featherston sludge survey report 29-11-12 - gw

CONHUR LTDPO BOX 204021

Highbrook Mail CentreEast Tamaki

34 Oakleigh AvenueTakanini, Auckland

Ph 09 278 7109Fax 09 278 7108

www.Conhur.com

www.conhur.com

SOUTH WAIRARAPADISTRICT COUNCIL

Featherston OxidationPonds

Sludge Survey Report

November 2012

FEATHERSTON OXIDATION PONDS SLUDGE SURVEY

Commercial in Confidence of 17 29 NOVEMBER 2012

Table of Contents

1. INTRODUCTION 3

2. METHODOLOGY 3

3. SITE PHOTOGRAPHS 5

4. RESULTS 9

5. CONCLUSION 12

6. FEATHERSTON OXIDATION PONDS SLUDGE SURVEY DRAWINGS 13



1. INTRODUCTION

Conhur provides sludge surveys for both sludge lagoons and oxidation ponds. We utilize the latest

technology to provide as accurate a result as possible. Our sludge surveys provide estimates of:

x The volume of sludge contained within the ponds

x The average solids content of the sludge contained in the ponds

x The total tonnes dry solids (tDS) contained within the ponds

Conhur was contracted by South Wairarapa District Council to survey the sludge contained in the

primary and secondary oxidation ponds at the Featherston WWTP. The survey was undertaken on

22 November 2012 in fine, settled weather conditions.

2. METHODOLOGY

Pond Base survey

The bases of the Ponds were surveyed utilizing high accuracy GPS equipment and integrated

topographic software. This survey was carried out from a survey boat on the ponds. The ponds

were surveyed on grid system with survey points at 15m centres.

For this sludge survey, the GPS coordinate system used was NZGD2000, NZ Transverse Mercator.

The reduced levels provided are relative only and have not been calibrated against known survey

reference heights.

Sludge water interfaceThe level of the sludge water interface was measured utilizing a Royce 711 suspended solids

interface meter. This tool provides an accurate indication of the level of the top of the sludge.

Conhur recorded this information with high accuracy GPS equipment and integrated topographic

software. This survey was carried out from a survey boat on the ponds and provides a reasonably

accurate profile of the top of the sludge layer.

Sludge VolumeThe sludge volume within the ponds was calculated by comparing the base surveys and the

surveys of the top level of the sludge. This calculation is carried out by the topographic survey

software and enables the production of both cross sections through the ponds and plan profiles of

the sludge within the ponds.



Sludge SamplesConhur utilized a purpose built grab sample tube to recover sludge samples from within each of the

ponds. The sample tube has proven to provide the best method of sludge sample retrieval.

Up to five samples were retrieved at specific sludge survey locations on each pond. The retrieval of

intact, undisturbed insitu sludge samples from oxidation ponds is a difficult process and does not

provide 100% accurate results. This is especially true when the sludge layer is less than 500mm

deep. Conhur Ltd has made every attempt and used best industry practice to retrieve

representative samples, however we cannot guarantee accuracy of the solids analysis results.

Sludge Sample Analysis

The individual sludge samples retrieved were analysed for total solids by Conhur utilising an AND

MX-50 Moisture Analyser in accordance with best industry practice. The results are provided in

Section 4 of this report.



3 SITE PHOTOGRAPHS

Primary Oxidation Pond 1 from SW corner

Retaining wall at SE corner of Pond 1



Bund between Ponds 1 and 2, including Pond 1 outlet chamber

NE corner of Secondary Pond 2, showing HDPE bund liner



Pond 2 (left) and north end of Pond 1 (right)

Pond 2 Outlet Chamber



Operations Building

Site Access Road



4. SLUDGE SURVEY RESULTS

Primary Oxidation Pond (Pond 1)The RL of the pond water surface when surveyed was 17.700m in Pond 1. This level relates to the

top of concrete of the outlet structure on the eastern side of Pond 1, which was measured as RL

18.413m.

The average depth to the pond base from the water surface is 1.40m.

The total volume of the pond is estimated to be 33,320m3.

The average depth to the sludge surface from the water surface is 1.15m.

The average depth of sludge in the pond is 0.26m.

The maximum depth of sludge in the pond is 0.95m.

The total volume of sludge in the pond is estimated to be 5,950m3.

The weighted average solids contents of the 5 samples retrieved was 6.9%

Based on the above we estimate that Pond 1 contains approximately 411 dry tonnes (tDS) of

sludge.

The individual solids contents of the 5 samples retrieved from Pond 1 were as follows:

Sample F1-1 8.09%Sample F1-2 4.51%Sample F1-3 6.71%Sample F1-4 9.24%Sample F1-5 4.86%



Secondary Oxidation Pond (Pond 2)The RL of the pond water surface when surveyed was 17.690m in Pond 2. This level relates to the

top of concrete of the outlet structure on the eastern side of Pond 2, which was measured as RL

18.493m.

The average depth to the pond base from the water surface is 1.46m.

The total volume of the pond is estimated to be 17,430m3.

The average depth to the sludge surface from the water surface is 1.31m.

The average depth of sludge in the pond is 0.15m.

The maximum depth of sludge in the pond is 0.85m.

The total volume of sludge in the pond is estimated to be 1,990m3.

The weighted average solids contents of the 3 samples retrieved was 9.3%

Based on the above we estimate that Pond 2 contains approximately 185 dry tonnes (tDS) of

sludge.

The individual solids contents of the 3 samples retrieved from Pond 2 were as follows:

Sample F2-1 7.73%Sample F2-2 6.68%Sample F2-3 12.91%



Sludge Survey Summary Table

PondID

WaterLevel(m)

Avg.PondDepth(m)

Avg.Depthto

Sludge(m)

Avg.SludgeDepth(m)

Max.SludgeDepth(m)

Est.TotalPondVolume(m3)

Est.SludgeVolume(m3)

WeightedAverageSludgeSolidsContent

Est.TonnesDrySolids(tDS)

Pond 1 17.70 1.40 1.15 0.26 0.95 33,320 5,950 6.9% 411

Pond 2 17.69 1.46 1.31 0.15 0.85 17,430 1,990 9.3% 185



5. CONCLUSION

Primary Oxidation Pond (Pond 1):The survey confirms the volume of sludge in Pond 1 is approximately 5,950m3. There is almost no

sludge at the eastern side of the pond, building up to an average sludge depth of 260mm along the

western side, to a maximum 950mm sludge depth in the SW corner of the pond.

The sludge samples retrieved from the pond indicate that the average solids content is 6.9%.

Based on Conhurs experience with previous pond surveys, this is at the high end of the normal

expected range for sewage sludge which Conhur has found typically falls within 3%-7% depending

on sludge depth.

Based on the above, we estimate that the Primary Oxidation Pond contains approximately 411 drytonnes (tDS) of sludge, which equates to Pond 1 being approximately 18% full of sludge.

Secondary Oxidation Pond (Pond 2):The survey confirms the volume of sludge in Pond 2 is approximately 1,990m3. There is almost no

sludge in the southern end of the pond, building up to an average sludge depth of 150mm at the

northern end, to a maximum 850mm sludge depth in the NW corner of the pond.

The sludge samples retrieved from the pond indicate that the average solids content is 9.3%.

Based on Conhurs experience with previous pond surveys, this is at the high end of the normal

expected range for sewage sludge which Conhur has found typically falls within 3%-7% depending

on sludge depth.

Based on the above, we estimate that the Secondary Oxidation Pond contains approximately 185dry tonnes (tDS) of sludge, which equates to Pond 2 being approximately 11% full of sludge.



6. FEATHERSTON OXIDATION PONDS SLUDGE SURVEY DRAWINGS

x Topographical Plan

x Sludge Depth Plan

x Profile Layout

x Cross Sections (Sheets 1 & 2)

ORIGINAL SIZE

A3

TITLE

OPER.APPR.CHKD.BY

SCALE

PROJECT No.

LOCATION DRAWN

CHECKED

DES. ENG.

PROJ. ENG.

APPROVED

OPERATIONS

REVISIONS

DESCRIPTIONDATENO

REVISIONDRAWING No

REF:

GENERAL NOTES1. Coordinates in terms of :2. Elevations in terms of : 3. Contour interval is :

34 Oakleigh AvenueCONHUR

PO Box 204021Takanini

East TamakiAUCKLAND 2161

Highbrook Mail CentreTOPOGRAPHICAL PLANSurveyed 22/11/12

FEATHERSTON-01 0

FEATHERSTON

125731:1250

L Vasey 29-11-12

M McLaughlin 30-11-12

. . . . . . .

Mean Sea Level (Approx.)0.5m

12573-01

Retaining wall

Outlet ChamberOutlet Manhole

Building

Inlet ChamberValve Box Lid

60m10

SCALE 1 : 1250

0 5040302010

Profile 1

Prof

ile 3

Profile 2

Prof

ile 4

11kVa Transformer Pole

BM01 (NE Corner of Chamber)1795055.64 mE5443483.46 mNEl 18.49m

Inlet Manhole

POND 1

POND 2

Outlet Chamber

ORIGINAL SIZE

A3

TITLE

OPER.APPR.CHKD.BY

SCALE

PROJECT No.

LOCATION DRAWN

CHECKED

DES. ENG.

PROJ. ENG.

APPROVED

OPERATIONS

REVISIONS

DESCRIPTIONDATENO

REVISIONDRAWING No

REF:





Highbrook Mail CentreSLUDGE DEPTHSurveyed 22/11/12

FEATHERSTON-02 0

FEATHERSTON

125731:1250

L Vasey 29-11-12


. . . . . . .

Mean Sea Level (Approx.)0.1m

12573-01

60m10

SCALE 1 : 1250

0 5040302010

POND 1 TOTAL VOLUME 33,320 m³POND 1 SLUDGE VOLUME 5,950 m³

POND VOLUMES as at 22nd Nov 2012

POND 2 TOTAL VOLUME 17,430 m³POND 2 SLUDGE VOLUME 1,990 m³

POND 1POND 2

ORIGINAL SIZE

A3

TITLE

OPER.APPR.CHKD.BY

SCALE

PROJECT No.

LOCATION DRAWN

CHECKED

DES. ENG.

PROJ. ENG.

APPROVED

OPERATIONS

REVISIONS

DESCRIPTIONDATENO

REVISIONDRAWING No

REF:





Highbrook Mail CentreCROSS SECTIONS - Sheet 1Surveyed 22/11/12

FEATHERSTON-03 0

FEATHERSTON

12573Hz 1:750 Vert 1:75

L Vasey 29-11-12


. . . . . . .

Mean Sea Level (Approx.)N/A

12573-01

Water Level Pond 1 17.70m Water Level Pond 2 17.69m

Water Level Pond 1 17.70m Water Level Pond 2 17.69m

Bottom of Pond

Top of Sludge

Bottom of Pond

Top of Sludge

Bottom of Pond

Top of Sludge

Bottom of PondTop of Sludge

ORIGINAL SIZE

A3

TITLE

OPER.APPR.CHKD.BY

SCALE

PROJECT No.

LOCATION DRAWN

CHECKED

DES. ENG.

PROJ. ENG.

APPROVED

OPERATIONS

REVISIONS

DESCRIPTIONDATENO

REVISIONDRAWING No

REF:





Highbrook Mail CentreCROSS SECTIONS - Sheet 2Surveyed 22/11/12

FEATHERSTON-04 0

FEATHERSTON

12573Hz 1:750 Vert 1:75

L Vasey 29-11-12


. . . . . . .

Mean Sea Level (Approx.)N/A

12573-01

Water Level Pond 1 17.70m

Water Level Pond 2 17.69m

Bottom of Pond

Top of Sludge

Bottom of Pond

Top of Sludge

featherston sludge survey report 29-11-12 - gw

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