OPTIMIZING STORM DETENTION AND TREATMENT FACILITY TO CONTROL NONPOINT SOURCE POLLUTION IN STEEL COMPANY

Abstract : Due to stormwater runoff along Pohang Bay at typhoon Rusa and Maemi in 2002 and 2003, P steel Company requires a counter measure for all future typhoons. P steel Company will have the challenge of both determining the benefits of their existing treatment facility and deciding what additional practices they will need to achieve the goal. In order to reduce the nonpoint source pollution during rainfalls, P steel Company is considering the installation of stormwater pits and the construction of a stormwater treatment plant. This study analyzed the reduction effect of nonpoint source pollution achieved through such measures using the Storm Water Management Model (SWMM). As a result, we found that the installation of stormwater pits (storage capacity 60mm/day) and stormwater treatment plant have reduced the pollution load (SS) by 38 to 87% compared to the existing state, and the concentration of SS in outflow also satisfied 20mg/L or lower

OPTIMIZING STORM DETENTION AND TREATMENT FACILITY TO CONTROL NONPOINT SOURCE POLLUTION IN STEEL COMPANY

1 Korea Environment Institute, 613-2 Bulgwang-Dong, Eunpyeng-Gu, Seoul, Korea

2 Han-River Basin Environmental Office, 231 Manwol-Dong, Hanam-City, Kyunggi-Do, Korea

3 Department of Environmental Engineering, University of Seoul, 90 Cheonnong-Dong, Dongdaemun-Gu, Seoul, Korea

Abstract : Due to stormwater runoff along Pohang Bay at typhoon Rusa and Maemi in 2002 and 2003, P steel Company requires a counter measure for all future typhoons P steel Company will have the challenge of both determining the benefits of their existing treatment facility and deciding what additional practices they will need to achieve the goal In order to reduce the nonpoint source pollution during rainfalls, P steel Company is considering the installation of stormwater pits and the construction of a stormwater treatment plant This study analyzed the reduction effect of nonpoint source pollution achieved through such measures using the Storm Water Management Model (SWMM) As a result, we found that the installation of stormwater pits (storage capacity 60mm/day) and stormwater treatment plant have reduced the pollution load (SS) by 38 to 87% compared to the existing state, and the concentration of SS in outflow also satisfied 20mg/L or lower

Key words : Nonpoint-source pollution, SWMM, Swormwater

INTRODUCTION

Impacts caused by storm water discharges from primary metals facilities will vary A number of factors will influence to what extent the activities at a particular facility will affect water quality These include: geographic location, hydrogeology, the amounts and types of materials stored outside, the types of processes taking place outside, the size of the operation, as well as the characteristics of a particular storm event Although operations at primary metals facilities may vary considerably, the elements with potential impact on storm water discharges are fairly uniform and consistent Facilities may include considerable areas of raw and waste material storage such as coal, coke, metal, ores, sand, scale, scrap, and slag Processes generally involve furnaces for heating and melting metals or for producing coke, any of which may result in significant particulate emissions Due to the nature of their operations some facilities will have large areas of exposed soil and heavy vehicle traffic which can lead to erosion Especially in such a large factory as P steel Company, due

to its wide impervious area, a sudden increase of stormwater runoff may occur during rainfall, and nonpoint source pollutants may flow into public waters, causing water pollution problems at typhoon

P steel Company is one of the largest steel makers in the world with total area size of 891ha, and steel production capacity of 12 million tons The researched area was iron and steel making area, a part of P steel Company with the area size of 461.82ha(P steel Company, 2003) To review the water treatment system of P steel Company; the wastewater generated from the industrial processes

is primarily treated in each individual treatment facility, which is then finally treated in the wastewater treatment plant before it is discharged The site has the separated sewer system, and most of the stormwater runoff, especially the initial stormwater runoff flows into and treated in the wastewater treatment plant, so nonpoint source pollution are being efficiently controlled However, whenever a typhoon brings heavy rainfalls, the stormwater runoff from the iron ores and coal yard would exceed the capacity of the treatment plant, discharging most of it to Hyeongsan River This

situation must be improved

Accordingly, on behalf of management of nonpoint source pollution for P steel Company, this study tries to derive effective alternatives to the installation of detention and treatment facilities, and find the optimum management practices for nonpoint source pollution control by analyzing the pollution reduction effects of the alternatives using the Storm Water Management Model(SWMM)

CONSTRUCTION OF MODEL FOR CATCHMENT USING SWMM

Scheme of SWMM

The United States Environmental Protection Agencies (USEPA's) Storm Water Management Model

is a comprehensive computer model for analysis of quantity and quality problems associated with urban runoff Both single-event and continuous simulation can be performed on catchments having storm sewers, or combined sewers and natural drainage, for prediction of flows, stages and pollutant concentrations Extran Block solves complete dynamic flow routing equations (St Venant equations) for accurate simulation of backwater, looped connections, surcharging, and pressure flow(Huber and Dickinson, 1988)

Construction of model

Distribution of sub-catchments and channel network of the study area is shown in Fig 1 The study area was divided into 16 drainage zones based on the treatment area divisions by channel networks and surface slopes For sub-catchments, informations such as catchment area , slope, roughness, impervious percentage, and land use were input For Conduit, informations such as conduit length, diameter, slope, shape, roughness werw input For the parameters related to depression storage and infiltration, the values in the references were applied, and then calibrated to exhibit the runoff characteristics of catchment during the calibration of the model For the information related to water flow and quality, the actual measured values were applied for average water flow and quality and temporal variation For the pollutants buildup and washoff parameters, after the values in the literature were applied, they were corrected during the model calibration process

Fig 1 Division of sub-catchment and channel network in the study area

The model was calibrated for the water flow and quality during dry weather and wet weather Fig.2 shows the comparisons between actual measured values and the simulated values for flow volume and water quality, and we can find that the overall trends of both flow volume and water quality are well simulated

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Fig 2 Calibration of Model

MANAGEMENT PRACTICES OF NOMPOINT SOURCE POLLUTION

As a method of nonpoint source pollution control during rainfall, P steel Company plans to install a stormwater pit for prevention of rapid runoff and removal of pollutants, and also construct a stormwater treatment plant This study tries to derive the optimum management practices for nonpoint source pollution by analyzing the pollution load reduction effect between different alternatives using the Storm Water Management Model

Proper storage capacity for stormwater pit

A stormwater pit temporarily keeps stormwater runoff during a rainfall to prevent rapid outflow of stormwater, and the storage water in the pit is transferred to the treatment plant after the rain stops The proper storage capacity of the stormwater pit was determined from analyses of the rainfall data

of Pohang-city and pollution reduction effects for different storage capacities using SWMM

First, after an analysis of the Phonag's rainfall data during the recent 43 years (1961 to 2003), we

found that 4,168days(97.6%) of the total 4,271 wet days had less than 60mm of rainfall, and 27 days(0.6%)had over 100mm

Next, to analyze the pollution load reduction effects by the installation of the stormwater pit, we set

up alternatives according to the storage capacity of stormwater pit, and simulate the runoff characteristics of each alternative using the SWMM

(a) Case 1 : The storage capacity of the stormwater pit : 60mm/day

(b) Case 2 : The storage capacity of the stormwater pit : 100mm/day

The rainfalls applied for model simulation are shown in Fig 3

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(d) Typhoon Maemi(175.0mm/event, 2003 9.11∼9.13)

Fig 3 Hyetograph of simulated rainfalls

Fig 4 shows the runoff characteristics for each alternative at the final discharge in the wastewater treatment plant If we look at the runoff characteristics for a rainfall of 30mm/event(Fig 4 (a), (b), (c)), the existing state exceeded 100mg/L of SS, when inflow exceeded the treatment capacity However, Alternatives 1 & 2 showed a good water quality of less than 30mg/L over the whole period During heavy rainfalls of over 60mm/event, the concentration in outflow was considerably reduced by the installation of the stormwater pit However, once the capacity of the stormwater pit and the treatment plant are exceeded, the concentration in outflow rapidly increased

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Fig 4 Result of simulation for each alternative (treatment outflow)

To analyze the nonpoint source pollution reduction effects of each alternative during rainfall, we compared the total pollution load for each alternative The total pollution load was determined by the following formula, where the outflow volume per unit time is multiplied by the concentration of pollutants

▪ Total pollution load(kg/event) = ∑ C i ⅹQ i

-10,000

20,000

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P re s e n t 3,211 3,942 31,303 9,744

Ca s e 1 1,888 3,201 15,120 6,258

Ca s e 2 1,651 2,855 14,685 5,887

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R u s a

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P re s e n t 6,322 7,511 82,837 26,814

Ca s e 1 1,027 6,967 60,319 20,909

Ca s e 2 830 6,366 58,332 19,474

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Fig 5 Total pollution load for each alternative

As shown in Fig 5, the differences of pollution load reduction effects are not great between alternatives When you review the average pollutants reduction effects compared to the existing state, COD was reduced by 37% for alternative 1 and 42% for alternative 2, and SS was reduced by 35% for alternative 1, and 40% for alternative 2

Therefore, considering the fact that about 97.6% of yearly rainfall events are 60mm or lower, and the pollutants reduction effects of alternative 1 and 2 are not very different, our recommendation for the proper storage capacity of the stormwater pit is about 60mm/day

Installation of wastewater treatment facility and stormwater treatment facility

P steel Company has the separated sewer system, and most of the stormwater runoff, especially the initial stormwater runoff flows into and treated in the wastewater treatment plant, but during heavy rainfall, polluted stormwater runoff from the iron ores and coal yards exceeds the capacity of the treatment plant, and directly discharged to the receiving water without proper treatments, deteriorating water pollution

Accordingly, this study reviewed the case that the wastewater is treated in a newly-installed wastewater treatment facility while the stormwater runoff is treated in the existing wastewater treatment plant retrofitted(Alternative 3) To quantify the pollution reduction effects of Alternative3,

we simulated the runoff characteristics of alternative 3 in comparison with Alternative 1

Table 1 Comparison of each alternative

Treatment of

Wastewater treatment plant (Q=50,000 mNewly-installed wastewater 3/day)

Treatment of

Stormwater runoff

Retrofit of existing wastewater treatment plant(Q=200,000 m3/day)

Existing wastewater treatment plant (Q=80,000 m3 /day)

Fig 6 shows the outflow characteristics of each alternative at the final discharge in the treatment plant Alternative 3 showed 20mg/L or lower SS concentration during 30mm/event and 60mm/event conditions as well as the rainfall from typhoon Maemi However, Alternative 1 exceeded 100mg/L of SS concentration for rainfalls of 60mm/event or more As the Typhoon Rusa brought a big rainfall of 394.5mm/event, both alternatives showed more than 100mg/L of SS concentration

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Fig 6 Result of simulation for each alternative(treatment outflow)

Fig 7 shows the nonpoint source pollution reduction effects of each alternative The average

pollution reduction effects of Alternative 3 was 27% for COD and 40% for SS In particular, its pollution reduction effects for heavy rainfalls such as 60mm/event and typhoon Maemi were high,

so we can conclude that with Alternative 3, we can secure relatively stable water quality in heavy rainfalls as well

-5,000

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Ca s e 1 1,888 3,201 15,120 6,258

Ca s e 3 1,360 2,139 13,040 4,250

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/e ve n t

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R u s a

Ty p h o o n

Ma e mi

-20,000 40,000 60,000 80,000

Ca s e 1 1,027 6,967 60,319 20,909

Ca s e 3 818 1,525 51,320 11,172

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Ma e mi

Fig 7 Total pollution load for each alternative

CONCLUSION

P steel Company has the separated sewer system, and most of the stormwater runoff, especially the initial stormwater runoff flows into and treated in the wastewater treatment plant, resulting in relatively good management of nonpoint source pollution During heavy rainfalls, however, polluted stormwater runoff from the iron ores and coal yards exceeds the capacity of the treatment plant, and directly discharged to Hyeongsan River This may be attributed to natural disasters such

as typhoons, but P steel Company, as a world-class company, tries to achieve perfect environmental management through optimum nonpoint source pollution control by complementing their existing treatment system

As a means to reduce the nonpoint source pollution during rainfall, we have derived the installation

of stormwater pits and stormwater treatment plant We analyzed the pollution load reduction effects

of these alternatives using SWMM

▪ By the installation of stormwater pits, pollution load(SS) could be reduced by up to 35% compared to the existing facility with Alternative 1 (storage capacity: 60mm/day), and 40% with Alternative 2 (storage capacity: 100mm/day) Further, in case of rainfalls of 30mm/event or lower, good water quality of 30mg/L or lower was estimated

▪ In addition to the stormwater pit installation, through a separate treatment of wastewater and stormwater runoff, we could reduce the pollution load(SS) by about 66% compared to the existing situation, and for most simulated rainfalls except typhoon Rusa, good water quality of 20mg/L or lower was estimated

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County of Sacramento(2002), Best management practices for industrial storm water pollution control, Sacramento, USA

Federal register, Final NPDES Storm Water Multi-Sector General Permit for Industrial Activities; Notice(1995), EPA, USA

Huber, W.C and R.E Dickinson (1988) Storm Water Management Model, Version 4, User's Manual EPA/600/3-88/001a (NTIS PB88-236641/AS), U.S EPA

Ji-Yong Choi, Chang-Min Shin (2002) Management of Nonpoint Pollution by Reducing Storm Runoff, Report RE-03, Korea Environment Institute, Seoul, Korea

Joint Task Force of the Water Environment Federation and American Society of Civil Engineers

(1998) Urban runoff quality management, Alexandria, USA

Ministry of Environment (2003) The Stormwater Design Manual by the Stormwater Manager Resource Center, Ministry of Environment, Seoul, Korea

P steel Company engineering & construction Co., Ltd (2003) A master plan of drainage system improvement at iron & steel making area in P steel Company, P steel Company engineering &

construction Co., Seoul, Korea

You-Sun Kang (2003) A Study on Model Applied in the Integrated Water Management in a Small Water System Master's thesis, Department of Environmental Engineering, Ewha Womans

University

Wisconsin Department of Natural Resources(1994) Industrial storm water pollution prevention planning, Wisconsin, USA.