Lake City Conceptual Plan v.3 - WSI€¦ · Introduction ... 11 Inflow Distribution Channels.....13...

2809 NW 161 Court Gainesville, FL 32609

(386) 462-1003 (386) 462-3196 fax

W H I T E P A P E R

City of Lake City - Conceptual Plan for the Conversion of Existing Spray Field Facilities to a Treatment Wetland TO: Interested Parties FROM: Chris Keller/WSI

Bob Knight/WSI DATE: May 24, 2006

Contents Contents .............................................................................................................................1 Introduction.......................................................................................................................1 Existing Site Description..................................................................................................2 Existing and Future Flows and WWTF Effluent Quality............................................5 Introduction to Treatment Wetlands .............................................................................5

Background of the Technology..........................................................................5 Types of Treatment Wetlands............................................................................9 Benefits of Treatment Wetlands ......................................................................10

Conceptual Treatment Wetland Plan ..........................................................................11 Perimeter Berms ................................................................................................11 Inflow Distribution Channels ..........................................................................13 Wetland Vegetation Establishment.................................................................13 Public Access Features......................................................................................14 Preliminary Cost Estimate................................................................................14

Estimated Wetland Performance..................................................................................19 Mass Loading Analyses....................................................................................19 k-C* Model .........................................................................................................19 Model Results.....................................................................................................20

Groundwater Discharge ................................................................................................25 Conclusions .....................................................................................................................26 References........................................................................................................................27 About the Authors..........................................................................................................27

Robert L. Knight, Ph.D......................................................................................27 Christopher H. Keller, P.E................................................................................27

Introduction The Lake City Wastewater Treatment Facility (WWTF) is an activated sludge plant with a permitted capacity of 3 million gallons per day (MGD). Treated effluent from the WWTF is pumped approximately 4 miles to a holding pond and land application (sprayfield) facility. Final effluent disposal at the sprayfield is to the upper Floridan aquifer through various

WETLAND SOLUTIONS, INC.

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infiltration features, including engineered underdrains and sand-filled infiltration pits, and natural karstic (sinkhole) drains. Ultimately, an unknown fraction of the drainage from the Lake City Sprayfield and the dissolved nitrogen associated with this flow reaches the Ichetucknee Spring System as artesian flow. Increasing nitrate nitrogen concentrations in the Ichetucknee Spring System are suspected to be at least partially a result of this nitrogen source. All nitrogen sources in the Ichetucknee Springshed are currently under scrutiny in an effort to reverse these increasing nutrient trends. Since the Lake City Sprayfield is a defined and concentrated nitrogen loading source in the springshed, reduction of that fraction of the nitrogen load may be a cost effective component of a basin-wide effort to protect the Ichetucknee Spring System and the Florida aquifer resource in general.

Conversion of municipal sprayfields to treatment wetlands may be a practical solution to the Ichetucknee Spring System groundwater nitrogen load issue. Treatment wetlands are renowned for their effective nitrogen removal performance at much lower operational costs than slow rate land application facilities (Kadlec and Knight 1996). Treatment wetlands throughout Florida and Georgia have demonstrated high nitrogen removal efficiencies at low per gallon costs. In addition to potentially saving money for Lake City and reducing nitrogen loads to the aquifer, treatment wetlands also create valuable wildlife habitat and provide a recreational and educational amenity for local students and residents.

Successful replacement of the Lake City Sprayfield with a constructed treatment wetland will require careful engineering to provide a technically sound design and cooperation from regulatory officials to overcome potential regulatory hurdles. It is essential that the fully reclaimed municipal wastewater from Lake City remain in the Ichetucknee Springshed without excess nitrogen. This water is essential to maintain spring flows and groundwater resources in the basin. This means that a treatment wetland option, if implemented, will need to be designed and permitted to discharge to the groundwater. In our opinion this is technically feasible on this site, but just as the sprayfield design required certain innovative engineering enhancements to properly function, a treatment wetland with zero surface discharge will need to continue to use or may need to upgrade those drainage enhancements.

This “White Paper” has been prepared as a preliminary proposal to the Lake City Department of Utilities and to potentially-interested partners such as the Suwannee River Water Management District, the Florida Department of Environmental Protection, and the Three Rivers, Inc., who may wish to combine their efforts in finding mutually beneficial solutions to the nitrogen loading issue. Wetland Solutions, Inc. (WSI) has prepared this White Paper at its own expense and with no expectations of financial return in an effort to describe a possible win-win solution for the protection of the Ichetucknee Spring System, a truly unique natural resource in north central Florida.

Existing Site Description Exhibit 1 shows the location of the Lake City WWTF and the existing sprayfields. The sprayfield facility consists of three separate parcels with a total functional area of approximately 334 acres (see Exhibit 2). The sprayfields are located southwest of Lake City along County Road 341. The sprayfield underdrain system does not effectively dispose of all the effluent that is applied during high rainfall periods, causing some of the effluent to flow


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overland to sinkholes and adjacent creeks. In an effort to minimize off-site discharges, the southernmost row of spray nozzles is no longer used.

The sprayfields are planted with a hay crop that is harvested to remove nutrients from the site. In the past this hayfield received fertilizer nitrogen loads in addition to the nitrogen in the applied treated effluent. Recently, the City discontinued fertilizer additions and planted cypress seedlings in depressional areas to provide for additional long-term nutrient removal and increased evapotranspiration (Henry Sheldon, personal communication).

EXHIBIT 1 Location Map for Lake City WWTP and Sprayfields


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EXHIBIT 2 Existing Lake City Sprayfields


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Existing and Future Flows and WWTF Effluent Quality The Lake City WWTF is currently permitted to discharge up to 3 MGD to the sprayfield system. Monthly water and nitrogen mass balances for average flows of 3.0, 3.5, and 4 .0 MGD were compiled by the City’s engineering consultant, Henry Sheldon (personal communication), and are summarized in Exhibits 3 through 5. Nitrogen is the primary parameter of interest for systems that discharge to groundwater.

Existing total loads to the sprayfields include nitrogen from the WWTF effluent, rainfall, fertilizer, and migratory birds that raft in the holding pond during the winter. The WWTF currently produces an effluent that ranges in total nitrogen (TN) concentration from 7 to 10 milligrams per liter (mg/L). The estimated concentration of TN in treated effluent discharged to groundwater through the sprayfield site ranges from 2 to 15 mg/L (see Exhibit 3). The peak occurs in June and in the past was heavily influenced by the application of fertilizer to the hay crop on the sprayfields. The primary mechanism for TN removal in effluent applied to the sprayfield is through the harvesting of hay (estimated 80,000 lbs TN/yr removed of 115,000 lbs TN/yr applied). About 36,000 lbs TN/yr were estimated to discharge to groundwater.

The estimated nitrogen mass balance for an average flow of 3.5 MGD assuming cessation of fertilizer applications (see Exhibit 4) shows no improvement in effluent quality from the WWTF, but does not include fertilizer application in the summer. TN concentrations discharging to groundwater under this proposed scenario are estimated to range from 2 to 4 mg/L. The mass loading to groundwater decreases from the 3.0 MGD case from 36,000 lbs TN/yr to about 26,000 lbs N/yr.

The estimated nitrogen mass balance for an average flow of 4.0 MGD assuming WWTF expansion and upgrades to provide advanced wastewater treatment for nitrogen removal to 3 mg/L is provided in Exhibit 5. Commensurate with the greatly reduced loading from the WWTF, the TN concentration of effluent discharged to groundwater is estimated to range from 1 to 2 mg/L. The mass loading to groundwater under this proposed future upgrade of the system is estimated to be about 13,000 lbs TN/yr.

Introduction to Treatment Wetlands Treatment wetlands are constructed ecosystems dominated by aquatic plants that naturally cleanse water. Throughout Florida, the U.S., and the world, treatment wetlands are providing a cost effective alternative for water and wastewater management.

Background of the Technology The feasibility of using wetlands for water treatment has been investigated since the 1950s when researchers first observed removal of trace organics and biochemical oxygen demand (BOD) in laboratory constructed wetlands. Since then, many scientists and engineers in North America and abroad have conducted further studies of treatment potential in both constructed and natural systems. Designs range from large open-water areas fringed with cattails and bulrushes, to shallow water ponds completely covered with sedges and rushes, to natural forested wetlands. However, because of the variety of wetland types, each with


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EXHIBIT 3 Nitrogen Mass Balance at 3.0 MGD (from Sheldon 2005)

Inputs - Loads to Ground Surface Output - Nitrogen Removal/Discharge

Rainfall WWTP Effluent Reservoir (Migratory

Birds) Fertilizer Total Soil/Crop UD Discharge to GW

Month Quantity TN Load Quantity TN Load Quantity TN Load Load Load Uptake Quantity TN load TN conc

(MG) (mg/l) (lbs) (MG) (mg/l) (lbs) (MG) (mg/l) (lbs) (lbs) (lbs) (lbs) (MG) (lbs) (mg/l)

Jan 30 0.5 127 90 7 5,248 90 2 1,500 0 6,875 4,812 95 2,062 3

Feb 37 0.5 155 84 7 4,904 84 2 1,401 0 6,460 4,522 96 1,938 2

Mar 39 0.5 162 90 8 5,998 90 2 1,500 0 7,660 5,362 97 2,298 3

Apr 29 0.5 119 78 8 5,204 78 1 651 0 5,974 4,779 69 1,195 2

May 33 0.5 139 81 9 6,050 81 0 0 0 6,189 4,951 70 1,238 2

Jun 63 0.5 262 96 10 8,006 96 0 0 27,000 35,268 21,161 112 14,107 15

Jul 71 0.5 297 109 10 9,049 109 0 0 0 9,346 7,477 131 1,869 2

Aug 64 0.5 265 109 10 9,049 109 0 0 0 9,314 7,452 127 1,863 2

Sep 51 0.5 214 105 9 7,881 105 0 0 0 8,095 6,476 115 1,619 2

Oct 29 0.5 119 87 8 5,791 87 0 0 0 5,910 4,137 80 1,773 3

Nov 21 0.5 87 81 8 5,404 81 2 1,351 0 6,843 4,106 74 2,737 4

Dec 32 0.5 135 87 8 5,791 87 2 1,448 0 7,374 4,424 94 2,950 4

Totals 499 2,080 1,095 78,377 1,095.0 7,850 27,000 115,307 79,658 1,162 35,649


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EXHIBIT 4 Nitrogen Mass Balance at 3.5 MGD assuming removal of hay crop fertilization (from Sheldon 2005)






Jan 30 0.5 127 105 7 6,153 105 2 1,758 0 8,038 5,627 110 2,411 3

Feb 37 0.5 155 95 7 5,558 95 2 1,588 0 7,300 5,110 108 2,190 2

Mar 39 0.5 162 102 8 6,825 102 2 1,706 0 8,694 6,086 109 2,608 3

Apr 29 0.5 119 93 8 6,205 93 1 776 0 7,099 5,680 84 1,420 2

May 33 0.5 139 96 9 7,213 96 0 0 0 7,352 5,882 86 1,470 2

Jun 63 0.5 262 111 10 9,257 111 0 0 0 9,519 7,615 127 1,904 2

Jul 71 0.5 297 124 10 10,342 124 0 0 0 10,639 8,511 147 2,128 2

Aug 64 0.5 265 124 10 10,342 124 0 0 0 10,607 8,486 142 2,121 2

Sep 51 0.5 214 120 9 9,007 120 0 0 0 9,221 7,377 130 1,844 2

Oct 29 0.5 119 102 8 6,825 102 0 0 0 6,944 4,861 96 2,083 3

Nov 21 0.5 87 93 8 6,205 93 1 776 0 7,068 4,241 86 2,827 4

Dec 32 0.5 135 99 8 6,619 99 1 827 0 7,581 4,548 107 3,032 3

Totals 499 2,080 1,266 90,552 1,265.5 7,431 0 100,063 74,023 1,332 26,040


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EXHIBIT 5 Nitrogen Mass Balance at 4.0 MGD assuming advanced treatment for nitrogen reduction to 3 mg/L (adapted from Sheldon 2005)






Jan 30 0.5 127 123 3 3,066 123 2 2,044 0 5,237 3,666 110 1,571 2

Feb 37 0.5 155 119 3 2,971 119 2 1,981 0 5,107 3,575 108 1,532 2

Mar 39 0.5 162 124 3 3,114 124 2 2,076 0 5,352 3,746 109 1,606 2

Apr 29 0.5 119 99 3 2,488 99 1 829 0 3,436 2,749 84 687 1

May 33 0.5 139 101 3 2,531 101 0 0 0 2,669 2,136 86 534 1

Jun 63 0.5 262 142 3 3,557 142 0 0 0 3,818 3,055 127 764 1

Jul 71 0.5 297 162 3 4,061 162 0 0 0 4,358 3,486 147 872 1

Aug 64 0.5 265 158 3 3,942 158 0 0 0 4,208 3,366 142 842 1

Sep 51 0.5 214 145 3 3,639 145 0 0 0 3,853 3,083 130 771 1

Oct 29 0.5 119 111 3 2,781 111 0 0 0 2,900 2,030 96 870 1

Nov 21 0.5 87 101 3 2,536 101 1 845 0 3,468 2,081 86 1,387 2

Dec 32 0.5 135 122 3 3,060 122 1 1,020 0 4,215 2,529 107 1,686 2

Totals 499 2,080 1,509 37,746 1,508.6 8,795 0 48,621 35,501 1,332 13,120


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differing hydrology, vegetation, and substrate, the observed treatment efficiency varies between systems.

In general, wetland water treatment systems have been found to lower concentrations and mass loads of biochemical oxygen demand (BOD), total suspended solids (TSS), and total nitrogen concentrations to 10 to 20 percent of the concentrations entering the systems. Treatment wetlands are also effective for reduction of concentrations of total phosphorus, metals, and organic compounds, with typically removal efficiencies from about 20 to 90 percent, depending upon design and operational considerations. Removal of pollutants in treatment wetlands is limited by the form and concentration of the constituents, water flow rates and residence time, the presence of oxygen, substrate type, and the entire chemical makeup of the water to be treated. WSI has been instrumental in collecting and analyzing treatment wetland data, and in developing models to accurately predict wetland performance. This information has been widely disseminated in publications and databases (Kadlec and Knight 1996, IWA 2000, North American Treatment Wetland Database v. 2 [www.wetlandsolutionsinc.com]).

Types of Treatment Wetlands Three types of treatment wetlands are typically used for water quality improvement: natural treatment wetlands, constructed surface flow treatment wetlands, and subsurface flow treatment wetlands. The first two of these alternatives are briefly described below. Subsurface flow wetlands are not considered to be suitable for the proposed conversion of the Lake City Sprayfield.

Natural Treatment Wetlands Natural treatment wetlands have been used for the disposal and treatment of secondary and tertiary wastewater effluents for many years. Hundreds of wastewater treatment facilities discharge to natural wetlands nationwide. While many of those systems were not originally designed for wastewater treatment, studies have led to an understanding of the natural potential of wetland ecosystems for pollutant assimilation and to the design of new natural treatment wetlands.

Properly using a natural wetland to treat secondary wastewater or stormwater involves a number of considerations. Hydraulic loads must be matched to the hydroperiod requirements and tolerances of the dominant wetland vegetation. The pretreated water should be well distributed throughout the wetland for optimal treatment and to reduce localized impacts. Ideally, alternative discharge areas should be used so that portions of the natural wetland can be taken offline periodically and allowed to undergo a natural hydroperiod.

Studies demonstrate that through careful design and operation, natural wetlands can consistently and cost-effectively provide advanced treatment of wastewater and stormwater constituents while retaining or enhancing their important ecological functions.

Constructed Surface Flow Treatment Wetlands Constructed surface flow treatment wetlands are typically shallow, man-made impoundments planted with emergent, rooted vegetation. Water flows overland through


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the wetland and primarily above the sediment surface. These wetlands may be planted manually or naturally colonized by volunteer plant communities. Some constructed surface flow treatment wetlands contain monocultures of cattails (Typha spp.) or bulrushes (Scirpus spp.), while others are planted with diverse plant communities that are more adaptable under changing seasonal and water quality conditions.

Unlike a natural treatment wetland in which hydrology is largely fixed by the tolerance limits of the existing plant community, a constructed treatment wetland can be designed to regulate water depth and residence time, two important factors in treatment wetland performance. Also, the design of constructed treatment wetlands can feature parallel cells or cells in series. Such a system can be operated to rotate discharge points or to use slightly different treatment capabilities of the various available plant species groups. Constructed treatment wetlands have relatively low construction, operation, and maintenance costs compared with conventional advanced treatment technologies (Kadlec and Knight 1996).

The plants in constructed treatment wetlands are not typically harvested to remove nutrients. Rather, the microbial flora (bacteria and fungi) that attach to the plants have the natural assimilative capacity to remove biodegradable organics and nitrogen (that is, organic carbon, ammonia, and nitrate) efficiently and reliably. Organic nitrogen is converted to ammonia in treatment wetlands by the natural process of mineralization and ammonification. Ammonia is in turn converted to nitrate nitrogen by the microbial process called nitrification. Nitrate nitrogen is converted to harmless atmospheric nitrogen through the natural microbial process of denitrification. Metals and phosphorus can be permanently sequestered in plant materials and wetland sediments.

Benefits of Treatment Wetlands Constructed and natural treatment wetlands provide several important benefits compared to more conventional treatment alternatives:

• In some cases, they are less expensive to construct than traditional secondary and tertiary wastewater treatment systems.

• In nearly every case they require less maintenance and are less expensive to operate than traditional wastewater treatment systems. Since treatment wetlands largely operate based on inputs of solar energy, they do not have steeply rising operational costs when fossil fuel energy or manufactured chemical costs rise.

• They introduce a reuse option (environmental enhancement through establishment of wildlife habitat and passive public use) for the wastewater facility.

• With proper design, portions of the treatment wetland may provide important wetland wildlife habitat, as well as human recreational opportunities such as birdwatching, hiking, and picnicking.

• Treatment wetlands are viewed as an asset by regulatory agencies in most areas and as a potentially effective method for replacing natural wetlands lost through agricultural practices, industrial and municipal development, and groundwater withdrawal. These systems frequently provide self-mitigation for any unavoidable impacts to on-site natural wetlands.


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Conceptual Treatment Wetland Plan The Lake City Sprayfield is a prime parcel for development of a treatment wetland system for several reasons:

• The parcel is already cleared and relatively level-graded

• There is an existing piping network to transfer effluent from the holding pond to the three sprayfields

• The existing underdrain system can be maintained as the ultimate discharge so that a surface water discharge permit is not required

• The parcels are sufficiently sized to accommodate the available flow at application rates consistent with other wetland systems

• Existing open water features can be maintained

Converting the sprayfield to a treatment wetland will require the following construction activities:

• Removal of existing spray gun equipment

• Construction of perimeter berms to contain water on site

• Modification of inflow distribution piping

• Construction of inflow distribution channels

• Enhancement/modification of soil drainage pits, if required

• Planting/establishment of wetland vegetation

• Construction of public access features

Exhibit 6 shows a conceptual layout for treatment wetlands at the Lake City Sprayfield site. Major features of this conceptual plan are described as follows.

Perimeter Berms Because the site is already cleared and relatively level, wetland creation only requires that low perimeter berms be constructed to keep water from discharging off site via surface flow. Berm top elevations are established based on a typical operating water depth of about 1 foot in the wetlands plus freeboard for design storm events and minimal sediment accretion over the life of the project. A berm height of approximately 4 feet above grade should be sufficient. Berm top widths should be a minimum of 12 feet to provide vehicular access to the entire perimeter of the site. Berm side slopes should be 4:1 to minimize erosion.


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EXHIBIT 6 Conceptual Plan for Conversion of Sprayfields to Treatment Wetlands


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Approximately 30,000 linear feet of berm will be required to compartmentalize the three proposed wetland cells. For a typical cross sectional area of 112 square feet (12 foot top width, 4 foot height, 4:1 slopes), approximately 125,000 cubic yards of fill will be required. Depending upon the quality of the existing soils, the necessary material could be borrowed on site by excavating the inflow distribution channels, creating open water features, or scraping the top 2 to 3 inches of soil. An undetermined amount of final grading may be desirable inside the wetland cells to even out topographical variation and enhance sheetflow of the reclaimed water.

Inflow Distribution Channels Inflow distribution channels will spread effluent across the width of each wetland cell. Channels are the preferred method of distributing flow due to the relative ease of maintenance and reduced construction cost as compared to a pipe manifold system. The existing piping from the holding pond would tie-in to each distribution channel so that flow is introduced below the normal operating water surface elevation.

Wetland Vegetation Establishment Emergent wetland vegetation is proposed as the dominant plant community for the treatment wetland cells. Experience from other projects indicates that it is generally not necessary to actively plant these types of wetlands. The native soils are expected to have sufficient nutrients and seed bank to provide adequate growth of wetland plants. Natural colonization, however, is slow and can lead to a lengthy start-up period (about 1-2 years). Planting of the entire wetland area would decrease the start-up period, but would greatly increase the project budget. A compromise between natural colonization and complete planting is to plant strips of vegetation arranged perpendicular to the water flow direction to insure windbreaks and accelerate colonization. Existing cypress trees recently planted in the sprayfields could be incorporated into the final treatment wetland plan.

Depending upon the level of public access envisioned by the City, the wetland planting plan can be adjusted as necessary. For example, if no public access is planned, natural recruitment may be preferred and is likely to result in a plant community dominated by cattails. If full public access is planned, a more diverse and aesthetically appealing plant community will be desired. In this case, much of the site should be planted with nursery-grown stock (see Exhibit 7).

Optimal growth of wetland emergent plant species is typically at a water depth of up to one foot. Growth of rooted emergent wetland plant species may occur up to a maximum water depth of about 3 feet, but at a declining rate with depth. It is unlikely that most hardy wetland plant species will tolerate a sustained depth as high as 2 feet. Higher water depths tend to stress emergent wetland plants and encourage other plant species that rely on floating or submerged adaptations. At the maximum optimal water surface elevation, the majority of the wetland is expected to be dominated by rooted emergent wetland macrophytes. However, deeper water areas are likely to be dominated by floating and submerged aquatic vegetation species. All of these species are effective for nutrient removal and should not be discouraged from growing in the wetland.


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EXHIBIT 7 Alternative Planting Schemes for Treatment Wetlands Cattail Monoculture (left) and Diverse Marsh (right)

Public Access Features Because of their myriad environmental benefits treatment wetlands are often popular human attractants. Either as an educational resource for other engineers and scientists, or as a public use facility for schools, bird watchers, and civic groups, treatment wetlands are frequently used and praised by the public (USEPA 1993, CH2M HILL 1998). Many municipalities and a few industrial dischargers have designed their treatment wetlands with public use in mind. Representative municipal treatment wetlands in Florida that invite public use include the Iron Bridge Easterly wetland in Orlando, Indian River County’s treatment wetland, the Blue Heron Wetland in Titusville, and the Wakodahatchee and Green Cay Wetlands in Palm Beach County. System design should fully consider the level (if any) of human use anticipated at the proposed treatment wetland.

Common public access features include boardwalks (Exhibit 8), trails, gazebos, interpretive and educational signage (Exhibits 9 and 10), and in some cases, open-air classrooms.

Preliminary Cost Estimate Exhibit 11 presents a preliminary order-of-magnitude cost estimate for two variations of the conceptual plan shown described above. The first option (Option 1) is for partial planting of the wetland to help establish vegetation more quickly than natural colonization alone. Option 1 also does not include any specific public access features, although public access is not precluded with this design. Option 2 includes complete planting of the wetland and


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EXHIBIT 8 Boardwalk and Public Use at a Treatment Wetland (Wakodahatchee Wetland, Palm Beach County, Florida)


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EXHIBIT 9 Interpretive Signage at a Treatment Wetland (Sweetwater Wetland, Tucson, Arizona)


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EXHIBIT 10 Educational Signage at a Treatment Wetland (Sweetwater Wetland, Tucson, Arizona)


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EXHIBIT 11 Estimated Construction Costs for a Treatment Wetland at the lake City Sprayfields Option 1 – Treatment Wetland with Minimal Planting and No Boardwalk

Item Units Quantity Unit Cost Extended Cost

Clearing and Grubbing AC 334 $ 500 $ 167,000

Removal of Existing Equipment LS 1 $ 50,000 $ 50,000

Levee Construction CY 125,000 $ 8 $ 1,000,000

Inflow Channel Construction CY 32,500 $ 4 $ 130,000

Rehab Drainage Pits EA 4 $ 25,000 $ 100,000

Sodding SY 150,000 $ 2.50 $ 375,000

Planting AC 35 $ 5,000 $ 175,000

Subtotal Construction $ 1,997,000

Engineering/Permitting 10% $ 199,700

Contingency 20% $ 399,400

Grading Allowance CY 538,853 $ 3 $ 1,616,560

Grand Total $ 4,212,660

Option 2 – Treatment Wetland with Complete Planting and 4,800-ft Boardwalk

Item Units Quantity Unit Cost Extended Cost

Clearing and Grubbing AC 334 $ 500 $ 167,000

Removal of Existing Equipment LS 1 $ 50,000 $ 50,000

Levee Construction CY 125,000 $ 8 $ 1,000,000

Inflow Channel Construction CY 32,500 $ 4 $ 130,000

Rehab Drainage Pits EA 4 $ 25,000 $ 100,000

Sodding SY 150,000 $ 2.50 $ 375,000

Planting AC 334 $ 5,000 $ 1,670,000

Boardwalk LF 4,800 $ 150 $ 720,000

Subtotal Construction $ 4,212,000

Engineering/Permitting 10% $ 421,200

Contingency 20% $ 842,400

Grading Allowance CY 538,853 $ 3 $ 1,616,560

Grand Total $ 7,092,160

about 4,800 linear feet of boardwalk to create an expansive, park-like setting. The actual extent of planting and public access features desired by the City can be determined during the project planning and preliminary design phases. These estimates were prepared to provide a likely range of construction costs.

Key assumptions related to the cost estimates above are as follows:


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• The existing pumps and pipelines are sufficient to deliver flow to the three sprayfield parcels that would be converted to wetlands.

• An allowance for 1 foot of grading across the site has been included.

• Clearing and grubbing only requires the removal of herbaceous vegetation.

• An allowance is provided for rehabilitation of the existing drainage pits to increase soil permeability.

• No attempt was made to investigate existing topography or balance earthwork volumes.

The total estimated cost for Option 1 (reduce planting and no boardwalk) is about $4.2 million. The total estimated cost for Option 2 is about $7.1 million. It should be noted that these costs are based on general assumptions and preliminary estimates of earthwork requirements.

Estimated Wetland Performance Wetland performance estimation methods include regression equations, mass loading versus outflow concentration analyses, and models that incorporate first-order removals with a background, such as the k-C* model of Kadlec and Knight (1996). Regression models and mass loading analyses are limited to the range of the data used to generate the original regression. First-order removal models are less limited but their performance estimates should be compared to and validated against actual operational data whenever possible. The mass loading versus outflow concentration analyses and k-C* model are further described below.

Mass Loading Analyses The North American Database (NADB) Version 2 houses design criteria and operational performance data from over 250 treatment wetlands that receive municipal wastewater, industrial wastewater, agricultural wastewater, and/or stormwater (CH2M HILL 1998). Inflow mass loads can be calculated from inflow rates and influent concentration values and plotted against observed effluent concentrations. Performance estimates from the k-C* model can be superimposed on these plots as a check of the wetland sizing approach. These plots are presented in the Results section below.

k-C* Model The simplest expression of the first-order, area-based plug flow wetland performance model, assuming no net rainfall or seepage, is:

ln (C1/C2) = k1/q [1]

where:

C1 = average inlet concentration, mg/L

C2 = average outlet concentration, mg/L


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k1 = first-order, area-based rate constant, m/y

q = average hydraulic loading rate, m/y

Data from many treatment wetlands indicate that internal and external loading of pollutants such as nitrogen and phosphorus may result in non-zero, irreducible wetland water column constituent concentrations (Kadlec and Knight 1996). In this situation, the plug flow model can be corrected by introducing a second parameter that represents the lowest achievable or irreducible concentration that will occur in a treatment wetland, C*. The two-parameter first-order, area-based plug flow model, or k-C* model, is:

ln[(C1-C*)/(C2-C*)] = k/q [2]

Temperature has been found to be an important determinant in wetland performance for some pollutants (Kadlec and Knight 1996). This effect can be modeled by the following equation:

kT = k20 (θ)(T-20) [3]

where:

kT = the first-order reaction rate at a temperature of T oC, m/yr

k20 = the first-order reaction rate at 20 oC, m/yr

θ = dimensionless constant

The estimated outflow concentration can be calculated by combining equations 2 and 3 and re-arranging the terms as follows:

C2 = C* + (C1 – C*)exp(-kT/q)

Model Results Exhibits 12 through 14 present estimated monthly outflow concentrations from the proposed wetland based on the three alternative estimated nitrogen mass balances presented above. These estimates are based on the following assumptions:

• Total wetland area = 334 acres

• Removal rate constant for TN at 20 oC (k20) = 22 m/yr (median value in the NADB)

• Background concentration for TN (C*) = 1.5 mg/L (median value in the NADB)

• Temperature coefficient (θ) = 1.05 (median value in the NADB)

The results show that over the range of current and possible future inflow conditions, a 334-acre treatment wetland is estimated to reduce TN concentrations close to the assumed conservative background concentration of 1.5 mg/L. Some treatment wetlands in Florida operate at background TN concentrations less than 1 mg/L (for example see the 16-year data record from the Orlando Easterly Wetland, Exhibit 15). Changing the model parameters so that C* is equal to 1 mg/L has the effect of lowering the estimated outflow concentration to less than 1.2 mg/L in all months.


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EXHIBIT 12 k-C* Model Results for 3.0 MGD Nitrogen Balance (see Exhibit 3)

Month Combined TN Load

(lbs) Flow (WWTF +

Rain, MGD)

TN In

C1 (mg/L) Water Temp

(oC) q (m/yr)

TN Out

C2 (mg/L)

January 6875 3.88 6.85 12.0 4.0 1.6

February 6460 4.32 6.40 14.0 4.4 1.6

March 7660 4.16 7.13 17.0 4.2 1.6

April 5974 3.55 6.72 19.5 3.6 1.5

May 6189 3.67 6.52 24.0 3.8 1.5

June1 8268 5.29 6.25 26.5 5.4 1.5

July 9346 5.80 6.23 27.5 5.9 1.5

August 9314 5.55 6.49 27.5 5.7 1.5

September 8095 5.21 6.21 26.0 5.3 1.5

October 5910 3.72 6.15 21.5 3.8 1.5

November 6843 3.40 8.05 17.0 3.5 1.5

December 7374 3.84 7.42 13.0 3.9 1.6

Average 7359 4.37 6.52 14.0 4.5 1.6

A = 334 acres; k20 = 22 m/yr; C* = 1.5 mg/L, θ = 1.05 1The June fertilizer load (see Exhibit 3) was not included as the wetland will not be fertilized.


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(lbs) Flow (WWTF +

Rain, MGD)

TN In


(oC) q (m/yr)

TN Out

C2 (mg/L)

January 8038 4.38 7.10 12.0 4.5 1.7

February 7300 4.72 6.62 14.0 4.8 1.7

March 8694 4.56 7.38 17.0 4.7 1.6

April 7099 4.05 7.01 19.5 4.1 1.5

May 7352 4.17 6.81 24.0 4.3 1.5

June 9519 5.79 6.57 26.5 5.9 1.5

July 10639 6.30 6.53 27.5 6.4 1.5

August 10607 6.05 6.78 27.5 6.2 1.5

September 9221 5.71 6.45 26.0 5.8 1.5

October 6944 4.22 6.37 21.5 4.3 1.5

November 7068 3.80 7.44 17.0 3.9 1.5

December 7581 4.24 6.91 13.0 4.3 1.6

Average 8339 4.83 6.67 14.0 4.9 1.7

A = 334 acres; k20 = 22 m/yr; C* = 1.5 mg/L, θ = 1.05


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(lbs) Flow (WWTF +

Rain, MGD)

TN In


(oC) q (m/yr)

TN Out

C2 (mg/L)

January 5237 4.93 4.11 12.0 5.0 1.6

February 5107 5.56 3.93 14.0 5.7 1.6

March 5352 5.27 3.93 17.0 5.4 1.6

April 3436 4.27 3.22 19.5 4.4 1.5

May 2669 4.34 2.38 24.0 4.4 1.5

June 3818 6.83 2.23 26.5 7.0 1.5

July 4358 7.53 2.24 27.5 7.7 1.5

August 4208 7.14 2.28 27.5 7.3 1.5

September 3853 6.56 2.35 26.0 6.7 1.5

October 2900 4.51 2.49 21.5 4.6 1.5

November 3468 4.08 3.40 17.0 4.2 1.5

December 4215 4.99 3.27 13.0 5.1 1.6

Average 4052 5.50 2.85 14.0 5.6 1.6

A = 334 acres; k20 = 22 m/yr; C* = 1.5 mg/L, θ = 1.05


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Inflow OutflowTN 2.37 0.80TP 0.279 0.063

P.O.R. = 1/88 - 4/04

Long-term Average (mg/L)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

Mar-86 Dec-87 Sep-89 Jun-91 Feb-93 Nov-94 Aug-96 Apr-98 Jan-00 Oct-01 Jun-03 Mar-05

Date

TN C

once

ntra

tion

(mg/

L)

Inflow Outflow

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

Mar-86 Dec-87 Sep-89 Jun-91 Feb-93 Nov-94 Aug-96 Apr-98 Jan-00 Oct-01 Jun-03 Mar-05

Date

TP C

once

ntra

tion

(mg/

L)

Inflow Outflow

EXHIBIT 15 Summary of monthly average TN and TP data from the Orlando Easterly Wetlands (Source: City of Orlando)


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Exhibit 16 compares the maximum monthly mass loading rate for TN (July; 3.5 MGD Case) to data from the NADB. For systems with a similar range of inflow concentrations, the estimated median outflow concentration is about 1.7 mg/L. This compares well with the estimate from the k-C* model of 1.5 mg/L.

NADB v.2 Monthly Averages

Mas

s Lo

adin

g A

vg =

1.1

9

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1 1 10 100 1000

TN Loading (kg/ha/d)

Ave

rage

TN

Out

, mg/

L

Constructed - Cin < 3 mg/LConstructed - Cin = 3-6 mg/LConstructed - Cin > 6 mg/LNatural - Cin < 3 mg/LNatural - Cin = 3-6 mg/LNatural - Cin > 6 mg/L

Median = 1.7

EXHIBIT 16 Comparison of Maximum Month (July, 3.5 MGD Nitrogen Balance) Nitrogen Mass Loading Rate versus Outflow Concentration to Operational Data from the NADB

Groundwater Discharge Most treatment wetlands are designed with surface water discharges to streams, rivers, or other natural wetlands. However, there are multiple precedents for treatment wetlands that discharge completely to groundwater and evapotranspiration (ET). Some of these systems are briefly described below.

Green Cay Wetlands, Palm Beach County, FL

• Approximately 70 acres (Phase 1) of constructed marsh

• Design flow of 3 MGD (annual average daily flow, AADF)

• Receives secondary treated effluent

• Discharges to groundwater


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Deer Park Wetlands, Pasco County, FL

• 146 acres of natural cypress dome wetlands

• Permitted capacity of 1.2 MGD (AADF)

• Permitted surface water discharge to river, but no physical conveyance from wetland to river. All applied flow discharged to groundwater.

Incline Village, NV

• 390 acres of constructed wetlands

• Design flow of 1.7 MGD (AADF)

• All applied flow lost to groundwater or ET

Pintail Lake and Redhead Marsh, AZ

• 201 acres of open water lakes and marshes

• Design flow of 1.4 MGD

• Some infiltration, but most applied water lost to ET

• Permit includes a surface discharge point for the 100-year storm event

Sweetwater Wetlands, Tucson, AZ

• 17.5 acres of constructed marsh wetlands

• Design flow of 1 MGD

• Wetlands discharge to groundwater recharge basins (14 acres)

Conclusions The preceding analysis indicates that the conversion of the Lake City Sprayfield to a constructed surface-flow treatment wetland will provide the City of Lake City with an improved level of effluent polishing that will help to safeguard the quality of sensitive downstream water bodies. In all cases evaluated above, the estimated effluent quality was better for treatment wetlands than for the sprayfields. A detailed cost comparison is expected to show that the treatment wetlands are a more cost effective option than upgrades to the existing sprayfield facility.

In addition to improving water quality, treatment wetlands provide numerous ancillary benefits not currently offered by the sprayfields. Operations and maintenance requirements may be reduced as the City would not need to operate high-pressure pumps, service the irrigation equipment, or harvest hay. Valuable, high quality wildlife habitat can be created and made accessible to the public for activities such as birdwatching and trail walking. A wetland park system could also be made available to educators at the grade school and college level.


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References CH2M HILL. 1998. Treatment Wetland Habitat and Wildlife Use Assessment Project. Prepared for U.S. Environmental Protection Agency Office of Wastewater Management, U.S. Bureau of Reclamation, and City of Phoenix, Arizona.

International Water Association (IWA) 2000. Constructed Wetlands for Pollution Control. Processes, Performance, Design, and Operation. IWA Specialist Group on the Use of Macrophytes in Water Pollution Control. London, UK.

Kadlec, R.H., and R.L. Knight. 1996. Treatment Wetlands. CRC/Lewis Publishers, Boca Raton, FL. 893 pp.

U.S. Environmental Protection Agency (USEPA) 1993. Constructed Wetlands for Wastewater Treatment and Wildlife Habitat. 17 Case Studies. EPA832-R-93-005.

About the Authors Robert L. Knight, Ph.D. Dr. Knight is a consulting environmental scientist and president of Wetland Solutions, Inc. (WSI) located in Gainesville, Florida. He has focused his professional career on researching wetland and aquatic ecosystems and engineering natural and constructed wetlands for treatment of wastewaters. During the past 17 years with CH2M HILL and eight years as head of WSI, Dr. Knight has been influential in applying treatment wetland technology nationwide for management of municipal, industrial, and agricultural wastewaters and stormwaters. He has conducted more than 250 treatment wetland projects including feasibility studies, designs, permitting efforts, construction, and operational monitoring and data analyses. He has worked in all aspects of treatment wetlands including: site selection, wetland process design, design of monitoring programs, system troubleshooting, training of owner staff in operation and maintenance (O&M), preparation of O&M manuals, development of planting plans and specifications, and field monitoring of sediments, biota, hydrology, and water quality.

Dr. Knight completed a review of the habitat values of treatment wetlands throughout North America for the Environmental Protection Agency (EPA). He also completed reviews of the use of treatment wetlands for management of concentrated animal wastes, petroleum industry wastewater management, and pollution control for the pulp and paper industry. Dr. Knight was lead author and co-principal investigator of the North American Treatment Wetland Database for EPA, was lead author of the wetland systems chapter in the Water Environment Federation’s Natural Systems Manual of Practice, and of the Arizona Department of Environmental Quality’s Treatment Wetland Guidance Manual. Dr. Knight is co-author with Dr. Robert Kadlec of the definitive book Treatment Wetlands published in 1996 by CRC Press/Lewis Publishers.

Christopher H. Keller, P.E. Mr. Keller is an environmental engineer with WSI in Gainesville, Florida. During his nine years with CH2M HILL and three years with WSI, Mr. Keller has conducted numerous projects, including water and air quality engineering, monitoring, treatment, and


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permitting. Mr. Keller has particular expertise in treatment wetlands design, performance optimization, data interpretation, and trouble shooting. Example projects completed by Mr. Keller include the following:

• Performance estimation and process design guidance for numerous large-scale stormwater treatment area (treatment wetland) projects in south Florida including the Nubbin Slough STA, Lake Okeechobee STAs, and the C-44 STAs.

• Final design of a pilot-scale treatment wetland system for the Village of Wellington, Florida. The design combined several different wetland ecosystem types to evaluate the lower limit of phosphorus removal from polluted stormwater. The Village of Wellington Aquatics Pilot Program was the first operational research-scale treatment system to combine floating aquatic plant, emergent marsh, submerged aquatic vegetation, and periphyton ecosystems in series.

• Conceptual designs for a stormwater treatment wetland for the Sweetwater Branch watershed in Gainesville, FL and for the Griffin Road watershed in Lakeland, FL.

• Development of a conceptual design for a 40-acre demonstration treatment wetland adjacent to the eastern boundary of Everglades National Park. The design was prepared for the U.S. Army Corps of Engineers to evaluate the phosphorus removal effectiveness of engineered wetland ecosystems.

• Preliminary design for the 150-acre Winsberg Farm Wetlands in Palm Beach County, Florida. The design blends various native wetland habitats with significant public access and educational components.

• Assistance with the design of the Wakodahatchee Wetlands, a 40-acre constructed wetland treatment system in Palm Beach County, Florida.

• Assistance with the permit renewal of the Deer Park wetlands treatment system, a 146-acre natural cypress dome system in Pasco County, Florida. This project included analysis of water quality data, nutrient removal modeling to determine possible impacts to the receiving waters, and preparation of an Operations and Monitoring plan.

• Resident engineer for wastewater treatment plant improvements, including the relocation of a reclaimed effluent surface water discharge in Hillsborough County, Florida.

Lake City Conceptual Plan v.3 - WSI€¦ · Introduction ... 11 Inflow Distribution Channels.....13...

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