Quality of Water drawn from the Aquifers and Contamination Issues

Water drawn from all wells feeding the City’s supply comply with the "Drinking Water Standards for New Zealand 1995" without being treated. Water from several wells in the northwest zone is however dosed to increase pH levels, to reduce the risk of corrosion of metal fittings.

 

The Regional Council carries out tests quarterly for hydrocarbons from various wells throughout the City. Incidences of groundwater contamination in the shallow (unconfined) aquifers, including the recharge area for the City’s supply, have occurred on numerous occasions over the past few years. Where these have been detected, concentrations have remained static, indicating that such contamination is long lived.

 

The effect of increasing demand on groundwater quality is significant for the City. Isotope investigations have shown that water from the deepest of the City’s wells is thousands of years old. As this water is abstracted, the danger is that water of lower quality will replace it.

 

So far, the quality of groundwater extracted by the City Council has not shown a significant degradation trend. However the Regional Council are now using improved analytical techniques and higher sampling frequencies which may reveal problems not readily identified using past methods.

 

Soils

There are approximately 8600 hectares of rural land with Land Use Capability class 1 and 2 soils. This includes soils that are classified as class 3, but with drainage would be classified as either class 1 or class 2. Class 1 and 2 soils account for 30 per cent of the rural soils in Christchurch. They are in limited quantities both regionally and nationally, and are valued for their high productivity potential. Traditionally they have been used in Christchurch for market gardening, berry fruit production and town supply dairying.

 

Soils with the lowest Land Use Capability tend to be associated with areas of the port hills, the coastal zone and areas associated with remnants of the Waimakariri gravels.

Table 2.9 Soil Quality in Rural Christchurch
Land Use Capability Class	Total Area in Rural Zone (ha)	Total Area in Christchurch City (ha)
Class 1	2,134	7,086
Class 2	6,496	12,019
Class 3	2,469	3,689
Class 4	2,035	2,596
Class 5	814	1,103
Class 6	10,134	13,312
Class 7	2,139	2,548
Areas not Classified	1,136	1,164
Total	27,357	43,517
Soil Versatility class 3wb*	2,730	7,858

* Class 3wb is soils are included in Class 1 and 2. They have the potential to be Class 1 and class 2 soils with drainage.

Source: Christchurch City Council

 

The Land Use Capability[4] is a general purpose, qualitative land evaluation system which has been widely applied in New Zealand for planning land use, especially for management for soil conservation. It identifies the degree of limitation to sustainable production. There are eight classes, with class 1 soils being the most productive and class 8 the least productive (Table 2.9).

 

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