in the matter - gw...2.9 should the proposed quarry operations remove material to a level below the...

BEFORE THE CARTERTON DISTRICT COUNCIL AND

GREATER WELLINGTON REGIONAL

COUNCIL

IN THE MATTER of the Resource Management Act 1991

AND

IN THE MATTER of resource consents application by

WAIRARAPA AGGREGATES LTD necessary

to establish a quarry and clean fill operation.

STATEMENT OF EVIDENCE OF

Dr JOHN (JACK) ALLEN McCONCHIE

1.0 INTRODUCTION

1.1 I am a Principal Water Resources Scientist working for Opus International Consultants

Ltd.

1.2 Prior to the start of 2008, I was an Associate Professor with the School of Earth Sciences

at Victoria University of Wellington. I hold a Bachelor of Science degree with first class

Honours, and a PhD. I am a member of the New Zealand Hydrological Society, the

American Geophysical Union, the New Zealand Geographical Society, the Australia-New

Zealand Geomorphology Group, and the Environment Institute of Australia and New

Zealand. I taught undergraduate courses in hydrology and geomorphology, and a post-

graduate course on hydrology and water resources that focused on hydrometric analysis

and groundwater. For more than 20 years my research focused on various aspects of

hydrology and geomorphology, including: slope and surface water hydrology; groundwater

dynamics, interactions, and contamination (including saline intrusion); soil-water

interactions; irrigation efficiency; fluvial geomorphology, including bank erosion and

sediment transport; and geomechanics and slope instability.

1.3 Within these fields I have edited one book. I have written or co-authored 10 book

chapters, and over 40 internationally-refereed scientific publications.

1.4 I was the New Zealand Geographical Society representative on the Joint New Zealand

Earth Science Societies’ Working Group on Geopreservation. This group produced the

first geopreservation inventory; published as the New Zealand Landform Inventory.

Wairarapa Aggregates Ltd consent hearing evidence 2 Opus International Consultants

1.5 Specific to this resource consent application I have undertaken three field visits to the

proposed quarry site. I have reviewed all the available information relating to groundwater

dynamics and hydrogeology of the area; this includes the Section 42A Officer’s Reports. I

have analysed the available groundwater data in detail. I have undertaken an intensive

geophysical survey of the proposed quarry site and surrounding area to define the

geoelectric structure. The results of this survey have been related back to the

hydrogeology of the site. I also supervised a Masters’ thesis that investigated the causes

and dynamics of groundwater contamination at the old Waingawa Freezing Works and

Masterton Borough Landfill. I therefore have a comprehensive understanding of the

climate, hydrology, and hydrogeology of the area potentially affected by this application.

1.6 In my evidence I will address specifically the potential effects of this proposal on:

• The groundwater regime and dynamics of the area;

• The interaction of groundwater with the wetland areas; and

• The existing hydrologic system and its various interactions.

1.7 My evidence concludes that the consents sought can be granted. The proposed

operations will have effects on the groundwater, surface water, and wetlands nearby that

are no more than minor, and probably less than minor. Consent conditions can be set

that mitigate or avoid any potential minor effects on runoff water quality. It is likely that

these conditions will actually result in an improvement of the current runoff situation which

is one of neglect.

2.0 BASIC CONCEPTS

2.1 Understanding the potential effect of the proposed quarry operation on the hydrologic

system in area is relatively simple. It requires only acknowledgment of the fact that water,

whether surface water or groundwater, flows down an energy gradient. Invariably this

means that water flows down hill.

2.2 Where the ground is porous, water will flow through the pores but still in a down-gradient

(down-hill) direction. Where the ground is saturated, or impermeable, water will flow on

the surface. The flow of water will be greatest down the steepest energy gradient

(steepest slopes) and where the restrictions to flow are least. Below ground this means

that flow is fastest (greatest) though the bigger pores (e.g., larger sediments). Above

ground, this means that flow is fastest within channels. Where water cannot flow down-hill

it will pond.

2.3 Groundwater is commonly understood to mean that water saturating all the voids within a

geologic stratum. This saturated zone (i.e., potential aquifer) is distinguished from the

unsaturated, or aeration zone, where the voids are filled with air as well as moisture. To

be classed as groundwater, however, the water in the saturated zone must also be held in

the pores by capillary forces that are less than the force of gravity. This then allows the

water in the pores to flow down-gradient.


2.4 In an unconfined aquifer, where water can saturate all the voids right up to the ground

surface, no rigid demarcation of waters between the two zones is possible as the

boundary fluctuates depending on the inputs and outputs of moisture. The top of the

saturated layer in an unconfined aquifer is often called the water table. The water table

will generally be highest during winter and lowest at the end of summer.

2.5 Where an aquifer intersects the ground surface the groundwater will form a spring, the

flow from which will often form a small stream. While the flow of water from springs tends

to be more stable than rain-fed streams, it still varies depending on groundwater

conditions. The higher the water table (i.e., top of the saturated zone), or pressures within

the groundwater system, the greater the flow.

2.6 Two such springs exist in the general vicinity of the proposed quarry. At least one of

these occurs because past quarrying operations have extended below the level of the

seasonally high groundwater level. During winter groundwater flows from the spring and

forms a small surface stream. This spring dries up once the water table drops below the

quarry floor.

2.7 High resolution LiDAR elevation data clearly indicates that the ground level after the

proposed quarry operations, assuming a base level of 124.5m RL, will still be from 1.5-

2.0m above the elevation of the wetland.

2.8 As a result, the quarry operations cannot drain the wetland. Furthermore, any water

within the quarry, such as that from the existing seasonal springs, that drains naturally

towards the wetland will continue to do so both during, and following, the proposed

activities.

2.9 Should the proposed quarry operations remove material to a level below the seasonally

high water table one or more new small localised springs may form during winter. Given

current groundwater patterns the only area where this may potentially occur is in the

extreme east of the site, towards BH1. Small ephemeral streams may flow from these

springs towards the wetland. The area will not become inundated or flooded provided that

the quarry floor levels are graded to provide for this flow. As long as this surface flow is

kept separate from any water from the proposed quarry operations, it will provide high

quality water to the wetland. This situation occurs under the present situation without any

detrimental effects on either stream flow or the wetland, and can be readily managed in

the future.

3.0 GENERAL SITUATION

3.1 The applicant proposes to establish a quarry and clean-fill operation that will include: the

excavation of gravels and sands; the stockpiling these materials on site; and, the

processing of approximately 10% of the extracted material by crushing on site.


3.2 The site covers an area of approximately 11.6ha; with 9.2ha proposed for the quarry

operations. Approximately 10% of the site is occupied by an existing quarry that was

established under a land use consent (CDC 010051) granted to Renalls Ltd in 2001. This

excavated area is close to the centre of the site. It is about 3-4m deep with stable 70

degree side slopes. This existing quarry is between the operations proposed under the

current consent applications and an area of wetland. The floor of the existing quarry

extends below the level proposed under this application. It therefore forms a local base

level and buffers any potential effects of the proposed operations.

3.3 To the east of this existing quarry pit is an older quarry that provided fill for the foundations

of the freezer units at the Waingawa works. The gully formed by this operation has now

been partially backfilled with demolition materials and organic waste. At its base is a

‘spring’, the flow from which exits the application site just beyond its southern entrance.

3.4 The ‘catchments’ formed by these two previous periods of quarrying activities intercept

any surface runoff, and some groundwater on occasion. All water from these catchments

flows into the wetland. This flow augments the input of water to the wetland, particularly

during winter and spring.

3.5 The natural ground slope is relatively flat but the area has a gentle slope from about 130m

above sea level in the NE to 122masl in the SW. The only notable natural ground feature

is the Masterton Fault scarp which runs in an east-west direction and forms the boundary

of the intended excavation area. The scarp itself, and the area to the south of the scarp

bordering the ‘Western wetland’, will not be excavated. This will further buffer any

potential effects of the proposed operations.

4.0 HYDROGEOLOGIC SETTING

4.1 The Wairarapa Valley is a structurally-controlled basin containing an accumulation of

coalescing alluvial fan sequences built up by the Ruamahanga River and its main

tributaries: the Waingawa, Waiohine, Waipoua, and Tauherenikau rivers. Late Quaternary

sediments fill the upper levels of the basin to depths of between <10m and about 100m;

with an average thickness of about 50m. These sediments host a dynamic groundwater

system that has a strong inter-relationship with the surface water environment.

4.2 The proposed quarry site is located on the Waiohine aggradation surface. In the vicinity

of this site the Waiohine surface is essentially an historic flood plain of the Waingawa

River formed during glacial conditions when erosion in the Tararua Ranges was

accelerated. A considerable volume of detritus was transported out of the mountains and

onto the plains. This material was deposited at the foot of the mountains and on the

valley floor where lower gradients caused a reduction in the stream power available to

transport sediment.


4.3 Figure 1 shows the current position of the Waingawa River. A closer look shows previous,

now abandoned, channels across the contemporary flood plain to both the left and right of

the river. These depressions can also be seen meandering across the older aggradation

surface in the vicinity of the site of the proposed quarry operation.

Figure 1: General site location and basic fluvial geomorphology of the area.

4.4 The alluvial origin of the sediments forming the flood plain and aggradation surface means

that they exhibit a high degree of variability. Deposits close to active river channels are

composed of larger material with fewer fines in the matrix. This is because of the higher

energy of this depositional environment. Silts and clays predominate in over-bank

deposits, or where flood waters pond allowing the finer material to settle out. The

evolution of the flood plain and aggradation surface, and the dynamic and migratory

nature of the river channels, has resulted in a three-dimensional mosaic of alluvial

sediments (Figure 2).

4.5 A shallow unconfined aquifer in the vicinity of the proposed quarry has formed in these

Quaternary gravels of the Waiohine formation (10-25kyr). These deposits comprise

greywacke-sourced, poorly-sorted gravels up to boulder size, and sand. The alluvial

gravels reflect a high energy, poorly sorted alluvial fan environment. These are inter-

fingered with fine-grained over-bank, swamp or lacustrine (lake) deposits. The alluvial

gravels are commonly clast-supported, rich in sand and silt, with sandier and siltier

horizons being common. As such, these sediments form generally poor aquifers except

where they have been reworked following initial deposition to remove the finer material.

These general characteristics of the alluvial deposits throughout the area are confirmed by


the consistency of bore logs (e.g., S26/0296, S26/0299, S26/0306, S26/0236 – and

investigation bores BH1, BH2, and BH3 drilled for this study) and trial pits. The same

range and types of materials are present in all holes even though their relative

stratigraphic position may change.

Figure 2: Variability of alluvial sediments at the proposed quarry site.

4.6 There are no fine-grained cover-beds overlying the Waiohine formation. This is because

this aggradation surface was the source of the most recent loess. Soils are therefore

shallow and only between 10-20cm deep. It is these characteristics of the Waiohine

formation that make the gravels attractive for quarrying.

4.7 The geology of the proposed quarry site is consistent with the description of the Waiohine

formation provided above. The specific site comprises Quaternary alluvium of old river

terraces of the Waingawa River. The alluvium is predominantly gravel and cobbles with a

matrix of coarse sand; with a small amount of fine to medium sand and minor silt

(estimated to be approximately 5%). There are occasional lenses of laminated sands

within the gravels. The gravels and cobbles are well-compacted and poorly-sorted. The

clasts are generally sub-rounded to sub-angular and flattish, with some indistinct current

bedding. Most cobbles are less than 0.25m, although there are rare larger bounders up to

0.4m in diameter. The site is covered with up to 0.3m of topsoil and 0.5m of subsoil and

low quality weathered gravel and sand. The existing quarry excavations and a number of

6m deep exploration pits have confirmed the presence of similar gravel and sand

materials across the site.

4.8 These sediments, although they form a single geomorphic unit, can exhibit significantly

different hydraulic properties over relatively short vertical and horizontal distances. These

variations are the result of different lithological characteristics, specifically: particle size,

gravel matrix composition, degree of sediment sorting/reworking, and degree of

compaction. Therefore, although the sediments host an interconnected groundwater


system, they are highly heterogeneous. The Waiohine gravels have a much lower

transmissivity than the more recent Holocene sediments found close to the current river

channels. This is probably a result of the higher clay and silt content of the older gravels.

Transmissivities typically range from less than 25 to 300m2/day. (Note: The term transmissivity

describes the ease with which water can move through an aquifer; as such, it is similar to hydraulic

conductivity. The main difference is that transmissivity is a measurement that applies across the vertical

thickness of an aquifer. E.g., if the thickness of the aquifer is b, the transmissivity (T) is bK where K is the

hydraulic conductivity.)

4.9 Pump test data that are available indicate a storativity of 0.1, while salt water tracer tests

suggest a hydraulic conductivity of 189-300m/day, and an average linear velocity of

6.5m/day. Groundwater flow determined from potentiometric surveys and salt water

tracer tests is predominantly in a S-SW direction with an average hydraulic gradient of

0.009m/m. Hydrographs indicate that groundwater is predominantly sourced from direct

precipitation rather than infiltration from local rivers. (Note: Storativity of an unconfined aquifer

describes the volume of water the aquifer releases from or takes into storage per unit surface area per unit

change in saturated aquifer thickness. A potentiometric survey maps the changes in water groundwater

pressure over an area. Groundwater moves from areas of higher pressure to areas of lower pressure.)

4.10 While flow is likely throughout the entire aquifer, it occurs preferentially in old river

channels. The larger particle size and better sorting of these deposits means that they

have higher permeability and flow velocities.

4.11 These alluvial deposits may in places be affected by the Masterton Fault. For example,

restriction of the groundwater movement across the fault north of Masterton may be

indicated by the occurrence of springs. However, in the vicinity of the proposed quarry the

fault forms a topographic rather than a hydraulic boundary. This has been confirmed by a

geophysical survey discussed later in this evidence. This conclusion is consistent with the

lithology and nature of the aquifer media which are continuous across the fault. While the

specific lithologic units may be offset by the fault, their new juxtaposition is against similar

units with similar properties. Therefore, groundwater flow is not disrupted across the fault

in the vicinity of the proposed quarry operation.

4.12 The ‘springs’ in the vicinity of the quarry are caused by the water table intersecting the

ground surface. This is the effect of an abrupt change in topography rather than by any

specific or distinctive hydrogeologic control along the fault. This is confirmed by the fact

that the ‘springs’ actually emerge a considerable distance behind the fault scarp and not

along it.

4.13 According to Melvin Pike, the Water Race Overseer for more than 30 years, the current

source of the larger ‘spring’ in the area which now flows into the ‘Central wetland’ is the

result of quarrying gravels for the foundations of the freezer units at the Waingawa

Freezing works.


4.14 In recent years the ‘gully’ formed by this excavation of gravels has been backfilled with

debris from the demolition of the freezing works, and more recently organic waste. The

depth of this excavation, and the overlying fill, means that the spring now emerges from

beneath the front of the ‘dump face’ (Figure 3).

Figure 3: Major modified ‘spring’ to the south and east of the proposed quarry site. Note that the

previously quarried area in the middle of the photograph is at the approximate level of the seasonally-high water table during winter/spring.

4.15 Previous periods of quarrying have affected approximately 10% of the proposed project

area. These activities have reduced the floor of the excavation to about 124m RL at its

lowest point in the ‘NW corner’ (Figure 4). This is about 0.5m above the level of the water

table in summer; and about 0.2m below the level of the water table in winter. As a result,

this corner of the old excavation acts as a spring for 4-5 months of the year depending on

the amount and duration of winter rainfall. Water from this ‘spring’ is channelled across

the quarry floor to intercept the channel draining the older spring shown in Figure 3.

4.16 It should be noted that both the quarry used for the freezing works, and the more recent

operations, have stopped at about the same RL depth (i.e., 124m). This depth is at the

approximate upper limit of the groundwater i.e., the water table, during winter and spring.

It is suggested that this is not just a coincidence. Since operators do not want to work in a

permanently wet pit it is highly likely that they did not excavate below the water table. The

RL of these pits therefore provides a practical indication of winter groundwater levels.

4.17 On the northern side of the ‘Western wetland’ is a ditch that was most likely initially dug to

help drain the swamp (Melvin Pike pers. comm.). This ‘drainage ditch’ was excavated

below the seasonally high water table on the down-throw side of the fault. As a result, this

drainage ditch has also acted as a ‘spring’ in the past when groundwater levels are high.

This ditch is a significant distance in front of the fault scarp which again indicates that any


‘springs’ are topographically rather than structurally controlled.

Figure 4: Artificial ‘spring’ caused by an old excavation extending below the seasonally high

water table.

4.18 Under the current situation no spring flow can be identified at any location besides the old

permanent spring and winter ‘leakage’ from the lowest area of the old quarry floor

discussed above.

4.19 A traverse of the entire length of the Masterton Fault scarp in the vicinity of the proposed

quarry operation identified no springs or even damp areas. The argument that the

wetlands are spring-fed is wrong. Evidence to support this conclusion will be discussed in

more detail later.

5.0 AQUIFERS

5.1 As mentioned above the alluvial sediments in this area, because of their composition and

particle size, provide the media for a number of aquifers. With regard to the potential

impact of any quarrying activities the shallow unconfined aquifer is of most relevance.

5.2 The Wairarapa plains have been divided into a number of aquifers by Greater Wellington

for management purposes. The criteria for the boundaries between the different aquifers

have not been able to be located despite intensive enquiry, but they would appear to be a

combination of inferred hydrologic, topographic, and stratigraphic controls. It is likely that

there is a high degree of interaction across the various inferred aquifer boundaries, and

they are not actually separate, discrete, units.

5.3 The proposed quarry lies on the boundary between the West and East Taratahi aquifers

(Figure 5). This boundary was likely defined by the presence of the Masterton Fault and


its associated topographic offset, and not a difference in hydraulic properties and

groundwater behaviour. While the Masterton Fault causes a topographic boundary, and

may offset the various gravel units, it has little effect on the movement and dynamics of

groundwater flow in this vicinity. The groundwater system is continuous across the fault.

Therefore the division of the aquifer system into two is considered to be quite arbitrary in

this location.

Figure 5: Inferred aquifer boundaries in the vicinity of the proposed quarry site.

5.4 As will also be discussed later, the groundwater dynamics of the Taratahi aquifer are

distinctly different to those of the aquifers close to the Waingawa River (i.e., Upper Plain)

and to the south-east (i.e., Parkvale). The Taratahi aquifer has long been identified as

having “limited” groundwater potential as opposed to both the Parkvale and Waingawa

River aquifers.

6.0 WATER RESOURCES

Local runoff

6.1 The proposed quarry site does not intercept any contemporary surface water courses.

While paleochannels of the Waingawa River are apparent, these were abandoned

thousands of years ago.


6.2 To identify the various flow paths, and the overall drainage situation at the proposed

quarry, high resolution LiDAR information was used to generate a 1m digital terrain model

(Figure 6).

6.3 The potential movement of water across each 1m2 of the project area was quantified

(Figure 7). It is apparent that any rain that falls on the flat pasture across the site soaks

into the soil to recharge the soil moisture and groundwater. Some minor, short, localised

movement of runoff towards the paleochannels is apparent from the lineations

‘meandering’ across Figure 7.

6.4 Localised runoff does occur in a number of areas where there is some distinctive ‘form’ to

the topography. For example, runoff occurs into the old quarry pits, particularly into the

gully formed when excavating fill for the foundations of the freezer units discussed earlier.

Also, some runoff occurs down the fault scarp towards the wetland, particularly to the west

where the scarp is flatter and longer providing a greater ‘catchment area’.

Figure 6: High resolution digital terrain model of the proposed quarry site showing the main hydrologic and topographic features.


Figure 7: Areas of localised runoff and the effect of existing topography on runoff patterns.

6.5 It should be noted that the drainage ditch on the northern side of the ‘Western wetland’

acts as a barrier to the surface movement of this runoff into the wetland (Figure 8). This

drainage ditch has significant bunds on either side where the material excavated during its

construction was dumped. Groundwater levels on the down-throw side of the fault are

elevated during winter because of its low elevation. This causes saturation of the soil.

This water, however, is prevented from draining directly into the wetland because of these

bunds.

6.6 It should be noted that all the drainage towards and within the older quarry sites, including

the gully now containing fill, has to flow out of the narrow entrance excavated in the past

through the fault scarp to provide access to these quarried and dump areas. This is

because the scarp has been left intact during these past operations forming a ridge which

confines any flow. This will simplify the management and control of runoff from the

proposed quarry operation. It also minimises any effects of the proposed quarry activities

and the resulting landscape change on the local hydrology and runoff patterns.

6.7 There is likely to be very limited runoff, if any, from land surrounding the proposed

operations. This is because the topography is essentially flat, and there are no physical

features such as depressions to concentrate the flow of water towards the site. This again

simplifies stormwater management and treatment within the proposed quarry.


Figure 8: What was initially a drainage ditch is now used to supply water to the Western wetland.

The bunds on either side limit the surface movement of water across the ditch and into

the wetland in the vicinity of the proposed quarry.

6.8 The main (almost only) source of surface water in the area potentially affected by the

applicant’s proposal is the Taratahi Water Race. This flows along the north-eastern

boundary of the project area (Figure 9). This water race feeds the wetland system via

controlled flows from an artificial storage lake. The storage lake was constructed to

maintain a reliable source of water for the Waingawa Freezing Works when abstractions

from the Waingawa River were restricted during periods of low flow. The reservoir is

now also used to ensure that sufficient water reaches the surrounding wetlands.

Controlled outlets from the storage lake feed the ‘Eastern’ and ‘Central’ wetlands

directly. The ‘Western wetland’ is fed indirectly from the ‘Central wetland’. Waingawa

Stream exits the ‘Western wetland’ and flows southeast. This is a tributary of the

Parkvale Stream and is at times referred to as part of the race system. However,

Greater Wellington considers it to be a ‘natural’ stream. To improve water quality for the

freezing works a settling pond was constructed on the up-throw side of the fault. Water

is piped from this pond into the artificial lake. This small settling pond is the proposed

site for the intermittent abstraction of 10l/s of water applied for under these consents.


Figure 9: Hydrological features in the vicinity of the proposed operation.

6.9 The water level in the artificial lake is approximately 1.0m above the adjoining ‘Eastern

wetland’; the water supply to which is maintained via a concrete control structure. The

water level is also about 1.1m higher than the ‘Western wetland’. This wetland is supplied

by ‘excess flow’ through the ‘Central wetland’, and flow from the ‘spring’ emerging from

under the in-filled gully. During winter additional flow comes from the ‘spring’ in the NW

corner of the disused quarry, the flow from which is channelled across the quarry floor.

Water levels in the wetlands are therefore maintained artificially using water from the large

storage lake. The water balance of the wetland is discussed in more detail later.

6.10 The majority of the inflow to the large artificial storage lake is returned to the Taratahi

Water Race system; most likely a continuation of the original water race that was diverted

into the lake. The race initially heads northeast and then travels around the perimeter of

the Kiwi Lumber property, under Waingawa Road, and down alongside Norman Ave

towards SH2.

6.11 As already indicated, the main hydrological feature in the vicinity of the proposal area is

the Waingawa Wetlands (Waingawa Swamp). This feature occupies a depression formed

where an extensional step-over along the Masterton Fault scarp has lowered the ground

surface relative to the surrounding topography (Figure 9). Such an interpretation is

consistent with measured water levels, local topography, and the resistivity survey results.


6.12 Water levels in the wetlands are now maintained almost entirely by discharge from a

Taratahi Water Race, buffered by the storage of water in an artificial lake. This is certainly

the case during summer when the water table is lowered, and drainage from the two small

springs reduces or stops (Figure 10). There is no indication of any inflow from springs at

the base of the fault scarp; flow from the disused quarry stops; and flow from the spring

under the in-filled gully reduces dramatically (i.e., <10l/s).

6.13 The outlet control structures from artificial lake, and the concrete control structure on the

outlet from the ‘Western wetland’ to Waingawa Stream, maintain artificial water levels

within the wetlands. Natural inflows to the wetland are less than minor.

Current groundwater situation

6.14 The floor of the disused quarry excavation is currently just above the winter-high

groundwater level, except in the NE corner where it is about 0.3m lower. During summer

the entire quarry floor is at least 0.4m above the groundwater level (Figure 10). It is

estimated therefore that the maximum winter groundwater level beneath the disused

quarry is approximately 123.5 to 124m RL. As discussed previously, this is consistent

with the inferred past quarrying practice.

Figure 10: During summer the water table is approximately 0.4m below the level of the existing

quarry. All surface ponding and drainage from the winter spring dries up. Compare with Figures 3 & 4.

6.15 The disused quarry, being the lowest elevation within the area to be affected by the

proposed operations, defines the base level (control) for both groundwater and surface

water in the vicinity. The proposed operation will not affect this existing base level.

6.16 Groundwater exiting via two springs, one in the existing quarry excavation and the other

beneath the back-filled gully, drains into the ‘Central’ and then ‘Western’ wetlands. The

water which currently leaves the site appears to be clean and clear, and shows no

indication of sediment load. There is also no sediment build up below the culvert where

this water discharges into the wetlands. Such a deposit would be present if the water

contained significant sediment load. As long as ‘spring-sourced’ flow is kept separate

from surface runoff affected by quarrying operations water quality will remain high. This


could be addressed by an appropriate consent condition. Any effects of this flow on the

wetlands therefore will be less than minor.

7.0 RESISTIVITY SURVEY

7.1 To more accurately define the subsurface structure and hydrogeology of the project area

a series of Dc resistivity measurements were made (Figure 11). A resistivity survey

measures the ease with which an electrical current can be passed through the ground.

The depth of measurement is related to the electrode spacing on the ground surface.

While many factors can affect the resistivity of the ground, the two major ones are water

content and lithology (i.e., material). From a hydrogeological perspective, increases in

water content are related to decreases in resistivity i.e., it is easier to pass an electrical

current through saturated ground.

7.2 Six resistivity traverses were undertaken during mid-September 2009 when groundwater

levels were at their seasonal maximum. Five traverses were used to define the 3D geo-

electric structure across the Wairarapa Fault, and between the top of the up-throw side

and the wetland. The sixth line defined the structure through the middle of the proposed

quarry site (Figure 12).

7.3 Measurements from these six traverses were inverted using Res2Dinv and Res3Dinv

produced by Geotomo Software to produce 2D and 3D resistivity models of the project

area (Figures 13 & 14).

7.4 The 2D and 3D models show that the Masterton Fault marks a boundary between dry

gravels with high resistivity on its north side, and saturated lower resistivity material on the

south side. There is no evidence of a hydrological discontinuity associated with the fault.

7.5 The resistivity survey shows a relatively homogenous structure across the up-throw

(North) side of the fault. A similar structure is shown along Lines 1, 5, and 6.

7.6 The high resistivity layer to an apparent depth of 2.5-5m on the up-throw side of the fault

is consistent with dry gravels.

7.7 The decrease in resistivity below this depth reflects the effect of the top of the water table,

and saturated gravels beneath. The estimated depth to the water table is consistent with

the water levels measured in the bores at the time of the survey.

7.8 Below a depth of about 10m there is significantly lower resistivity which may reflect either

a change in lithology, or a change in water chemistry.

7.9 The fault therefore separates a layer of 3-5m of dry gravels on the up-throw side from

essentially saturated material on the down-throw side. Although there is a thin layer of

unsaturated gravels immediately adjacent to the fault on the down-throw side, saturation


1

2

3

4

5

6

quickly reaches the surface towards the ‘drainage ditch’ and wetland during winter.

7.10 There does not appear to be a hydrologic discontinuity caused by the fault in this vicinity;

apart from the greater thickness of dry gravels on the up-throw side. This conclusion is

consistent with the test pits, bore holes, and inspection of the existing quarry faces.

7.11 On the up-throw side of the fault the water table would appear to be essentially horizontal,

and at a depth of approximately 3.4m during winter-high conditions close to the old quarry.

The lowest points of the old quarry floor appear to intersect the water table forming a

spring. The measured position of the water table supports the interpretation of the

resistivity survey.

Figure 11: Resistivity traversing with the Western wetland and bunds on either side of the water

race/drain in the background.

Figure 12: Location of resistivity traverses.


Figure 13: 2D resistivity models for Lines 1-5. Horizontal and vertical scales are in metres.

Topography is included in the models for Lines 1 and 5 which cross the Masterton Fault scarp. Locations at which perpendicular lines cross are also marked.

W

L1 E

L5

Line 2

W

L1 E

L5

Line 3

W L1

E

L5

Line 4

N S L2 L3 L4

Line 1

N S L2 L3 L4

Line 5


7.12 The lower resistivity values on the down-throw (South) side of the fault would appear

to be a function of a thicker silty layer, saturated soil, and possibly increased peat

content associated with wetter conditions.

Figure 14: Horizontal sections through the 3D resistivity model derived from the data for Lines 1-5.

No topography is included in the model. Horizontal distances are in metres. The locations of Lines 1-5 are marked by the red lines. For each section N is to the top of the diagram and E to the right.


8.0 INITIAL INVESTIGATION

8.1 As part of their initial assessment of the proposed site, the applicant excavated a number

of exploration pits on the 12th December 2005 (Figure 15). These confirmed the nature

and relative homogeneity of the gravel resource. They also provided information on the

position of the water table at the time of the investigation.

Figure 15: Locations of the various test pits, and the depths to the water table at the time.

8.2 The water table was intercepted in all the exploration pits (Figure 16). However, the depth

to groundwater varied depending on the exact location.

8.3 The water table was shallowest below the floor of the existing quarry (i.e., 0.4m). This is

to be expected because this site has the lowest elevation and therefore acts as a local

base level.

8.4 Since the elevations of the various sites were not recorded any interpretation of water

levels must be qualitative in nature. However, since the ground surface is essentially level

this should not have a significant effect on the groundwater level.

8.5 The depth to the water table is greatest in those pits closest to the existing quarry (i.e.,

approximately 4.5m below ground level). It is possible that this is because the quarry pit,

acting as the local base level, lowers the water table passively by allowing water to drain

out.


8.6 The water table is about 0.5-1.0m higher towards the back of the project area, and

towards the Taratahi Water Race. The higher water table in these locations may be

because of the dissipation of the effect of the quarry. It may also be because leakage

from the unlined water race helps to maintain groundwater levels during early summer.

Figure 16: Test pits excavated on 12/12/2005 showing the nature of the material and the depth to

water table. From L-R the photographs are of Pit 2, Pit 3, and Pit 6.

9.0 DYNAMICS OF GROUNDWATER

9.1 At the commencement of the development of this application little quantitative information

existed regarding the nature and dynamics of the groundwater in the area likely to be

affected by the proposal. At Greater Wellington’s suggestion, three bores were installed

on the site and a hydrological report was provided as part of a ‘further information’

request.

9.2 Notwithstanding the information provided by the applicant, there remain a number of

assumptions, errors and misunderstandings in submissions relating to the application, and

in the Section 42A reports. Some of these have been highlighted already relating to the

surface–groundwater interactions and the cause and significance of the ‘springs’. The

discussion below will help to clarify various other issues.

9.3 The proposed quarry operation is located close to the boundary between the conceptual

West and East Taratahi Groundwater Zones. At this location groundwater is mostly

recharged by rainfall rather than from infiltration from the rivers in the immediate vicinity.

The topography of the area results in groundwater movement in a generally southerly

direction across the site.


9.4 During a field visit on 16 September 2009 the lowest corner of the old quarry was acting

as a ‘spring’; with a small pond approximately 0.3m deep (Figure 4). The spring

discharged to a drain across the quarry floor. On the basis that the quarry floor in this

location has an RL of 124.0m, this places the top of the water table at about 124.3mRL.

The elevation of the groundwater levels in the three bores on the site at the time were

126.550, 124.510, and 122.730m RL for BH1, BH2, and BH3 respectively. BH2 is the

closest to the existing quarried area approximately 50m away. It should therefore be

noted that the water table at this time was essentially horizontal, with a very flat hydraulic

gradient towards the corner of the quarry. These results also confirm that the

groundwater is draining essentially south across the site as anticipated from the

topography.

9.5 GWRC has made available groundwater level data from a number of bores in the wider

area (Figure 17). The closest monitoring bore with a long period of record is S26/0299

(Figure 18). Water levels in this bore have been measured approximately quarterly since

1997/98 as part of Greater Wellington’s water quality monitoring programme. Because of

the good groundwater record, similar elevation, and proximity to the proposed quarry,

bore S26/0299 was also measured during various site visits relating to this study. This

bore is also the closed well used as a water supply.

Figure 17: Location of various monitored groundwater bores in the general area of the proposed quarry. Note: BH1, BH2 and BH3 in the top left corner are the bores installed for this project (See Figure 9

for more detail). These bores are also known as S26/1062, S26/1063, and S26/1064 in the GW bore database.


Figure 18: The closest monitored bore to the project area is S26/0299; this is also the closest well

used for water supply. Intermittent pumping of this bore potentially affects the

representativeness of the groundwater level record.

9.6 It should be noted that the various bores shown in Figure 17 are measured in different

ways, over different time periods, and most importantly with different frequencies. This

has significant implications with regard to the comparisons that can be made, and the

validity of assumptions regarding the behaviour of groundwater at different locations.

9.7 It should also be recognised that these bores are located in several different aquifers

identified by GWRC for management purposes. Some of the bores are used for water

supply and irrigation and therefore the water levels are modified by periodic pumping.

That is, the water levels and their variation over time do not reflect natural conditions.

9.8 Bore S26/0738 is GWRC’s principal monitoring bore in the area (Towgood bore at the

extreme bottom left on Figure 17). It has the longest and most detailed water level record.

However, it is located over 8km from the project area. It is: separated from the study area

by a number of streams; close to permanent water courses; in a different aquifer (the

Parkvale aquifer); and it is likely to be located in distinctly different aquifer media. As will

be shown later, these factors mean that the water level response in this bore is distinctly

different to that in the project area. The reliance on the groundwater level from this bore

as a surrogate for the groundwater response in the project area therefore severely

compromises the credibility of the ‘comparative’ results.

9.9 It is also important to place groundwater levels and the dynamics of an aquifer into a

temporal as well as spatial context. That is, an unconfined aquifer is essentially a sponge

that responds to the inputs and outputs of moisture. Water levels will rise when there is

an increase in inputs, and fall when either the inputs drop or outputs increase. The

availability and variability of the input of moisture over time is therefore a critical


consideration when reviewing groundwater information.

9.10 It is generally accepted that rainfall is the main source of groundwater recharge in the

project area. Assuming that recharge of the unconfined aquifer at this location is

approximately the same as in the Parkvale aquifer, GWRC suggest that annual recharge

is about 37% of the annual rainfall. Using the longest rainfall record available (i.e.,

Wairarapa Cadet Farm), and assuming that this is typical of rainfall at the project site, the

mean annual recharge is 310mm. Figure 19 shows that the past few years have been

wetter, and therefore recharge greater, than the long term average. As a result,

groundwater levels are likely to have been higher during this investigation than on

average. Discussions regarding the groundwater system beneath the project area are

therefore likely to be conservative (i.e., are based on higher than average groundwater

levels).

1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008

0

100

200

300

400

500

600

Rec

harg

e (m

m)

Mean (310mm)

Annual recharge from 1-Jan-1952 09:00:00 to 1-Dec-2009 08:00:00 Total = 17198.3mm Figure 19: Long term potential groundwater recharge. Note that the past few years have been wetter than

average, with greater recharge. This would likely make the current situation conservative, with higher than

average groundwater levels.

9.11 A comparison of the groundwater levels from all the monitored bores in the vicinity of the

proposed quarry with a common period of record highlights the aquifer-specific and even

site-specific nature of the variation in groundwater (Figure 20). No clear, distinctive, or

consistent patterns are apparent besides an expected seasonal response i.e., higher

groundwater levels in winter and lower levels in summer. This makes it extremely difficult

to relate the groundwater dynamics at one site to another. This becomes increasingly

difficult as the distance between the bores increases.

9.12 The two short but detailed groundwater records in the middle of Figure 20 are from

S26/0298 and S26/0308. These bores are close to the Waingawa River, and in the Upper

Plain aquifer. Their range of response is very small but very rapid when compared to the

other bores. These bores are essentially responding to water levels within the Waingawa

River, and as a result they are atypical when compared to the other bores.


9.13 Bores S26/0242 and S26/0223 are about 2.5km from the proposed quarry and are likely

to be in the East Taratahi aquifer. Although these two bores are less than 500m apart the

response of each is distinctly different to the other. The range of groundwater levels in

these bores is up to 6m, and a strong seasonal pattern is apparent. However, both the

degree of variability in water levels, and the variability each year are different for the

specific bores (Figure 20). Therefore, while the ‘average’ pattern of groundwater

variability is similar, there are significant differences in the more detailed response pattern.

It should be noted that these differences exist between two bores only 500m apart in the

same aquifer. Significantly bigger differences would be expected between bores further

apart, and in different aquifers.

Figure 20: Groundwater levels at various bores in the vicinity of the proposed quarry over their

common period of record.

9.14 Bore S26/0236 is about halfway between the two bores discussed above and the project

area. Again, the response in this bore is different to all others. While a seasonal pattern

is apparent, the degree of groundwater fluctuation is significantly less (i.e., only 2m).

Also, the variability throughout the record appears to be significantly less than apparent in

the bores located to the south-west (Figure 20).

9.15 Bore S26/0299 is the closest to the proposed quarry. It is about 1km away from BH1.

The response of this bore is therefore most likely to reflect the existing groundwater

patterns under the proposed quarry. It is obvious that the groundwater variability in this

bore is distinctly different to that of all other bores shown in Figure 20. While a seasonal

pattern is still apparent, groundwater fluctuations are very small, only about 1m. Also, the

variability from year to year is different to that shown for the other bores. Therefore, while

the groundwater levels in this bore are likely to be most representative of those in the

proposed quarry, they are very different to that of bores down-gradient, and in other


aquifers. The fact that this bore is pumped to provide a water supply could, however,

mask the natural groundwater response pattern. Groundwater variability is likely to be

greater than would occur naturally because of the intermittent pumping.

9.16 If the groundwater in this area is largely recharged by rainfall a strong relationship should

be apparent between rainfall and groundwater level. Using the long-term monitoring

record from bore S26/0738, even though it is over 8km from the study site and has a

different detailed groundwater response pattern than at the proposed quarry, the general

control of rainfall on water levels is apparent (Figure 21). However, the groundwater

response to rainfall is not simple, nor is it consistent over time. There are a range of other

controls on groundwater levels. The use of a fixed percentage of rainfall as an indicator of

groundwater recharge is therefore overly simplistic.

1984 1989 1994 1999 2004 2009

0

100

200

300

400

67

Mon

thly

rai

nfal

l (m

m)

Wat

er le

vel (

m)

Total = 21053.0mm

Figure 21: Groundwater levels variability at S26/0738 in response to rainfall. Note rainfall is in blue and

groundwater level in green.

9.17 At a number of climate stations around New Zealand, where the necessary data and

parameters exist, an indication of the expected runoff (surplus rainfall) is calculated.

Therefore, using the climatic data available from the Wairarapa Cadet Farm the timing

and volume of runoff was calculated. Runoff is expressed as depth in millimetres so the

units are the same as for rainfall.

9.18 These estimates of runoff are based on a water balance model using rainfall,

evapotranspiration, and potential soil moisture storage as variables. Runoff is calculated

by assuming that any precipitation that falls is absorbed until the ground is saturated, and

then the rest runs off. The available water holding capacity of the soil is assumed to be a

standard 150mm.

9.19 It is likely that this model under-estimates runoff since the potential evapotranspiration

data used does not fully account for restricted moisture losses from the soil and the leaves

of plants. Also, no allowance is made for rainfall events where the precipitation intensity

exceeds the infiltration rate of the soil. However, while the ‘absolute accuracy’ of the


index might be questioned for the project area, the use of runoff in relative terms should

provide a valid measure of potential recharge i.e., it should help explain variation in

groundwater levels.

9.20 Figure 22 therefore shows the groundwater level record from S26/0738 and the runoff

predicted using the available climatic data. The runoff index would appear to provide a

better indication of potential groundwater recharge than simply rainfall. This is likely

because it considers various losses of moisture from the system, and storage within the

soil.

1984 1989 1994 1999 2004 2009

0

50

100

150

200

250

300

67

Mon

thly

run

off

(mm

)

Wat

er le

vel (

m)

Total = 5174.8

Figure 22: Groundwater levels variability at S26/0738 in response to estimated runoff. Note runoff is

in blue and groundwater level in green.

9.21 The longer term variation in estimated monthly runoff is shown in Figure 23. Again, this

figure highlights the greater than average runoff over the past few years. This will be

reflected in higher groundwater levels in the project area, and conservative conclusions

when looking at the potential impact of any quarrying activities. Both winter and summer

groundwater levels are likely to have been higher over recent years than the longer term

average.

1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008

0

100

200

300

400

500

600

700

Run

off

(mm

)

Mean (250mm)

Total = 13713.6 Figure 23: Annual variability in the runoff index. Recent years have been wetter than average.


9.22 While estimated runoff provides a useful indication of potential groundwater recharge, and

therefore water level fluctuations, the relationship is still not simple or consistent over time.

There are a number of potential reasons for this including: the timing and distribution of

rainfall; abstraction from the bores; and antecedent conditions. The general control of the

runoff index on groundwater levels in the vicinity of the proposed quarry is shown in

Figure 24 with reference to bore S26/0299, the closest monitored bore.

1998 2000 2002 2004 2006 2008 2010

0

60

120

180

240

300

125

Mon

thly

run

off

(mm

)

Wat

er le

vel (

m)

Total = 2752.6

Figure 24: Groundwater levels variability at S26/0299 in response to estimated runoff. Note runoff is

in blue and groundwater level in green.

9.23 Considerable emphasis has been given in the Officer’s report to an argued correlation

between the water levels between different bores. As indicated above, this is overly

simplistic. While there may be a general pattern of seasonal response, each bore has a

distinctive character that is not reflected in other bore’s record. In particular, emphasis

has been placed on an inferred relationship between water levels in S26/0738 and both

S26/0242 and S26/0299.

9.24 Figure 25 shows the water level records for both S26/0738 and S26/0242. While the

seasonal pattern of response is consistent, many of the ‘peaks’ in the groundwater

records do not correspond in either relative magnitude or time. Particular care must

therefore be exercised when attempting to relate the water levels in these two bores. It

must also be remembered that these two bores are significantly closer together (~6km

apart) than the distance between S26/0738 and any of the monitoring bores in the

project area (~8.5km apart).

9.25 An inferred correlation between the water levels in various bores has been used by

others to predict the response of groundwater levels in the proposed quarry. There are

number of problems with this approach. First, correlation is not the same as causation.

Second, correlation should only be attempted between independent variables. As

shown above, the groundwater levels of different bores are not independent. Finally,

while correlation may provide some explanation for the general pattern it will not explain

the detailed groundwater response and ‘peaks’. This is because a simple relationship


does not exist between the water levels in the bores as highlighted by Figure 25.

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

65000

70000

75000

80000W

ater

leve

l

Figure 25: Groundwater variability at S26/0738 (blue line) and S26/0242 (green line).

9.26 Differences between the water level responses of S26/0738 and S26/0299, the bore

closest to the proposed quarry operations, are even greater than illustrated in Figure 25

(Figure 26). To therefore argue a statistical correlation between the measured

groundwater levels in these two bores, and therefore cause and effect, is both wrong

and highly misleading. While a seasonal pattern is apparent the relative magnitude,

variability, and duration of groundwater levels is not consistent over time.

1998 2000 2002 2004 2006 2008 2010

65000

70000

125

Wat

er le

vel

Wat

er le

vel

Figure 26: Groundwater variability at S26/0738 (green line) and S26/0299 (blue line).

9.27 While the use of a statistical correlation between these two water level records is both

wrong and misleading in this situation, it is also important to understand the wider

implications of such usage. For example, the apparent relationship between the

variability in groundwater levels at S26/0738 and S26/0299 may be quantified by a

correlation analysis, even though such a ‘test’ is inappropriate. Having done such an

analysis, as presented in the Officer’s report, it is important that the full implications are


understood. The regression line fitted to the data is simply the ‘average’ relationship. It

does not show variability or uncertainty – both of which are critical considerations.

9.28 A more detailed, accurate, and statistically correct analysis of the correlation between

S26/0738 an S26/0299 is presented in Figure 27. This shows not only the relationship

between ‘average’ conditions but also the uncertainty around the general trend. It has

been argued that an r2 (the coefficient of determination) of 0.8 shows a strong

association. This is not totally correct. While the relationship may mean that 80% of the

variability of water levels in S26/0299 can be explained by variation in water levels at

S26/0378, it also means that 20% of the variability cannot be explained. This is the

variability away from average conditions, those of most interest and concern (Figure 27).

Figure 27: Correlation between water levels in S26/0738 and S26/0299. Note the blue lines are the 90%

confidence interval and the pink lines the 90% prediction interval.

9.29 When reviewing Figure 27 it is also important to understand the wider implications and

what exactly is being reflected. The confidence interval (blue boundaries) is used when

estimating the mean ‘Y’ (water level at S26/0299) for a given ‘X’ (water level at

S26/0738). The prediction interval, however, should be used when estimating a

particular value of ‘Y’ for a given ‘X’. A close look at Figure 27 shows that at any

particular water level in S26/0738 we are actually only 90% sure that the water level at

S26/0299 will be within 0.6m. It should also be noted that at least four of the data points

lie beyond this 90% bound. That is, we cannot even be 90% sure that our estimated

water level at S26/0299 will be within 0.6m of the actual value. If one wanted to be 95%

sure of our prediction interval of the water level then the potential ‘accepted error’


increases to almost 1m. This 1m of uncertainty needs to be placed in context. It

represents more than the total variability measured in bore S26/0299 over the past 18

months, and 50% of the total variability ever recorded at this site. The correlation

analysis presented therefore is both misleading and inaccurate. The uncertainty and

inappropriateness of any inferred relationship between groundwater levels in S26/0738

and S26/0299 is also illustrated in Figure 5 from the appendix to the Officer’s report.

This figure shows that the ‘model’ is a very poor predictor of the two ends of the

variability in water level.

9.30 The use of water level records from various bores in the wider vicinity to predict

groundwater conditions at the proposed quarry can therefore be misleading. While a

general association between water levels and their seasonal variability is apparent, the

actual response of an individual bore is very site-specific.

9.31 It is recognised that the initial lack of site-specific data for the proposed quarry site

presented some problems when assessing the potential effect of this proposal.

However, it is important that the use of surrogate sites is placed in context, and is both

realistic and appropriate. Key to the use of surrogate sites is the realisation that

correlation does not equal causation. That is, just because two sites may respond in a

similar manner does not mean that their behaviour is related.

9.32 In response to the lack of site-specific information for the proposed quarry site GWRC

advised the applicant to undertake some on-site groundwater investigation. Three

monitoring bores were consequently drilled along the north-western edge of the site at

the end of November 2008 (Figure 28). While there is only just over one year’s data

from these bores, and sampling has been sporadic, they do provide a valuable record of

groundwater levels, seasonal fluctuations, and variability in response across the site.

9.33 The relationship of these three bores to S26/0299 is shown in Figure 29 and the data are

summarised in Table 1. It is apparent that the variability of BH1 is very similar to

S26/0299, although the actual response is different. This is to be expected since these

two bores are in relatively close proximity, however, S26/0299 is used as a water supply.

Variability of BH1 is only about 0.9m. Note that this is less than the level of uncertainty

discussed earlier relating to a correlation based on water level variations in S26/0738.

The variability in water levels appears to increase southwards across the site. This is

likely a reflection of the groundwater flow direction and drainage.

9.34 All three bores respond in a similar, but still distinctly different way, to variability in the

runoff index (Figure 30). This is likely to reflect changes in elevation, topography, and

possibly the presence of the existing quarry.


Figure 28: Location of the three investigation bores in relation to bore S26/0299.

Dec-2008 Feb-2009 Apr-2009 Jun-2009 Aug-2009 Oct-2009 Dec-2009 Feb-2010 Apr-2010

120

125

130

Wat

er le

vel (

m)

Bore Hole 1 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Bore Hole 2 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Bore Hole 3 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Bore S26/0299 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00

Figure 29: Water level variability in the three investigation bores and bore S26/0299. Note: the green

line is S26/0299, the dark blue line BH 1, the mid-blue line BH 2, and the pale-blue BH 3.

Table 1: Summary of groundwater levels (m RL) in project area. Note: S26/0299 (Recent) covers the

same period as the record from BH1, BH2, and BH3.

Minimum Mean Maximum Standard deviation

Median Range

Bore Hole 1 125.790 126.856 127.350 0.327 126.940 1.560 Bore Hole 2 123.420 124.574 125.020 0.338 124.668 1.600 Bore Hole 3 121.510 122.545 123.350 0.476 122.606 1.840 S26/0299 (Recent) 126.309 127.274 127.750 0.266 127.374 1.441 S26/0299 (Total) 125.830 127.021 128.020 0.342 127.003 2.190


Figure 30: Water level variability in the three investigation bores in response to the runoff index. Note: the dark blue line is BH 1, the mid-blue line BH 2, and the pale-blue BH 3.

9.35 Given the site specific response of the three investigation bores, and the difficultly in

predicting water level variation in the project site, it is suggested that any consent

conditions relating to predicted water levels using distant bores are both inappropriate and

unrealistic. Consent conditions relating to the separation of any ‘spring flow’ from surface

runoff, the maintenance of spring flow water quality, and the continued diversion of the

limited spring flow into the wetlands will ensure that any effects of the proposed operation

on the hydrology are less than minor.

10.0 TAKE FROM WATER RACE

10.1 It is proposed to abstract intermittently 10l/s of water from the Taratahi Water Race from

the ‘settling pond’ located on the up-throw side of the fault scarp above the main reservoir

(Figure 31). This pond is located at approximately NZMS 260 S26 272800 602350. The

water race is supplied by flow diverted from higher on the Waingawa River. An

agreement with CDC limits this take to approximately 385 hours each year, and the

maximum volume of the take to 13,860m³.

10.2 According to Melvin Pike, the Water Race Overseer, Carterton District Council is

operating under a former consent to take up to 480l/s from the Waingawa River with two

step downs to 375 and 332l/s respectively. The consent has lapsed, but operation

continues pursuant to section 124 of the RMA. This flow is then diverted into two races,

one of which flows past the proposed quarry site. This race normally conveys about

200l/s but this can drop to about 140l/s during the summer low flow period.

10.3 There are few actual measurements of flow in the water race. Greater Wellington

undertook a flow gauging at two locations on 21 March 2001. Five locations were gauged

as part of the investigations related to this consent application (Figure 31). Both these

sets of gauging were therefore collected towards the end of summer and therefore

represent low flow conditions.

Dec-2008 Mar-2009 Jun-2009 Sep-2009 Dec-2009 Mar-2010

120

125

130

0

5

10

15

20

25

30

Wat

er le

vel (

m)

Run

off

(mm

)

Bore Hole 1 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Bore Hole 2 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Bore Hole 3 from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00Daily runoff from 24-Nov-2008 00:00:00 to 12-Apr-2010 00:00:00 Total = 263.3


10.4 The flow of 140l/s measured by GW within the race is consistent with the low flow

estimate provided by Melvin Pike. The lower flow of 85l/s measured by the applicant on 3

May 2010 was because the coffer dam at the intake on the Waingawa River had been

washed out. This reduces the head and therefore flow into the intake. Consequently, the

water race had only about one-third (Melvin Pike’s estimate) of its usual summer flow.

This was not known when the gaugings were undertaken, although a local farmer did

comment on the exceptionally low flow in the race.

Figure 31: Low flow gauging in the vicinity of the proposed quarry site. The yellow numbers are

the measured flows at that location. Note: the numbers in italics are from GW’s survey, the rest

were from flow measurements for the applicant.

10.5 The proposed abstraction of 10l/s therefore represents 7% of the usual instantaneous

summer low flow in the water race. Consequently, an abstraction of this magnitude could

not actually be detected by stream gauging; which using best practice has an error of

±8%. Any effects of this take, since it would not be able to be quantified accurately, would

therefore be less than minor. Even under the extremely low flow conditions measured by

the applicant, the proposed abstraction represents only 12.5% of flow.

10.6 The potential effect of the proposed abstraction is actually even less than indicated above.

This is because the water will only be taken for a maximum of 9 hours and day, for a

maximum of 40 days of the year. The water will also be taken from a pond that buffers

any short term fluctuations.


10.7 On a daily basis an abstraction of 10l/s over 9 hours represents only 2.7% of the daily

flow; assuming an average flow of 140l/s. Even if an abnormally low flow of 85l/s was in

the water race the abstraction would still represent only 4.4% of the daily flow.

10.8 It must also be recognised that water would only be abstracted for a maximum of 40 days

each year. That is, even this small daily abstraction (2.7%) would only be taken for 11%

of the year.

10.9 There is no doubt that the effects of the proposed take of 10l/s over 9 hours for a

maximum of 40 days each year would not be able to be quantified. Any effects must

therefore be assessed to be less than minor.

11.0 HYDROLOGY OF THE WETLAND

11.1 There are a number of misconceptions and misunderstandings regarding the hydrology of

the Western Wetland. These relate to: its naturalness, and the significance of

groundwater to its viability.

11.2 As already discussed the wetland lies in a topographic depression on the down-throw side

of the fault.

11.3 The flow of water both in to and out of (via Waingawa ‘Stream’) the Western Wetland is

now controlled by concrete structures. Inflows are from the artificial reservoir via a water

race/drain through the Central Wetland. At the western end of the Central Wetland

approximately 10l/s of water is added from the ‘spring’ that emerges from under the fill

immediately to the north. The combined flow then passes through a culvert (Figure 32)

and into an artificial race/drain that runs along the northern edge of the wetland. This

drain has bunds on either side which prevent water from either entering or leaving until

towards the western end of the wetland (Figure 33). An old drain is clearly visible through

the wetland to the outlet into Waingawa Stream (Figure 31). The flow of water into

Waingawa Stream is controlled via a concrete weir (Figure 34).

11.4 The current hydrology of the wetland is therefore not natural but is maintained by flow

diverted from the water race system. This situation is confirmed by past behaviour of the

wetland. For example, the wetlands were maintained by the flow of coolant water from

the Waingawa Freezing works. When the works were closed, the source of coolant water

was cut off and the wetland started to dry out rapidly. To ‘save’ the wetland a diversion of

water from the race system was requested and implemented by CDC. At the time the

wetland dried out, flow also ceased down Waingawa Stream. This resulted in a large kill

of the resident eel population (Melvin Pike, pers comm.).


Figure 32: Artificially maintained flow passing through a culvert into the Western Wetland.

Figure 33: A possible old drainage ditch now supplies flow from the water race system into the

Western Wetland.


Figure 34: Concrete weir controlling outflow from the Western Wetland into Waingawa ‘Stream’.

11.5 Flow gauging at the end of summer, when the wetland is potentially most hydrologically-

stressed, shows that the Western wetland is acting as a reservoir. Inflows equal outflows

and therefore the water level is in equilibrium.

11.6 Again, it must be stressed that these flows were measured when the water race was

exceptionally low. These flows are therefore likely to reflect extreme low inflow conditions

rather than the normal situation. This is confirmed by the fact that when GW gauged the

outflow during late summer in 2001 they measured almost twice the flow of the latest

survey (Figure 31).

11.7 There is no evidence that the wetland is sustained by spring flow. The only spring flow

during summer that could be located is from under the fill in the old quarry discussed

earlier. This conclusion is supported by fact that even during a period of extremely dry

conditions and low flows, the inflows via the drain were almost identical to the outflow into

Waingawa ‘Stream’.

11.8 The absence of a significant groundwater input to the wetland is confirmed by the

groundwater data collected by the applicant. As shown in Figure 31 the water level in the

Western Wetland is approximately 122.3m RL, maintained by the weir at its outlet to

Waingawa ‘Stream’. This water elevation is almost 1m above the summer groundwater

level recorded in Bore 3, and about 0.7m higher than the mean groundwater level in this

bore (Table 1). This difference in ‘head’ between water in the wetland and that in the

groundwater would mean that any flow of water should be out of rather than in to the

wetland. The magnitude of this potential outflow of water from the wetland gets greater


during summer as the head difference increases.

11.9 It must also be recognised that although the peat and other organic material in wetlands is

saturated, their permeability is actually very low (Table 2). In the current situation it is

likely that the organic material in the wetlands acts as a permeability barrier to the

potential passage of water both in to and out of the wetland from the surrounding ground.

Table 2: Permeability of typical materials.

K (cm/s) 10² 101 100=1 10−1 10−2 10−3 10−4 10−5 10−6 10−7 10−8 10−9 10−10

K (ft/day) 105 10,000 1,000 100 10 1 0.1 0.01 0.001 0.0001 10−5 10−6 10−7

Relative

Permeability Pervious Semi-Pervious Impervious

Aquifer Good Poor None

Unconsolidated

sand & gravel

Well Sorted

Gravel

Well Sorted Sand

or Sand & Gravel

Very Fine Sand, Silt,

Loess, Loam

Unconsolidated

clay & organic Peat Layered Clay Fat / Unweathered Clay

Consolidated

rocks Highly Fractured Rocks

Oil Reservoir

Rocks

Fresh

Sandstone

Fresh

Limestone,

Dolomite

Fresh

Granite

Source: modified from Bear, 1972

11.10 The groundwater regime therefore has little effect on the hydrology of the wetland and its

viability. This conclusion is supported by discussions with Melvin Pike, the Water Race

Overseer, who agrees with the above discussion. He maintains that if the water race was

closed for two days the Western Wetland would go dry. He has apparently communicated

this belief to Greater Wellington in the past.

11.11 The effects of the proposed quarry operations on the wetland therefore relate solely to the

risk of sediment within any runoff from the crushing plant. This risk can be appropriately

addressed by the proposed Quarry Management Plan and associated settling ponds.

11.12 The proposed quarry operations will have an effect on the water balance of the wetland

which is less than minor.

12.0 CONCLUSIONS

• The use of water level data from bores outside of the project area is problematic. None of

these bores provide a reliable indication of likely groundwater variability and dynamics

beneath the proposed quarry. The use of such data for this purpose is highly misleading

and inappropriate.

• The groundwater system beneath the proposed quarry is controlled to a large degree by

topography. This will change as a result of the proposed operations. Therefore, even the


use of the existing groundwater information from within the proposed project area may not

provide a clear indication of the situation during and after completion of quarrying. Any

changes, however, are likely to be relatively minor and they cannot be reliably quantified.

• The existing quarry base is lower than that proposed for the new operation. This acts as a

local base level, controlling drainage and mitigating any potential effects of future quarrying

activities. From site investigations, it is clear that most of the quarry operation will take

place where the winter water table is lower than the quarry floor.

• The drainage provided by one corner of the existing quarry during winter may affect

groundwater patterns and dynamics in the immediate vicinity. Any effects will dissipate

rapidly moving away from the quarry area. These effects are not of the same type as those

imposed by pumping from a water supply well, as they are passive.

• There are no adverse effects currently of localised spring flow. However, there are some

positive effects with regard to the volume, and continuity of water supply, to the wetland.

• Water from springs that may form when groundwater levels are high during winter appears

to be of high quality. It poses no risk to the wetland. It is relatively easy for water from any

springs to be isolated from the proposed quarry operations. This would maintain the quality

of water flowing into the wetland system. This separation of any spring flow can be

achieved readily during future operations.

• If there are perceived problems with the existing consented quarry, the situation will actually

improve under the proposed quarry management plan.

• All proposed works are upstream of the existing quarry, the ridge formed by the Masterton

Fault scarp, and the drainage ditch. Therefore several barriers’ already exist to mitigate

any potential direct or indirect adverse effects of granting this consent on the wetland.

• The existing quarry, which extends below the water table in one location on occasion

resulting in a spring just ‘downstream’ of the application site, has had no quantified adverse

effects on the wetlands.

• Groundwater levels beneath the proposed operation will predominantly remain below the

base of the existing quarry.

• Even if water levels should rise above the quarry floor for short periods (such as following

prolonged periods of extreme rainfall), there will be no adverse effects. This has been

shown by the behaviour and effects of the existing quarry which is below the level proposed

in this application.

• The clean-fill component of the operation will also raise the finished quarry floor level above

the minimum quarried level. On top of any clean-fill will be an additional 300mm minimum


of topsoil following site rehabilitation. The final effects of the proposed operation on

maximum winter groundwater levels will therefore be small. There will be no effect on

groundwater levels throughout most of the year.

• All the surface flows of water will continue to reach the wetland. If anything, this water may

be in greater volume, and have higher quality since it will be managed.

• Water quality will not be compromised. Water from the existing quarry spring is of high

quality and there is nothing to suggest that this situation will change with the proposed

development.

• Any concerns regarding water quality can be mitigated by appropriate conditions. This will

ensure that water quality is maintained. It is intended that any spring flow and the quarry

runoff should be kept separate, and managed in different ways.

• As long as the base of the proposed operations is maintained above the current quarry

floor, approximately 124m RL, any water draining from and through the site will still reach

the wetland. The isolation of any spring flow will ensure its continued quality when

discharged to the wetland. Appropriate stormwater and runoff treatment from within the

area of quarry operations will ensure that this water also does not compromise the wetland.

If the spring flow is kept separate from surface runoff from the quarry, the amount of water

needing to be treated will be relatively small.

• The groundwater regime has little effect on the hydrology of the wetland and its viability.

Water levels in the wetland are maintained almost entirely by artificial flows provided from

the water race system. This conclusion is supported by gauging information and past

experience.

• The proposed quarry operations will therefore have an effect on the water balance of the

wetland which is less than minor.

• Any effects of the proposed abstraction of 10l/s from the existing settling pond within the

water race system will be so small they will not be able to be quantified. The abstraction

would represent approximately 2.7% of the daily summer low flow. Even this small amount

of water would only be utilised for about 11% of the year. Consequently, the effects of the

proposed abstraction will be less than minor.

In summary, the potential effects of the proposed quarry operation on the local hydrology and

groundwater system are expected to be minor at most. The indirect effect of any changes to the

dynamics of the groundwater on the wetland will be less than minor. Any potential changes to

the local hydrology will be so small they will not be able to be quantified.

It is therefore my professional opinion that the consents applied for can be granted with

appropriate conditions.


John (Jack) McConchie

Principal Water Resources Scientist

17 May 2010

in the matter - gw...2.9 should the proposed quarry operations remove material to a level below the...

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