Groundwater Quality

Major Ions

The most common elements found in groundwater include four cations (positively charged ions) – calcium, magnesium, potassium, and sodium, – and three anions (negatively charge ions) – bicarbonate, chloride, and sulphate.

None of these elements has been found to cause health problems at the concentrations found in groundwater, but some may give the water undesirable properties. For example, high concentrations of calcium and magnesium, common in limestone areas, make the water hard and cause scale formation. High concentrations of sodium and chloride, which may indicate that sea water is entering the groundwater, can give the water a salty taste and may affect the suitability of the water for irrigation.

Conductivity

This is a measure of how well the water conducts electricity, and it increases with the amount of dissolved material in the water. High conductivity values can sometimes indicate that contaminants are present.

pH

Groundwater in Canterbury is commonly slightly acidic, especially in the shallow alluvial aquifers of the Canterbury Plains and some inland basins. The acidity (low pH) will not affect your health, but slightly acidic groundwater is corrosive and can dissolve metals, especially copper, from pipes and pumps. The corrosion can shorten the economic life of plumbing and hot water cylinders, and in some cases, the dissolved metals in the water may cause illness.

Bacteria and pathogenic organisms

Microbiological indicator organisms such as E. coli and faecal coliform bacteria are commonly detected in Canterbury wells. For the most part, these organisms are not harmful themselves, but they indicate the presence of faecal material, which may contain disease-causing (pathogenic) organisms. The most common sources of microbiological contamination in wells are 1) surface matter that enters the well through a poorly constructed wellhead, and 2) nearby septic tanks. Other potential sources include intensive stock grazing the disposal of sewage or animal effluent on land near the well.

Nitrate-nitrogen

Sources of nitrates in groundwater include agricultural activities, septic tanks, and effluent disposal. The Ministry of Health has set a drinking-water standard for nitrate based on health risks to pregnant women and bottle-fed infants up to 6 months of age. The standard is exceeded in some parts of Canterbury, especially where the groundwater is shallow and unconfined with little dilution from rivers.

Iron and manganese

Iron and manganese concentrations can be elevated in situations where a well draws water from a groundwater zone that is low in oxygen. When this water is pumped up to the surface and exposed to air, the iron and manganese precipitate out of the water as insoluble oxides that can block pipes, pumps, shower heads, and irrigation systems. These oxides can also cause red or black staining in sinks or laundry, and they may give the water a peculiar taste. Such effects occur at concentrations below health guidelines, but they can be troublesome. At high concentrations, manganese can cause health problems.

Arsenic

Arsenic is a metalloid that occurs naturally in the environment and is often associated with the weathering of some minerals and rocks, geothermal fluids and from some coals, peat and fine sediment deposits. Arsenic can also be present in groundwater as a result of waste discharges, such as from timber treatment sites, sheep dips, and pesticides. Naturally occurring arsenic at concentrations above drinking water standard has been found in the groundwater in some coastal areas of Canterbury.

Other Metals

Heavy metals such as lead, zinc, copper, and chromium can be present in groundwater as a result of the disposal of wastes containing metals, including tannery or timber treatment discharges, waste from metal stripping or electroplating activities, and landfill leachate.

Hydrocarbons

Hydrocarbons are present in a variety of household and industrial chemicals, including petroleum products, refrigerators, insecticides, solvents, propellants, and cleaners. They are unlikely to be present in groundwater unless there is a nearby contaminant source such as a spill or a leaking storage tank.

Pesticides

Pesticides include any substance that is used to control a target organism, such as fungicides, insecticides, herbicides, and growth regulators. Most pesticides are rarely found in groundwater because they stick to soil particles or break down readily, but some, like the triazine herbicides (simazine, atrazine, and terbuthylazine), have been detected in Canterbury groundwater.

Disclaimers

The attached information is supplied on the basis that it is accurate to the best of the Environment Canterbury's knowledge and belief and is based on the information currently held by the Environment Canterbury. While Environment Canterbury has exercised all reasonable skill and care in controlling this information, Environment Canterbury accepts no liability in contract, tort or otherwise howsoever, for any loss, damage, injury or expense (whether direct, indirect or consequential) arising out of the provision of this information or its use by you.

The results relate to groundwater quality in the well at the time that the sample was collected. However, it is important to note that groundwater quality can change over time. The information is limited to the determinands that were analysed.

The locations of wells in Environment Canterbury's Wells database are generally accurate to within a few hundred metres. Therefore, it is possible that any details of wells included in this response may not actually be on the property in question. Likewise, there may be other wells on the property that ECan does not have on record, or for which ECan has inaccurate location details. If you have more detailed information on wells on the property, contact Environment Canterbury staff.