3"
2- to 3" I Gravel
Gravel Water
Treatment Zone Surface Outlet
Inlet Manifold '/z to 1'/; Gravel Manifold
Cold Climates
Membrane Line or
Impermeable Soils
Source: Adapted from drawing by S.C. Reed, 2000.
FIGURE 1 SUBSURFACE FLOW
WETLAND
systems. The biological reactions are believed due
to the activity of microorganisms attached to the
available submerged substrate surfaces. In the case
of FWS wetlands these substrates are the
submerged portion of the living plants, the plant
litter, and the benthic soil layer. In SF wetlands the
available submerged substrate includes the plant
roots growing in the media, and the surfaces of the
media themselves. Since the media surface area in
a SF wetland can far exceed the available substrate
in a FWS wetland, the microbial reaction rates in a
SF wetland can be higher than a FWS wetland for
most contaminants. As a result, a SF wetland can
be smaller than the FWS type for the same flow rate
and most effluent water quality goals.
The design goals for SF constructed wetlands are
typically an exclusive commitment to treatment
functions because wildlife habitat and public
recreational opportunities are more limited than
FWS wetlands. The size of these systems ranges
from small on-site units designed to treat septic tank
effluents to a 1.5x 10' liters per day (4 MGD) system
in Louisiana treating municipal wastewater. There
are approximately 100 systems in the U.S. treating
municipal wastewater, with the majority of these
treating less than 3.8x 103 m3/day (1 MGD). Most of
the municipal systems are preceded by facultative or
aerated treatment ponds. There are approximately
1,000 small scale on-site type systems in the U.S.
treating waste waters from individual homes,
schools, apartment complexes, commercial
establishments, parks, and other recreational
facilities. The flow from these smaller systems
ranges from a few hundred gallons per day to
151,400 liters per day (40,000 gallons per day),
with septic tanks being the dominant preliminary
treatment provided. SF wetlands are not now
typically selected for larger flow municipal systems.
The higher cost of the rock or gravel media makes
a large SF wetland uneconomical compared to a
FWS wetland in spite of the smaller SF wetland area
required. Cost comparisons have shown that at flow
rates above 227,100 liters per day (60,000 gallons
per day) it will usually be cheaper to construct a
FWS wetland system. However, there are
exceptions where public access, mosquito, or
wildlife issues justify selection of a SF wetland. One
recent example is a SF wetland designed to treat the
runoff from the Edmonton Airport in Alberta,
Canada. The snow melt runoff is contaminated with
glycol de-icing fluid and a SF wetland treating
1,264,190 liters per day (334,000 gallons per day)
was selected to minimize habitat values and bird
problems adjacent to the airport runways.
SF wetlands typically include one or more shallow
basins or channels with a barrier to prevent seepage
to sensitive groundwaters. The type of barrier will
depend on local conditions. In some cases
compaction of the local soils will serve adequately,
in other cases clay has been imported or plastic
membrane (PVC or HDPE) liners used.
Appropriate inletand outlet structures are employed
to insure uniform distribution and collection of the
applied wastewater. A perforated manifold pipe is
most commonly used in the smaller systems. The
depth of the media in these SF wetlands has ranged
from 0.3 to 0.9 meters (1 to 3 feet) with 0.6 meters
(2 feet) being most common. The size of the media
in use in the U.S. ranges from fine gravel (>_0.6
centimeters or >_ 0.25 in.) to large crushed rock
(>_15.2 centimeters or >_6 in.); A combination of
sizes from 1.3 centimeters to 3.8 centimeters (0.5 to
1.5 inches) are most typically used. This gravel
medium should be clean, hard, durable stone capable
of retaining it's shape and the permeability of the
wetland bed over the long term.
The most commonly used emergent vegetation in
SF wetlands include cattail (Typha spp.), bulrush
(Scirpus spp.), and reeds (Phragmites spp.). In
Europe, Phragmites are the preferred plants for
these systems. Phragmites have several advantages
since it is a fast growing hardy plant and is not a
food source for animals or birds. However, in some
parts of the U.S. the use of Phragmites is not
permitted because it is an aggressive plant and there
are concerns that it might infest natural wetlands. In
these cases cattails or bulrush can be used. In areas
where muskrat or nutria are found, experience has
shown that these animals, using the plants for food
and nesting material, can completely destroy a stand
of cattails or bulrush planted in a constructed
wetland. Many of the smaller on-site systems
serving individual homes use water tolerant
decorative plants. The vegetation on a SF wetland
bed is not a major factor in nutrient removal by the
system and does not require harvesting. In cold
climates, the accumulating plant litter on top of the
gravel bed provides useful thermal insulation during
the winter months. The submerged plant roots do
provide substrate for microbial processes and since
most emergent macrophytes can transmit oxygen
from the leaves to their roots there are aerobic
microsites on the rhizome and root surfaces. The
remainder of the submerged environment in the SF
wetland tends to be devoid of oxygen. This general
lack of available oxygen limits the biological
removal of ammonia nitrogen (NH3/NH4 - N) via
nitrification in these SF wetlands, but the system is
still very effective for removal of BOD, TSS,
metals, and some priority pollutant organics since
their treatment can occur under either aerobic or
anoxic conditions. Nitrate removal via biological
denitrification can also be very effective since the
necessary anoxic conditions are always present and
sufficient carbon sources are usually available.
The limited availability of oxygen in these SF
systems reduces the capability for ammonia removal
via biological nitrification. As a result, a long
detention time in a very large wetland area is
required to produce low levels of effluent nitrogen
with typical municipal wastewater influents unless
some system modification is adopted. These
modifications have included installation of aeration
tubing at the bottom of the bed for mechanical
aeration, the use of an integrated gravel trickling
filter for nitrification of the wastewater ammonia,
and vertical flow wetland beds. These vertical flow
beds usually contain gravel or coarse sand and are
loaded intermittently at the top surface. The
intermittent application and vertical drainage
restores aerobic conditions in the bed permitting
aerobic reactions to proceed rapidly. Cyclic filling
and draining of a horizontal flow system has been
successfully demonstrated at the 130,000 gallons
per day SF wetland system in Minoa, NY. The
reaction rates for BOD5 and ammonia removal
during these cyclic operations were double the rates
observed during normal continuously saturated
flow.
The phosphorus removal mechanisms available in all
types of constructed wetlands also require long
detention times to produce low effluent levels of
phosphorus with typical municipal wastewater. If
significant phosphorus removal is a project
requirement then a FWS wetland will probably be
the most cost effective type of constructed wetland.
Phosphorus removal is also possible with final
chemical addition and mixing prior to a final deep
settling pond.
The minimal acceptable level of preliminary
treatment prior to a SF wetland system is the
equivalent of primary treatment. This can be
accomplished with septic tanks or Imhoff tanks for
smaller systems or deep ponds with a short
detention time for larger systems. The majority of
existing SF wetland systems treating municipal
waste waters are preceded by either facultative or
aerated ponds. Such ponds are not necessarily the
preferred type of preliminary treatment. At most of
these existing systems the SF wetland was selected
to improve the water quality of the pond effluent.
Since the SF wetland can provide very effective
removal for both BODS and TSS, there is no need to
provide for high levels of removal of these
constituents in preliminary treatments.
The SF wetland does not provide the same level of
habitat value as the FWS wetland because the water
in the system is not exposed and accessible to birds
and animals. However, wildlife will still be present,
primarily in the form of nesting animals, birds, and
reptiles. If provision of more significant habitat
values is a project goal it can be accomplished with
deep ponds interspersed between the SF wetland
cells. The first pond in such a system would be
located after the point where water quality is
approaching at least the secondary level
APPLICABILITY
SF wetland systems are best suited for small to
moderate sized applications (<_ 227, 100 liters/day or
<_60,000 gallons per day) and at larger systems
where the risk of public contact, mosquitoes, or
potential odors are major concerns. Their use for
on-site systems provides a high quality effluent for
in-ground disposal, and in some States a significant
reduction in the final disposal field area is allowed.
SF wetlands will reliably remove BOD, COD, and
TSS, and with sufficiently long detention times can
also produce low levels of nitrogen and phosphorus.
Metals are removed effectively and about a one log
reduction in fecal coliforms can be expected in
systems designed to produce secondary or advanced
secondary effluents.
ADVANTAGES AND DISADVANTAGES
Some advantages and disadvantages of subsurface
flow wetlands are listed below.
Advantages
• SF wetlands provide effective treatment in a
passive manner and minimize mechanical
equipment, energy, and skilled operator
attention.
• SF wetlands can be less expensive to
construct and are usually less expensive to
operate and maintain as compared to
mechanical treatment processes designed to
produce the same effluent quality.
• Year-round operation for secondary
•
treatment is possible in all but the coldest
climates.
• Year-round operation for advanced or
tertiary treatment is possible in warm to
moderately temperate climates. The SF
wetland configuration provides more
thermal protection than the FWS wetland
type.
• SF wetland systems produce no residual
biosolids or sludges requiring subsequent
treatment and disposal.
• The SF wetland is very effective and reliable
for removal of BOD, COD, TSS, metals,
and some persistant organics in municipal
wastewaters. The removal of nitrogen and
phosphorus to low levels is also possible but
requires a much longer detention time.
• Mosquitoes and similar insect vectors are
not a problem with SF wetlands as long as
the system is properly operated and a
subsurface water level maintained. The risk
of contact by children and pets with
partially treated wastewater is also
eliminated.
Most of the water contained in the SF
wetland is anoxic and this limits the
potential for nitrification of wastewater
ammonia. Increasing the wetland size and
detention time will compensate, but this may
not be cost effective. Alternative methods
for nitrification in combination with a SF
wetland have been successful. SF wetlands
cannot be designed for complete removal of
organic compounds, TSS, nitrogen, and
coliforms. The natural ecological cycles in
these wetlands produce "background"
concentrations of these substances in the
system effluent.
• SF wetland systems can typically remove
fecal coliforms by at least one log. This is
not always sufficient to meet discharge
limits in all locations and post disinfection
may be required. UV disinfection has been
successfully used in a number of
applications.
• Although SF wetlands can be smaller than
FWS wetlands for the removal of most
constituents, the high cost of the gravel
media in the SF wetland can result in higher
construction costs for SF systems larger
than about 227,100 liters per day (60,000
gallons per day).
Disadvantages
• A SF wetland will require a large land area
compared to conventional mechanical
treatment processes.
The removal of BOD, COD, and nitrogen in
SF wetlands are continuously renewable
processes. The phosphorus, metals, and
some persistent organics removed in the
system are bound in the wetland sediments
and accumulate over time.
• In cold climates the low winter water
temperatures reduce the rate of removal for
BOD, NH,, and NO,. An increased
detention time can compensate for these
reduced rates but the increased wetland size
in extremely cold climates may not be cost
effective or technically possible.
DESIGN CRITERIA
Published models for the design of SF wetland
systems have been available since the late 1980's.
More recent efforts in the mid to late 1990's have
produced three text books containing design models
for SF wetlands (Reed, et al 1995, Kadlec & Knight
1996, Crites & Tchobanoglous, 1998). In all three
cases, the models are based on first order plug flow
kinetics, but results do not always agree due to the
author's developmental choices and because the
same databases were not used for derivation of the
models. The Water Environment Federation (WEF)
presents a comparison of the three approaches in
their Manual of Practice on Natural Systems (WEF,
2000) as does the US EPA design manual on
wetland systems (EPA, 2000). The designer of a SF
wetland system should consult these references and
select the method best suited for the project under
consideration. A preliminary estimate of the land
area required for a SF wetland can be obtained from
Table 1 of typical areal loading rates. These values
can also be used to check the results from the
previously cited references.
The SF wetland size is determined by the pollutant
which requires the largest land area for it's removal.
This is the bottom surface area of the wetland cells
and, for that area to be 100 percent effective, the
wastewater flow must be uniformly distributed over
the entire surface. This is possible with constructed
wetlands by careful grading of the bottom surface
and use of appropriate inlet and outlet structures.
The total treatment area should be divided into at
least two cells for all but the smallest systems.
Larger systems should have at least two parallel
trains of cells to provide flexibility for management
and maintenance.
These wetland systems are living ecosystems and
the life and death cycles of the biota produce
residuals which can be measured as BOD, TSS,
nitrogen, phosphorus and fecal coliforms. As a
result, regardless of the size of the wetland or the
characteristics of the influent, in these systems there
will always be a residual background concentration
of these materials. Table 2 summarizes these
background concentrations.
It is necessary for the designer to determine the
water temperature in the wetland because the
removal of BOD, and the various nitrogen forms are
temperature dependent. The water temperature in
large systems with a long HRT (>10 days) will
approach the average air temperature except during
subfreezing weather in the winter. Methods for
estimating the water temperature for wetlands with
a shorter HRT (<10 days) can be found in the
published references mentioned previously.
It is also necessary to consider the hydraulic aspects
of system design because there is significant
frictional resistance to flow through the wetland
caused by the presence of the gravel media and the
plant roots and other detritus. The major impact of
this flow resistance is on the configuration selected
for the wetland cell. The longer the flow path the
higher the resistance will be. To avoid these
hydraulic problems an aspect ratio (L: W) of 4:1 or
less is recommended. Darcy's law is generally
accepted as the model for the flow of water through
SF wetlands and descriptive information can again
be found in the published references mentioned
previously. The flow of water through the wetland
cell depends on the hydraulic gradient in the cell and
on the hydraulic conductivity (kJ, size, and porosity
(n) of the media used. Table 3 presents typical
characteristics for potential SF wetland media.
These values can be used for a preliminary estimate
and for design of very small systems. For large
scale systems the proposed media should be tested
to determine these values.
TABLE 1 TYPICAL AREAL LOADING RATES FOR SF CONSTRUCTED WETLANDS
Constituent Typical Influent Target Effluent Mass Loading Rate
Concentration mg/L Concentration mg/L Ib/ac/d*
Hydraulic Load (in./d) 3 to 12**
BOD 30 to175 10 to 30 60 to 140
TSS 30 to 150 10 to 30 40 to 150
NH3/NH4 as N 2 to 35 1 to 10 1 to 10
N03 as N 2 to 10 1 to 10 3 to 12
TN 2 to 40 1 to 10 3 to 11
TP 1 to 10 0.5 to 3 1 to 4
Note: Wetland water temperature » 20°C.
TABLE 2 "BACKGROUND" SF
WETLAND CONCENTRATIONS
Constituent Units Concentration
Range
BODS mg/L 1 to 10
TSS mg/L 1 to 6
TN mg/L 1 to 3
NH)NH4 as N mg/L less than 0.1
NO, as N mg/L less than 0.1
TP mg/L less than 0.2
Fecal Coliforms MPN/100ml 50 to 500
Source: Reed et al., 1995 and U.S. EPA, 1993
PERFORMANCE
A lightly loaded SF wetland can achieve the
"background" effluent levels given in Table 2. In
the general case, the SF constructed wetland is
typically designed to produce a specified effluent
quality and Table I can be used for a preliminary
estimate of the size of the wetland necessary to
produce the desired effluent quality. The design
models in the referenced publications will provide a
more precise estimate of treatment area required.
Table 4 summarizes actual performance data for 14
SF wetland systems included in a US EPA
Technology Assessment (EPA, 1993).
In theory, the performance of a SF wetland system
can be influenced by hydrological factors. High
evapotranspiration (ET) rates may increase effluent
concentrations, but this also increases the HRT in
the wetland. High precipitation rates dilute the
pollutant concentrations but also shorten the HRT
in the wetland. In most temperate areas with a
moderate climate these influences are not critical for
performance. These hydrological aspects need only
be considered for extreme values of ET and
precipitation.
OPERATION AND MAINTENANCE
The routine operation and maintenance (O&M)
requirements for SF wetlands are similar to those
for facultative lagoons, and include hydraulic and
water depth control, inlet/outlet structure cleaning,
grass mowing on berms, inspection of berm
integrity, wetland vegetation management, and
routine monitoring.
The water depth in the wetland may need periodic
adjustment on a seasonal basis or in response to
increased resistance over a very long term from the
accumulating detritus in the media pore spaces.
Mosquito control should not be required for a SF
wetland system as long as the water level is
maintained below the top of the media surface.
Vegetation management in these SF wetlands does
not include a routine harvest and removal of the
TABLE 3 TYPICAL MEDIA CHARACTERISTICS FOR SF WETLANDS
Media Type Effective Size D,o
(mm)* Porosity, n (%) Hydraulic Conductivity ks
(ft3 /ft2/d)*
Coarse Sand 2 28 to 32 300 to 3,000
Gravelly Sand 8 30 to 35 1,600 to 16,000
Fine Gravel 16 35 to 38 3,000 to 32,000
Medium Gravel 32 36 to 40 32,000 to 160,000
Coarse Rock 128 38 to 45 16 x 104 to 82 x 104
" mm x 0.03937 = inches
ft3/ft2/d x 0.3047 = m3/m2/d, or x 7.48 = gal/ft2/d
Source: Reed et al., 1995.
TABLE 4 SUMMARY OF PERFORMANCE FOR 14 SF WETLAND SYSTEMS*
Constituent Mean Influent mg/L Mean Effluent mg/L
BODS 28** (5-51)*** 8** (1-15)***
TSS 60(23-118) 10 (3-23)
TKN as N 15(5-22) 9(2-18)
NH3/NH4 as N 5(1-10) 5(2-10)
N03 as N 9(1-18) 3(0.1-13)
TN 20(9-48) 9(7-12)
TP 4(2-6) 2(0.2-3)
Fecal Coliforms (#/100ml) 270,000 (1,200-1,380,000) 57,000 (10-330,000)
* Mean detention time 3 d (range 1 to 5 d).
** Mean value.
*** Range of values.
Source: U.S. EPA, 1993.
harvested material. Plant uptake of pollutants
represents a relatively minor pathway so harvest and
removal on a routine basis does not provide a
significant treatment benefit. Removal of
accumulated litter is unnecessary, and in cold
climates it serves as thermal insulation to prevent
freezing in the wetland bed. Vegetation
management may also require wildlife management,
depending on the type of vegetation selected for the
system, and the position of the water. Animals such
as nutria and muskrats have been known to
consume all of the emergent vegetation in
constructed wetlands. These animals should not be
attracted to a SF wetland as long as the water level
is properly maintained. Routine water quality
monitoring will be required for all SF systems with
an NPDES permit, and the permit will specify the
pollutants and frequency. Sampling for NPDES
monitoring is usually limited to the untreated
wastewater and the final system effluent. Since the
wetland component is usually preceded by some
form of preliminary treatment, the NPDES
monitoring program does not document wetland
influent characteristics. It is recommended, in all
but the smallest systems that periodic samples of the
wetland influent be obtained and tested for
operational purposes in addition to the NPDES
requirements. This will allow the operator a better
understanding of wetland performance and provide
a basis for adjustments if necessary.
COSTS
The major items included in the capital costs for SF
wetlands are similar to many of those required for
lagoon systems. These include land costs, site
investigation, site clearing, earthwork, liner, gravel
media, plants, inlet and outlet structures, fencing,
miscellaneous piping, etc., engineering, legal,
contingencies , and contractor's overhead and
profit. The gravel media and the liner can be the
most expensive items from this list. In the Gulf
States where clay soils often eliminate the need for
a liner the cost of imported gravel can often
represent 50 percent of the construction costs. In
other locations where local gravel is available but a
membrane liner is required the liner costs can
approach 40 percent of the construction costs. In
many cases compaction of the in-situ native soils
provides a sufficient barrier for groundwater
contamination. Table 5 provides a summary of
capital and O & M costs for a hypothetical 378,500
liters/day (100,000 gallons per day) SF constructed
wetland, required to achieve a 2 mg/L ammonia
concentration in the effluent. Other calculation
assumptions are as follows: influent NH,= 25 mg/L,
water temperature 20°C (68°F), media depth = 0.6
meters (2 ft), porosity = 0.4, treatment area = 1.3
hectares (3.2 ac), land cost =$12,3 55/hectare ($5,000/ac).
TABLE 5 CAPITAL AND O&M COSTS FOR 100,000 GALLONS PER DAY SF WETLAND
Item Cost $*
Native Soil Liner Plastic Membrane Liner
Land Cost $16,000 16,000
Site Investigation 3,600 3,600
Site Clearing 6,600 6,600
Earthwork 33,000 33,000
Liner 0 66,000
Gravel Media** 142,100 142,100
Plants 5,000 5,000
Planting 6,600 6,600
Inlets/Outlets 16,600 16,600
Subtotal $229,500 $295,500
Engineering, legal, etc. $133,000 $171,200
Total Capital Cost $362,500 $466,700
O & M Costs, $/yr $6,000/yr $6,000/yr
* June 1999 costs, ENR CCI = 6039
**12,000 cy of 0.75 in. gravel
TABLE 6 COST COMPARISON SF WETLAND AND CONVENTIONAL WASTEWATER
TREATMENT
Cost Item Process
Wetland SBR
Capital Cost $466,700 $1,104,500
O &M Cost $6,000/yr $106,600/yr
Total Present Worth Costs* $530,300 $2,233,400
Cost per 1000 gallons treated** $0.73 $3.06
*Present worth factor 10.594 based on 20 years at 7 percent interest (June 1999 costs, ENR CCI = 6039)
**Daily flow rate for 365 d/yr, for 20 yr, divided by 1000 gallons
Source: WEF, 2000.
Table 6 compares the life cycle costs for this
wetland to the cost for a conventional treatment
system designed for the same flow and effluent
water quality. The conventional process is a
sequencing batch reactor (SBR).
REFERENCES
Other Related Fact Sheets
Free Water Surface Wetlands
EPA 832-F-00-024
September, 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. Crites, R.W., G. Tchobanoglous (1998) TVA
Small and Decentralized Wastewater Mr James Watson
Management Systems, McGraw Hill Co., 311 Broad Street, HB 25 270C - C
New York, New York. Chattanooga, TN 37402-2801
2. Kadlec, R.H., R. Knight (1996)Treatment EMC Group, Inc.
Wetlands, Lewis Publishers, Boca Raton, Mr Charles King
Florida. PO Box 22503
Jackson, MS 39205
3. Reed, S.C., R.W. Crites, E.J. Middlebrooks
(1995) Natural Systems for Waste Village of Minoa WWTP
Management and Treatment - Second Mr Steve Giarrusso
Edition, McGraw Hill Co, New York, New 213 Osborne Street
York. Minoa, NY 13116
4. U. S. EPA (1999) Free Water Surface The mention of trade names or commercial products
Wetlands for Wastewater Treatment: A does not constitute endorsement or recommendation
Technology Assessment, US EPA, OWM, for use by the U.S. Environmental Protection
Washington, DC. (in press.) Agency.
5. U.S. EPA (2000) Design Manual
Constructed Wetlands for Municipal
Wastewater Treatment, US EPA CERI,
Cincinnati, Ohio (in press.)
6. US. EPA (1993) Subsurface Flow
Constructed Wetlands for Wastewater
Treatment A Technology Assessment, EPA
832-R-93-008, US EPA OWM,
Washington, DC.
7. Water Environment Federation (2000)
Natural Systems for Wastewater Treatment,
MOP FD-16, WEF, Alexandria, Virginia (in
press.)
ADDITIONAL INFORMATION
Southwest Wetlands Group
Mr Michael Ogden
901 W. San Mateo, Suite M,
Santa Fe, NM 87505
City of Mandeville
Mr Joe Mistich, Public Works Director
3101 E. Causway Approach
Mandeville, LA 70448-3592
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, NW
Washington, D.C., 20460
oMTB
ExCelerlCe In CorI"p irxt tlxaigh op[" tecN*al soluUgtt
MUNICIPAL TECHNOLOGY BRAN H