Deep Creek West Regional Stormwater Treatment (RST) Facility Tri-County Agricultural Area, St. Johns County Water Quality Report

Transcription

1 Deep Creek West Regional Stormwater Treatment (RST) Facility Tri-County Agricultural Area, St. Johns County Water Quality Report Alicia Steinmetz, AMEC-BCI Pam Livingston Way, St. Johns River Water Management District Lower St. Johns River Basin Program Division of Environmental Sciences April

2 Contents Introduction... 4 Background... 4 Project Objective... 4 Project Treatment Components... 5 Operation and System Hydraulics... 5 Operation and Management Hydrologic Monitoring Water Levels, Flow, and Hydraulic Loading Wetland Dye Tracer Study Methods - Data Collection and Analysis Ambient Data Collection Storm Event Data Collection Pollutant Loading and RST Treatment Performance (Mass Removal) Volume Estimates Results Ambient Load Storm Load Total Load Reductions Ambient and Storm Load Combined 2009 and Conclusions and Recommendations Literature Cited

3 Figures and Tables Figures Tables 1 Location of the Deep Creek Regional Stormwater Treatment Facility a. RST operation... 8 b. Wetland header ditches and bypass structure... 9 c. Ambient and storm sampling stations a-c. Annual and seasonal ambient total nitrogen load Monthly ambient total nitrogen load a-c. Annual and seasonal ambient nitrate+nitrite load a-c. Annual and seasonal ambient total phosphorus load a. Monthly ambient total phosphorus load b. Monthly rainfall a-c. Annual and seasonal ambient orthophosphate load a-c. Annual and seasonal ambient total suspended solids load Monthly ambient total suspended solids load Total nitrogen storm load Nitrate+Nitrite storm load Total phosphorus storm load Orthophosphate storm load Total suspended solids storm load Ambient loading into and out of facility and 2010 loading for sampled storms Annual and seasonal storm event loading into and out of facility 2009-August Annual and seasonal total mass removals (ambient and storm)

4 Introduction The Deep Creek West Regional Stormwater Treatment Facility was constructed by the St. Johns River Water Management District (SJRWMD) in 2006 to improve the quality of water exiting priority subbasins in the tri-county agricultural (TCAA) watershed. This is the sixth report on water quality for the Deep Creek West RST facility, but the first report to present water quality treatment in terms of mass removals. Previous reports presented only concentration data for key water quality constituents due to the lack of flow data needed to calculate pollutant loading and treatment performance. Pollutant loading data are now available for the inflow and outflow of the facility, which provides a more accurate measure of treatment performance since some treatment systems can effectively capture and reduce the volume of water discharged, thus reducing the pollutant load (U.S. EPA 2008). Data collected under ambient conditions are presented for 2008 through 2010 and data collected for storm conditions are presented for 2009 through August Background Since 1998, best management practices (BMPs) designed to reduce nutrient rich runoff have been implemented in the TCAA, primarily through growers voluntarily participating in the St. Johns River Water Management District s TCAA Water Quality Protection Cost Share Program. Based on row crop acreage from 2000 land use data, implementation of in-field BMPs (e.g., IFAS recommended fertilizer rates, fertilizer application timing, fertilizer placement, water table management, etc.) on all rowcrop acres has been estimated to reduce watershed nitrogen loading by 24% and phosphorus loading by 14% (Pam Livingston-Way, SJRWMD Division of Environmental Sciences, pers. comm. 2008). Unfortunately, these nutrient reductions are not sufficient to reduce loads to the level required by the Total Maximum Daily Loads (TMDLs) for the freshwater section of the river, which were mandated by the Clean Water Act after these waters were added to the 303 D list of impaired waters by the Florida Department of Environmental Protection. In order to meet TMDL allocations for the freshwater segment of the LSJR, the TCAA is obligated to implement BMPs on 100% of all agricultural acreage and achieve a 37% reduction in nitrogen and a 15% reduction in phosphorus (LSJR TMDL Executive Committee 2008). Model predictions suggest that nutrient reductions through full implementation of current in field BMPs will not be sufficient to meet nitrogen and phosphorus reductions for the freshwater section of the river. Thus, the District constructed regional stormwater treatment facilities to assist in meeting the TMDL allocations. Project Objective The Deep Creek West RST facility was the first regional treatment system constructed in the TCAA. The facility is located in St. Johns County near Hastings, FL within the 38,928-acre Deep Creek basin, and it services a high-priority ranked subbasin comprising 93% agricultural land (Figure 1). The facility receives drainage from a 1,196-acre drainage area 4

5 serviced by Canals 1 and 2 in the Hastings Drainage District. Project goals are to reduce watershed loading total phosphorus by 60%, total nitrogen by 50%, and total suspended solids by 70% from a combination of both ambient (e.g, baseflow and irrigation runoff) and storm events. In addition, the Lower St. Johns River Basin Management Action Plan (LSJR BMAP) was finalized in October 2008, as a management plan developed to meet the rule-adopted TMDLs. The BMAP states that an estimated 1,000 kg/yr of nitrogen and 818 kg/yr of phosphorus is expected to be removed by the facility (LSJR TMDL Executive Committee 2008). Project Treatment Components The Deep Creek West RST facility is a BMP treatment train consisting of a 15-acre wet detention pond at the forefront, followed by a 38-acre constructed treatment wetland; George Miller Road separates the wet detention pond and the treatment wetland. The wetland component of the facility is on a former agricultural site, and such sites may release stored phosphorus during flooding (Pant and Reddy 2003). Soil tests conducted by the District determined that elevated levels of phosphorus were stored in the mineral soils. To abate the existing soil phosphorus, soils were amended with an aluminum sulfate drinking water treatment residual to bind legacy phosphorus resulting from 20 plus years of agricultural production. Operation and System Hydraulics Beginning in February 2006, the wet detention pond was intermittently the sole functioning component. Full operation commenced in October 2006, at which time, both components of the treatment train were online (i.e., wet detention pond and constructed wetland). The RST operates by diverting a portion of agricultural runoff from the confluence of Hastings Drainage District Canals 1 and 2, located at the north end of the wet detention pond, into the wet detention facility (Figure 2a). Runoff gravity flows into a small forebay basin (i.e., approximately 0.25 acre), where it is then pumped into the 15-acre wet detention pond for initial treatment. The pump station was designed to capture up to 90% of flow, with pumps to accommodate peak flow rates of 20 cubic feet per second (cfs) and 10 cfs under general baseflow conditions. The actual percentage of canal flow treated by the RST is unknown at this time, but it will be determined as the Division of Hydrologic Data Services (HDS) began monitoring the canal flow in HDS will develop flow rating curves after sufficient data have been collected. The RST is dynamic and essentially event-driven by hydraulic patterns in the watershed created by seasonal weather conditions and agricultural activities. Hydraulic loading depends upon a combination of pumping capacity and fluctuating water levels in Canals 1 and 2 resulting from agricultural irrigation during the agricultural growing season (January May) and/or storm events. Tidal fluctuations can also affect canal levels. Variable pumping regimes are 5

6 implemented based on water levels in the forebay basin, which are directly influenced by canal levels. Either one pump or two pumps are activated based on the forebay basin water level. Furthermore, pumping regimes are not determined by water level in the wet detention pond or the volume of water exiting the pond outfall structure, except under extreme conditions when the wet detention pond water level overtops the emergency overflow structure and the pumps are programmed to shut off. After runoff is pumped into the wet detention pond from the forebay basin and pond water level rises, water is directed to the constructed wetland header ditch via a concrete weir outfall structure. Water stages up in the header ditch and flows into the wetland via subsurface and/or surface flow, where it is treated and discharged from the outflow of the wetland to Deep Creek (Figure 2c). Residence times within the treatment system vary widely. From 2007 to 2009, the hydraulic residence time in the pond was estimated to range from 9 to 72 days with an annual average of 24 days in 2009 (Yang and Richmond 2009). Likewise, average residence time within the wetland under baseflow conditions was estimated at 7.2 days, and between 1 and 3 days under storm conditions based on results of a tracer dye study (WSI 2010). 6

7 Figure 1. Location of the Deep Creek West Regional Stormwater Treatment Facility. Pond Wetland 7

8 Figure 2a. RST operation. Canal 1 1-Canal Inflow 2-Pond Outflow Canal 2 3-Wetland Outflow 8

9 Figure 2b. Wetland header ditches and bypass structure. Figure 2c. Ambient and storm sampling stations. Canal Inflow Wetland Outflow Pond Outflow 9

10 Operation and Management Since inception of the project, the RST has been operated and managed by SJRWMD. Beginning in October 2010, St. Johns County assumed various operation and management responsibilities in order to receive credit towards their required reductions in nitrogen and phosphorus loading as outlined in the LSJR BMAP (LSJR TMDL Executive Committee 2008). Some of the tasks assumed by the county include pump station maintenance; vegetation removal; pond exotic and invasive plant management; mowing; fencing and security; maintenance of parking and roadways; and public access monitoring. A more comprehensive listing of entity responsibilities are outlined in the operation and management plan (SJRWMD 2010a). Hydrologic Monitoring Water Levels, Flow, and Hydraulic Loading The Environmental Sciences Division s (ES) Lower St. Johns River Basin Program (LSJR) staff continue to conduct weekly maintenance and equipment calibration at monitoring and telemetry stations, as well as daily remote monitoring of the pump system and storm sampling programs. Since implementing a weekly maintenance schedule in January 2008, water level and flow data collection have continued uninterrupted. As mentioned in previous reports, flow rates for Canal 1 will be developed by HDS using continuous stage and acoustic velocity data. HDS installed the monitoring equipment and began collecting data in October HDS continues to perform periodic equipment calibrations by recording manual stage and velocity measurements. Estimates of facility capture rates are pending completion of this work. Canal 1 water elevations (NGVD29) measured at the RST inflow from February 2008 to June 2009 have ranged from 0.17 to 7.72 ft, which include measurements of stage affected by irrigation runoff during the agricultural growing season, storm events, and lack of agricultural activity during the fallow season (note: previous reports on water quality at the RST presented canal water levels; water elevations were not available at the time). Water elevations greater than 1.36 ft typically are associated with storm events. The highest recorded water elevation in the canal was 7.72 ft in May 2009, and the second highest elevation was 6.67 ft in August 2008 during the passage of Tropical Storm Fay. Monthly average water elevations have ranged from 0.83 to 2.60 ft. Several significant changes to hydrologic calculations are continuing to occur. First, a mass balance water budget is being developed by the Division of Engineering to estimate flow volume exiting the pond. The mass balance water budget will be used to estimate pollutant loading data for water quality constituents at the outflow of the pond. Albeit the outflow of the pond is not the outflow of the treatment system, but estimates of pollutant loading discharged from the pond are essential to adequately manage the facility to optimize treatment performance. Second, the weir equation 10

11 used to calculate flow rates at the outflow of the wetland was revised by the Division of Engineering in June The revised equation is now being used to calculate pollutant loading at the outflow of the facility (wetland). Historical flow/volume data were revised using the new equation. In addition, Environmental Sciences and Engineering project staff met in November 2009 and discussed the possibility of an adjustable weir plate at the outflow of the wetland to increase the wetland weir height during dry periods and stage up water levels in the wetland. The Division of Engineering determined that adjusting the weir height from its current level of 4 feet to 4.5 or 5 feet, would result in an additional 3 and 6 acres of inundation, respectively. The resulting area of inundation was deemed insufficient to warrant the additional expense and risk that would result from an adjustable weir plate. Another issue discussed was reverse flow from Deep Creek into the wetland over low areas of the berm during extreme storm conditions. Project management and Engineering staff requested the berm be surveyed by the Division of Survey to determine the locations and elevations of the low areas. It was determined, however, that the areas of low elevation along the entire length of the north and east ends of the berm were so numerous that they could not be feasibly and economically repaired. Thus, the proposed survey was canceled. Wetland Dye Tracer Study In June 2010, the Division of Environmental Sciences executed a contract with Wetland Solutions, Inc. (WSI) to conduct a dye tracer study at the wetland to identify areas of hydraulic short-circuiting and dead zones; estimate existing average residence time within the wetland; provide recommendations for cost-effective solutions to correct short-circuits; and estimate increased residence times if short-circuit improvements were implemented. Study findings indicated that dead zones likely accounted for approximately 11 acres or 29% of the wetland interior; only 5.1 acres or 13% of the wetland had standing water when water levels were at or below the wetland weir elevation (i.e., 3.96 ft.); and average residence time was 7.2 days. Under storm conditions, residence time was estimated to range from 1 to 3 days (WSI 2010). Recommendations included several construction alternatives (i.e., alternative 1 and 2) comprised of a suite of improvements to enhance wetland functioning. Suggested improvements were grading the wetland to a constant elevation; backfilling areas of the inflow header ditch; deepening portions of the inflow header ditch; construction of a deep zone within the center of the wetland; installation of adjustable weir gates at the outfall so that weir height could be increased; replanting of vegetation; and significant reconstruction of the north and east berms. The most significant improvements under alternative 1 that could be implemented would be grading the wetland and increasing the wetland weir control elevation to 5.5 feet, which could result in a wetted area of 38 acres with a potential expected nutrient removal increase of 600%. Albeit there are other factors to consider when estimating nutrient removal that were not included in this estimate as they were beyond the scope of the study. The most significant improvement under alternative 2 that could be implemented would be to increase the wetland weir control elevation to 5.0 feet, which could increase the wetted area from 5.1 acres to 11.1 acres (note: the predicted wetted area increase differs from that 11

12 estimated by the Division of Engineering, which was a wetted area of only 6 acres with a weir elevation at 5 ft). Expected nutrient removal could potentially double with a wetted area of 11.1 acres (WSI 2010). Methods - Data Collection and Analysis Ambient Data Collection LSJR field staff collected monthly grab samples on the same day to characterize water quality at: inflow to the treatment system (Canal 1), pond outflow, and wetland outflow (outflow of the treatment system) (Figure 2c). These samples represented water quality under ambient conditions (e.g., baseflow and irrigation runoff). Since June 2008, samples were also collected at the wetland outflow two weeks following the same-day grab sampling to capture the lag time or the expected time it takes for a slug of water to move through the wetland after being discharged from the pond. When available, data collected at the wetland outflow on the two-week sampling schedule were used in the analyses. Samples were collected in accordance with the SJRWMD Field Standard Operating Procedures for Surface Water Sampling 2010 (SJRWMD 2010b). Recent estimates from a tracer dye study conducted in June 2010 indicated that average residence time within the wetland was likely 7.2 days, and between 1 and 3 days following storm events (WSI 2010). The average residence time within the wet detention pond of the treatment train was estimated to be 24 days in 2009, ranging from 9 to 72 days (Yang and Richmond, 2009). Presumably, residence times within both treatment components fluctuate based on variability in pumped inflow volumes. Ambient data collected at the outflow in September and October 2008, and in May and June 2009, were not included in the analyses. In September 2008 and May 2009, two significant storm events caused the reverse flow of water from Deep Creek into the wetland where water overtopped the wetland berm and outfall structure. Wetland water quality was likely influenced by the input of water from Deep Creek. Thus, data collected at the wetland outflow immediately following the reverse flow occurrences and the subsequent month were excluded from the dataset. This report includes pollutant loading estimates for 2008, 2009, and January through August Water quality collection began in February 2007; however, accurate flow/volume estimates were not available to calculate pollutant loading for Storm Event Data Collection Water quality samples associated with storm events were collected from January to December 2009 and from January to September 2010 (data available only through August 2010 for this report). Several events were collected in 2008; however, those data were deemed questionable due to equipment failures. Automated refrigerated sampling units were located at the canal inflow, pond outflow, and wetland outflow (Figure 2c). Automated samplers were triggered by stage increases indicative of storm events as well as triggered manually to capture lag times at the pond and wetland outflow. 12

13 The storm sampling program at each monitoring station collected daily composite samples over a seven day period to ensure sampling covered the complete storm hydrograph. Analyses of stage fluctuations in Canal 1 during several storm events verified that storm the hydroperiod typically occurred over seven days. The program collected 8 sample aliquots (100 ml/aliquots) per bottle every 8 minutes for the first 2 hours to capture the rising limb of the storm hydrograph and first-flush of nutrients, succeeded by sampling at equal time intervals for the remainder of the first day of the storm (for example, if 4 hrs remained in the day then samples were collected every 0.5 hr). Samples were then collected every 3 hours per day as a daily composite sample of eight aliquots for the next six days. District laboratory Quality Assurance and Quality Control was maintained as much as logistically possible considering sampling methodology. Samples were refrigerated within the autosampler unit when the first sample was collected. Sample temperatures were maintained according to the SJRWMD Field Standard Operating Procedures for Surface Water Sampling 2010 (FSOP SWS 2010) until samples were retrieved and transported to the District lab for analysis. Cooling of samples assists in reducing microbial activity and species transformation; however, specific analytes were required to be coded for Q = holding time exceeded, Y = samples not acid preserved within 15 minutes of collection, and J = sample not filtered within 15 minutes of collection (pers. comm. Steve Richter, SJRWMD Division of Laboratory Services). Sample containers were not pre-preserved upon deployment since some forms of nutrients (i.e., dissolved orthophosphate and dissolved nitrate+nitrite) and total suspended solids did not require acidification. Typically, samples were preserved and filtered between day 8 and day 14 after collection and immediately submitted to the lab for analysis. Pollutant Loading and RST Treatment Performance (Mass Removal) Treatment performance was calculated as a mass load reduction and a percent mass removal for TP, TN and TSS, which included volumetric comparisons or total load entering and exiting the facility (Canal 1 inflow vs. wetland outflow) (Figure 2c). Comparison of inflow and outflow water quality concentrations alone does not accurately evaluate treatment performance since some treatment systems can effectively capture and reduce the volume of water discharged, thus reducing the pollutant load (U.S. Environmental Protection Agency 2008). Mass loading and percent mass removal (i.e., removal efficiencies) were estimated annually, as well as seasonally (i.e., growing and fallow seasons) for both ambient and storm conditions at the inflow and outflow of the RST. Loading data from the outflow of the pond were not available during the writing of this report. These data are pending completion of a mass balance water budget provided by the Division of Engineering. Pollutant loads for the ambient and storm datasets were calculated separately. Pollutant loads representative of ambient conditions were calculated by multiplying monthly concentrations of key parameters by the relevant, monthly total volumes pumped into the facility and discharged from the facility. Volumes associated with sampled storm 13

14 events in 2009 (i.e., 20 events) and 2010 (i.e., 10 events) were removed from the ambient dataset prior to ambient load calculations. Similarly, pollutant loads associated with storm events were calculated by multiplying sample concentrations by the volume of water pumped into the facility and volume of water discharged from the facility during the timeframe storm samples were collected. Daily storm loads were then summed, yielding a total mass load for a 7- day sampled event. Next, mass loads per sample event were totaled resulting in annual and seasonal storm loads. Finally, ambient and storm loads were then summed yielding estimated total loads for the RST. Percent mass removal (i.e., removal efficiency) was calculated as: where % Mass removal = 100 X QiCi-QoCo QiCi Qi = inflow volume (volume pumped into RST), m 3 Ci = canal concentration, mg L -1 Qo = wetland outflow volume, m 3 Co = wetland outflow concentration, mg L -1 Volume Estimates Inflow volumes used to calculate pollutant loading into the facility from Canal 1 were obtained from the pump runtimes and average flow rates for the two pumps located at the inflow of the RST. Flow rate for pump 1 was 10 cfs through March 25, After March 25, average flow rate was estimated to be 12.4 cfs. For pump 2, flow rate was 10 cfs through February 16, Flow rate increased to 11.9 cfs after February 16. Average pump flow rates increased in February and March 2009 because of the conversion of pumps from a belt-driven operating system to a direct drive system. Pump flow rate testing was conducted in August 2009 (HSA 2009). Volumes associated with the outflow of the RST (wetland outflow) were calculated using a sharp crested weir equation (minus the end contractions): Q = L x C x (h) 3/2 where L = weir length (11.71 ft) C = weir discharge coefficient (3.2) h = wetland water surface elevation(ft) weir elevation (3.96 ft) 14

15 This equation was provided by the District s Division of Engineering in June Results Ambient Load Ambient Total Nitrogen Load. Annual total nitrogen (TN) load from 2008 to 2010 pumped into the facility ranged from 905 to 3,310 kg and TN discharged ranged from 617 to 1,314 kg (Table 1). Annual reductions in TN loads for all three years ranged from 271 to 1,996 kg (Figure 3a). Loads varied month to month with some months having higher export loads than incoming loads (Figure 4). TN loading pumped into the RST under ambient conditions was greater during the fallow seasons compared to the growing seasons within years (Table 1). This is likely attributed to allochthonous inputs of organic compounds comprised of proteins, amino sugars, nucleic acids, and urea. When rainfall increases in northeast Florida, particularly from June to September, native uplands dominated primarily by pine flatwoods and saw palmetto experience rising water tables that leach organic solutes into receiving streams through flows of interstitial water, which increases total nitrogen and total organic nitrogen. These events also can influence the seasonal water chemistry in agricultural streams as forms of inorganic nitrogen are replaced by organic forms of nitrogen (Livingston-Way 2001). Facility load reductions were also greater during the 2008 and 2009 fallow seasons compared to the growing seasons. Growing season reduction in 2008 was 317 kg and 54 kg in 2009, whereas 122 kg were exported during 2010 growing season (Figure 3b). Fallow season load reductions across years ranged from 217 kg to 1,679 kg (Figures 3c). Annual removal efficiency of total nitrogen was 60% in 2008, 19% in 2009, and 32% in (Table 1). Ambient Nitrate+Nitrite Load. The nitrate+nitrite (NOx) load pumped annually into the facility ranged from 204 to 307 kg from 2008 to 2010 and NOx discharged ranged from 18 to 180 kg (Table 1). Annual reductions in NOx across all three years ranged from 90 to 289 kg (Figure 5a). Similar to TN load, NOx load pumped into the RST was greater during the fallow seasons compared to the growing seasons within years (Table 1). Growing season reductions for 2008 and 2009 were 19 kg and 133 kg, respectively; whereas, 87 kg were exported in Fallow season reductions ranged from 95 kg to 178 kg (Figures 5b,c). The greatest annual removal efficiency of NOx load occurred in 2008, which was 94%, followed by 55% in 2009, and 33% in 2010 (Table 1). Ambient Total Phosphorus Load. Annual total phosphorus (TP) load pumped into the facility ranged from 294 to 1,801 kg and TP discharged ranged from 164 to 1,110 kg (Table 1). Load reductions occurred only in 2008 and 2010 with 691 kg and 130 kg removed, respectively (Figure 6a). In 2009, 165 kg were exported. Loading appeared to increase from July to September in 2008 and 2009, concurrent with the northeast Florida rainy season (Figure 7a, b). Consequently, TP loading pumped into the RST was greatest during the fallow seasons compared to the growing seasons 15

16 within years (Table 1). Growing season reductions ranged from 19 kg to 216 kg and fallow season reductions ranged from 106 kg and 475 kg; however, 184 kg were exported during the 2009 fallow season (Figures 6b,c). Annual removal efficiencies were 38% in 2008, -23% in 2009, and 44% in 2010 (Table 1). Ambient Orthophosphate Load. Annual orthophosphate (PO4) load pumped into the facility ranged from 135 to 1,167 kg and PO4 discharged ranged from 130 to 996 kg (Table 1). Load reductions occurred only in 2008 and 2010 of which 171 kg and 6 kg were removed, respectively; whereas, 283 kg of PO4 were exported in 2009 (Figure 8a). Similar to TN, NOx, and TP, PO4 loading pumped into the facility was greater during the fallow seasons compared to the growing seasons within years (Table 1). The 2008 growing season was the only growing season when loading was reduced (118 kg), whereas 35 kg and 37 kg were exported in 2009 and 2010, respectively (Figure 8b). Load reductions during the fallow seasons occurred only during the 2008 and 2010 fallow seasons with 53 kg removed in 2008 and 43 kg removed in 2010, whereas 248 kg were exported in PO4 concentrations in the TCAA are generally seasonally dynamic. Typically during the fallow season, concentrations in TCAA receiving waters are approximately two times greater than those exhibited during the growing season. This flux of soluble phosphorus can result from changes in the soil s chemical properties (i.e., decreases in redox potential, increase in ionic strength, etc.) brought about by flood conditions experienced during the fallow season that increases the solubility of phosphorus (Livingston-Way 2001). Annual removal efficiencies of PO4 were 15% in 2008 and 4% in In 2009, removal efficiency was negative due to an export of PO4 (Table 1). Ambient Total Suspended Solids Load. Total suspended solids (TSS) load pumped into the RST ranged from 9,224 to 19,011 kg and TSS discharged ranged from 2,615 to 10,205 kg. TSS load was reduced in 2008 and 2010, but in 2009, 981 kg were exported (Figure 9a). TSS load was reduced during all three growing seasons, with the greatest removal in 2008 (i.e., 9,089 kg). TSS reductions did occur during the 2008 and 2010 fallow seasons, whereas 1,400 kg were exported during the 2009 fallow season (Figures 9c). TSS load entering the facility across years did not appear to be greater during the fallow seasons as was the case for TN, NOx, TP and PO4. The 2010 fallow season was the only season when loading pumped in was greater than the growing season. Moreover, there did not appear to be a consistent monthly trend in TSS load entering the facility or discharged from the wetland across years (Figure 10). However, there did appear to be cyclic variations across years. Annual removal efficiencies were 68% and 86% in 2008 and 2010, respectively. In 2009, removal efficiency was negative due to an export of suspended solids (Table 1). 16

17 Table 1. Ambient Loading into and out of facility Total Nitrogen Load (kg) Total Phosphorus Load (kg) Total Suspended Solids Load (kg) In Out Removal In Out Removal In Out Removal Efficiency (%) Efficiency (%) Efficiency (%) 2008 Annual % % % Growing Season % % % Fallow Season % % % 2009 Annual % % % Growing Season % % % Fallow Season % % % Through August 2010 Annual % % % Growing Season % % % Fallow Season % % % Nitrate+Nitrite Load (kg) Orthophosphate Load (kg) In Out Removal In Out Removal Efficiency (%) Efficiency (%) 2008 Annual % % Growing Season % % Fallow Season % % 2009 Annual % % Growing Season % % Fallow Season % % Through August 2010 Annual % % Growing Season % % Fallow Season % % 17

18 18

19 Total Nitrogen Load (kg) Figure 4. Monthly ambient total nitrogen load Ambient Total Nitrogen Load In Out J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

20 20

21 Total Phosphorus Total Load (kg) Total Phosphorus Total Load (kg) Total Phosphorus Total Load (kg) Figures 6a-c. Annual and seasonal ambient total phosphorus load. A. Annual Total Phosphorus Ambient Load kg removed kg exported 130 kg removed In Out Through August 2010 Year B. Growing Season Total Phosphorus Ambient Load kg removed 19 kg removed 24 kg removed In Out Through August 2010 Growing Season C. Fallow Season Total Phosphorus Ambient Load kg removed 184 kg exported 106 kg removed In Out Through August 2010 Fallow Season 21

22 Rainfall (in) Total Phosphorus Load (kg) Figure 7a. Monthly ambient total phosphorus load Ambient Total Phosphorus Load In Out J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D Figure 7b. Monthly rainfall Monthly Rainfall Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Growing Season (Jan-May) Fallow Season (Jun-Dec)

23 Orthophosphate Total Load (kg) Orthophosphate Total Load (kg) Orthophosphate Total Load (kg) Figures 8a-c. Annual and seasonal ambient orthophosphate load A. Annual Orthophosphate Ambient Load kg removed 283 kg exported kg removed In Out Through August 2010 Year B. Growing Season Orthophosphate Ambient Load kg removed 37 kg exported 35 kg exported Through August 2010 Growing Season In Out C. Fallow Season Orthophosphate Ambient Load kg removed 248 kg exported Through August 2010 Fallow Season 43 kg removed In Out 23

24 Total Suspended Solids Total Load (kg) Total Suspended Solids Total Load (kg) Total Suspended Solids Total Load (kg) Figures 9a-c. Annual and seasonal ambient total suspended solids load. A. Annual TSS Ambient Load ,887 kg removed 981 kg exported 16,396 kg removed Through August Year 2010 In Out B. Growing Season TSS Ambient Load ,089 kg removed 3,034 kg removed Through August 2010 Growing Season 3,252 kg removed In Out C. Fallow Season TSS Ambient Load ,799 kg removed 1,400 kg exported Through August 2010 Fallow Season 13,144 kg removed In Out 24

25 Total Suspended Solids Load (kg) Figure 10. Monthly ambient total suspended solids load Ambient Total Suspended Solids Load In Out J F MA M J J A S O N D J F MA M J J A S O N D J F MA M J J A S O N D

26 Storm Load Event Storm Load. Table 2 depicts the pollutant loads associated with sampled storms in 2009 and 2010 for the inflow and outflow, as well as the range in loads. Overall, storm loads for each event were considerably less at the outflow compared to the inflow indicating the facility functioned well in reducing storm load. 26

27 Table Loading for sampled storms In Loading (kg) Out Loading (kg) TN TP TSS Nox PO4 TN TP TSS Nox PO4 January January January January February February April , April May , April 28-May May 26-June , May 8 - May June 2-June , May June June 2-8 June 30-July June July , July July August July 29-August , August August , September August , September August , December September , December 29-Jan September , December , December , December , N N Minimum Minimum Maximum Maximum Table 2 continued Loading for sampled storms In Loading (kg) Out Loading (kg) TN TP TSS Nox PO4 TN TP TSS Nox PO4 January , January January 26-Feb January 26 - Feb February , February February , February 23-Mar March , March April 25-May , March 30-April May , April 25-May July , May August May August , July August August N N Minimum Minimum Maximum Maximum

28 Annual and Seasonal Storm Load Storm Total Nitrogen. Annual TN storm load entering the RST in 2009 was 4,283kg with only 930 kg discharged and in 2010, 2,976 kg were pumped in and 855 kg were discharged (Table 3). Removal efficiencies were 78% in 2009 and 71% in 2010 (Table 3; Figure 11). Seasonal reductions were greater during the 2009 and 2010 growing seasons than the fallow seasons. Growing season percent mass removals were 83% and 72% in 2009 and 2010, respectively and 75% and 67%, respectively during the fallow seasons (Table 3). Storm Nitrate+Nitrite. Removal of NOx during 2009 and 2010 was relatively high at 98% efficiency and 81% efficiency, respectively (Table 3; Figure 12). Loads entering and exiting in 2009 were 1,210 kg and 25 kg, respectively, and in 2010, 734 kg entered and 138 kg exited. Growing and fallow season reductions for both years were also high ranging from 78%-98% (Table 3). Storm Total Phosphorus. Annual TP load was reduced as well with a removal efficiency of 70% in 2009 and 75% in 2010 (Table 3; Figure 13). Loads entering and exiting in 2009 were 2,603 kg and 770 kg, and in 2010, 1,131 kg entered and 287 kg exited. Removal efficiencies were slightly higher in the growing seasons compared to fallow seasons for both years. In 2009 and 2010, growing season efficiencies were 71% and 77%, respectively and fallow season efficiencies were 70% and 69%, respectively (Table 3). Storm Orthophosphate. Removal efficiencies for PO4 were 61% in 2009 and 51% in 2010 (Table 3; Figure 14). Loads entering and exiting in 2009 were 1,340 kg and 520 kg and in kg entered and 183 kg exited. Growing season removal efficiencies were 71% in 2009 and 44% in 2010 and fallow season percent removals were 58% in 2009 and 54% in 2010 (Table 3). Storm Total Suspended Solids Storm Load. TSS removal efficiencies were relatively high for both years and seasonally. Annual TSS percent removals for 2009 and 2010 were 79% and 91%, respectively (Table 3; Figure 15). Growing season removals were 76% and 89%, respectively and fallow season removals were 81% and 94%, respectively. TSS load in was 64,219 kg in 2009 and load out was 13,207 kg. In 2010, 81,314 kg entered and 7,255 kg exited (Table 3). 28

29 Table 3. Annual and Seasonal storm event loading into and out of facility 2009-August Total Nitrogen Load (kg) Total Phosphorus Load (kg) Total Suspended Solids Load (kg) In Out Removal In Out Removal In Out Removal Efficiency (%) Efficiency (%) Efficiency (%) 2009 Annual % % % Growing Season % % % Fallow Season % % % Through August 2010 Annual % % % Growing Season % % % Fallow Season % % % Nitrate+Nitrite Load (kg) Orthophosphate Load (kg) In Out Removal In Out Removal Efficiency (%) Efficiency (%) 2009 Annual % % Growing Season % % Fallow Season % % Through August 2010 Annual % % Growing Season % % Fallow Season % % 29

30 1/12/2009 2/16/2009 4/29/2009 5/13/2009 6/2/2009 6/13/2009 7/4/2009 7/22/2009 8/3/2009 8/17/2009 8/28/2009 9/8/2009 9/18/ /8/ /19/2009 1/13/2010 1/26/2010 2/5/2010 2/16/2010 3/12/2010 4/3/2010 5/11/2010 5/22/2010 7/3/2010 8/4/2010 8/25/2010 Nitrate + Nitrite Storm Load (kg) 1/12/2009 2/16/2009 4/29/2009 5/13/2009 6/2/2009 6/13/2009 7/4/2009 7/22/2009 8/3/2009 8/17/2009 8/28/2009 9/8/2009 9/18/ /8/ /19/2009 1/13/2010 1/26/2010 2/5/2010 2/16/2010 3/12/2010 4/3/2010 5/11/2010 5/22/2010 7/3/2010 8/4/2010 8/25/2010 Total Nitrogen (kg) Figure 11. Total Nitrogen Storm Load Percent Mass Removal: 2009 = 78% and 2010 = 71% Sample Date In Out Figure 12. Nitrate + Nitrite Storm Load Percent Mass Removal: 2009 = 98% and 2010 = 81% In Sample Date Out 30

31 1/12/2009 2/14/2009 4/19/2009 5/4/2009 5/16/2009 6/3/2009 6/12/2009 7/1/2009 7/12/2009 7/26/2009 8/4/2009 8/17/2009 8/26/2009 9/4/2009 9/12/2009 9/21/ /9/ /18/2009 1/3/2010 1/21/2010 1/30/2010 2/7/2010 2/16/2010 3/1/2010 3/30/2010 4/27/2010 5/14/2010 5/23/2010 7/2/2010 8/1/2010 8/19/2010 8/29/2010 Orthophosphate Load (kg) 1/12/2009 2/15/2009 4/21/2009 5/10/2009 5/20/2009 6/8/2009 6/18/2009 7/10/2009 7/25/2009 8/4/2009 8/18/2009 8/28/2009 9/7/2009 9/16/ /6/ /15/2009 1/1/2010 1/18/2010 1/30/2010 2/8/2010 2/18/2010 3/13/2010 4/3/2010 5/2/2010 5/20/2010 5/30/2010 7/12/2010 8/19/2010 8/30/2010 Total Phosphorus Load (kg) Figure 13. Total Phosphorus Storm Load Percent Mass Removal: 2009 = 70% and 2010 = 75% Sample Date In Out Figure 14. Orthophosphate Storm Load Percent Mass Removal: 2009 = 61% and 2010 = 51% Sample Date In Out 31

32 1/12/2009 2/15/2009 4/21/2009 5/10/2009 5/20/2009 6/8/2009 6/18/2009 7/10/2009 7/25/2009 8/4/2009 8/18/2009 8/28/2009 9/7/2009 9/16/ /6/ /15/2009 1/1/2010 1/18/2010 1/30/2010 2/8/2010 2/18/2010 3/13/2010 4/3/2010 5/2/2010 5/20/2010 5/30/2010 7/12/2010 8/19/2010 8/30/2010 Total Suspended Solids (kg) Figure 15. Total Suspended Solids Storm Load 14, , , , , , , Percent Mass Removal: 2009 = 79% and 2010 = 91% Sample Date In Out 32

33 Total Load Reductions Ambient and Storm Load Combined 2009 and 2010 Differences in loads entering and exiting the facility for ambient and storm conditions were summed to estimate annual total load reductions. Table 4 presents the annual and seasonal total load removals. In 2009, 3,625 kg of total nitrogen were removed and 1,298 kg of nitrate+nitrite; 1,668 kg of total phosphorus and 537 kg of orthophosphate; and 50,032 kg of total suspended solids were removed. From January to August 2010, 2,409 kg of total nitrogen were removed and 686 kg of nitrate+nitrite; 974 kg of total phosphorus were removed and 195 kg of orthophosphate; and 90,455 kg of total suspended solids were removed. Table 4. Annual and seasonal total mass removals (ambient and storm) Total Nitrogen Mass Removal (kg) Total Phosphorus Mass Removal (kg) Total Suspended Solids Mass Removal (kg) Ambient Storm Total Ambient Storm Total Ambient Storm Total Removal Removal Removal 2009 Annual Growing Season Fallow Season Through August 2010 Annual Growing Season Fallow Season Nitrate + Nitrite Mass Removal (kg) Orthophosphate Mass Removal (kg) Ambient Storm Total Ambient Storm Total Removal Removal 2009 Annual Growing Season Fallow Season Through August 2010 Annual Growing Season Fallow Season Note: 2008 loads not presented; storm data suspect for

34 Conclusions and Recommendations Higher treatment efficiencies and the greatest mass removals were associated with sampled storm events compared to ambient conditions in 2009 and Treatment under ambient conditions from was limited, and in some cases, nutrients were exported from the system. Total nitrogen removed for both ambient and storm conditions combined exceeded the estimated load reduction outlined in the LSJR BMAP (LSJR TMDL Executive Committee 2008), which was 1,000 kg/yr. In 2009, 3,625 kg were removed and from January 2010 through August 2010, 2,409 kg were removed. Total phosphorus removals in 2009 and January 2010 through August 2010 also exceeded the LSJR BMAP (LSJR TMDL Executive Committee 2008) reduction estimate of 818 kg. In ,668 kg were removed and from January 2010 through August 2010, 974 kg were removed. Construction improvements at the treatment wetland. Based on the findings of the wetland dye tracer study conducted in June 2010, the treatment wetland is considerably under-utilized. Currently, only 5.1 acres of the wetland are functioning under baseflow conditions (water level at or below the wetland weir elevation of 4.0 ft.). Understandably, construction costs are high and current funding is limited, however, the District and St. Johns County may be able to work together to determine which improvements could cost-effectively be implemented through in-kind services, or otherwise, to increase the wetted area of the wetland, thereby increasing residence time. Mass balance water budget for pond outflow. A mass balance water budget for the pond outflow is necessary to calculate pollutant loading discharged from the pond to the wetland. Quantification of the loading discharged from the pond is necessary to make informed management decisions that would optimize treatment performance of the entire RST. Pollutant loading from the pond is necessary to determine if biological processes in the pond are contributing additional nutrients within the system. Calculation of the Canal 1 flow rating curves. Flow rating curves are necessary to calculate actual flows in Canal 1. Once flows are available, watershed load reductions can be calculated and used to evaluate project objectives and estimate load reductions from the TCAA. Continued monitoring. Continued water quality monitoring is crucial for evaluating system performance so that informed management decisions can be made to improve treatment. Furthermore, the RST was identified in the LSJR BMAP (LSJR TMDL Executive Committee 2008) as a nutrient reduction project for the TCAA. The load reductions currently allocated to the RST are based on literature values (CDM 2003) and not actual site-specific data. Actual data will be more precise during the LSJR BMAP revision process when load reductions required for the TCAA are re-calculated. Additionally, St. Johns County is now a primary stakeholder in the project and 34

35 receives nutrient credits by performing operation and management tasks at the RST. Nutrient credits given to the County could potentially increase (or decrease) based on actual treatment performance. 35

36 Literature Cited Bottcher, D Phase II Final Report - Tri-County Agricultural Area Best Management Practices Study. Gainesville: Soil and Water Engineering Technology, Inc. Prepared for the St. Johns River Water Management District. [CDM] Camp, Dresser, and McKee Implementation of regional stormwater treatment systems Yarborough Tract tri-county agricultural area. Prepared for the St. Johns River Water Management District. [HSA] HSA Engineers and Scientists Yarborough pump station pump flow verification testing report. Prepared for the St. Johns River Water Management District. Livingston-Way, P Water quality monitoring and assessment of agricultural best management practices in the Tri-County Agricultural Area. Phase II final report (June 2001) submitted to Florida Department of Environmental Protection in fulfillment to Contract No. WM602. [LSJR TMDL Executive Committee] Lower St. Johns River Total Maximum Daily Load Executive Committee. (2008, October). Basin management action plan for the implementation of total maximum daily loads for nutrients adopted by the Florida Department of Environmental Protection for the Lower St. Johns River Basin. Pant, H.K. and K.R. Reddy Potential internal loading of phosphorus in a wetland constructed in agricultural land. Water Research 37, [SJRWMD] St. Johns River Water Management District. 2010a. Operation and management plan for the Deep Creek West (Yarborough) Regional Stormwater Treatment Facility St. Johns County, Florida. [SJRWMD] St. Johns River Water Management District. 2010b. Field standard operating procedures for surface water sampling. [U.S. EPA] U.S. Environmental Protection Agency Three Keys to BMP Performance -Concentration, Volume and Total Load. Retrieved August 18, 2008, from U.S.Environmental Protection Agency, National Pollutant Discharge Elimination System: [WSI] Wetland Solutions Inc Deep Creek West Regional Stormwater Treatment Wetland Facility - Tracer Study. Prepared for the St. Johns River Water Management District. Yang, C. and J. Richmond Deep Creek West Regional Stormwater Treatment Facility, Treatment Performance and Treatment Efficiency for Phosphorus. Palatka: St. Johns River Water Management District, Division of Engineering. 36