793 23 Economics The economics of treatment wetlands consists of two major factors: capital costs and operating costs. The capital cost components of free water surface (FWS) and subsurface ow (SSF) wetlands are essentially the same, except for the cost of the gravel required for SSF wetlands (Campbell and Ogden, 1999; U.S. EPA, 2000a). However, SSF systems have generally been implemented for smaller ows than FWS systems. For instance, the system database compiled by the Water Environment Research Foundation (WERF) has 214 FWS wetlands with a median design ow of 1,050 m 3 /d, 707 HSSF wetlands with a median design ow of 9.5 m 3 /d, and 566 VF wetlands with a median design ow of only 2.1 m 3 /d (Wallace and Knight, 2006). System areas from the WERF database show 330 FWS wetlands with a median area of 1.6 ha (16,000 m 2 ), 710 horizontal subsurface ow (HSSF) wet- lands with a median area of 140 m 2 , and 544 vertical ow (VF) wetlands with a median area of 44 m 2 . Therefore, SSF wetlands do not enjoy the economy of scale experienced by FWS wetlands. There is now enough information to deter- mine approximate capital cost functions that represent these scale effects. Because wetland systems are constructed using local labor and local materials, it is not possible to offer precise universal cost estimates that will apply to all treatment sys- tems. Generally, the basic components of a wetland treatment system—earthwork, gravel (in the case of SSF wetlands), lin- ers, and plants—are produced in regional markets that are distance sensitive. For instance, the installed cost per cubic meter of gravel is highly dependent on the distance between the source of supply (a local gravel pit) and the site of wet- land construction. Labor costs are also highly variable. To assess the feasibility of a wetland treatment system, local cost gures should be used to compare the capital and oper- ating costs of a wetland system against that of other treatment technologies. Within the United States, Construction Cost Indices (CCI) are published by the Engineering News Record (ENR). These cost indices track inationary changes within the con- struction industry over time. The ENR CCI started at 100 in the year 1913 and has increased to 7,856 in March 2007. Cost indices are available as a national average, but are also pub- lished for 20 major metropolitan areas in the United States. For the purposes of this chapter, costs are based on the 2006 United States national average ENR CCI of 7,751. As a side note, construction in high-cost metropolitan areas is almost double that of low-cost metropolitan areas. In general, capital costs of treatment wetlands are comparable to alternative technologies for accomplishing the same task. However, the costs of operating a treatment wetland are typically much lower than for competing tech- nologies. Mechanical devices are always more energy inten- sive, and will always be more expensive to operate, than a passive wetland system (Type A) (Brix, 1999). The basic exchange is land for energy (Campbell and Ogden, 1999). As a consequence, the lifecycle cost of a wetland project, as represented by the present worth of capital and operating expenses, is very often quite favorable compared to alterna- tive treatment technologies. Operating costs can be quite low, especially for Type A passive systems. Energy costs are typically close to zero for gravity-driven FWS wetlands, and are generally low for all t y pes of treatment wetlands (see Table 1.1). Water quality monitoring is often a principal part of O&M costs. However, operation and maintenance (O&M) costs can become appre- ciable if it is attempted to maintain specic vegetation types, thus encountering “weeding” costs. 23.1 CAPITAL COSTS Although it is not possible to offer universal cost guidelines, every system shares a similar set of construction compo- nents. Therefore, it is possible to estimate the cost of each component within a regional market. The basic direct cost components of a wetland treatment system include: Land Site investigation and system design Earthwork Liners Media Plants Water control structures and piping Site work (site preparation, fencing, access roads, etc.) Human use facilities These costs include material, labor, overhead, and prot, and represent the contractors installed cost. Additionally, there are indirect costs associated with permitting, engineering, nancing, mobilization, and construction management. In general, these costs are all incurred prior to system start-up. Detailed estimates are usually made after nal sizing and sit- ing. More precise economic estimating is possible after nal design drawings have been prepared. REGIONAL VARIATION Economics vary geographically because of differing unit costs, and because of differences in the selection of materials • • • • • • • • • © 2009 by Taylor & Francis Group, LLC 794 Treatment Wetlands and other design features. The cost of labor and materials within a particular regional market plays a large role in the cost of a wetland treatment system. Cost differentials are even greater when comparing across worldwide geographic locations and their accompanying economies. The effect of regional market cost factors is illustrated in Figure 23.1, which demonstrates treatment wetland capital cost distri- butions for various locations. HSSF wetland systems in Poland (Kowalik and Obarska-Pempkowiak, 1998) exhibit lower capital costs than those in Nicaragua (Platzer et al., 2002) or the Czech Republic (Vymazal, 1996). Severn Trent tertiary systems in the United Kingdom (Green and Upton, 1994) are more expensive than those in the Czech Repub- lic; HSSF systems in the United States have a distribution of capital costs that spans the range from the inexpensive Czech systems to those that are more expensive than the U.K. systems. Some of the regional differences have to do with design sizing criteria. Different criteria are used in different coun- tries, and also at different times in the same country. Others have to do with structural specications. For instance, a num- ber of U.K. systems are sited in basins lined with brick or concrete, and some have stainless steel level and ow con- trol elements. Clearly, such systems will have greater capital costs than those sited in earthen basins with plastic piping and simplied ow control elements. There are also economies of scale, which will be addressed in a subsequent section. However, it is useful to rst examine the various components of capital costs in more detail. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1 10 100 1,000 10,000 Cost ($1000 USD/ha) Percentile Poland FWS USA Central America Czech USA Severn Trent FIGURE 23.1 Capital costs distribution for treatment wetlands. All are HSSF systems except FWS (United States). Costs adjusted to 2006 using CCI 7,751 and the 2006 exchange rate. Data for Poland from Kowalik and Obarska-Pempkowiak (1998) In Constructed Wetlands for Wastewater Treatment in Europe. Vymazal et al. (Eds.), Backhuys Publishers, Leiden, The Netherlands, pp. 217–225. Data for the Czech Republic from Vymazal (1996) Ecological Engineering 7: 1–14. Data for Severn Trent from Green and Upton (1994) Water Environment Research 66(3): 188–192. Data for Central America from Platzer et al. (2002) Investigations and Experiences with Subsurface Flow Con- structed Wetlands in Nicaragua, Central America. Mbwette (Ed.). Proceedings of the 8th International Conference on Wetland Systems for Water Pollution Control, 16–19 September 2002, Comprint International Limited: University of Dar Es Salaam, Tanzania, pp. 350 –365. Data for the United States: Various. DIRECT COSTS Land Land costs are highly site specic. Information on land avail- ability and land costs is generally obtained with the assis- tance of real estate professionals who are familiar with local market conditions. Wetlands are more land intensive than many other wastewater treatment processes. If land needs to be purchased for the project, this can be a signicant cost component. In the United States, treatment wetland land purchase prices have ranged from $3,000/ha in remote loca- tions with low population density and low agricultural utility to over $100,000/ha in urbanizing agricultural landscapes. Land acquisition in or near urban areas is sometimes viewed as preservation of green space, and valued for ancillary benets. Land costs can be a signicant fraction of the total capi- tal cost. For example, Wossink and Hunt (2003) identify three categories of land cost for urban stormwater wetlands in North Carolina: zero cost because the project is required for community green space, $125,000/ha for vacant land that may be used for residential development, and $550,000/ha for land that may be used for commercial development. As will be discussed, land costs occupy a special role in the present worth analysis of a wetland system. Site Evaluation The design and construction of a wetland requires that site characteristics be well understood—including soils, © 2009 by Taylor & Francis Group, LLC Economics 795 groundwater elevations, and site topography. These activi- ties usually precede or accompany engineering design, but are additional to that design. Topographic Survey The ground elevation of the site is a critical factor in design, because it controls the cut-and-ll calculations that normally dictate the elevations of berms and bottoms. Associated with balancing of earth import and export is the issue of the potential for gravity ow. Sometimes proper cell elevations can eliminate the need for one or more pumps, and thus may interact with cut-and-ll considerations. The topographic sur- vey will inuence the direction of ow and the sequencing of cells, and the need for long or short distribution and collec- tion canals, which for large systems can inuence the project cost. The potential need to level cell bottoms for purposes of evening the hydraulic ow distribution can only be evalu- ated with detailed site topography. The shallow water depths in wetlands, especially large FWS systems, creates a need for accurate as-built topography as an aid to understanding water depth and movement. The costs for such surveys are typically $50/ha–$500/ha, depending on scale and grid size requirements. For instance, the topographic survey for the Incline Village, Nevada, treatment wetland cost $370/ha for the 175-ha wetland, adjusted to 2006. However, the survey work for cell 4 of STA2 of the Everglades phosphorus control project required only $45/ha. Geotechnical Investigations Many small-scale wetland projects are designed in conjunc- tion with soil inltration systems. In these situations, it is common to use shallow soil borings or backhoe pits to deter- mine local soil characteristics. Costs for these initial site investigations vary with the size of the project. In the U.S., the cost for a site investigation can range from a few hundred dollars (for a single-home system) up to several thousand dol- lars (for a system serving a small community). Larger-scale projects, including those that discharge to surface waters, also require soil investigations. Even though such large projects rarely require liners, there is a need to assess the potential for seepage from the project, and hence the need for seepage collection canals. It is critical to deter- mine if site soils are adequate for the berms and levees, and if so how much compaction may be required, and how much allowance for subsidence. Soils that may be used for rooting media in FWS systems, as well as the gravel substrate for SSF systems, may need to be assessed for contaminants of concern, including nutrients. A modest amount of chemical testing may be required to identify any potential problems, or to form the basis for fore- casting the sorption life expectancy for contaminants. Hydrogeological Investigations The location of the groundwater table and direction of groundwater movement can be a critical factor in wetland design. For small community and on-site systems involving soil inltration, the depth to groundwater is an important consideration. For “normal” inltration beds (septic elds), there is a required minimum unsaturated depth that is likely to carry over to the wetland/inltration situation. For a wetland with a liner, it is also necessary to know the depth to groundwater, because rising, shallow water tables can lift a synthetic wetland liner, displacing air from the soil environment. This has the potential to create large under- liner bubbles that push the liner up out of the water; these are commonly called “whale backs.” The solution to such poten- tial difculties is the construction of an under-drain system beneath the wetland liner that vents air and controls the level of the water table. The need for this feature, and its associ- ated cost, will be determined through site-specic hydrogeo- logical investigations. In some cases, there may be a concern for regional use of the groundwater as a potable water supply. The treatment wetland might be viewed as a possible source of contamina- tion if partially treated water entered into the unprotected drinking water aquifer, and moved to the wells that withdraw potable water. This would usually occasion the need for a hydrogeological study to ascertain the depths and directions of regional groundwater ow, and the consequences of even small leaks from the treatment wetland to the water quality of the aquifer. This was the case at the Columbia, Missouri, proj- ect. The hydrogeological study included calibration and mod- eling to address this issue, at a cost of $750/ha for the 36-ha wetland, adjusted to 2006 (Brunner et al., 1992). Ea r thwork The construction of a wetland treatment system requires excavation and grading of the site to produce level basins that are enclosed by earthen berms. For small systems (generally less than 0.05 ha) backhoes or similar types of excavation equipment are commonly used. Larger basins are generally constructed using bulldozers or construction scrapers. Area- specic earthwork costs are the product of two components. The rst component is the cost to move earth, which is a volumetric (per cubic meter) cost. This cost component is a function of equipment costs, labor costs, and the source of earth supply (on-site or imported). The second compo- nent is the amount of earth that must be moved to grade the site. This areal requirement (m 3 of earth per m 2 of wetland area) is a function of the project site conditions. Earthwork costs are lowest on at sites that require minimal grading and have suitable soils on-site (low areal grading require- ment and volumetric cost). Sloping a site requires terracing, which increases earthwork costs (due to the large areal grad- ing requirement). If the ll needs to be imported, earthwork costs will increase (due to the high volumetric cost). Earth- work construction techniques are essentially the same for FWS and HSSF wetlands, and hence volumetric earthwork costs for the two types should be comparable for similar- sized wetlands. © 2009 by Taylor & Francis Group, LLC 796 Treatment Wetlands Clearing and Grubbing If the undeveloped site has undesirable vegetation, build- ings, or other existing features that are incompatible with the wetland, these will need to be removed as part of the earthwork process. Brush and trees were removed from the sites at Ouray, Colorado; Sorrento, Louisiana; and West Jack- son County, Mississippi, at an average cost of $9,800/ha. On larger projects, roads and ditches may require degrading, and buildings may require removal. FWS Wetlands In a study of two municipal FWS wetland systems (West Jackson County, Mississippi and Gustine, California) the U.S. Environmental Protection Agency (EPA) estimated a volumetric cost of $10.80/m 3 when adjusted to 2006 USD (U.S. EPA, 2000a). The 20.2-ha wetland system in West Jackson County, Mississippi, had an areal grading require- ment of only 0.26 m 3 /m 2 , and the 9.7-ha system in Gustine, California, had an areal grading requirement of 0.35 m 3 /m 2 . Larger treatment wetlands require far less earthmoving on a per-hectare basis than do small systems. For instance, Cell 4 of STA2 of the Everglades phosphorus control proj- ect required only 0.056 m 3 /m 2 of earthmoving based on the 816-ha wetland footprint. However, the construction of such a large system does not involve scraping a thin layer from the entire footprint. Rather, the inlet spreader canal, outlet col- lection canal, and seepage return canal are the source of the ll material for the containment levees. Even large wetlands may require signicant earthmov- ing if built on sloping terrain. For example, the Inman Road treatment wetland in Clayton County, Georgia, has 22 wetted hectares in a terraced arrangement of 22 cells. The site pre- sented slopes of 2–25%, and about 30 m of vertical variation (Inman et al., 2001, 2003). Construction required moving 420,000 m 3 of earth, or 1.9 m 3 /m 2 . Regional factors and site conditions can alter the cost of earthmoving. Cell 4 of STA2 of the Everglades phosphorus control project moved 460,000 m 3 of material, in a nearly balanced cut and ll. The breakdown of per cubic meter costs was: $2.61 to blast rock, $2.13 to excavate, and $2.09 to build levees, for a total of $7.96/m 3 (adjusted to 2006 USD). HSSF Wetlands Earthwork costs for some HSSF wetland systems in the Minnesota–Wisconsin regional market are summarized in Ta ble 23.1. Data from these seven HSSF wetland systems clearly show the impact of local site conditions on earthwork costs. Areal grading requirements varied from 0.21 m 3 /m 2 to 1.73 m 3 /m 2 , with a median value of 1.03 m 3 /m 2 . Volumetric earthwork costs for the systems in Table 23.1 varied between $2.17/m 3 and $18.15/m 3 , with a median value of $7.56/m 3 (cost adjusted to 2006 USD, ENR CCI 7751). Combining areal grading requirements with volumetric earthwork costs resulted in areal earthwork costs ranging between $1.68/m 2 and $13.97/m 2 , with a median value of $5.06/m 2 (adjusted to 2006 USD). Liners The decision to install a liner in a wetland system, and which type of liner to use, depends on the project goals, regulatory requirements, and feasibility. Some wetlands are unlined, either because the in situ native soils are deemed to have suf- cient sealing properties, or because groundwater recharge is a function of the system. Very large FWS wetlands cannot be plastic lined because it is not feasible for systems of more than a few hectares, but clay lining has been implemented on sys- tems up to 40 ha, such as Columbia, Missouri. If the wetland must be lined, there are a variety of liner materials available. The two most common liner materials used are 0.76-mm polyvinyl chloride (PVC) and 1.0-mm high-density poly- ethylene (HDPE). PVC liners are generally factory seamed, one-piece liners used on small projects less than 0.1 ha in size. HDPE liners generally come in rolls and are eld seamed for larger projects. The total installed cost of the liner includes not only the material cost but also the labor cost associated with eld seaming, seam testing, material inspection, and leak test- ing. If local soil conditions include sharp or angular rocks, TABLE 23.1 Earthmoving Costs for HSSF Wetlands in Minnesota System Name Design Flow (m 3 /d) Wetland Area (m 2 ) Earthwork Volume (m 3 ) Cost Volumetric ($/m 3 ) Grading Req. (m 3 earth per m 2 wetland) Cost (Areal) ($/m 2 ) St. George, Minnesota 25 595 631 8.54 1.06 9.06 Darfur, Minnesota 38 1,301 383 5.70 0.29 1.68 Northern Tier High Adventure Base, Minnesota 34 297 306 13.56 1.03 13.97 Lakes of Fairhaven, Minnesota 59 1,828 383 7.56 0.21 1.58 Delft, Minnesota 22 664 306 18.15 0.46 8.36 St. Croix Chippewa, Wisconsin 251 6,141 6,885 4.51 1.12 5.06 Prinsburg, Minnesota 206 4,094 7,069 2.17 1.73 3.75 Median Values 7.56 1.03 5.06 © 2009 by Taylor & Francis Group, LLC Economics 797 a layer of sand or other granular material may have to be placed before the liner can be installed. If the gravel used to line the bed has sharp or angular edges, it may be neces- sary to cover the interior of the liner with a protective layer of geotextile fabric, since sharp rock can puncture a liner. Table 23.2 shows approximate installed costs of a variety of liner materials. Liner costs for the FWS wetland system at Ouray, Colo- rado, were $6.97/m 2 , and $13.23/m 2 for the HSSF wetland sys- tem at Ten Stones, Vermont (both adjusted to 2006 USD) (U.S. EPA, 2000a). Liner and geotextile fabric costs for 12 HSSF wetlands in the Minnesota–Wisconsin regional market are summarized in Table 23.3. Data from these wetland systems indicate that installed liner costs (adjusted to 2006 USD; ENR CCI 7751) ranged from $3.74/m 2 to $19.71/m 2 , with a median cost of $8.66/m 2 . The use of a geotextile fabric will increase the installed liner cost. The data in Table 23.3 indicate that the installed cost will increase by approximately $3.00/m 2 when a geotextile fabric is used. If soil at the site contains rocks or other debris that could damage the liner during installation, a layer of sand or similar granular material is often placed prior to installing the liner. For example, 8 cm of sand was placed prior to installing the liner in three Minnesota HSSF wetlands. The installed cost for sand bedding ranged from $1.38/m 2 to $3.08/m 2 , with a median cost of $2.24/m 2 (2006 USD; ENR CCI 7751). Media and Mulch The major cost variation between FWS and SSF wetlands results from differences in the rooting media. FWS systems typically use 30–40 cm of soil, which may be entirely avail- able on the site, whereas SSF wetlands use 50–80 cm of gravel or other similar media, which must usually be pur- chased and transported to the site. Soils for FWS Systems If in situ native soils are suitable, they are typically used as the rooting substrate for emergent wetland plants in FWS systems. If in situ native soils are unsuitable for use as root- ing media, soil may be imported and mixed with existing soil to create conditions adequate for rooting wetland plants. For these reasons, the cost of the rooting medium is usu- ally reected in the volumetric earthwork costs. However, it is sometimes advantageous to add organic material to the rooting soil for a FWS system, to provide sorption capac- it y immediately upon start-up (Figure 23.2). Such a blending TABLE 23.2 Approximate Cost of Installed Liners (2006 USD) Material Thickness Installed Cost ($/m 2 ) Bentonite 10 kg/m 2 7.96 Native clay a 30 cm 7.50 Clay geotextile sandwich NS 4.84 Polyvinyl chloride 0.76 mm 4.09 High-density polyethylene 1.02 mm 4.73 Polypropylene 1.02 mm 5.92 Reinforced polypropylene 1.14 mm 6.89 Hypalon 0.76 mm 6.89 Hypalon 1.52 mm 8.07 XR-5 NS 11.19 a Assumes $25/m 3 delivered, placed, and compacted. Source: Data from U.S. EPA (2000a) Constructed wetlands treatment of municipal wastewaters. EPA 625/R-99/010, U.S. EPA Ofce of Research and Development: Washington D.C.; and Interstate Technology and Regula- tory Council (2003) Technical and Regulatory Guidance Document for Con- structed Treatment Wetlands. http://www.itrcweb.org/WTLND-1.pdf. TABLE 23.3 Liner and Geotextile Costs for Example HSSF Wetlands System Name Design Flow (m 3 /d) Wetland Area (m 2 ) Liner ($/m 2 ) Geotextile ($/m 2 ) St. George, Minnesota 25 595 8.04 — Darfur, Minnesota 38 1,301 7.36 3.35 Northern Tier High Adventure Base, Minnesota 34 297 8.93 1.84 Opole, Minnesota 35 725 6.57 3.94 Tamarack, Minnesota 26 418 19.71 3.29 Lakes of Fairhaven, Minnesota 59 1,828 6.84 3.02 Delft, Minnesota 22 664 13.70 12.45 Cedar Mills, Minnesota 35 1,073 9.95 1.76 St. Croix Chippewa, Wisconsin 251 6,141 3.74 0.82 Prinsburg, Minnesota 206 4,094 10.19 — Mulberry Meadows, Minnesota 72 1,580 8.39 2.47 Cambridge-Isanti School District, Minnesota 39 1,196 9.07 3.13 Median Value 8.66 3.08 Note: Geotextile is a nonwoven, needle-punched polypropylene material (230 g/m 2 fabric weight) used as a protective layer on top of the liner. © 2009 by Taylor & Francis Group, LLC 798 Treatment Wetlands operation may involve approximately 10 cm of amendment material, thus adding 0.1 m 3 /m 2 of earthmoving to the proj- ect, plus the cost of the composting material. Municipal yard waste compost has been successfully used at Isanti-Chisago, Minnesota, and at Saginaw, Michigan, treatment wetlands. The use of purchased topsoil, either entirely or as an amend- ment, is a very expensive option, because high-quality (hor- ticultural) topsoil typically sells for up to $25/m 3 . Media for SSF Wetlands A number of innovative types of media have been used in SSF treatment wetlands. Examples include recycled glass fragments, such at Millersylvania State Park, Washington, blast furnace slag (Mann and Bavor, 1993; Drizo et al., 1999), and lightweight expanded clay aggregates (LECA) (Zhu et al., 1997; Jenssen and Krogstad, 2003). The cost of LECA is quite high; for instance, Scholz et al. (2001) report $204/m 3 (2006 costs), but it is available in large units (Figure 23.3). The wide variety of SSF wetland media leads to wide varia- tions in costs, but gravel is perhaps the most common mate- ri al used in Europe and North America (Figure 23.4). In a HSSF wetland, the rooting medium comprises the material used in the main wetland bed (typically gravel) and the coarser material used in the inlet and outlet zones (typi- cally coarse rock). Costs for these materials are a function of regional market conditions as well as the distance between the source of supply and the project site. For instance, the 4.0- ha VF wetland at Connell, Washington, utilized 36,000 m 3 of 2.6-mm coarse sand that was available immediately adjacent to the bed, thus incurring only a cut-and-ll cost (Burgoon et al., 1999). That situation is extremely rare, and most often media will be mined, screened, washed, and transported to the wetland site at considerable cost. Media costs for 12 selected HSSF wetlands in the Minne- so t a – W i s c o n s i n r e g i o n a l m a r k e t a r e s u m m a r i z e d i n Ta b l e 2 3 . 4 . This region was glaciated and typically has ample sources of gravel within a reasonable distance of a project. Data indicate that installed gravel media costs (used in the main portion of the bed) range between $15.95/m 3 and $70.26/m 3 , with a median cost of $41.87/m 3 (adjusted to 2006 USD). The gravel used in these systems was 9–25 mm in size. Within the Min- nesota–Wisconsin regional market, distances between the source of supply (local gravel pit) and the project site were the primary factor in determining unit costs. As the depth of the bed media is established during the design process, cal- culation of areal costs is relatively straightforward. All of the HS SF systems in Table 23.4 were designed with a bed depth of 0.45 m, resulting in a median areal cost of $18.84/m 2 . Media costs presented in Table 23.4 are higher than those presented in the literature for other HSSF systems. For three HSSF wetlands (Mesquite, Nevada; Carville, Louisiana; and Ten Stones, Vermont), U.S. EPA (2000a) reported bed media costs of $14.33, $23.58, and $14.74/m 2 , respectively (2006 USD). These were deeper beds (0.8, 0.75, and 0.75 m, respec- tively), and the volumetric cost of the media was less. FIGURE 23.2 Organic materials may be added to the rooting soils to promote early sorption potential. At the Hillsdale, Michigan, site, soils were borrowed from an adjacent oodplain, creating a pond and island complex in the borrow site. FIGURE 23.3 Light expanded clay aggregate (LECA) can be pur- chased in large units in Europe. © 2009 by Taylor & Francis Group, LLC Economics 799 Mulch In cold-climate regions, it may be necessary to insulate a HSSF system. This may be done with straw, or cover blankets for small systems. Mulch may be used as an insulating layer for cold-climate wetlands, and is a common design feature of HSSF wetlands in Canada and the northern regions of the United States (Figure 23.5). All of the wetlands in Table 23.4 were insulated with 0.09 m of reed-sedge peat. Installed costs for this peat material (2006 USD) ranged between $23.94/m 3 and $82.98/m 3 , with a median cost of $49.89/m 3 . This con- verts to an areal cost of $4.49/m 2 . Coarse Stone The berm slopes of FWS wetlands may be armored against burrowing animals and wave erosion by the use of rip rap. Co arse rock is a common choice (see Figure 18.19), but con- crete matting has also been used (see Figure 18.23). HSSF wetlands commonly use a coarser material (drain ro ck) in the inlet and outlet portions of the bed (Figure 23.6). In the United Kingdom, the stone inlet and outlet zones are typically 0.5 m wide, at full bed depth, and packed with 50– 200 mm stone (Cooper et al., 1996). Drain rock used in the 12 HSSF wetlands summarized in Table 23.4 was 20–75 mm in size. Installed drain rock costs ranged from $25.53/m 3 to $74.41/m 3 , with a median cost of $47.59/m 3 (adjusted to 2005 USD). U.S. EPA (2000a) reports that costs for outlet materials were $10.39/m 3 (50-mm stone) and $24.24/m 3 (100-mm stone) for the HSSF wetland at Ten Stones, Vermont (2006 USD). Plants The plant component of capital cost varies according to the method chosen for vegetation establishment. It is presup- posed that the media is in place, either the soil layer in a FWS system or the gravel in an SSF system. The FWS FIGURE 23.4 Gravel media being placed at the Grand Lake, Minnesota, HSSF wetland. TABLE 23.4 Media Costs for Selected HSSF Wetlands System Name Design Flow (m 3 /d) Wetland Area (m 2 ) Gravel ($/m 3 ) Mulch ($/m 3 ) Coarse Stone ($/m 3 ) St. George, Minnesota 25 595 31.32 82.98 48.00 Darfur, Minnesota 38 1,301 45.56 81.36 47.18 Northern Tier High Adventure Base, Minnesota 34 297 70.26 76.64 74.41 Opole, Minnesota 35 725 15.95 49.47 31.11 Tamarack, Minnesota 26 418 23.94 23.94 25.53 Lakes of Fairhaven, Minnesota 59 1,828 33.27 45.36 52.92 Delft, Minnesota 22 664 42.33 37.80 36.30 Cedar Mills, Minnesota 35 1,073 39.83 64.02 52.65 St. Croix Chippewa, Wisconsin 251 6,141 41.40 32.44 30.31 Prinsburg, Minnesota 206 4,094 45.53 55.48 52.65 Mulberry Meadows, Minnesota 72 1,580 51.65 46.22 51.66 Cambridge-Isanti School District, Minnesota 39 1,196 46.22 50.30 44.87 Median Value 41.87 49.89 47.59 © 2009 by Taylor & Francis Group, LLC 800 Treatment Wetlands wetland offers the largest number of options, including natu- ral recruitment, seeding, and planting. Natural Recruitment This option is the least costly but the least controllable, and usually of the longest duration. It is not free from cost, because moist soil conditions must be maintained, which in turn requires water management on the wetland. Virtually all of the Florida stormwater treatment wetlands (STAs) were established in this way. A newer strategy for these STAs is the use of a seeded sacricial rice cover crop (Oryza sativa), which assists in soil stabilization and initial nutrient immobi- lization. This cover crop lasts only one growing season, does not renew itself, and gives way to other wetland vegetation. Seeding Seeding is the next least expensive method of vegetation establishment. The techniques range from scattering in the wi nd (Figure 23.7), to back-pack broadcasting, to the use of seed drills. The seed is then pressed into the soils using a roller or cultipacker, or by light raking. The use of foot travel has also been used effectively, at the Isanti-Chisago site in Minnesota (Loer et al., 1999). Volunteer labor has been used successfully at Brighton, Ontario, and Roblin, Manitoba, where grades 9 and 10 science students participated in seed- ing (PFRA, 2002). Hydroseeding has been used successfully (U.S. EPA, 2000a) but requires the addition of detergent to loosen the seed covering. In the Great Lakes region of the United States, the optimum seeding time is autumn through late spring. Seeds for wetland plants may be harvested from local sources as part of the project work, particularly for Typha, which produces large seed heads with extremely numerous seeds, and which are easily picked in autumn. Seeds are also available from wetland nurseries in the United States, for over a hundred wetland species. The cost is considerable, ranging from $125 to $1,500 per kilogram of live seeds for common wetland plants in the northern United States (Table 23.5). The seeding rate is typically on the order of 2–4 kg of live seed per hectare. The purchased price of the seed is consequently in the range of $400–$3,000 per hectare, with a median of about $1,200 per hectare. The cost of installation includes the seeding itself (minor) and the fostering of germination and growth, via soil moisture/water management (major). Dry seeding has been estimated at ten man-hours per hectare, and hydroseeding at $145/ha (U.S. Army Corps of Engineers, 2000). Such required activities are usually inexpensive, and are less than the cost of the seed itself. FIGURE 23.5 Peat mulch in place at the Grand Lake, Minnesota, wetland. FIGURE 23.6 Inlet coa rse rock zone at t he Fish and Royer, I ndia na , HSSF wetland. © 2009 by Taylor & Francis Group, LLC Economics 801 Planting The choice to plant originates with the desire to propagate a selected suite of plant species in a short period of time. Planting costs are a function of several different factors. These include the form of plant material (plugs or rootstock), FIGURE 23.7 Seeding of the Brighton, Ontario, wetland (a) and the resulting growth (b). (Photos courtesy J. Pries.) (a) (b) TABLE 23.5 Examples of Prices for Plants and Seeds (2007 USD) Seed Bare Root Plugs ($/kg) ($/ha) ($/Plant) ($/ha) ($/Plant) ($/ha) Individual Species Phragmites australis Common reed — — 0.65 6,500 0.95 9,500 Phalaris arundinacea Reed canarygrass — — 0.55 5,500 — — Typha latifolia Broad leaf cattail 127 381 0.80 8,000 0.98 9,750 Typha angustifolia Narrow leaf cattail 127 381 0.80 8,000 1.08 10,750 Scirpus validus Great bulrush 485 1,454 0.65 6,500 0.80 8,000 Scirpus acutus Hard-stemmed bulrush 717 2,152 0.85 8,500 0.88 8,750 Scirpus atrovirens Dark green rush 329 986 0.85 8,500 0.88 8,750 Scirpus pungens Common three-square 1,072 3,217 0.65 6,500 0.90 9,000 Scirpus cyperinus Woolgrass 326 978 0.60 6,000 0.83 8,250 Iris virginica Blue-ag iris 357 1,070 0.85 8,500 1.15 11,500 Leersia oryzoides Rice cutgrass 419 1,258 0.40 4,000 0.80 8,000 Juncus effusus Common rush 599 1,797 0.55 5,500 0.88 8,750 Sagittaria latifolia Common arrowhead 374 1,121 0.55 5,500 1.25 12,500 Pontederia cordata Pickerel weed 317 952 2.00 20,000 3.13 31,250 Sparganium eurycarpum Common bur reed 431 1,293 0.55 5,500 1.28 12,750 E mergent Wetland Mix (20 species plus cover crop) — 3,088 — — — — Stormwater Wetland Mix (18 species plus cover crop) — 1,914 — — — — Rush/Bulrush Mix (5 species) — 556 — — — — Median 1,189 0.65 6,500 0.93 9,250 Note: The planting rate is assumed to be 10,000/ha, and the seeding rate is assumed to be 3.0 kg/ha. The cover crop is 25 kg/ha common oats (Avena sativa) and 8 kg/ha of annual rye (Lolium multiorum). Source: Data based on averages from J.F. New, Walkerton, Indiana (http://www.jfnew.com/) and Southern Tier Consulting, West Clarksville, New York (http://www.southerntierconsulting.com/). the source of material (locally harvested, on-site nursery, or commercial nursery), the method of planting (manual or mechanical, volunteer or, contractor labor), and the overall planting density (number of plants per square meter). Because © 2009 by Taylor & Francis Group, LLC 802 Treatment Wetlands of these variables, planting costs vary widely among wetland projects. In projects that employ hand planting, plant mate- rial costs may be a small fraction of the installed cost. Commercial nurseries sell a wide range of wetland plants as potted “plugs” or bare root stock (Table 23.5). The median (2007) cost of bare root propagules was $0.65 (n 14), and for plugs, $0.93 (n 13). Transportation costs must be added to these, leading to a delivered cost of about $1.20 per plant. It is sometimes possible to obtain plants from existing stands, such as cattails from roadside ditches. Extraction requires mechanical digging, typically with a backhoe, to a depth of about 30 cm, so as to gather the majority of the root mass. The plants are then separated from the mass by hand, with each propagule containing at least one healthy shoot and at least 20 cm of associated rhizome. The shoot is topped to a height of 30–40 cm, to reduce the amount of foliage that the transplant must maintain after the trauma of transplanting. On-site nurs- eries may also be established prior to wetland construction, for the purpose of supplying plant materials. However, the plant- ing contractor may prefer to avoid the effort needed to extract and prepare the plants, and opt for the use of purchased plants, as was the case at Columbia, Missouri (Brunner and Kadlec, 1993). Established treatment wetlands may serve as sources of plant materials for new systems. For example, the plants for the Connell, Washington, system (Kadlec et al., 1997) were extracted from the Arcata, California, project, and success- fully established in the new wetland. Marsh establishment on the Texas coast required 11.3–29.3 man-hours per 1,000 plants to hand-dig, separate, and transplant various propagule types of 11 marsh species (Dodd and Webb [1975], as refer- enced by U.S. Army Corps of Engineers [2000]). The total cost of plants depends on planting density, which ranges over about 0.25–4.0 plants per square meter (spacing of 0.5–2.0 m). If the plants are on 1-m centers, there a r e 10,000 per hectare. This value is used in Table 23.5 to establish the per-hectare cost of nursery-purchased plant plugs, which ranges from $8,000 to $31,000, with a median of $9,250/ha. The cost of putting the plants into the ground can be extremely variable. In some instances, innovation has been employed to quickly and efciently plant a wetland with mechanical equipment (Figure 23.8). However, most small wetlands are planted by hand, with rates of up to 150 plants per person per hour for experienced planting crews. Allowing for lesser efciency of 50 plants per person per hour, thus requir- ing 200 man-hours per hectare at 10,000 plants per hectare. This matches estimates provided by the U.S. ACE publication (U.S. Army Corps of Engineers, 2000). For labor at $20/h, insertion costs would be about $2,000/ha at 10,000 plants per hectare, or $0.40 per plant. When combined with the per-plant purchase price, the cost would be $1.60 per plant installed. U.S. EPA (2000a) suggests a planting cost for FWS wet- lands of $0.83 per plant installed (adjusted to 2006 USD). This may be a reasonable estimate for locally harvested plants, but is probably too low for nursery-purchased plants. Table 23.6 summarizes planting costs for HSSF wet- land systems in the Minnesota–Wisconsin, U.S. regional market. All of these systems were hand-planted with root- stock (primarily Scirpus atrovirens, Scirpus uviatilis, and Scirpus cyperinus) purchased from commercial wetland plant nurseries in Wisconsin. All 12 systems were planted at a density of 2.7 plants/per square meter. This represents an aggressive planting approach that uses well-established rootstock and is designed to achieve complete plant cover- age in about two growing seasons (which is approximately 18 weeks per year in this climatic region). The median of $4.58 per plant installed, in Table 23.6, is much higher than the estimate mentioned previously. The difference may be attributable not only to labor costs and other regional market factors but also to the unfamiliarity of the contrac- tors with planting as a construction activity. On an areal basis, Table 23.6 shows a median of $12.32/m 2 . In another adjacent climatic region, for the Minoa, New York, HSSF wetland, planting costs were $9.45/m 2 . For small to medium size wetlands (less than 10 ha), planting costs are less than 10% of the total capital cost. This FIGURE 23.8 Homemade planter used for the Hillsdale, Michigan, treatment wetland (a). The 1.4 ha of basins were quickly planted (b). See Figure 19.6 for a view of the wetland one year later. (a) (b) © 2009 by Taylor & Francis Group, LLC [...]... 000 (23. 4) where A wetland area, ha C cost, 2006 dollars in thousands Q flow rate, m 3 /d in thousands TABLE 23. 11 Selected Bid Results for a 300-m2 HSSF Wetland on the U.S.–Canadian Bordera Engineer Item Pea gravel Drain rock Peat Plants Earthwork cut/fill 0.76-mm PVC liner Granular bedding Protective fabric 100-mm Sch 40 PVC (insulated) 50-mm Sch 80 PVC (insulated) 50-mm Sch 40 PVC (insulated) 100-mm... replace worn-out components © 2009 by Taylor & Francis Group, LLC 0 0 816 Treatment Wetlands $50,000 $40,000 Cash in Bank $30,000 $20,000 $10,000 Cash in Bank Recommended Capacity $0 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2 023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 –$10,000 FIGURE 23. 17 Example of cash-flow projection for a 53-home treatment. .. about $26/kg The concept of nutrient credit trading, coupled with the land needed for treatment wetlands, has spurred consideration of the use of off-site wetlands to remove nitrogen and phosphorus rather than on-plant-site mechanical equipment (Hey et al., 2005) The loads that need to be removed at large wastewater treatment plants are easily identified, as can the costs of such nutrient removal at... system is shown in Table 23. 13 Most of the O&M is associated with permit-related sampling and correspondence, followed by management of pumps, septic tanks, control y FIGURE 23. 16 Operation and maintenance (O&M) costs for FWS wetlands (N © 2009 by Taylor & Francis Group, LLC 95,315 4,766 40,032 22,876 x 21) Economics 811 TABLE 23. 13 Example Annual Operational Costs for a 46-Home Residential Development... of 10–30% are typically used 806 Treatment Wetlands ILLUSTRATIONS It is instructive to combine the various elements of capital cost into a summary by category There are too many variables to do this in a general way, and consequently a few illustrations are presented here Table 23. 8 shows a capital cost list for a hypothetical small-scale FWS treatment wetland The 1-ha system might receive a hydraulic... at the perforations Infiltration chambers (Figure 23. 9) have a louvered sidewall which provides a greater number FIGURE 23. 9 Placement of inlet distribution chamber at Lake Elmo, Minnesota (From Wallace and Knight (2006) Small-scale constructed wetland treatment systems: Feasibility, design criteria, and O&M requirements Final Report, Project 01-CTS-5, Water Environment Research Foundation (WERF):... the time of final conceptual design, was $163,000 per year (Table 23. 12) Permit-related sampling and reporting, combined with maintenance of upstream and downstream treatment processes, constitute most of the routine O&M associated with FWS wetlands At Arcata, California, it has been estimated that O&M tasks directly associated with the wetlands require about $1600/ha·yr when adjusted to 2006 USD (U.S... then this screening device may be unnecessary © 2009 by Taylor & Francis Group, LLC In small- to mid-sized HSSF wetlands, flow is generally distributed across the width of the bed in the inlet zone using perforated pipes or infiltration chambers Perforated PVC pipe (100-mm diameter) is commonly used as a low-cost distribution method for small systems The drawback of using perforated pipe is that the... for financing wastewater treatment projects In fact, in the United States, a homeowner may well be paying the two bills separately each month: one payment to pay off the debt on building the system, and a second to pay for operating costs Unfortunately, only a very few literature sources deal with the combination of both types of project costs for treatment wetlands Treatment wetlands are distinctively... plausible that treatment wetlands should be ascribed a basic life of 40–50 years, with mechanical components being replaced at greater frequency Present Worth of Future One-Time Costs The amount of money needed for a future expenditure reflects the discount rate in a simple, compound interest sense: P © 2009 by Taylor & Francis Group, LLC S 1 (1 i)m (23. 9) (1 i) N 1 Y Fpw i(1 i) N (23. 10) where i discount . Regulatory Guidance Document for Con- structed Treatment Wetlands. http://www.itrcweb.org/WTLND-1.pdf. TABLE 23. 3 Liner and Geotextile Costs for Example HSSF Wetlands System Name Design Flow (m 3 /d) Wetland. Isanti-Chisago, Minnesota, and at Saginaw, Michigan, treatment wetlands. The use of purchased topsoil, either entirely or as an amend- ment, is a very expensive option, because high-quality (hor- ticultural). layer for cold-climate wetlands, and is a common design feature of HSSF wetlands in Canada and the northern regions of the United States (Figure 23. 5). All of the wetlands in Table 23. 4 were