Introduction and a note of caution on treatment methodologies
"Laser particle sizing has also indicated that a considerable proportion of the particulates in road runoff are less than 10 µm. This size fraction is difficult to capture in current stormwater pollution control devices and has been shown to contain significant quantities of heavy metals, which are of concern in aquatic ecosystems." (Drapper et al)
In the extreme case, treatment of urban and suburban stormwater by traditional wastewater treatment plants (WWTP) based on the tertiary removal process may be required. This may imply considerable capital costs and operation & maintenance.
Rate of settling in pure, still water
Rate of settling in pure, still water (temp=10oC, sp. gravity of particles=2.65, shape of particles=spherical) (Welch, 1935)
Wetlands are receiving attention as attractive systems for removing
pollutants from stormwater surface runoff before the runoff enters
downstream lakes, streams, and other open water bodies. Wetlands have long
been employed for the treatment of wastewaters from municipal, industrial
(particularly acid mine drainage), and agricultural sources. The U.S.
Environmental Protection Agency (EPA) encourages the use of constructed
wetlands for water pollution control.
"The term `wetlands' means those areas that are inundated or
saturated by surface or ground water at a frequency and duration
sufficient to support, and that under normal circumstances do support, a
prevalence of vegetation typically adapted for life in saturated soil
conditions. Wetlands generally include swamps, marshes, bogs, and similar
areas".
A significant issue is whether natural wetland systems should be used
as stormwater control measures. In general, natural wetlands have been
found to be somewhat less predictable than constructed wetlands in terms
of pollutant removal efficiency. This difference may be due to the fact
that constructed wetlands have generally been engineered to provide
favorable flow capacity and routing patterns.
People often question whether it is appropriate to use a natural,
healthy wetland for such purposes. The concern is whether the modified
flow regime and the accumulation of pollutants will result in undesirable
environmental effects. A general consensus from the literature is that the
use of a healthy natural wetland for stormwater pollution control should
be discouraged.
One pre-treatment technique would be to use pond areas to provide an
opportunity for suspended materials to settle out before the flows enter
the wetland. Other possible options include routing inflows to the
wetlands through upstream grass swales, oil/water separators, heavily
vegetated areas (e.g. thick, shallow cattail area), and overland flow
areas.
"....... several trends were noted. First, constructed systems were
generally found to have a higher average removal performance than natural
systems, with less variability; and second, larger wetlands as compared to
watershed size also showed the same trend, a higher average removal
performance, with less variability".
Adequate sizing is imperative:
Following is a listing of the wetlands that were researched for their ability to treat stormwater runoff as well as a map of the USA showing their location. Some of the constructed wetlands are located in regions with harsher climate and/or more intensive snow cover than in Nova Scotia (cf.Strecker et al., 1992).
Design Features of Constructed Wetlands for Nonpoint Source (NPS) Treatment
Constructed wetlands are employed to treat nonpoint sources such as excess runoff, eroded soil and nutrients. Natural wetlands should not be used to treat NPS pollution without first conducting a thorough environmental assessment to insure that the wetland can support the necessary treatment without becoming degraded. Likewise, using wetlands for treating toxic wastes is not recommended without extensive evaluation.
How do constructed wetlands work to reduce NPS pollution?
Constructed wetlands provide storage capacity for runoff water within their basins. In addition, organic soils found in mature wetland systems act like a sponge to retain water and allow infiltration of surface water into the groundwater. This decreases not only runoff volume, but also peak discharges which may otherwise cause flooding or erosion downstream. As channelized flow enters a wetland, the velocity is reduced as the water spreads out over the wetland. Velocity is further reduced by the frictional resistance of aquatic vegetation. It is this reduction in velocity which is most responsible for sediment and nutrient retention in constructed wetlands. As the velocity of flowing water slows, it loses the energy needed to keep particles in suspension, and these particles and associated nutrients then settle out.
Nutrients such as phosphorus and nitrogen are trapped and retained in constructed wetlands by several mechanisms: burial in sediments, chemical breakdown (e.g., denitrification and ammonia volatilization), and through assimilation by aquatic plants and bacteria. The primary mechanism for phosphorus removal is adsorption to wetland soils and precipitation reactions with calcium, aluminum and iron. In most cases, phosphorus retention by vegetation is only seasonal, as it is taken up by growing plants and released with vegetation dieback in the Fall.
How can you enhance the functioning of constructed wetlands?
Ideally, for optimal performance, the size of the constructed wetland should be from 1 to 5 % of the size of its drainage area. Designing hydraulic loading by analyzing existing channel discharge or watershed runoff coefficients is more precise than the 1 to 5 % rule above and this more intensive hydraulic loading determination is recommended.
Phosphorus removal efficiency declines with increasing phosphorus loading. With high loading rates, adsorption sites become saturated and there is insufficient capacity for biotic assimilation. There are cases where overloaded wetlands have become phosphorus sources to downstream lakes.
The longer water remains in the wetland the greater chance of sedimentation, adsorption, biotic processing and retention of nutrients. Proper sizing of the wetland is important, but restricting the size of the wetland outlet is also effective. For wetlands with channel flow, the outlet cross sectional area should be less than 1/3 that of the inlet.
Peak water velocities through the wetland should not exceed 1.5 fps. High velocities can wash out rooted vegetation and scour deposited sediments. Ideally, flow velocities should be less than 0.6 fps.
fine-textured clay soils and soils with high organic matter content have more adsorption sites for retaining nutrients. Available calcium, aluminum and iron in the soil enhance precipitation reactions with phosphorus.
Sinuous edges between the terrestrial and aquatic zones provide more resistance to flow and more edge habitat for plants and animals. Islands create additional edge, plus they provide refuge from predation for nesting birds.
The terrestrial-aquatic boundary should have a very gradual slope. This allows for the establishment of a continuum of emergent species and reduces the erosive effects of waves hitting a sharp shoreline boundary.
Persistent emergent vegetation has stems which persist even after the growing season. This provides year-round resistance to water flow.
These plants include: cattail (Typha sp.), iris (Iris pseudacorus or I. Versicolor), rush (Juncus sp.), cordgrass (Spartina sp.), reedgrass (Calamagrostis sp.), sawgrass (cladium jamaicense) and switchgrass (Panicum virgatum).
Woody plants, such as alder (Alnus sp.), buttonbush (Cephalanthus occidentalis), black willow (Salix nigra) and others are useful edge species with persistent stems.
Aquatic bed or submergent vegetation removes nutrients seasonally, but does not offer significant frictional resistance to suspended sediments.
Constructed wetland planning should not overlook the need for long-term maintenance. Additional vegetation planting may be required to speed plant coverage, replace damaged plants or to try more suitable varieties. Perimeter fencing may be required. Maintenance may be needed to control the spread of undesired plant species such as purple loosestrife. Inlets and outlets can become blocked with debris which will require periodic removal. Inlet and outlet structures should be inspected weekly and especially following big storm events. Most importantly, if the wetland functions well as a sediment and nutrient trap, it may eventually require dredging to remove accumulated materials. Thus, vehicular access to the site must be provided for maintenance vehicles and possibly dredging equipment.
Case histories of constructed wetlands and ponds:
In contrast to the treatment of municipal or mining waste water, whose flow rates and compositions tend to be predictable and relatively constant, storm-water flows and compositions vary considerably, depending on the land uses in the catchment basin and the frequency and intensity of rain/snow events. In addition, constructed wetlands may not be effective in treating certain storm-water contaminants, such as road salt and some organic compounds.
Pretreatment of sediment using sedimentation/siltation ponds may be necessary to prevent the sediment from choking the wetland soils and rendering them ineffective.
Several trends were noted. First, constructed systems were generally found to have a higher average removal performance than natural systems, with less variability; and second, larger wetlands as compared to watershed size also showed the same trend, a higher average performance, with less variability. Assessment was made based on <2% and >2% size wetlands in relationship to the catchment areas, and 2% seems to be sufficient, although note the following quote, "........... at this time we are not suggesting that minimum of a 2 per cent DAR is the proper design criteria for constructed wetlands." (Strecker et al. 1992).
"People often question whether it is appropriate to use a natural, healthy wetland for such purposes. The concern is whether the modified flow regime and the accumulation of pollutants will result in undesirable environmental effects. .......................................... A general consensus from the literature is that the use of a healthy natural wetland for stormwater pollution control should be discouraged."
This facility consisted of a 30-acre detention basin with an average
depth of 1.2 feet and a 6.2-acre constructed wetland with an average depth
of 2.5 feet. The detention basin received stormwater and then discharged to the wetland. The contributing watershed consists of 600 acres of primarily
urban land use. The predominant vegetation in the wetland consists of
cattails with other emergent plant species.
Overall, they found very good results for the system. The following removal efficiencies were given:---
% removal for Detention basin:
TSS-91%
TP-78%
TN-85%
TPb-85%
% removal for Wetland:
TSS-87%
TP-36%
TN-24%
TPb-68%
The detention basin removed the fraction of pollutants that are more readily settled and treated, leaving the wetland with the finer, more difficult to treat pollutants.
Recommendations of Berezowsky, Boojum Technologies Ltd., Toronto:
Considering the diverse nature of the contaminants found in urban stormwater, the most effective solution appears to be a multi-stage system, such as the "marsh-pond-meadow" or the "Max-Planck-Institute" process.
The marsh-pond-meadow system: This consists of (1) a bar screen and aeration cell using a floating surface aeratior, (2) a lateral-flow marsh planted with cattails in a sand medium, (3) a pond with aquatic macrophytes and herbivorous fish, (4) a meadow planted with red canary grass, and (5) a chlorination chamber. The removal efficiency is reported to be 77% for ammonia nitrogen and 82% for total phosphorus.
The Max-Planck-Institute Process: This design is used in France and was a model for a system implemented in Oaklands Park, United Kingdom. The system consists of four or five stages in cascade, each with several basins laid out in parallel and planted with emergent macrophytes in gravel. The flow pattern in the first two stages is vertical, while the final ones have horizontal flow. In the French system, removal of suspended solids and BOD is good, but with poor results for nitrogen and phosphorus, perhaps because of high loading rates.
Wetlands treatment of stormwater has been reported (Reuter et al 1992,
Verry et al 1982, Brown 1985). Results from a newly constructed wetland
to treat stormwater in a cold climate region of California at Lake Tahoe
were encouraging. Gravel-filled constructed wetlands (Lake Tahoe) provide
a much greater surface area for bacterial attachment than is possible in
natural wetlands, thereby enhancing the substratum to water volume contact
ratio, and hence need less land area than natural wetlands. Constructed
Wetlands are most suitable as mitigation for small development projects
where land is limited. These projects include golf courses that receive
fertilizers, small commercial facilities, small housing developments, etc.
They are generally limited in efficiency by the volume of water they
can retain (4-8 day retention). It may be unrealistic to rely on small
constructed wetlands to treat large urban areas. Other solutions like
partial diversion, a combination of treatment systems, etc will have to be
found. The age-old excuse of questioning the utility of constructed
wetlands in cold climate regions was irrefutably proven to be false in not
only the Lake Tahoe case but also in other cases elsewhere.
State-of-the-art stormwater treatment system for removing phosphorous
in runoff from a 460-acre residential development incorporates a dry pond
for detention and a wet vault for pretreatment, followed by a filter with
underdrains.
Based on peer reviewed literature, a concept was developed in the State of Colorado, where experts advised mandatory removal of 50% of the expected post-development export of total phosphorus in urban stormwater before approving new subdivisions . They felt anything above 50% would be unduly costly. For that, their consultants recommended utilizing wet detention ponds (not dry ponds) to intercept the first half-inch of runoff (the first flush carries most of the urban pollutants, not just TP), a certain detention time (based on chemistry, etc.) followed by sand filtration prior to discharge into natural watercourses, directly or indirectly. It appears, there was a successful demonstration project, the Shop Creek Project which implemented sound engineering methodology of reducing the TP load in the storm water in a new subdivision prior to discharge into the Cherry Creek Reservoir (consult the Cherry Creek Basin Water Quality Authority, Englewood, Colorado).
Summary of Design Criteria Recommendations for "Settleability Design Storms":
Fairfax County, Virginia:
22.9 mm (Runoff amount)
Delaware Raritan Canal Comm.:
31.8 mm in 2 hrs. (Rainfall amount)
South Florida Flood Management District:
25.4 mm (Runoff amount)
3 yr. storm (Rainfall amount)
Austin, Texas:
12.7 mm (Runoff amount)
Central Florida:
12.7 mm (Runoff amount)
After evaluation of the literature, the rainfall characteristics in Denver and the various concerns, the authors chose the following basic design parameters for the standard design:
Provide a detention volume equal to 12.7 mm of runoff from the impervious surfaces in the watershed.
Provide an outlet to drain the detention volume in approximately 40 hours and use a perforated riser pipe for an outlet.
Provide a follow-up sand filter (masonry sand gradation) with underdrains. The surface area of the filter bed is to be based on a maximum hydraulic loading of 0.61 m3/sec/ha.
Allow both wet and dry ponds, but encourage wet ponds.
Require the pond length to be at least twice the pond width to reduce short circuiting.
Provide a baffle structure near the inflow point to diffuse the inflow currents.
Permit the water quality enhancement facilities to be a part of on-site or regional stormwater quantity management ponds.
The 12.7 mm of runoff from impervious surfaces can be calculated using,
VQ = 1.27 A I
in which, VQ = required pond volume in cubic meters
A = area of the tributary watershed in hectares
I = impervious portion of tributary watershed in percent
It is recommended that this water quality volume be located, wherever possible, within the 100-year flood routing facilities.
The water quality detention pond outlet releases its flow onto a sand filter consisting of a 30 centimetre thick layer of mortar sand over a gravel/pipe underdrain. Sizing of the filter bed depends on the allowable unit loading rate for the filter material which is built into the following equation. Thus, the surface area for the filter can be calculated using,
AF = 1.65 QQ
in which, AF = surface area of sand filter in hectares
QQ = peak discharge rate from the water quality pond in m3/sec
The peak discharge rate from the outlet can also be easily calculated using,
QQ = 0.00191 a DQ1.4
in which, QQ = peak discharge from water quality outlet in m3/second
a = area of one row of perforations in the riser pipe in cm2
DQ = maximum depth of water above bottom row of perforations in riser in meters
Examination of the equation for AF reveals that the allowable unit hydraulic loading rate on the sand filter (i.e. 0.61 m3/sec/ha) is one-fifth to one-tenth of what can be expected for clean mortar sand. The difference represents a safety factor which accounts for the clogging of the filler with time. Estimates indicate that under the permitted loading rates the filter is expected to last 2 to 6 years before the top 15 cm layer of sand has to be replaced.
An alternative pond configuration provides for a permanent pool of water having a volume equal to 13 mm of runoff from all tributary impervious areas in the watershed.
This is a preferred configuration since the existing field data indicate "wet" ponds outperform "dry" ponds.
It is also expected that the "wet" ponds will provide greater aesthetic appeal.
(cf. University of Wisconsin-Extension UWEX and Wisconsin Priority Watersheds Program GWQ 017)
Stormwater ponds are not a new, untested idea. They are widely used due
to their effectiveness in removing pollutants, their long-term reliability
and their versatility in serving other needs such as reducing the risk of
flooding, and providing open space. Ponds designed for pollutant removal
have enough storage to hold all the runoff from a 1.5 inch storm. In an
average year, ponds this size will remove 80% of total suspended solids in
the runoff. They are most effective when they have permanent pools of
water 3 to 8 feet deep. A depth of 3 feet or more enhances settling rates,
and prevents sediments from being stirred up and washed out during the
next storm. However, depths greater than 8 feet may create problems due to
thermal stratification. During summer, the water in deeper ponds
stratifies into two layers that seldom mix- cooler bottom water and warmer
surface water. The cooler bottom water is likely to have no oxygen.
Without oxygen, water chemistry changes and pollutants such as phosphorus
are likely to be released into the water rather than staying in the
sediment.
Key features:
Permanent pool: 3 to 8 feet deep
Basinshape: 3 times as long as it is wide
Inlet and outlet locations: at opposite ends of the basin
Capacity: large enough to hold the runoff from a 1.5 inch storm
Detention time: long enough for most sediment to settle out (6-24 hours)
Emergency overflow: for storms that exceed basin capacity
Safety features: gentle side slopes, underwater safety shelf, an
outlet in the embankment, a trash rack over the outlet pipe, and signs
Maintenance features: an access road, a forebay where much of the
sediment settles, and an emergency drain to completely dewater the pond
Landscaping: to provide attractive scenery and open space for the
neighborhood and to prevent nuisances such as geese (an unmowed landscape
with shrubs and trees also discourages geese)
Urban detention ponds, typically with well-cropped lawns leading
directly up to water's edge have been partly responsible for the
phenomenal increase in Canada geese across many states. Literature cites a
typical Canada goose dropping frequency at 28-92 times/day, dry wt. of
droppings ranges 1.17-1.9 g, and dry phosphorus content at 1.34-1.0%. In
addition, the geese are known to be carriers of Salmonella,
Chlamydia, and the vectors for swimmers itch. A study on Green
Lake, Seattle estimated that 52% of the annual phosphorus budget was
attributable to waterfowl.
Hence it is necessary to design ponds and wetlands in a manner that
they would not be too conducive to the geese.
Integrating Constructed Wetlands With Stormwater Management
Stormwater management is a subset of land use planning and urban design. Both exercises must be coordinated and consider the downstream impact of urban development with respect to water use and management and aquatic ecosystem conservation.
Stormwater management involves the use of many devices and techniques with a range of purposes and benefits, including:
flood protection and flow control
water quality improvement
landscape and recreational amenity
provision of wildlife habitat
A typical stormwater management system:
Gross pollutant trap (GPT) – to trap artificial and natural litter and
coarse particles like gravel and sand.
Pollution control pond/constructed wetland inlet zone – to trap sand- to
silt-sized particles and improve water quality. This module can have some
secondary benefits, including landscape aesthetics and flow attenuation.
Macrophyte zone i.e., an area of plants such as rushes, reeds and sedges – to
improve water quality through the trapping of fine particles and soluble
pollutants. This module can have some secondary benefits, including
wildlife habitat and flow attenuation.
Lake/island – to provide passive recreation, landscape enhancement and
wildlife habitat. Depending on the outlet structure, lakes can significantly
attenuate flow. Lakes can also provide water quality benefits, but this
function can be compromised if the lake attracts large populations of
wildlife, which can degrade water quality.
Flood retarding basin – to protect downstream areas from flooding and
to control stream hydrology. This module can provide more open space
within the urban landscape. Stormwater treatment modules located in
flood retarding basins can benefit from the extra hydrologic control
provided by the basin.
In practice, the boundaries of these stormwater management modules need
not be as distinct as in Figure 1. Early planning and identifying
the uses and their priorities for each module in a stormwater management
system allows improved integration of the modules and optimal utilisation
of the available open space.
Removal of Gross Pollutants From Stormwater Runoff Using Liquid/Solid Separation Structures for four in-situ technologies, the Vortechnics, Stormceptor, CDS Technologies, and traditional baffle boxes
These stand-alone proprietory devices are not expected to remove all of the typical post-development post-human occupation derived pollutants, for e.g., phosphorus, nitrogen, heavy metals, hydrocarbons, pesticides. This is because varying percentages of these post-development pollutants absorb/adsorb to particles smaller than 100 microns and/or are in dissolved form. One recommended way is to develop specially constructed wetlands to polish the effluent from these stand-alone devices. The wetland plants have to be carefully selected by `qualified and experienced wetland biologists' to remove the specific pollutants that are inevitable after the whole watershed is populated. These stand-alone devices will indeed remove larger particles to a considerable degree and/or act as gross pollutant traps thus serving as pre-treatment devices.
For a pictorial representation of a gross pollutant trap together with a constructed wetland, click on Figure 1.
Removal of Gross Pollutants From Stormwater Runoff Using Liquid/Solid Separation Structures for four in-situ technologies
During 1998-99, evaluations were conducted for the City of Orlando, the City of Winter Haven, and the City of Atlantic Beach related to the removal of gross pollutants. Based on information found in the literature and information obtained from technology manufacturers. removal efficiencies were estimated and compared for the four separate technologies.
The evaluation considered removal efficiencies for litter, debris, and coarse sediments; estimated inmitial cost; and operation and maintenance requirements.
Based on removal efficiencies for coarse sediments, removal efficiencies were, estimated for common stormwater constituents, including total nitrogen, total phosphorus, total suspended solids, BOD, and heavy metals. Based on typical fractions of particulate matter in runoff, liquid/solid separators are capable of removing approximately 20-50% of nutrients and heavy metals under ideal conditions.
Limitations of liquid/solid separators must be understood when considering these systems for retrofit applications. While performing the evaluations, it became apparent that there is insufficient field data to accurately predict the removal efficiencies for various gross pollutants contained in stormwater runoff in the United States.
Gross pollutants in stormwater runoff generally consist of litter, debris, and coarse sediments. Most gross pollutants cannot be sampled by traditional automatic samplers, and gross pollutants are often overlooked when evaluating the impact of stormwater runoff on receiving waters.
Litter is typically defined as human-derived material, including paper, plastic, metal, glass, cloth, or any other man-made material.
Debris is typically defined as any natural organic matter transported by stormwater runoff, such as leaves, twigs, and grass clippings.
Coarse sediments are defined as inorganic particulates. Particle diameters of inorganic particulates considered as gross pollutants vary from 5 mm (or 5,000 µm) to much smaller diameter suspended solids.
Comparison of Estimated Removal Efficiencies (cf.Herr and Harper)
The removal of sediments from stromwater runoff using liquid/solids separation structures will remove a portion of the particulate fraction of various pollutants contained in runoff which attach to sediment particles. A typical distribution of dissolved and particulate pollutant runoff fractions for residential runoff is provided in Table.
However, particulate matter contributing to loadings of nutrients and havey metals in stormwater runoff is typically 500-100 µm or smaller. The removal efficiencies for particles of this size range from 20-70%, with lower removals at smaller particle sizes. For purposes of this evaluation, a removal efficiency of 50% is assumed for particles in the 0.1-0.5 nun range.
Estimated Net Mass Reduction in Stormwater Constituents Achieved Based on 70% TSS Removal (cf.Herr and Harper)
Parameter
Estimated Annual Mass Load Reduction (%)
Total N
30
Total P
25
TSS
70
BOD
20
Cadmium
15
Chromium
18
Copper
15
Lead
38
Nickel
15
Zinc
33
Capital Cost Comparison for Liquid/Solids Separation Structures (cf.Herr and Harper)
Perhaps the first facility in North America, the City of Nepean within the
Regional Municipality of Ottawa-Carleton has augmented the conventional
retention pond treatment system with ultraviolet light instal lation. The
system will handle surface runoff from new subdivisions located near the
Rideau River and the settled stormwater will be subjected to a minimum 20
seconds exposure to UV radiation.
References
Berezowsky, M. 1997. Constructed Wetlands for Remediation of Urban Waste Waters. In Eyles, N. (Ed.). Environmental Geology of Urban Areas. Geological Association of Canada. 203-213.
Bland, J.K. 1996. A gaggle of geese ... or maybe a glut. In
LakeLine, North Am. Lake Manage. Soc. 16(1):10-11,45-47.
Brown, R.G. 1985. Effects of an urban wetland on sediment and
nutrient loads in runoff. In Wetlands. 4: 147-158.
Dillon, P.J., and Molot, L.A. 1996. Long-term phosphorus budgets and an examination of the steady state mass balance model for central Ontario lakes. Wat. Res. 30:2273-2280.
Drapper, D., Tomlinson, R., and Williams, P. An Investigation of the Quality of Stormwater Runoff From Road Pavements; A South-East Queensland Case Study. School of Environmental Engineering, Griffith University, Nathan Campus, Queensland, Australia. 8p.
Engel, S. 1985. Aquatic Community Interactions of Submerged Macrophytes.
Tech. Bull. No. 156. Dept. of Natural Resources, Wisconsin. 79pp.
Good, R.E., Whigham, D.F., and Simpson,L. 1978. Freshwater Wetlands,
Ecological Processes and Management Potential. Academic Press, New York.
Hart, W.C., Scott, R.S., and Ogden III, J.G. 1978. A Phosphorus
Loading Model for Lakes in the Shubenacadie Headwaters. Tech. Rpt. #2. 34p.
Herr, J.L., and Harper, H.H. Removal of Gross Pollutants From Stormwater Runoff Using Liquid/Solid Separation Structures. Environmental Research & Design, Inc., Orlando, FL. 14p.
Hickok, E.A., Hannaman, M.C., and Wenck, N.C. 1977. Urban Runoff
Methods. Vol. I. Non-structural Wetland Treatment. USEPA. EPA-600/2-77-217.
Hutchinson, N.J., Neary, B.P., and Dillon, P.J. 1991. Validation and use of Ontario's Trophic Status Model for establishing lake development guidelines. Lake and Reserv. Manage. 7(1): 13-23.
Jones, W.W. 1996. Design features of constructed wetlands for nonpoint source treatment. Lakeline, N. Am. Lake Manage. Soc. 16(3):14-15,52-53.
Lee, G.F., and Jones, R.A. 1990. Suggested Approach for Assessing Water Quality Impacts of Urban Stormwater Drainage. Presented at
Symposium on Urban Hydrology and Drainage Issues at the 26th Annual
American Water Resources Association Conference and Sy mposia, Denver,
Colorado, November 1990.
Mandaville, S.M. 2000. Limnology- Eutrophication and Chemistry, Carrying Capacities, Loadings, Benthic Ecology, and Comparative Data. Soil & Water Conservation Society of Metro Halifax. xviii, Synopses 1, 2, 3, 13, and 14. 210p.
Mandaville, S.M. 2000. Limnology in Nova Scotia: Lake Data and Predictive Phosphorus Models (Archives in Electronic Format. First Ed. Soil & Water Conservation Society of Metro Halifax. xii, 74p, a-d. 90p., & CD media.
Panuska, J.C., and Schilling, J.G. 1993. Consequences of Selecting Incorrect Hydrologic Parameters When Using the Walker Pond Size and P8 Urban Catchment Models. Lake and Reserv. Manage. 8(1): 73-76.
Reuter, J.E., Djohan, T. and Goldman, C.R. 1992. The Use of Wetlands for Nutrient Removal from Surface Runoff in a Cold Climate Region of California- Results from a Newly Constructed Wetland at Lake Tahoe. In J. Env. Manage. 36: 35-53.
Sartor, J.D., and Boyd, G.B. 1972. Water Pollution Aspects of Street Surface Contaminants. USEPA. EPA-R2-72-081.
Soil & Water Conservation Society of Metro Halifax. 1993. Compendium of Synopsis and Briefs, being extracts from credible literature in Theoretical/Applied Limnology with emphasis on Lake Restoration/Management. 135 p.
Soil & Water Conservation Society of Metro Halifax. 1999. Synopsis-3: Unit Loadings (Nonpoint and Point sources), and Bacteriological Contamination.
Strecker, E.W., Kersnar, J.M., Driscoll, E.D., and Horner, R.R. 1992. The Use of Wetlands for Controlling Stormwater Pollution. Technical Advisor: Thomas E. Davenport, U.S. EPA, Region V. The Terrene Institute. iv, 66pp.
Taylor, M.E., & Associates. 1992. Constructed Wetlands for Stormwater Management: A Review: Ontario Ministry of Environment and Energy. 52p.
Underwood, J.K. 1984. An Analysis of the Chemistry of Precipitation in Nova Scotia 1977-1980. PhD thesis. xvi,264p.
Urbonas, B., and Ruzzo, W.P. 1985. Standardization of Detention Pond
Design for Phosphorus Removal. In Procs. NATO Advanced Research Workshop,
France, Aug. 1985. NATO ASI Series, Vol. G10. Springer-Verlag. 1986.
USDA, 1986. Urban hydrology for small watersheds-Technical Release No. 55 (Sec. Ed.). 160p.
Verry, E.S., and Timmons, D.R. 1982. Waterborne Nutrient Flow through an Upland-Peatland Watershed in Minnesota. In Ecology. 63(5): 1456-1467.
Vokey, J. 1998. Development of Unit Urban Phosphorus Export Coefficients in the local watersheds of 2 Mesotrophic Lakes within the Halifax Regional Municipality (HRM), NS, Canada. Project-C. (2 Lakes: Settle and Bissett). Soil & Water Conservation Society of Metro Halifax. viii, 51p.
Walker, W.W. 1987. Phosphorus Removal by Urban Runoff Detention
Basins. In Lake and Reserv. Manage. N. Am. Lake Manage. Soc. 3: 314-326.
Waller, D.H., and Novak, Z. 1981. Pollution loading to the Great Lakes from municipal sources in Ontario. J. WPCF. 53(3): 387-395.
Welch, P. S. 1935. Limnology. McGraw-Hill Book Co., Inc. 471p.
Wong, T.H.F., Breen, P.F., Somes, N.L.G., and Lloyd, S.D. 1999. Managing Urban Stormwater Using Constructed Wetlands. Industry Report 98/7, Second Ed., 1999. CRC for Catchment Hydrology and the CRC for Freshwater Ecology, Monash University, Victoria, Australia. 50pp.
We salute the Chebucto Community Net (CCN) of Halifax, Nova Scotia, Canada for hosting our web site, and we applaud its volunteers for their devotion in making `CCN' the best community net in the world!
![[Img: animated doors]](../VIEW/ICON/AN/doorin2.gif){kind=icon}
for a bibliography on wetlands
![[Img-CDS+Constructed Wetland]](PIC/cds-wetland.jpg)
