It was only a couple of weeks ago that our little group of citizen scientists reported a pollution incident to the Environment Agency (EA). Fortunately, the EA reacted quickly and put a stop to it before there was too much ecological damage.
While the pollution event above was initially identified thanks to a member of the public, the next incident was the result of our twice a week testing schedule. The first indication that something was amiss was a significant increase in the concentrations of orthophosphate (OP) and total ammonium nitrogen (TAN) at one of our site (U034). This regular test site on the Newton Brook is marked by the black spot in Figure 1.
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| Figure 1: Google Map Showing All the Test Locations |
Figure 1 is a Google Map showing the Newton Brook tributary to the River Wye. As we move upstream along the Newton Brook from the River Wye (top to bottom of Figure 1), I have marked 5 locations:
- Test Site U034, part of the Wye Alliance Test Network (black spot)
- Confluence of the two branches of the Newton Brook & downstream of the pollution source (red spot)
- Pollution site (green spot)
- Upstream of the pollution (blue spot)
- Outlet from the former Three Counties Pool, see earlier blog (brown spot)
The first indication of a potential pollution incident was the sudden increase in OP and TAN values measured on the 13th July 2025 (see Figure 2). The following two measurements (16th and 20th July) showed decreasing values suggesting the pollution was dissipating slowly. Generally, point source pollution events dissipate quickly (sometimes within minutes or hours) but the water levels in Newton Brook are so low (the lowest we have seen in 4 years of testing) that the reduced flows are less efficient at diluting away pollutants.
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| Figure 2: Orthophosphate (OP) and Total Ammonium Nitrogen (TAN) Measurements at Site 1 (U034) |
The next 3 measurements (23rd, 25th, 27th July), however, showed OP/TAN levels similar to or higher than those observed on the 13th July. Clearly there was an issue that required investigation. On the 25th July, I made a quick sortie upstream to the outflow from the Three Counties Hotel pool (Site 5, brown spot in Figure 1) to take some measurements. I also retested Site 1 (U034, black spot in Figure 1) on my return for comparison. Why choose Site 5 for testing? Firstly, the side brook (labelled as Newton Brook in Figure 1) was dry so an unlikely pollution source. Secondly, Site 5 was the upstream limit of the brook as it exited the Three Counties Hotel pool. If Site 5 was pollution-free then the pollution source was somewhere between Site 1 and Site 5. The results for these two sites are reported in Table 1.
Table 1: Water Analysis of Site 1 and Site 5 on 25th July 2025 |
Site Location | Site 1 (U034, black spot) | Site 5 (brown spot) |
OP* (ppm) | 4.2 | 0.93 |
TAN** (ppmN) | 6.3 | 0.12 |
TON*** (ppmN) | 2 | 2 |
Nitrite, [NO2]-, (ppmN) | 0.3 | 0 |
Conductivity (μS/cm) | 645 | 549 |
Temperature (oC) | 19.6 | 18.6 |
Turbidity (NTU) | 4.5 | 9.5 |
pH | 7.8 | 7.8 |
Dissolved Oxygen (mg/L) | 3.2 | 5.0 |
% Dissolved Oxygen | 34.8 | 53.9 |
*Orthophosphate (OP) determined using the Molybdenum Blue method; **Total Ammoniacal Nitrogen (TAN) determined using the Nessler method; ***Total Oxidised Nitrogen (nitrogen in the form of both Nitrate and Nitrite) determined using Hach colourimetric test strips.
Clearly, the Orthophosphate (OP) and Total Ammoniacal Nitrogen (TAN) concentrations were much higher downstream (Site 1) compared to the upstream (Site 5) values (Table 1). Our pollution source was somewhere between these two sites. The drop in dissolved oxygen (DO) measurements as the brook water travelled downstream was also a strong indicator of pollution; low DO levels would explain the high concentrations of nitrite and TAN which are both reduced forms of nitrate (reference the Nitrogen Cycle)
Alan & I carried out a more detailed investigation on the 27th July 2025. As we walked upstream from Site 1, we noticed some pollution at the confluence of the two arms of Newton Brook (Site 2, red spot). This is shown in Photo 2, taken 3 days later (30th July) when the pollution had dissipated somewhat. The steps are actually part of the Newton Brook (Figure 1) but this section had dried up. The pollution, a whitish surface layer, is less evident in this photo (taken 30th July) compared to our previous visit 3 days earlier when we collected samples.
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| Photo 1: Confluence of the Two Arms of Newton Brook |
Further upstream, we encountered a strong candidate for the pollution source (Photo 2) located between two blocks of houses at Site 3 (green spot in Figure 1). |
| Photo 2: Main Pollution Site (green spot in Figure 1) |
My first instinct was that this might be a laundry or cleaning product discharged from one or more of the nearby houses (see Figure 1), although another possibility was this road drainage grid (Photo 3) about one metre away from the pollution seen in Photo 2. |
| Photo 3: Drainage Grid Adjacent to the Main Brook Pollution |
In the UK, most houses built after 1970 have separate drains for disposing of rainwater/surface water and foul water/wastewater. The former can be returned to a nearby watercourse without treatment whereas the latter must be treated at the sewage works before being returned to a watercourse. Prior to 1970, most houses had a combined system so all the water had to be treated; potentially overwhelming the capacity of the sewage works as well as wasting resources and energy. Some useful background information on this topic can be found
here.
The advantage of separate drainage systems can be lost if household appliances (e.g. washing machines, dishwashers, showers) are misconnected to the rainwater drain instead of the wastewater drain. While this may be a bigger issue with do-it-yourself plumbing installations, even trained plumbers may take short cuts and connect to the wrong waste pipe.
So, back to the sortie upstream. Alan & I took samples at Site 1, Site 2 and Site 4 performing some on-site tests before returning back to base for the remaining tests (OP, TAN, Turbidity). No sample was taken at the main pollution site (Site 3, green spot, Figure 1) because (i) health & safety considerations regarding an unknown pollution source, and (ii) potentially severe contamination of our testing equipment with highly polluted water. The analytical results for Site 1, Site 2 and Site 4 are reported in Table 2:
TABLE 2: Water Analysis at Site 1, Site 2 and Site 4 on 27th July 2025 |
Site Location | Site 1 (U034, black spot) | Site 2 (red spot) | Site 4 (blue spot) |
OP* (ppm) | 5.6 | 7.8 | 1.24 |
TAN (ppmN) | 9.9 | 15.9 | 0.15 |
TON* (ppmN) | 2 | 0**** | 2 |
Nitrite, [NO2]-, (ppmN) | 0.15 | 0**** | 0 |
Conductivity (μS/cm) | 668 | 730 | 560 |
Temperature (oC) | 17.0 | 16.6 | 17.3 |
Turbidity (NTU) | 5.0 | 77 | 2.5 |
pH | 7.7 | 7.8 | 7.9 |
Dissolved Oxygen (mg/L) | 3.5 | 3.5 | 5.5 |
% Dissolved Oxygen | 35.6 | 35.8 | 57.1 |
*Orthophosphate determined using the Molybdenum Blue method
**Total Ammonium Nitrogen determined using the Nessler method;
***Total Oxidised Nitrogen (nitrogen in the form of both Nitrate and Nitrite)
****Test strip reading not possible due to the water pollution
The first thing to note is that the analytical results for Sites 4 & 5, taken on different days, are very similar (Tables 1 & 2). These analyses set the baseline for 'unpolluted' brook water and clearly indicate a huge increase in pollution downstream (Site 2) with some dissipation of pollutants further downstream (Site 1). Comparing Site 4 versus Site 2 (unpolluted vs polluted, Table 2), there is an approximate 100-fold increase in TAN, a 6-fold increase in OP, a 30-fold increase in turbidity and a 40% drop in dissolved oxygen content as a result of the water pollution. The situation at the main pollution site (Site 3, green spot) will, of course, be significantly worse than this.
With photographic evidence backed up by analytical data, I reported this pollution incident on 31st July 2025 to the Environment Agency (EA). I also notified Dwr Cymru (Welsh Water) because it was possible the pollution source was a domestic property and, if so, its resolution would be down to the local water company. The EA do not provide updates on their investigations of reported pollution incidents; however, the Wye Alliance could follow this up during their regular meetings with the EA. Fortunately, Dwr Cymru do provide feedback on reported incidents and, a few days later, I heard from one of their environmental field officers that the source had been identified and they would be visiting the property to confirm and pass on the information to the Local Authority (Herefordshire Council).
Have we seen any signs that the pollution has decreased since I reported the incident (⬇) on the 31st July? Yes, indeed. In Figure 3, I have plotted the TAN/OP ratios as a time series (Figure 3) for Site 1 which Alan monitors on a twice weekly basis (so plenty of data!). Why TAN:OP Ratio? Because both TAN & OP increased as a result of the pollution but the most important pollutant was TAN (>100-fold increase).
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| Figure 3: TAN:OP Ratio Time Series at Site 1 |
It is clear from Figure 3 that the pollution first identified on 13th July had subsided by 10th August, some ten days after it was first reported, thanks to Dwr Cymru's quick response.
We can also see evidence of pollution in the dissolved oxygen measurements, as shown in
Figure 4. The data are noisier but the pollution incident can still be seen by comparing
Figure 3 and
Figure 4.
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| Figure 4: Dissolved Oxygen (mg/L) Time Series |
An excess of ammonium ions, [NH4]+, may be drawing down the dissolved oxygen content in the water in order to accomplish the conversion of ammonium ions to nitrite and then nitrate by nitrifying bacteria (i.e. Nitrogen Cycle: Ammonium + O2 bacteria_＞ Nitrite bacteria_＞ Nitrate). Alternatively, the lower dissolved oxygen content caused by the pollution may be limiting the conversion efficiency of the nitrifying bacteria.Finally, I have tested my home distilled water (collected from a heat pump tumble dryer) and found it contains significant amounts of TAN, typically 2 - 3 ppmN. This is lower than that observed in the polluted Newton Brook samples; however, the brook samples were not distilled! I suspect the high TAN values come from laundry products and, particularly, fabric softeners. Fabric softeners contain quaternary ammonium salts ('quats') as their main active ingredient and these will break down during the washing & drying process to produce 'ammonium' ions detected by our test method. Modern fabric conditioners are designed to be biodegradable so will break down more readily into ammonium ions - an unintended consequence of the move to eco products?
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