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APPLICATION FORM: WORKS APPROVAL

Attachment 3A – Yungngora WWTP Overview

1. Existing WWTP

Yungngora community wastewater is gravity sewer reticulated to the sewage pump station (SPS)

located in Lot 108B Wargaree St (within the community) and subsequently pumped via a DN100 PVC

pressure main to the WWTP.

The existing WWTP consists of a primary pond, two (2) secondary ponds and a HDPE lined tertiary

pond; there are no existing evaporation ponds. There is currently insufficient containment of treated

effluent with continuous overflow to environment via a concrete overflow weir. The overflow is

generally contained within the perimeter fencing of the WWTP site and therefore does not present

significant community health risk.

Figure 1 Yungngora WWTP ponds

A review of the WWTP treatment capacity was completed in 2017. Water sampling was taken to verify

the raw wastewater constituents and treatment results for calibration of the treatment capacity

model. Refer Table 1.

Table 1 Yungngora WWTP influent and effluent samples 27/3/2017

Parameter Influent Sample Effluent Sample Effluent Limit Environmental

Discharge Sample

BOD5 68 mg/L 78 mg/L 30 mg/L 56 mg/L

TSS 48 mg/L 170 mg/L 40 mg/L 180 mg/L

Ammonia - N 43 mg/L 0.03 mg/L - 0.04 mg/L

TN 48 mg/L 20 mg/L 50 mg/L 14 mg/L

TP 6.1 mg/L 4.0 mg/L 12 mg/L 2.3 mg/L

E. coli 1,400,000 cfu/100mL 0 1000 cfu/ 100mL Estimated (5)

Hookworm ova Nematode Larvae

0 28

0 <1

<1 egg / L

Note: Helminth egg positive results as nematode larvae; no hookworm detected.

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2. Planned Upgrade Design

The land tenure at the existing WWTP is defined in Yungngora Layout Plan 2 (Amendment 6); also

refer Works Approval application Attachment 7:

• Lot 255, Pastoral Lease with the Yungngora Association Inc as the primary interest holder.

The Layout Plan sets out as the Lot 108 public utility reserve (sewage ponds) with a 500m odour

buffer zone.

Figure 2 Yungngora WWTP Land Tenure

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The proposed upgrade is designed for a forecast Yungngora population of 465 persons in 2028.

Respective design flow rates are listed in Table 2.

Table 2 Yungngora forecast wastewater flows 2028

2017 2028

Population 378 (Estimated, Layout Plan 2) 465

Flow per person / day 257 L/person/day (calculated) 287 L/person/day (calculated)

Commercial estimate - -

ADWF Monitored 97.3 kL/day Forecast 133.4 kL/day

ADWF / AWWF ratio 1.22 1.22

AWWF Calculated 119 kL/day Forecast 162.4 kL/day

Site Constraints to WWTP Extension

The Yungngora Layout Plan 2 recommends land use planning above the designated flood level of

73mAHD, based on historic peak flood levels (1982/82) and 2002. The existing WWTP surveyed toe of

embankment is at 73.2 – 73.5 mAHD, and the top of embankments is at 73.8 – 74.0 mAHD.

Geotechnical investigation test pits TP1- TP12 detailed the soil profile around the wastewater

treatment ponds as CLAY with gravel, fine to medium grained, with medium to high plasticity with

sub-rounded gravel. Topsoil to approx. 100mm depth was present at most test pits as clayey, silty,

SAND.

The geotechnical conditions of the site are poor for treated water infiltration and therefore will require

additional land area for evaporation loss of the water volume. Assuming 40% sludge clogging the

actual infiltration rate is estimated at 2.8 x 10 -3 mm/day (or permeability K20 = 5.41 x 10-11 m/s). The

permeability is suitable for pond lining to prevent infiltration and is recommended as lining material

for construction.

Due to the following constraints the expansion of the ponds is planned to the north and west of the

existing WWTP, with a small primary pond addition to the south:

• location of residences at the odour buffer perimeter prevented WWTP expansion south,

• ground topography further to the west falls below the 73.0mAHD flood level,

• area to the east is within the Calwynyarda – Noonkanbah Rd reserve, and further east is the

Lot 500 Crown Reserve 26355 which was not accessible for WWTP development.

The Yungngora Drinking Water Source Protection Assessment (DWSPA, PB, 2009) cited that the

wastewater treatment ponds are unlikely to contaminate the groundwater source due to the

confining characteristics of the aquifer.

The three (3) existing Yungngora drinking water bores are screened in the Poole Sandstone at 400 m

– 490 m depth. The bore log for drinking water bore 1/96 reports CLAY in the top 18.0m surface

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geology, overlying the three main aquifers of the alluvium, Noonkanbah Formation and Poole

Sandstone. The clay formation is a water quality aquiclude.

Design Capacity – Treatment

Additional pond area is not required for treatment capacity. However, due to the poor condition of

the existing ponds it is proposed to construct a new primary pond to accept wastewater during

refurbishment works on the existing WWTP. A new primary pond will contribute to the evaporation

requirements of the final water balance.

Refer to Attachment 2, as general arrangement drawing 1026-06-3-DWG-001.

It is planned to divide the existing primary pond and modify the pipework to align the new primary

pond in an east-west direction, into the prevailing wind. The two primary ponds will operate in parallel.

The following three (3) ponds will operate as secondary ponds in series for efficient nutrient removal.

The existing tertiary pond is HDPE lined. The liner should be removed and the pond embankments

refurbished.

A summary of the design treatment capacity for each pond is detailed below.

Table 3 Yungngora WWTP design treatment capacity; effluent quality reported for each pond.

BOD TN TP E. coli Helminths

Unit mg/L mg/L mg/L cfu / 100mL ova / L

Influent 80.0 50.0 7.0 1.40E+06 30

Primary pond 1 (parallel) 1.49 31.0 2.15E+05 <1

Primary pond 2 (parallel) 1.22 30.7 1.87E+05 <1

Secondary pond 1 0.27 19.5 2.37E+04 <1

Secondary pond 2 0.05 12.3 2709 <1

Secondary pond 3 0.02 7.9 457 <1

Tertiary pond 0.002 4.7 5.3 18 <1

Effluent limit 30 50 12 1000 <1

Design Capacity – Water Balance

A water balance was undertaken for the evaporation and infiltration associated with proposed 2028

inflow rates. No infiltration to land was included in the water balance (refer geotechnical information

above).

The full volume of the ponds have been designed to cater for both design 2028 wastewater inflow and

the 1:10 year rainfall event including a minimum 500mm freeboard.

Bureau of Meteorology data used for the water balance included:

• Station 003006 / 3093 Fitzroy Crossing – closest rainfall data

• Station 003003 Broome Airport – closest evaporation data

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Figure 3 Yungngora climate data referenced (Bureau Meteorology)

Total pond area required is 18,515m2. The existing WWTP water surface area is approximately

6,387 m2 and the planned new primary pond area is 800m2. The additional evaporation ponds area

required is 11,100 m2 of surface water area.

Drawing 1026-06-3-DWG-01, shows the planned evaporation pond construction as:

▪ Evaporation pond 1 – 2375 m2,

▪ Evaporation pond 2 – 7200 m2,

▪ Evaporation pond 3 – 1950 m2.

The bulk storage volume required for the 2028 water balance was calculated at 9,350 m3. As

evaporation ponds are designed at a minimum 1.0m depth to prevent vegetation growth, the planned

construction of 11,100 m3 evaporation pond volume will easily contain all seasonal flows.

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Figure 2 Yungngora WWTP & Evaporation pond bulk seasonal storage = 9350 m3.