Petrographic and Geochemical Study of Low Grade Metamorphic Rocks around Negash with Reference to Base Metal Mineralization and Groundwater Quality, Tigray, Northern Ethiopia

Petrographic and geochemical data of Upper Proterozoic, low grade metamorphic rocks (Tsaliet Group) in and around Negash is interpreted in this paper with their mineralization potential and influence on groundwater quality. Among the three types of metamorphic rocks, metavolcanics (MV), metavolcaniclastics (MVC) and metasediments (metapelites) (MP) are present in the study area. Metavolcanics are massive, non-foliated and show presence of relicts of plagioclase feldspar and pyroxenes set in a fine grained matrix. Metavolcaniclastics show presence of clasts set in a fine grained tuffaceous groundmass and indicate a significant compositional contrast between these, probably volcanic derived, groundmass and the clasts. The clasts vary in size and shape from angular, subrounded to rounded and even elliptical (due to shearing). Phyllite, the predominant lithounit of metasediments is composed of fine grained muscovite, quartz and chlorite with incipient foliation and at places well developed crenulations. Presence of chlorite together with poorly developed muscovite and biotite (rare) suggests low grade metamorphic conditions that prevailed in the area. Geochemical data of metavolcanics indicate variation in their composition from basalt to andesite. Metavolcaniclastics are relatively enriched in alkalis and silica and deficient in MgO compared to metavolcanics. Phyllite on the other hand is enriched in K2O and silica compared to metavolcanics. Development of chlorite, sericite and other minerals due to low grade metamorphism and hydrothermal alteration have modified the chemistry of the rocks particularly MgO by chlorite in phyllite. Shear zones are common in the rocks of the study area, trending N-S and showing presence of clasts with non-ideal tails, relatively higher amount of quartz veins, malachite stains, Cu anomalies and sericitisation. These stains and anomalies strongly suggest a shear zone-controlled copper mineralization. Island arc-setting, bimodal volcanism, intrusive granitic plutons and similar type of shear zone –controlled Zn-mineralization in the nearby Abrha Atsbha area indicate possible presence of a similar kind of mineralization elsewhere in the basement rocks around these plutons. Hydrogeochemical data indicate that groundwater is relatively fresh and among major elements Na, Ca and Mg show relatively higher values compared to K. Water from metasediments is relatively harder among others. Na though shows higher values compared to Ca and Mg does not indicate any particular trend. Ca and Mg concentrations are related to the mafic and plagioclase feldspar minerals. Among trace elements, iron, nickel and lead show relatively higher values compared to other analyzed elements. Fe and Ni are related to metavolcanics and metavolcaniclast, and Pb to metapelite. Key words: Low grade metamorphic rocks, Base metal mineralization, Petrography, Hydrogeochemistry, Negash, Ethiopi

Prospects and Constraints of Household Irrigation Practices, Hayelom Watershed, Tigray, Northern Ethiopia

Constraints and prospects of hand dug wells related to household irrigation were assessed in Hayelom watershed (~1045 ha), by evaluating groundwater suitability for irrigation, soil quality and impact of intervention. 181 hand dug wells have come into existence in the watershed due to intervention and benefiting about 166 families. Eight groundwater and twenty soil samples were tested to understand the suitability of groundwater and soil in the area. Impact of the intervention on livelihood of the household was assessed on the basis of the data obtained through questionnaire, and discussions held with focal groups and individuals. Water and soil samples were analyzed for major cations and anions, boron, pH and electrical conductivity and the data is computed both sodium absorption ratio and exchangeable sodium percentage. The results suggest that groundwater is suitable for irrigation purpose and the soils are free from soil salinity and sodicity hazards. Introduction of new tree plants, improvement in the households feeding habits, income, and introduction and adoption of water lifting technologies are some of the changes observed in terms of prospects. On the other hand, spacing of hand dug wells, sliding of its walls, similar and simultaneous production of vegetable crops, wastage of land, maintenance of water lifting technology and water scarcity are some of the major constraints identified in the watershed. Intervention though undoubtedly has helped to improve the standard of life in the watershed, has introduced some of these constraints. Continuation of the irrigation activities in this virgin area is expected to bring changes in the quality of water and soil as well. It may emerge as a serious constraint in future if proper attention is not paid at this juncture. Key words: Constraints, Groundwater, Hand dug well, Intervention, Irrigation, Soil quality

Groundwater Suitability for Irrigation: a Case Study from Debre Kidane Watershed, Eastern Tigray, Ethiopia

The present paper tries to assess groundwater suitability for irrigation purpose in Debre Kidane Watershed (45.09 km2), northern Ethiopia. The goal was to evaluate the suitability of the groundwater for irrigation, examine the water types and to investigate possible long and short term impact on groundwater quality. Thirty six water samples each were collected in rainy and dry (irrigation) seasons from the active shallow hand dug wells. The well selection for detailed study and water sampling was done using stratified followed by random sampling technique. The number of wells selected for study is accounting 10% of the total available hand dug wells in the area. Parameters such as electrical conductivity (EC), pH, Total Dissolved Solids (TDS), temperature and other physical properties were recorded in the field. Major anions and cations (Ca2+, Mg2+, K+, Na+, CO32-, HCO3-, Cl-, SO42- and NO3-) were analyzed in the laboratory. Chemical data suggests that the water type in the area though varies from Mg-HCO3, Ca-HCO3, Mg-Cl, Na-HCO3 to K- HCO3, predominantly it is mixed cation-HCO3 type in the rainy season; and Ca-HCO3 (Piper diagram) and Na-HCO3 (Stiff diagram) in irrigation season. Dominance of Na in irrigation season and increase in Sodium Absorption Ratio (SAR) are primarily due to possible increase of Na absorption in the soil replacing Ca. According to the guidelines for irrigation water quality, the groundwater is suitable for irrigation with some minor exceptions. In rainy season, 89% of the samples fall under the water class “good” and 11% “permissible” whereas in irrigation season only 30% are classified as “good” and 70% under “permissible” class. Toxicity in terms of SAR and salinity though presently under control and there is no specific toxicity effect on vegetables and field crops, however, there are indications of their increase in due course of time if proper measures are not taken. Keywords: Groundwater, Irrigation, Salinity, SAR, Toxicity, Water quality, Hand dug well, Ethiopia

Geochemistry of metavolcanics and granitic intrusive from western margin of northern afar depression, Dallol, Northern Ethiopia

The western margin of northern Afar Depression constitutes various rock units of Neoproterozoic basement complex. Major oxide data of metavolcanic and granitoid rock samples from basement complex indicate significant variation in the concentration of major oxides (e.g. Fe2O3, TiO2, CaO, MgO). Metavolcanic rocks of Dallol demonstrate heterogeneous nature of magma source. The mafic metavolcanics indicate two distinct groups, (i) CaO-enriched and (ii) tholeiitic composition. Another group of magmatic series, the felsic metavolcanic group, shows a co-genetic relationship with the tholeiitic metavolcanics. Granitoids on the other hand have a wider range of SiO2 (61.5 – 76.65 wt %) and are peraluminous to metaluminous in nature.Keywords: Geochemistry, Metavolcanics, Granitioids, Dallol, Northern Afar Depression, Ethiopia

Hydrogeological Investigation and Groundwater Potential Assessment in Haromaya Watershed, Eastern Ethiopia

The paper assesses groundwater quality and productivity in Haromaya watershed, eastern Ethiopia. Continuous pumping test data, collected from seven boreholes was used to determine productivity of the aquifers. 14 water samples were tested for water quality. The aquifers on the basis of permeability, potential and extent of aquifers, are categorized into i) extended and shallow aquifers with intergranular porosity and permeability, and with moderate to high potential (alluvial and lacustrine sediments); ii) limited and shallow aquifers with fracture and/or karstic porosity and permeability, and with moderate potential (sandstone and limestone); and iii) limited and shallow aquifers with intergranular and fracture porosity and permeability, and with low potential (granite). On the basis of chemical data, the water is fresh except in lacustrine and swampy areas. HCO3-, Ca2+, Na+ and Mg2+ are the dominating ions in water from granite, sandstone and alluvium; and Cl and SO4 dominate in water from lacustrine sediments apart from HCO3-, Ca2+, Na+ and Mg2+. Areas suitable for groundwater development in the area are discussed. Keywords: Aquifer, Ethiopia, Groundwater potential, Haromaya, Hydrogeochemistry

Initiatives, Opportunities and Challenges in Shallow Groundwater Utilization: a Case Study from Debrekidane Watershed, Hawzien Woreda, Tigray Region, Northern Ethiopia

This paper assesses the opportunities and challenges of household irrigation practices that use groundwater as source in an area in Debrekidane watershed (45.1 km2), Tigray region, northern Ethiopia. It was done by evaluating the recharge and discharge potential of the aquifers, different water harvesting recharge structures and the impact of the intervention on the livelihood of the households. The recharge and discharge potential of the wells were determined from the pumping tests conducted on selected wells. The potential of different recharge structures were determined by evaluating size and nature of their construction. Impact of the intervention on livelihood of the household was assessed through developed semi-structure questionnaires, and by conducting focal group, individual, formal and informal discussions. There are about 360 hand dug wells in the study area getting recharged through the water harvesting structures and directly from rainfall. The numbers of beneficiaries are 326, out of which 5 % are women headed households. Nine per cent of the owners have double hand dug wells. The major opportunities identified in the area include planting variety of new trees, plants, and cultivating of highly valued crops, improvement of the households feeding habits and generation of regular income; and introduction and adoption of water lifting technologies. At the same time spacing and sliding of walls of the hand dug wells, simultaneous production of similar type of vegetable crops by many farmers, wastage of lands due to many wells and the waste debris material, maintenance of water lifting technology, water scarcity; and proper water utilization are some of the major challenges that are faced in the area. Though intervention has changed the situation from meager to significant production, the benefits can further be enhanced by overcoming the identified challenges

Suitability of Groundwater Quality for Irrigation with Reference to Hand Dug Wells, Hantebet Catchment, Tigray, Northern Ethiopia

The purpose of the project has been to assess the suitability of groundwater quality for irrigation purpose in the Hantebet catchment (24.4 km2), Tigray region, northern Ethiopia. The total numbers of hand dug wells in the area are 154. Out of these, 110 are functional and the remaining dried out. Stratified and random sampling techniques were utilized to select representative samples of groundwater. Accordingly, twenty groundwater samples were collected from twenty hand dug wells for chemical analysis. Twenty soil samples were also collected from the command area of the hand dug wells from where the groundwater samples were collected. Both groundwater and soil samples were analyzed for Ca2+, Mg2+, K+, Na+, CO3 2- , HCO3 -, Cl-, SO4 2-, and NO3 - besides pH and electrical conductivity (EC). Further, the Sodium Adsorption Ratio (SAR) for the both the groundwater and soil samples and Exchangeable Sodium Percentage (ESP) for the soil samples were also computed. Out of the analyzed 20 groundwater samples, 8 show EC values below 0.7 and the remaining between 0.71 and 1.12 dS/m, and pH values from 6.55 to 7.26. Chloride ion concentrations in groundwater range from 0.435 to1.393 (meq/l); bicarbonate from 5.124 to 9.660 (meq/l); and nitrate (NO3 - N) values below 5 (mg/l) except in one sample that has 5.87 mg/l. In soil samples, EC values range from 1.36 to 4.65 dS/m (at 25°C) (mean 2.487), and pH values range from 6.77 to 7.79 with a mean value 7.20. SAR values are well below 3 in groundwater, except in one sample and in soil it ranges from 0.111-1.571. ESP values in the soil vary from 2.016 to 4.863. The results indicate that the groundwater in general is suitable for irrigation purpose. In the case of soils about 80% of the soil samples indicate no hazard but 20% are saline. The soils are free of sodicity hazards. However, i) to achieve a full yield potential; ii) to sustain it for long period of time; iii) to avoid the possibility of increase in salinity, and iv) to avoid the possibility of occurrence of sodicity and toxicity hazardous in future, proper irrigation scheme is required in the form of crop selection, fertilizer usage and suitable alternative management

Effect of Chemical and Mineralogical Composition of Rocks on the Groundwater Chemistry of Hewanie and its Surrounding Areas, Southern Tigray, Ethiopia

The study was conducted in Hewanie and its surrounding areas of 169.82 km2 with a major objective of identifying the effect of chemical and mineralogical composition of rocks on the chemistry of the groundwater quality. This was conducted by taking 11 groundwater and 5 rock samples from the main geological units of the study area. Water samples were analyzed for major cations and anions, trace elements, TDS, total hardness, pH, electrical conductivity, and alkalinity the rock samples for major cations and anions and trace elements using AAS. The data was used to qualify and assess the quality of groundwater in the study area. Concentration of Ca2+, Mg2+, Na+, K+, HCO3-, Cl- and SO42- of groundwater samples in mg/l varied from 84 to 412, 96 to 211.2, 19.09 to 43.93, 2.34 to 51.09, 244 to 585.6, 71 to 340.8 and 49.49 to 122.5, respectively. Concentrations of Ca2+, Mg2+, Na+, K+, HCO3-, Cl- and SO42- of rock samples in ppm varied from 2586.4 to 28540, 2575.8 to 5289.6, 28.83 to 6134.9, 190.3 to 2379, 293.74 to 3717.6, 433.1 to 1143.1, 2787.8 to 27849.6, respectively. The predominant cations trend in both the groundwater and rock samples the study area was Ca2+ > Mg2+ > Na+> K+. Therefore, it is concluded that the local rock chemistry is seriously affecting the groundwater chemistry.Key words: Rock-water interaction, groundwater, rock, mineralogical composition, quality, Hewanie, Ethiopia

Mineralogical and Geochemical Characterization of Clay and Lacustrine Deposits of Lake Ashenge Basin, Northern Ethiopia: Implication for Industrial Applications

The paper tries to characterize and evaluate clay, lacustrine and diatomaceous earth deposits of Lake Ashenge basin, near Koram, northern Ethiopia and comment on its industrial implications. The country rocks are dominantly basalts and basaltic agglomerates overlain by minor amounts of rhyolite and ignimbrite. Sedimentary deposits, clays and associated sediments include 1) intercalations of lacustrine diatomaceous earth, other lacustrine and clays with channel deposits (gravel, pebbly sand and silt); 2) intercalations of diatomaceous earth, peat and clays with channel deposits exposed; and 3) intercalations of clay with channel deposits. X-ray diffractometer analysis of clay samples indicates kaolinite as a dominant clay mineral among others. On the basis of the abundance of different minerals, the clays are subdivided into four groups, 1) Kaolinite (K), 2) Microcline-Kaolinite (MK), 3) Muscovite-Kaolinite (MuK), and 4) Muscovite-Microcline-Kaolinite (MuMK). Other minor mineral phases include quartz, vermiculite, low-high albite, calcite and calcite magnesia. Diatomaceous clays are almost free from kaolinite. Kaolinite, being the dominant clay mineral varies from 6% in light brown to 77% in light grey clays. Al2O3 and SiO2 dominate the clay geochemistry among other oxides and based on the Al2O3 content, the kaolinite variety is subdivided into high Al2O3 (16-21 wt %) and low Al2O3 (8-13 wt%) types. Higher Al2O3 and similar SiO2 and Fe2O3 values in clays compared to the source basaltic rocks are related to the topography, mineralogy and climatic conditions that exist in the area. Compared to the low grade kaolinite type (about 56*106 tones), diatomaceous earth variety (77.3*105 tones) is relatively of good quality with high SiO2 content.Keywords: Clay and lacustrine deposits, Kaolinite, Diatomite, Lake Ashenge, Tigray, Ethiopi

Disinfection of impression materials: A comprehensive review of disinfection methods

Impression making is one of the most common procedures that are performed by dentists in day-to-day practice. These impressions can act as vehicles of transmission and carry various types of microorganisms, which further cause diseases like Hepatitis B, C, HIV, Tuberculosis etc. This contamination and cross contamination of microorganisms can be prevented by disinfecting the impressions immediately after removing from the mouth and label them as disinfected. Usually the impressions are placed under running water to remove saliva and blood, but this will eliminate the disease-causing microorganisms, so a standard protocol to disinfect the impressions and casts should be known to dentists and dental personnel. Various methods of impression disinfection like chemical disinfection, Microwave, Autoclave, Ultraviolet radiation have been described in literature having their own advantages, disadvantages and effects on impression material and casts. Recently antimicrobials and nanoparticles have been incorporated into the impression material itself to make it self- disinfecting. This will not only disinfect the impression material from inside but also disinfect the impressions from the time it is inserted in patient’s mouth.  A broad search on the literature available was performed to provide knowledge about mechanism of action, concentration of usage along with commercial preparations available of different disinfectants. This review article will enhance the knowledge and improve the behavior of dental health care workers about impression disinfection