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Assessment of the impacts of pit latrines on groundwater quality in rural areas: A case study from Marondera district, Zimbabwe
Physics and Chemistry of the Earth 31 (2006) 779–788 www.elsevier.com/locate/pce
Assessment of the impacts of pit latrines on groundwater quality in rural areas: A case study from Marondera district, Zimbabwe Bloodless Dzwairo a
a,*
, Zvikomborero Hoko a, David Love
b,c
, Edward Guzha
d
Civil Engineering Department, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe b Geology Department, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe c WaterNet, P.O. Box MP600, Mount Pleasant, Harare, Zimbabwe d Mvuramanzi Trust, P.O. Box MR103, Marlborough, Harare, Zimbabwe
Abstract In resource-poor and low-population-density areas, on-site sanitation is preferred to off-site sanitation and groundwater is the main source of water for domestic uses. Groundwater pollution potential from on-site sanitation in such areas conflicts with Integrated Water Resources Management (IWRM) principles that advocate for sustainable use of water resources. Given the widespread use of groundwater for domestic purposes in rural areas, maintaining groundwater quality is a critical livelihood intervention. This study assessed impacts of pit latrines on groundwater quality in Kamangira village, Marondera district, Zimbabwe. Groundwater samples from 14 monitoring boreholes and 3 shallow wells were analysed during 6 sampling campaigns, from February 2005 to May 2005. Parameters analysed were total and faecal coliforms, NHþ 4 –N, NO3 –N, conductivity, turbidity and pH, both for boreholes and shallow wells. Total and faecal coliforms both ranged 0-TNTC (too-numerous-to-count), 78% of results meeting the 0 CFU/100 ml WHO guidelines value. NHþ 4 –N range was 0–2.0 mg/l, with 99% of results falling below the 1.5 mg/l WHO recommended value. NO 3 –N range was 0.0–6.7 mg/l, within 10 mg/l WHO guidelines value. The range for conductivity values was 46–370 lS/cm while the pH range was 6.8–7.9. There are no WHO guideline values for these two parameters. Turbidity ranged from 1 NTU to 45 NTU, 59% of results meeting the 5 NTU WHO guidelines limit. Depth from the ground surface to the water table for the period February 2005 to May 2005 was determined for all sampling points using a tape measure. The drop in water table averaged from 1.1 m to 1.9 m and these values were obtained by subtracting water table elevations from absolute ground surface elevation. Soil from the monitoring boreholes was classified as sandy. The soil infiltration layer was taken as the layer between the pit latrine bottom and the water table. It averaged from 1.3 m to 1.7 m above the water table for two latrines and 2–3.2 m below it for one pit latrine. A questionnaire survey revealed the prevalence of diarrhoea and structural failure of latrines. Results indicated that pit latrines were microbiologically impacting on groundwater quality up to 25 m lateral distance. Nitrogen values were of no immediate threat to health. The shallow water table increased pollution potential from pit latrines. Raised and lined pit latrines and other low-cost technologies should be considered to minimize potential of groundwater pollution. 2006 Elsevier Ltd. All rights reserved. Keywords: Groundwater quality; Groundwater pollution; Pit latrines; On-site sanitation; Infiltration layer; Sandy soil
1. Introduction Worldwide, water-borne diseases are a major cause of morbidity and mortality in humans (WHO, 1996). While *
Corresponding author. Tel.: +263 912 68640. E-mail addresses: [email protected], [email protected] Dzwairo).
(B.
1474-7065/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2006.08.031
water-borne pathogens infect around 250 million people per year, resulting in 10–20 million deaths (Anon, 1996), many of these infections occur in developing nations that have sanitation problems (Nsubuga et al., 2004). Lewis et al. (1980) also reiterate that diseases caused by pathogens and related to the use of contaminated groundwater, are the greatest cause of death in developing countries. In countries such as Zimbabwe and South Africa, most of
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the rural communities are poverty-stricken, lack access to portable water supplies and rely mainly on shallow wells, rivers, streams and ponds for their daily water needs (Nevondo and Cloete, 1999). In most cases water from these sources is used directly without treatment and the water sources may be faecally contaminated (WHO, 1993). Simple low-cost on-site sanitation methods have been developed to dispose faecal matter, mainly because of their economic advantage. However, the biggest drawback is the well-recognized potential to pollute groundwater resources (ARGOSS, 2001; Lewis et al., 1980), which conflicts with Integrated Water Resources Management principles, in particular to preserve the integrity of vital ecosystems and to maintain water quality and quantity. Given the widespread use of groundwater for domestic purposes in rural areas, maintaining groundwater quality is a critical livelihood intervention. Globally, the larger part of the population lives in rural areas and in Africa it is estimated that these people represent approximately 70–80% of the continent’s population. In Zimbabwe, according to figures derived from the Census 2002 Zimbabwe Preliminary Report (CSO, 2002), the rural population is about 70% (the derived figure is 68%), with that same percentage relying on groundwater (Chenje et al., 1998). The reliance may be higher in some districts as noted by Hoko (2005), where rural communities like Gokwe, Nkayi, Mwenezi and Lupane mainly use groundwater for domestic purposes with very little reliance on surface water. Yet there is an information gap on the levels of groundwater contamination from pit latrines (Chenje et al., 1998; Chidavaenzi et al., 2000). Therefore the quality of groundwater, which potentially can be affected by on-site sanitation systems, must be carefully assessed in order to reduce the health and environmental risks. This study was carried out in Kamangira village, Marondera district, Zimbabwe. As is the case with most rural communities in the country, the people of Kamangira village mainly use shallow wells as a source of domestic water and other purposes and pit latrines for sanitation. The geological setup and soil type in the area, compounded by a generally high water table, are thought to have caused several pit latrine failures such as cracking and sinking. According to Lewis et al. (1980), failure of on-site sanitation systems may result in serious pollution of groundwater, the primary cause for health concerns being the excreted pathogens and certain chemical constituents like nitrate. The study assessed impacts of pit latrines on groundwater quality, taking levels of total and faecal coliforms, ammonium ðNHþ 4 –NÞ, nitrate ðNO3 –NÞ, conductivity, turbidity and pH as impact indicators. The parameters were chosen because a wide range of studies internationally have demonstrated that they are problematic with regards to onsite sanitation. Some of the parameters also tend to have an effect on the perceived water quality and health. A disease incidence survey was carried out in order to assess the possible health impacts of groundwater pollution. The overall
aim of the study is to contribute towards the improvement of safe water supply and sanitation. 2. Study area Kamangira village is in Chihota rural area, Marondera district, in Zimbabwe and the district’s geographical location is shown in Fig. 1. The village has a population of about 100 people. The peak of the rain period is December to February, while June–September is the dry period, with very isolated rainy days in June and August. The predominant form of sanitation is pit latrines. The main source of domestic water is shallow wells. The geology of Chihota rural area is truncated by numerous faults, of which two major sets are outstanding namely, the north/ north-east and north-east trending sets. These faults tend to have a major influence on the drainage of the area (Mukandi, 2005). Intrusive features like dykes enhance the groundwater potential, by creating confined aquifers (Maziti, 2002). At a localized scale, Kamangira village is covered with granitic rocks while the soils are generally sandy resulting in high transmission of water. 3. Materials and methods 3.1. Study design Fig. 2 presents the study site design. The study site was situated on a watershed, which meant that the experimental setup could exclude flow of groundwater from outside this site as direction of groundwater flow would most likely follow ground slope. Pit latrines under investigation were named PL1, PL2 and PL3, and the shallow wells close to those latrines were named SW1, SW2, and SW3, respectively. Shallow well number 1 (SW1) was located 44 m
Fig. 1. Location map of study area (Kamangira village) in Marondera district, Zimbabwe.
B. Dzwairo et al. / Physics and Chemistry of the Earth 31 (2006) 779–788 TW10
SW2 SW2
N
7990560
TW9
TW8 TW7 PL2 TW6
7990540
7990520 TW13
PL2
CONTROL
TW5
PL3
TW12 7990500 PL3 TW11
TW4 TW3
7990480
PL1
TW2
SW3
7990460SW3
781
SW1
PL1 TW1
SW1 300660 300680 300700 300720 300740 300760 300780 300800 300820 300840
KEY
∗
Monitoring borehole Pit latrine Shallow well Absolute ground level elevation (m)
Fig. 2. Study design. PL is pit latrine, SW is shallow well, TW is monitoring borehole, Control is control borehole. X-axis is eastings and Y-axis is northings, both in Universal Transverse Mercaptor (UTM).
south-east of pit latrine (PL1), SW2 at 38 m north of PL2, and SW3 was located 44 m south of PL3. The positions of pit latrines within the study site defined a transect (for example PL1 to PL2) and impacts on groundwater quality were investigated along this transect or for individual pit latrines. A total of 14 monitoring boreholes were drilled upstream and downstream of pit latrines, at positions shown in Fig. 2, using a manual drilling rig called a Vonder rig. The boreholes were cased using perforated 125 mm PVC pipes. The control borehole was located 80 m north-east of PL1 and 100 m east of PL2. The position of the control was determined in order to minimize influence of the nearest pit latrine or other topographical structures that would influence any of the other characteristics under investigation. At this position there was no evidence of settlements, farming or animal pens that could influence results. The control borehole was also cased in the same manner as the other monitoring boreholes. 3.2. Sampling and analysis methods Six sampling campaigns, corresponding to six data sets, were made from February 2005 to May 2005, covering the rainy season. Boreholes were flushed once before commencement of the sampling campaign. Subsequent flushing at every sampling event could not be done because some of the parameters which were to be tested for were sensitive to water disturbances. Furthermore, the perforation of the casing was assumed to allow free through-flow of groundwater. Groundwater samples were collected at the water
surface from the monitoring boreholes and the shallow wells. Brickwork and heavy concrete slabs protected the boreholes and the casings were opened only for sampling purposes. Water quality and water table elevation data was plotted on clustered column and line graphs, respectively, using Microsoft Excel. Results (individual values) were compared to WHO guidelines for drinking water (WHO, 2004). Ground elevation was krieged on Surfer 7 software. 3.2.1. Water and soil tests For coliforms, microbiological tests were performed on duplicate 50 ml samples, after filtering the sample portions through individual 0.45 lm membrane filter papers, as stipulated in the Membrane Filter Technique for members of the coliform group method number 9222 (APHA, 1989). NHþ 4 –N was determined as described in method number 4500-NH3 F while NO 3 –N was determined according to the Ultraviolet Spectrophotometric Screening Method number 4500 NO 3 B (APHA, 1989). Conductivity was determined using a WTW model Cond 340i test kit. Turbidity was measured using a HACH 2100 N turbidity kit. A WTW microprocessor pH/ion meter model pMX 3000 was used for pH measurement. The sieve test was performed on soil samples collected, at varying depths during monitoring boreholes drilling, for soil characterization. The analysis was performed on a series of B.S. sieves nested as follows: 19 mm, 9.5 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 lm, 300 lm, 150 lm and 75 lm. Permeability was calculated from the obtained sieve analysis data.
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Fig. 3 highlights the relationships between pit base and water table elevations along transect 1. Considering boreholes close to PL1 (TW1 and TW2), the base of the pit latrine was generally above the water tables of TW1 and TW2 throughout the sampling period. It ranged 0.2–1.2 m above water tables for TW1 and 0.6– 1.8 m above those for TW2. These ranges gave an average soil infiltration layer range of 0.4–1.5 m above the water table. The infiltration layer is the soil layer between the bottom or base of the pit latrine and the water table in a case where the water table is below the pit latrine base. PL2 sat on and below the water table throughout the study. It ranged 0.9 m below the water table to 0.2 m above the water table for TW6. PL2 base was 1.7–0.6 m below the water table for TW7. Along transect 2 in Fig. 4, PL3 base sat below the water table throughout the study, ranging from 3.2 m to 1.2 m and 3.1 m to 1.2 m below the water tables for TW11 and TW12, respectively. The fact that there was little or no soil infiltration layer between the pit latrine base and the water table meant that effluent was seeping into and contaminating the groundwater. A review of typical case studies done by Lewis et al. (1980) shows that water quality tends to depend on the depth of the soil infiltration layer allowed between the pit base and the water table.
3.2.2. Disease incidence Incidences of water-borne diseases in the study area were investigated by conducting a survey in Kamangira village. Direct interviews were held using semi-structured questionnaires. A total of 38 people representing 38 homesteads were interviewed, including the 3 homesteads that comprised the study site. Information gathered included sources of water for domestic purposes, protection of the water source, relative distances between sanitary structures and domestic water sources, awareness of potential water contamination from pit latrines, and the most common water related diseases that affected the villagers. Results from the survey were used to make preliminary inferences of health impacts of groundwater pollution and contamination by pit latrines. 4. Results and discussion 4.1. Groundwater flow and water table Transect 1 comprised PL1, PL2 and the boreholes TW1 to TW10, while transect 2 comprised PL3 and TW11 to TW13. From the water levels of groundwater in the monitoring boreholes, flow along the transects was assumed as follows: For transect 1 the flow was from TW1 towards TW4, from TW7 towards TW4 and from TW7 towards TW10. In terms of groundwater flow, monitoring boreholes TW1 and TW7 were upstream in relation to pit latrine positions while TW2 and TW6 were downstream boreholes. For transect 2, flow was assumed to be from TW11 towards TW13, with TW11 being upstream and TW12 and TW13 being the downstream boreholes of pit latrine (PL3). The contour map in Fig. 2 and the water table elevations as in Fig. 3 indicated that there was a depression around TW4.
4.2. Soil characterization Soil characterization was done and results showed that the soils were generally sandy and collapsible. Soil permeability ranged from 0.02 to 2.7 m d1, which was within the range of 0.01–2.8 m d1 as noted by (Wright, 1992) for a crystalline basement. Permeability values for soils around PL1 and PL2 were found to be lower than those for soils
Groundlevel 21-Feb 21-Mar 18-Apr PL1
1426.5
just after drilling 7-Mar 4-Apr 5-May PL2
Elevation (m)
1425.5
1424.5
tw9
tw8
tw10
Sampling points
tw7
tw6
tw5
tw4
tw3
tw2
1422.5
tw1
1423.5
Fig. 3. Water table elevations for boreholes TW1–TW10 on transect 1 plotted in relation to pit base elevations for PL1 and PL2.
1426
Ground level 7-Mar 18-Apr
just after drilling 21-Mar 5-May
21-Feb 4-Apr PL3
1425
pH
1423
Sampling points
EC
Fig. 4. Water table elevations for monitoring boreholes 11–13 on transect 2.
0–0.2 (0.0 ± 0.1) 0–0.8 (0.1 ± 0.3) 0–0 0–2 (0.3 ± 0.8) 0–0.6 (0.1 ± 0.3) 0–0 0–0 0–0 0–0 0–0.3 (0.0 ± 0.1) 0–0 0.6–1.2 (0.8 ± 0.2) 0–0.3 (0 ± 0.1) 0–1.4 (0.2 ± 0.6) 0–0 0–0 0–0 0–0 0–880 (147 ± 359) 0–3000 (633 ± 1191) 0–200 (33 ± 82) 0–0 0–0 0–1880 (438 ± 767) 0–0 0–1080 (251 ± 431) 0–0 0–0 0–0 0–0 0–0 80–1900 (708 ± 706) 58–690 (479 ± 286) 90–1800 (817 ± 847) TW1 TW2 TW3 TW4 TW5 TW6 TW7 TW8 TW9 TW10 TW11 TW12 TW13 Control SW1 SW2 SW3
0–0 0–34 (6 ± 14) 0–3000 (541 ± 1206) 0–0 0–0 0–0 0–38 (6 ± 16) 0–0 0–33 (6 ± 14) 0–0 0–0 0–0 0–0 0–0 4–488 (165 ± 196) 12–98 (54 ± 49) 2–820 (242 ± 348)
NHþ 4 FC TC Sampling point
Parameters with statistical analysis (range, average and standard deviation) for n = 6a
Table 1 Groundwater analysis results for the six sampling campaigns
For the parameters total coliforms (TC), faecal coliforms (FC), nitrate–nitrogen, ammonium–nitrogen, conductivity, turbidity and pH, results are presented for all the 17 sampling points in Table 1. The results show wide variation for all sampling points for all the sampling dates as the sampling period progressed. Total and faecal coliforms both ranged 0-TNTC (toonumerous-to-count) where a value of 3000 CFU was assigned for TNTC for statistical purposes, with 78% of the total results meeting the 0 CFU/100 ml WHO guidelines value. Table 1 summarises the ranges, averages and standard deviations at each sampling point for the six sampling campaigns. The shallow wells were located 38–44 m away from the nearest pit latrines, thereby placing them outside the pit latrines’ radii of influence of 30 m as generally accepted in Zimbabwe (Morgan, 2001). All of them were partially protected and they indicated elevated levels of both total and faecal coliforms. This could be due to water withdrawal and hygienic practices around the water points which could have caused the introduction of coliforms by the users. Shallow wells SW1 and SW3 served more people (5 and 7, respectively) than SW2 (3 people), resulting in a higher demand on the former two shallow wells, with consequential soil re-suspension and a higher potential for microbiological contamination due to frequent use. Variations of coliform counts are presented graphically in Figs. 5 and 6. WHO guidelines value of 0 CFU/100 ml was not met in 100% of total and faecal coliform results obtained for the shallow wells. The results obtained for some boreholes located within a 5 m radius of the pit latrines indicate that a
NO 3
4.3. Coliforms
2.5–3.2 (2.9 ± 0.4) 0–0.5 (0.2 ± 0.2) 0–0.2 (0.1 ± 0.1) 1.2–6.7 (2.6 ± 2.1) 0.4–0.5 (0.5 ± 0) 0.2–0.3 (0.3 ± 0.1) 2.2–5.6 (3.4 ± 1.2) 1.1–3.2 (2 ± 0.9) 0.3–0.8 (0.5 ± 0.2) 0.4–1.6 (1 ± 0.5) 0.9–1.3 (1.2 ± 0.2) 0–0.7 (0.2 ± 0.3) 1.6–2.2 (1.9 ± 0.2) 1.8–2.2 (2 ± 0.2) 0.7–3 (1.4 ± 0.9) 0–0.1 (0.1 ± 0) 3.4–3.9 (3.6 ± 0.3)
around PL3. Permeability affects the movement of water and pollutants in the ground.
TC = total coliforms, FC = faecal coliforms, NHþ 4 ¼ ammonium–nitrogen, NO3 ¼ nitrate–nitrogen, EC = conductivity.
tw13
tw12
1419
tw11
1420
a
Turbidity
1421
4–17 (10 ± 4) 2–20 (6 ± 7) 2–28 (8 ± 10) 1–2 (2 ± 0.5) 1–4 (2 ± 1) 1–8 (3 ± 3) 1–3 (1 ± 0.8) 2–3 (3 ± 0.8) 2–9 (5 ± 3) 10–24 (17 ± 5) 4–24 (9 ± 8) 8–45 (20 ± 14) 4–33 (14 ± 11) 1–4 (2 ± 1) 20–36 (27 ± 6) 2–7 (5 ± 2) 3–35 (11 ± 14)
1422
76–197 (108 ± 45) 88–222 (115 ± 53) 113–260 (153 ± 54) 96–357 (147 ± 104) 95–168 (111 ± 28) 91–228 (122 ± 53) 100–235 (127 ± 53) 100–218 (132 ± 43) 106–151 (121 ± 16) 136–370 (210 ± 85) 144–233 (161 ± 36) 169–269 (190 ± 39) 94–154 (106 ± 24) 88–139 (98 ± 20) 46–62 (52 ± 7) 49–62 (54 ± 6) 89–98 (94 ± 4)
Elevation (m)
1424
783
7.1–7.6 (7.3 ± 0.1) 7.0–7.4 (7.3 ± 0.1) 6.96–7.65 (7.3 ± 0.2) 6.92–7.3 (7.2 ± 0.1) 7.3–7.7 (7.4 ± 0.1) 7.1–7.6 (7.3 ± 0.2) 6.76–7.4 (7.2 ± 0.2) 7.2–7.7 (7.3 ± 0.2) 7.4–7.7 (7.6 ± 0.1) 7.5–7.9 (7.7 ± 0.1) 7.0–7.7 (7.5 ± 0.3) 7.2–7.9 (7.7 ± 0.2) 6.8–7.8 (7.5 ± 0.4) 7.2–7.4 (7.3 ± 0.1) 6.8–7.6 (7.0 ± 0.3) 7.0–7.1 (7.0 ± 0.1) 7.0–7.3 (7.1 ± 0.1)
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2016 1816
PL1
PL2
PL3
CFU/100mL
1616 1416
21-Feb 21-Feb
7-Mar 7-Mar
1216
21-Mar 21-Mar
4-Apr 4-Apr
1016
18-Apr 18-Apr
5-May 5-May
816 616 416 216
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
16
Fig. 5. Total coliform variation among the sampling points, showing pit latrine (PL) locations in relation to monitoring boreholes.
900 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
800 700
CFU/100mL
600 500 400 300 200 100
sw3
sw2
sw1
tw13
tw12
control
Sampling points
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
0
Fig. 6. Faecal coliform variation among the sampling points.
pit latrine can influence up to 5 m of its radius. Beyond 5 m the faecal coliforms were greatly reduced. Borehole TW10 did not show indications of impacts from the old and collapsed pit latrine located some 5 m away from that borehole in terms of coliforms. The presence of faecal coliform bacteria in some samples indicated that the water had been contaminated with the faecal material of man or other animals and therefore there was a risk of contamination of water by pathogens or disease producing bacteria or viruses. 4.4. Ammonium–nitrogen Ammonium–nitrogen range was 0–2.0 mg/l for all sampling points, with 99% of total results falling within 1.5 mg/ l WHO recommended value. Ranges, average values and
standard deviations are presented in Table 1 for all sampling points during the six sampling campaigns. According to WHO (2004), the threshold odour concentration of ammonia at alkaline pH is approximately 1.5 mg/l, and a taste threshold of 35 mg/l has been proposed for the ammonium cation ðNHþ 4 Þ. Ammonium–nitrogen persisted in samples from TW12 as indicated in Fig. 7. This could have been because that monitoring borehole was located downstream of PL3, whose pit base was below the water table throughout the study period. Because ammonia gas dissolves completely and dissociates into ammonium ions in water, they would travel together with the groundwater towards downstream sampling points. Ammonium usually occurs in drinking water at concentrations well below those at which toxic effects may occur. The collapsed and disused pit latrine could have affected the results of TW10. Ammo-
B. Dzwairo et al. / Physics and Chemistry of the Earth 31 (2006) 779–788
785
2.50 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
+
NH4 -N (mgN/L)
2.00
1.50
1.00
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
0.00
tw1
0.50
Fig. 7. Ammonium–nitrogen variation among sampling points.
8.0 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
7.0
NO3- -N (mg/L)
6.0 5.0 4.0 3.0 2.0 1.0
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
0.0
Fig. 8. Nitrate–nitrogen variation among sampling points.
nium is not of direct relevance to health at levels generally detected in groundwater, and no health-based guideline value has been proposed. 4.5. Nitrate–nitrogen Nitrate–nitrogen for all sampling points ranged from 0.0 to 6.7 mg/l and this was within the 10 mg/l WHO guidelines value. Ranges, average values and standard deviations are also presented in Table 1. Nitrate ions, just like the ammonium ions, dissolve and travel within and with the groundwater towards downstream sampling points, as noted at the depression at TW4 in Fig. 8. The collapsed and disused pit latrine did not affect the results of TW10. High levels of nitrate–nitrogen are directly associated with methaemoglobinaemia, or ‘‘blue baby syndrome’’, an acute condition which is most frequently found among bottle-fed
infants of less than three months of age. Nitrates have been suggested as causing methaemoglobinaemia and also as possible carcinogens by a number of researchers (Johns and Lawrence, 1973; Lewis et al., 1980; WHO, 1993). Cave and Kolsky (1999) has also confirmed that nitrate can be used as a crude indicator of faecal pollution where microbiological data are unavailable. 4.6. Conductivity Conductivity ranged 46–370 lS/cm for all sampling points as indicated in Fig. 9. Individual sampling point values are presented in Table 1 together with the averages and standard deviations. There are no WHO guideline values for conductivity. On transect 1 involving TW1 up to TW10, conductivity rose from TW1 towards TW4 and peaked at a location 25 m away (TW4) before it dropped
B. Dzwairo et al. / Physics and Chemistry of the Earth 31 (2006) 779–788
total results, 59% met the 5 NTU WHO guidelines limit. Turbidity had a decreasing trend from TW1 to TW7 and increased along transect 1, with a peak at TW10. The high turbidity at TW10 could be as a result of loose soil from the collapse of the disused pit latrine near that borehole. Since soil acts as a filter, turbidity decrease towards the depression at TW4 was expected. Transect 2 turbidity values were generally much higher than those for transect 1 possibly because of direct injection of colloidal suspended solids from the pit latrines. High turbidity values were also recorded for the shallow wells SW1 and SW3 and this could be due to soil disturbance and resuspension within the well during water withdrawal. The depth of the shallow wells, and in particular, the depth of the water level above the well bottom may affect the turbidity. In this study, the deepest well was SW3 and the shallowest was SW2. The water levels also showed the same trend for all sampling dates. The turbidity values though were highest at SW1 and lowest at SW2, and this could be due to the fact that the base of SW2 was covered by a large boulder, making the soil intact, whereas the soil in SW1 and SW3 was loose. The control borehole recorded very low values for turbidity. Turbidity affects water aesthetics.
sw3
7-Mar 4-Apr 5-May
sw1
tw13
Sampling points
control
tw12
tw11
tw9
tw10
tw8
tw7
tw6
Fig. 9. Conductivity variation among sampling points.
gradually towards PL2. It also rose gradually from TW7 towards TW10, which was located 45 m away from TW7. Transect 2 involving TW11 to TW13, showed that conductivity was lower at TW11, which was located 5 m upstream of PL3 than at TW12, which was located 5 m downstream of that pit latrine. Conductivity is a measure of dissolved ions and their behaviour is also similar to that of ammonium and nitrate ions, concentrating at lower points within the study area. The high levels of ammonium at TW12 could possibly explain the high conductivity at TW12 if the chemical composition of the geology is the same. Conductivity dropped significantly at a distance 15 m downstream of PL3 to values almost similar to those for the control borehole. The concentration of ions at TW4, TW10 and TW12 could be due to impacts of PL1, PL2 and PL3 as well as the collapsed pit latrine 5 m away from TW10. The low values for the shallow wells indicated that there were no impacts from within the vicinity of the shallow wells.
4.8. pH The pH ranged 6.8–7.9 for both shallow wells and boreholes as indicated in Fig. 11. Values recorded for boreholes along transect 1 were relatively close to those for the control, although they peaked at TW10. Table 1 presents the variation per sampling point as the sampling campaign progressed. The values are given as range, average and standard deviation. Transect 2 pH values started relatively low for TW11 located 5 m upstream of the pit latrine, PL3, and peaked at TW12 that is 5 m downstream, before dropping noticeably at TW13 located 15 m downstream of PL3. The presence of ammonium-nitrogen at TW12 could have caused the elevated pH levels at borehole TW12. Ammo-
4.7. Turbidity Turbidity ranged 1–45 NTU when all sampling points were considered. Table 1 presents the results for individual sampling points as range, average and standard deviation to allow for comparison in parameter variation throughout the sampling campaign. Fig. 10 presents the results for all points during the whole six sampling runs. Of the
50.0 45.0
21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
35.0 30.0 25.0 20.0 15.0 10.0 5.0
Sampling points
Fig. 10. Turbidity variation among sampling points.
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw8
tw7
tw6
tw5
tw4
tw3
tw2
0.0 tw1
Turbidity (NTU)
40.0
tw9
tw5
tw4
tw3
tw2
200.0 150.0 100.0 50.0
21-Feb 21-Mar 18-Apr
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7. 9
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pH
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tw 13
tw 12
tw 11
tw 10
tw 9
tw 8
tw 7
tw 6
tw 5
tw 4
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Fig. 11. pH variation among sampling points.
nium–nitrogen presence makes the environment alkaline, thereby raising pH. Shallow wells recorded much lower pH values. They also recorded lower values of nitrogen as compared to the monitoring boreholes especially those downstream of the pit latrines. This suggests that pH variation could be linked to nitrogen possibly coming from the pit latrines. 4.9. Questionnaire survey A total of 38 villagers from different homesteads were interviewed, and the figure translated to 38% of the population of Kamangira village. Of the respondents who owned a pit latrine, 45% of them were unusable because they were dilapidated and unsafe (according to sentiments passed by the respondents during the interviews) or they were now too full to be used hygienically. Some 42% of the respondents did not have a water point within the homestead. This percentage is quite typical of rural communities in the third world countries where half the population remain unserved, with water and sanitation facilities of acceptable quality and standard according to WHO/ UNICEF (2004). Diarrhoea was widespread, with those having suffered from it making up 50% of the interviewed number for the sampling period, which covered most of the rainy season. Those who did not own a water point and also suffered from diarrhoea constituted 24% of the respondents. There was no incidence of health impacts from nitrate, as depicted by 0% reported occurrence of ‘‘blue-baby’’ syndrome, whose symptoms had been explained to the villagers by the interviewer during the interviews. Preference of eco-san, which is a form of on-site sanitation, was at 37% of the respondents, although 100% of them cited lack of adequate financial resources as the major drawback. Seven 50 kg cement bags are required to build the structure, apart from the labour and brick requirements according to a local Non-Governmental Organisation, which was implementing eco-san in the district.
5. Conclusions 1. Total and faecal coliforms were found to be impacting negatively on groundwater quality. Samples, from monitoring boreholes and shallow wells that gave the 0 CFU/100 ml limit, represented 78% of the total results. According to WHO guidelines (2004), 100% of the results should have a value of 0 CFU/100 ml in order for that water to be considered safe for human consumption. 2. Ammonium and nitrate were found to be impacting on the groundwater quality while there was a possibility that pit latrines were a source of nitrogen. However, their levels were not yet of health concern according to WHO guidelines. 3. Although there is no WHO guideline value for conductivity (a parameter that quantifies the concentration of dissolved solids), results obtained showed a similar trend to the other dissolved ions under investigation, that is, nitrate and ammonium. 4. Turbidity of the water was above the limit of 1.5 NTU for 41% of the results, making it aesthetically unpleasant for domestic purposes. Pit latrine excavations and subsequent loosening of the soil matrix could be the cause of these high turbidity values. 5. The sandy nature of the soils in the study site, compounded by the high water table, renders the area unsuitable for pit latrine construction. This could be the cause of the structural failures observed. 6. Generally, it may be risky to abstract water from within 25 m lateral distance of an unlined pit latrine within the study area and also possibly in an area with similar soil and water table characteristics, according to the water quality parameters investigated.
6. Recommendations • The economics and logistics of low-cost sanitation schemes are such as to preclude the routine use of costly
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hydrogeological field investigations therefore critical parameters like depth of the infiltration layer and direction of groundwater flow could be used during assessment of impacts of pit latrines on groundwater quality. • Raised or lined pit latrines and other low-cost technologies could be considered as alternatives to unlined pit latrines, because they minimize the risk of releasing pit latrine effluent flow across the thin infiltration layer. • An integrated approach involving geotechnology, hydrogeology and groundwater pollution could be considered as a way forward in efforts to solve the sanitation problems, in view of potential groundwater pollution and structural failures within the larger Kamangira village. The results obtained from the study are true for the study area but could also apply to areas with similar soil, geology and rainfall patterns.
Acknowledgements This paper contains research results from a M.Sc. project by B. Dzwairo at the University of Zimbabwe. It was funded by a scholarship awarded to B. Dzwairo by WaterNet and a research grant from Mvuramanzi Trust. The Departments of Civil Engineering and Geology at the University of Zimbabwe, the people of Kamangira village and the Institute of Water and Sanitation Development are acknowledged for logistical, material and moral support. The Water Research Fund for Southern Africa (WARFSA) is acknowledged for facilitating the presentation of this paper at the 6th WARFSA/WaterNet/GWP-SA annual symposium that was held in Swaziland in November 2006. References Anon, J., 1996. World Water Environmental Engineering. Cambridge University Press, Cambridge, United Kingdom. APHA (American Public Health Association), 1989. Standard Methods for the Examination of Water and Wastewater, 17th ed. APHA, Washington, DC, United States of America. ARGOSS, 2001. Guidelines for assessing the risk to groundwater from on-site sanitation.British Geological Survey Commissioned Report, CR/01/142. United Kingdom, pp. 97.
Cave, B., Kolsky, P., 1999. Groundwater, latrines and health. WELL Study Task No: 163. London School of Hygiene & Tropical Medicine, WEDC, Loughborough University, United Kingdom. CSO (Central Statistical Office), 2002. Census 2002. Zimbabwe Preliminary Report. Government Printers, Zimbabwe. Chenje, M., Sola, L., Paleczny, D. (Eds.), 1998. The State of Zimbabwe’s Environment, 1998. Government of the Republic of Zimbabwe, Ministry of Mines, Environment and Tourism, Harare, Zimbabwe. Chidavaenzi, M., Bradley, M., Jere, M., Nhandara, C., 2000. Pit Latrine effluent infiltration into groundwater: The Epworth case study. Schriftener Ver Wasser Boden Lufthyg 105, 179–185. Hoko, Z., 2005. An assessment of water quality of drinking water in rural districts in Zimbabwe. The case of Gokwe South, Nkayi, Lupane and Mwenezi districts. Physics and Chemistry of the Earth 30 (11–16), 859– 866. Johns, M.W., Lawrence, C.R., 1973. Nitrate-rich groundwater in Australia: A possible cause of methaemoglobinaemia in infants. The Medical Journal of Australia 2, 925–927. Lewis, J.W., Foster, S.D., Draser B.S., 1980. The risk of groundwater pollution by on-site sanitation in developing countries, a literature review. International Reference Centre for Wastes Disposal (IRCWD) Report No. 01/82, Duebendorf, Switzerland. Maziti, A., 2002. Groundwater occurrence and development potential for lineament orientations of crystalline rock aquifers of Gutu-Buhera area. M.Sc.Thesis, University of Zimbabwe, Harare, Zimbabwe. Morgan, P., 2001. Ecological sanitation in Zimbabwe. A compilation of manuals and experiences, Vol. II. Zimbabwe. Mukandi, M.A., 2005. The geology of a portion of Seke-Chihota Communal Lands (Based on Landsat and SPOT Image Interpretation). Zimbabwe Geological Survey, Harare, Zimbabwe. Nevondo, T.S., Cloete, T.E., 1999. Bacterial and chemical quality of water supply in the Dertig village settlement. Water SA 25 (2), 215–220. Nsubuga, F.B., Kansiime, F., Okot-Okumu, J., 2004. Pollution of protected springs in relation to high and low density settlements in Kampala – Uganda. Physics and Chemistry of the Earth 29, 1153– 1159. WHO (World Health Organisation), 1993. Guidelines for drinking water quality. Recommendations, Vol. 1, second ed. World Health Organisation, Geneva, Switzerland. WHO (World Health Organisation), 1996. Guidelines for drinking water quality, second ed. Health and Supporting Criteria, Vol. 2, World Health Organisation, Geneva, Switzerland. WHO (World Health Organisation), 2004. Guidelines for Drinking-Water Quality, Vol. 1, third ed. World Health Organisation, Geneva, Switzerland. WHO/UNICEF (World Health Organisation/ United Nations Children’s Educational Fund), 2004. Joint Monitoring Programme for Water Supply and Sanitation; Meeting the MDG drinking water and sanitation target: a mid-term assessment of progress. Geneva, Switzerland. Wright, E.P., 1992. The hydrogeology of crystalline basement aquifers in Africa. Geology Society Special Publication Number 66. pp. 1–27.
Assessment of the impacts of pit latrines on groundwater quality in rural areas: A case study from Marondera district, Zimbabwe Bloodless Dzwairo a
a,*
, Zvikomborero Hoko a, David Love
b,c
, Edward Guzha
d
Civil Engineering Department, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe b Geology Department, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe c WaterNet, P.O. Box MP600, Mount Pleasant, Harare, Zimbabwe d Mvuramanzi Trust, P.O. Box MR103, Marlborough, Harare, Zimbabwe
Abstract In resource-poor and low-population-density areas, on-site sanitation is preferred to off-site sanitation and groundwater is the main source of water for domestic uses. Groundwater pollution potential from on-site sanitation in such areas conflicts with Integrated Water Resources Management (IWRM) principles that advocate for sustainable use of water resources. Given the widespread use of groundwater for domestic purposes in rural areas, maintaining groundwater quality is a critical livelihood intervention. This study assessed impacts of pit latrines on groundwater quality in Kamangira village, Marondera district, Zimbabwe. Groundwater samples from 14 monitoring boreholes and 3 shallow wells were analysed during 6 sampling campaigns, from February 2005 to May 2005. Parameters analysed were total and faecal coliforms, NHþ 4 –N, NO3 –N, conductivity, turbidity and pH, both for boreholes and shallow wells. Total and faecal coliforms both ranged 0-TNTC (too-numerous-to-count), 78% of results meeting the 0 CFU/100 ml WHO guidelines value. NHþ 4 –N range was 0–2.0 mg/l, with 99% of results falling below the 1.5 mg/l WHO recommended value. NO 3 –N range was 0.0–6.7 mg/l, within 10 mg/l WHO guidelines value. The range for conductivity values was 46–370 lS/cm while the pH range was 6.8–7.9. There are no WHO guideline values for these two parameters. Turbidity ranged from 1 NTU to 45 NTU, 59% of results meeting the 5 NTU WHO guidelines limit. Depth from the ground surface to the water table for the period February 2005 to May 2005 was determined for all sampling points using a tape measure. The drop in water table averaged from 1.1 m to 1.9 m and these values were obtained by subtracting water table elevations from absolute ground surface elevation. Soil from the monitoring boreholes was classified as sandy. The soil infiltration layer was taken as the layer between the pit latrine bottom and the water table. It averaged from 1.3 m to 1.7 m above the water table for two latrines and 2–3.2 m below it for one pit latrine. A questionnaire survey revealed the prevalence of diarrhoea and structural failure of latrines. Results indicated that pit latrines were microbiologically impacting on groundwater quality up to 25 m lateral distance. Nitrogen values were of no immediate threat to health. The shallow water table increased pollution potential from pit latrines. Raised and lined pit latrines and other low-cost technologies should be considered to minimize potential of groundwater pollution. 2006 Elsevier Ltd. All rights reserved. Keywords: Groundwater quality; Groundwater pollution; Pit latrines; On-site sanitation; Infiltration layer; Sandy soil
1. Introduction Worldwide, water-borne diseases are a major cause of morbidity and mortality in humans (WHO, 1996). While *
Corresponding author. Tel.: +263 912 68640. E-mail addresses: [email protected], [email protected] Dzwairo).
(B.
1474-7065/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2006.08.031
water-borne pathogens infect around 250 million people per year, resulting in 10–20 million deaths (Anon, 1996), many of these infections occur in developing nations that have sanitation problems (Nsubuga et al., 2004). Lewis et al. (1980) also reiterate that diseases caused by pathogens and related to the use of contaminated groundwater, are the greatest cause of death in developing countries. In countries such as Zimbabwe and South Africa, most of
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the rural communities are poverty-stricken, lack access to portable water supplies and rely mainly on shallow wells, rivers, streams and ponds for their daily water needs (Nevondo and Cloete, 1999). In most cases water from these sources is used directly without treatment and the water sources may be faecally contaminated (WHO, 1993). Simple low-cost on-site sanitation methods have been developed to dispose faecal matter, mainly because of their economic advantage. However, the biggest drawback is the well-recognized potential to pollute groundwater resources (ARGOSS, 2001; Lewis et al., 1980), which conflicts with Integrated Water Resources Management principles, in particular to preserve the integrity of vital ecosystems and to maintain water quality and quantity. Given the widespread use of groundwater for domestic purposes in rural areas, maintaining groundwater quality is a critical livelihood intervention. Globally, the larger part of the population lives in rural areas and in Africa it is estimated that these people represent approximately 70–80% of the continent’s population. In Zimbabwe, according to figures derived from the Census 2002 Zimbabwe Preliminary Report (CSO, 2002), the rural population is about 70% (the derived figure is 68%), with that same percentage relying on groundwater (Chenje et al., 1998). The reliance may be higher in some districts as noted by Hoko (2005), where rural communities like Gokwe, Nkayi, Mwenezi and Lupane mainly use groundwater for domestic purposes with very little reliance on surface water. Yet there is an information gap on the levels of groundwater contamination from pit latrines (Chenje et al., 1998; Chidavaenzi et al., 2000). Therefore the quality of groundwater, which potentially can be affected by on-site sanitation systems, must be carefully assessed in order to reduce the health and environmental risks. This study was carried out in Kamangira village, Marondera district, Zimbabwe. As is the case with most rural communities in the country, the people of Kamangira village mainly use shallow wells as a source of domestic water and other purposes and pit latrines for sanitation. The geological setup and soil type in the area, compounded by a generally high water table, are thought to have caused several pit latrine failures such as cracking and sinking. According to Lewis et al. (1980), failure of on-site sanitation systems may result in serious pollution of groundwater, the primary cause for health concerns being the excreted pathogens and certain chemical constituents like nitrate. The study assessed impacts of pit latrines on groundwater quality, taking levels of total and faecal coliforms, ammonium ðNHþ 4 –NÞ, nitrate ðNO3 –NÞ, conductivity, turbidity and pH as impact indicators. The parameters were chosen because a wide range of studies internationally have demonstrated that they are problematic with regards to onsite sanitation. Some of the parameters also tend to have an effect on the perceived water quality and health. A disease incidence survey was carried out in order to assess the possible health impacts of groundwater pollution. The overall
aim of the study is to contribute towards the improvement of safe water supply and sanitation. 2. Study area Kamangira village is in Chihota rural area, Marondera district, in Zimbabwe and the district’s geographical location is shown in Fig. 1. The village has a population of about 100 people. The peak of the rain period is December to February, while June–September is the dry period, with very isolated rainy days in June and August. The predominant form of sanitation is pit latrines. The main source of domestic water is shallow wells. The geology of Chihota rural area is truncated by numerous faults, of which two major sets are outstanding namely, the north/ north-east and north-east trending sets. These faults tend to have a major influence on the drainage of the area (Mukandi, 2005). Intrusive features like dykes enhance the groundwater potential, by creating confined aquifers (Maziti, 2002). At a localized scale, Kamangira village is covered with granitic rocks while the soils are generally sandy resulting in high transmission of water. 3. Materials and methods 3.1. Study design Fig. 2 presents the study site design. The study site was situated on a watershed, which meant that the experimental setup could exclude flow of groundwater from outside this site as direction of groundwater flow would most likely follow ground slope. Pit latrines under investigation were named PL1, PL2 and PL3, and the shallow wells close to those latrines were named SW1, SW2, and SW3, respectively. Shallow well number 1 (SW1) was located 44 m
Fig. 1. Location map of study area (Kamangira village) in Marondera district, Zimbabwe.
B. Dzwairo et al. / Physics and Chemistry of the Earth 31 (2006) 779–788 TW10
SW2 SW2
N
7990560
TW9
TW8 TW7 PL2 TW6
7990540
7990520 TW13
PL2
CONTROL
TW5
PL3
TW12 7990500 PL3 TW11
TW4 TW3
7990480
PL1
TW2
SW3
7990460SW3
781
SW1
PL1 TW1
SW1 300660 300680 300700 300720 300740 300760 300780 300800 300820 300840
KEY
∗
Monitoring borehole Pit latrine Shallow well Absolute ground level elevation (m)
Fig. 2. Study design. PL is pit latrine, SW is shallow well, TW is monitoring borehole, Control is control borehole. X-axis is eastings and Y-axis is northings, both in Universal Transverse Mercaptor (UTM).
south-east of pit latrine (PL1), SW2 at 38 m north of PL2, and SW3 was located 44 m south of PL3. The positions of pit latrines within the study site defined a transect (for example PL1 to PL2) and impacts on groundwater quality were investigated along this transect or for individual pit latrines. A total of 14 monitoring boreholes were drilled upstream and downstream of pit latrines, at positions shown in Fig. 2, using a manual drilling rig called a Vonder rig. The boreholes were cased using perforated 125 mm PVC pipes. The control borehole was located 80 m north-east of PL1 and 100 m east of PL2. The position of the control was determined in order to minimize influence of the nearest pit latrine or other topographical structures that would influence any of the other characteristics under investigation. At this position there was no evidence of settlements, farming or animal pens that could influence results. The control borehole was also cased in the same manner as the other monitoring boreholes. 3.2. Sampling and analysis methods Six sampling campaigns, corresponding to six data sets, were made from February 2005 to May 2005, covering the rainy season. Boreholes were flushed once before commencement of the sampling campaign. Subsequent flushing at every sampling event could not be done because some of the parameters which were to be tested for were sensitive to water disturbances. Furthermore, the perforation of the casing was assumed to allow free through-flow of groundwater. Groundwater samples were collected at the water
surface from the monitoring boreholes and the shallow wells. Brickwork and heavy concrete slabs protected the boreholes and the casings were opened only for sampling purposes. Water quality and water table elevation data was plotted on clustered column and line graphs, respectively, using Microsoft Excel. Results (individual values) were compared to WHO guidelines for drinking water (WHO, 2004). Ground elevation was krieged on Surfer 7 software. 3.2.1. Water and soil tests For coliforms, microbiological tests were performed on duplicate 50 ml samples, after filtering the sample portions through individual 0.45 lm membrane filter papers, as stipulated in the Membrane Filter Technique for members of the coliform group method number 9222 (APHA, 1989). NHþ 4 –N was determined as described in method number 4500-NH3 F while NO 3 –N was determined according to the Ultraviolet Spectrophotometric Screening Method number 4500 NO 3 B (APHA, 1989). Conductivity was determined using a WTW model Cond 340i test kit. Turbidity was measured using a HACH 2100 N turbidity kit. A WTW microprocessor pH/ion meter model pMX 3000 was used for pH measurement. The sieve test was performed on soil samples collected, at varying depths during monitoring boreholes drilling, for soil characterization. The analysis was performed on a series of B.S. sieves nested as follows: 19 mm, 9.5 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 lm, 300 lm, 150 lm and 75 lm. Permeability was calculated from the obtained sieve analysis data.
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Fig. 3 highlights the relationships between pit base and water table elevations along transect 1. Considering boreholes close to PL1 (TW1 and TW2), the base of the pit latrine was generally above the water tables of TW1 and TW2 throughout the sampling period. It ranged 0.2–1.2 m above water tables for TW1 and 0.6– 1.8 m above those for TW2. These ranges gave an average soil infiltration layer range of 0.4–1.5 m above the water table. The infiltration layer is the soil layer between the bottom or base of the pit latrine and the water table in a case where the water table is below the pit latrine base. PL2 sat on and below the water table throughout the study. It ranged 0.9 m below the water table to 0.2 m above the water table for TW6. PL2 base was 1.7–0.6 m below the water table for TW7. Along transect 2 in Fig. 4, PL3 base sat below the water table throughout the study, ranging from 3.2 m to 1.2 m and 3.1 m to 1.2 m below the water tables for TW11 and TW12, respectively. The fact that there was little or no soil infiltration layer between the pit latrine base and the water table meant that effluent was seeping into and contaminating the groundwater. A review of typical case studies done by Lewis et al. (1980) shows that water quality tends to depend on the depth of the soil infiltration layer allowed between the pit base and the water table.
3.2.2. Disease incidence Incidences of water-borne diseases in the study area were investigated by conducting a survey in Kamangira village. Direct interviews were held using semi-structured questionnaires. A total of 38 people representing 38 homesteads were interviewed, including the 3 homesteads that comprised the study site. Information gathered included sources of water for domestic purposes, protection of the water source, relative distances between sanitary structures and domestic water sources, awareness of potential water contamination from pit latrines, and the most common water related diseases that affected the villagers. Results from the survey were used to make preliminary inferences of health impacts of groundwater pollution and contamination by pit latrines. 4. Results and discussion 4.1. Groundwater flow and water table Transect 1 comprised PL1, PL2 and the boreholes TW1 to TW10, while transect 2 comprised PL3 and TW11 to TW13. From the water levels of groundwater in the monitoring boreholes, flow along the transects was assumed as follows: For transect 1 the flow was from TW1 towards TW4, from TW7 towards TW4 and from TW7 towards TW10. In terms of groundwater flow, monitoring boreholes TW1 and TW7 were upstream in relation to pit latrine positions while TW2 and TW6 were downstream boreholes. For transect 2, flow was assumed to be from TW11 towards TW13, with TW11 being upstream and TW12 and TW13 being the downstream boreholes of pit latrine (PL3). The contour map in Fig. 2 and the water table elevations as in Fig. 3 indicated that there was a depression around TW4.
4.2. Soil characterization Soil characterization was done and results showed that the soils were generally sandy and collapsible. Soil permeability ranged from 0.02 to 2.7 m d1, which was within the range of 0.01–2.8 m d1 as noted by (Wright, 1992) for a crystalline basement. Permeability values for soils around PL1 and PL2 were found to be lower than those for soils
Groundlevel 21-Feb 21-Mar 18-Apr PL1
1426.5
just after drilling 7-Mar 4-Apr 5-May PL2
Elevation (m)
1425.5
1424.5
tw9
tw8
tw10
Sampling points
tw7
tw6
tw5
tw4
tw3
tw2
1422.5
tw1
1423.5
Fig. 3. Water table elevations for boreholes TW1–TW10 on transect 1 plotted in relation to pit base elevations for PL1 and PL2.
1426
Ground level 7-Mar 18-Apr
just after drilling 21-Mar 5-May
21-Feb 4-Apr PL3
1425
pH
1423
Sampling points
EC
Fig. 4. Water table elevations for monitoring boreholes 11–13 on transect 2.
0–0.2 (0.0 ± 0.1) 0–0.8 (0.1 ± 0.3) 0–0 0–2 (0.3 ± 0.8) 0–0.6 (0.1 ± 0.3) 0–0 0–0 0–0 0–0 0–0.3 (0.0 ± 0.1) 0–0 0.6–1.2 (0.8 ± 0.2) 0–0.3 (0 ± 0.1) 0–1.4 (0.2 ± 0.6) 0–0 0–0 0–0 0–0 0–880 (147 ± 359) 0–3000 (633 ± 1191) 0–200 (33 ± 82) 0–0 0–0 0–1880 (438 ± 767) 0–0 0–1080 (251 ± 431) 0–0 0–0 0–0 0–0 0–0 80–1900 (708 ± 706) 58–690 (479 ± 286) 90–1800 (817 ± 847) TW1 TW2 TW3 TW4 TW5 TW6 TW7 TW8 TW9 TW10 TW11 TW12 TW13 Control SW1 SW2 SW3
0–0 0–34 (6 ± 14) 0–3000 (541 ± 1206) 0–0 0–0 0–0 0–38 (6 ± 16) 0–0 0–33 (6 ± 14) 0–0 0–0 0–0 0–0 0–0 4–488 (165 ± 196) 12–98 (54 ± 49) 2–820 (242 ± 348)
NHþ 4 FC TC Sampling point
Parameters with statistical analysis (range, average and standard deviation) for n = 6a
Table 1 Groundwater analysis results for the six sampling campaigns
For the parameters total coliforms (TC), faecal coliforms (FC), nitrate–nitrogen, ammonium–nitrogen, conductivity, turbidity and pH, results are presented for all the 17 sampling points in Table 1. The results show wide variation for all sampling points for all the sampling dates as the sampling period progressed. Total and faecal coliforms both ranged 0-TNTC (toonumerous-to-count) where a value of 3000 CFU was assigned for TNTC for statistical purposes, with 78% of the total results meeting the 0 CFU/100 ml WHO guidelines value. Table 1 summarises the ranges, averages and standard deviations at each sampling point for the six sampling campaigns. The shallow wells were located 38–44 m away from the nearest pit latrines, thereby placing them outside the pit latrines’ radii of influence of 30 m as generally accepted in Zimbabwe (Morgan, 2001). All of them were partially protected and they indicated elevated levels of both total and faecal coliforms. This could be due to water withdrawal and hygienic practices around the water points which could have caused the introduction of coliforms by the users. Shallow wells SW1 and SW3 served more people (5 and 7, respectively) than SW2 (3 people), resulting in a higher demand on the former two shallow wells, with consequential soil re-suspension and a higher potential for microbiological contamination due to frequent use. Variations of coliform counts are presented graphically in Figs. 5 and 6. WHO guidelines value of 0 CFU/100 ml was not met in 100% of total and faecal coliform results obtained for the shallow wells. The results obtained for some boreholes located within a 5 m radius of the pit latrines indicate that a
NO 3
4.3. Coliforms
2.5–3.2 (2.9 ± 0.4) 0–0.5 (0.2 ± 0.2) 0–0.2 (0.1 ± 0.1) 1.2–6.7 (2.6 ± 2.1) 0.4–0.5 (0.5 ± 0) 0.2–0.3 (0.3 ± 0.1) 2.2–5.6 (3.4 ± 1.2) 1.1–3.2 (2 ± 0.9) 0.3–0.8 (0.5 ± 0.2) 0.4–1.6 (1 ± 0.5) 0.9–1.3 (1.2 ± 0.2) 0–0.7 (0.2 ± 0.3) 1.6–2.2 (1.9 ± 0.2) 1.8–2.2 (2 ± 0.2) 0.7–3 (1.4 ± 0.9) 0–0.1 (0.1 ± 0) 3.4–3.9 (3.6 ± 0.3)
around PL3. Permeability affects the movement of water and pollutants in the ground.
TC = total coliforms, FC = faecal coliforms, NHþ 4 ¼ ammonium–nitrogen, NO3 ¼ nitrate–nitrogen, EC = conductivity.
tw13
tw12
1419
tw11
1420
a
Turbidity
1421
4–17 (10 ± 4) 2–20 (6 ± 7) 2–28 (8 ± 10) 1–2 (2 ± 0.5) 1–4 (2 ± 1) 1–8 (3 ± 3) 1–3 (1 ± 0.8) 2–3 (3 ± 0.8) 2–9 (5 ± 3) 10–24 (17 ± 5) 4–24 (9 ± 8) 8–45 (20 ± 14) 4–33 (14 ± 11) 1–4 (2 ± 1) 20–36 (27 ± 6) 2–7 (5 ± 2) 3–35 (11 ± 14)
1422
76–197 (108 ± 45) 88–222 (115 ± 53) 113–260 (153 ± 54) 96–357 (147 ± 104) 95–168 (111 ± 28) 91–228 (122 ± 53) 100–235 (127 ± 53) 100–218 (132 ± 43) 106–151 (121 ± 16) 136–370 (210 ± 85) 144–233 (161 ± 36) 169–269 (190 ± 39) 94–154 (106 ± 24) 88–139 (98 ± 20) 46–62 (52 ± 7) 49–62 (54 ± 6) 89–98 (94 ± 4)
Elevation (m)
1424
783
7.1–7.6 (7.3 ± 0.1) 7.0–7.4 (7.3 ± 0.1) 6.96–7.65 (7.3 ± 0.2) 6.92–7.3 (7.2 ± 0.1) 7.3–7.7 (7.4 ± 0.1) 7.1–7.6 (7.3 ± 0.2) 6.76–7.4 (7.2 ± 0.2) 7.2–7.7 (7.3 ± 0.2) 7.4–7.7 (7.6 ± 0.1) 7.5–7.9 (7.7 ± 0.1) 7.0–7.7 (7.5 ± 0.3) 7.2–7.9 (7.7 ± 0.2) 6.8–7.8 (7.5 ± 0.4) 7.2–7.4 (7.3 ± 0.1) 6.8–7.6 (7.0 ± 0.3) 7.0–7.1 (7.0 ± 0.1) 7.0–7.3 (7.1 ± 0.1)
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2016 1816
PL1
PL2
PL3
CFU/100mL
1616 1416
21-Feb 21-Feb
7-Mar 7-Mar
1216
21-Mar 21-Mar
4-Apr 4-Apr
1016
18-Apr 18-Apr
5-May 5-May
816 616 416 216
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
16
Fig. 5. Total coliform variation among the sampling points, showing pit latrine (PL) locations in relation to monitoring boreholes.
900 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
800 700
CFU/100mL
600 500 400 300 200 100
sw3
sw2
sw1
tw13
tw12
control
Sampling points
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
0
Fig. 6. Faecal coliform variation among the sampling points.
pit latrine can influence up to 5 m of its radius. Beyond 5 m the faecal coliforms were greatly reduced. Borehole TW10 did not show indications of impacts from the old and collapsed pit latrine located some 5 m away from that borehole in terms of coliforms. The presence of faecal coliform bacteria in some samples indicated that the water had been contaminated with the faecal material of man or other animals and therefore there was a risk of contamination of water by pathogens or disease producing bacteria or viruses. 4.4. Ammonium–nitrogen Ammonium–nitrogen range was 0–2.0 mg/l for all sampling points, with 99% of total results falling within 1.5 mg/ l WHO recommended value. Ranges, average values and
standard deviations are presented in Table 1 for all sampling points during the six sampling campaigns. According to WHO (2004), the threshold odour concentration of ammonia at alkaline pH is approximately 1.5 mg/l, and a taste threshold of 35 mg/l has been proposed for the ammonium cation ðNHþ 4 Þ. Ammonium–nitrogen persisted in samples from TW12 as indicated in Fig. 7. This could have been because that monitoring borehole was located downstream of PL3, whose pit base was below the water table throughout the study period. Because ammonia gas dissolves completely and dissociates into ammonium ions in water, they would travel together with the groundwater towards downstream sampling points. Ammonium usually occurs in drinking water at concentrations well below those at which toxic effects may occur. The collapsed and disused pit latrine could have affected the results of TW10. Ammo-
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785
2.50 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
+
NH4 -N (mgN/L)
2.00
1.50
1.00
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
0.00
tw1
0.50
Fig. 7. Ammonium–nitrogen variation among sampling points.
8.0 21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
7.0
NO3- -N (mg/L)
6.0 5.0 4.0 3.0 2.0 1.0
Sampling points
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw9
tw8
tw7
tw6
tw5
tw4
tw3
tw2
tw1
0.0
Fig. 8. Nitrate–nitrogen variation among sampling points.
nium is not of direct relevance to health at levels generally detected in groundwater, and no health-based guideline value has been proposed. 4.5. Nitrate–nitrogen Nitrate–nitrogen for all sampling points ranged from 0.0 to 6.7 mg/l and this was within the 10 mg/l WHO guidelines value. Ranges, average values and standard deviations are also presented in Table 1. Nitrate ions, just like the ammonium ions, dissolve and travel within and with the groundwater towards downstream sampling points, as noted at the depression at TW4 in Fig. 8. The collapsed and disused pit latrine did not affect the results of TW10. High levels of nitrate–nitrogen are directly associated with methaemoglobinaemia, or ‘‘blue baby syndrome’’, an acute condition which is most frequently found among bottle-fed
infants of less than three months of age. Nitrates have been suggested as causing methaemoglobinaemia and also as possible carcinogens by a number of researchers (Johns and Lawrence, 1973; Lewis et al., 1980; WHO, 1993). Cave and Kolsky (1999) has also confirmed that nitrate can be used as a crude indicator of faecal pollution where microbiological data are unavailable. 4.6. Conductivity Conductivity ranged 46–370 lS/cm for all sampling points as indicated in Fig. 9. Individual sampling point values are presented in Table 1 together with the averages and standard deviations. There are no WHO guideline values for conductivity. On transect 1 involving TW1 up to TW10, conductivity rose from TW1 towards TW4 and peaked at a location 25 m away (TW4) before it dropped
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total results, 59% met the 5 NTU WHO guidelines limit. Turbidity had a decreasing trend from TW1 to TW7 and increased along transect 1, with a peak at TW10. The high turbidity at TW10 could be as a result of loose soil from the collapse of the disused pit latrine near that borehole. Since soil acts as a filter, turbidity decrease towards the depression at TW4 was expected. Transect 2 turbidity values were generally much higher than those for transect 1 possibly because of direct injection of colloidal suspended solids from the pit latrines. High turbidity values were also recorded for the shallow wells SW1 and SW3 and this could be due to soil disturbance and resuspension within the well during water withdrawal. The depth of the shallow wells, and in particular, the depth of the water level above the well bottom may affect the turbidity. In this study, the deepest well was SW3 and the shallowest was SW2. The water levels also showed the same trend for all sampling dates. The turbidity values though were highest at SW1 and lowest at SW2, and this could be due to the fact that the base of SW2 was covered by a large boulder, making the soil intact, whereas the soil in SW1 and SW3 was loose. The control borehole recorded very low values for turbidity. Turbidity affects water aesthetics.
sw3
7-Mar 4-Apr 5-May
sw1
tw13
Sampling points
control
tw12
tw11
tw9
tw10
tw8
tw7
tw6
Fig. 9. Conductivity variation among sampling points.
gradually towards PL2. It also rose gradually from TW7 towards TW10, which was located 45 m away from TW7. Transect 2 involving TW11 to TW13, showed that conductivity was lower at TW11, which was located 5 m upstream of PL3 than at TW12, which was located 5 m downstream of that pit latrine. Conductivity is a measure of dissolved ions and their behaviour is also similar to that of ammonium and nitrate ions, concentrating at lower points within the study area. The high levels of ammonium at TW12 could possibly explain the high conductivity at TW12 if the chemical composition of the geology is the same. Conductivity dropped significantly at a distance 15 m downstream of PL3 to values almost similar to those for the control borehole. The concentration of ions at TW4, TW10 and TW12 could be due to impacts of PL1, PL2 and PL3 as well as the collapsed pit latrine 5 m away from TW10. The low values for the shallow wells indicated that there were no impacts from within the vicinity of the shallow wells.
4.8. pH The pH ranged 6.8–7.9 for both shallow wells and boreholes as indicated in Fig. 11. Values recorded for boreholes along transect 1 were relatively close to those for the control, although they peaked at TW10. Table 1 presents the variation per sampling point as the sampling campaign progressed. The values are given as range, average and standard deviation. Transect 2 pH values started relatively low for TW11 located 5 m upstream of the pit latrine, PL3, and peaked at TW12 that is 5 m downstream, before dropping noticeably at TW13 located 15 m downstream of PL3. The presence of ammonium-nitrogen at TW12 could have caused the elevated pH levels at borehole TW12. Ammo-
4.7. Turbidity Turbidity ranged 1–45 NTU when all sampling points were considered. Table 1 presents the results for individual sampling points as range, average and standard deviation to allow for comparison in parameter variation throughout the sampling campaign. Fig. 10 presents the results for all points during the whole six sampling runs. Of the
50.0 45.0
21-Feb
7-Mar
21-Mar
4-Apr
18-Apr
5-May
35.0 30.0 25.0 20.0 15.0 10.0 5.0
Sampling points
Fig. 10. Turbidity variation among sampling points.
sw3
sw2
sw1
control
tw13
tw12
tw11
tw10
tw8
tw7
tw6
tw5
tw4
tw3
tw2
0.0 tw1
Turbidity (NTU)
40.0
tw9
tw5
tw4
tw3
tw2
200.0 150.0 100.0 50.0
21-Feb 21-Mar 18-Apr
sw2
400.0 350.0 300.0 250.0
tw1
Conductivity (uS/cm)
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21-Feb 21-Mar 18-Apr
7. 9
7-Mar 4-Apr 5-May
7. 7
pH
7. 5 7. 3 7. 1 6. 9 6. 7
Sample points
sw 3
sw 2
sw 1
control
tw 13
tw 12
tw 11
tw 10
tw 9
tw 8
tw 7
tw 6
tw 5
tw 4
tw 3
tw 2
tw 1
6. 5
Fig. 11. pH variation among sampling points.
nium–nitrogen presence makes the environment alkaline, thereby raising pH. Shallow wells recorded much lower pH values. They also recorded lower values of nitrogen as compared to the monitoring boreholes especially those downstream of the pit latrines. This suggests that pH variation could be linked to nitrogen possibly coming from the pit latrines. 4.9. Questionnaire survey A total of 38 villagers from different homesteads were interviewed, and the figure translated to 38% of the population of Kamangira village. Of the respondents who owned a pit latrine, 45% of them were unusable because they were dilapidated and unsafe (according to sentiments passed by the respondents during the interviews) or they were now too full to be used hygienically. Some 42% of the respondents did not have a water point within the homestead. This percentage is quite typical of rural communities in the third world countries where half the population remain unserved, with water and sanitation facilities of acceptable quality and standard according to WHO/ UNICEF (2004). Diarrhoea was widespread, with those having suffered from it making up 50% of the interviewed number for the sampling period, which covered most of the rainy season. Those who did not own a water point and also suffered from diarrhoea constituted 24% of the respondents. There was no incidence of health impacts from nitrate, as depicted by 0% reported occurrence of ‘‘blue-baby’’ syndrome, whose symptoms had been explained to the villagers by the interviewer during the interviews. Preference of eco-san, which is a form of on-site sanitation, was at 37% of the respondents, although 100% of them cited lack of adequate financial resources as the major drawback. Seven 50 kg cement bags are required to build the structure, apart from the labour and brick requirements according to a local Non-Governmental Organisation, which was implementing eco-san in the district.
5. Conclusions 1. Total and faecal coliforms were found to be impacting negatively on groundwater quality. Samples, from monitoring boreholes and shallow wells that gave the 0 CFU/100 ml limit, represented 78% of the total results. According to WHO guidelines (2004), 100% of the results should have a value of 0 CFU/100 ml in order for that water to be considered safe for human consumption. 2. Ammonium and nitrate were found to be impacting on the groundwater quality while there was a possibility that pit latrines were a source of nitrogen. However, their levels were not yet of health concern according to WHO guidelines. 3. Although there is no WHO guideline value for conductivity (a parameter that quantifies the concentration of dissolved solids), results obtained showed a similar trend to the other dissolved ions under investigation, that is, nitrate and ammonium. 4. Turbidity of the water was above the limit of 1.5 NTU for 41% of the results, making it aesthetically unpleasant for domestic purposes. Pit latrine excavations and subsequent loosening of the soil matrix could be the cause of these high turbidity values. 5. The sandy nature of the soils in the study site, compounded by the high water table, renders the area unsuitable for pit latrine construction. This could be the cause of the structural failures observed. 6. Generally, it may be risky to abstract water from within 25 m lateral distance of an unlined pit latrine within the study area and also possibly in an area with similar soil and water table characteristics, according to the water quality parameters investigated.
6. Recommendations • The economics and logistics of low-cost sanitation schemes are such as to preclude the routine use of costly
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hydrogeological field investigations therefore critical parameters like depth of the infiltration layer and direction of groundwater flow could be used during assessment of impacts of pit latrines on groundwater quality. • Raised or lined pit latrines and other low-cost technologies could be considered as alternatives to unlined pit latrines, because they minimize the risk of releasing pit latrine effluent flow across the thin infiltration layer. • An integrated approach involving geotechnology, hydrogeology and groundwater pollution could be considered as a way forward in efforts to solve the sanitation problems, in view of potential groundwater pollution and structural failures within the larger Kamangira village. The results obtained from the study are true for the study area but could also apply to areas with similar soil, geology and rainfall patterns.
Acknowledgements This paper contains research results from a M.Sc. project by B. Dzwairo at the University of Zimbabwe. It was funded by a scholarship awarded to B. Dzwairo by WaterNet and a research grant from Mvuramanzi Trust. The Departments of Civil Engineering and Geology at the University of Zimbabwe, the people of Kamangira village and the Institute of Water and Sanitation Development are acknowledged for logistical, material and moral support. The Water Research Fund for Southern Africa (WARFSA) is acknowledged for facilitating the presentation of this paper at the 6th WARFSA/WaterNet/GWP-SA annual symposium that was held in Swaziland in November 2006. References Anon, J., 1996. World Water Environmental Engineering. Cambridge University Press, Cambridge, United Kingdom. APHA (American Public Health Association), 1989. Standard Methods for the Examination of Water and Wastewater, 17th ed. APHA, Washington, DC, United States of America. ARGOSS, 2001. Guidelines for assessing the risk to groundwater from on-site sanitation.British Geological Survey Commissioned Report, CR/01/142. United Kingdom, pp. 97.
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