Abstract:The purpose of this study was to investigate the movement of chloride through a vadose zone located under failed and non-regulated septic tanks of Duhok city, Kurdistan of Iraq, potentially contaminating its groundwater. A physical vadose model (PVM) of a vertical flow direction was built in the laboratory to represent the city soil profile. The size of the PVM was 210 × 122 × 9.7 cm (height, width, and depth). Preliminary soil tests were conducted to better represent the lithology of study area. The PVM was then packed with regional silt clay soil, after modifying its texture, using an innovative packing procedure to preserve natural soil density and porosity. The model was run for a period of three months with newly collected septic water (black water from a septic tank) as an exclusive source of contaminants. Water samples from eight vertically arranged portals representing 12.5, 37.5, 62.5, 87.5, 112.5, 137.5, 162.5, and 187.5 cm levels in the subsurface soil profile were collected on a daily basis and analyzed weekly. Logistic regression and logarithmic models were developed to spatially predict the movement of chloride ions at different sampling depths in the soil profile until the system had reached the equivalent chloride concentration of the septic water or had stabilized. There was a good agreement between the physical model and the statistical models, however each model had its strengths and weaknesses. This study demonstrated that there is a potential for septic water to reach the water table within a 2-3 weeks period. Dilution and dispersion appear to play important roles in the fate and transport of septic water. This study has the potential to help the local authorities predict percolation rates and establish strategies for groundwater management in order to protect the public health.

The purpose of this study was to assess the effect of non-regulated (and directly contacted) septic tanks on ground water quality through designing a laboratory physical vadose model (PVM) with a vertical flow direction. The model was packed with silt-Clay soil using a new packing approach other than the ordinary (standard, modified and static) compaction methods, which was adopted upon its homogeneity and efficiency approval. The effect of septic tanks as an exclusive source of contaminants was represented by supplying the designed model with newly collected septic water (black water from a septic tank). Preliminary in-situ soil tests were conducted to better represent the lithology of area of this study. The model was run for a period of three months and water samples were collected on daily basis however, weekly analyzed. Selected physical and chemical parameters were studied for assessment including pH, Temperature, Dissolved Oxygen (DO), Electrical Conductivity (EC), Total Hardness (TH), Ammonium (NH 4 -N), Nitrate (NO 3¯N ), and Phosphorus (P). Analytical results were used to identify and model trends to estimate and predict future trends, which mostly led to a conclusion of bad category and very low ground water quality as a result of its direct contact with non-regulated septic tanks. This study helped the local government in establishing precaution strategies for ground water management in order to protect the public health.

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This study was conducted to assess the impact of septic water on soil water infiltration in Duhok city potentiallycontaminating regional groundwater through designing a large-scaled laboratory physical model of vertical flowdirection packed homogenously with silt-Clay soil. The designed model was supplied with newly collected septicwater. With steady-state flow condition, the model was run, water samples were collected and analyzed weekly.Various parameters and constituents that may influence soil structure and water infiltration were examined including : Electrical conductivity, sodium, calcium, magnesium, carbonate, bicarbonate, residual sodium carbonate (RSC), pHc and adjusted sodium absorption ratio (adj. SAR). For assessing groundwater quality, bacteriological analysis were conducted. Analytical results were used to estimate the examined parameters and predict their future trends. Results revealed that electrical conductivity (EC) was accumulating until it reaches the carrying capacity. Sever hazard of (RSC) was detected within 25 meter depth. Average pHc was 6.74 indicating the tendency of lime (CaCO3) to precipitate from applied septic water. adj. SAR for port A and port B were 11.1 and 8.65 respectively which, caused severe soil deterioration, but on the other hand helped in decreasing the rate of contaminants transport for treatment within the soil before reaching the groundwater. Results of bacteriological analysis indicated that groundwater shallower than 31 meter was contaminated by fecal and total coliform bacteria. This study helped local authorities in establishing precaution strategies of groundwater management to protect public health.