Ongare Point Environmental Monitoring Results Update
(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 (NH4-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
1
2
3
4
Description
Spring south of boat ramp
Spring by toilet block
Harbour View Road drain
Potu Road drain
5
Ongare Stream
Catchment
Predominantly rural
Encompasses much of the northern Ongare village
Drains small area of central Harbour View Road
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/m3. 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 NH4-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.
0.3
6
0.25
5
0.2
4
0.15
3
0.1
2
0.05
1
0
01/01/06
16/05/07
27/09/08
09/02/10
NH4-N
DRP
24/06/11
NNN
05/11/12
0
20/03/14
NNN (g/m3)
NH4-N & DRP (g/m3)
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.
100000
E.coli (cfu/100ml)
10000
1000
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
Figure 1
Bathing surveillance orange alert
Bathing surveillance red action
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 NH4-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.
6
5
4.5
5
4
4
NH4-N (g/m3)
NNN (g/m3)
3.5
3
2.5
2
3
2
1.5
1
1
0.5
0
0
01/04
02/05
03/06
Site 1
04/07
06/08
Site 3
07/09
08/10 09/11
Site 4
10/12
11/13
Site 5
12/14
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
100000
0.5
10000
0.4
1000
E.coli (cfu/100ml)
DRP (g/m3)
0.6
0.3
0.2
100
10
1
0.1
0
05/03
02/06
Site 1
Figure 2
11/08
Site 3
08/11
Site 4
05/14
Site 5
0.1
05/04
09/05
01/07
06/08
Site 1
Site 4
Bathing surveillance red action
10/09
03/11
07/12
11/13
Site 3
Site 5
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 NH4-N
concentrations have been recorded. High NH4-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.
E.coli
50000.0
5000.0
Median
25%-75%
Non-Outlier Range
Outliers
Extremes
500.0
n/100ml
50.0
5.0
0.5
Site 2
Site 1
Site 3
Site 4
Lindoch Drain Te Puna
Site 5
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
Enterococci (cfu/100ml)
1000
800
600
400
200
0
10/03
02/05
Enterococci
Figure 5
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.