Age and quality of groundwater in

New Zealand

Chris Daughney

Groundwater Research Leader

GNS Science

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

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

NGMP: National Status of Groundwater Quality

• A simple summary of groundwater quality:

– “Natural Fresh” (32%): little or no human impact, low ion concentrations

– “Natural Evolved” (26%): risk of high iron, manganese, arsenic but no risk of high nitrate

– “Impacted” (42%): elevated nitrate, but no risk of high iron, manganese or arsenic

N

0 100 200 Kilometers

Northland

Auckland

Waikato

Taranaki

Manawatu - Wanganui

Bay of Plenty

Gisborne

Hawkes Bay

Wellington

Tasman

Marlborough

Canterbury

Otago

West Coast

Southland

2E+0062.2E+0062.4E+0062.6E+0062.8E+0063E+0063.2E+0063.4E+0063.6E+0063.8E+0065.2E+006

5.4E+006

5.6E+006

5.8E+006

6E+006

6.2E+006

6.4E+006

6.6E+006

6.8E+006

7E+006

GNS Science

NGMP: Groundwater Nitrate-Nitrogen Levels

6%

5%

14%

17%58%

Background

Significant Impact

Substantial Impact

Threat to Ecosystem

Unsafe for HumanConsumption

1.6 mg/L

3.5 mg/L

7.2 mg/L

11.3 mg/L

GNS Science

Nitrate concentrations are independent of

surrounding land use

log

10

(no

3)

Ag

riculture

Dair

y

Hort

icultura

l

Ind

ustr

ial

Pa

rk/R

ese

rve

Unkn

ow

n

Urb

an

-3

-2

-1

0

1

2

GNS Science

Why is it difficult to relate groundwater quality

to surrounding land use?

c o n f i n e d

u n c o n f i n e d u n c o n f i n e d

Contaminated waterImpacted

Groundwater

• 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 time from the recharge zone to the well, such that the groundwater we are 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

NGMP: Relating groundwater age to quality

Mosaic Chart for mrtclass by medclust2

medclust21A1B2

A: <5

B: 5 to 40

C: 40-100

D: >100

“Natural Fresh”

“Natural Evolved”

“Impacted”

0 to 10 years old

11 to 40 years old

41 to 100 years old

100+ years old

GNS Science

DELINEATION METHODS - resultsPemberton (MRT = 95 years)

0

1

2

3

4

5

6

7

8

1995 1998 2001 2004 2006 2009

Date

Co

ncen

trati

on

(m

g/l

)

Nitrate-N

Chloride