Kulabako N R, Nalubega M, Thunvik R
Department of Civil Engineering, Makerere University, P.O.Box 7062, Kampala, Uganda.
Sci Total Environ. 2007 Aug 1;381(1-3):180-99. doi: 10.1016/j.scitotenv.2007.03.035. Epub 2007 May 23.
A study to assess the impacts of land use and hydrogeological characteristics on the shallow groundwater in one of Kampala's peri-urban areas (Bwaise III Parish) was undertaken for a period of 19 months. Water quality monitoring was carried out for 16 installed wells and one operational protected spring to ascertain the seasonal variation. The aspects of hydrogeological setting investigated in the study were the subsurface unconsolidated material characteristics (stratigraphy, lithology, hydraulic conductivity, porosity and chemical content), seasonal groundwater depths and spring discharge, topography and rainfall of the area. Both laboratory and field measurements were carried out to determine the soil and water characteristics. Field surveys were also undertaken to identify and locate the various land use activities that may potentially pollute. The results demonstrate that the water table in the area responds rapidly to short rains (48 h) due to the pervious (10(-5)-10(-3) ms(-1)) and shallow (<1 mbgl) vadose zone, which consists of foreign material (due to reclamation). This anthropogenically influenced vadose zone has a limited contaminant attenuation capacity resulting in water quality deterioration following the rains. There is widespread contamination of the groundwater with high organic (up to 370 mgTKN/l and 779 mgNO-3/l), thermotolerant coliforms (TTCs) and faecal streptococci (FS) (median values as high as 126E3 cfu/100 ml and 154E3 cfu/100 ml respectively) and total phosphorus (up to 13 mg/l) levels originating from multiple sources of contamination. These include animal rearing, solid waste dumping, pit latrine construction and greywater/stormwater disposal in unlined channels leading to increased localised microbial (faecal) and organic (TKN/NO-3) contamination during the rains. The spring discharge (range 1.22-1.48 m3/h) with high nitrate levels (median values of 117 and 129 mg/l in the wet and dry seasons) did not vary significantly with season (p=0.087) suggesting that this source is fed by regional base flow. However, the microbial quality deterioration observed in the spring discharge after a rain event (median values of 815TTCs cfu /100 ml and 433 FS cfu/100 ml) was attributed to the poor maintenance of the protection structure. Identification and selection of appropriate management solutions for the protection of shallow groundwater in informal settlements should not only be based on water quality problems and the causal physical characteristics as demonstrated by this study, but also institutional and socio-economic factors.
开展了一项为期19个月的研究，以评估土地利用和水文地质特征对坎帕拉一个城郊地区（布瓦西三区教区）浅层地下水的影响。对16口已安装的水井和一处正在使用的受保护泉水进行了水质监测，以确定季节变化。该研究中调查的水文地质背景方面包括地下未固结物质特征（地层、岩性、水力传导率、孔隙率和化学成分）、季节性地下水位和泉水流量、该地区的地形和降雨量。通过实验室和现场测量来确定土壤和水的特征。还进行了实地调查，以识别和定位各种可能产生污染的土地利用活动。结果表明，由于渗透系数为10(-5)-10(-3) m·s(-1)且浅层（<1 m bgl）的包气带由外来物质（由于开垦）组成，该地区的地下水位对短时间降雨（48小时）反应迅速。这种受人为影响的包气带污染物衰减能力有限，导致雨后水质恶化。地下水受到广泛污染，有机污染物含量高（总凯氏氮高达370 mg/l和硝酸根高达779 mg/l）、耐热大肠菌群（TTCs）和粪链球菌（FS）（中位数分别高达126×10³ cfu/100 ml和154×10³ cfu/100 ml）以及总磷含量高（高达13 mg/l），污染源多种多样。这些污染源包括动物饲养、固体废物倾倒、坑式厕所建设以及在无衬砌渠道中排放灰水/雨水，导致降雨期间局部微生物（粪便）和有机污染物（总凯氏氮/硝酸根）污染增加。泉水流量范围为1.22-1.48 m³/h，硝酸盐含量高（湿季和干季中位数分别为117和129 mg/l），季节变化不显著（p=0.087），这表明该水源由区域基流补给。然而，降雨事件后泉水流量中观察到的微生物质量恶化（中位数为815 TTCs cfu /100 ml和433 FS cfu/100 ml）归因于保护结构维护不善。为保护非正式定居点的浅层地下水而确定和选择合适的管理解决方案，不仅应基于本研究所示的水质问题和相关物理特征，还应考虑制度和社会经济因素。
