OXNARD’S MEMBRANE CONCENTRATE PILOT PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT

James Bays, CH2M HILL, Tampa, FL Paul Frank, CH2M HILL, Oakland, CA Ken Ortega, Public Works Department, Oxnard, CA

Introduction

As membrane separation becomes more widespread as a water quality improvement technology, the need for environmentally acceptable methods of concentrate disposal has become acute. Recently, a range of beneficial and non-traditional uses of membrane concentrate were reviewed and summarized with the intention of informing the water and treatment community about alternatives to conventional disposal methods (WRA, 2006). One such alternative is the use of concentrate to create or enhance productive brackish . Because of the long history and expanding horizon of wetlands treatment of industrial, municipal, and agricultural effluents and runoff (Kadlec and Knight, 1996), a technological basis exists for investigating wetlands reuse of concentrate. Recently, the City of Oxnard in Ventura County CA conducted the Membrane Concentrate Pilot Wetlands Study to investigate the feasibility of reuse of concentrate as part of the City’s Groundwater Recovery Enhancement and Treatment (GREAT) Program, a project implemented to develop additional sources of alternative water supply to continue meeting the City’s goal of providing current and future residents and businesses with a reliable and affordable source of high-quality water. This program combines wastewater recycling and reuse; groundwater injection, storage, and recovery; and groundwater for water supply solutions to the Oxnard region (CH2M HILL, 2004). The GREAT Program includes construction of two treatment plants: • The “Desalter” will remove salts and minerals from brackish groundwater for potable use. • The “Advanced Water Purification Facility”, or AWPF, will remove nutrients, salts, minerals, and other contaminants from secondary effluent from the City’s plant (WWTP) for reuse, including agricultural , , and municipal and industrial (M&I) uses. Membrane concentrate to be generated by these treatment plants will be disposed of through the Oxnard WWTP deep ocean outfall. A conceptual alternative to ocean disposal could be the use of membrane concentrate as a water source to create or restore brackish or wetlands, if found to be compatible with the local environment. Because California’s coastal wetlands occur in where freshwater streams meet the sea, there is a pronounced gradient in these estuaries that overlaps membrane concentrate ionic strength and composition. If feasible, membrane concentrate could be used for beneficial creation of new coastal or for enhancing flow to existing marshes. To begin to address the feasibility of this concept, the City decided early in the Program that a pilot study would be necessary to provide preliminary design criteria and a tangible proof of the concept. Three phases of pilot testing were conducted as follows: • Initial testing was conducted that included construction, operation, and testing of pilot wetland mesocosms from June 2003 through May 2004. The goal of this testing was to demonstrate the safety and potential beneficial use of concentrate for wetlands restoration (CH2M HILL 2003, 2004).

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

• Additional testing was conducted by re-configuring the initial pilot wetland mesocosms over a 6- month period from September 2004 through March 2005. The goal of this testing was to assess the treatment effectiveness of an optimized series of pilot wetlands mesocosms (CH2M HILL, 2005). • Final sampling of the mesocosms was conducted in July 2006 to quantify the distribution and accumulation of salts (CH2M HILL, 2007). The paper describes the Research Plan, key findings and approaches of the two testing phases, final sampling, and description of AWPF. Original reports and additional information on the GREAT Program and the Membrane Concentrate Pilot Wetlands can be accessed at the City of Oxnard’s Water Division web site www.oxnardwater.org/projects/great/wetlands.asp. Research Plan

A detailed Research Plan was prepared outlining the rationale, testable hypotheses, research platform and sampling plan (CH2M HILL 2003). The rationale for conducting the study includes the following:  If shown to be environmentally safe, membrane concentrate may be useful as a source of water for the creation of new wetlands or for the restoration of existing salt marsh wetlands.  The potential supply of membrane concentrate may be useful to the restoration of the Ormond Beach wetlands.  An environmentally safe reuse of membrane concentrate could minimize the need and cost of other disposal options.  Very little information is available in the published literature on the effects, treatment, or reuse of membrane concentrate. Results obtained from this study could prove beneficial to water supply managers worldwide, particularly in the arid west and sunbelt states.

The Membrane Concentrate Pilot Wetlands Project is designed to test the following hypotheses concerning the reuse of membrane concentrate:  Concentrate can sustain viable native plant communities. By planting the pilot system with native wetland plants, and monitoring their growth characteristics, species water quality tolerance and improvement potential can be determined under hydraulic regimes similar to those that might be implemented on a larger scale  Removal of non-conservative elements will occur through natural biological and chemical transformation processes and will vary among wetland types. The types of pilot systems selected have been based upon known configurations that have been reported to treat common . This study is designed to allow comparison of wetland influent and effluent water quality within each cell to determine cell removal performance and compare to published water quality improvement models. For the purpose of this study, “non-conservative” elements include those with removal pathways significantly affected directly or indirectly by biological uptake and transformations, including , , carbonaceous compounds, and metals (specifically: Al, Sb, As, Ba, Be Cd, Cr, Cu, Fe, Mn, Pb, Hg, Ni, Se, Ag, Th, V, Zn).  Some removal of conservative elements can occur through physical/chemical processes, and removal will vary among wetland types. Few studies are available in the literature have reported on treatment of brackish waters and their compounds. For this study, conservative elements are considered to be salts or inorganic compounds, aggregated as hardness, , alkalinity, or specific conductance, and specific ions (i.e., B, Ca, Mg, K, Na, SO4, Cl, and F).  Discharge is ecologically safe to wetland biota. By comparing samples taken of the brackish

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

concentrate at the influent and effluent from each of the cells, changes in toxicity of the effluent to brackish and saltwater organisms can be assessed. This information can be used to determine if water quality components exceed criteria or pose a concern to native aquatic organisms.

The Pilot Wetlands research platform consisted of twelve one-cubic meter wetland tank mesocosms constructed from agricultural fruit storage bins comprising two replicates of six wetland types (Table 1; Figure 1). Pilot testing conducted from 2003 through May 2006 consisted of supplying the tanks with 25 to 75 gallons per day from a storage tank filled weekly with concentrate trucked from the nearby Brackish Water Reclamation Demonstration Facility operated by the Port Hueneme Water Authority.

Table 1. Summary of Mesocosm Types, Media, Water Depth and Plants Mesocosm Type ID Media Water Depth Plants Surface flow SFHM 12 inches local 4 inches Distichlis, Anemopsis, Jaumea Surface flow SFLM 12 inches local 18 inches Scirpus Horizontal subsurface flow SSF 24 inches -4 inches Jaumea, Anemopsis, Salicornia Peat-based vertical upflow VF 8 inches peat saturated Distichlis, Anemopsis, over 18 inches Jaumea, Juncus, gravel Monanthochloe Submerged aquatic SAV 12 inches local 18 inches Potamogeton Saltgrass evaporation SE 18 inches local saturated Distichlis

Of the wetland types selected, the SF high marsh, SF low marsh, and the SAV cells represent the major brackish water plant communities known to exist within the existing Ormond Beach wetlands. Testing this broad spectrum of plant types will establish if any are inherently more sensitive than other types to this water source and quality. The SSF and VF cells test two wetland technologies that offer potential for reduction of water quality parameters of greatest concern to plant life and wetland , such as boron and selenium, while significantly minimizing potential contact with wildlife. These types of wetlands represent natural "end-of-pipe" treatment systems that could further buffer or polish water that is discharged from the membrane treatment facility before its application to a wetland restoration site. All of the mesocosms were planted with local species typically found in southern California assigned to each mesocosm by hydroperiod tolerance. For example, the surface flow marsh systems were planted with species of bulrush and mixed emergent species commonly found in brackish marshes, such as bulrush (Schoenoplectus californicus, S. americanus, and S. maritima). The subsurface flow wetlands were planted with species typically found at the highest elevation within a tidal flooding gradient, where would be saturated or inundated infrequently, such as saltgrass (Distichlis spicata), yerba mansa (Anemopsis californica), jaumea (Jaumea carnosa), and pickerelweed (Salicornia virginica). Key Findings

Hydrology

During the first Phase, the twelve tanks were operated and monitored individually. Initial testing conducted included construction, operation, and testing of pilot wetland mesocosms from June 2003 Hydraulic loading rates varied from 0.8 to 1.6 cm/d. Theoretical hydraulic retention times were relatively long, compared to average HRTs of 15-30 days reported in Kadlec and Knight (1996). The

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

Figure 1. Initial Configuration of Oxnard Membrane Concentrate Wetlands Pilot Study

effect of evapotranspiration (ET) on the water balance, measured here as the difference between inflow and outflow rates, was greatest in the SFLM and SAV systems with little or no outflow measured frequently. In contrast, the SSF and VF systems, with no surface water, minimized evaporation losses.

In the second phase of testing, six of the tanks were re-plumbed as two series, or trains, of three cells each. Train 1 consisted of VF, SSF, and SAV cells to provide the least potential exposure of concentrate to wildlife. Train 2 consisted of VF, SFHM, and SFLM cells to approximate the varied plant communities of a natural salt marsh. The VF cells were placed first to maximize anaerobic treatment. Testing was conducted on the two treatment trains over a 6-month period from September 2004 through March 2005. Table 3 summarizes hydrologic data for the January – February 2005 period. Hypothesis 1: Concentrate can sustain viable native plant communities. Within 11 months of planting, all mesocosms had achieved more than 100% cover by native species, all of the plant species installed in the mesocosms had survived, and height measurements indicated a normal range of growth ranging from 1 foot for low ground cover species such as Jaumea to over 9 feet for bulrush (CH2M HILL 2004). This trend in dominance by native brackish marsh species continued through the final phase of testing, supplemented by an assessment indicating normal to above-average biomass development compared to other marshes (see Final Phase).

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

Table 2. Median Inflow and Outflow Data Summary, Oct – Nov 2003 Parameter Units SAV SFHM SFLM SSF VF Q in (gpd) 3.87 3.38 6.18 4.35 4.23 Q out (gpd) 0.81 0.63 0.22 2.44 1.81 HLR in (cm/d) 1.19 0.79 1.58 1.35 1.30 HLR out (cm/d) 0.04 0.19 0.00 0.83 0.55 HLR median (cm/d) 0.61 0.49 0.79 1.09 0.93 HRT (d) 88 30 62 19 32 Bin Area = 1.18 m2; 12.8 ft2

Table 3. Median Inflow and Outflow Data Summary, Jan – Feb 2005 Parameter Units Treatment Train 1 Treatment Train 2 VF SSF SAV VF SFHM SFLM Q in (gpd) 51.1 27.5 26.3 56.5 33.7 31.9 Q out (gpd) 27.5 26.3 39.5 33.7 31.9 27.5 HLR in (cm/d) 16.3 8.8 8.4 18.1 10.8 10.2 HLR out (cm/d) 8.8 8.4 12.6 10.8 10.3 8.8 HRT (d) 2.4 1.9 6.3 2.1 2.6 6.5 Bin Area = 1.18 m2; 12.8 ft2

Hypothesis 2: Removal of non-conservative elements will occur through natural biological and chemical transformation processes and will vary among wetland types. Long-term agricultural practices in the Oxnard region have contributed to elevated groundwater concentrations of this common plant nutrient. During both phases of the Pilot Study, significant concentration reductions were measured in -nitrogen, total phosphorus, and most metals in all wetland types. Figure 2 compares the average inflow and outflow concentrations of nitrate-nitrogen and selenium. In Phase A, nitrate was reduced from 54 mg/L to the WHO standard of < 10 mg/L, by the low marsh and vertical flow wetlands, presumably through their greater extent of anaerobic habitat. Lower concentrations in Phase B were treated at higher hydraulic loading rates to <4 mg/L by the treatment trains. Nitrate concentrations were reduced consistently through each cell in Train 2 but varied between cells in Train 1. The single bins of the remaining wetland types consistently achieved <4 mg/L nitrate. Concentrations of other constituents decreased through physical, chemical and biological processes. Phosphorus 50% from 0.2 to 0.1 mg/L through the wetlands in Phase A, and >90% from >0.9 mg/L to 0.03-0.09 mg/L in the two treatment trains in Phase B (CH2M HILL 2005). Chemical demand (COD) generally increased through the system as the water came in contact with biomass and .

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

70

60

50 Phase A - Single Bins Phase B - Train 1 Phase B - Train 2 Phase B - Single Bins Inflow NO3-N = 54 mg/L Inflow NO3-N = 11.7 mg/L Inflow NO3-N = 11.7 mg/L Inflow NO3-N = 12.5 mg/L Inflow Se = 22.3 µg/L Inflow Se = 12 µg/L Inflow Se = 12 µg/L Inflow Se = 19 µg/L 40

30 NO3-N Phase A NO3-N Phase B Se Phase A Se Phase B

20 Nitrate-Nitrogen (mg/L); SeleniumNitrate-Nitrogen (mg/L); (µg/L) 10

0 VF VF VF SSF SSF SSF SAV SAV SAV INFL INFL INFL SFLM SFLM SFLM SFHM SFHM SFHM

Figure 2. Nitrate-nitrogen and Selenium in Wetland Inflow and Outflow by Pilot Study Phase.

Eight metals (Ag, Be, Cd, Pb, Hg, Mn, Ni, and Zn) varied within quantitation limits in either the concentrate or in the wetlands discharge during either testing phase and showed no consistent trend. Four metals (Al, Cr, Th, V) exhibited slight concentration increases, presumably related to soil leaching. The remaining six metals (As, Ba, Cu, Fe, Se, Sb) showed variable decreases in one or both testing phase. As shown in Figure 2, selenium concentrations were reduced from 22 µg /L to 7.3 µg /L in Phase A by the VF wetland and variably by the other systems, in Phase B from 12 µg/L to 5.6-9 µg /L in the two treatment trains, and from 19 µg/L to 3.3-5.8 µg /L in the remaining bins. Hypothesis 3: Some removal of conservative elements can occur through physical/chemical processes, and removal will vary among wetland types. With the exception of the SAV system, inorganic parameters analyzed (hardness, Ca, Mg, K, Na, B, SO4, CL, F, alkalinity, specific conductance and TDS) generally increased in concentration through the Pilot wetlands. For example, average TDS for non-SAV wetlands in Phase A increased 15% from 4,560 mg/L to 5,222 mg/L and 17% in Phase B for Train 2 (without SAV) from 4,200 mg/L to 4,900 mg/L. In contrast, TDS in the SAV mesocosm decreased 2% to 4,478 mg/L in Phase A, showed no change in Train 2, and decreased 7% in the single SAV tank in Phase B. The difference in performance between the SAV tanks and treatment series, and the other wetlands, is attributable to the open aspect and the dense growth of pondweed in the tank (Potamogeton). As the submerged plants grow, unshaded by other plants, they consume free CO2 for photosynthesis and shift the hydrogen ion equilibrium to

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL alkaline conditions. This increases the pH, creating conditions appropriate for precipitation of carbonate, which can also co-precipitate calcium and calcium sulfate. However, even with the slight increase in concentration, all of the parameters measured tended to show significant mass removal through the Pilot wetlands in response to water loss through plant transpiration. For example, Table 4 compares the average concentration and mass reductions for nitrate, selenium, and TDS for the vertical upflow cells in the first testing phase. Concentrations were reduced in the non-conservative parameters (nitrate, Se and Fe) by 67-83% and 93-96% mass removals were estimated based on inlet/outlet differences in flow. In contrast, TDS concentrations increased by 15% from 2350 to 2695 mg/L, presumably through evaporative concentration of solids, but the overall mass of TDS decreased by 76% because of the significant evapotranspiration of flow. Similar reductions in mass were calculated for all other parameters. Table 4. Comparison of Concentration and Mass Reduction for Selected Parameters, Phase A Nutrient Metal Salt

Parameter Units NO3 Se Fe TDS Influent mg/L 54.4 0.022 0.30 2350 Effluent mg/L 9.5 0.007 0.05 2695 CR % % 83% 67% 82% -15% Mass loading g/m2/yr 246 0.10 1.36 10616

Mass out g/m2/yr 9 0.01 0.05 2548 MR g/m2/yr 237 0.09 1.31 8068 MR % % 96% 93% 96% 76%

Hypothesis 4: Discharge is ecologically safe to wetland biota. Two measures of the ecological “safety” of the concentrate and the treated wetlands were investigated during the Pilot Study. First, water column concentrations of parameters with known eco-toxicological properties were reviewed and compared to available benchmarks. Of the metals analyzed, only copper and selenium were measured at levels in the concentrate that exceeded toxicity thresholds. Phase A inflow concentrations of copper (26.7 µg/L) and selenium (22.3 µg/L) were greater than their respective guidance thresholds of 12 µg/L and 5 µg/L (NOAA, 1999). Copper concentrations were reduced to detection levels in all wetlands while the subsurface flow wetlands (VF, SSF) most consistently reduced the selenium to 7.3 µg/L in Phase A and to 5.6 µg/L in Treatment Train 1 in Phase B. Removal rate constants determined from these data can provide a basis for wetland sizing to achieve discharges below this threshold. Second, whole effluent toxicity studies were performed using mysid shrimp (Mysidopsis bahia) and topsmelt (Atherinops affinis) on the concentrate and on the effluent of the individual mesocosms and the treatment trains. Data from 96-hour acute toxicity tests on mysid shrimp during the initial phase of testing showed a large variance in survival on inflow concentrate duplicates (37.5-90%), with wetlands ranked in order of decreasing survivorship: SAV and SSF (tied, 52.5-65%), SFHM and SFLM (tied, 40- 45%), and VF (30-47.5%) (CH2M HILL, 2004). Topsmelt acute test survival was generally equivalent

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

among all wetland types and inflow concentrate, with wetland ranked in terms of decreasing survivorship: SAV (100%), SFHM (90-100%), SSF (90-95%), VF (85-100%), and SFLM (70-72.5%). Follow-up acute testing of the effluent from the treatment trains showed a more consistent survivorship of the membrane concentrate (20-40%) and significant increase in mysid survival over the concentrate and the individual test results from Phase A, with survivorship ranging from 60-95% for Train 1 and 50- 75% for Train 2 (CH2M HILL, 2005). For topsmelt, the inflow concentrate was more toxic than tested in Phase A, with 64-84% survival, and survivorship ranged from 76-92% in Train 1 and 76% in Train 2. Chronic 7-day whole effluent testing in both phases of testing showed that the concentrate and the wetland effluents were not toxic to mysid shrimp. Using an IC50, and estimate of the effluent concentration that causes 50 percent reduction in growth or reproduction, the concentrate IC50 in Phase A ranged from 82-97%, indicating that the concentrate would have little or no chronic effect on mysid survival. Mysid shrimp IC50 growth and survival values from the wetland discharges ranged from >100% for SAV and SSF, indicating that the concentration would have to be greater than tested to have a significant effect on mysid survival, to 80-97% for SFHM, and 81.5-86% for SFLM. Topsmelt chronic IC50 values were all >100%, meaning that the concentrate would have to be a higher strength than that tested to reduce growth and survival by 50%. The SFLM effluent showed an IC50 of 94-100%, indicating no significant effect on growth and survival. Phase B testing of the treatment train concept showed mysid shrimp survival IC50 values that showed the effluent from the treatment train series was substantially less toxic than the inflow concentrate. All wetland effluent samples had IC50 values at 100%, except for one sample of 98% for Train 2. Mysid shrimp IC50 values were all >100% and showed no chronic effect for the concentrate and none for the effluents from both treatment train series. All of the topsmelt IC50 values in Phase B were >100%. As with the acute tests, topsmelt growth and survivorship was not adversely affected by the concentrate. Final Phase A third and final phase of testing was conducted in July 2006 to determine the location and extent of salt accumulation in the mesocosms. By quantifying the concentration and distribution of various elements in soil and plant components and comparing these results with the samples collected and analyzed at various times during the pilot wetlands project, preliminary accumulation rates could be developed. By this time, brackish test water had been allowed to flow for an additional 13 months through the pilot wetland system following the first two phases of pilot testing conducted from 2003 through May 2005. One replicate of each of the six wetland mesocosms (i.e., bins) was chosen randomly for sampling. Two opposing faces of each bin were cut off, exposing the profile of the wetland system. This enabled access to the soil horizon and plant zones, which in the past had been difficult or impossible to sample due to the dense growth of vegetation in the bins. This sampling could not have been accomplished at any other point in the project because water was actively flowing through them during pilot testing. At the conclusion of three years of growth with membrane concentrate as a water source, all of the mesocosms exhibited dense growth and a complete cover of brackish marsh vegetation (Table 5). Some differences in the number of species and cover between years may be attributed to a slight difference in sampling methodology, because estimates of plant cover collected initially were for all layers of plant growth, whereas the final sampling focused on the uppermost, dominant layer, given the sheer density of plant growth. But most of this difference, though, is attributed to ecological competitive interactions between plant species, and shading of lower or slower growing plant species by the dominant plant species. For the VF, SSF, and SFHM wetlands, saltgrass and yerba remained dominant through all years (see Figure 3 for typical view). Saltgrass shared dominance in the SE wetland with soft-rush. In the

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

SFLM wetland, bulrush species dominated. The SAV remained covered by pondweed. All species are salt-tolerant flora native to brackish marshes and saline soils in North America. Dense root and shoot development was found in all mesocosms (Figure 4). The shoot biomass for the pilot wetlands study ranged from <1 kg/m2 to ~7 kg/m2, which agrees with the range of observed primary production in brackish and freshwater marshes (e.g., Kadlec and Knight, 1996; Mitsch and Gosselink, 2000). The root biomass standing crop ranged from 2 to 14 kg/m2 in the pilot mesocosms which generally exceeded the observed range of literature values. Tissue concentrations of sodium and chloride were significantly greater in the low marsh and saltgrass bed than the other wetland types (Figure 5). Sediment concentrations of sodium and chloride followed a similar trend with the exception of the vertical flow peat bed, which showed significantly greater concentrations (Figure 6). While these data indicate a strong affinity between the peat and these monovalent ions, the differences are largely attributable to the difference in bulk density of peat, which was four times lower (81% moisture content) than the sandy loam soil (23% moisture content) used in the other marshes. Throughout the project, the low marsh and saltgrass evaporation beds lost the greatest proportion of inflow water by evapotranspiration, likely resulting in the relatively greater sodium and chloride content in the and sediments of these two wetlands. Importantly, the accumulation of salts remains significantly below published maximum concentrations associated with healthy plants. For example, sediment chloride averaged 828 mg/kg d.w. in the low marsh and 1,200 mg/kg d.w. in the saltgrass bed in 2006, compared to 10,000 mg/kg d.w. associated with healthy populations of Schoenoplectus maritima (Kantrud, 1996). Similarly, the soil salinity in the low marsh and saltgrass bed was 5.2-5.8 mg/kg d.w. compared to 35 mg/kg d.w. in healthy saltgrass communities (Richards, 1994). These data indicate that there remains a substantial margin for chloride and soil salinity to increase before approaching levels stressful to the dominant plant species (e.g., saltgrass, bulrush). It might take on the order of 230 years to reach the theoretically allowable increase in soil sodium concentration, assuming the observed change in sodium concentration in the low marsh system from 1,610 to 2,040 mg/kg d.w. from 2003-2006 is extrapolated to a maximum of 35,000 mg/kg. Other constituents may accumulate to more rapidly in the vertical flow beds, given the significant difference in concentrations (Figure 6), but as of the conclusion of the Pilot Study, no deleterious effects were evident in the vegetation community of this wetland type. In fact, chloride concentrations decreased during the period of operation, indicating leaching and possible replacement by other ions. With regard to metals, data from the Pilot Study indicate little or no risk of accumulation to ecotoxicological thresholds. All selenium samples and mercury analyses in 2006 were below the reporting limit (CH2M HILL 2007), even in the vertical flow wetland, which had the greatest selenium removal rate (CH2M HILL 2005). Plant roots showed measurable concentrations of selenium but shoots generally did not. Another factor affecting the longevity of a concentrate wetland may be more pragmatic, in that the precipitation and accumulation of salts in pipes and gravel and soil media may ultimately impede flow and cause unacceptable hydraulic head loss or short circuiting. However, visual inspections of the pipes and valves used in the Pilot Study found no indication of excessive salt build-up and flows were maintained throughout the study. Clogging may happen but over a period of many years. In general, where comparisons could be made between pilot system soil chemical properties and reported upper values for healthy natural ecosystems, Oxnard Pilot Wetland soil concentrations were substantially below maximum values associated with healthy natural ecosystems, except for magnesium and sulfate. After three years of operation, the plant tissue and soil concentrations indicate that a full scale system would likely have a lifespan similar to other wastewater treatment wetlands, which have been found to be on the order of decades or longer (Kadlec and Knight, 1996).

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

Table 5. Comparison of 2004 and 2006 Relative Cover by Wetland Mesocosm Type SSF SE SFHM SFLM VF SAV Plant Species 2004 2006 2004 2006 2004 2006 2004 2006 2004 2006 2004 2006 Anemopsis 26% 41% 6% 32% 51% 23% 47% californica Distichlis 8% 22% 84% 55% 49% 36% 28% 37% spicata Frankenia 1% 13% 1% 6% salina Juncus balticus 3% 24% 35% 12% 13% 1%

Jaumea 42% 6% 8% 16% 9% carnosa Muhlenbergia 1% asperifolia Monanthochloe 9% 13% littoralis Potamogeton 7% 100% 75% natans Scirpus acutus 3% Sporobolus 1% 1% airoides Scirpus 68% 80% americanus Scirpus 10% 1% 22% 13% californicus Scirpus 3.5% maritimus Salicornia 10% 3% 4% 3% virginica latifolia 6% 3.5% 5%

Figure 3. Top View of SSF (L) and SFHM (R ), showing typical vegetative growth after 3 years.

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

16 14

12 Root Mass 10 Shoot Mass 8 6 4

Dry Biomass (kg/m2) Dry Biomass 2 0 SFHM SE SFLM VF SAV SSF

Figure 4. Root and Shoot Biomass by Wetland Type.

Chloride in Plant Tissue Sodium in Plant Tissue

30000 30000

Root 25000 Shoot 25000 Root Shoot

20000 20000

15000 15000 Cl [mg/kg] Na [mg/L] Na

10000 10000

5000 5000

0 0 SFHM SE SFLM VF SSF SAV SFHM SE SFLM VF SSF SAV Wetland Type Wetland Type

Figure 5: Chloride (L) and sodium (R ) in plant tissues in 2006.

Chloride in Sediment Sodium in Sediment 6000

12000 5000 10000

4000 8000

3000 6000 Cl [mg/kg] Na [mg/kg]Na 2000 4000

2000 1000

0 0 SFHM SE SFLM VF SAV SFHM SE SFLM VF SAV Wetland Type Wetland Type

Figure 6: Chloride (L) and sodium (R ) in sediments in 2006.

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

Advanced Water Purification Facility As a central component to the GREAT Program, an Advanced Water Purification Facility (AWPF) is being designed to improve secondary-treated reclaimed effluent to a quality sufficient to meet criteria for groundwater recharge and all purpose irrigation. The City plans to implement the AWPF in two overall phases: (1) an Initial Phase to treat 6.5 million gallons per day (mgd) producing 5 mgd product water, and (2) an Ultimate Phase to treat 32.5 mgd producing 25 mgd product water. The AWPF will include a multiple barrier treatment train consisting of microfiltration/ultrafiltration (MF/UF), (RO), and ultraviolet (UV) light based advanced oxidation (AOX) processes (CH2M HILL, 2006). Water for aquifer recharge will be blended with raw water at the well after additional stabilization including decarbonation and liquid lime addition. The proposed treatment processes are considered as the best technology to reduce total dissolved solids (TDS) and trace organics, while fully satisfying stakeholder and California Department of Health Services (DHS) requirements and expectations.

The concentrate will be returned to the inflow of the City’s water control facility (WPCF). As a demonstration of the ecological benefit of concentrate reuse in wetlands, a sidestream of up to 20,000 gpd of concentrate will be routed to a series of wetlands modeled after the technologies evaluated during the Membrane Concentrate Wetlands Pilot study. Given a compact site footprint limited to approximately 450 feet by 450 feet, the demonstration wetlands will be integrated into the site plan and architectural design of the AWPF and associated interpretive center. Figure 7 depicts an architectural rendering of the proposed facility currently being designed (final configuration may vary).

Horizontal Subsurface Flow

Vertical Upflow Submerged Aquatic Vegetation Emergent Marsh Figure 7. Wetland Layout at the Oxnard Advanced Wastewater Purification Facility.

Because the water source for the AWPF is reclaimed secondary effluent, the membrane concentrate will have significantly greater concentrations of constituents of concern than measured during the Pilot Study (Table 6). Using the same types of wetland technologies evaluated in the Pilot Study, the concentrate will be treated by first by a horizontal subsurface flow wetland followed by a vertical upflow wetland to achieve a water quality that can discharged safely to an emergent marsh suitable for aesthetic public use. Water will flow below ground in these two types of systems, preventing any potential for odor or vector concerns to develop. Bulrush (Schoenoplectus), the key plant species for both subsurface flow systems, thrived in the relatively dilute concentrations tested during the Pilot Study and have been shown to grow normally in natural and constructed wetlands receiving concentrations similar to those anticipated from the AWPF. For example, bulrush occurs regularly in natural brackish and inland salt marshes with TDS concentrations of 13,000 mg/L or more (Hammer and Heseltine, 2004; Keate, 2004). Equal or greater concentrations have been treated in livestock wastewater treatment wetlands (Knight et al., 2000). Selenium concentrations of 30 µg/L up to 4 mg/L have been treated in constructed wetlands

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

(Hansen et al., 1998; Huddleston et al., 2005). Bulrush and other emergent marsh species show no effect for boron concentrations of 2-4 mg/L (Ye et al, 2001) and tolerate >10 mg/L (Powell et al, 1997). Table 6. Comparison of Constituent Concentrations Concentrate by Water Total Dissolved Ammonia Selenium Boron Source solids (mg/L) (mg/L) (µg/L) (mg/L) Groundwater (Pilot Study) 4,560 0.1 22 1.0 Reclaimed Effluent (AWPF) 11,400 140 36 4.0

The horizontal subsurface flow wetlands will be configured to allow supplemental aeration of the gravel bed to reduce the BOD content and support natural of the ammonia. The vertical upflow beds will be configured as thick beds of peat and , supplemented with reduced to facilitate the of the nitrified effluent from the horizontal subsurface flow wetlands, as well as biological selenium reduction, where selenium in the form of selenate will be reduced to selenite and eventually to elemental selenium and precipitate to the bottom of the wetland. Because the high concentrations of salts will precipitate and lead to scale formation and clogging, four cells are planned for each subsurface flow technology to create two flow paths of two cells each to minimize short- circuting potential and to allow wetland cells to be taken off-line for maintenance as needed, a recommended feature in wetland design (Kadlec and Knight, 1996). The treated water from the subsurface flow wetlands will flow to an open interspersed with alternating bands of marsh vegetation, submerged aquatic vegetation, and open water. This final marsh- pond system will be designed and maintained as an aesthetic public use, education and research facility. Conclusion Oxnard’s Membrane Concentrate Pilot Wetlands have created a proof-of-concept that addresses the key questions related to the beneficial use of concentrate as a water source for wetlands. Clearly, productive and diverse brackish marshes can be created and sustained from membrane concentrate. The treatment technologies demonstrated a conceptual sequence of natural treatment and habitat creation that offers an alternative approach to reduce the concentration of contaminants in the concentrate and reduce the volume for disposal. Hypotheses that membrane concentrate can support viable native plant species, remove conservative and non-conservative water quality constituents, and that the wetland discharge would be ecologically safe were tested and accepted. Future operations will expand the range of potential applications and provide verification of the process, operational requirements and benefits of wetlands receiving concentrate. References CH2M HILL. 2003. Membrane Concentrate Pilot Wetlands Project Research Plan. Final Report prepared for the City of Oxnard Water Division. Thousand Oaks, CA.

CH2M HILL. 2004. Membrane Concentrate Pilot Wetlands Project. Final Report prepared for the City of Oxnard Water Division. Thousand Oaks, CA.

CH2M HILL. 2005. Additional Testing for the Membrane Concentrate Pilot Wetlands Project. Final Report prepared for the City of Oxnard Water Division. Thousand Oaks, CA. CH2M HILL. 2006. Preliminary Design Report. Advanced Water Purification Facility Initial Phase 6.25 mgd. Prepared for City of Oxnard Water Division, Oxnard CA. Thousand Oaks, CA.

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OXNARD’S MEMBRANE CONCENTRATE PILOT WETLANDS PROJECT BAYS FRANK AND ORTEGA PRESENTED AT WATER REUSE SYMPOSIUM, SEPTEMBER 9-12 2007, TAMPA FL

CH2M HILL. 2007. Results of Final Plant Tissue and Sediment Testing for the Membrane Concentrate Pilot Wetlands Project. Final Report Prepared for City of Oxnard Public Works Department. Thousand Oaks, CA. Hammer, U.T. and J.M. Heseltine. 2004. Aquatic macrophytes in saline lakes of the Canadian Prairies. Hydrobiologia 158 (1): 101-116. Hansen, D., P.J. Duda, A. Zayed and N. Terry. 1998. Selenium removal by constructed wetlands: role of biological volatilization. Environ. Sci. Technol. 1998, 32, 591-597. Huddleston, G.M. III, J.H. Rodgers, Jr., C. Murray-Gulde, and F.D. Mooney. 2005. Designing constructed wetlands for mitigating risks from flue gas desulfurization wastewater. Proc. 2005 Georgia Water Resources Conference, held April 25-27, 2005, at the University of Georgia. Kathryn J. Hatcher, editor, Institute of , The University of Georgia, Athens, Georgia. Kadlec, R.H. and R.L. Knight. 1996. Treatment Wetlands. CRC Press/Lewis Publishers. Boca Raton. FL. Kantrud, H. A. 1996. The alkali (Scirpus maritimus L.) and saltmarsh (S. robustus Pursh) bulrushes: A literature review. National Biological Service, Information and Technology Report 6. Jamestown, ND: Northern Prairie Wildlife Research Center Online. http://www.npwrc.usgs.gov/resource/plants/bulrush/index.htm (Version 16JUL97).

Keate, N. 2004. Great Basin slope and depressional wetlands in Utah by Subclass. Utah Division of Wildlife Resources. http://www.epa.gov/region8/water/wetlands/documents.html Knight, R.L., V.W.E. Payne, R. Borer, R. Clarke Jr., and J.H. Pries. 2000. Constructed wetlands for livestock wastewater treatment. Ecol. Engr. 15:41-55. Mitsch, W. J. and J. G. Gosselink. 2000. Wetlands. John Wiley & Sons, Inc. New York. NOAA. 1999. Screening Quick Reference Tables. http://response.restoration.noaa.gov/cpr/sediment/ squirt.pdf. Powell, R.L., R.A. Kimerle, G.T. Coyle, and G.R. Best. 1997. Ecological risk assessment of a Wetland exposed to boron. Env. Toxicol. Chem. 16 (11): 2409-2414. Richards, J. H. 1994. Physiological limits of plants in desert playa environments. Technical Completion Report Prepared for California State Lands Commission and The Great Basin Air Pollution Control District. Contract No. CA-SLC c-9176. May 1994. Water Reuse Foundation. 2006. Beneficial and Non-traditional Use of Membrane Concentrate. Alexandria, VA. Ye, Z.H., S.N. Whiting, J.H. Qian, C.M. Lytle, Z-Q. Lin, and N. Terry. 2001. Trace element removal from coal ash by a 10-year-old . J. Environ. Qual. 30:1710-1719.

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