Surface Water Quality and Risk Analysis in a Peri-urban Area, Thailand

J. Price1*, T. Chaosakul2, N. Surinkul2, J. Bowles2, S. Rattanakul2, N. Pradhan2, W. Simphan2, A. Ghimire2, K. Wilaingam2,L. M. Truong2, T.V. Nguyen2, T. Pussayanavin2, N. Proysurin2,

S. Singjan2, V. Longaphai2, S.N. Kalaimathy2, T. Koottatep2, K.N. Irvine1

1) Geography and Urban Planning and Center for Southeast Asia Environment and Sustainable Development, Buffalo State, State University of New York, USA

*(Email: jameieka14@yahoo.com)2) Environmental Engineering and Management, Asian Institute of Technology, Thailand

Abstract

The Rangsit Canal, Pathum Thani, Thailand, receives runoff and contaminant inputs from urban and agricultural activities. Water quality in a section of the canal was examined by comparing sample results with Thailand’s water quality standards, the approximate delta method to characterize system metabolism, and a microbial risk analysis to assess potential for waterborne infections. Dissolved oxygen and BOD levels did not meet Thailand’s Class 3 standards. Continuous, automated monitoring of dissolved oxygen revealed a pronounced diel trend driven by photosynthesis during the day and respiration at night. Compared to many water bodies, however, the primary production of the canal was low and can be classified as heterotrophic. Based on microbial risk analysis and considering infection risk standards, E. coli levels in the local sewer system (106 CFU/100 mL) and canal (104 CFU/100 mL) produced unacceptably high risk for activities that included swimming, vegetable farming, fishing, and sewer pump station operations. E. coli in piped water to an informal community on the canal was 0 CFU/100 mL in half the samples. The highest E. coli level (800 CFU/100 mL) associated with the piped water source came from a traditional (uncovered) water storage tank, which emphasizes the importance of appropriate water storage.

Keywords: dissolved oxygen, metabolism, BOD, E. coli, microbial risk analysis

1. Introduction

Rattanakosin Village, Rangsit Municipality, Thailand, is a small, peri-urban area that experiences frequent surface flooding due to monsoon rains, a limited amount of topographic relief, and an aging, low slope, combined sewer system. Furthermore, although on-site treatment is practiced, ultimately the village’s combined sewage is pumped directly to a local canal. In each of the past three years, our wastewater design class at Asian Institute of Technology (AIT) has undertaken a project to model the combined sewer system quantity and quality for the village and make design recommendations to reduce surface flooding and the impact of combined sewer overflows (CSOs) (e.g. Chaosakul et al., 2009). This year, as part of the class effort, water quality samples were collected in the sewer system, main receiving water body (Khlong Rangsitprayoonrasak or Rangsit Canal), and at the drinking water sources of an informal community along the canal to provide a preliminary assessment of the impact that the CSOs, direct sewage discharge, urban, and agricultural runoff may have on local water quality. In particular, a preliminary health risk assessment is presented using a microbial risk analysis approach and metabolism characteristics within the Rangsit Canal also are assessed using the approximate delta method (McBride and Chapra, 2005).

Rattanakosin Village is located in Pathum Thani Province, about 10 km south of the AIT campus and 7 km north of Don Mueang Airport (Figure 1). Land use in the village primarily is residential, although there are some light industry and commercial areas as well. The village is bounded on the south by the Rangsit Canal, which outlets to the Chao Phraya River. Historically, Pathum Thani was a rural, agriculturally-based province that grew in importance during the late 19th century with the construction of the Prem Prachakorn Canal (1869, and just west of the village). This canal provided a transportation connection between Ayutthaya and Bangkok and subsequently, the Tung Rangsit project (1890-1900) added 43 canals. One of the main east-west canals of the Tung Rangsit project was the Rangsit Canal (Figure 1) (Suwanarit, 2010) and in addition to the east-west canals, 17 north-south oriented canals, 20-30 km long, were constructed at intervals of approximately 2.5 km (Figure 1) together with a number of tertiary canals. The Rangsit Canal and larger north-south canals were used for both transportation and irrigation while the tertiary canals were used solely for irrigation (Ongsakul and Sajor, 2006; Suwanarit, 2010). Since the 1970’s, Pathum Thani has experienced a dramatic increase in population and industrial activity as well as a shift in agricultural production from mono-culture rice to a mix that includes orange plantations, orchards, and vegetable farms (Ongsakul and Sajor, 2006; Pradhan and Perera, 2006).

Concern has been expressed about declining water quality in the canals of the Tung Rangsit, particularly in those areas where housing and industries discharge directly to the canals (Ongsakul and Sajor, 2006; Pradhan and Perera, 2006). Patarasiriwong (2000) sampled water and sediment at six sites along Rangsit Canal once in the dry season and analyzed for pesticides, metals, and benthic organisms. It was concluded that the canal was not contaminated by organochlorine pesticides since most compounds were not detected in sediments and those detected were at low (ppb) levels. However, site 6 (furthest east, near Khlong 14) frequently had the lowest metals (Cd, Cu, Cr, Fe, Mn, Ni, Pb) levels in water and sediment, the highest dissolved oxygen (D.O.), and the greatest abundance of pollutant intolerant benthic organisms. Site 2, in the Rattanakosin Village area, had the highest Cd (0.65 mg/kg), Cr (9.52 mg/kg), Ni (36.12 mg/kg) and Pb (2.51 mg/kg) in sediments compared to all other sites, as well as the lowest D.O. and exhibited only the presence of Chironomidae as a benthic organism. Ongsakul and Sajor (2006) averaged data for main and secondary canals and reported that in 2000, Mn (1.25 mg/L), Pb (1.5 mg/L) and Cd (7.3 mg/L) exceeded Thailand’s Class 3 water quality standards (suitable for agricultural use). Furthermore, Ongsakul and Sajor (2006) reported that D.O. in these canals ranged between 1.1 and 2.0 mg/L and Biochemical Oxygen Demand (BOD) ranged between 4.0 and 6.0 mg/L in 2002.

2. Material and methods

Manual grab samples and spot measurements of D.O. and temperature (YSI Model 58 meter) and oxygen reduction potential (ORP)(Mettler Toledo Model SG2 meter) were collected between 6 June and 29 June, 2011 at three locations in the Rattanakosin sewer system (two locations at pump station 1) and at two sites in the Rangsit Canal (upstream and downstream of the CSO discharges to the canal from the village)(Figure 2). At pump station 1, samples were collected both of the sewage that remained in the system and in the pipe leading to the Rangsit Canal. When the pump station was not operating there was no sewage to sample in the pipe leading to the canal. The samples were placed on ice in the field and taken to AIT for analysis. E. coli was analyzed using the Coliscan Easygel system (Irvine et al., in press), BOD and COD were analyzed using Standard Methods (APHA, 1999). Water for informal

housing on the south side of Rangsit Canal is provided by pipe and samples were collected at six locations (five different homes) for E. coli analysis using Coliscan Easygel. A YSI 6920 datasonde was installed in the Rangsit Canal between 13 June and 29 June, 2011 and programmed to measure D.O., pH, conductivity, temperature, and turbidity at 15 minute time intervals. For security, the datasonde was chained and locked to a stilted house in the canal.

Figure 1: Location of Rattanakosin Village (star symbol) and canal system of Tung Rangsit.

3. Results and discussion

Early June was relatively wet (95.5 mm total rainfall on successive days, 1-7 June), but the remainder of the month to 28 June totaled 74.4 mm (Don Mueang airport gauge) and there was an extended dry period, 16 to 26 June. The early samples of the campaign, in particular, represent wet weather conditions. E. coli results are summarized in Figure 3, while BOD,

Figure 2: Rattanakosin Village and sample sites. The star symbol indicates the furthest upstream sewer sample site (Sewer Site 1), the large circles indicate the upstream (to the east) and downstream (to the west) sites in the Rangsit Canal, the square is the location of the YSI 6920, and PS is pump station (after Chaosakul et al., 2009).

Khlong 14

Khlong 1

Chao Phraya R.

Rangsit Canal

Available area Boeng

Yai

PS 2

PS 3

PS 1

Main road

Main road no.3

Main road

COD, D.O., and ORP results are summarized in Table 1. The YSI time series are shown in Figure 4, but for space considerations, turbidity and D.O. %saturation are not presented.

Sewer

Site 1

PS 1 In

system

PS1 Can

al

Canal

Up

Canal

Down

10000

100000

1000000

10000000

Geo

met

ric

Mea

n E.

col

i/10

0 m

L

Figure 3: E. coli levels (n=9 for Sewer Site 1, PS1 Insystem, Canal Up and Canal Down; n=3 for PS1 Canal). Canal Up and Down are the upstream and downstream sites on Rangsit Canal; PS1 Insystem means the sewage remaining in the system at pump station 1 and PS1 Canal is the sewage being pumped to the Rangsit Canal from pump station 1. Units for E. coli are CFU/100 mL.

E. coli sampled in the domestic, piped water at the informal housing was 0 CFU/100 mL for three of the six samples, while levels were 60, 200, and 800 CFU/100 mL in the other three samples. The highest level (800 CFU/100 mL) was determined for a sample taken from a traditional clay storage tank that was not covered, while the 60 CFU/100 mL result represented a sample collected immediately after going through the home’s filter box. Water in the pipe leading to the house had 0 CFU/100 mL E. coli.

Table 1: Mean and standard deviation (in bracket) of spot measurements (n=4 for COD, D.O., and ORP, except for PS1 Canal where only 1 sample was collected; n=3 for BOD, except for PS1 Canal where only 1 sample was collected)

Site BOD, mg/L COD, mg/L D.O., mg/L ORP, mVSewer Site 1PS1 InsystemPS1 CanalCanal UpCanal Down

28.4 (14.9)33.3 (11)

217.5 (2.1)6.7 (1.5)

169 (8.9)148 (17.7)

12462.9 (26.3)69.2 (39.9)

0.98 (0.4)0.82 (0.1)

1.221.18 (0.1)1.36 (0.4)

-185 (22.1)-231 (25.5)

-20180 (56.2)93 (61.3)

BOD levels in the sewage were relatively low compared to temperate climates, but are consistent with other data for Thailand (Noophan et al., 2009; Tsuzuki et al., 2009). The lower BOD levels result from using on-site leaching septic tanks, even in urban areas; traditional use of bidet rather than toilet paper; and high degradation rates in tropical climates (Tsuzuki et al., 2009). BOD levels for the Rangsit Canal are consistent, but higher than the values from Ongsakul and Sajor (2006). This may reflect Ongsakul and Sajor’s (2006) reporting of an average for all canals of the area and generally it has been shown this section of the Rangsit Canal is more polluted, although it also may partially reflect an increasing pollution load in the past 10 years. All samples collected in the Rangsit Canal in this study exceeded Thailand’s Class 3 (agricultural use) BOD Water Quality Standard of 2.0 mg/L.

The D.O. levels in the Rangsit Canal were low and the mean D.O. level recorded by the YSI 6920 for every day between 13 June and 28 June was less than Thailand’s Class 3 Water

Quality Standard of 4.0 mg/L. Figure 4 also shows a pronounced diel cycle for D.O. and temperature, with peak values normally occurring in the afternoons.

11/6/2011 0:00

16/6/2011 0:00

21/6/2011 0:00

26/6/2011 0:00

1/7/2011 0:00

27

28

29

30

31

32

Time, 15 minute steps

Tem

pera

ture

, C

0.3

0.4

0.5

0.6

0.7

0.8

Time, 15 minute steps

Sp

. C

on

du

cti

vit

y,

mS

/c

m

11/6/2011 0:00

16/6/2011 0:00

21/6/2011 0:00

26/6/2011 0:00

1/7/2011 0:00

0123456

Time, 15 minute steps

D.O

., m

g/L

11/6/2011 0:00

16/6/2011 0:00

21/6/2011 0:00

26/6/2011 0:00

1/7/2011 0:00

6

6.5

7

7.5

8

Time, 15 minute steps

pH

Figure 4: YSI 6920 time series data for Rangsit Canal.

As originally outlined by Odum (1956), the rate of change of D.O. in an aquatic system is primarily a function of gross primary production, the rate of respiration, and the rate of oxygen uptake by diffusion and this can be expressed as (after McBride and Chapra, 2005):

dDdt

+ka D=R−P(t) (1)

Where D is the dissolved oxygen deficit, mg/L, calculated as C sat – C, with C being the D.O. concentration (mg/L) and Cs its saturated value; t is time (day); ka is the first –order stream reaeration coefficient (per day); R is the respiration rate (mgO/L/day); and P(t) is the time-varying plant primary production (photosynthesis) rate (mgO/L/day).

System metabolism can be characterized by examining values for P(t), R, and ka, calculated in this study using the approximate delta method. This method was presented in detail by McBride and Chapra (2005) and we employed a spreadsheet tool developed by Pelletier (2007) for the calculations. We found the half-area centroid option as most suitable in the spreadsheet tool. Values for P(t), R, and ka are presented in Table 2, together with data from other rivers (and one lake) throughout the world. The diel D.O. trend exhibited in the Rangsit Canal (Figure 4) is driven by dominance of photosynthesis during the day and respiration at night, although compared to a number of rivers (some urban-impacted, some rural), the primary production of the canal is low, while the respiration rate is high (Table 2). The reaeration coefficient is within the general range reported in the literature. Odum (1956) originally proposed the P/R ratio (photosynthesis:respiration) to classify waterbodies as being autotrophic (P/R>1) or heterotrophic (P/R<1) and this ratio has been used in a number of studies (e.g. Ansa-Asare et al., 1999; Williams et al., 2000; Wang et al., 2003). The P/R ratio

for the Rangsit Canal site is <1, meaning it is dominated by heterotrophs. This result may be somewhat surprising, given the sewage input to the canal and the assumption that there would be a concurrent increase in blue-green algae growth, but Odum (1956) showed that respiratory metabolism can far exceed primary production up to 32 km downstream of a major sewage outfall, as the sewage decomposes. After a threshold point, however, Odum (1956) showed that primary production then can rise rapidly due to increased organic growth.

Table 2: Summary of metabolism parameters, mean (with standard deviation in bracket, when reported)

Site ka, per day P(t), mgO/L/day R, mgO/L/day P/R ratio

Rangsit CanalThames R., U.K.1

Pang R., U.K.1

Kennet R., U.K.1

Grand R., U.S.2

Santa Margarita R. #1, U.S.2

Santa Margarita R. #2, U.S.2

Waithou Str., N. Zealand2

Mangaoronga Str., N. Zealand2

Weija Lake, Ghana3

5.7 (8.4)5.7 (2.4)11.6 (7.7)5.0 (9.0)

5.511.515.46.08.53.6

5.0 (2.9)4.9 (2.1)9.6 (5.3)29 (7.4)

1612

11.70.613.332.1

46.2 (63.5)11.6 (6.0)17.9 (15.7)32.1 (31.0)

17.39

7.95.7277.5

0.200.420.540.900.921.31.50.10.494.3

1Williams et al., 2000; 2Wang et al., 2003; 3Ansa-Asare et al., 19993

For health risk assessment, concentrations of E. coli from the sewer system (106 CFU/100 mL) through the canal network (104 CFU/100 mL) were used (Figure 3). Activities related to health risk such as fishing, vegetable farming, and swimming in the canal are practiced in this area. In this study, risk assessment focused on four scenarios. Scenario A is ingestion by children from swallowing water while swimming in the canal. It is assumed that the volume of water swallowed is approximately 100 mL per single exposure for 52 times/year. Scenario B is the accidental ingestion by a farmer during vegetable farming actvities or fishing in the canal which is approximately 5 mL per single exposure for 300 days in year. Scenario C occurs during the consumption of 100 g of raw vegetables, equivalent to 10 mL of canal water, for 52 times/year. Scenario D is the accidental ingestion by a worker at the pumping station with the exposure of 0.5 mL for 52 times/year. Results of risk of infection for the different scenarios are shown in Table 3.

Table 3: Microbial risk analysis resultsExposure scenario PI a PD b

A 5.0E-02 1.3E-02B 1.5E-03 3.8E-04C 5.2E-05 1.3E-05D 2.6E-04 6.5E-05

a) Risk of infection, Beta-Poisson model, PI=1-[1+D/N50 (21/α – 1)]-α (Haas et al., 1999) α = 0.1778, N50=8.60x107 for E. coli (Haas and Eisenberg, 2001); b) Annual risk of diarrhea disease, PD = PI x PD/I, reported as per person per year (pppy) (Howard et. al., 2006); c) Risk of illness (PD/I) per infection by diarrhegenic E. coli = 0.25 (Howard et. al., 2006).

The acceptable health risk determined by the USEPA (1994) is 1.0E-4 and comparing this guideline to the annual risk of infection results in Table 3, really only the consumption of raw vegetables (Scenario C) has a consistently lower health risk than the guideline. The other

activities of swimming, vegetable farming and fishing in the canal, and working at the pump station are activities which are not safe.

4. Conclusions

The section of the Rangsit Canal that we studied has water quality problems, based on a comparison with Thailand’s standards for D.O. and BOD. The approximate delta method was a reasonable approach to determine that this canal section is a relatively low productivity, heterotrophic water body. Results of the microbial risk analysis showed unacceptable risk for a number of activities (swimming, fishing, vegetable farming, pump station operation). The results could be used by local authorities to implement barriers/intervention for health risk reduction such as education campaigns about washing or bathing after exposures or using disinfection gel. However, wastewater treatment is needed before discharging wastewater into the canal as a long-term planning solution to prevent the pollution entering the canal. Based on limited sampling, the piped water to the informal housing on the canal was good, although poor handling and storage practices could negatively affect the quality.

5. Acknowledgements

Thanks to the Katheryn Whittemore Fund, Department of Geography/Planning; Office of Graduate Studies; and School of Natural and Social Sciences, Buffalo State for funding.

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