Article

Implications of Fecal Bacteria Input from Latrine-Polluted Ponds for Wells in Sandy Aquifers

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Abstract

Ponds receiving latrine effluents may serve as sources of fecal contamination to shallow aquifers tapped by millions of tube-wells in Bangladesh. To test this hypothesis, transects of monitoring wells radiating away from four ponds were installed in a shallow sandy aquifer underlying a densely populated village and monitored for 14 months. Two of the ponds extended to medium sand. Another pond was sited within silty sand and the last in silt. The fecal indicator bacterium E. coli was rarely detected along the transects during the dry season and was only detected near the ponds extending to medium sand up to 7 m away during the monsoon. A log-linear decline in E. coli and Bacteroidales concentrations with distance along the transects in the early monsoon indicates that ponds excavated in medium sand were the likely source of contamination. Spatial removal rates ranged from 0.5 to 1.3 log(10)/m. After the ponds were artificially filled with groundwater to simulate the impact of a rain storm, E. coli levels increased near a pond recently excavated in medium sand, but no others. These observations show that adjacent sediment grain-size and how recently a pond was excavated influence the how much fecal contamination ponds receiving latrine effluents contribute to neighboring groundwater.

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... mechanisms for tubewell contamination with fecal pathogens include infiltration into the groundwater aquifers from nearby latrines, septic tanks and ponds, short-circuiting of contaminated surface water into the wells through leaky seals of various tubewell components or harboring of bacteria in contaminated hand pumps (3,6,7). Tubewell water also becomes contaminated during collection, handling and storage in households. ...
... Surveillance updates R ecent studies in Bangladesh have demonstrated that up to 65% of tubewell water is contaminated by fecal pathogens; however, the level of contamination is low (1)(2)(3)(4)(5). Possible mechanisms for tubewell contamination with fecal pathogens include infiltration into the groundwater aquifers from nearby latrines, septic tanks and ponds, short-circuiting of contaminated surface water into the wells through leaky seals of various tubewell components or harboring of bacteria in contaminated hand pumps (3,6,7). ...
... Surveillance updates R ecent studies in Bangladesh have demonstrated that up to 65% of tubewell water is contaminated by fecal pathogens; however, the level of contamination is low (1)(2)(3)(4)(5). Possible mechanisms for tubewell contamination with fecal pathogens include infiltration into the groundwater aquifers from nearby latrines, septic tanks and ponds, short-circuiting of contaminated surface water into the wells through leaky seals of various tubewell components or harboring of bacteria in contaminated hand pumps (3,6,7). Tubewell water also becomes contaminated during collection, handling and storage in households. ...
Technical Report
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W e conducted a randomized controlled trial to assess whether improved microbial quality of tubewell drinking water by chlorination and safe storage would reduce diarrhoea among children aged <2 years in rural Bangladesh. We randomly assigned 1800 households into one of three arms: chlorine plus safe storage, safe storage only and control (use of neither safe storage nor chlorine). In the chlorine plus safe storage arm, 9% of stored water samples had Escherichia coli concentrations exceeding 10 colony forming units/100 mL, compared to 21% in the safe storage arm and 61% in the control arm (p <0.05). Compared to controls, diarrhoea prevalence in children aged <2 years was 36% lower in the chlorine plus safe storage arm and 31% lower in the safe storage only arm (p <0.05). This study suggests that safe storage of drinking water can substantially reduce illness among children in rural Bangladesh.
... Theoretical advances and a considerable number of laboratory and field experiments conducted in recent years have contributed to an improved understanding of pore-scale microbial removal processes 2,13-15 but some significant puzzles remain 16,17 . For example, microbial removal efficiencies across distance (D -1 ) observed in field experiments [16][17][18][19][20][21][22][23][24][25] are usually lower than measured with columns in the laboratory 2,18,26,27 . This has tentatively been attributed to preferential flow paths in the field that are not reproduced within sediment columns 28 . ...
... In the present study, we seek to understand the reason for the apparently more restricted movement of bacteria in column experiments relative to the field 29 . Kinetic interaction parameters modeled on laboratory column experiments packed with sand from the base of a freshly excavated pond in Bangladesh are compared with those obtained from modeling a previously documented breakthrough of E. coli through the bottom of the pond following an induced rise in pond water level 25 . ...
... Previous studies reported on widespread fecal contamination in private tubewells in sandy villages 6,7 and identified ponds dug recently into the unconfined aquifer as point sources of fecal contamination during the early monsoon 25 . The field component of the present study was previously reported and carried out in the village of Char Para in Araihazar upazilla where the local sandy aquifer extends to the surface and is therefore vulnerable to microbial contamination 6,7,25,32 . ...
... However, recent studies have shown that groundwater is often fecally contaminated and latrines that drain into ponds that are leaching into the water table could be a source of fecal contamination of shallow wells. [15][16][17][18] This is concerning because the number of diarrheal disease cases is still high. 13 Bangladesh is one of the countries that is most vulnerable to climate change and climate variablity, 19 which has been linked to the increase in waterborne disease. ...
... 15 The hydrogeological features of shallow aquifer in these areas have also been described in literature. 17,26 Satellite data and image processing USGS land cover classification system 27 was adopted to classify the land cover in both areas. Based on the characteristics of land cover in these areas, land cover was classified into 6 types, which include agriculture (e.g. ...
... In the early wet season, when the water table is low, pond water can rapidly drain into the aquifer. 17 Second, during heavy rain, runoff with fecal bacteria may directly contaminate tubewells if their wellhead is not well protected. 17 In addition, rainwater carrying bacteria may directly enter tubewells. ...
Article
Climate extremes in conjunction with some land use practices are expected to have large impacts on water quality. However the impacts of land use and climate change on fecal contamination of groundwater has not been well characterized. This work quantifies the influences of extreme weather events and land use practices on E. coli presence and concentration in groundwater from 125 shallow wells, a dominant drinking water resource in rural Bangladesh, monitored over a 17-month period. The results showed that E. coli presence was significantly associated with the number of heavy rain days, developed land and areas with more surface water. These variables also had significant impacts on E. coli concentration, with risk ratios of 1.52 (95% CI = 1.08, 1.81), 1.07 (95% CI: 1.05, 1.09), and 1.02 (95% CI = 1.01, 1.03), respectively. Significant synergistic effects on E.coli presence and concentration were observed when land use and weather variables were combined. The findings suggest that climate extremes and land use practices, particularly urbanization, might promote fecal contamination of shallow well water, thus increasing the risk of diarrheal diseases.
... Therefore, the optimal T is equivalent, for example, to a deep aquifer system thickness of 200 m and horizontal hydraulic conductivity (K h ) of 60 m/day. The values for K h in the deep aquifer agrees with past modeled (43 m/day in Michael and Voss, 2008) and measured values in shallow Bangladesh aquifers in Araihazar (22 m/day in Nakaya et al., 2011; 35 m/day in Knappett et al., 2012). ...
... m/yr, respectively. Assuming a porosity of 0.4 (Knappett et al., 2012) these correspond to average linear groundwater velocities of 0.54(±0.14) and 0.56(±0.14) ...
... Vertical hydraulic conductivity can be used to calculate hydraulic anisotropy (K h /K v ) across the study area. Measured horizontal hydraulic conductivities (K h ) in sands in Araihazar and surrounding regions typically range from 10 to 40 m/day (Ahmed, 1994;Ravenscroft et al., 2005;Radloff, 2010;Nakaya et al., 2011;Knappett et al., 2012). Combining the upper and lower bounds for both K v (2.2 ± 0.4 Â 10 À2 ) and K h , we calculate a range of hydraulic anisotropy from 335 to 2579. ...
... Therefore, the optimal T is equivalent, for example, to a deep aquifer system thickness of 200 m and horizontal hydraulic conductivity (K h ) of 60 m/day. The values for K h in the deep aquifer agrees with past modeled (43 m/day in Michael and Voss, 2008) and measured values in shallow Bangladesh aquifers in Araihazar (22 m/day in Nakaya et al., 2011; 35 m/day in Knappett et al., 2012). ...
... m/yr, respectively. Assuming a porosity of 0.4 (Knappett et al., 2012) these correspond to average linear groundwater velocities of 0.54(±0.14) and 0.56(±0.14) ...
... Vertical hydraulic conductivity can be used to calculate hydraulic anisotropy (K h /K v ) across the study area. Measured horizontal hydraulic conductivities (K h ) in sands in Araihazar and surrounding regions typically range from 10 to 40 m/day (Ahmed, 1994;Ravenscroft et al., 2005;Radloff, 2010;Nakaya et al., 2011;Knappett et al., 2012). Combining the upper and lower bounds for both K v (2.2 ± 0.4 Â 10 À2 ) and K h , we calculate a range of hydraulic anisotropy from 335 to 2579. ...
... We performed a cluster-randomized trial building upon the WASH Benefits Bangladesh study (22,21), which was conducted in Gazipur, Mymensingh, Tangail and Kishoreganj districts of central Bangladesh. These areas were selected because they had low groundwater arsenic and iron (to avoid interference with chlorine water treatment) and no other WSH or nutrition programs. ...
... These areas were selected because they had low groundwater arsenic and iron (to avoid interference with chlorine water treatment) and no other WSH or nutrition programs. WASH Benefits randomly assigned clusters to: 1) drinking water treatment and safe storage, 2) sanitation, 3) handwashing, 4) combined water + sanitation + handwashing (WSH) 5) nutrition, 6) combined nutrition + WSH, and 7) control (no intervention) (22). WASH Benefits investigators randomized treatment within geographic blocks containing adjacent clusters. ...
... Since WASH Benefits eligibility depended on pregnancy timing, we expected trial participants and adjacent neighbors to be equivalent on average except for their proximity to the WSH intervention, allowing us to make inferences about spillover effects by relying only on the cluster randomization. Our primary analysis estimated unadjusted prevalence ratios and differences for binary outcomes (22) and unadjusted fecal egg count reduction ratios (1-ratio of mean intensity in intervention vs. control arm neighbors) for fecal egg counts. Our secondary analysis adjusted for covariates with bivariate associations with each outcome (likelihood ratio test p-value<0.2) ...
Article
Full-text available
Water, sanitation, and handwashing interventions may confer spillover effects on neighbors of intervention recipients by interrupting pathogen transmission. We measured geographically local spillovers in WASH Benefits, a cluster-randomized trial in rural Bangladesh, by comparing outcomes among neighbors of intervention vs. control participants. WASH Benefits randomly allocated geographically-defined clusters to a compound-level intervention (chlorinated drinking water, upgraded sanitation, and handwashing promotion) or control. From January to August 2015, in 180 clusters, we enrolled 1,799 neighboring children age-matched to trial participants that would have been eligible for WASH Benefits had they been conceived slightly earlier or later. After 28 months of intervention, we quantified fecal indicator bacteria in toy rinse and drinking water samples, measured soil-transmitted helminth infections, and recorded caregiver-reported diarrhea and respiratory illness. Neighbors' characteristics were balanced across arms. The prevalence of detectable E. coli in tubewell samples was lower for neighbors of intervention vs. control trial participants (prevalence ratio = 0.83; 0.73, 0.95). There was no difference in fecal indicator bacteria prevalence between arms for other environmental samples. Prevalence was similar in neighbors of intervention vs. control participants for soil-transmitted helminth infection, diarrhea, and respiratory illness. A compound-level water, sanitation, and handwashing intervention reduced neighbors' tubewell water contamination but did not impact neighboring children's health.
... Tubewell Water Quality and Diarrheal Disease in Bangladesh 301 Latrine ponds are possible secondary point sources to the aquifer because they collect human waste from surrounding latrines (Knappett et al. 2011), especially during heavy rainfall in the early monsoon, when rapid overland flow washes latrine waste into depressions (Knappett et al. 2012a). During the late monsoon, latrine ponds overflow, spreading fecal matter across the surface. ...
... Relationships varied by distance, and unsanitary latrines were more correlated with tubewell fecal contamination than sanitary latrines. This supports our hypothesis that surface contamination influences tubewell water quality via indirect pathways such as infiltration from latrine ponds (Knappett et al. 2012a) or the lateral transport to and leakage along unsealed annuli (Knappett et al. 2012b). ...
... The stronger and yet further distance correlation between unsanitary latrines and E. coli contamination in tubewells in the late monsoon compared with the early monsoon suggests that transport mechanisms vary by season. During the early monsoon, transport from spatially discrete sources such as latrine ponds (Knappett et al. 2011) would be limited to subsurface transport and unlikely to reach beyond 20 m (Knappett et al. 2012a). Further, surface spreading of fecal contamination from unsanitary latrines to reach unsealed tubewell annuli would be localized at the bari scale (20-40 m). ...
Article
Full-text available
Diarrheal diseases are endemic in Bangladesh, where sanitation is poor, and untreated drinking water extracted from shallow (Escherichia coli concentrations for 100 wells, monthly diarrheal events for all children under five, and a detailed water and sanitation infrastructure database created through a submeter accuracy Global Positioning System survey. We developed sanitation metrics to measure the relationship between tubewell water fecal contamination and estimates of human fecal loadings at varying scales. The relationship between childhood diarrhea and E. coli in drinking water was measured for households that obtained drinking water from survey wells. Results show that tubewells surrounded by unsanitary latrines, latrine-polluted ponds, and higher population densities were more frequently contaminated with fecal coliforms. The analysis also showed that poor sanitation infrastructure might affect childhood diarrheal disease via tubewell contamination. Our findings shed light on the importance of integrating population and environment data to identify circumstances in which shallow well water quality is compromised and children are put at risk of contracting diarrheal diseases. Sanitation interventions should highlight the spatial separation of latrines and drinking water wells to limit contamination.
... Hoque, 1998;Luby et al., 2008;Ercumen et al., 2017;Misati et al., 2017). A possible explanation for this poor correlation is that the contents of the standard WHO sanitary inspection are necessary but not sufficient because it excludes factors such as well construction, the survival and growth of bacteria inside pipes and pumps, and the use of dirty priming water (Ferguson et al., 2011;Hoque, 1998;Knappett et al., 2012a). ...
... Although there is some indication of greater near-field contamination in the monsoon, we find no correlation between contamination events and 3-day or 7-day antecedent rainfall (SI-S4). Parr and Caldwell (1933), Hoque (1998), Knappett et al. (2012a) and Ferguson et al. (2011) draw attention to the role of the borehole -well -pump system in contaminating drinking water (Table 3) including: (i) dirty priming water; (ii) leaking casing joints; (iii) cement grouting of the borehole annulus reducing contamination of shallow wells; and (iv) elastomeric components of hand-pumps acting as bacterial reservoirs. The high frequencies of faecal contamination in the pilot study tubewells SI-1) and piezometers compared to piezometers in this study (sampled with a peristaltic pump) support the conclusion that the in-situ microbiological quality of groundwater is much superior to that of well water. ...
Article
Faecal contamination of groundwater from pit latrines is widely perceived as a major threat to the safety of drinking water for several billion people in rural and peri-urban areas worldwide. On the floodplains of the Ganges-Brahmaputra-Meghna delta in Bangladesh, we constructed latrines and monitored piezometer nests monthly for two years. We detected faecal coliforms (FC) in 3.3–23.3% of samples at four sites. We differentiate a near-field, characterised by high concentrations and frequent, persistent and contiguous contamination in all directions, and a far-field characterised by rare, impersistent, discontinuous low-level detections in variable directions. Far-field FC concentrations at four sites exceeded 0 and 10 cfu/100 ml in 2.4–9.6% and 0.2–2.3% of sampling events respectively. The lesser contamination of in-situ groundwater compared to water at the point-of-collection from domestic wells, which itself is less contaminated than at the point-of-consumption, demonstrates the importance of recontamination in the well-pump system. We present a conceptual model comprising four sub-pathways: the latrine-aquifer interface (near-field); groundwater flowing from latrine to well (far-field); the well-pump system; and post-collection handling and storage. Applying a hypothetical dose-response model suggests that 1–2% of the diarrhoeal disease burden from drinking water is derived from the aquifer, 29% from the well-pump system, and 70% from post-collection handling. The important implications are (i) that leakage from pit latrines is a minor contributor to faecal contamination of drinking water in alluvial-deltaic terrains; (ii) fears of increased groundwater pollution should not constrain expanding latrine coverage, and (iii) that more attention should be given to reducing contamination around the well-head.
... [4] Attachment rates for bacteria have been inferred under various conditions from aquifer-scale forced gradient and natural gradient tracer tests [Harvey et al., 1989;Bales et al., 1997;Knappett et al., 2012] or centimeter-scale column experiments [Harvey et al., 1993;Litton and Olson, 1993;Fitzpatrick and Spielman, 1973] using stained bacteria or latex microspheres with size and surface properties that are similar to bacteria. Recent reviews have focused on the apparent discrepancy between rates of bacterial transport measured in laboratory columns versus field transport experiments, generally manifested as an apparent decrease in measured attachment rates with increasing scale of the experiment [Foppen and Schijven, 2006;Dong et al., 2006;Pang et al., 2008;Scheibe et al., 2011]. ...
... [12] Artificial groundwater (AGW) was made at ionic strengths of 3.5 and 20 mM with KCl and was designed to encompass the range of ionic strength observed in ponds contaminated with fecal bacteria, which are believed to be a source of aquifer contamination [Knappett et al., 2012], at the field site in Bangladesh where the cores were collected. Specifically, an ionic strength of 3.5 mM is approximately representative of pond conditions during the monsoon season, whereas higher ionic strengths of approximately 20 mM are observed during the dry season [van Geen et al., 2011]. ...
... Hoque, 1998;Luby et al., 2008;Ercumen et al., 2017;Misati et al., 2017). A possible explanation for this poor correlation is that the contents of the standard WHO sanitary inspection are necessary but not sufficient because it excludes factors such as well construction, the survival and growth of bacteria inside pipes and pumps, and the use of dirty priming water (Ferguson et al., 2011;Hoque, 1998;Knappett et al., 2012a). ...
... Although there is some indication of greater near-field contamination in the monsoon, we find no correlation between contamination events and 3-day or 7-day antecedent rainfall (SI-S4). Parr and Caldwell (1933), Hoque (1998), Knappett et al. (2012a) and Ferguson et al. (2011) draw attention to the role of the borehole -well -pump system in contaminating drinking water (Table 3) including: (i) dirty priming water; (ii) leaking casing joints; (iii) cement grouting of the borehole annulus reducing contamination of shallow wells; and (iv) elastomeric components of hand-pumps acting as bacterial reservoirs. The high frequencies of faecal contamination in the pilot study tubewells SI-1) and piezometers compared to piezometers in this study (sampled with a peristaltic pump) support the conclusion that the in-situ microbiological quality of groundwater is much superior to that of well water. ...
Article
Full-text available
Faecal contamination of groundwater from pit latrines is widely perceived as a major threat to the safety of drinking water for several billion people in rural and peri-urban areas worldwide. On the floodplains of the Ganges-Brahmaputra-Meghna delta in Bangladesh, we constructed latrines and monitored piezometer nests monthly for two years. We detected faecal coliforms (FC) in 3.3-23.3% of samples at four sites. We differentiate a near-field, characterised by high concentrations and frequent, persistent and contiguous contamination in all directions, and a far-field characterised by rare, impersistent, discontinuous low-level detections in variable directions. Far-field FC concentrations at four sites exceeded 0 and 10 cfu/100 ml in 2.4-9.6% and 0.2-2.3% of sampling events respectively. The lesser contamination of in-situ groundwater compared to water at the point-of-collection from domestic wells, which itself is less contaminated than at the point-of-consumption, demonstrates the importance of recontamination in the well-pump system. We present a conceptual model comprising four sub-pathways: the latrine-aquifer interface (near-field); groundwater flowing from latrine to well (far-field); the well-pump system; and post-collection handling and storage. Applying a hypothetical dose-response model suggests that 1-2% of the diarrhoeal disease burden from drinking water is derived from the aquifer, 29% from the well-pump system, and 70% from post-collection handling. The important implications are (i) that leakage from pit latrines is a minor contributor to faecal contamination of drinking water in alluvial-deltaic terrains; (ii) fears of increased groundwater pollution should not constrain expanding latrine coverage, and (iii) that more attention should be given to reducing contamination around the well-head.
... Therefore, contamination varied according to the seasons as well as the lateral and vertical distances of the monitoring wells. Previous study [19] also supports more contamination of E. coli during the wet season (61 %) than the dry season (9 %) in shallow wells. Infiltration of faecal contamination into the shallow aquifer is most likely during the early monsoon under favourable hydraulic gradient [19] and shallow water table. ...
... Previous study [19] also supports more contamination of E. coli during the wet season (61 %) than the dry season (9 %) in shallow wells. Infiltration of faecal contamination into the shallow aquifer is most likely during the early monsoon under favourable hydraulic gradient [19] and shallow water table. ...
Article
Full-text available
Background Groundwater drawn from shallow tubewells in Bangladesh is often polluted by nearby pit latrines, which are commonly used toilets in rural and sub-urban areas of the country. Methods To determine the minimum safe distance of a tubewell from a pit latrine in different hydrogeological conditions of Bangladesh, 20 monitoring wells were installed at three study sites (Manda, Mohanpur and Bagmara) with the vertical and horizontal distances ranging from 18–47 to 2–15 m, respectively. Water samples were collected three times in three seasons and tested for faecal coliforms (FC) and faecal streptococci (FS) as indicators of contamination. Soil samples were analysed for texture, bulk density and hydraulic conductivity following standard procedures. Sediment samples were collected to prepare lithological logs. ResultsWhen the shallow aquifers at one of the three sites (Mohanpur) were overlained by 18–23-m-thick aquitards, the groundwater of the monitoring wells was found contaminated with a lateral and vertical distances of 2 and 31 m, respectively. However, where the aquitard was only 9 m thick, contamination was found up to lateral and vertical distances of 4.5 and 40.5 m, respectively. The soil textures of all the sites were mainly composed of loam and sandy loam. The hydraulic conductivities in the first aquifer at Manda, Mohanpur and Bagmara were 5.2–7.3, 8.2 and 1.4–15.7 m/h, respectively. Conclusions The results showed that the safe distance from the tubewell to the pit latrine varied from site to site depending on the horizontal and vertical distances of the tubewell as well as hydrogeological conditions of a particular area.
... 5 Latrines in southern coastal Bangladesh are often installed in a way that untreated effluent discharges directly into unconsolidated shallow groundwater. 6,7 Flooding due to heavy rainfall, tidal surges, or cyclones increases the threat of surface and groundwater contamination from traditional pit latrines. 8,9 Slow or intermittent sand filters have been used for centuries to treat wastewater from sewer systems and septic tanks. ...
... While leaching from the pit latrine is an important source, other potential nonleaching sources of groundwater fecal contamination are animal feces and connection with polluted ponds. 7 Animal feces contributes to the fecal contamination of household's soil in Bangladesh, 24 which can ultimately contaminate the shallow groundwater. The effect of sand barrier may be masked if the nonleaching related sources of fecal contamination of groundwater are significant. ...
Article
Full-text available
We evaluated the effectiveness of a sand barrier around latrine pits in reducing fecal indicator bacteria (FIB) leaching into shallow groundwater. We constructed 68 new off-set single pit pour flush latrines in Galachipa sub-district of coastal Bangladesh. We randomly assigned 34 latrines to include a 50-cm thick sand barrier under and around the pit and 34 received no sand barrier. Four monitoring wells were constructed around each pit to collect water samples at baseline and subsequent nine follow-up visits over 24 months. Samples were tested using the IDEXX Colilert method to enumerate E. coli and thermotolerant coliforms most probable number (MPN). We determined the difference in mean log10MPN FIB counts/100ml in monitoring well samples between latrines with and without a sand barrier using multilevel linear models and reported cluster robust standard error. The sand barrier latrine monitoring well samples had 0.38 mean log10MPN fewer E. coli (95% CI: 0.16, 0.59; p = 0.001) and 0.38 mean log10MPN fewer thermotolerant coliforms (95% CI: 0.14, 0.62; p = 0.002), compared to latrines without sand barriers, a reduction of 27% E. coli and 24% thermotolerant coliforms mean counts. A sand barrier can modestly reduce the risk presented by pit leaching.
... 5 Latrines in southern coastal Bangladesh are often installed in a way that untreated effluent discharges directly into unconsolidated shallow groundwater. 6,7 Flooding due to heavy rainfall, tidal surges, or cyclones increases the threat of surface and groundwater contamination from traditional pit latrines. 8,9 Slow or intermittent sand filters have been used for centuries to treat wastewater from sewer systems and septic tanks. ...
... While leaching from the pit latrine is an important source, other potential nonleaching sources of groundwater fecal contamination are animal feces and connection with polluted ponds. 7 Animal feces contributes to the fecal contamination of household's soil in Bangladesh, 24 which can ultimately contaminate the shallow groundwater. The effect of sand barrier may be masked if the nonleaching related sources of fecal contamination of groundwater are significant. ...
Article
We evaluated the effectiveness of a sand barrier around latrine pits in reducing fecal indicator bacteria (FIB) leaching into shallow groundwater. We constructed 68 new offset single pit pour flush latrines in the Galachipa subdistrict of coastal Bangladesh. We randomly assigned 34 latrines to include a 50 cm thick sand barrier under and around the pit and 34 received no sand barrier. Four monitoring wells were constructed around each pit to collect water samples at baseline and subsequent nine follow-up visits over 24 months. Samples were tested using the IDEXX Colilert method to enumerate E. coli and thermotolerant coliforms most probable number (MPN). We determined the difference in mean log10MPN FIB counts/100 mL in monitoring well samples between latrines with and without a sand barrier using multilevel linear models and reported cluster robust standard error. The sand barrier latrine monitoring well samples had 0.38 mean log10MPN fewer E. coli (95% CI: 0.16, 0.59; p = 0.001) and 0.38 mean log10MPN fewer thermotolerant coliforms (95% CI: 0.14, 0.62; p = 0.002), compared to latrines without sand barriers, a reduction of 27% E. coli and 24% thermotolerant coliforms mean counts. A sand barrier can modestly reduce the risk presented by pit leaching.
... Ambient (pond) water quality has been shown to affect groundwater quality. 40 Source water quality, in turn, is a known determinant of stored water quality. 41 A link between contamination of stored water and hands has also been demonstrated. ...
... Indeed, ponds with a latrine within 10 m and ponds receiving latrine effluent had higher E. coli levels in our study, consistent with previous evidence from rural Bangladesh. 40,45 Chickens presented the most prevalent domestic animal exposure in our study. Roughly 90% of compounds had chickens, followed by cows (69%) and goats/sheep (39%). ...
Article
Full-text available
Fecal-oral pathogens are transmitted through complex, environmentally mediated pathways. Sanitation interventions that isolate human feces from the environment may reduce transmission but have shown limited impact on environmental contamination. We conducted a study in rural Bangladesh to (1) quantify domestic fecal contamination in settings with high on-site sanitation coverage; (2) determine how domestic animals affect fecal contamination; and (3) assess how each environmental pathway affects others. We collected water, hand rinse, food, soil and fly samples from 608 households. We analyzed samples with IDEXX Quantitray for the most probable number (MPN) of E. coli. We detected E. coli in source water (25%), stored water (77%), child hands (43%), food (58%), flies (50%), ponds (97%) and soil (95%). Soil had >120,000 mean MPN E. coli per gram. In compounds with vs. without animals, E. coli was higher by 0.54 log10 in soil, 0.40 log10 in stored water and 0.61 log10 in food (p<0.05). E. coli in stored water and food increased with increasing E. coli in soil, ponds, source water and hands. We provide empirical evidence of fecal transmission in the domestic environment despite on-site sanitation. Animal feces contribute to fecal contamination, and fecal indicator bacteria do not strictly indicate human fecal contamination when animals are present.
... [4] Attachment rates for bacteria have been inferred under various conditions from aquifer-scale forced gradient and natural gradient tracer tests [Harvey et al., 1989;Bales et al., 1997;Knappett et al., 2012] or centimeter-scale column experiments [Harvey et al., 1993;Litton and Olson, 1993;Fitzpatrick and Spielman, 1973] using stained bacteria or latex microspheres with size and surface properties that are similar to bacteria. Recent reviews have focused on the apparent discrepancy between rates of bacterial transport measured in laboratory columns versus field transport experiments, generally manifested as an apparent decrease in measured attachment rates with increasing scale of the experiment [Foppen and Schijven, 2006;Dong et al., 2006;Pang et al., 2008;Scheibe et al., 2011]. ...
... [12] Artificial groundwater (AGW) was made at ionic strengths of 3.5 and 20 mM with KCl and was designed to encompass the range of ionic strength observed in ponds contaminated with fecal bacteria, which are believed to be a source of aquifer contamination [Knappett et al., 2012], at the field site in Bangladesh where the cores were collected. Specifically, an ionic strength of 3.5 mM is approximately representative of pond conditions during the monsoon season, whereas higher ionic strengths of approximately 20 mM are observed during the dry season [van Geen et al., 2011]. ...
... [4] Attachment rates for bacteria have been inferred under various conditions from aquifer-scale forced gradient and natural gradient tracer tests [Harvey et al., 1989;Bales et al., 1997;Knappett et al., 2012] or centimeter-scale column experiments [Harvey et al., 1993;Litton and Olson, 1993;Fitzpatrick and Spielman, 1973] using stained bacteria or latex microspheres with size and surface properties that are similar to bacteria. Recent reviews have focused on the apparent discrepancy between rates of bacterial transport measured in laboratory columns versus field transport experiments, generally manifested as an apparent decrease in measured attachment rates with increasing scale of the experiment [Foppen and Schijven, 2006;Dong et al., 2006;Pang et al., 2008;Scheibe et al., 2011]. ...
... [12] Artificial groundwater (AGW) was made at ionic strengths of 3.5 and 20 mM with KCl and was designed to encompass the range of ionic strength observed in ponds contaminated with fecal bacteria, which are believed to be a source of aquifer contamination [Knappett et al., 2012], at the field site in Bangladesh where the cores were collected. Specifically, an ionic strength of 3.5 mM is approximately representative of pond conditions during the monsoon season, whereas higher ionic strengths of approximately 20 mM are observed during the dry season [van Geen et al., 2011]. ...
Article
Fecal bacteria are frequently found at much greater distances than would be predicted by laboratory studies, indicating that improved models that incorporate more complexity are might be needed to explain the widespread contamination of many shallow aquifers. In this study, laboratory measurements of breakthrough and retained bacteria in columns of intact and repacked sediment cores from Bangladesh were fit using a two-population model with separate reversible and irreversible attachment sites that also incorporated bacterial decay rates. Separate microcosms indicated an average first order decay rate of 0.03 log10 / day for free bacteria in both the liquid phase and bacteria attached to the solid phase. Although two-thirds of the column results could be well fit with a dual deposition site, single population model, fitting of one third of the results required a two-population model with a high irreversible attachment rate (between 5 and 60 hr(-1)) for one population of bacteria and a much lower rate (from 5 hr(-1) to essentially zero) for the second. Inferred attachment rates for the reversible sites varied inversely with grain size (varying from 1 - 20 hr(-1) for grain sizes between 0.1 and 0.3 mm) while reversible detachment rates were found to be nearly constant (approximately 0.5 hr(-1)). Field simulations based on the fitted two-population model parameters predict only a two-fold reduction in fecal source concentration over a distance of 10 m, determined primarily by the decay rate of the bacteria. The existence of a secondary population of bacteria with a low attachment rate might help explain the observed widespread contamination of tubewell water with E. coli at the field site where the cores were collected, as well as other similar sites.
... The health impact of pathogenic bacteria in groundwater is particularly severe in developing regions. In sub-Saharan Africa and South Asia shallow groundwater is a common drinking water source for low-income communities (Howard et al., 2003;Knappett et al., 2011b). Groundwater-fed springs in periurban Kampala, Uganda, are frequently, particularly in the rainy season, infected by fecal coliforms (Howard et al., 2003;Kulabako et al., 2007), which are often considered to represent E. coli (Unc and Goss, 2003). ...
... In Bangladesh, most households use water from ponds for hygiene, such as bathing and brushing teeth (Knappett et al., 2011a). These could receive latrine effluents and cattle manure, hence contaminating nearby aquifers, which are tapped by tube-wells that provide drinking water (Knappett et al., 2011b). Knappett et al. (2011a) detected cultured E. coli in 42 of 43 surveyed ponds in rural Bangladesh. ...
Article
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The vadose zone can function as both a filter and a passage for bacteria. This review evaluates when and why either effect will apply based on available literature. It summarizes theories and experimental research that address the related, underlying bacterial attenuation processes, the applied macro-scale modeling approaches, and the influencing factors - including the cell, soil, solution and system characteristics. Results point to that the relative importance of each removal mechanism depends on the moisture content and the solution ionic strength. The limitations of available modeling approaches are discussed. It remains unclear in which contexts these are reliable for predictions. The temporal first-order kinetic Escherichia coli (E. coli) removal coefficient ranges three orders of magnitude, from 10−4 to 10−1/min. Results suggest that this rate depends on the pore-water velocity. Spatial filtration of E. coli increases with slower flow and higher collector surface heterogeneity. It could be insignificant in the case of heavy and sudden infiltration and subsequent transport in preferential flow paths, induced, for example, by plant roots or cracks in clayey soils. Future research thus needs to address transport as an effect of extreme weather events such as droughts and subsequent floods.
... Ambient (pond) water quality has been shown to affect groundwater quality. 40 Source water quality, in turn, is a known determinant of stored water quality. 41 A link between contamination of stored water and hands has also been demonstrated. ...
... Indeed, ponds with a latrine within 10 m and ponds receiving latrine effluent had higher E. coli levels in our study, consistent with previous evidence from rural Bangladesh. 40,45 Chickens presented the most prevalent domestic animal exposure in our study. Roughly 90% of compounds had chickens, followed by cows (69%) and goats/sheep (39%). ...
... m/yr, respectively. Assuming a poros- ity of 0.4 ( Knappett et al., 2012) these correspond to average linear groundwater velocities of 0.54(±0.14) and 0.56(±0.14) ...
... Vertical hydraulic conductivity can be used to calculate hydrau- lic anisotropy (K h /K v ) across the study area. Measured horizontal hydraulic conductivities (K h ) in sands in Araihazar and surrounding regions typically range from 10 to 40 m/day (Ahmed, 1994;Ravenscroft et al., 2005;Radloff, 2010;Nakaya et al., 2011;Knappett et al., 2012). Combining the upper and lower bounds for both K v (2.2 ± 0.4 Â 10 À2 ) and K h , we calculate a range of hydraulic anisotropy from 335 to 2579. ...
Conference Paper
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Deep aquifers (>100m) are increasingly relied upon for arsenic free drinking water in rural Bangladesh. The long term sustainability of this drinking water source is in question due to the massive depressurization by urban pumping. In places where confining clay layers are absent deep aquifer depressurization will draw young water into the deep aquifer. This water may contain high arsenic from shallow aquifers or, if it comes from rivers, labile organic matter released from organic-rich sediments that could promote the reductive dissolution of iron oxides and therefore release arsenic to groundwater. Here we explore the impacts of Dhaka pumping on changing recharge sources in the deep drinking water aquifers of Bangladesh. The study area is Araihazar upazila, a rural 150km2 region 20 km east of Dhaka and bounded to the east by the Meghna River. Eighteen pressure transducers were placed within deep community drinking water wells spread across an 8x8km area 2-10km west of the Meghna. One transducer was placed in a river piezometer in the Meghna River. The transducers measured water level fluctuations every 20 minutes from March, 2012 through May 2013. Within the deep aquifer, hydraulic gradients trended towards Dhaka throughout the year. During the early monsoon westward gradients positively correlated with short term fluctuations in the level of the Meghna indicating a strong hydraulic connection to the deep aquifer. In the late monsoon and the dry season however, hydraulic heads in the eastern side of the deep aquifer were higher than the level of the Meghna and the westward hydraulic gradient was not influenced by short term fluctuations in the Meghna. This suggests that Dhaka pumping is creating optimal conditions for enhanced movement of river water into underlying aquifers. This process may buffer the deep aquifer from depletion, but the long term impact on the deep aquifer water quality may be substantial.
... Household-level access to an improved latrine is intended to prevent transmission of fecal-borne pathogens by separating household members from their own waste, but it does not account for transmission pathways that originate from outside the home, including environmental contamination from neighbors that do not have safely managed sanitation facilities. Humans, animals, and flies can carry fecal pathogens into the home environment from outside sources, and pathogens can infiltrate into surface-and groundwater sources from neighbors' open defecation or unhygienic latrines, contributing to transmission independent of household-level sanitation access (Julian, 2016;Knappett et al., 2011Knappett et al., , 2012. Increasing the proportion of households in the community with safely managed sanitation facilities hypothetically could reduce transmission by limiting opportunities for pathogen spread from outside the home, as fewer people in the community are contributing uncontained feces. ...
Article
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Background Household-level sanitation interventions have had limited effects on child health or environmental contamination, potentially due to low community coverage. Higher community-level coverage with safely managed sanitation can reduce opportunities for disease transmission. Methods We estimated associations between community sanitation coverage, environmental fecal contamination, and child health among 360 compounds in the control arm of the WASH Benefits trial in rural Bangladesh (NCT01590095). In each compound, we enumerated E. coli in environmental samples and recorded the 7-day prevalence of caregiver-reported diarrheal disease and acute respiratory infections (ARI) in children under five. We observed indicators of latrine access and quality among all neighboring compounds within 100 m of study compounds. We defined community coverage as the proportion of neighboring compounds with (1) at least one latrine, and (2) exclusively hygienic latrines (improved facility observed to safely contain feces), within both 50 m and 100 m of study compounds. We assessed effect modification by population density and season. Results Adjusted for confounders, study compounds surrounded by 100% coverage of at least one latrine per compound within 50 m had slightly lower log10 E. coli counts in stored water (Δlog = −0.13, 95% CI -0.26, −0.01), child hand rinses (Δlog = −0.13, 95% CI -0.24, −0.02), and caregiver hand rinses (Δlog = −0.16, 95% CI -0.29, −0.03) and marginally lower prevalence of diarrheal disease (prevalence ratio [PR] = 0.82, 95% CI 0.64, 1.04) and ARI (PR = 0.84, 95% CI 0.69, 1.03) compared to compounds surrounded by <100% coverage. Effects were similar but less pronounced at 100 m. At higher population densities, community latrine coverage was associated with larger reductions in E. coli on child and caregiver hands and prevalence of diarrheal disease. Coverage with exclusively hygienic latrines was not associated with any outcome. Conclusion Higher community sanitation coverage was associated with reduced fecal contamination and improved child health, with stronger effects at highly local scales (50m) and at high population densities. Our findings indicate that the relationship between community sanitation coverage, environmental contamination, and child health varies by definition of coverage, distance, and population density. This work highlights significant uncertainty around how to best measure sanitation coverage and the expected health effects of increasing sanitation coverage using a specific metric. Better understanding of community-level sanitation access is needed to inform policy for implementing sanitation systems that effectively protect community health.
... High spatial attenuation rates of E. coli and other fecal indicator bacteria through sandy aquifers have been found by other studies (Pang, 2009;Knappett et al., 2012). Although we did not conduct microbial source tracking studies to determine the sources of generic E. coli and Enterococcus spp. in groundwater, the resistance to multiple veterinary or medical drugs among a subset of these bacteria points to human-or animal-wastederived sources of antibiotic-resistant organisms. ...
Article
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Surveys of microbiological groundwater quality were conducted in a region with intensive animal agriculture in California, USA. The survey included monitoring and domestic wells in eight concentrated animal feeding operations (CAFOs) and 200 small (domestic and community supply district) supply wells across the region. Campylobacter was not detected in groundwater, whereas Escherichia coli O157:H7 and Salmonella were each detected in 2 of 190 CAFO monitoring well samples. Nonpathogenic generic E. coli and Enterococcus spp. were detected in 24.2% (46/190) and 97.4% (185/190) groundwater samples from CAFO monitoring wells and in 4.2% (1/24) and 87.5% (21/24) of CAFO domestic wells, respectively. Concentrations of both generic E. coli and Enterococcus spp. were significantly associated with well depth, season, and the type of adjacent land use in the CAFO. No pathogenic bacteria were detected in groundwater from 200 small supply wells in the extended survey. However, 4.5 to 10.3% groundwater samples were positive for generic E. coli and Enterococcus. Concentrations of generic E. coli were not significantly associated with any factors, but concentrations of Enterococcus were significantly associated with proximity to CAFOs, seasons, and concentrations of potassium in water. Among a subset of E. coli and Enterococcus isolates from both surveys, the majority of E. coli (63.6%) and Enterococcus (86.1%) isolates exhibited resistance to multiple (≥3) antibiotics. Findings confirm significant microbial and antibiotic resistance loading to CAFO groundwater. Results also demonstrate significant attenuative capacity of the unconfined alluvial aquifer system with respect to microbial transport.
... Coliforms are a group of facultative anaerobes that possess mechanisms for adapting to various oxygen stress [26]. Fecal coliforms such as E. coli have often been used to indicate fecal pollution in As-contaminated aquifer ecosystems [27]. The count of arsenate-resistant E. coli increased at greater depths, indicating their prevalence at those depths [ Figure 4]. ...
... [7][8][9][10][11][12] In Bangladesh, shallow tubewells are the primary source of drinking water and contain fecal indicator bacteria as well as human enteric pathogens. [13][14][15][16][17][18] Mechanisms that lead to this contamination include infiltration from ponds and latrines, 19,20 short-circuiting at the wellhead through unsealed parts, 21 and biofilm formation on the handpump. 22 A previous study in rural Bangladesh found no correlation between sanitary scores that quantify these pathways and tubewell water quality. ...
Article
Accurately assessing the microbiological safety of water sources is essential to reduce waterborne fecal exposures and track progress toward global targets of safe water access. Sanitary inspections are a recommended tool to assess water safety. We collected 1,684 water samples from 902 shallow tubewells in rural Bangladesh and conducted sanitary surveys to assess whether sanitary risk scores could predict water quality, as measured by Escherichia coli We detected E coli in 41% of tubewells, mostly at low concentrations. Based on sanitary scores, 31% of wells were low risk, 45% medium risk, and 25% high or very high risk. Older wells had higher risk scores. Escherichia coli levels were higher in wells where the platform was cracked or broken (Δlog10 = 0.09, 0.00-0.18) or undercut by erosion (Δlog10 = 0.13, 0.01-0.24). However, the positive predictive value of these risk factors for E coli presence was low (< 50%). Latrine presence within 10 m was not associated with water quality during the wet season but was associated with less frequent E coli detection during the dry season (relative risk = 0.72, 0.59-0.88). Sanitary scores were not associated with E coli presence or concentration. These findings indicate that observed characteristics of a tubewell, as measured by sanitary inspections in their current form, do not sufficiently characterize microbiological water quality, as measured by E coli Assessments of local groundwater and geological conditions and improved water quality indicators may reveal more clear relationships. Our findings also suggest that the dominant contamination route for shallow groundwater sources is short-circuiting at the wellhead rather than subsurface transport.
... Hydraulic conductivities were compared with the distribution of subsurface resistivity. Pneumatic rising head slug tests were performed at each piezometer using a pressure transducer (Levelogger Edge, Solinst Canada Ltd., Georgetown, Ontario, Canada) and a pneumatic slug test device (Knappett et al. 2012). This method is described here briefly. ...
Article
Oceanic tidal fluctuations which propagate long distances up coastal rivers can be exploited to constrain hydraulic properties of riverbank aquifers. These estimates, however, may be sensitive to degree of aquifer confinement and aquifer anisotropy. We analyzed the hydraulic properties of a tidally influenced aquifer along the Meghna River in Bangladesh using: (1) slug tests combined with drilling logs and surface resistivity to estimate Transmissivity (T); (2) a pumping test to estimate T and Storativity (S) and thus Aquifer Diffusivity (DPT ); and (3) the observed reduction in the amplitude and velocity of a tidal pulse to calculate D using the Jacob-Ferris analytical solution. Average Hydraulic Conductivity (K) and T estimated with slug tests and borehole lithology were 27.3 m/d and 564 m(2) /d, respectively. Values of T and S determined from the pumping test ranged from 400 to 500 m(2) /d and 1 to 5 × 10(-4) , respectively with DPT ranging from 9 to 40 × 10(5) m(2) /d. In contrast, D estimated from the Jacob-Ferris model ranged from 0.5 to 9 × 10(4) m(2) /d. We hypothesized this error resulted from deviations of the real aquifer conditions from those assumed by the Jacob-Ferris model. Using a 2D numerical model tidal pulses were simulated across a range of conditions and D was calculated with the Jacob-Ferris model. Moderately confined (Ktop /Kaquifer < 0.01) or anisotropic aquifers (Kx /Kz > 10) yield D within a factor of 2 of the actual value. The order of magnitude difference in D between pumping test and Jacob-Ferris model at our site argues for little confinement or anisotropy.
... There are issues related to the use (Clasen et al. 2012), acceptance (Nayono et al. 2010), and diffusion (Jenkins and Cairncross 2010) of latrines in developing countries, influence of latrines on water quality in sandy aquifers (Knappett et al. 2012), degree of improvement realized (Exley et al. 2015), methane (Reid et al. 2014), and volatile compound (Lin et al. 2013) emissions, microbial fuel cells for latrines (Castro et al. 2014), and the spread of fecal matter from latrine floors (Pickering et al. 2012) that are also important, but beyond the scope of this work. ...
Article
Full-text available
Providing sanitation for water-starved areas is crucial to environmental sustainability. Composting latrines are a sustainable sanitation method since they do not require water. However, little analysis has been done on the decomposition process occurring inside the latrine, including what temperatures are reached and what variables most affect the composting process. Having better knowledge of how outside variables affect composting latrines can aid designers and users on the choice, design, and use. Detailed field measurements of pit temperature in a latrine for several months were taken with the compost being frequently mixed and moistened. Ambient temperatures and the mixing of liquid to the compost resulted in temperature increases 100 % of the time, with seasonal ambient temperatures determining the rate and duration of the temperature increases. However, compost only reached total pathogen destruction levels in 10 % of the measurements. Storage time recommendation outlined by the World Health Organization should be complied with. If these storage durations are obtainable, the use of composting latrines is an economical and sustainable solution to sanitation while conserving water resources.
... However, a more specifically designed monitoring network with site-specific installation of deeper monitoring boreholes of varying distance from tanks could provide further details on whether significant trends of conservative tracers might be detectable on smaller scales. We therefore propose that studies following a hydrochemical approach as presented here combined with more site-specific monitoring networks as for example outlined in Knappett et al. (2012) and (Stahl et al., 2014) could be informative for the future. ...
Article
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The majority of India’s rural drinking water supply is sourced from groundwater, which also plays a critical role in irrigated agriculture, supporting the livelihoods of millions of users. However, recent high abstractions are threatening the sustainable use of groundwater, and action is needed to ensure continued supply. Increased managed aquifer recharge (MAR) using the >200,000 existing tanks (artificially created surface water bodies) is one of the Indian government’s key initiatives to combat declining groundwater levels. However, few studies have directly examined the effectiveness of tank recharge, particularly in the complex fractured hydrogeology of Peninsular India. To address this gap, this study examined the impact of tanks in three crystalline bedrock catchments in Karnataka, southern India, by analysing the isotopic and hydrochemical composition of surface waters and groundwaters, combined with groundwater level observations. The results indicate that tanks have limited impact on regional groundwater recharge and quality in rural areas, where recharge from precipitation and groundwater recycling from irrigation dominate the recharge signal. In the urban setting (Bengaluru), impermeable surfaces increased the relative effect of recharge from point sources such as tanks and rivers, but where present, pipe leakage from public-water-supply accounted for the majority of recharge. Shallow groundwater levels in the inner parts of the city may lead to groundwater discharge to tanks, particularly in the dry season. We conclude that the importance of aquifer recharge from tanks is limited compared to other recharge sources and highly dependent on the specific setting. Additional studies to quantify tank recharge and revisions to the current guidelines for national groundwater recharge estimations, using a less generalised approach, are recommended to avoid over-estimating the role tanks play in groundwater recharge.
... In the last few years, many waterborne diseases from contaminated groundwater have been reported in countries at all levels of economic development, with outbreaks that result in large socioeconomic impacts [1][2][3]. As with other aquatic matrices, groundwater can be contaminated by microorganisms that originate from human activities (urban, industrial, and agricultural) and are released into the environment through direct discharge, insufficiently treated wastewater, leaking sewage, and septic systems [4][5][6][7][8][9][10][11][12][13][14]. For these reasons, groundwater quality becomes extremely important for human consumption or irrigation purpose. ...
Article
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According to Italian Ministerial Decree No. 185 of 12 June 2003, water is considered suitable for irrigation if levels of fecal bacteria (i.e., Escherichia coli and Salmonella) are within certain parameters. The detection of other microorganisms is not required. The aim of this study is to determine the bacteriological quality of groundwater used for irrigation and the occurrence of enteric viruses (Norovirus, Enterovirus, Rotavirus, Hepatovirus A), and to compare the presence of viruses with the fecal bacteria indicators. A total of 182 wells was analyzed. Widespread fecal contamination of Apulian aquifers was detected (141 wells; 77.5%) by the presence of fecal bacteria (i.e., E. coli, Salmonella, total coliforms, and enterococci). Considering bacteria included in Ministerial Decree No. 185, the water from 35 (19.2%) wells was unsuitable for irrigation purposes. Among 147 wells with water considered suitable, Norovirus, Rotavirus, and Enterovirus were detected in 23 (15.6%) wells. No Hepatovirus A was isolated. Consequently, 58 wells (31.9%) posed a potential infectious risk for irrigation use. This study revealed the inadequacy of fecal bacteria indicators to predict the occurrence of viruses in groundwater and it is the first in Italy to describe the presence of human rotaviruses in well water used for irrigation.
... In western Araihazar, approximately 10 km west of S3, Stute et al. (2007) and Mozumder et al. (2020a) conducted slug tests on 23 monitoring wells over 7 sites and reported K values ranging from 3.6 to 40.2 m/day, with an average of 17.0 m/day and a SD of 10.9 m/day. Approximately 11 km west of S2, Knappett et al. (2012) conducted slug tests in 50 monitoring wells over 9 transects throughout one village and reported K values ranging from 1.5 to 40.6 m/day with an average of 18.6 m/day and a SD of 11.8 m/ day. Therefore, the observed K in the riverbank aquifer sites S1, S2 and S4 are within the range of the inland shallow aquifer but K in the single well in S3 is approximately double the high-end value in 94 previously tested wells throughout the area. ...
Article
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Shallow (<30 m) reducing groundwater commonly contains abundant dissolved arsenic (As) in Bangladesh. We hypothesize that dissolved As in iron (Fe)-rich groundwater discharging to rivers is trapped onto Fe(III)-oxyhydroxides which precipitate in shallow riverbank sediments under the influence of tidal fluctuations. Therefore, the goal of this study is to compare the calculated mass of sediment-bound As that would be sequestered from dissolved groundwater As that discharges through riverbanks of the Meghna River to the observed mass of As trapped within riverbank sediments. To calculate groundwater discharge, a Boussinesq aquifer analytical groundwater flow model was developed and constrained by cyclical seasonal fluctuations in hydraulic heads and river stage observed at three sites along a 13 km reach in central Bangladesh. At all sites, groundwater discharges to the river year-round but most of it passes through an intertidal zone created by ocean tides propagating upstream from the Bay of Bengal in the dry season. The annualized groundwater discharge per unit width at the three sites ranges from 173 to 891 m²/yr (average 540 m²/yr). Assuming that riverbanks have been stable since the Brahmaputra River avulsed far away from this area 200 years ago and dissolved As is completely trapped within riverbank sediments, the mass of accumulated sediment As can be calculated by multiplying groundwater discharge by ambient aquifer As concentrations measured in 1969 wells. Across all sites, the range of calculated sediment As concentrations in the riverbank is 78–849 mg/kg, which is higher than the observed concentrations (17–599 mg/kg). This discovery supports the hypothesis that the dissolved As in groundwater discharge to the river is sufficient to account for the observed buried deposits of As along riverbanks.
... 11 In low-income countries, fecal contamination is pervasive on surfaces and objects in the domestic environment 12 and ambient waters used for bathing and washing dishes. 13 Flies carry fecal pathogens 14,15 and can transmit these to stored food; 16 fly control programs have successfully reduced diarrheal diseases. 17,18 Soil is increasingly recognized as a reservoir for fecal organisms and has been linked to fecal contamination of drinking water, hands, and food; 19 ingestion of soil by children has been associated with environmental enteric dysfunction and stunting. ...
... Firstly, in sand aquifers, coliform bacteria are rapidly attenuated and typically travel only a few metres (e.g. Harvey et al. 1989;Carre and Dufils, 1991;Weiss et al. 2005;Hijnen et al. 2005;Knappett et al. 2012a;Ravenscroft et al. 2017). Secondly, bacterial analysis of well waters has poor repeatability so repeat analysis are essential before concluding that coliforms inhabit the aquifer. ...
Article
Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain, in southern Sindh Province, concentrations of As exceeded the WHO guideline value of 10 μg/L in 38%, with 22% exceeding 50 μg/L, Pakistan's guideline value. The As pollution is caused by microbially‐mediated reductive dissolution of sedimentary iron‐oxyhydroxides in anoxic groundwaters; oxic groundwaters contain < 10 μg/L of As. In the upper Indus River plain, in Punjab Province, localised As pollution of groundwater occurs by alkali desorption as a consequence of ion‐exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion‐exchange in the aquifer and so has values > 0 for residual sodium carbonate. In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (EC up to 6 mS/cm). High salinities result from local inputs of waste‐water from unsewered sanitation, but mainly from evaporation/evapotranspiration of canal water and groundwater used for irrigation. The process does not concentrate As in the groundwater owing to sorption of As to soils. Ion‐exchange exerts a control on concentrations of Na, Ca, and B, but not on As. High values of Cl/Br mass ratios (most » 288, the marine value) reflect the pervasive influence on groundwater of sewage‐contaminated water from irrigation canals through seepage loss and deep percolation of irrigation water, with additional, well‐specific, contributions from unsewered sanitation.
... Recent research has shown that, in the absence of precipitation, similar strata are effective barriers to the downward migration of even high concentrations of EC in surface sources ( Knappert et al. 2012;Stall et al. 2014). Since coliform bacteria are less frequently detected in wells in the CP, it is likely that similar-and larger-sized bacterial and protozoan pathogens should also occur infrequently. ...
Article
In compliance with the New Jersey Private Well Testing Act, 78,546 wells (93,787 samples, including samples from 13,290 wells that were analyzed more than once) were analyzed for total coliform (TC) bacteria by one or more of 39 laboratories over a 10-year period. Samples containing TC bacteria were further analyzed for the presence of either fecal coliform or E. coli (FC/EC) bacteria. The large population of wells sampled multiple times permitted a systematic study of the effect of repeat sampling on coliform bacteria detection rates. The detection rate increased with the number of times wells were sampled. In bedrock, TC bacteria were detected in 21% of the population of wells analyzed only once, 33% in the population sampled twice, and 43% in the population sampled three times. It was estimated that TC bacteria would be detected in 90% of all wells if each well was analyzed 10 times. For FC/EC bacteria, it was estimated that 21 and 68 samples, respectively, would be required to reach the 50% and 90% population detection rates. In the Coastal Plain (CP), many more samples would be required to achieve the same estimated population detection rates. The population detection rate estimates were also dependent on the type of method used, the pH of the well water, and the geologic formation in which wells were located. A single sample was not sufficient to detect coliform bacteria when present in well water.
... 11 In low-income countries, fecal contamination is pervasive on surfaces and objects in the domestic environment 12 and ambient waters used for bathing and washing dishes. 13 Flies carry fecal pathogens 14,15 and can transmit these to stored food; 16 fly control programs have successfully reduced diarrheal diseases. 17, 18 Soil is increasingly recognized as a reservoir for fecal organisms and has been linked to fecal contamination of drinking water, hands, and food; 19 ingestion of soil by children has been associated with environmental enteric dysfunction and stunting. ...
Article
Full-text available
Sanitation improvements have had limited effectiveness in reducing the spread of fecal pathogens into the environment. We conducted environmental measurements within a randomized controlled trial in Bangladesh that implemented individual and combined water treatment, sanitation, handwashing (WSH) and nutrition interventions (WASH Benefits, NCT01590095). Following approximately 4 months of intervention, we enrolled households in the trial’s control, sanitation and combined WSH arms to assess whether sanitation improvements, alone and coupled with water treatment and handwashing, reduce fecal contamination in the domestic environment. We quantified fecal indicator bacteria in samples of drinking and ambient waters, child hands, food given to young children, courtyard soil and flies. In the WSH arm, E. coli prevalence in stored drinking water was reduced by 62% (prevalence ratio=0.38 (0.32, 0.44)) and E. coli concentration by 1-log (log10 = -0.88 (-1.01, -0.75)). The interventions did not reduce E. coli along other sampled pathways. Ambient contamination remained high among intervention households. Potential reasons include non-community-level sanitation coverage, child open defecation, animal fecal sources or naturalized E. coli in the environment. Future studies should explore potential threshold effects of different levels of community sanitation coverage on environmental contamination.
... Therefore, in order to protect drinking water supply wells against microbial contamination, it is essential to establish safe setback distances between wastewater disposal services and water wells (Blaschke et al., 2016). Following numerous laboratory and field-based studies, these safe setback distances should be defined as a function of local soil parameters (e.g., grain sizes, Knappett et al., 2012a, andangularity, Saiers andRyan, 2005), and general hydrogeology conditions (e.g., Knappett et al., 2008, Pang 2009). ...
Article
Groundwater is the major source of drinking water in most rural areas in developing countries. This resource is threatened by the potential presence of faecal bacteria coming from a variety of sources and pollution paths, the former including septic tanks, landfills, and crop irrigation with untreated, or insufficiently treated, sewage effluent. Accurately assessing the microbiological safety of water resources is essential to reduce diseases caused by waterborne faecal exposure. The objective of this study is to discern which are the most significant sanitary, hydrogeological, geochemical, and physical variables influencing the presence of faecal bacterial pollution in groundwater by means of statistical multivariate analyses. The concentration of Escherichia coli was measured in a number of waterpoints of different types in a rural area located in the coast of Kenya, assessing both a dry and a wet season. The results from the analyses reaffirm that the design of the well and their maintenance, the distance to latrines, and the geological structure of the waterpoints are the most significant variables affecting the presence of E. coli. Most notably, the presence of faecal bacteria in the study area correlates negatively with the concentration of ion Na+ (being an indirect indicator of fast recharge in the study site), and also negatively with the length of the water column inside the well.
... Our study was not designed to differentiate contamination occurring at the source from contamination introduced during storage at home. The increased contamination we observed could be due to child feces in the compound environment entering the tubewell by subsurface infiltration or through unsealed head works [47,48], or due to contact with hands and utensils during storage that have been contaminated by exposure to child feces [49,50]. Several previous randomized control trials that assessed the association between sanitation and drinking water quality found no effect from sanitation [5][6][7], while a trial in Tanzania found reduced E. coli in drinking water associated with sanitation improvements [51]. ...
Article
Full-text available
Child open defecation is common in low-income countries and can lead to fecal exposure in the domestic environment. We assessed associations between child feces management practices vs. measures of contamination and child diarrhea among households with children <5 years in rural Bangladesh. We visited 360 households quarterly and recorded caregiver-reported diarrhea prevalence, and defecation and feces disposal practices for children <5 years. We examined caregiver and child hands for visible dirt and enumerated E. coli in child and caregiver hand rinse and stored drinking water samples. Safe child defecation (in latrine/potty) and safe feces disposal (in latrine) was reported by 21% and 23% of households, respectively. Controlling for potential confounders, households reporting unsafe child defecation had higher E. coli prevalence on child hands (prevalence ratio [PR] = 1.12, 1.04–1.20) and in stored water (PR = 1.12,1.03–1.21). Similarly, households reporting unsafe feces disposal had higher E. coli prevalence on child hands (PR = 1.11, 1.02–1.21) and in stored water (PR = 1.10, 1.03–1.18). Effects on E. coli levels were similar. Children in households with unsafe defecation and feces disposal had higher diarrhea prevalence but the associations were not statistically significant. Our findings suggest that unsafe child feces management may present a source of fecal exposure for young children.
... These water matrices have been suffering a sharp deterioration in their quality through diffuse sources that are difficult to identify in order to adequate management and remediation planning. Among them, urban, forest, and livestock runoff, the latter, occurs mainly through livestock and other animal access to rivers and streams as well as their solid waste (Amaral 2004;Knappett et al. 2012;Staggemeier et al. 2015). In rural areas, these situations are accentuated because the use of biodigesters has not been widely adopted yet, being common the use of landfills and direct disposal of wastewater in the soil and water resources (Amaral 2004;de Oliveira et al. 2012;Spilki et al. 2013). ...
Article
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This study aims to expand the knowledge about fecal contamination by humans and animals using Adenovirus (AdV) as bioindicators in different water sources from rural areas, to evaluate the viral infectivity, and to compare the different techniques used to detect the Human mastadenovirus (HAdV). For that, 124 samples were collected (86 from groundwater and 38 from surface water) along the Rio dos Sinos Basin. Escherichia coli count was carried out, and the samples were submitted for the detection and characterization tests of AdV by different methods (qPCR, multiplex qPCR, and nested PCR). In addition, the viral infectivity was realized by integrated cell culture quantitative PCR (ICC-qPCR). E. coli was detected in 63% of groundwater samples (geometric mean of 16.7 MPN/100 mL) and 68% (geometric mean: 5.08×10 2 MPN/100 mL) in surface waters. Among the viral indicator in the groundwater , the HAdV was detected in 49% of the samples, followed by Canine mastadenovirus (CAV, 20%), Bovine mastadenovirus (BAdV, 17%), Aviadenovirus (AvAdV, 15%), and Porcine mastadenovirus (PAdV, 03%). In surface water, HAdV was detected in 45%, followed by CAV (42%), BAdV (29%), and PAdV and AvAdV (13%). The quantification of genomic copies per liter ranged from 9.40×10 4 to 5.54×10 10 gc/L. In groundwater samples, it was possible to observe infectious adenovirus in 12% of the samples, as well as in surface water for 18%. The results showed an increase in the sensitivity of positive samples when a combined set of techniques were used for HAdV detection.
... 3−5 A significant source of pathogens in water treatment are due to fecal contamination from inadequate or improperly managed sanitation systems. 6,7 In these contexts, open defecation or improperly sited sanitation interventions such as pit latrines leach wastewater and associated pathogens into onsite and downstream water supplies. 8,9 As of 2018 an estimated 4.5 billion people do not have access to safely managed sanitation services, almost 900 million of whom still practice open defecation. ...
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Electrochemical disinfection—a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode—has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.
... In medium-and fine-grained non-confined aquifers, contamination of tubular wells by indicator bacteria transported in the porous medium of the soil from the infiltration of locally disposed excreta is relatively limited. In rainy periods, the rapid route of downward flow of water from the surface or surface layers of the soil can alternatively explain this contamination when the annular space of the well is not sealed (Knappett, et al., 2012a(Knappett, et al., , 2012b. The collections of the present study were carried out predominantly in the dry period and, therefore, the contamination of tubular wells by EC must have had little influence from the unsealed annular space. ...
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Rural environments lack basic sanitation services. Facilities for obtaining water and disposing sewage are often under the initiative of each resident, who may not be able to build and maintain them properly. Thus, water for human consumption is subject to fecal contamination and, consequently, the presence of waterborne pathogens, such as enteric viruses. This study evaluated fecal contamination of water samples from individual sources used for domestic water supply on small farms in the state of Goiás, Brazil. Samples were collected from 78 houses whose water sources were tubular wells, dug wells, springs, and surface waters. Escherichia coli (EC) bacteria, analyzed by the defined chromogenic substrate method, was used as a traditional indicator of fecal contamination. The enteric viruses Human mastadenovirus (HAdV) and Enterovirus (EV), analyzed by qPCR, were tested as complementary indicators of fecal contamination. At least one of these markers was found in 89.7% of the samples. Detection rates were 79.5% for EC, 52.6% for HAdV, and 5.1% for EV. The average concentration for EC was 8.82 × 101 most probable number (MPN) per 100 mL, while for HAdV and EV the concentrations were 7.51 × 105 and 1.89 × 106 genomic copies (GC) per liter, respectively. EC was the most frequent marker in ground and surface water samples. HAdV was detected significantly more frequently in groundwater than in surface water and was more efficient in indicating contamination in tubular wells. There was no association of frequencies or correlation of concentrations between EC and HAdV. HAdV indicated human fecal contamination and performed well as a complementary indicator. The results reveal that a large part of the analyzed population is vulnerable to waterborne diseases caused by enteric pathogens.
... Tubewells in rural Bangladesh are often located in close proximity to latrines and ponds. Possible mechanisms for tubewell contamination with fecal pathogens include infiltration into the groundwater aquifers from nearby latrines, septic tanks and ponds [18,19], short-circuiting of contaminated surface water into the wells through unsealed tubewell components [14], or harboring of bacteria in contaminated handpumps [20]. ...
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Shallow tubewells are the primary drinking water source for most rural Bangladeshis. Fecal contamination has been detected in tubewells, at low concentrations at the source and at higher levels at the point of use. We conducted a randomized controlled trial to assess whether improving the microbiological quality of tubewell drinking water by household water treatment and safe storage would reduce diarrhea in children <2 years in rural Bangladesh. We randomly assigned 1800 households with a child aged 6-18 months (index child) into one of three arms: chlorine plus safe storage, safe storage and control. We followed households with monthly visits for one year to promote the interventions, track their uptake, test participants' source and stored water for fecal contamination, and record caregiver-reported child diarrhea prevalence (primary outcome). To assess reporting bias, we also collected data on health outcomes that are not expected to be impacted by our interventions. Both interventions had high uptake. Safe storage, alone or combined with chlorination, reduced heavy contamination of stored water. Compared to controls, diarrhea in index children was reduced by 36% in the chlorine plus safe storage arm (prevalence ratio, PR = 0.64, 0.55-0.73) and 31% in the safe storage arm (PR = 0.69, 0.60-0.80), with no difference between the two intervention arms. One limitation of the study was the non-blinded design with self-reported outcomes. However, the prevalence of health outcomes not expected to be impacted by water interventions did not differ between study arms, suggesting minimal reporting bias. Safe storage significantly improved drinking water quality at the point of use and reduced child diarrhea in rural Bangladesh. There was no added benefit from combining safe storage with chlorination. Efforts should be undertaken to implement and evaluate long-term efforts for safe water storage in Bangladesh. ClinicalTrials.gov NCT01350063.
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A survey of young adults was conducted at several 3rd level agricultural institutions across Ireland over a 6-month period. The results from the agri-student survey were compared and contrasted with those of an identical survey of private well owners. Students (n = 246) scored significantly lower than well owners (n = 245) in two developed metrics, namely “groundwater source awareness” and “groundwater contamination awareness” (p n = 476). Clusters comprised four predictors: presence of an elderly householder (predictor importance = 0.91), residence within the household during well design (predictor importance = 0.55), presence of an infant or young child (≤5 years) in the household (predictor importance = 0.48) previous instance of gastrointestinal illness or symptoms within the household (predictor importance = 0.31) The results of this research may be used to inform future risk management, communication and knowledge transfer policies, which are currently required to ensure the safeguarding of private groundwater supplies both in Ireland and further afield.
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Arsenic contamination of groundwater is a global health crisis, especially in Bangladesh where an estimated 40 million people are at risk. The release of geogenic arsenic bound to sediments into groundwater is thought to be influenced by dissolved organic matter (DOM) through several biogeochemical processes. Abiotically, DOM can promote the release of sediment bound As through the formation of DOM-As complexes and competitive interactions between As and DOM for sorption sites on the sediment. Additionally, the labile portion of groundwater DOM can serve as an electron donor to support microbial growth and the more recalcitrant humic DOM may serve as an electron shuttle, facilitating the eventual reduction of ferric iron present as iron oxides in sediments and consequently the mobilization of sorbed As and organic material. The goal of this study is to understand the source of DOM in representative Bangladesh groundwaters and the DOM sorption processes that occur at depth. We report chemical characteristics of representative DOM from a surface water, a shallow low-As groundwater, mid-depth high-As groundwater from the Araihazar region of Bangladesh. The humic DOM from groundwater displayed a more terrestrial chemical signature, indicative of being derived from plant and soil precursor materials, while the surface water humic DOM had a more microbial signature, suggesting an anthropogenic influence. In terms of biogeochemical processes occurring in the groundwater system, there is evidence from a diverse set of chemical characteristics, ranging from 13C-NMR spectroscopy to the analysis of lignin phenols, for preferential sorption onto iron oxides influencing the chemistry and reactivity of humic DOM in high As groundwater in Bangladesh. Taken together, these results provide chemical evidence for anthropogenic influence and the importance of sorption reactions at depth controlling the water quality of high As groundwater in Bangladesh.
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The relationship between pit latrine siting and the quality of groundwater points has gained currency in extant literature. This paper aims to examine this relationship in some communities in Ghana. We argue that while the construction and use of pit latrines have been a welcome upgrade intervention to improve on-site sanitation, the consequent contamination of groundwater quality remains a challenge. Drawing on research in Ghana and evidence from selected communities in the Sissala West District, we found that there is the contamination of groundwater which are attributable to the siting of pit latrines with a depth above 2 m. Through our analysis of the siting of groundwater points in relation to existing pit latrines as currently practiced, it reveals that contamination occurred within a 50 m radius of water points and where the water points were located downstream of the pit latrines. In this relationship as revealed from our findings, we recommend that guidelines governing the siting, construction, and usage of pit latrines should be adhered to strictly to prevent contamination of groundwater sources.
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In some high As groundwater systems, correlations are observed between dissolved organic matter (DOM) and As concentrations, but in other systems such relationships are absent. The role of labile DOM as the main driver of microbial reductive dissolution is not sufficient to explain the variation in DOM-As relationships. Other processes that may also influence arsenic mobility include complexation of As by dissolved humic substances, and competitive sorption and electron shuttling reactions mediated by humics. To evaluate such humic DOM influences, we characterized the optical properties of whole waters sampled from groundwater, spanning an age gradient in Araihazar, Bangladesh. Further, we analyzed fulvic acids (FA) isolated from large volume samples for optical properties, C and N content and 13C-NMR spectroscopic distribution. Old groundwater (> 30 years old) contained primarily sediment-derived DOM and had significantly higher (p < 0.001) dissolved arsenic concentration than groundwater that was < 5 years old. Younger groundwater had DOM spectroscopic signatures similar to surface water DOM and characteristic of a sewage pollution influence. Associations between dissolved arsenic, iron, and FA concentration, and fluorescence properties of isolated FA suggest that aromatic, terrestrially-derived FAs promote arsenic-iron-FA complexation reactions that enhance arsenic mobility.
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Laboratory column experimental results are frequently used to estimate field-scale, fecal bacterial transport distances. However, it is not uncommon for fecal bacteria to be observed at greater distances than predicted by up-scaling laboratory results. Fluctuating or varying velocity conditions is one complex in-situ condition that might account for such inaccurate prediction, yet it is often neglected in laboratory column experiments. In this study, one-dimensional, laboratory column experiments were performed under both constant and varying velocity conditions using 2 μm microspheres and 100 μm glass beads to simulate bacterial transport in saturated porous media. Particle breakthrough curves and particle concentrations retained in the column at the end of an experiment were obtained for five constant and three varying velocity conditions. The range of constant velocities investigated was between 3.17 m/day and 27.65 m/day. For varying velocity conditions, the velocity was steadily increased and/or decreased over the period of the experiment within the same range. Results from the constant velocity experiments were successfully modeled using first order, irreversible particle attachment kinetics. The irreversible attachment coefficients obtained from the constant velocity experiments were used to derive a power function relationship between a dimensionless irreversible attachment coefficient, Ki* and velocity, v. This relationship was then used to model the varying velocity experiments, with limited success (NRMSE > 10% for all model fits). A comparison of Ki* values obtained from direct fitting of the varying velocity tests, with the Ki* values derived from the results of the constant velocity experiments, revealed a potential dependence of Ki* on the rate of change of velocity. Observed particle breakthrough curves (BTCs) for the varying velocity experiments were also modeled using a constant value of Ki* based on the average velocity of each experiment. The results of this modeling under-estimated observed maximum breakthrough concentrations for the column experiments where velocity increased, and especially under conditions where velocity increased then decreased. Overall, the results of this study point to the need for better understanding of how varying velocity conditions impact bacterial transport in the field.
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Recent studies have demonstrated that the supply of relatively young organic carbon stimulates the release of arsenic to groundwater in Bangladesh. This study explores the potential role of human and livestock waste as a significant source of this carbon in a densely populated rural area with limited sanitation. Profiles of aquifer sediment samples were analyzed for phytosterols and coprostanol to assess the relative contributions of plant-derived and human/livestock waste-derived organic carbon at two well-characterized sites in Araihazar. Coprostanol concentrations increased with depth from non-detection (<10m at Site B and <23m at Site F) to maxima of 1.3 and 0.5ng/g in aquifer sands recovered from 17m (Site B) and 26m (Site F), respectively. The commonly used sewage contamination index ([5β-coprostanol]/([5α-cholestanol]+[5β-coprostanol])) exceeds 0.7 between 12 and 19m at Site B and between 24 and 26m at Site F, indicating input of human/livestock waste to these depths. Urine/fecal input within the same depth range is supported by groundwater Cl/Br mass ratios >1000 compared to Cl/Br <500 at depths >50m. Installed tube wells in the area's study sites may act as a conduit for DOC and specifically human/livestock waste into the aquifer during flood events. The depth range of maximum input of human/livestock waste indicated by these independent markers coincides with the highest dissolved Fe (10-20mg/L) and As (200-400μg/L) concentrations in groundwater at both sites. The new findings suggest that the oxidation of human/livestock waste coupled to the reductive dissolution of iron-(oxy)-hydroxides and/or arsenate may enhance groundwater contamination with As.
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Shallow, anoxic aquifers within the Ganges–Brahmaputra–Meghna Delta (GBMD) commonly contain elevated concentrations of arsenic (As), iron (Fe) and manganese (Mn). Highly enriched solid-phase concentrations of these elements have been observed within sediments lining the banks of the Meghna River. This zone has been described as a Natural Reactive Barrier (NRB). The impact of hydrological processes on NRB formation, such as transient river levels, which drive mixing between rivers and aquifers, is poorly understood. We evaluated the impact of groundwater flow dynamics on hydrobiogeochemical processes that led to the formation of an Fe- and Mn-rich NRB containing enriched As, within a riverbank aquifer along the Meghna River. The NRB dimensions were mapped using four complementary elemental analysis methods on sediment cores: XRF, aqua regia bulk extraction, HCl, and sodium phosphate leaching. It extended from 1.2 to 2.4 m in depth up to 15 m from the river’s edge. The accumulated As was advected to the NRB from offsite and released locally in response to mixing with aged river water. Nearly all of the As was subsequently deposited within the NRB before discharging to the Meghna. Significant FeII release to the aqueous phase was observed within the NRB. This indicates the NRB is a dynamic zone defined by the interplay between oxidative and reductive processes, causing the NRB to grow and recede in response to rapid and seasonal hydrologic processes. This implies that natural and artificially induced changes in river stages and groundwater-tables will impact where As accumulates and is released to aquifers.
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Widespread groundwater arsenic contamination in south, southwestern and northeastern regions and high salinity in the southwestern coastal region are the two major challenges for drinking water supply in Bangladesh. In this study, we assessed various water supply technologies used for mitigating arsenic and salinity in Laksam of Cumilla and Assasuni of Satkhira district. Water samples were analyzed for Arsenic, Iron, Chloride (indicator for salinity) and FC from different water extraction systems (shallow, deep and Tara tubewells), groundwater arsenic treatment units (SIDKO and READ-F), rainwater harvesting systems (RWH), pond sand filters (PSF), and managed aquifer recharge units. Most shallow tubewells, both in Laksam and Assasuni, have been found to produce arsenic contaminated water. But water from deep and Tara tubewells have been found arsenic-free, though high concentration of iron was observed in the wells in Laksam. Rainwater harvesting systems, PSF and MAR units in Assasuni have been found to provide water free from the common chemical contaminants but suffer from high bacterial contamination. Deep tubewell appear to be the most preferred option where a suitable aquifer is available. The community-scale groundwater treatment systems would require strong operation and maintenance support from the service providers to be successful.
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Groundwater supports agriculture and provides domestic water for over 250 million people in the Bengal Basin. Our analysis of stable water isotope ratios in rain, surface, and groundwater shows that the proportion of groundwater recharge originating from stagnant surface water bodies has increased by about 50% over the last seventy years while the relative contribution from direct infiltration of rain has decreased. This regional shift in the source of groundwater shows how the simultaneous expansion of irrigated rice, excavated ponds and groundwater pumping has changed the hydrologic system by cycling evaporated standing water through the subsurface. Analysis of water isotope data also reveals that most recharge from standing water enters during the latter part of the dry season (February-April), while most rainwater recharge occurs in the early months of the monsoon (June-August) before aquifers fill to capacity and reject additional recharge of rainwater.
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Access to clean water has been identified as one of the primary Sustainable Development Goals. Rapid urbanization is going on in developing nations creating additional pressure on water resources in most of these places which in turn also affects individuals which is largely reliant on proper sanitation and drinking water quality. In addition, open sanitation practice is becoming major public health problem in rural and in some urban areas in India. Groundwater contamination by pathogenic bacteria sourced from both sanitation system and surface water is becoming one of the major concerns now-a-days. The residents of the Ganges river basin in India are already stressed with natural arsenic pollution as well as other various types of water pollution, and microbial pollution from sanitation is a new addition to it. A field-based hydrogeological investigation with the identification of sanitation sites (surface and subsurface) was conducted in some parts of the Ganges basin, in and around a lower order distributary river, River Churni in West Bengal state, to identify the natural and human influences on sanitation drinking water pollution in a highly populated part of South Asia. Groundwater was found to be contaminated severely with total (TC) and fecal (FC) coliform bacteria. The abundance of TC was found to be the highest in monsoon season (78%) than in pre-monsoon (48%) and post-monsoon (29%) seasons. The results revealed that the groundwater samples from shallow depths and close to sanitation sites were highly contaminated with coliform bacteria than the deeper and higher distant (>30 m distance) ones. Shallow groundwater samples near to surface water (River Churni) source, other than sanitation sites, showed elevated TC levels. The occurrence of coliform bacteria in studied groundwater samples was observed to be positively correlated with conductivity, TDS, TOC, chloride, and sulfate, while the abundance was restricted by pH and temperature of groundwater. Thus, improper sanitation systems and contaminated surface water were identified as one of the major sources of pathogenic contamination of groundwater-sourced drinking water in the studied area, whereas improper human practices further complicate the scenario which needs to be managed properly.
Technical Report
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A systematic review of evidence on lags in water quality response to diffuse pollution control measures implemented in Scotland is reported. The review focused on key pollutants in catchments smaller than 300 km2 in temperate regions. Findings were evaluated based on catchment typologies (e.g. catchment size, precipitation, land use, pollutant residence time, and soil /waterbody type) and data/analyses (e.g. monitoring design and record length). There was no evidence supporting fixed timeframes for a water quality response to measures or catchment typology -based lags. Observed lags varied: 1-25 years for river pollutants and potentially longer than 20 years for groundwater nitrate. Long-term water quality and catchment data are key to quantifying lags. It is recommended to keep monitoring and adjust expectations by planning for longer-term lags.
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A microwave-enhanced acid digestion method that was integrated with inductively coupled plasma-atomic emission spectrometry was developed and validated for determining total, soluble, and precipitated sulfur in wastewater treatment sludges. The coefficient of variation of this method was less than 4.0%. The recovery of dosed sulfur from sludge samples was between 97.1% and 100.5%. The composition of sulfur in primary and waste-activated sludge (WAS) before and after anaerobic digestion at 35 and 55 degrees C was characterized by employing this developed method. There was not an apparent relationship between the precipitated sulfur and nonsoluble iron concentrations in sludges. Raw WAS had a more consistent organic sulfur fractionation because of its relatively homogeneous composition. The organic-sulfur-containing components (proteins) of WAS had reduced degradability as compared with that in primary sludge during anaerobic digestion. Digestion at 55 degrees C increased solubilization but not ultimate conversion of organic sulfur in sludge.
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Removal of model viruses by dune recharge was studied at a field site in the dune area of Castricum, Netherlands. Recharge water was dosed with bacteriophages MS2 and PRD1 for 11 days at a constant concentration in a 10- by 15-m compartment that was isolated in a recharge basin. Breakthrough was monitored for 120 days at six wells with their screens along a flow line. Concentrations of both phages were reduced about 3 log10 within the first 2.4 m and another 5 log10 in a linear fashion within the following 27 m. A model accounting for one-site kinetic attachment as well as first-order inactivation was employed to simulate the bacteriophage breakthrough curves. The major removal process was found to be attachment of the bacteriophages. Detachment was very slow. After passage of the pulse of dosed bacteriophages, there was a long tail whose slope corresponds to the inactivation rate coefficient of 0.07- 0.09 day21 for attached bacteriophages. The end of the rising and the start of the declining limbs of the
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Investigations of colloid movement through geologic materials are driven by a variety of issues, including contaminant transport, soil-profile development, and subsurface migration of pathogenic microorganisms. In this review, we address recent advances in understanding of colloid transport through partially saturated porous media. Special emphasis is placed on features of the vadose zone (i.e., the presence of air-water interfaces, rapid fluctuations in porewater flow rates and chemistry) that distinguish colloid transport in unsaturated media from colloid transport in saturated media. We examine experimental studies oncolloid deposition and mobilization and survey recent developments in modeling colloid transport and mass transfer. We conclude with an overview of directions for future research in this field.
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Millions of households throughout Bangladesh have been exposed to high levels of arsenic (As) causing various deadly diseases by drinking groundwater from shallow tubewells for the past 30 years. Well testing has been the most effective form of mitigation because it has induced massive switching from tubewells that are high (>50 µg/L) in As to neighboring wells that are low in As. A recent study has shown, however, that shallow low-As wells are more likely to be contaminated with the fecal indicator E. coli than shallow high-As wells, suggesting that well switching might lead to an increase in diarrheal disease. Approximately 60,000 episodes of childhood diarrhea were collected monthly by community health workers between 2000 and 2006 in 142 villages of Matlab, Bangladesh. In this cross-sectional study, associations between childhood diarrhea and As levels in tubewell water were evaluated using logistic regression models. Adjusting for wealth, population density, and flood control by multivariate logistic regression, the model indicates an 11% (95% confidence intervals (CIs) of 4-19%) increase in the likelihood of diarrhea in children drinking from shallow wells with 10-50 µg/L As compared to shallow wells with >50 µg/L As. The same model indicates a 26% (95%CI: 9-42%) increase in diarrhea for children drinking from shallow wells with ≤10 µg/L As compared to shallow wells with >50 µg/L As. Children drinking water from shallow low As wells had a higher prevalence of diarrhea than children drinking water from high As wells. This suggests that the health benefits of reducing As exposure may to some extent be countered by an increase in childhood diarrhea.
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To determine whether the installation of deep tube wells to reduce exposure to groundwater arsenic in rural Bangladesh had an effect on the incidence of childhood diarrhoeal disease. Episodes of diarrhoeal disease in children aged under 5 years that occurred on one specified day each month between 2005 and 2006 were reported to community health workers for six rural villages. A geographical information system containing details of household water use and sanitation in the villages was built using data obtained by a global positioning system survey. The information system also included health, spatial and demographic data. A field survey was carried out to determine whether households obtained drinking water from deep tube wells installed in 2005. The effect of deep tube well use on the incidence of childhood diarrhoea was assessed using a random effects negative binomial regression model. The risk of childhood diarrhoea was 46% lower in the 179 households that used a deep tube well than in the 364 that used a shallow tube well (P=0.032). Neither socioeconomic status, latrine density, population density nor study year had a significant influence on disease risk. The incidence of childhood diarrhoea declined dramatically between 2005 and 2006, irrespective of water source. The introduction of deep tube wells to reduce arsenic in drinking water in rural Bangladesh had the additional benefit of lowering the incidence of diarrhoea among young children.
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The health risks of As exposure due to the installation of millions of shallow tubewells in the Bengal Basin are known, but fecal contamination of shallow aquifers has not systematically been examined. This could be a source of concern in densely populated areas with poor sanitation because the hydraulic travel time from surface water bodies to shallow wells that are low in As was previously shown to be considerably shorter than for shallow wells that are high in As. In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli. On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall. The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge. The health implications of higher fecal contamination of shallow tubewells, to which millions of households in Bangladesh have switched in order to reduce their exposure to As, need to be evaluated.
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The origin of dissolved arsenic in the Ganges Delta has puzzled researchers ever since the report of widespread arsenic poisoning two decades ago. Today, microbially mediated oxidation of organic carbon is thought to drive the geochemical transformations that release arsenic from sediments, but the source of the organic carbon that fuels these processes remains controversial. At a typical site in Bangladesh, where groundwater-irrigated rice fields and constructed ponds are the main sources of groundwater recharge, we combine hydrologic and biogeochemical analyses to trace the origin of contaminated groundwater. Incubation experiments indicate that recharge from ponds contains biologically degradable organic carbon, whereas recharge from rice fields contains mainly recalcitrant organic carbon. Chemical and isotopic indicators as well as groundwater simulations suggest that recharge from ponds carries this degradable organic carbon into the shallow aquifer, and that groundwater flow, drawn by irrigation pumping, transports pond water to the depth where dissolved arsenic concentrations are greatest. Results also indicate that arsenic concentrations are low in groundwater originating from rice fields. Furthermore, solute composition in arsenic-contaminated water is consistent with that predicted using geochemical models of pond-water-aquifer-sediment interactions. We therefore suggest that the construction of ponds has influenced aquifer biogeochemistry, and that patterns of arsenic contamination in the shallow aquifer result from variations in the source of water, and the complex three-dimensional patterns of groundwater flow.
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Information about the microbial removal efficiencies of subsurface media is essential for assessing the risk of water contamination, estimating setback distances between disposal fields and receiving waters, and selecting suitable sites for wastewater reclamation. By analyzing published data from field experiments and large intact soil cores, an extensive database of microbial removal rates was established for a wide range of subsurface media. High microbial removal rates were found in volcanic soils, pumice sand, fine sand, and highly weathered aquifer rocks. Low removal rates were found in structured clayey soils, stony soils, coarse gravel aquifers, fractured rocks, and karst limestones. Removal rates were lower for enteroviruses than for other human viruses; for MS2 phage than for other phage species; for waste-associated microbes than for those cultivated in the laboratory; and for contaminated media than for uncontaminated media. Microbial removal rates are inversely correlated with infiltration rates and transport velocity. The assumption of first-order law, or a constant removal rate (when the transport scale reaches a representative elementary volume), is appropriate for most of field data analyzed. However 30% of the datasets (26 out of 87 pairs) are better described with the power law, implying reduced removal rates with transport distance. The latter is most prominent for organically contaminated media, especially in relatively fine aquifer media. The presence of organic matter, heterogeneity in microbial properties, change in solution chemistry, detachment, and physical straining, may have caused the discrepancies from the first-order law traditionally used in transport models for describing microbial removal.
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Small numbers of Cryptosporidium parvum oocysts can contaminate even treated drinking water, and ingestion of oocysts can cause diarrheal disease in normal as well as immunocompromised hosts. Since the number of organisms necessary to cause infection in humans is unknown, we performed a study to determine the infective dose of the parasite in healthy adults. After providing informed consent, 29 healthy volunteers without evidence of previous C. parvum infection, as determined by the absence of anti-cryptosporidium-specific antibodies, were given a single dose of 30 to 1 million C. parvum oocysts obtained from a calf. They were then monitored for oocyst excretion and clinical illness for eight weeks. Household contacts were monitored for secondary spread. Of the 16 subjects who received an intended dose of 300 or more oocysts, 14 (88 percent) became infected. After a dose of 30 oocysts, one of five subjects (20 percent) became infected, whereas at a dose of 1000 or more oocysts, seven of seven became infected. The median infective dose, calculated by linear regression, was 132 oocysts. Of the 18 subjects who excreted oocysts after the challenge dose, 11 had enteric symptoms and 7 (39 percent) had clinical cryptosporidiosis, consisting of diarrhea plus at least one other enteric symptom. All recovered, and there were no secondary cases of diarrhea among household contacts. In healthy adults with no serologic evidence of past infection with C. parvum, a low dose of C. parvum oocysts is sufficient to cause infection.
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We describe a new PCR-based method for distinguishing human and cow fecal contamination in coastal waters without culturing indicator organisms, and we show that the method can be used to track bacterial marker sequences in complex environments. We identified two human-specific genetic markers and five cow-specific genetic markers in fecal samples by amplifying 16S ribosomal DNA (rDNA) fragments from members of the genus Bifidobacterium and theBacteroides-Prevotella group and performing length heterogeneity PCR and terminal restriction fragment length polymorphism analyses. Host-specific patterns suggested that there are species composition differences in the Bifidobacterium andBacteroides-Prevotella populations of human and cow feces. The patterns were highly reproducible among different hosts belonging to the same species. Additionally, all host-specific genetic markers were detected in water samples collected from areas frequently contaminated with fecal pollution. Ease of detection and longer survival in water made Bacteroides-Prevotella indicators better than Bifidobacterium indicators. Fecal 16S rDNA sequences corresponding to our Bacteroides-Prevotellamarkers comprised closely related gene clusters, none of which exactly matched previously published Bacteroides orPrevotella sequences. Our method detected host-specific markers in water at pollutant concentrations of 2.8 × 10−5 to 2.8 × 10−7 g (dry weight) of feces/liter and 6.8 × 10−7 g (dry weight) of sewage/liter. Although our aim was to identify nonpoint sources of fecal contamination, the method described here should be widely applicable for monitoring spatial and temporal fluctuations in specific bacterial groups in natural environments.
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Public health protection requires an indicator of fecal pollution. It is not necessary to analyse drinking water for all pathogens. Escherichia coli is found in all mammal faeces at concentrations of 10 log 9(-1), but it does not multiply appreciably in the environment. In the 1890s, it was chosen as the biological indicator of water treatment safety. Because of method deficiencies, E. coli surrogates such as the 'fecal coliform' and total coliforms tests were developed and became part of drinking water regulations. With the advent of the Defined Substrate Technology in the late 1980s, it became possible to analyse drinking water directly for E. coli (and, simultaneously, total coliforms) inexpensively and simply. Accordingly, E. coli was re-inserted in the drinking water regulations. E. coli survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (temperature, microflora, etc.). Bacteria and viruses are approximately equally oxidant-sensitive, but parasites are less so. Under the conditions in distribution systems, E. coli will be much more long-lived. Therefore, under most circumstances it is possible to design a monitoring program that permits public health protection at a modest cost. Drinking water regulations currently require infrequent monitoring which may not adequately detect intermittent contamination events; however, it is cost-effective to markedly increase testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.
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