Residents’ Meeting - Water Supply

Arsenic levels in Groundwater

May 2018

1. Background information on:i. arsenic in groundwaterii. Identifying the issue

2. Sampling results to identify: i. affected areasii. likely source of arsenic

3. Water supply options for residents

This presentation covers:

Introduction1. Residents’ and Hawke’s Bay agency

responsibilities2. The issue3. International/ national context4. Groundwater sampling results5. Options for residents

1. Agency responsibilitiesi. HB Regional Council

Natural resource knowledge and management

ii. HB District Health BoardWe want everyone in the region to be healthy

iii. Napier City Council and/or Hastings District Council

To provide facilities and services

www.horizons.govt.nz/HRC/media/Media/Water/Guidelines-for-well-owners.pdf?ext=.pdf

District Health Board

City Council

Well siting

Regional Council

1. Agency responsibilities

Facilities and ServicesEnvironmental Health Officers

Natural Resource Knowledge & Management

Groundwater ScientistsResource Use Officers

Health ServicesDrinking Water AssessorsHealth Protection Officers

DWGCJoint Working Group

City/ District Council

1. Rural resident involvement

2. The issue – a private bore: 3 separate locations

i.e. arsenic concentration = 500 µg/LMaximum Acceptable Value (MAV) =10 µg/L(based on long-term exposure)

500 µg/L

2. The issue – a private bore

Arsenic concentration = 500 µg/LMaximum Acceptable Value (MAV) =10 µg/LLethal dose is approx. 70,000 µg

3. New Zealand context1. Arsenic >MAV in groundwater is found:

i. Canterburyii. Marlboroughiii. Manawatuiv. Bay of Plentyv. Waikato

2. Natural arsenic may be associated with:1. Geothermal activity2. Volcanic geology3. Reducing conditions (very low oxygen)4. Peat and carbon-rich material

3. New Zealand context1. Arsenic >MAV in groundwater is found:

i. Canterburyii. Marlboroughiii. Manawatuiv. Bay of Plentyv. Waikato

2. Natural arsenic may be associated with:1. Geothermal activity2. Volcanic geology3. Reducing conditions (very low oxygen)4. Peat and carbon-rich material

3. New Zealand context1. Arsenic >MAV in groundwater is found:

i. Canterburyii. Marlboroughiii. Manawatuiv. Bay of Plentyv. Waikato

2. Natural arsenic may be associated with:1. Geothermal activity2. Volcanic geology3. Reducing conditions (very low oxygen)4. Peat and carbon-rich material

3. Worldwide context

USA natural sources > 1,000

3. Worldwide context

USA natural sources > 1,000

3. In Hawke’s Bay – Breckenridge 2017

3. Hawke’s Bay – Breckenridge 2017

3. Hawke’s Bay – Breckenridge 2017

3. Private bore – Poraiti Hill, 2018

3. Poraiti Hill – potential sources

Information presented to residents 19 April:

• No contaminated sites identified from HAIL database

• No known land use activities that might be a source

• Possibly a natural source, mobilised by groundwater conditions

4. Sampling plan – 19 April 2018

4. Sampling results

4. Sampling results

4. Sampling results

-180

-140

-100

-60

-20

20

60

100

140

180

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Redo

x Po

tent

ial (

mV)

Arsenic Concentration (mg/L)

4. Sampling results

-180

-140

-100

-60

-20

20

60

100

140

180

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Redo

x Po

tent

ial (

mV)

Arsenic Concentration (mg/L)

-180

-140

-100

-60

-20

20

60

100

140

180

0.00 0.02 0.04 0.06 0.08 0.10

Redo

x Po

tent

ial (

mV)

Arsenic Concentration (mg/L)

MAV

4. Sampling results• Arsenic exceedances in more than one

bore• No particular area affected – the issue is

not uniform. • No evidence of a contamination plume• Arsenic is strongly associated with anoxic

groundwater• Highly likely to be a natural source of

arsenic

Resident’s involvement

Agency responsibilities

Facilities and ServicesEnvironmental Health Officers

Natural Resource Knowledge & Management

Groundwater ScientistsResource Use Officers

Health ServicesDrinking Water AssessorsHealth Protection Officers

DWGCJoint Working Group

City/ District Council

5. The role of HBRC• Sampling is completed in Poraiti Hill area • Our role is now to ensure all households

are informed, including advice to test groundwater supplies for arsenic

• Regional investigation and information to domestic groundwater (self-supply) users

5. Options for owners of affected bores1. Arsenic greater than 10 mcg/L is not potable2. Point of use treatment3. Alternative suppli

5. Options for owners of affected bores3. Alternative supplies:

• Rainwater collection?• Community groundwater supply?• Reticulated supply?• Other options?

5. Options for owners of affected bores1. Suggestion for residents to consider

preference for:a) household solutions, orb) community solution

Summary1. Although not all bores are affected, arsenic

exceedances may occur in groundwater throughout aquifer systems

2. Highly likely to be a natural source, associated with anoxic groundwater

3. HBRC will inform all residents, including advice to test groundwater supplies

4. Options and alternatives for residents to consider – with support from Agencies