Introduction
Study area and setting
Physical setting
Hydrogeological insights from well records
Summary statistics | n | Range | Mean |
---|---|---|---|
Well depth (m) | 41 | 30.5–260 | 71.6 |
Airlift yield (m3/h) | 41 | 1.1–56.8 | 6.8 |
Pump test rate (m3/h) | 24 | 1.2–40.9 | 8.3 |
Static water level (m bgs) | 24 | 0.8–53.3 | 9.0 |
Drawdown (m) | 24 | 0.2–27.6 | 6.4 |
Specific capacity (m3/h-m) | 24 | 0.2–77.4 | 1.9 |
Hydraulic conductivity (m/day) | 12 | 0.05–90 | 1.3 |
Storativity | 12 | 0.003–0.100 | 0.008 |
Methods
ID | Well type | Elev. (masl) | Borehole depth (m) | Static water level | Pumping rate (L/s) | Screen interval depths (m) | Notes | Lithology and well construction | |
---|---|---|---|---|---|---|---|---|---|
Elev. (masl) | mm/yyyy | ||||||||
P1 | Drilled | 87 | 79 | 66.4 | – | 0.4 | 18.3–73 | Community hand pump well | – |
P2 | Drilled | 14 | 60 | 7.9 | 05/2008 | – | 14.3–33.5; 39–45.4; 50.9–57.3 | Municipal well. Yields reported >6 L/s | 0–5′: topsoil 5–30′: clays 30–50′: silt, sands and clays 50–105′: fractured sandstone 105–165′: consolidated sandstone 165–200′: fractured sandstone |
P3 | Drilled | 24 | 48.8 | 9.5 | 12/2016 | 0.25 | 12–48.7 | Community hand pump well, airlift yield of 0.25 L/s | 0-6 m: topsoil and silty clay 9-12 m: with rock fragments 12–48.8 m: hard sandstone |
P4 | Drilled | 65 | 93 | 12 | 06/2016 | 1.2 | – | Private well with submersible pump | Reportedly layers of fractured rock separated by hard consolidated rock. |
P5 | Drilled | 32 | 200 | 3.25 | 04/2014 | – | 60–200 | Airlift yield reported at 15–19 L/s | 0-3 m: topsoil 3–6.5 m: soft silt and clay 6.5–18.3 m: clays 18.3-198 m: sandstone with some fractures |
P6/MW-02 | Drilled | 22 | 76 | 16 | 04/2014 | 6.6 | 12–16.8; 25.9–41; 48.8–53.4; 73.2–76.2 | Private well with submersible pump | 0-6 m: alluvium, pyroclastic rock and pumice 6-43 m: fractured sandstones 43-46 m: pyroclastic rock and pumice 46–54: fractured sandstones 54-74 m: sandstone and clay layers |
P7 | Hand dug | 68 | 22 | 46.2 | 04/2014 | – | – | Hand dug well | – |
P8 | Hand dug | 14 | 10 | 8 | 04/2014 | – | – | Hand dug well with rope pump | – |
MW-01 | Drilled | 28 | 34 | 7.2 | 04/2014 | 5.0 | 16–28 | Private well with submersible pump | Reportedly layers of fractured rock separated by hard consolidated rock. |
MW-03 | Drilled | 24 | 48 | 16.8 | 04/2014 | 8.9 | 9–32; 38–44.2 | Private well with submersible pump | 0-9 m: alluvium, soft clays and sandstones 9-17 m: pyroclastic rock and tuff 17-48 m: fractured sandstones |
Results
Groundwater flow
Water quality and hydrochemistry
Summary statistics | n | Range | SD | Mean |
---|---|---|---|---|
Temperature (C) | 31 | 26.5–35.2 | 1.46 | 28.3 |
Conductivity (μS/cm) | 31 | 391–1,128 | 156 | 656 |
pH | 31 | 6.5–8.1 | 0.34 | 7.3 |
Hardness (mg/L) | 31 | 180–330 | 37.8 | 235 |
NO3-N (mg/L) | 12 | 0–6.3 | 2.23 | 2.2 |
NO2-N (mg/L) | 12 | 0–0.01 | 0.003 | 0.003 |
Turbidity (NTU) | 12 | 0.5–73.2 | 20.69 | 8.1 |
Static water level (m bgs) | 20 | 3.5–30.5 | 7.3 | 9.5 |
Sample ID | Latitude (dd) | Longitude (dd) | Tempa °C | Turbidityb (NTU) | pHa | Conductivitya (μS/cm) | Hardnessb (mg/L) | NO3-Nb (mg/L) | NO2-Nb (mg/L) | Total coliforma |
---|---|---|---|---|---|---|---|---|---|---|
AN-255 | 11.4584 | −86.0380 | 27.7 | 0.90 | 7.09 | 642 | 288 | 0.81 | 0.00 | P |
AN-256 | 11.4621 | −85.9793 | 27.5 | 0.80 | 7.20 | 607 | 300 | 0.85 | 0.01 | P |
AN-257 | 11.5089 | −85.9613 | 28.3 | 0.50 | 7.43 | 670 | 272 | 2.38 | 0.00 | P |
AN-259 | 11.4433 | −85.9508 | 27.8 | 10.70 | 7.09 | 391 | 180 | 4.70 | 0.00 | P |
AN-260 | 11.4442 | −85.9128 | 28.2 | 1.00 | 7.66 | 590 | 264 | 6.34 | 0.00 | P |
AN-237 | 11.5293 | −86.0517 | 29.0 | 73.20 | 8.06 | 678 | 274 | 0.00 | 0.00 | P |
AN-238 | 11.5093 | −86.0520 | 28.5 | 2.40 | 7.32 | 580 | 235 | 3.13 | 0.00 | A |
AN-239 | 11.5141 | −86.0785 | 29.7 | 1.00 | 7.46 | 720 | 278 | 0.05 | 0.00 | P |
AN-240 | 11.5257 | −86.1467 | – | 0.80 | 7.53 | 816 | 267 | 0.14 | 0.00 | P |
AN-274 | 11.3890 | −85.9229 | 28.4 | 2.90 | 7.22 | 880 | 330 | 1.08 | 0.00 | P |
AN-275 | 11.4571 | −85.9503 | 27.9 | 2.00 | 7.52 | 558 | 251 | 5.52 | 0.01 | P |
AN-276 | 11.4545 | −86.0150 | 27.6 | 0.90 | 7.21 | 660 | 301 | 1.33 | 0.00 | P |
Parameter | Detection Limit | Units | Sample ID | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
P1 | P2 | P3 | P4 | P5 | P6 | P7 | P8 | S1 | |||
Date | 13-Dec | 15-Dec | 12-Dec | 14-Dec | 13-Dec | ||||||
Elevation | masl | 87 | 18 | 24 | 65 | 32 | 20 | 68 | 14 | 87 | |
Alkalinity, total (CaCO3) | 5 | mg/L | 64 | 62 | 42 | 50 | 28 | 56 | 56 | 64 | 52 |
Alkalinity, bicarbonate (CaCO3) | 5 | mg/L | 64 | 62 | 42 | 50 | 28 | 56 | 56 | 64 | 52 |
Alkalinity, carbonate (CaCO3) | 5 | mg/L | <5 | <5 | <5 | <5 | <5 | <5 | <5 | <5 | <5 |
Chloride | 1 | mg/L | 31 | 46 | 59 | 26 | 134 | 81 | 12 | 195 | 13 |
Sulfate | 15 | mg/L | <15 | 42 | 79 | 115 | 15 | 36 | 22 | 57 | 21 |
Boron | 0.05 | mg/L | <0.05 | 0.45 | 0.50 | 0.88 | 2.61 | 1.43 | 0.07 | 0.37 | 0.12 |
Calcium | 0.5 | mg/L | 93.6 | 110 | 116 | 49.8 | 6.2 | 103 | 100 | 160 | 78.2 |
Magnesium | 0.5 | mg/L | 14.5 | 7.1 | 4.3 | 2.3 | 0.9 | 4.3 | 6.9 | 11.1 | 12.9 |
Potassium | 0.5 | mg/L | 0.8 | <0.5 | 0.8 | 0.9 | 5.3 | 0.7 | 0.8 | 1.3 | 1.1 |
Sodium | 0.5 | mg/L | 20.4 | 39.9 | 30.5 | 127 | 128 | 72.6 | 20.5 | 86.0 | 22.5 |
pH @ 25 °C | – | 7.09 | 7.22 | 7.14 | 7.51 | 8.68 | 7.20 | 7.02 | 7.12 | 7.72 | |
Conductivity | 5 | μS/cm | 552 | 715 | 673 | 742 | 680 | 780 | 551 | 1230 | 515 |
Total dissolved solids | 10 | mg/L | 326 | 484 | 470 | 510 | 380 | 520 | 320 | 788 | 363 |
δD H2O | – | ‰ | −44.6 | −47.1 | −47.6 | −46.3 | −46.0 | −46.8 | −47.6 | −47.1 | −44.5 |
δ18O H2O | – | ‰ | −6.56 | −6.94 | −6.79 | −7.02 | −6.78 | −6.90 | −7.09 | −6.83 | −6.50 |
Monitoring
Hand dug wells
Drilled wells
Chloride and mass balance
Date | Cl−(mg/L) | Precipitationa (cm) |
---|---|---|
20-Mar-2014 | 19 | 0.90 |
26-Aug-2014 | 4.6 | 11 |
23-Sep-2014 | 22 | 1.36 |
15-Nov-2014 | 17.4 | 1.86 |
09-Jun-2015b | 5 | 1.0 |
10-Jun-2015b | 16 | 1.76 |
11-Jun-2015b | 12.4 | 3.8 |
26-Sep-2015 | 7.7 | 4.2 |
08-Oct-2015 | 15.2 | 0.04 |
22-Oct-2015 | 5.2 | 4.3 |
20-Nov-2015 | 2.7 | 1.12 |
12-Jan-2016 | 13.3 | 0.76 |
06-May-2016 | 5.62 | 5.96 |
11-Jun-2016 | 7.1 | 2.84 |
18-Jul-2016 | 24.3 | 0.60 |
29-Aug-2016 | 5.5 | 3.88 |
Stable isotopes
Petrology and rock properties
Sample ID | 1 | 2 | 3 | 4 | 5 | 6 | 7 | TS1 | TS2 | TS3 |
---|---|---|---|---|---|---|---|---|---|---|
Lat. (dd) | 11.3963 | 11.4009 | 11.4022 | 11.3868 | 11.3887 | 11.3890 | 11.4009 | 11.3886 | 11.3979 | 11.3916 |
Long. (dd) | −86.0311 | −86.0200 | −86.0213 | −86.0145 | −86.0104 | −86.0071 | −86.0255 | −86.0260 | −86.0274 | −86.0289 |
Mineral composition % | ||||||||||
Quartz | 48.92 | 58.40 | 58.72 | 35.88 | 83.40 | 11.55 | 52.48 | 47.03 | 70.97 | 59.15 |
Illite (muscovite) | 3.69 | 2.07 | 3.78 | 3.01 | 0.50 | 3.26 | 0.94 | 0.97 | 1.05 | 4.67 |
Illite-smectite | 3.86 | 1.54 | 3.08 | 1.06 | 0.61 | 6.70 | 1.23 | 1.51 | 1.19 | 1.25 |
Smectite | 2.98 | 2.46 | 4.95 | 6.78 | 10.05 | 3.24 | 0.85 | 0.49 | 1.06 | 2.39 |
Chlorite | 8.54 | 5.34 | 7.43 | 1.08 | 1.39 | 12.94 | 2.81 | 2.88 | 2.79 | 2.08 |
Muscovite/kaolinite | 0.06 | 0.03 | 0.45 | 0.13 | 0.29 | 0.02 | 0.06 | 0.03 | 0.04 | 0.06 |
Plagioclase | 21.67 | 26.86 | 18.20 | 32.58 | 2.74 | 32.31 | 6.35 | 5.85 | 10.70 | 26.28 |
Carbonate-clay interphase | 4.45 | 1.81 | 1.53 | 6.50 | 0.53 | 13.80 | 9.13 | 10.16 | 3.22 | 1.85 |
Calcite | 1.04 | 0.03 | 0.08 | 10.15 | 0.01 | 9.27 | 19.06 | 23.08 | 3.41 | 0.03 |
Dolomite | 2.99 | 0.45 | 1.17 | 1.64 | 0.04 | 4.10 | 4.62 | 5.81 | 4.68 | 1.57 |
Pyrite | 0.64 | 0.39 | 0.00 | 0.00 | 0.00 | 0.33 | 2.22 | 1.94 | 0.00 | 0.00 |
Ti-mineral | 0.57 | 0.26 | 0.35 | 0.91 | 0.36 | 0.46 | 0.08 | 0.06 | 0.16 | 0.29 |
Apatite | 0.14 | 0.09 | 0.03 | 0.07 | 0.05 | 0.06 | 0.06 | 0.06 | 0.12 | 0.03 |
Others | 0.44 | 0.27 | 0.22 | 0.21 | 0.05 | 1.96 | 0.11 | 0.12 | 0.60 | 0.34 |
Porosity % | 0.22 | 0.23 | 1.89 | 0.73 | 0.26 | 0.42 | 1.09 | 1.70 | 1.28 | 3.14 |
Interpreted rock type | Lithic wacke | Feldspathic arenite | Lithic wacke | Lithic arenite | Sub-litharenite | Lithic wacke | Lithic arenite | Lithic arenite | Sub-litharenite | Feldspathic arenite |