Groundwater protection zones for community drinking water supply - - PowerPoint PPT Presentation

GNS Science

Groundwater protection zones for community drinking water supply wells in the Wellington Region

Mike Toews 30 May 2018

GNS Science

Who Am I?

• Mike Toews (pronounced Taves)
• Studied as a Hydrogeologist and Groundwater

Modeller in Canada, with a M.Sc. Degree

• Over ten years of experience as a GW modeller
• Employed by GNS Science since 2011
• First capture zone work from 2006, as part of my

M.Sc. Degree

• Developed CZs for several areas in Waikato
• Developed CZs for Wellington in 2015

GNS Science

Purpose

• Present mapped groundwater protection zones

to drinking water supply wells

• Discuss how the zones can be used to protect

against discharges to land from:

– Microorganisms (<1 year residence time) – Other potential contaminants that are more persistent or accumulate with distance and time

§ 1.1, p. 1

GNS Science

Capture zone (CZ)

Total source area where water may potentially travel from Protection against non-easily degraded chemicals

Protection zone (PZ)

Protection against pathogens

(distance/ 1-year travel time)

Definitions

§ 1.2, p. 2–3

GNS Science

Attached / detached PZ

• Fig. 1.2, § 1.2, p. 3

GNS Science

Scope of report

• Use existing GW models

– Hutt Valley – Mark Gyopari’s HAM3 model – Kapiti Coast – Doug’s model – Wairarapa Valley – Mark & Doug’s FEFLOW models

• Methods similar to Toews & Donath (2015)

– Similar resources and uncertainty simulations – Simplified language and mapped outputs

• Use PNRP Schedule M2 wells
• Evaluate a range of PZ time thresholds

– 1-year, 2-year, 5-year, etc.

§ 1.1, p. 1–2

GNS Science

Methods

• Groundwater flow models
• Particle tracking

– Forwards and backwards – From groundwater table to well (saturated only)

• Time-based methods

– Hard science for pathogen removal based on decay rates over distance (i.e. distance-based) – PZs defined by travel time from water table to well – Conservative to include extra distance

• Sensitivity analysis

– Multiple models used, different flow paths – Parameters were adjusted ±25% – Simplest way to consider preferential flow pathways

§ 3, p. 7–9

GNS Science

Areas

• Fig. 1.1, § 1.1, p. 1

GNS Science

Hutt Valley

• Model runs for 5 years, between 2007–2012
• Extends beneath Wellington Harbour
• Simulates interaction between Hutt River, Ocean

and the Wai

Location WRC Well number Description

Petone R27/7354 Buick Street public bore Gear Island BQ32/0033 Gear 3 Gear Island BQ32/0034 Gear 2 Gear Island BQ32/0035 Gear 1 Waterloo R27/4064 Colin Grove Waterloo R27/0001 Hautana Street Waterloo R27/4063 Bloomfield Terrace Waterloo R27/1179 Penrose 7 Waterloo R27/4057 Penrose 4 Waterloo R27/1180 Willoughby 8 Waterloo R27/4058 Willoughby 5 Waterloo R27/1181 Mahoe 6

Table 2.3 § 2.2, p. 5

GNS Science

Hutt Valley

• Fig. 4.1, p. 11

§ 4.2, p. 10–11

GNS Science

Hutt Valley

• Provisional PZ

based on geology (Begg & Morgenstern, 2017)

• SW extent where

Petone Marine Beds change between thin to continuous aquitard

• Boundary can be

refined (Begg)

S42A Loe (2018)

• p. 55–57

GNS Science

Kāpiti Coast

• Longest running model, 19 years (1992–2011)
• Simulates several aquifers, 38 km long

Location WRC Well number Description

Ōtaki R25/5228 Rangiuru Road Bore Ōtaki R25/5235 Tasman Road Bore Hautere S25/5379 next to Ōtaki River Hautere S25/5443 next to Ōtaki River Waikanae R26/6291 K4 – Cooper 1 Waikanae R26/6293 K5 – Ngā Manu Waikanae R26/6299 K12 Waikanae R26/6307 Kb4 – Landfill Waikanae R26/6311 KB7 Waikanae R26/6559 Otaihanga Bore PW1 Waikanae R26/6664 Otaihanga Bore PW5 Waikanae R26/6666 Rangihiroa – not implemented Waikanae R26/6804 K10 – Market Garden Waikanae R26/6839 K6 – Wooden Bridge Waikanae R26/7255 N2 Paekakariki R26/7158 adjacent to water treatment plant

Table 2.4, p. 6 § 2.3, p. 5–6

GNS Science

Ōtaki

• Fig. 4.2

§ 4.3, p. 12

GNS Science

Hautere

• Fig. 4.3, p. 13

§ 4.3, p. 12–13

GNS Science

Waikanae

• Fig. 4.4, p. 14

§ 4.3, p. 13–14

GNS Science

Paekakariki

• Fig. 4.5, p. 15

§ 4.3, p. 14–15

GNS Science

Wairarapa Valley

• Three separate FEFLOW models
• 15 to 16 years (1992 to 2007/2008)

Model Location WRC Well number

UV Opaki T26/0259 UV Masterton T26/0243 UV Masterton T26/0549 UV Wainuioru T26/0492 UV Wainuioru T26/0493 MV Carterton S26/0705 MV Carterton S26/0824 MV Carterton S26/0919 MV Greytown S26/0880 MV Greytown and Featherston BP33/0008 MV Greytown and Featherston BP33/0009 MV Greytown and Featherston BP33/0022 LV Martinborough S27/0396 LV Martinborough S27/0404 LV Martinborough S27/0695 LV Martinborough S27/0910

Table 2.5 § 2.4, p. 6

GNS Science

Masterton

• Fig. 4.6

§ 4.4, p. 16

GNS Science

Carterton

• Fig. 4.7, p. 17

§ 4.4, p. 16–17

GNS Science

Greytown and Featherston

• Fig. 4.8, p. 18

§ 4.4, p. 17–18

GNS Science

Martinborough

• Fig. 4.9, p. 19

§ 4.4, p. 18–19

GNS Science

Discussion

• Different sizes and shapes of PZs
• Overconservative, but targeted to cover land

where groundwater may flow to a well

• Groundwater sourced from:

– Rainfall recharge from land surface – Surface water recharge from streams, rivers

• Drinking water standard requires groundwater to

have at least 1-year residence time

• National Environmental Standard (NES) is

legislation to preserve drinking water quality

§ 5, p. 20–21

GNS Science

Recommendations

• 1-year PZs can be used to protect against

microorganisms

• Older PZs can be used to protect against other

contaminants with longer filtration or decay times

• Detached PZ may require an additional arbitrary

fixed radius zone around wellhead (min. 5 m)

• PZs should be re-evaluated with new models,

information, wells, pumping scenarios, etc.

§ 6, p. 23

GNS Science

Questions

Mike Toews m.toews@gns.cri.nz