South West River Basin District Mining pollution: catchment characterisation report

Project details Project name: and Gwindra Stream - PROTECT Contact name: Karolina Krupska Contact team: Analysis and Reporting, Area Environment Manager: Bruce Newport Water body summary information Water body names: Gwindra Stream (includes Coombe Stream) Water body ids: GB108048001350 Water body type: River – Low, Small, Siliceous Catchment: West Cornwall and the Fal RBP Measure Investigate discharges from abandoned metal, and other non-coal mines. Prioritise for inclusion in national agreement with relevant mines partner organisations. Related catchments Lower Fal River GB108048001270 Water body classification Bad Poor Moderate Zn (2009), Fish(2009) Good Invertebrates (2009) High Cu (2009) Heavily modified water body? Not designated A/HMWB Comments: The River Fal is approximately 29 km in length. The Fal system is impacted by historical copper, uranium and china clay mining activity. Gwindra Stream which joins the River Fal from the north east is impacted by Great Dowgas mine which is located in the lower reaches of Coombe Stream. Classification (2009) for the Lower Fal : High – Zn, Pb, Ni, Cu, Fe, As; Moderate – Cd; Good – Invertebrates, Macrophytes.

1. Geology, Geography and Hydrology

The River Fal is located in Cornwall in South West . The Fal catchment consists of Devonian and Carboniferous mudstone and sandstone to the south and west. To the north of the river, the Intrusion (granite) has further metamorphosed Devonian sedimentary rocks into strata such as Hornfelsed Slate which contain small amounts of metaliferous mineralisation (Figure 1). Land use is mainly agricultural with some woodland.

The River Fal flows into large estuary known as Carrick Roads. Other tributaries of Carrick Roads include the River, Tresillian River, River Kennal, Penryn River and River Carnon. These also contribute significantly to metals pollution in the estuary.

Figure 1 . Geology of the River Fal catchment.

2. EA Previous Investigations

Gwindra Stream – Zinc 2011/12

Five sites have been assessed for zinc compliance - Treway Bridge (81930903), Gwindra Bridge (81930938), Goonabarn (81930961), D/S Drinnick (81930965) and U/S Drinnick (81930985). Gwindra at Treway Bridge is non-compliant with the annual mean standard of 50ug/l. Gwindra Bridge and Goonabarn are both compliant with the 50ug/l standard. Above Goonabarn the hardness decreases slightly dropping the annual mean standard to 8ug/l. This makes the sites D/S and U/S of Drinnick non-compliant even though actual levels of zinc are comparable with the compliant sites at Goonabarn and Gwindra. Mean zinc levels 2008 to date (including metal mines samples) are:

Treway 59ug/l (bottom site at confluence with Fal)

Gwindra 28ug/l

Goonabarn 25ug/l

D/S Drinnick 29ug/l

U/S Drinnick 19ug/l (top site in headwaters)

Above Gwindra Bridge there are relatively low background levels of zinc, probably arising from the local natural environment combined with the china clay industry in the headwaters. However, there is clearly a very significant input between Gwindra Bridge and the bottom site at Treway Bridge. There are two large tributaries in this stretch, the Coombe Stream joining at Coombe and the Carpalla Stream joining just below the monitoring site at Gwindra Bridge. The mean zinc level in the Carpalla Stream is relatively low at 18ug/l and unlikely to be the main cause of failure at Treway. The most recent data for the Coombe Stream at the Gwindra confluence shows a mean zinc level of 161ug/l, indicating that it is the main source of the failure at Treway. The most likely source of zinc into the Coombe Stream would appear to be the old St Austell Consols mineworkings near Polclose.

Results of ad hoc samples (all total Zn ug/l):

Gwindra Bridge 16.2

Carpalla at Gwindra 6.6

Gwindra above Coombe 16

Gwindra at Treway (below Coombe Stream) 48.1

Coombe d/s Burngullow (u/s St Austell Consols) 31.4

Coombe at Coombe (d/s St Austell Consols) 187

These results suggest that the Coombe Stream is the cause of the zinc failure at Treway Bridge. Also that the major source of zinc into the Coombe Stream is in the area of the old St Austell Consols mine workings.

NOTE - the Gwindra has been included for cadmium sampling as part of the investigation into Cd failures in the lower Fal. This sampling suggests the Gwindra is failing for cadmium as well as zinc with means levels at Treway of 0.14ug/l against the standard of 0.09ug/l. Monitoring is ongoing but early indications suggest the same sources as for zinc.

Recent results from Treway Bridge (81930903) show a mean zinc value of 57ug/l against the standard of 50 ug/l. The mean zinc value above Coombe village and at Gwindra Bridge (both above confluence with Coombe Stream) are 16ug/l and 27ug/l respectively, both compliant with the standard. The mean zinc level in the Coombe stream prior to the Gwindra is 160ug/l. The mean zinc in the Coombe Stream below Burngullow (u/s old mine workings) is 27ug/l. This seems to clearly reinforce that the main source of zinc into the Gwindra Stream is via the Coombe Stream and that the area around the old St Austell Consols mine is the source of zinc in the Coombe Stream.

3. Mining activities in the Fal catchment

Mining has taken place in the area since the Bronze Age (2500-600BC), however it became much more extensive and intensive with the industrial revolution.

Historical data suggested that the Great Dowgas Mine (Figure 3) is the source of Zn to the Coombe, Gwindra and therefore to the the Fal River. Great Dowgas Mine was a tin and copper mine which also produced pyrite, some cobalt and nickel ores and a considerable amount of ochre. It was first worked around 1719, when it sold some black tin, and reworked many times until 1913.

Great Dowgas Mine

Coombe Adit

Goffins Lode

Figure 3. Map showing location and extent of the Great Dowgas Mine.

The mine worked several SE-trending lodes. The main lode was Goffins Lode, which was developed from several shafts on a length of 300 fms along strike. It occupied a crush zone and was composed of killas fragments and a filling of mainly quartz and pyrite. Cassiterite only occurred sporadically, except in the eastern part where the lode intersected an elvan before it passed into killas and died out.

In the 18th century, the lode had already been worked from open gunnises, but they were abandoned at shallow depth, probably because the tin grades became poor.

The mine is reported to have sold some tin in 1719, but early production figures are not known. Up to 1832, it produced copper ores worth at least £12,000, and tin worth more than £9,000 is reported for the years 1828-1832. Official records give an output of 120 tons of black tin for 1856-1860, and another 47 tons for 1907-1913. In 1857, it also raised 4 tons of cobalt ores, but their mode of occurrence is not known. When it was worked for the last time, it mainly raised pyrite, which came from the upper levels. It finally closed in 1913. During its last period of working, Great Dowgas Mine was amalgamated with Ventonwyn Mine. For some time during the 18th century, it also included Wheal Unanimity, which adjoined the sett on the east (not on the south, as suggested by Hamilton Jenkin; Dines, 1994). In 1873, it was worked for a short period of time together with parts of St Austell Consols under the name St Stephen Tin and Copper Mines.

4. Monitoring programme

The Fal catchment is heavily impacted by historic mining activity throughout its entire length, but especially in the Coombe Village area. On 15/01/2013 a walk over survey was conducted resulting in discovery of an adit discharging into the Coombe Stream. Thirteen sites were selected for water chemistry sampling to quantify the various impacts, using past knowledge and data as a guide. Flow monitoring has been achieved with a mixture of spot gauging and continuous flow measurement from fixed structures. At those sites where flow measurement was not possible (e.g. Coombe Adit), it was deemed suitable to calculate derived flows from upstream and downstream monitoring. Due to health and safety issues the flow measurement at the River Fal at Grampound site was only taken once. The monitoring programme was delivered by the local A&R and H&T teams. Figure 3 shows the sampling locations. Figure 4 shows the conceptual model.

Gwindra Stream Coombe above Coombe Village Coombe Stream at Stream Coombe below Burngullow Gwindra D/S River Fal above Coombe Coombe Gwindra Confluence Adit Coombe Stream U/S Coombe Trenowth Trib Gwindra Stream Coombe Stream D/S Adit at Treway Bridge Coombe Adit Treway Trib

River Fal at Grampound

River Fal at Tregony

Figure 3. Map showing sites locations investigated in the study. Conceptual Model – The Fal River

Coombe Stream below Coombe Stream Burngullow Gwindra Stream U/S Coombe above Coombe Adit Village

Coombe Stream River Fal D/S Coombe Adit above Adit Gwindra ochre confluence

Coombe Stream at Coombe Adit Coombe* Great Dowgas Mine Trenowth Trib Gwindra D/S Coombe

Gwindra Stream at Treway Bridge*

Treway trib

Fal at Grampound Bridge *

* WFD designated site

River Fal at Tregony Direction of flow Gauging Station * Mining areas

Figure 4. Conceptual model – The River Fal

5.0 Results

5.1 Water Quality – Coombe Stream, Gwindra Stream and River Fal

Table 1 shows metals concentrations greater than the WFD standards in the catchment.

Table 1. Total and dissolved metal concentrations (ug/l) in Coombe Stream, Gwindra Stream and the River Fal. Cond Mean Hardn at pH in- Cd Total Cd Diss Cu Total Cu Diss Zn Total Zn Diss Site Name Min ess 25C situ ug/l ug/l ug/l ug/l ug/l ug/l Max uS/cm 41 Mean 204.2 6.8 0.6 0.6 14.7 12.7 179.3 174.5 COOMBE STREAM AT Min 192.9 6.8 0.5 0.5 14.0 12.1 155.0 150.0 COOMBE* Max 208.7 6.9 0.7 0.6 16.0 13.5 214.0 205.0 48 Mean 200.4 6.4 0.9 0.6 21.7 13.2 260.8 160.0 COOMBE D/S COOMBE Min 188.0 6.1 0.6 0.4 14.2 10.0 161.0 116.0 ADIT Max 215.0 6.5 1.5 0.6 40.2 16.3 500.0 190.0 44 Mean 186.9 6.6 0.2 <0.1 3.4 2.6 31.2 29.5 COOMBE U/S COOMBE Min 177.6 6.6 0.1 0.1 2.9 2.3 29.9 28.3 ADIT Max 191.8 6.7 0.2 0.2 4.1 3.2 32.4 30.1 186.9 6.6 0.2 <0.1 3.4 2.6 31.2 29.5 Mean COOMBE STREAM BELOW 177.6 6.6 0.1 0.1 2.9 2.3 29.9 28.3 41 Min BURNGULLOW 191.8 6.7 0.2 0.2 4.1 3.2 32.4 30.1 Max Mean 211.2 6.6 <0.1 <0.1 3.9 2.5 20.5 17.5 GWINDRA STREAM ABOVE 42 Min 199.4 6.6 <0.1 <0.1 3.2 2.2 18.4 16.1 COOMBE VILLAGE Max 218.8 6.6 <0.1 <0.1 4.5 2.7 23.7 19.5 Mean 206.7 6.7 0.2 0.2 6.5 5.1 62.3 59.2 GWINDRA D/S COOMBE 44 Min 195.3 6.6 0.2 0.2 6.0 4.9 50.4 47.8 Max 218.2 6.7 0.2 0.2 6.9 5.6 75.4 69.5 44 Mean 212.2 6.8 0.2 0.2 6.3 4.6 58.8 54.1 GWINDRA STREAM AT Min 198.2 6.7 0.2 0.1 5.9 4.5 50.8 45.1 TREWAY BRIDGE * Max 221.0 6.8 0.2 0.2 6.8 4.7 63.5 59.8 36 Mean 186.8 7.0 <0.1 <0.1 5.1 3.2 19.8 16.6 RIVER FAL ABOVE Min 162.3 6.8 <0.1 <0.1 3.5 2.4 17.3 12.2 GWINDRA CONFLUENCE Max 212.0 7.1 <0.1 <0.1 6.2 4.0 22.9 22.3 Mean 208.6 7.1 <0.1 <0.1 5.2 3.2 40.4 34.8 Min 183.5 7.0 <0.1 <0.1 4.1 2.9 33.6 26.5 RIVER FAL AT 44 GRAMPOUND BRIDGE* Max 220.2 7.1 0.2 <0.1 5.7 3.5 44.1 40.0

50 Mean 219.9 7.1 <0.1 <0.1 5.2 2.9 37.5 30.0 RIVER FAL AT TREGONY * Min 195.8 7.1 <0.1 <0.1 3.9 2.7 33.6 23.2

Max 233.7 7.3 0.2 0.1 5.9 3.2 39.5 34.3 *designated site Hardness <50 WFD standard for: Zn (8 ug/l) ; Cu (1 ug/l) WFD fail Hardness >50 WFD standards for: Zn (50 ug/l); Cu (6 ug/l) WFD comply For Cd Concentrations below WFD Concentrations greater than WFD

The mean of total and dissolved Cd, Cu and Zn concentration (ug/l) in the Coombe Stream, Gwindra Stream and the River Fal exceeded WFD standards at most sites. As far as designated sites are concerned Coombe Stream at Coombe and Gwindra Stream at Treway Bridge (Gwindra at the confluence with Fal) sites fail for Cd, Cu and Zn dissolved concentrations; River Fal at Grampound Bridge site is not compliant for Cu and Zn dissolved concentrations; River Fal at Tregony due to higher band hardness is compliant for Cd, Cu and Zn dissolved concentrations.

In the Coombe Stream there is a steady increase of total and dissolved Cu, Cd and Zn concentrations where the stream flowed through the historic mining area. There is also a sharp rise at the site Coombe D/S Coombe where the Coombe adit joins the main stream. The effect of dilution and spatial decay with distance from the source of contamination is not readily observable due to possible remobilisation of metals during high flow.

In the Gwindra Stream there is a sharp raise of Cd, Cu and Zn concentrations in Gwindra Stream downstream the Coombe Stream (Gwindra D/S Coombe). Dissolved concentrations (means) of: Cd increased from <0.1 (ug/l) to 0.2 (ug/l); Cu dissolved concentrations increased from 2.5 (ug/l) to 5.1 (u/g); and Zn dissolved concentrations increased from 17.5 (ug/l) to 59.2 (ug/l). The effect of dilution and spatial decay with the distance from the Coombe Stream can be seen, however due to high flows the decrease is marginal.

In the River Fal the increase in Zn concentrations (ug/l) is readily observable after the Gwindra Stream joins the River Fal. The dissolved concentration (mean) of Zn (ug/l) at the River Fal above Gwindra confluence was 16.6 (ug/l) and downstream of the confluence was 34.8 (ug/l).

5.2 Water Quality – Inputs and adits

Tables 2 and 3 show mean metal concentrations greater than WFD standards in the inputs.

In general, metal concentrations were higher in the inputs than in the Coombe Stream, Gwindra Stream and the River Fal. Mean total concentrations of Zn and Cu were higher than dissolved concentrations. Cd, Cu and Zn total and dissolved concentrations were greater than WFD standards at all input sampling locations. The highest total and dissolved concentrations of Cu, Cd and Zn were recorded at Coombe Adit. Additionally, total and dissolved Fe and Ni concentrations in the Coombe Adit exceeded WFD standards, however immediately downstream of the point source Fe and Ni concentrations were below WFD standards.

5.2.1 Inputs

Table 2. Total and dissolved metal concentrations (ug/l) in Trenowth and Treway Tributaries. pH Mean Cond at Cd Total Cd Diss Cu Total Cu Diss Zn Total Zn Diss Site Name Hardness in- Min 25C uS/cm ug/l ug/l ug/l ug/l ug/l ug/l situ Max TRENOWTH TRIB 242.1 6.8 Mean 0.6 0.5 4.2 2.2 102.4 96.4 63 208.4 6.8 Min 0.4 0.3 3.5 1.7 72.5 63.5 254.2 6.9 Max 0.7 0.6 4.7 2.6 123.0 120.0 TREWAY TRIB 69 253.9 6.9 Mean 0.8 0.7 3.0 1.6 190.8 173.8 236.3 6.8 Min 0.7 0.6 1.8 1.2 172.0 151.0 297.6 6.9 Max 1.0 0.8 3.8 1.8 224.0 199.0 Hardness >50 WFD standards for: Zn (50 ug/l); Cu (6 ug/l) For Cd 0.09 ug/l (Hardness 50-<100) Concentrations below WFD Concentrations greater than WFD 5.2.2. Adits

Table 3. Total and dissolved metal concentrations (ug/l) in Coombe Adit

Cond pH Mean Cd Cu Zn Fe Ni Hardness Cd Diss Cu Diss Zn Diss Fe Diss Ni Diss Site Name at 25C in- Min Total Total Total Total Total ug/l ug/l ug/l ug/l ug/l uS/cm situ Max ug/l ug/l ug/l ug/l ug/l

COOMBE 271.8 5.6 Mean 2.9 2.9 75.2 73.0 989.3 956.3 1817.5 1422.5 34.1 33.5 ADIT 73 270.4 5.5 Min 2.8 2.7 72.3 70.7 946.0 931.0 1630.0 1310.0 33.9 32.2

273.0 5.6 Max 3.1 3.1 77.0 75.6 1050.0 986.0 1930.0 1600.0 34.3 34.4 Hardness >50 WFD standards for: Zn (50 ug/l); Cu (6 ug/l) For Cd 0.09 ug/l (Hardness 50-<100) Concentrations below WFD Concentrations greater than WFD

5.3 Hydrological context

The flow-duration curve for Tregony gauging station (the nearest gauging station to the Fal upper reaches) is shown in Figure 5. Red dots on the curve illustrate that the monitoring has been carried out under high flow conditions (Q3-Q10). Ideally a flow in the range Q50 – Q60 should also have been captured; however prolonged precipitation caused continuously high groundwater levels during the studies.

Although Tregony flow data are used to provide a wider hydrological context, it is recognised that daily mean flows nearer the study area are more likely to be influenced by groundwater levels.

Flow duration curve - Tregony Gauging Station

14 23-Jan-13 Q10 12 29-Jan-13 Q3 05-Feb-13 Q4 10 07-Feb-13 Q9

8 m3/sec 6

4

2 11 13 15 17 19 21 24 26 28 30 32 34 36 38 41 43 45 47 49 51 53 56 58 60 62 64 66 68 70 73 75 77 79 81 83 85 88 90 92 94 96 98 0 0 2 4 6 9

precentage (%)

Figure 5. Flow duration curve – Tregony gauging station.

Synchronized chemical and flow sampling was conducted 4 times during January and February 2013. A summary of the data collected during the four monitoring events is shown in Figure 6 and 7. Figures 6 and 7 show dissolved Cd, Cu and Cd mean concentrations (ug/l) and mean loading (kg/day), whereas tables 4,5,6 show total as well as dissolved Cd, Cu and Zn mean concentrations (ug/l) and flux (kg/day).

Figures 6 and 7 clearly show that the Coombe Adit discharge is the most important source of Zn, and Cd at the Great Dowgas mine site. This also infuences the metal loading at the designated sites including Coombe Stream at Coombe, Gwindra at Treway Bridge and to some extent the River Fal at Grampound Bridge and River Fal at Tregony. The flow of the Coombe Adit discharge varied between monitoring events from 25 l/s to 77 l/s. The Zn and Cu flux fluctuated between 2 and 6.5 kg/d and between 0.15-0.47 kg/d respectively. Conversely Cd flux remained fairly constant between 0.01 and 0.02 kg/d.

There is an increase in Zn, Cu and Cd concentrations between sites Coombe Stream below Burngullow and Coombe U/S Coombe Adit, this can be explained by ocherous seepages possibly enriched in heavy metals entering the stream between these two locations.

As stated above, the Coombe Adit is an important source of Zn, Cu and Cd to the four designated sites of concern. This is demonstrated by the significant increase in the metals loading observed within the Coombe Stream between the monitoring locations upstream and downstream of the Coombe Adit discharge under flow conditions Q3-Q10.

The second important source of Zn to the River Fal designated sites (Grampound and Tregony) is Treway Trib. There is evidence of a slight increase in Zn concentrations at higher flows when comparing most recent and historical data. In contrast, the Trenowth Trib is of least importance in terms of Zn pollution to River Fal at designated sites, however there is also evidence of an increase in Zn concentrations at higher flows when comparing most recent and historical data.

During the studies Zn, Cu and Cd concentrations and loadings were fairly constant between locations Coombe D/S Coombe Adit and Coombe Stream at Coombe and between Gwindra D/S Coombe and Gwindra at Treway Bridge. This indicates that at higher flows the remobilisation of metals from metal‐contaminated river sediments contributes an amount of Zn, Cu and Cd greater than that which is attenuated. Under low flow conditions, some attenuation processes such as: precipitation; loss to solution; hydraulic sorting; physical dilution; biological uptake; mixing with uncontaminated sediment; and floodplain storage are expected to occur within the Coombe Stream as well as Gwindra Stream. Conversely, there is evidence of metal decay processes between the River Fal at Grampound and the River Fal at Tregony, where the river is deeper, thus more stream power is needed to disturb the river bed.

Coombe Adit Coombe Stream below Burngullow Metal Diss ug/l l/sec Kg/day Metal Diss ug/l l/sec Kg/day 0.1 0.002 2.9 0.01 Cd Cd (0.1-0.2) (0.001-0.002) (2.7-3.1) (0.01-0.02) 136.8 2.6 0.03 73 49.8 0.31 Cu (101-162) (2.3-3.2) (0.02-0.04) Coombe Stream at Coombe* Cu (70.7-75.6) (25-77) (0.15-0.47) 29.5 0.3 Metal Diss ug/l l/sec Kg/day 956.3 4.1 Zn Zn (28.3-30.1) (0.3-0.4) Cd 0.6 0.01 (931-986) (2-6.5) (0.5-0.6) (0.01-0.01) 245 12.7 (230-257) 0.27 Cu (12.1-13.5) (0.26-0.28)

174.5 3.67 Zn (150-205) (3.33-4.07)

Gwindra U/S Coombe Metal Diss ug/l l/sec Kg/day 0.1 0.01 Cd (0.1-0.1) (0.01-0.01) Coombe U/S Coombe Adit 713.8 2.5 0.15 Cu (623-847) Metal Diss ug/l l/sec Kg/day (2.2-2.7) (0.12-0.2)

17.5 1.1 0.004 Zn 0.2 (16.1-19.5) (0.9-1.2) Cd (0.003- (0.2-0.3) 192.5 0.005) (155-238) Coombe D/S of Coombe Adit 4.5 0.07 Cu (4.1-4.9) (0.06-0.09) Metal Diss ug/l l/sec Kg/day 0.6 0.01 51.2 0.8 Cd 242.3 Zn (0.4-0.6) (0.01-0.02) (48.1-54.2) (0.7-1) (200-290) 13.2 0.28 Cu (10-16.3) (0.2-0.41)

160 3.33 Gwindra D/S Coombe Zn (116-190) (2.65-4.46) Metal Diss ug/l l/sec Kg/day 0.2 0.02 Cd (0.2-0.2) (0.01-0.02) 1074.3 5.1 0.47 Cu (815-1393) (4.9-5.6) (0.39-0.62)

59.2 5.53 Zn (47.8-69.5) (4.23-8.36)

Figure 6. Map showing dissolved Cd, Cu and Zn concentrations (ug/l) and loadings (kg/l) at each location. *WFD designated site River Fal above Gwindra confluence Gwindra Stream at Treway Bridge* Diss ug/l Metal l/sec Kg/day Metal Diss ug/l l/sec Kg/day 0.1 0.02 0.2 0.02 Cd Cd (0.1-0.1) (0.01-0.03) (0.1-0.2) (0.02-0.02) 2360 1216.5 3.2 0.64 4.6 0.48 Cu (1659-3327) Cu (960-1463) (2.4-4) (0.4-1) (4.5-4.7) (0.39-0.58)

16.6 3.21 54.1 5.6 Zn Zn (12.2-22.3) (2.71-3.51) Treway Trib (45.1-59.8) (5-5.9)

Metal Diss ug/l l/sec Kg/day 0.7 0.01 Cd Trenowth Trib (0.6-0.8) (0.01-0.01) 1.6 144.5 0.02 Metal Diss ug/l l/sec Kg/day Cu 0.5 0.01 (1.2-1.8) (107-180) (0.01-0.03) Cd 173.8 2.1 (0.3-0.6) (0.01-0.01) Zn 2.2 127.8 0.02 (151-199) (1.6-2.5) Cu (1.7-2.6) (99-181) (0.01-0.04) 96.4 1 Zn (63.5-120) (1-1)

Fal at Tregony* Metal Diss ug/l l/sec Kg/day Fal at Grampound Bridge* 0.1 0.04 Cd Metal Diss ug/l l/sec Kg/day (0.1-0.1) (0.04-0.05) 0.1 2.9 4522.8 1.1 Cd 0.04** Cu (0.1-0.1) (2.7-3.7) (3461-5720) (0.9-1.5) 3.2 30 11.4 Cu 3098** 0.9** Zn (2.9-3.5) (23.2-34.3) (10.1-12.8) 34.8 Zn 10.7** (26.5-40)

Figure 7. Map showing dissolved Cd, Cu and Zn concentrations (ug/l) and loadings (kg/l) at each location. *WFD designated site **Flux (kg/day) estimated on the basis of one flow monitoring (due to health and safety issues)

Table 4

Mean Cd Cd Site Name Min Total L/s Kg/day Dissolved L/s Kg/day Max ug/l ug/l

COOMBE STREAM AT mean 0.6 245.0 0.01 0.6 245.0 0.01

COOMBE * min 0.5 230.0 0.01 0.5 230.0 0.01

max 0.7 257.0 0.01 0.6 257.0 0.01

COOMBE D/S COOMBE mean 0.9 242.3 0.02 0.6 242.3 0.01 ADIT min 0.6 200.0 0.01 0.4 200.0 0.01 max 1.5 290.0 0.03 0.6 290.0 0.02 COOMBE U/S COOMBE mean 0.3 192.5 0.004 0.2 192.5 0.004 ADIT (Input) min 0.2 155.0 0.004 0.2 155.0 0.003 max 0.3 238.0 0.005 0.3 238.0 0.005 COOMBE ADIT mean 2.9 49.8 0.01 2.9 49.8 0.01 min 2.8 25.0 0.01 2.7 25.0 0.01 max 3.1 77.0 0.02 3.1 77.0 0.02 STREAM BELOW mean 0.2 10 0.0001 0.1 10 0.0001 BURNGULLOW min 0.1 10 0.0001 0.1 10 0.0001 max 0.2 10 0.0001 0.2 10 0.0001 GWINDRA ABOVE mean 0.1 713.8 0.01 0.1 713.8 0.01 COOMBE VILLAGE min 0.1 623.0 0.01 0.1 623.0 0.01

max 0.1 847.0 0.01 0.1 847.0 0.01 GWINDRA D/S COOMBE mean 0.2 1074.3 0.02 0.2 1074.3 0.02 min 0.2 815.0 0.01 0.2 815.0 0.01 max 0.2 1393.0 0.03 0.2 1393.0 0.02 GWINDRA STREAM AT mean 0.2 1216.5 0.02 0.2 1216.5 0.02 TREWAY BRIDGE * min 0.2 960.0 0.02 0.1 960.0 0.02

max 0.2 1463.0 0.02 0.2 1463.0 0.02

RIVER FAL ABOVE mean 0.1 2360.0 0.02 0.1 2360.0 0.02

GWINDRA CONFLUENCE min 0.1 1659.0 0.01 0.1 1659.0 0.01

max 0.1 3327.0 0.03 0.1 3327.0 0.03

TRENOWTH TRIB (Input) mean 0.6 127.8 0.01 0.5 127.8 0.01 min 0.4 99.0 0.01 0.3 99.0 0.01 max 0.7 181.0 0.01 0.6 181.0 0.01 TREWAY TRIB (Input) mean 0.8 144.5 0.01 0.7 144.5 0.01

min 0.7 107.0 0.01 0.6 107.0 0.01

max 1.0 180.0 0.01 0.8 180.0 0.01 FAL AT GRAMPOUND mean 0.1 3098 0.04 0.1 3098 0.04 BRIDGE * min 0.1 3098 0.1 3098 max 0.1 3098 0.1 3098 FAL AT TREGONY* mean 0.1 4522.8 0.04 0.1 4522.8 0.04 min 0.1 3461.0 0.04 0.1 3461.0 0.04

max 0.2 5720.0 0.1 0.1 5720.0 0.05 *WFD designated site

Table 5

Mean Cu Cu Total Site Name Min L/s Kg/day Dissolved L/s Kg/day ug/l Max ug/l COOMBE STREAM AT mean 14.7 245.0 0.31 12.7 245.0 0.27 COOMBE * min 14.0 230.0 0.30 12.1 230.0 0.26 max 16.0 257.0 0.32 13.5 257.0 0.28 COOMBE D/S COOMBE mean 21.7 242.3 0.47 13.2 242.3 0.28 ADIT min 14.2 200.0 0.25 10.0 200.0 0.20 max 40.2 290.0 0.92 16.3 290.0 0.41 COOMBE U/S COOMBE mean 5.0 192.5 0.083 4.5 192.5 0.075 ADIT min 4.5 155.0 0.067 4.1 155.0 0.060 max 5.4 238.0 0.102 4.9 238.0 0.090 COOMBE ADIT mean 75.2 49.8 0.32 73.0 49.8 0.31 min 72.3 25.0 0.16 70.7 25.0 0.15 max 77.0 77.0 0.48 75.6 77.0 0.47 COOMBE STREAM mean 3.4 136.8 0.04 2.6 136.8 0.03 BELOW BURNGULLOW min 2.9 101 0.3 2.3 101 0.02 max 4.1 162 0.6 3.2 162 0.04 GWINDRA ABOVE mean 3.9 713.8 0.24 2.5 713.8 0.15 COOMBE VILLAGE min 3.2 623.0 0.18 2.2 623.0 0.12 max 4.5 847.0 0.29 2.7 847.0 0.20 GWINDRA D/S mean 6.5 1074.3 0.61 5.1 1074.3 0.47 COOMBE min 6.0 815.0 0.47 4.9 815.0 0.39 max 6.9 1393.0 0.84 5.6 1393.0 0.62 GWINDRA STREAM AT mean 6.3 1216.5 0.66 4.6 1216.5 0.48 TREWAY BRIDGE* min 5.9 960.0 0.50 4.5 960.0 0.39 max 6.8 1463.0 0.80 4.7 1463.0 0.58 RIVER FAL ABOVE mean 5.1 2360.0 1.05 3.2 2360.0 0.64 GWINDRA min 3.5 1659.0 0.58 2.4 1659.0 0.40 CONFLUENCE max 6.2 3327.0 1.78 4.0 3327.0 1.00

TRENOWTH TRIB mean 4.2 127.8 0.05 2.2 127.8 0.02 min 3.5 99.0 0.03 1.7 99.0 0.02 max 4.7 181.0 0.07 2.6 181.0 0.03 TREWAY TRIB mean 3.0 144.5 0.04 1.6 144.5 0.02 min 1.8 107.0 0.06 1.2 107.0 0.01 max 3.8 180.0 0.1 1.8 180.0 0.03 FAL AT GRAMPOUND* mean 5.2 3098 1.47 3.2 3098 0.92 BRIDGE min 5.1 3098 1.47 3.2 3098 0.92 max 5.7 3098 1.47 3.2 3098 0.92

mean 5.2 4522.8 2.1 2.9 4522.8 1.1 FAL AT TREGONY* min 3.9 3461.0 1.3 2.7 3461.0 0.9 max 5.9 5720.0 2.9 3.2 5720.0 1.5

*WFD designated site

Table 6

Mean Zn- Zn Total Site name Min L/s Kg/day Dissolved L/s Kg/day ug/l Max ug/l

COOMBE STREAM AT mean 179.3 245.0 3.77 174.5 245.0 3.67

COOMBE * min 155.0 230.0 3.44 150.0 230.0 3.33

max 214.0 257.0 4.25 205.0 257.0 4.07 COOMBE D/S COOMBE mean 260.8 242.3 5.63 160.0 242.3 3.33 ADIT min 161.0 200.0 2.78 116.0 200.0 2.65 max 500.0 290.0 11.40 190.0 290.0 4.46 COOMBE U/S COOMBE mean 51.6 192.5 0.857 51.2 192.5 0.851 ADIT min 48.0 155.0 0.738 48.1 155.0 0.726 max 55.1 238.0 1.032 54.2 238.0 1.003 COOMBE ADIT mean 989.3 49.8 4.28 956.3 49.8 4.13 min 946.0 25.0 2.04 931.0 25.0 2.02

max 1050.0 77.0 6.72 986.0 77.0 6.49 STREAM BELOW mean 31.2 136.8 0.4 29.5 136.8 0.3 BURNGULLOW min 29.9 101.0 0.3 28.3 101.0 0.3 max 32.4 162.0 0.4 30.1 162.0 0.4 GWINDRA ABOVE mean 20.5 713.8 1.3 17.5 713.8 1.1 COOMBE VILLAGE min 18.4 623.0 1.0 16.1 623.0 0.9 max 23.7 847.0 1.5 19.5 847.0 1.2 GWINDRA D/S mean 62.3 1074.3 5.85 59.2 1074.3 5.53 COOMBE min 50.4 815.0 4.34 47.8 815.0 4.23 max 75.4 1393.0 9.07 69.5 1393.0 8.36 GWINDRA STREAM AT mean 58.8 1216.5 6.10 54.1 1216.5 5.60 TREWAY BRIDGE min 50.8 960.0 5.27 45.1 960.0 4.96 max 63.5 1463.0 6.54 59.8 1463.0 5.89 RIVER FAL ABOVE mean 19.8 2360.0 3.99 16.6 2360.0 3.21 GWINDRA min 17.3 1659.0 2.90 12.2 1659.0 2.71 CONFLUENCE max 22.9 3327.0 5.52 22.3 3327.0 3.51 TRENOWTH TRIB mean 102.4 127.8 1.1 96.4 127.8 1.0 min 72.5 99.0 1.1 63.5 99.0 1.0 max 123.0 181.0 1.1 120.0 181.0 1.0 TREWAY TRIB mean 190.8 144.5 2.4 173.8 144.5 2.1 min 172.0 107 1.7 151.0 107 1.6

max 224.0 180 2.8 199.0 180 2.5 FAL AT GRAMPOUND mean 40.4 3098 0.03 34.8 3098 0.03 BRIDGE* min 33.6 3098 26.5 3098 max 44.1 3098 40.0 3098 FAL AT TREGONY* mean 37.5 4522.8 14.5 30.0 4522.8 11.4 min 33.6 3461.0 11.8 23.2 3461.0 10.1

max 39.5 5720.0 17.6 34.3 5720.0 12.8 *WFD designated sites 6. Summary of the Results and Recommendations

The importance of point and diffuse sources of mining pollution in the Fal catchment has been assessed by means of synchronous flow and quality monitoring at thirteen monitoring sites. The most important source of Cd, Zn and to lesser extend Cu in the catchment is the Coombe Adit discharge which dominates the metals loadings to the Coombe Stream at Coombe and Gwindra Stream at Treway Bridge.

The greatest increase in Zn loading, however, occurs between the River Fal above Gwindra Confluence and The River Fal at Grampound Bridge, indicating that the Treway and Trenowth tributaries are an additional important source of Zn to the River Fal at Grampound Bridge and the River Fal at Tregony. Due to higher hardness band the River Fal at Tregony is compliant for Cd, Cu and Zn, however that might change when annual mean hardness for that particular site is calculated. The historic data suggest that hardness at the sites may change from year to year.

There is also evidence of lack of attenuation of metals during high flow conditions and possible remobilisation of metals, or metal‐contaminated river sediments during higher flows within researched area. The overall decline of metal concentrations with the distance from the source of contamination, which indicates the presence of chemical and physical processes such as: precipitation; loss to solution; hydraulic sorting; physical dilution; biological uptake; mixing with uncontaminated sediment; and floodplain storage is expected during low and moderate flows.

Despite the observed increase of Cd, Cu and Zn from diffuse sources during high flows, remediation of the Coombe Adit discharge would make a significant improvement to the quality of the Coombe Stream and Gwindra Stream, even during the highest flows. This is illustrated in Figure 8, in which Cd, Cu and Zn loading data have been used to predict metal concentrations in the four WFD designated sites, using a mass‐balance approach. The data in Figure 8 are arranged according to the flow condition in the Tregony Gauging station (The River Fal at Tregony) site, including flows Q3-Q10. For each of these hydrological conditions the effect of treatment on water quality is calculated for two scenarios:

(1) Treatment of the Coombe Adit discharge (shown in blue on Figure 8) and (2) Treatment of the Coombe Adit and Treway and Trenowth Tributaries (shown in orange on Figure 8)

In the first case (treatment of the Coombe adit alone) Zn, Cu and Cd treatment efficiency are assumed as follow (Figure 8):

 54.2% -100% Zn efficiency; 57.7%-100% Cu efficiency; 100% Cd efficiency for the Coombe Stream at Coombe designated site  34.6% - 100% Zn efficiency; 34.1%-81% Cu efficiency; 50%-100% Cd efficiency for Gwindra Stream at Treway Bridge designated site  35.8 % Zn efficiency; 32.2% Cu efficiency ; 25% Cd efficiency for the River Fal at Grampound designated site  18.2%-56.6% Zn efficiency ; 17.4%- 31.5% Cu efficiency; 40% -25% Cd efficiency for the River Fal at Tregony designated site In the second scenario (treatment of the Coombe Adit and Treway and Trenowth tributaries) Zn, Cu and Cd treatment efficiency are assumed as follow (Figure 8):

 65% Zn efficiency; 37% Cu efficiency; 75% Cd efficiency for the River Fal at Grampound site  42.1%-87.4% Zn efficiency; 20.9-35.6% Cu efficiency; 75%-80% Cd efficiency

What is clear from Figure 8 is that treatment of the Coombe Adit discharge will result in a substantial improvement in Cd, Cu and Zn concentrations along the study area. Under higher flows, reduction in Zn concentration is predicted to be as much as 100% immediately downstream of the mine site, at Coombe Stream at Coombe and at Gwindra Stream at Treway Bridge designated sites. Treatment of the Coombe Adit discharge will result in some improvement to Zn, Cu and Cd concentration in the River Fal, as far as high flows are concerned.

Figure 8 shows that treatment of the Coombe Adit as well as Treway and Trenowth tributaries will result in further decrease of Zn and Cd and to lesser extend Cu concentrations in the River Fal, particularly the River Fal at Grampound Bridge and the River Fal at Tregony designated sites.

The metal contaminants in the Coombe Adit may become associated with stream sediments below the discharge. This overall decline of metal concentrations with the distance from the source of contamination is associated with chemical and physical processes such as: precipitation; loss to solution; hydraulic sorting; physical dilution; biological uptake; mixing with uncontaminated sediment; and floodplain storage. Metals associated with stream sediments may be released during high flows, and therefore contribute to the very high downstream metal loadings under storm conditions. Thus, remediating the point source may reduce the mass of metal associated with stream sediments, and therefore reduce the magnitude of the metal loading and concentration during storm events. For that reason predicted improvements during low and moderate flows are expected to be greater, however this hypothesis needs to be tested.

Recommended further studies:

 monitoring during moderate and low flows  walkover surveys to investigate the possible point sources of heavy metal concentrations recorded at Trenowth and Treway tributaries

Gwindra Stream at Treway Bridge * Tregony Q10 Q3 Q4 Q9 Current Zn Diss 59.8 45.1 52.2 59.4 Predicted Zn Diss 13.6 0 15.2 38.9 Coombe Stream at Coombe * Zn Reduction % 77.2 100 71 34.6 Tregony Q10 Q3 Q4 Q9 Current Cu Diss 4.7 4.6 4.6 4.5 Current Zn Diss 205.0 150.0 160.0 183.0 Predicted Cu Diss 1.2 0.9 1.6 3.0 Predicted Zn Diss 12.1 0.0 0.0 83.9 Cu Reduction % 74.4 81 65.4 34.1 Zn Reduction % 94.1 100 100 54.2 Current Cd Diss 0.2 0.1 0.2 0.2 Current Cu Diss 13.5 12.1 12.4 12.8 Predicted Cd Diss 0.1 0 0.09 0.09 Predicted Cu Diss 0 0 0 5.4 Zn Reduction % 50 100 50 50 Cu Reduction % 100 100 100 57.7 Current Cd Diss 0.6 0.5 0.5 0.6 Predicted Cd Diss 0 0 0 0 Zn Reduction % 100 100 100 100

River Fal at Tregony* Tregony Q10 Q3 Q4 Q9 Current Zn Diss 33.9 23.2 28.6 34.3 River Fal at Grampound Predicted Zn Diss 21.1 10.1 19.2 28.0 Bridge* Zn Reduction % 37.8 56.6 32.7 18.2 Tregony Q10 Predicted Zn Diss 10.8 2.9 11.8 19.9 Current Zn Diss 40.0 Zn Reduction % 68.1 87.4 58.8 42.1 Predicted Zn Diss 25.7 Current Cu Diss 3.2 3.0 2.7 2.7 Zn Reduction % 35.8 Predicted Cu Diss 2.3 2.1 2 2.2 Predicted Zn Diss 14 Cu Reduction % 29.9 31.5 28.1 17.4 Zn Reduction % 65 Predicted Cu Diss 2.1 1.9 1.8 2.1 Cu Reduction % 34 35.6 32.2 20.9 Current Cu Diss 3.5 Current Cd Diss 0.1 0.1 0.1 0.1 Predicted Cu Diss 2.3 Predicted Cd Diss 0.09 0.07 0.09 0.09 Cu Reduction % 32.2 Predicted Cu Diss 2.2 Cd Reduction % 25 40 25 25 Legend Predicted Cd Diss 0.03 0.02 0.03 0.02 Cu Reduction % 37 Cd Reduction % 75 80 75 75 Current Cd Diss 0.1 Current Dissolved metal concentrations (ug/l) Predicted Cd Diss 0.09 Scenario 1- treatment of the Coombe adit alone Cd Reduction % 25 Scenario 2 –treatment of Coombe adit as well Predicted Cd Diss 0.03 as Trenowth and Treway tributaries Cd Reduction % 75

Figure 8. Use of Cd, Cu and Zn loadings data to predict downstream improvements in dissolved metal concentration at four designated sites*, under two scenarios: (1) treatment of the Coombe Adit discharge (data in blue) and (2) treatment of Coombe Adit as well as Trenowth and Treway Tributaries. All metals concentrations in units of μg/l. 6. Constrains

6.1 Stakeholders and Occupiers

Coombe Adit

Name Address 1 Address 2 Address 4 Address 5 Postcode Anthony John Buckingham Coombe Meadow Coombe ST. AUSTELL Cornwall PL26 7LJ BODINNICK FARM BODINNICK FARM ST STEPHEN ST AUSTELL PL26 7LL BOYD A P Hendra Farm Coombe ST. AUSTELL Cornwall PL26 7LG H.D.TEAGUE FAIRVIEW DOWGAS ST AUSTELL PL26 7LU J M VENNING Tregargus Farm St. Stephen St. Austell Cornwall PL26 7QD M A GRIGG TRELINHAY LOWER STICKER ST AUSTELL CORNWALL PL26 7JL Messrs Hulme Downderry House Coombe ST. AUSTELL Cornwall PL26 7LT MR G AND MRS JS DUNN HAY FARM COOMBE ST AUSTELL CORNWALL PL26 7LF MRS D HILLS ROSE COTTAGE POLGOOTH ST AUSTELL CORNWALL PL26 7BY P A CROSS Hendra Lodge Coombe ST. AUSTELL Cornwall PL26 7LG HIGHER P J & V C EAD & SON HENSAVISTEN FARM HIGH STREET ST AUSTELL PL26 7ST RICHARDS, H J COYTE FARM ST MEWAN ST AUSTELL PL26 7DR LOWER Teague, M E & K G DOWNDERRY FARM COOMBE ST AUSTELL PL26 7LT TRETHEWEY A A ALFUNLIN HEWASWATER ST AUSTELL PL26 7JF V G E AND J D SCOTT Trevithick House Ruan High Lanes TRURO Cornwall TR2 5LN W I & EM Hoskins Little Pengelly Farm Lower Sticker St Austell Cornwall PL26 7JJ 6.2 Conservation and heritage designations

Only one site of SSSI was recorded in the researched area from five present in the Fal catchment. The Crowhill Valley SSSI between Grampound and St Stephen is an ancient woodland dominated by sessile oak on the slopes, and of willow and alder carr on the floodplain which has a rich ground flora. The species list includes many ancient woodland indicators including lichens such as Parmelia endochlora.

Site Notified to Secretary of State on 1986

COUNTY: Cornwall SITE NAME: CROWHILL VALLEY DISTRICT: Carrick/

Status: Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlife and Countryside Act 1981 (as amended)

Local Planning Authority: Carrick District Council, Restormel Borough Council, Cornwall County Council

National Grid Reference: SW 934513 Area: 42.5 (ha) 105.0 (ac) Ordnance Survey Sheet 1:50,000: 204 1:10,000: SW 95 SW Date Notified (Under 1949 Act): 1951 Date of Last Revision: 1973 Date Notified (Under 1981 Act): 1986 Date of Last Revision: – Other Information:

Site boundary amended by deletion and extension. Site includes part of the SSSI formerly known as Trenowth Wood (notified 1951).

Description and Reasons for Notification (Natural England, 2013):

Crowhill Valley lies on the upper reaches of the River Fal between Grampound and St Stephen. The site is of importance for its woodland complex. The valley sides carry ancient broadleaved woodland dominated by Sessile Oak Quercus petraea. The wet flood plain supports an extensive area of carr woodland, predominantly of Willow Salix spp and Alder Alnus glutinosa, with a very rich ground flora. Very few comparably large areas of Sump Alder Woodland are known from south-west England.

The valley at Crowhill runs north-south and cuts at right angles across the junction between Upper Devonian rocks of Grampound Grit and the older Meadfoot Beds. Well-drained steep valley sides fall from an altitude of 100 m to a narrow waterlogged flood plain at 35m. The soils of the valley floor are alluvial stagnogleys while those of the slopes are well drained silty loams. The main watercourses of the site are the river Fal itself and a mill race which runs, parallel with the Fal, from a stream-fed pool at the foot of Carnwinnick Wood. Between the race and the river the valley floor is criss-crossed with old man-made drains as well as innumerable small natural streams and rivulets which meander between these. A series of small pools are probably a remnant of tin-streaming operations.

The valley side Oak woodlands are of ancient origins and a variety of past management techniques has resulted in a wide range of structure and ground flora. Large areas are dominated by Bilberry Vaccinium myrtillus and Great Woodrush Luzula sylvatica with a good associated bryophyte ground flora as well as woodland herbs including Wood Sorrel Oxalis acetosella, Wood Sage Teucrium scorodonia, Wood Anemone Anemone nemoralis and Bluebell Hyacinthoides non-scripta. Of particular note is the presence of the local grass Wood Millett Milium effusum. The woody understorey is typically dominated by Holly Ilex aquifolium, with Rowan Sorbus aucuparia and Hazel Corylus avellana. There is a rich epiphyte flora with Honeysuckle Lonicera periclymenum, Ivy Hedera helix and Polypody Polypodium vulgare. The wet valley bottom, extending to nearly 20 hectares, is dominated by a closed canopy of Willow mainly Salix cinerea with Alder. Higher drier islands within this have some selfseeded Oak, Holly and Blackcurrant Ribes nigrum.

The water table fluctuates and in periods of high rainfall much of the woodland is inundated. Hemlock Water Dropwort Oenanthe crocata forms extensive stands which are interspersed with areas of mixed tall herbs including Meadowsweet Filipendula ulmaria, Common Valerian Valeriana officinalis, Yellow Loosestrife Lysimachia vulgaris, Water Figwort Scrophularia aquatica, Marsh Speedwell Veronica acutellata and ferns, notably Royal Fern Osmunda regalis. Prostrate herbs include Marsh Violet Viola palustris, Yellow Pimpernel Lysimachia nemorum and the rare Cornish Moneywort Sibthorpia europaea. Scattered pools within the carr support a rich flora with Sphagnum moss species, Marsh Cinquefoil Potentilla palustris, Broad-leaved Pondweed Potamogeton natans and Common Water Plantain Alisma plantago-aquatica. The site is of local importance for lichens. The species list includes seven ancient woodland indicator species and there is a record of the nationally rare Parmelia endochlora. Appendix 1- Site Details