Browsing by Author "Aziz Amoozegar, Committee Member"

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Effect of Urban Stormwater BMPs on Runoff Temperature in Trout Sensitive Regions
(2008-11-17) Jones, Matthew Paul; William F. Hunt, Committee Co-Chair; Aziz Amoozegar, Committee Member; Garry L. Grabow, Committee Member; Daniel H. Willits, Committee Co-Chair
While the negative impact of warm urban stormwater runoff on coldwater stream environments has been studied, little is known about the effect of urban stormwater best management practices (BMPs) on runoff temperature. A monitoring study was conducted from May through October of 2005, 2006, and 2007 in western North Carolina, along the southeastern extent of United States trout populations, to examine the effect of urban stormwater BMPs on runoff temperature. The monitoring sites consisted of a stormwater wetland, wet pond, and four bioretention areas. Runoff temperatures at all monitoring locations significantly (p<0.05) exceeded the 21Â°C trout temperature threshold from June through September. Monitored runoff temperatures at a parking lot surrounded by a mature tree canopy and a parking lot covered with a light-colored chip seal were cooler than nearby un-shaded and standard asphalt parking lots. Both the stormwater wetland and wet pond increased water temperatures significantly. Effluent temperatures from the wet pond were significantly warmer than flows from the stormwater wetland from June through September. At both sites, water temperatures were coolest at the bottom depths, and water was cooler than 21Â°C at the bottom of the stormwater wetland during the early summer and early fall, indicating the thermal benefit of an outlet structure that would draw water from these bottom depths. Water was significantly cooler after conveyance in buried pipes when discharged into the stormwater wetland and wet pond. All of the bioretention areas monitored during the course of this study significantly reduced maximum stormwater temperatures; however, only bioretention areas smaller than 10% of their contributing watershed significantly reduced median stormwater temperatures. The larger bioretention areas provided evidence of substantial reductions in runoff volume, which would reduce effluent thermal loads. Despite temperature reductions, all bioretention areas discharged effluent significantly warmer than 21Â°C during the summer months. Evaluation of bioretention temperature profiles showed that the coolest effluent temperatures could be obtained from bioretention areas with a soil depth between 90 and 120 cm. Due to its ability to reduce runoff temperatures and flows, bioretention areas are considered to be an effective treatment option for mitigating thermal pollution from urban stormwater runoff. A computer model was developed to simulate the thermal dynamics of a bioretention area. The model used a Green-Ampt based approach to simulate bioretention hydraulics. Pavement and runoff temperature were calculated using a finite difference solution for thermal conduction within the pavement profile in conjunction with a surface heat balance. A number of analytical and empirical methods were used to estimate weather parameters and the antecedent soil temperature profile. Soil and water temperature profiles during infiltration were simulated using a model for conduction and convection in porous media that utilized separate energy equations for the fluid and solid phases. The bioretention thermal model was validated by comparing simulation results with temperature data collected during the course of the monitoring study. The majority of simulated storm events had a root mean squared error less than 2.0Â°C for bioretention effluent estimates. Predicted effluent temperatures were typically warmer than measured values between 10:00 and 17:00 hours, and cooler for the remainder of the day. A sensitivity analysis showed that effluent temperatures were most affected by input parameters related to the soil and pavement surface heat balances. Simulation results suggested that volume reductions had a larger impact on effluent thermal loads than temperature reductions. Overall, the bioretention thermal model was considered to serve as a valuable tool for predicting bioretention effluent temperatures in trout sensitive regions.
Evaluation of Evapotranspiration-based and Soil-Moisture-based Irrigation Control in Turf
(2008-01-29) Vasanth, Arjun; Rodney L. Huffman, Committee Member; Aziz Amoozegar, Committee Member; Grady L. Miller, Committee Member; Daniel C. Bowman, Committee Member; Garry L. Grabow, Committee Chair
A gravimetric approach to real-time monitoring of substrate water content in container-grown nursery crops.
(2008-09-15) Prehn, Alison E; Aziz Amoozegar, Committee Member; Stuart Warren, Committee Co-Chair; Ted Bilderback, Committee Co-Chair
Isovolumetric Weathering of Granite in Wake County, North Carolina
(2004-07-15) Witanachchi, Channa Devinda; Aziz Amoozegar, Committee Member; Edward Stoddard, Committee Member; Stanley W Buol, Committee Chair; Michael Vepraskas, Committee Member
Saprolite, formed by chemical weathering of rocks near the earth's surface, holds water, serves as a parent material of soils, and is a medium for waste disposal. Saprolite formation consumes CO₂ and may stabilize atmospheric CO₂ levels. This dissertation examined the influence of joint orientation on isovolumetric weathering of saprolite developed on the Rolesville granitic batholith at Knightdale, North Carolina. Rock density (ρ[subscript s]) (μ α[subscript 0.05]) was 2.62±0.01 g cm⁻³. Mass altered per unit volume (m[subscript A/V[subscript T]) of saprolite was taken as the difference between rock density (ρ[subscript s]) and primary mineral mass remaining per unit volume (m1⁰[subscript R]/V[subscript T]). Altered mass lost per unit volume (m[subscript AL/V[subscript T]) was taken as the difference between ρ[subscript s] and bulk density (ρ[subscript b]). Altered mass retained per unit volume (m[subscript AR/V[subscript T]) was taken as (m[subscript A]/V[subscript T]) - (m[subscript AL/V[subscript T]). Saprolite with steeply-dipping joints showed a uniformly sandy texture. The distribution (mass percent) of sand-, silt-, and clay-sized particles (μ α[subscript 0.05]) was 82.4±2.7, 10.3±1.8, and 2.3±2.5, respectively, on a whole saprolite basis, and ρ[subscript b] (μ α[subscript 0.05]) was 1.66±0.06 g cm⁻³. Saprolite with horizontally-oriented unloading joints was extensively altered and occurred between horizontal slabs of unweathered rock. The saprolite was composed of sandy layers alternating with clayey layers on the scale of approximately 1 to 2 cm. The distribution of sand-, silt-, and clay-sized particles (μ α[subscript 0.05]) in the saprolite was 50.1±10.4, 3.1±0.5, and 46.8±10.5, respectively, on a whole saprolite basis. Bulk density (μ α[subscript 0.05]) was 1.55±0.01 g cm⁻³. The mean content of sand-, silt-, and clay-sized particles in the two saprolites differed statistically at α = 0.001, and mean bulk density differed at α = 0.01. The fine-earth fraction of saprolite with steeply-dipping joints was characterized (μ α[subscript 0.05]) by pH of 5.8±0.2, mass percent Fe2O3 of 0.21±0.09, cation exchange capacity (CEC) at pH 7.0 of 3.95±0.88 cmol⁺kg⁻¹, and percent base saturation (% BS) of 36.66±9.93. The fine-earth fraction of saprolite with horizontal joints was characterized (μ α[subscript 0.05]) by pH of 5.1±0.2, mass percent Fe2O3 of 2.68±0.28, CEC (in cmol⁺[superscript kg]⁻¹) at pH 7.0 of 8.28±0.91 and % BS of 19.73±9.22. The means of pH, mass percent Fe2O3, and CEC in the two saprolites differed statistically at α = 0.01, and the means of % BS differed at α = 0.05. The differences in mean values of individual extractable bases are not significant at α = 0.05. Density of unweathered granite (μ α[subscript 0.05]) was 2.62±0.01 g cm⁻³. Calculated mean (μ α[subscript 0.05]) values of m[subscript A]/V[subscript T], m[subscript AL]/V[subscript T], and m[subscript AR]/V[subscript T] (all in g cm⁻³) in saprolite with steeply-dipping joints were 1.17±0.12, 0.96±0.06 and 0.21±0.05, respectively. Corresponding values in saprolite with horizontal joints were 1.85±0.15, 1.08±0.02 and 0.77±0.17, respectively. Calculated mean (μ α[subscript 0.05]) values of m[subscript AL]/m[subscript A] were 0.82±0.03 for the former saprolite and 0.58±0.06 for the latter, indicating greater leaching losses in the former. Differences in the calculated means of m[subscript A]/V[subscript T], m[subscript AR]/V[subscript T], m[subscript AR]/m[subscript A] and m[subscript AL]/m[subscript A] in the two saprolites are statistically significant at α = 0.001, and m[subscript AL]/V[subscript T] differed at α = 0.05. Saprolite with steeply dipping joints was composed predominantly of plagioclase and potassium feldspar. Saprolite with horizontal joints contained approximately equal proportions of potassium feldspar and kaolinite (or halloysite). Nordstrandite occurred in both types of saprolite. Saprolite was classified based on the relative proportions of (m1⁰[subscript R]/V[subscript T]) 100/ρ[subscript s], (m[subscript AR]/V[subscript T]) 100/ρ[subscript s], and (m[subscript AL]/V[subscript T]) 100/ρ[subscript s]. Saprolite with steeply-dipping joints classified as 'moderately altered, highly leached', and saprolite with horizontal joints classified as 'severely altered, moderately leached'. Joint orientation appears to be a significant variable in saprolite formation.
Permeability Reduction and Emulsified Soybean Oil Distribution in Aquifer Sediments: Experimental and Modeling Results
(2004-04-08) Coulibaly, Kapo Martin; Robert Borden, Committee Co-Chair; david Genereux, Committee Co-Chair; Aziz Amoozegar, Committee Member; John Fountain, Committee Member
Chlorinated aliphatic hydrocarbons (CAH) are among the most common and difficult to treat contaminants in soil and groundwater. The available information suggests that edible oil permeable reactive barriers (PRBs) can be a very cost effective approach for plume control because of their low capital and O&M costs. However important issues need to be addressed to assure its efficiency. This work will address permeability losses and oil retention along with oil distribution in the subsurface after injection. PRBs design issues will also be dealt with through the implementation of a model to predict soybean oil spatial distribution after injection. First, pure soybean oil was injected in laboratory columns packed with different materials varying in grain size distribution and clay content. Water permeability was measured before and after oil injection followed by deaired water flush and sediment oil content assessed at the end of the experiment. This preliminary experiment revealed major difficulties related to the injection of pure NAPL soybean oil. Among others: higher residual saturation (more than 20% of the pore volume), high hydraulic gradient during injection (2 order of magnitude increase over initial gradient with water injection). Because of these problems emulsified soybean oil was considered as an alternative to the injection of NAPL soybean oil. Using a mixture of surfactants (glycerol monooleate and polysorbate 80), a fine and stable soybean oil in water emulsion was prepared. Injection of the emulsion induced very low to moderate permeability losses and low oil retention. To investigate emulsion transport in the subsurface, long 1-D columns (80 cm long 1 inch in diameter), packed with a fine clayey sand amended with kaolinite were flushed with emulsion while monitoring effluent concentration. The columns were then cut in 10 sections of 8 cm, with each section analyzed for oil content to characterize the oil spatial distribution. A colloidal transport model based on deep bed filtration was successfully fitted to the long columns data. This model was validated by conducting two 3-D sandbox experiments (1.2 m x 0.98 m x 0.98 m) filled with the same fine clayey sand used previously. The first sandbox experiment consisted of one layer. The second experiment contained three layers varying in clay content. Parameters independently estimated from the long columns experiments were used to predict emulsion transport in the sandbox. Experimental results indicate that emulsified soybean oil can be effectively distributed in the sandbox at least 1 m away from the injection well without any observation of buoyancy effect. The mathematical model calibrated using independently estimated parameters yielded a good fit with measured data. This implies that the colloids transport model can be used to model soybean oil emulsion transport in the subsurface.
Phosphorus Leaching in the Coastal Plain Soils of North Carolina.
(2007-11-01) Kang, Ji-Hoon; Robert O. Evans, Committee Member; Aziz Amoozegar, Committee Member; Deanna L. Osmond, Committee Chair; Dean L. Hesterberg, Committee Co-Chair
Some soils in areas of intensive livestock farming have shown significant phosphorus (P) leaching. The objectives of this research were: i) to examine the relationships between soil properties and P sorption capacity, ii) to investigate leaching of P as affected by fertilizer sources, iii) to examine the effects of manure-derived dissolved organic carbon (DOC) on P sorption, and iv) to evaluate deep leaching of P. The P sorption maximum (Smax) of seventy two soil samples from various horizons of Coastal Plain soils of North Carolina (NC) was determined according to the Langmuir equation. Soil samples were analyzed for pH, clay content, organic matter (OM) content, oxalate extractable Al (Alox), Fe (Feox), and P (Pox), Mehlich-3 extractable Al (AlM3), Fe (FeM3), and P (PM3). The Smax was positively correlated with extractable Al (r = 0.76 for Alox and r = 0.86 for AlM3) and OM content (r = 0.61). The positive linear relationship between OM and Smax showed a change point where there was a two-fold decrease in the regression slope for OM > 42 ± 4 g kg-1. Results indicated that Al and Fe in organic-rich soils were likely to be less accessible for P sorption compared to those in mineral soils. Leaching of P as affected by fertilizer sources was investigated with repacked soil columns (10-cm long). The fertilizer sources were dairy lagoon liquid (DL), poultry compost (PC), poultry litter (PL), swine lagoon sludge (SS), swine lagoon liquid (SL), triplesuperphosphate (TSP), and dissolved KH2PO4 (KP). When these fertilizer sources were applied on a total P basis (75 and 150 kg ha-1) as a pulse, inorganic P sources (TSP and KP) showed about two-fold greater P loss than organic P sources (PC, PL, SL and SS). The loss of source-derived P was well correlated with water extractable P in source materials (r2 = 0.87). Enhanced P transport was observed in the soil columns treated with liquid wastes as compared to the KP. Concurrent sorption of P and DOC was investigated with batch sorption experiments using the aqueous extracts of PL and SS in Autryville sandy loam. The presence of manure-derived DOC did not inhibit P sorption, while the sorption of DOC decreased in the presence of manure-derived P. Results suggested that the formation of new surface sites through metal bridges between manure-derived OM and mineral oxides outweighed the competitive efficacy of DOC against P on the soil sorption sites. Deep leaching of P was evaluated with intact soil columns (90-cm long) collected from the Coastal Plain regions of NC. The selected sites were dominated by Autryville loamy sand, Cape Fear loam, and Goldsboro fine sandy loam, and Wasda muck. A limited pore volume of leached water (2.1 ± 0.1) resulted in low concentration of dissolved reactive P in most column leachates (< 0.02 mg L-1) except Wasda muck (0.034 mg L-1). The increased P concentration in Wasda muck was attributable to the higher Mehlich-3 P concentration in deep subsoils (22 to 69 mg kg-1 at 75-90 cm depth) than the other soils (0 to 7 mg kg-1 at 75-90 cm depth).
Soil Development in Created Salt Marshes; Its Spatial Patterns and Implication for Subsurface Water Flow
(2003-01-09) Freese, Robert Carl; Stephen W. Broome, Committee Chair; Aziz Amoozegar, Committee Member; Theodore Shear, Committee Member; Michael J. Vepraskas, Committee Member
We examined soil development trends in a 28-year chronosequence of created salt marshes. Our objective was to determine whether created marshes reach ecological equivalence with natural marshes. Therefore, we studied soil properties that are likely indicators for ecological function. Marsh age is a good predictor of soil carbon and nitrogen levels, bulk density, macro-organic matter dry weight and nitrogen content of the 0 to 10 cm soil depth. Levels equivalent to the average natural marsh are predicted to occur within 22 years. Soil textural changes occur more slowly and are less closely predicted by marsh age. The 10 to 30 cm soil depth of created marshes does not change much with time and does not become equivalent to natural marshes within the time frame of this study. We examined spatial patterns by comparing soil properties 1 m inland from the marsh edge with soil properties 15 m inland. There were no significant differences in the 4-year old marsh but the 11- and 29-year old marshes had higher levels of soil carbon and nitrogen, silt, clay, porosity at the 1 m position than at the 15 m position. Geomorphologic characteristics of created marshes appear to account for this trend. The 29-year old marsh has a gradient in soil morphology and classification from a weakly developed Typic Psammaquent soil 30 m from marsh edge to a Mollic Psammaquent at 15 m to a Mollic Endoaquent at 1 m. Reshaping created marshes to more closely resemble natural marshes would likely enhance soil development and ecological function of the inland part of these marshes. Water tables and hydraulic properties of created marshes were studied to determine if there was greater flushing of nutrients from the soils of created marshes relative to natural marshes. The amplitude of a tidal cycle relative to marsh elevation affects the hydraulic gradients and soil water flux across the marsh. Water tables in salt marshes contiguous with upland areas have higher flux than in marshes without associated uplands due to fresh water recharge. At low tensions, a larger volume of water is released from the soil of a natural marsh relative to a 4-year old created marsh. The highest levels of discharge and nutrient export occurred from the edge of the natural marsh.
Spatial and Temporal Variability of Streambed Hydraulic Conductivity in West Bear Creek, NC
(2007-04-11) Leahy, Scott Thomas; David Genereux, Committee Chair; John Fountain, Committee Member; Aziz Amoozegar, Committee Member
Spatial and temporal variability of vertical hydraulic conductivity (KV) in a sandy streambed were evaluated from 487 field permeameter KV measurements taken during a 1-year study from December 2005 to December 2006. Bimonthly KV measurements were made at 46 locations (38 in December 2005) in a 262.5 m reach (the "large reach") of West Bear Creek in eastern North Carolina. More closely-spaced measurements were also made in two smaller (62.5 m) reaches within the large reach (Small Reach 1, measured in July 2006, and Small Reach 2, measured in August 2006). Vertical conductivity was calculated from field permeameter tests with data analysis based on Hvorslev (1951, case E, page 44). Results show significant spatial (transverse and longitudinal) and temporal variability in KV. Calculated arithmetic mean KV values for the large reach ranged from 3.85 to 21.33 m⁄day and the mean of the 7 arithmetic mean values (one for each bimonthly run) averaged 15.44 m⁄day. Overall, the range of streambed KV was 0.01 to 66.21 m⁄day. Variance in lnKV (s2lnKv) ranged from 1.88 to 4.18 for the large reach measurement runs and s2lnKv values measured from Small Reach 1 and Small Reach 2 were 1.88 and 6.04, respectively. Smaller s2lnKv values were calculated in the center of the stream channel, compared to values of s2lnKv for measurements taken from the left or right sides of the stream channel. The opposite is true for average KV values, where the highest averages come from the center measurement points. While measurement spacing in the small reach runs was about 4-5 times closer than in the large reach runs, results from the two types of reaches had similar results with respect to range of KV, s2lnKv, and distribution of KV in the stream channel. Correlation lengths calculated from exponential model curves fit to the experimental lnKV semi-variograms were 1.4 and 8.2 for Small Reach 1 and Small Reach 2, respectively. Correlation lengths from the small reaches bracket those calculated from the large reaches. Temporal changes in K are probably due to deposition and erosion of stream sediment, and possibly time-varying behavior of biofilms and/or gas bubbles in sediment, but not to changes in temperature. Contour maps of lnKV were created using three different interpolation techniques. Two of the three interpolation methods (radial basis function and kriging with a linear semi-variogram model) produced similar and fairly realistic looking maps. Large reach run maps showed a decrease in lnKV from the right bank to the left bank in some areas. However, overall the data show higher lnKV in the center of the channel. Small reach contour maps show higher lnKV in the center. Average uncertainty in KV is equal to about 16.2%. This was calculated by adding, in root mean square fashion, the uncertainty due to lack of knowledge of the transformation ratio "m" ( 5%) to each uncertainty value arising from propagation of uncertainty in the measurands, and then averaging these 430 uncertainty values. Percent uncertainty in KV is larger for smaller KV values since the slope of the linear regression needed to calculate KV is less accurately constrained from the field measurements of head with time when KV is low.
Urban Stormwater: First Flush Analysis and Treatment by an Undersized Constructed Wetland
(2007-10-17) Tucker, Robert Smith; Jean Spooner, Committee Chair; Jean Spooner, Committee Chair; William F. Hunt, Committee Co-Chair; William F. Hunt, Committee Co-Chair; Aziz Amoozegar, Committee Member; Aziz Amoozegar, Committee Member
Nonpoint stormwater runoff remains a leading threat to surface water quality in the U.S. Increased impervious surfaces, climate change, and increasing water demands put even more pressure on stormwater managers to improve stormwater management practices with regards to cost effectiveness, removal performance, and ecological sustainability. More effective BMPs can be designed by understanding the nature of pollutant runoff loads with respect to the hydrograph. Many studies have been performed on the first flush (FF) phenomenon (the assumption that the initial portion of a rainfall-runoff event is more polluted than the later portions). However, controversy remains on whether or not the first flush truly exists, which environmental factors influence a first flush, and how best to define the first flush phenomenon. The objective of this study as to evaluate the first flush occurrence in two small urban watersheds (differing in extent of impervious area) using multiple analytical methods and definitions previously published in the literature. The first watershed is 4.8 acres with 67% impervious roadway and the second watershed is 5.6 acres with 87% wooded land cover. Statistical tests were performed to analyze for site-specific correlations between first flush strength and rainfall characteristics (e.g. rainfall depth, peak flow rate, runoff volume, peak rainfall intensity, and antecedent dry period) and determine differences in FF strength between different land uses and pollutants. Furthermore, the FF study was utilized to perform an annual treatable load analysis in order to evaluate the effectiveness of two hypothetical BMPs sized to treat stormwater from the highly impervious watershed based on the 1.3 cm, 1.9 cm, 2.6 cm and 3.2 cm of rainfall water quality volumes. A year-long study captured stormwater samples from over 33 storm events and analyzed for TSS, turbidity, nutrients and heavy metals. Samples were collected using flow-based sampling frequencies that yield a more accurate quantification of pollutant mass transport throughout the storm event than time-paced sampling used in most of the previous first flush studies. For each collected storm, normalized cumulative pollutant load (L') and runoff volume curves (V') were generated for each pollutant with a minimum of seven discrete curve points to quantify the first flush effect and evaluate for first flush occurrence based on several published methods and definitions (e.g., max L'>V', max L'-V' > 0.2, and 80% of total load runoff in first 30% of total runoff volume). Linear regression analyses were performed to determine the first flush coefficient (b) for the power function L' = V'b to quantify the FF strength. Relationships between the first flush strength and rainfall characteristics were examined. Analysis of covariance (ANCOVA) was utilized to determine if FF strength (i.e. b-value) significantly differed between wooded and impervious watersheds, and a nonparametric ANOVA (Kruskal-Wallis test) was used to evaluate differences in FF strength among the pollutants within each watershed. As indicated by all the methods utilized in this study, most pollutants exhibit a slight FF effect on average but substantial pollutant loading still occurred in the latter portion of the storm's total runoff volume. Thus, to treat the majority of a storm's total pollutant load requires capturing almost the same fraction of runoff volume. Although the FF phenomenon was not dominant, this study did define a "most efficient" design volume (first 40% of runoff or approximately 1.3 cm of rainfall), which was where the fraction of total pollutant load was greatest compared to the fraction of total runoff volume. Of the rainfall characteristics analyzed, rainfall and runoff volume both inversely affected the FF strength of TSS and heavy metals on the impervious watershed. Although the runoff nature of orthophosphate (O-PO4) at the first portion of the storms did not have a first flush, the relative FF strength for O-PO4 actually increased with increasing rainfall or runoff. Land use did not influence the first flush strength of the pollutants except for Pb, which had significantly stronger FF effect on the more impervious watershed compared to the heavily wooded one. Disregarding the estimated pollutant load from a large 18.2 cm tropical storm, the 1.3 cm and 2.6 cm of rainfall design volumes could potentially capture and treat on average 64% and 82% of the annual runoff volume and 67% and 85% of the annual pollutant load for all the pollutants on the impervious watershed. Although stormwater BMPs designed to capture the first 2.5 cm of rainfall can potentially treat a substantial fraction of yearly pollutant load, this study suggests that in watersheds with limited and expensive land area it is more efficient to use multiple smaller BMPs near the source that capture the smaller, more frequent storms (1.3 cm of rainfall or less). Among all the stormwater BMPs currently utilized to reduce peak runoff volumes and remove contaminants from urban runoff, constructed wetlands have emerged as an optimal choice because of their high performance of water quality improvement and ecological benefits. Due to a stormwater wetland's high land requirement, however, they are often difficult to size properly in urban environments. This study also evaluated the pollutant removal efficiencies of a newly constructed flow-through stormwater wetland that is sized to only capture 20% of runoff generated by the recommended design storm in N.C. (first 2.5 cm of rainfall). The wetland was constructed in December 2006 as a retrofit to a failing level-spreader in order to repair a rapidly eroding head-cut between two stormwater outfall channels and the receiving stream. Following addition of the extended detention function, the undersized wetland has initially removed, on average, 71% of the TSS load, between 39% and 60% of the nutrient load, and 60% of the heavy metal load. For all the pollutants except TP and TKN, lower removal efficiencies were observed for the storms with flow bypass (5 out of 9 events since the extended detention function) on average as compared to the smaller events without bypass. When evaluated for all the sampled storms, event mean concentrations proved to be statistically lower at the outlet for all pollutants except Ti and V. For most pollutants, higher influent EMCs were observed for the storms with higher removal efficiencies. It is important to note, however, that these initial results are skewed by a small number of storms with low rainfall depths (median = 0.46 cm). With that considered, the average removal efficiencies are actually higher than predicted for the 1.3 cm design storm BMP. Undersized wetlands with "flow through" design might provide effective and efficient pollutant removals if designed to safely pass the larger storms. Longer term research will provide a more definitive evaluation.