The document discusses a national groundwater monitoring programme in New Zealand that collects data from 112 sites across 15 regions. The data shows that 32% of groundwater is classified as "Natural Fresh" with little human impact, 26% is "Natural Evolved" with potential for higher levels of some parameters, and 42% is "Impacted" with elevated nitrate levels. Relating water quality to surrounding land use is difficult as recharge areas can be distant and travel times long, allowing natural processes to alter indicators over time. Groundwater age is also related to water quality, with younger water generally showing more impact.

1. Age and quality of groundwater in
New Zealand
Chris Daughney
Groundwater Research Leader

2. National Groundwater Monitoring Programme
(NGMP): Introduction
• Current size 112 sites, 15
regions
• Quarterly collection of
samples by regional council
staff (GNS method)
• Analysis of 25+ parameters
at GNS Wairakei
• Lots of data on quality of
New Zealand groundwater!
GNS Science

3. National Groundwater Monitoring Programme
(NGMP): Introduction
• Current size 112 sites, 15
regions
• Quarterly collection of
samples by regional council
staff (GNS method)
• Analysis of 25+ parameters
at GNS Wairakei
• Lots of data on quality of
New Zealand groundwater!
GNS Science

4. NGMP: National Status of Groundwater Quality
7E+006
• A simple summary of 6.8E+006
N
groundwater quality: Northland
6.6E+006
– “Natural Fresh” (32%): Auckland
Bay of Plenty
little or no human impact, 6.4E+006
Waikato
Gisborne
low ion concentrations Taranaki
6.2E+006
Manawatu - Wanganui Hawkes Bay
Tasman
– “Natural Evolved” (26%): 6E+006
Wellington
risk of high iron, West Coast Marlborough
manganese, arsenic but 5.8E+006
no risk of high nitrate Canterbury
Southland
5.6E+006
– “Impacted” (42%): 5.4E+006
Otago
0 100 200 Kilometers
elevated nitrate, but no
risk of high iron, 5.2E+006
2E+006.2E+006
2 2.4E+006
2.6E+006
2.8E+006E+006.2E+006
3 3 3.4E+00
manganese or arsenic
GNS Science

5. NGMP: Groundwater Nitrate-Nitrogen Levels
11.3 mg/L
7.2 mg/L 5%
Background
6%
Significant Impact
14%
Substantial Impact
3.5 mg/L
58%
17% Threat to Ecosystem
Unsafe for Human
Consumption
1.6 mg/L
GNS Science

6. Nitrate concentrations are independent of
surrounding land use
2
1
log10(no3)
0
-1
-2
-3
Unknown
Urban
Park/Reserve
Industrial
Horticultural
Dairy
Agriculture
GNS Science

7. Why is it difficult to relate groundwater quality
to surrounding land use?
• It is land use in the aquifer’s
recharge zone that has the
potential to influence
groundwater quality, and the
recharge zone might be far
away from the monitoring
site.
• There may be a long travel unconfined
time from the recharge zone confined
to the well, such that the Impacted
groundwater we are Groundwaterwater
Contaminated
monitoring today might pre-
date land use intensification.
• Indicators of land use
activity, e.g. nitrate, can be
removed from groundwater
by natural processes.
GNS Science

8. NGMP: Relating groundwater age to quality
Mosaic Chart for mrtclass by medclust2
medclust2
A: <5
0 to 10 years old 1A “Natural Fresh”
1B
2 “Natural Evolved”
11 to 40 yearsto 40
B: 5 old
“Impacted”
41 to 100 C: 40-100
years old
100+ years>100
D: old
GNS Science

9. DELINEATION METHODS - results
Pemberton (MRT = 95 years)
8
7
Concentration (mg/l)
6
5
Nitrate-N
4
Chloride
3
2
1
0
1995 1998 2001 2004 2006 2009
Date
GNS Science