Journal of Korean Society on Water Environment, Vol. 33, No. 6, pp. 715-721 (November, 2017) pISSN 2289-0971 eISSN 2289-098X https://doi.org/10.15681/KSWE.2017.33.6.715

Hydrologic and Hydraulic Factors Affecting the Long-term Treatment Performance of an Urban

Franz Kevin F. Geronimo Jungsun Hong Lee-Hyung Kim†

Department of Civil and Environmental Engineering, Kongju National University

도시 강우유출수를 처리하는 나무여과상자의 장기 처리효율에 영향을 주는 수리학적 및 수문학적 인자 연구

Franz Kevin F. Geronimo․홍정선․김이형†

국립공주대학교 건설환경공학과 (Received 26 October 2017, Revised 23 November 2017, Accepted 23 November 2017)

Abstract Tree box filters, an example of systems, were compacted and versatile urban stormwater low impact development technique which allowed volume and treatment performance to be adjusted based on the hydrologic, runoff quality and catchment characteristics. In this study, the overall performance of a 6 year-old tree box filter receiving parking lot stormwater runoff was evaluated. Hydrologic and hydraulic factors affecting the treatment performance of the tree box filter were also identified and investigated. Based on the results, the increase in rainfall depth caused a decrease in hydrologic and hydraulic performance of the tree box filter including volume, average flow, and peak flow reduction (r = -0.53 to -0.59; p <0.01). TSS, organics, nutrients, and total and soluble heavy metals constituents were significantly reduced by the system through media filtration, adsorption, , and evapotranspiration mechanisms employed in the tree box filter (p <0.001). This significant pollutant reduction by the tree box filter was also found to have been caused by hydrologic and hydraulic factors including volume, average flow, peak flow, hydraulic retention time (HRT) and runoff duration. These findings were especially useful in applying similarly designed tree box filter by considering tree box filter surface area to catchment area of less than 1 %.

Key words : Bioretention, Hydrologic and hydraulic factors, Low Impact Development, Tree box filter

1. Introduction1) Nichols, 2015). Bioretention media including soil and supports the growth of plants during intermittent wet and dry Low impact development (LID) is a stormwater manage- periods (Winston et al., 2016). ment approach that mimics the predevelopment hydrology of Tree box filters were an example of bioretention system an area by using decentralized technologies that infiltrate, fil- that have large planting pit with additional storage, a storm ter, store, evaporate and detain runoff close to its source flow inlet from the street or sidewalk and an underdrain sys- (Flores et al., 2015; Hinman, 2005). One example of LID tem (Hinman, 2005). These tree box filters were compacted technology was bioretention systems which were widely im- urban stormwater low impact development technique which plemented in different countries due to its minimal space re- allowed volume and water quality treatment performance to quirements, versatility and appropriateness as small landscape be adjusted based on the hydrologic, runoff quality and areas, and good pollutant removal and peak hydraulic flow catchment characteristics. Tree box filters were usually ap- reduction efficiency (Geronimo et al., 2017). Bioretention plied to treat stormwater runoff from transportation land uses systems treat stormwater via a range of physical, chemical including roads, bridges, parking lots, highways and and biological processes (Geronimo et al., 2014; Lucke and sidewalks. In USA, tree box filters attained pollutant removal greater than 85 % and 45 % for (TSS)

†To whom correspondence should be addressed. and nutrients, respectively while heavy metal removal ranged [email protected] from 54 % to 88 % (Penmetcha, 2015).

This is an Open-Access article distributed under the terms of the Creative While there were several researches evaluating long term Commons Attribution Non-Commercial License (http://creativecommons.org/ hydrologic and water quality performance of bioretention licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. systems both for field scale and laboratory scale, there was

Journal of Korean Society on Water Environment, Vol. 33, No. 6, 2017 716 Franz Kevin F. Geronimo․Jungsun Hong․Lee-Hyung Kim

no study conducted to identify hydrologic and hydraulic fac- hance phytoremediation potential of the system and to in- tors affecting long term performances of tree box filters crease capability of soils to remove pollutants. The 379 m2 (Lucke and Nichols, 2015; O’Neill and Davis, 2011; Thomas parking lot was constructed using rough asphalt with slope et al., 2015). Evaluation of long term performance was used and runoff coefficient (mean ± standard deviation) of less as a common performance indicator for LID practices includ- than 1 % and 0.27 ± 0.42. The surface area of the tree box ing bioretention systems (Li and Lam, 2015). Limited re- filter occupied less than 1 % of the parking lot area. search works were conducted at present completely assessing the long term performance of tree box filters for stormwater 2.2 Storm event monitoring, data collection and analyses management. In addition, most of the recent studies have In order to evaluate the long-term performance of the tree considered limited storm events and short term monitoring box filter in managing parking lot storm water runoff, storm which is not sufficient and may not accurately represent the events were monitored for years from July 2010 to April system’s long term performance. As such, this study eval- 2016. Following the typical sampling scheme in South uated the long term treatment and hydraulic performance of Korea, six grab samples were collected during the first hour tree box filter. Specifically, hydrologic and hydraulic factors when the stormwater runoff entered and was discharged by affecting the long-term treatment performance of the tree box the tree box filter for the inflow and outflow water samples, filter were identified and investigated. respectively (Jung et al., 2008). The first grab sample was collected as soon as the runoff entered the tree box filter 2. Materials and Methods and after 5, 10, 15, 30 and 60 mins respectively. After the first hour, a sample was collected at an interval of 1 hour 2.1 Description of tree box filter and its catchment area until the storm water runoff stopped flowing into the tree The tree box filter with infiltration function was con- box filter. Similar sampling scheme was conducted for the structed in 2010 inside Kongju National University, Cheonan storm water discharged by the tree box filter. Runoff and city, South Korea to manage urban stormwater runoff from a discharge flow rates were measured at a 5-min interval. 100 % impervious parking lot. The aspect ratio (L:W:H) of Climatological characteristics of the monitored rainfall events the tree box filter was 1:0.67:0.87. The schematic repre- including the antecedent dry days (ADD), rainfall depth and sentation of the media arrangement in the tree box filter and rainfall intensity were obtained from the Korea Meteorological its catchment area was illustrated in Fig. 1. The tree box fil- Administration. Water samples were analytically analyzed for ter was equipped with a small sedimentation basin (2.8 % of particulates (TSS); organics including biochemical oxygen the total facility storage volume) with geotextile fabric for demand (BOD) and (COD); nutrients the retardation clogging in the system and for ease of such as total nitrogen (TN) and total phosphorus); soluble maintenance. Filter media including woodchip, sand and heavy metals such as chromium (Cr), copper (Cu), zinc (Zn) gravel were employed in the tree box filter resulting to a to- and lead (Pb), and their total heavy metal counterpart name- tal facility storage volume of 0.71 m3. Metasequoia tree ly, total chromium (TCr), total copper (TCu), total zinc (Dawn redwood) was planted in the tree box filter to en- (TZn) and total lead (TPb) parameters in the laboratory in

Fig. 1. Schematic representation of tree box filter and its catchment area.

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accordance with the standard methods for the examination of significant volume, average flow and peak flow reduction were water and wastewater (APHA, AWWA, and WEF, 1992). 14 % to 86 %, 14 % to 71 % and 20 % to 88 %, respectively The efficiency of tree-box filter was evaluated using load (p < 0.001). Rainfall depth was found to be negatively cor- and volume ratio which were calculated by dividing the dis- related with volume, average flow and peak flow reduction charged load and volume with the runoff load and volume, of the system implying that the increase in rainfall depth respectively. Statistical analyses including Pearson correlation causes decreased hydraulic performance of the system (r = (r) and paired sample sign test were conducted using SYSTAT -0.53 to -0.59; p < 0.01). The hydraulic retention time (HRT) 12 and Origin Pro 8. Significant correlations and differences in the tree box filter was found to be significantly correlated between parameters were accepted at 95 % confidence level with antecedent dry days (ADD) and runoff duration (r = implying that probability (p) values were less than 0.05. 0.55 to 0.63; p < 0.05). This finding implied that the inter- mittent dry and wet condition affected by evapotranspiration 3. Results and Discussion mechanism of the tree box filter affected the system’s hy- draulic performance. Lastly, there was no correlation found 3.1 Characteristics of monitored storm events and water between ADD and the system’s hydraulic and pollutant re- quality load duction performance. The mean runoff and discharged unit pollutant loads in the tree box filter were demonstrated in A total of 21 storm events were monitored in the tree box Fig. 2. Inflow TSS unit load amounting to 0.26 ± 0.49 g/m2 filter. 70 to 80 % of the monitored storm events were less was significantly reduced to outflow TSS unit load of 0.02 ± than 10 mm which was in the same range of daily rainfall 0.04 g/m2 (p < 0.001). Despite the negative organic loads re- depth occurring in Cheonan city (Maniquiz et al, 2010). moval efficiency in some of the monitored storm events, the Cheonan city received an annual rainfall (mean ± standard inflow unit BOD and COD loads were significantly reduced deviation) from 2010 to 2016 amounting to 1176 ± 340 mm. by -50 % to 100 % and –13 % to 100 %, respectively (p < Listed in Table 1 was the statistical summary of hydrologic 0.001). Negative BOD and COD removal efficiencies were and hydraulic characteristics of monitored storm events in observed for the rainfall depth of 17.5 mm which was be- the tree box filter. The minimum and maximum rainfall yond the design rainfall capacity of the system of about 5 depth monitored corresponded to 34 % and 80 % to 90 %, mm. Similarly, significant nutrients and heavy metals unit respectively of the rainfall occurring in Cheonan city. These load reduction with mean value ranges of 79 % to 83 % and findings implied that the storm events monitored in the study 77 % to 86 %, respectively (p < 0.001). The heavy metals in objectively represented the rainfall depth occurring in stormwater runoff including Cr, Cu, Zn and Pb were mostly Cheonan city. Among the 21 storm events monitored, only in dissolved or soluble form ranging from 46 % to 67 % of ten storm events were able to produce outflow wherein 40 % TCr, TCu, TZn and TPb, respectively. On the other hand, of these occurred from June to August. The mean rainfall in- the percentage of discharged soluble heavy metals further in- tensity of storm events that produced outflow was 34 % creased to 64 % to 83 % implying that the system developed greater than those which have no outflow. Excluding the was more effective in reducing particulate heavy metals storm events where the tree box filter has no discharge, the

Table 1. Statistical summary of hydrologic and hydraulic characteristics of monitored storm events Parameter Unit n Minimum Maximum Mean Median Standard deviation Antecedent dry days (ADD) day 21 0.20 19.30 5.21 3.90 4.76 Rainfall depth mm 21 1.00 22.50 6.29 3.50 5.99 Rainfall duration hr 21 0.53 8.22 3.66 3.07 2.62 Average rainfall intensity mm/hr 21 0.36 25.40 3.23 1.22 5.65 Runoff duration hr 21 0.08 7.00 1.70 1.17 1.64 Hydraulic retention time (HRT) hr 10 0.12 2.63 1.12 0.96 0.97 Runoff volume m3 21 0.01 5.07 0.84 0.10 1.37 Discharged volume m3 10 0.01 3.97 0.97 0.42 1.30 Average inflow rate m3/hr 21 0.01 3.20 0.58 0.08 0.94 Average outflow rate m3/hr 10 0.02 2.25 0.64 0.34 0.69 Peak inflow rate m3/hr 21 0.02 11.61 2.26 0.30 3.41 Peak outflow rate m3/hr 10 0.03 5.12 1.64 1.52 1.50

Journal of Korean Society on Water Environment, Vol. 33, No. 6, 2017 718 Franz Kevin F. Geronimo․Jungsun Hong․Lee-Hyung Kim

Fig. 2. Runoff and discharged unit pollutant loads (mean ± standard deviation). compared to soluble heavy metals. This finding was attrib- organics and nutrients constituents’ reduction ranging from uted to the filtration capability of the system where in larger 30 % to 55 % and 40 % to 60 %, respectively. Lastly, the particles tend to be reduced through filter media in the tree corresponding total and soluble heavy metal reduction ranged box filter. In addition, larger soluble heavy metal fraction in from 55 % to 70 % (except for TCr and TPb) and 50 % to the outlets could also be attributed to the hydraulic retention 55 % for volume reduction of 50 %. Lower reduction for time in the tree box filter similar to the study conducted by TCr, TPb and soluble heavy metals supported the findings of Egemose et al. (2015) which evaluated heavy metal retention a previous study wherein soluble heavy metals tend to in stormwater treatment ponds. High mean unit pollutant by-pass the system only with the volume reduction through load reduction were attributed to the storm events with rain- infiltration and retention as the main factor for heavy metal fall depth less than 6.5 mm in which the runoff were either reduction (Geronimo et al., 2014). While the reduction of retained or infiltrated fully in the system resulting to 100 % heavy metals may be attributed to ion exchange and adsorp- pollutant load reduction. These findings suggested that the tion, the retention of Pb decreased significantly as a result of tree box filter showed efficiency in volume, flow, and pollutant competition with other heavy metals being adsorbed in the load reduction. Retention, infiltration and evapotranspiration system (Oh et al., 2009). Among the pollutants analyzed, were the volume, flow and pollutant removal mechanisms BOD, TPb and Cr and Cu were found to have probability of that occurred in the tree box filter. leaching when the discharged volume in the tree box filter were greater than 75 %, 65 %, 95 % and 95 % of the runoff 3.2 Relationship between pollutant load, volume and flow rate volume. The leaching of these pollutants was observed dur- reduction ing the two storm events with the highest rainfall depth Apparent in Fig. 3, TSS has the lowest pollutant load ratio amounting to 17.5 mm and 22.5 mm. In a study conducted of 0.15 which is equivalent to 85 % TSS load reduction for by Scholes et al. (2008), medium potential reduction of volume ratio 0.5 among all the stormwater constituents. BOD may be expected through mechanisms including ad- Similarly, reduction of runoff volume by 50 % will result to sorption, settling, microbial degradation, filtration and plant

Fig. 3. Polynomial regression of the changes in pollutant load ratio with respect to volume ratio.

한국물환경학회지 제33권 제6호, 2017 Hydrologic and Hydraulic Factors Affecting the Long-term Treatment Performance of an Urban Stormwater Tree Box Filter 719

uptake. Similar studies about bioretention systems have reduction performance of tree box filter for all the storm- found that volume reduction through infiltration, retention water constituents. The hydraulic performance of the system and intermittent conditions in the stormwater treatment sys- was also found to be important not only for pollutant re- tems, specifically bioretention, have affected pollutant load moval but also to support plant life and growth in bio- reduction (Geronimo et al, 2014; Mangangka et al. 2015; retention systems such as tree box filters (Fassman-Beck et Subramaniam et al., 2015). al., 2015; Guo et al., 2015). By attaining average flow reduction of 50 %, greater pollu- tant load reduction by the system may be expected ranging 3.3 Runoff duration and hydraulic retention time from 55 % to 90 % exhibited in Fig. 4(a) except for BOD. The varying pollutant load ratios with respect to the ratio Lower BOD removal amounting to approximately 43 % with of HRT to runoff duration (RD) were demonstrated in Fig. respect to 50 % average flow reduction was observed. This 5. Among the stormwater constituents, TSS was found to finding was attributed with the BOD leaching during the have the greatest load ratio of about 0.1 corresponding to 90 monitoring of storm events with highest rainfall depth % TSS reduction at an HRT to runoff duration ratio of 0.5. amounting to 17.5 mm and 22.5 mm and the increase in Increased HRT to runoff duration ratio from 0.2 to 0.5 re- rainfall depth which caused the pollutants to by-pass the sulted to increased organics and nutrients removal by 20 % system. Similarly, 25 % to greater than 80 % pollutant reduc- to 30 % and 25 % to 35 %, respectively. Consequently, 0.5 tion may be expected from the tree box filter for a 50 % HRT to runoff duration ratio caused 67 % to 71 % and 55 % peak flow reduction as can be seen in Fig. 4(b). Among the to 82 % soluble and total heavy metal reduction, pollutant constituents, only TSS, TP, COD and TZn had respectively. Low HRT in constructed wetlands, another type greater pollutant removal amounting to 55 % to 90 % at 50 of low impact development technology used for stormwater % peak flow reduction. Greater pollutant reduction was ob- and wastewater treatment, resulted to incomplete de- served with corresponding average flow reduction compared nitrification and nitrogen removal required longer HRT com- to peak flow reduction. These findings suggested that hydro- pared with that required for organics removal (Lee et al., logic and hydraulic factors including volume, average flow 2009). Heavy metal retention of a stormwater treatment fa- and peak flow were found have affected the pollutant load cility depended on several facility related factors such as

a

b Fig. 4. Polynomial relationship of pollutant reduction with a. average flow and b. peak flow reduction.

Journal of Korean Society on Water Environment, Vol. 33, No. 6, 2017 720 Franz Kevin F. Geronimo․Jungsun Hong․Lee-Hyung Kim

Fig. 5. Logarithmic regression of pollutant load ratio at varying HRT to runoff duration ratio. type, age, volume/CA ratio and HRT and runoff character- compared to the soluble heavy metal evident in the higher istics including pH, alkalinity, organic matter and other sub- percentage of soluble heavy metal in the discharged volume stances (Egemose et al, 2015). Previous studies in USA and of the tree box filter. Both organics and nutrients, which South Korea confirmed that longer HRT in the media or in were observed to have leached at a rainfall depth of 17.5 the stormwater treatment system resulted to greater pollutant mm, have the lowest removal efficiencies with ranges of -50 reduction efficiency (Geronimo et al., 2017; Peterson et al, % to 90 % and -20 % to 94 %, respectively. Significant hy- 2015). Longer HRT enabled longer contact time between drologic and hydraulic factors including volume, average stormwater runoff and filter media in the tree box filter in- flow, peak flow, HRT and runoff duration affected the pollu- creasing the pollutant reduction efficiency of the system. tant reduction efficiency of the tree box filter. An increase in the volume ratio corresponded to an increase in pollutant 4. Conclusion load ratio. In addition to volume reduction, an increase in both average and peak flow reduction corresponded to in- In this study, a tree box filter developed to treat parking creased pollutant reduction efficiency of the tree box filter. lot stormwater runoff was evaluated to identify the long term However, greater pollutant reduction was observed with cor- treatment performance and the corresponding hydrologic and responding average flow reduction compared to peak flow hydraulic factors affecting its performance. Based on the re- reduction. The hydraulic performance of the tree box filter sults of this study, the increase in rainfall depth caused the was not only important for pollutant removal but also for decreased hydraulic performance of the tree box filter in- sustaining plant life. At an HRT to runoff duration ratio of cluding volume, average flow and peak flow reduction (r = 0.5 the removal of TSS, organics, nutrients, and total and -0.53 to -0.59; p <0.01). The intermittent dry and wet con- soluble heavy metals were 90 %, 60 % to 70 %, 70 % to 80 dition of the tree box filter affected the hydraulic perform- %, 55 % to 82 % and 67 % to 71 %, respectively. Longer ance since ADD and runoff duration were found to affect HRT resulted to longer contact time between stormwater run- the HRT of the system (r = 0.55 to 0.63; p <0.05). off and filter media in the tree box filter and increased pollu- Significant reduction in volume, flow and pollutant loads tant removal efficiency of the system. For similar tree box fil- through media filtration, infiltration and evapotranspiration ter design and application, it is suggested that a small sed- were observed after the runoff entered the tree box filter (p imentation basin be included to slow down clogging and for < 0.001). Significant volume, average flow and peak flow the ease of maintenance through coarse particle and debris reduction amounting to 14 % to 86 %, 14 % to 71 % and 20 removal. These findings were especially useful in applying % to 88 %, respectively for storm events where the tree box similar tree box filter which may be designed by considering filter has no discharge. Among the pollutants, TSS showed tree box filter surface area to catchment area of less than 1 %. the greatest removal amounting to 70 % to 98 % for rainfall events in which tree box filter produced outflow. This was 국문요약 followed by satisfactory total and soluble heavy metal re- moval that ranged from 18 % to 93 % and 14 % to 88 %, 식생체류지 기법 중 하나인 나무여과상자는 유역면적 및 respectively. Apart from volume reduction, total heavy metal 강우유출수의 특성에 따라 기법의 용적 및 수질 저감 능력 removal was attributed to the filtration mechanism in the 조정이 가능한 도시 저영향개발 기술이다. 본 연구는 주차장 system wherein greater particulate metals tend to be reduced 강우유출수 처리를 위해 6년동안 운영된 나무여과상자의 성

한국물환경학회지 제33권 제6호, 2017 Hydrologic and Hydraulic Factors Affecting the Long-term Treatment Performance of an Urban Stormwater Tree Box Filter 721

능을 평가하기 위하여 수행되었다. 또한 나무여과상자의 저 Bioretention Systems, Desalination and Water Treatment, 감 능력에 영향을 미치는 수리·수문학적 요인들을 조사하였 54(13), 3661-3667. 다. 분석 결과, 강수량의 증가는 나무여과상자의 유출량, 평 Hinman, C. (2005). Low Impact Development Technical Guidance Manual for Puget Sound, Available from: www.psp.wa.gov/ 균유량 및 첨두유량 감소 등의 수리·수문학적 성능이 감소되 downloads/LID/LID_manual2005.pdf (accessed 01 August 2017). 는 것으로 평가되었다 유 (r = -0.53 to -0.59; p < 0.01). TSS, Jung, Y. J., Stenstrom, M. K., Jung, D. I., Kim, L. H., and Min, 기물 영양물질 및 중금속 등의 오염물질은 나무여과상자 내 , K. S. (2008). National Pilot Projects for Management of 충진된 여재의 여과 및 흡착, 침투, 증산발 기작 등을 통하여 Diffuse Pollution in Korea, Desalination, 226(1-3), 97-105. 저감되는 것으로 나타났다(p < 0.001). 또한 유출량, 평균유 Lee, C. G., Fletcher, T. D., and Sun, G. (2009). Nitrogen 량, 첨두유량, 체류시간 및 강우지속시간 등과 같은 수리·수 Removal in Systems, Engineering in 문학적 요인의 영향을 받는 것으로 평가되었다. 이는 나무여 Life Sciences, 9(1), 11-22. Li, Z. Y. and Lam, K. M. (2015). 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