Groundwater vulnerability Groundwater vulnerability depends on a number of soil and geologic characteristics, including depth to the water table, texture of the soil, and bedrock characteristics. For example, groundwater underlying sandy soil is more vulnerable than groundwater under clay soils. Shallow groundwater is much more vulnerable than deeper aquifers. The vulnerability of the geologic area where the well is located is an important factor in determining risk of contamination. Another important factor influencing contamination levels is the well depth.
Shallow wells are much more likely to be contaminated than deep wells.
Contamination of a particular well can also depend on the well construction. In some cases, the top portion of the well is not adequately sealed when constructed, and contamination occurs around the top of wellhead. Potential sources of nitrate contamination Septic systems, fertiliser, and livestock wastes are all potential sources of nitrate that can leach to groundwater. It is usually difficult to assess the particular nitrate source when well water is found to be contaminated, since often the contamination is the result of the sum of many sources. Septic systems, especially if poorly constructed or maintained, are a potential source of nitrate and bacteria.