Assessment of On-site sanitation system on local groundwater regime in an alluvial aquifer
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The present study is an attempt to study the impact of the On-site sanitation system on the groundwater sources in its vicinity. The study has been undertaken in the Agra city of Yamuna sub-basin. In this context, sampling sites (3 nos) namely Pandav Nagar, Ayodhya Kunj and Laxmi Nagar were selected for sampling. The groundwater samples were analyzed for major cations, anions and faecal coliform. Critical parameters namely chloride, nitrate and Faecal coliform were considered to assess the impact of the On-site sanitation systems. The analytical results shown that except for chloride, most of the samples exceeded the Bureau of Indian Standard limits for drinking water for all the other analyzed parameters, i.e., nitrate and faecal coliform in the first two sites. In Laxmi Nagar, except for faecal coliform, all the samples are below the BIS limits. In all the three sites, faecal coliform was found in majority of the samples. A comparison of present study indicates that the contamination of groundwater in alluvial setting is less as compared to hard rock where On-site sanitation systems have been implemented.
KeywordsOn-site sanitation Seasonal variation Groundwater Nitrate Faecal coliform
On a global scale, fresh water constitutes approximately 2.5% on earth and groundwater constitutes only 0.76% of fresh water. Hence, it is essential to protect the fresh groundwater as per the quality and quantity points of view. In the last decade, the growing population has increased the stress on groundwater resources due to which the quality has degraded due to anthropogenic as well as geogenic factors. The contamination of groundwater in many parts of India is caused by the disposal of domestic waste (Pujari et al. 2007, 2012; Jangam et al. 2015). The anthropogenic factors are, namely, the disposal of untreated industrial and municipal wastewater, application of fertilizers and pesticides in the agricultural fields, leakage from underground storage tanks, underground pipelines, and plumes generation from landfill site and septic tank effluents. The problem assumes more importance when proper safeguards are not in place during the disposal of waste. The groundwater pollution caused by On-site sanitation was a major concern in many urban and peri-urban areas when organized sewerage is lacking and where the drinking water requirements are met from groundwater sources. The contamination is likely to take place in the event of a pathway existing between a source, i.e., On-site sanitation system and a receptor, i.e., groundwater source. The growing population has led to adopt the On-site sanitation system as compared to conventional sewerage. The On-site sanitation system poses a significant adverse impact on the groundwater quality in the long run. It assumes more importance when the geological settings favor the migration of contaminants. The problem becomes alarming when the groundwater table is shallow. The groundwater quality studies were reported by numerous authors (NEERI 2005; Pujari et al. 2007, 2012; Lu et al. 2008; Jangam et al. 2015) pertaining to the impact of septic tanks. Pujari et al. (2007) found that the increased concentration of nitrate and bacteria in groundwater near On-site sanitation system and showing the impact on groundwater quality.
The geohydrological issues, i.e., water table, soil characteristics and separation between the On-site sanitation system and groundwater source are key parameters affecting groundwater contamination (Lawrence et al. 2001). Dzwairo et al. (2006) clarified through pit latrine studies at Zimbabwe that the groundwater quality parameters, mainly total coliforms, faecal coliforms and nitrate were affected by the pit latrine. The studies on microbial movement near On-site sanitation systems show that the increased concentration of total and faecal coliform in period of monsoon in saturated condition of sandy soils and less in clay soils (Banerjee 2011). Similar study carried out in India by Pujari et al. (2012), Jangam et al. (2015) indicated that the contamination level in alluvial terrain in Kolkata and Lucknow was negligible as compared to the hard rock terrain in Indore in India. The National Environmental Engineering Research Institute, Nagpur conducted study on impact of On-site sanitation on groundwater in selected cities in India and the study concludes that geological setting is one of the key parameters in groundwater contamination. The groundwater pollution due to On-site sanitation system relates primarily to unconfined and to semi-confined aquifers. If groundwater supplies are drawn from deep and confined aquifers, On-site sanitation does not pose a significant hazard (NEERI 2005).
Agra city is located at latitude N 27°10′ and Longitude E 78°03′ in western part of Uttar Pradesh and northern part of India (Fig. 1) covering an area of 188.4 km2. The city has a population of 1,567,709 as per the 2011 census (censusindia.gov.in). The maximum and minimum temperatures of Agra city in summer are 45 and 21.9 °C, respectively, whereas in winter, the maximum and minimum temperatures are 31.7 and 4.2 °C (agra.nic.in), respectively. The present area annual rainfall is 687.2 mm (GWYB 2014–2015) through the southwest monsoon.
Physiographically, the city is situated in the Indo-Gangetic plains (Yamuna sub-basin). It is mainly covered by quaternary sediments constituting an admixture of sand, silt, clay and canker. The aquifers are unconfined to semi-confined type. The city has partial sewerage coverage and On-site sanitation is the preferred mode in the unsewered areas and the city has limited sewer connection. Most of the areas have septic tanks.
The sampling has been undertaken by the grab sampling approach. As far as bacteriological parameters are concerned, they were collected in glass bottles of 300 mL. The bottles were thoroughly cleaned and sterilized before sampling. The bacteriological samples were carried to the laboratory in freezing condition (4 °C). Parameters viz. pH, EC and temperature, were measured at the site with the help of portable sensors (Eutech make). Suspended particles were filtered by filter paper (Whatman make: no. 4) before analysis. The physicochemical parameters were analyzed by the standard protocols (American Public Health Association (APHA) 1998). The NO3 was carried out with the help of UV–Visible spectrophotometer 118 (Make: Systronic). Membrane filter technique (APHA 1998) has been followed for bacteriological analysis. The processed sample is kept in incubator to maintain at 45.5 °C for 24 h. Colony formations are done by using 50 mm sample and the bacterial count is in colony forming unit (CFU/100 mL).
A questionnaire survey was undertaken to study the presence of any water-borne disease in the area and its relation vis-à-vis the On-site sanitation systems. The residents dependent on the groundwater source were asked about the prevalence of any water-borne disease like jaundice and cholera in the area.
Results and discussion
There are various factors upon which groundwater contamination depends. Broadly, the factors are local hydrogeological characteristics like depth to water table, porosity and permeability of underlying strata, confined and unconfined rock types. As far as the anthropogenic contamination, i.e., from On-site sanitation system is concerned, the parameters affected will be namely, chloride, nitrate and faecal coliforms (Pujari et al. 2007, 2012; Jangam et al. 2015). The rock composition will not affect parameters like chloride and nitrate. It is found that the quantity of nitrogen releases of 4 kg/year/person (Lawrence et al. 2001) and it is also reported that chloride 4 g/day is released per person through urine, faces, and sweat. Microbiological organisms are significant effect during their movements in the unsaturated zone (Lawrence et al. 2001). However, every attempt is made to figure out the sources of contamination based on the existing field conditions. Twenty-seven groundwater samples were collected at selected locations in pre-and post-monsoon seasons from Agra city. An attempt has been made to consider three samples as control sites for comparison. Samples namely, ASP8, ASP9 and ASP10 in Laxmi Nagar were collected as a control samples from locations away from On-site sanitation activity.
Pandav Nagar (SITE I)
Ayodhya Kunj (Site II)
Laxmi Nagar (Site III)
A systematic questionnaire survey was undertaken at the time of sampling and the people dependent on the sources were asked about the prevalence of water-borne disease. The localities, Laxmi Nagar and Pandav Nagar, have sparse density of houses and better amenities; hence, the respondents have so far not encountered chronic water diseases. The respondents complained of jaundice during the period (1996–2000) in Ayodhya Kunj locality. It is likely that the outbreak of jaundice may be linked to the presence of coliforms as well as the poor sewerage in Ayodhya Kunj as compared to Laxmi Nagar and Pandav Nagar where there is better sewerage. The overall sanitation in Pandav Nagar and Laxmi Nagar also looks better.
The sites at Agra are characterized by alluvial setting. It appears that the septic tanks have not able to contain the contamination by coliform. However, they do indicate significant concentration of nitrate and faecal coliform. The nitrate concentration exceeds the BIS permissible limit (45 mg/L) and hence the situation is alarming for the two localities, namely, Pandav Nagar and Ayodhya Kunj. It is observed that the densely populated locality of Ayodhya Kunj recorded high concentration of nitrate (range 29–220 mg/L) as compared to Pandav Nagar and Laxmi Nagar which are relatively less populated. The samples are contaminated by faecal coliform in both pre-monsoon and post-monsoon. As the soil type is mostly coarse sand, in which the movement of contaminants will be faster as compared to fine sand, the aquifer is affected more due to the coarse sand structure. The findings are contrary to those from other alluvial areas like Lucknow (Jangam et al. 2015) and Kolkata (Pujari et al. 2012). As per the BIS guidelines, faecal coliform should be absent to render the water potable. Hence, there is health risk due to presence of faecal coliform.
A systematic hydrogeological mapping of the aquifers in the study area should be undertaken before implementation of On-site sanitation system. If multiple aquifers are present, the groundwater from the deeper aquifer should be tapped for drinking as compared to the shallow aquifer. If off-site sanitation cannot be provided, best design for the On-site sanitation should be ensured.
Mandatory monitoring of faecal coliforms should be carried out monthly and critical parameter like nitrate should be carried out at least in pre-monsoon and post-monsoon season.
It is desired that the people drinking the faecal coliform contaminated sources should boil the water before it is used for drinking.
The authors express gratitude to CPHEEO–WHO for sponsoring the research study. The authors thank Director, CSIR-NEERI, P. R. Pujari (Project Leader) and Pawan Labhasetwar (Head of Division), Water Technology and Management Division, CSIR-NEERI, Nagpur, for their support and encouragement during entire period of the study.
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