(April 2014)
Introduction
Many of the Bay of Plenty’s coastal communities are served by on-site wastewater treatment systems. In areas of more concentrated dwellings, located near sensitive water bodies or in areas utilised by the public, there is the potential for adverse environmental effects from on-site treatment systems. Adverse effects can include: odours, contamination of surface waters, addition of nutrients to water bodies, contamination of shellfish and foreshore environments and negative health effects of water body users.
What Bay of Plenty Regional Council monitors
Methods employed to detect contamination in the environment involve surveying surface waters
(drains, seepages, streams) and groundwaters and using analytical and microbiological techniques to determine contaminant concentrations and/or loadings. Water samples are commonly analysed for nitrogen and indicator bacteria ( Escherichia coli ( E.coli
) and faecal coliform). Similarly, lake or harbour waters are also monitored for indicator bacteria as a potential symptom of contamination.
What do the results tell us?
Nitrogen, particularly in its ammonia form (NH
4
-N) and to a lesser extent in its oxidised form, nitrate
–nitrite-nitrogen (NNN) is used to help detect the presence of wastewater in water. Elevated results can indicate sewage contamination. Washing powders and liquids contain phosphorus which can pass through septic tanks and contaminate groundwater. This is reported as Dissolved reactive phosphorus (DRP) and an elevated level in groundwater indicates contamination from septic tank systems.
Micro-organisms such as bacteria, protozoa and viruses can be removed from septic tank effluent in the top soil layers, dependant on soil pH, moisture, temperature, and soil microbial population. If effluent mixes with a saturated zone (e.g. elevated water table) connected to surface waters then faecal micro-organisms and pathogens can be readily transported into the environment. Elevated results of these indicators or the presence of them in shellfish can indicate a contamination problem. Bacterial contamination may have human or animal origin.
Monitoring Sites
Site Description
1 Spring south of boat ramp
Catchment
Predominantly rural
2
3
Spring by toilet block Encompasses much of the northern Ongare village
Harbour View Road drain Drains small area of central Harbour View Road
4
5
Potu Road drain
Ongare Stream
Drains Potu Road and the linking drain behind north Harbour
View properties
Rural catchment, with very minor input from Potu Road
Refer to the map at the end of this report for site locations (Figure 5). Site 1 is included in this suite of test sites to provide an indicator of a spring fed stream. Site 5 is included to provide an example of an intensively farmed runoff. The remaining three Sites (2,3,4) are indicators of runoff from the residential area. Figure 5 includes some coloured lines to mark the sub-catchment boundaries.

Results
Much of the regular monitoring in Ongare Point has occurred in the small drain near Harbour View
Road upstream of the toilet block, labelled as Site 2. Due to its normally constant flow, proximity to residences, and outflow to the foreshore it is the flow that potentially could be the largest contributor of contamination from septic tanks. The results since 2004 are shown in Figure 1b. Site
2 had no observable flow in January 2013 under drought conditions and no result is shown.
Figure 1a shows dissolved nutrient and E.coli
concentrations at Site 2. Nitrate-nitrite-nitrogen
(NNN) at Site 2 generally has concentrations above 3 g/m 3 . Similar concentration of these mobile nitrogen species through groundwater are also observed in the rurally influenced Site 1 (Figure 2), indicating nitrogen input from rural sources as well as from septic tanks. Other drains monitored have lower NNN concentrations on average but higher NNN to NH
4
-N ratio. Ammonium-nitrogen has been lower over the past few years and this may be in part due to increased renovation of nitrogen through the ground in the dry summer conditions, also potentially explaining the increased nitrate-nitrite-nitrogen concentrations.
Recent (summer 2013/14) E.coli
levels have been above the orange alert contact recreation limit of
260 E.coli
/100ml, and may reflect increased summer loading of septic tanks when people visit their holiday homes. More intensive sampling over rainfall events in mid-2008 showed elevated E.coli
levels do occur during a period of high rainfall. Sampling above the toilet block (Site 2) and below
(where the drain exits to the foreshore) showed no real change in bacterial loading.
0.3
0.25
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0.15
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0 0
01/01/06 16/05/07 27/09/08 09/02/10 24/06/11 05/11/12 20/03/14
NH4-N DRP NNN
2
1
6
5
4
3

100000
10000
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100
10
1
14/01/04 28/05/05 10/10/06 22/02/08 06/07/09 18/11/10 01/04/12 14/08/13 27/12/14
E.coli
Bathing surveillance orange alert Bathing surveillance red action
Figure 1 E.coli and dissolved nutrient concentrations, Site 2, Ongare Point.
The Potu Road drain (Site 4) is often observed to be growing sewage fungus, smells of septic tank effluent and at times shows elevated E.coli
, DRP, NNN and NH
4
-N concentrations (Figure 2).
These elevated levels indicate contamination from septic tanks. Site 3 has to a lesser extent also been found to have occasional higher levels of indicator bacteria and nutrients. Comparison of ammonium and E.coli
levels from Sites 3 and 4 with the rurally sourced spring waters from Site 1 clearly show contamination. E.coli
levels often exceed recreational guideline levels at site 4 and on lesser occasion Site 3. Flow from the Site 4 is almost year round while the Site 3 drain experiences only intermittent flow and is therefore influenced by rainfall and higher water table levels.
5
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4
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3
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2
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Site 1 Site 3 Site 4 Site 5
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0
01/04 02/05 03/06 04/07 06/08 07/09 08/10 09/11 10/12 11/13 12/14
Site 1 Site 3 Site 4 Site 5

0.6
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0.1
0
05/03
Site 1
02/06
Site 3
11/08
Site 4
08/11
Site 5
05/14
100000
10000
1000
100
10
1
0.1
05/04 09/05 01/07 06/08
Site 1
Site 4
Bathing surveillance red action
10/09 03/11
Site 3
Site 5
07/12 11/13
Figure 2 E.coli and nutrient concentrations, drains, Ongare Point.
Figure 2 also shows E.coli
and nutrient data from the local stream, Site 5. The stream shows signs of contamination from rural sources and has predominantly cattle grazing around its lower extent.
E.coli
concentrations are often above the contact recreational guideline and elevated NH
4
-N concentrations have been recorded. High NH
4
-N concentrations may have been a result of reduced flow and stagnation caused by the build-up of sea lettuce and the configuration of the culverts. The new culvert seems to have alleviated some of this build up.
Comparison of the faecal contamination loading represented by E.coli
concentrations with another community using on-site wastewater treatment systems (Te Puna) is shown in Figure 3. Waitui drain (Te Puna) is severely impacted by on-site wastewater effluent with frequent high E.coli
levels as well as ammonium. It is geographically similar to the Potu drain (Site 4) with residential housing located in an area with a high water-table. The Lindoch drain is located in an area of newer lower density housing more elevated above the water-table and while not directly comparable, this drain is similar geographically to Site 2 at Ongare Point. Figure 3 shows that the most faecally contaminated drain, Site 4 (Potu drain), has not been compromised as severely as the Waitui drain. The three Ongare Point drains do show slightly higher contamination than the moderately impacted Lindoch drain, and are at a similar contamination level as the rurally impacted stream,
Site 5. All drains have E.coli concentrations well above the concentration of the samples taken from the spring at Site 1.

50000.0
5000.0
500.0
Median
25%-75%
Non-Outlier Range
Outliers
Extremes n/100ml
50.0
5.0
E.coli
0.5
Site 1
Site 2
Site 3
Site 4
Site 5
Lindoch Drain Te Puna
Te Puna Waitui Drain
Figure 3 Box whisker plot of E.coli concentration at Ongare Point (shaded boxes) and Te
Puna, 2009-2013 (note log scale).
The technique of quantitative PCR (qPCR)-based microbial source tracking (MST) markers within for identifying the presence and relative contributions of human and ruminant sources of faecal pollution in waterways, has also been employed. Results have found faecal contamination from human sources in the Potu street drain (site 4), but no evidence of human markers at site 5. No other sites were tested.
Swimming Water Quality, Ongare Point
Bathing water quality at Ongare Point can at times be compromised with levels exceeding the
Microbiological Water Quality Guidelines (2003) orange alert mode of 140 enterococci per 100ml
(Figure 5). The 2013/14 season has experienced some elevated results after rainfall, with one result (the highest) not rainfall influenced. Similar elevated results have been seen locally in the larger rivers near Ongare Point (Tuapiro and Uretara). Results of 1000 enterococci per 100ml occurred in 2006 and 2007. Both samples were taken after substantial rain had fallen.
1200
1000
800
600
400
200
Figure 5
0
10/03 02/05
Enterococci
06/06 11/07 03/09
Bathing surveillance orange alert
08/10 12/11 05/13
Bathing surveillance red action
Bathing surveillance monitoring results, Enterococci, Ongare Point.

Figure 5 Ongare Point sample site location map with approximations of subsurface drainage catchments relative to sample locations shown.
Conclusion
Communities located in the near coastal environment who use on-site wastewater (septic tank) systems for sewage disposal can compromise the values of adjacent waters. Monitoring of the
Ongare Point discharges adjacent to the foreshore show contamination from septic tank effluent.
These drains regularly exceed the Microbiological Water Quality Guidelines red action mode, with most exceedances occurring at site 4, Potu drain. A study of the sub-catchments outlined in
Figure 5 will show that the most likely source of surface water contamination is septic tanks.
Comparison of the contamination with a similar community indicates contamination is occurring but is not as severe as seen at one drain from the other community.
5
Swimming water quality is at times compromised at Ongare Point, usually as result of rainfall runoff. While local drains will be adding to compromised swimming water quality, they are only a minor contributor with most of the local contribution from the local rurally impacted stream and other nearby rivers. The greater risk to community health is from direct contact with contaminated drain waters. Contact with the water in these drains or where they discharge onto the foreshore should be avoided.