Prosperity EA Review. Taseko Mines Limited Responses to June 24, 2009 Federal Review Panel Prosperity Gold-Copper Mine Project Deficiency Statement

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1 Prosperity EA Review Taseko Mines Limited Responses to June 24, 2009 Federal Review Panel Prosperity Gold-Copper Mine Project Deficiency Statement Information Requests from the Federal Review Panel 3.0 Hydrology I.R 3.2 Effects of Project on Beece Creek The Panel requests that Taseko provide a rationale for the conclusion that the increased flow into Beece Creek is within the range of natural variability for the creek. Given that Beece Creek also flows through the property of the Taseko Lake Lodge, the Panel requests that Taseko assess whether the additive effect of an additional 4% increase in flow will result in any channel instability in the creek and if so, whether water quality would be affected due to increased suspended solids.

2 Taseko Mines Ltd West Pender Street Vancouver, BC V6C 1L6 Canada Tel.: (778) Fax: (778) Re: 3.2 Effects of Project on Beece Creek A report from Knight Piesold dated August 2 nd, 2009 provides clarification on a number of issues with regards to Hydrology/Geomorphology/Fish Compensation. Included in this report is a detailing of the rationale for the conclusion that the increase inflow into Beece creek is within the range of natural variability for the creek.. This report discusses the flow increases and the potential geomorphic effects on Beece creek due to diverted flows through Prosperity Lake. The water balance model was run with low, most probable, and high estimates of the mean annual runoff; and low and high estimates of mean annual precipitation. The water balance model was run using Monte Carlo simulation techniques. Formative discharge was used to evaluate the potential impact of the flow from modeled results on Beece Creek. Regional data was used to determine the mean annual peak daily flow for Beece Creek. Increases in peak daily flows for low, probable and high runoff scenarios were 5%, 11%, and 15% respectively. These values seem unlikely to significantly affect channel morphology in Beece Creek. Evaluation of available information indicates that if the maximum volume of overflows from Wasp lake were released steadily over 2 months, then 95% of the year the flow would not exceed the current formative discharge.

3 Suite West Pender Street Vancouver, BC Canada V6C 2T8 File No.:VA /9-A.01 Cont. No.:VA Tel: Fax: August 2, 2009 Mr. Roderick Bell-Irving Manager, Environmental Assessment Taseko Mines Limited Suite West Pender Street Vancouver, British Columbia Canada, V6C 1L6 Dear Rod, Re: Hydrology/Geomorphology/Fish Compensation Additional Information Knight Piésold Ltd (KPL) has been requested to provide additional input to the Environmental Assessment Report for the Prosperity Project related to Hydrology, Geomorphology and Fish Compensation. This is information detailed in the Federal Panel Review, dated June 24, 2009, as well as from the BC Environmental Assessment Office, dated July 8, Furthermore, correspondence between DFO and Taseko following the issuance of these two letters has detailed information requests regarding the Fish Compensation Plan. The four main areas that will be addressed with information included in this letter include the following: Sensitivity analysis of the site water balance; Discussion of possible fluctuations in the TSF pond and Prosperity Lake volumes and water levels, and implications of those conditions; Discussion of flow increases and potential geomorphologic effects on Beece creek due to diverted flows through Prosperity Lake; Discussion of the mechanics of the conceptual diversion system from Prosperity Lake to the TSF pond. Water Balance Sensitivity Analysis A sensitivity analysis was completed with the Project s operational water balance to assess the ability of the proposed water and tailings management plan to accommodate the full range of possible climatic scenarios. This wide range incorporates both climatic uncertainty and climatic variability, as follows: 1) Climatic Uncertainty: There is considerable uncertainty associated with estimates of mean annual precipitation and mean annual runoff in the Project area. This is a result of many factors, including the high variability and sparsity of regional data, challenging site data collection conditions, and localized climatic influences such as orographic effects. Correspondingly, there is a wide range of possible mean annual precipitation (MAP) and mean annual unit runoff values (MAUR) applicable to the Project area. As a means of addressing this uncertainty, the water balance model was run with low, most probable, and high estimates of mean annual runoff from undisturbed drainage areas, and low and high estimates of mean annual precipitation applicable to lake areas and disturbed areas (such as tailings beaches, which are assumed to have a very high runoff coefficient). The low, most probable and high estimates of mean annual natural unit runoff were determined to be 88

4 mm, 128 mm, and 168 mm, respectively. These values were generated on the basis of short-term site streamflow data and long-term regional streamflow patterns. The low and high estimates of mean annual precipitation were determined to be 380 mm and 527 mm, respectively. These values were generated on the basis of short-term site precipitation data and long-term regional precipitation patterns. The three runoff and two precipitation values resulted in a total of six different modelling scenarios. For all scenarios, mean annual lake evaporation was assumed to be 452 mm. 2) Climatic Variability: Climate conditions change from year to year, month to month, and day to day. The proposed water and tailings management plan has been designed to accommodate such variability through the incorporation of storage and diversion features. To assess this capability, the water balance model was run using Monte Carlo simulation techniques. For each of the six climatic uncertainty scenarios described above, the mean annual values were distributed into mean monthly components, and the potential variability within each month was quantified with statistical values derived from regional data. The monthly statistics were used to develop monthly distributions, as required for a Monte Carlo simulation, with the precipitation and runoff values directly correlated. For each of the six climatic variability scenarios, Monte Carlo simulations were run with 10,000 iterations, such that every conceivable combination of wet, dry, and average months and years of precipitation and runoff are considered. Key output parameters from the model, such as tailings pond volumes and water discharges to Beece Creek, are tracked for each iteration and distributions of possible results are provided. These distributions provide a means of assessing probabilities of occurrence. The water balance model used for the analyses was essentially the same as that outlined in the Report on Tailings Storage Facility Seepage Assessment (Ref. No. VA /8-1), Rev 0, March 13, 2009, with the following modifications: Precipitation and runoff values were modelled on a monthly basis, as described above. Runoff that is collected in the headwater channel and directed into the Headwater Channel Retention Pond (HCRP) was assumed to only occur during the months of April to June according to the distribution of 10% in April, 70% in May, and 20% in June. Consideration of seepage and evaporation losses from the HCRP and Prosperity Lake were added to the model. Surplus water from Prosperity Lake was routed to the Tailings Storage Facility (TSF) whenever the TSF pond volume dropped below 3 million m 3. The monthly water balance was run for the period extending from the pre-production years to the end of operations (Year -2 to 19). TSF and Prosperity Lake Pond Volumes and Water Levels Table 1a presents estimates of the annual volumes of water deficit that may occur in the TSF pond under the most probable mean annual precipitation and runoff scenario, for various probabilities of occurrence, when trying to maintain a minimum TSF pond volume of 3 million m 3. The values indicate that under the most probable mean annual precipitation and runoff scenario there is approximately a 50% probability that no water deficit in the pond will occur in almost all years of operation, a 20% probability that there will be an annual deficit of approximately 2 to 4 million m 3 of water during the first 13 years of operations, and a 5% probability that there will be an annual deficit of upwards of 7 million m 3 of water in Years 2 to 12. It is possible for the deficit value to exceed the pond volume target of 3 million m 3 because of the 2 of 7 VA August 2, 2009

5 substantial volume of water that is required to saturate the tailings and waste rock mass. In the instance that there is not be sufficient water available to fully meet the 3 million m 3 pond water volume, mine production would have to be slowed or water would have to be obtained from alternate sources such as: The redirection of water in the North Flowing Diversion Headwater Channel that under the current operational plan discharges into Fish Creek. Under the most probable climate scenario this channel directs, on average, approximately 1.2 million m 3 of runoff into Fish Creek; The capture of water that under the current operational plan spills from Prosperity Lake into Wasp Lake. This situation potentially occurs even when there is a deficit in the TSF pond because of the monthly variability of inflows and the constant nature of water demand. Even during very dry conditions, Prosperity Lake usually has overflow water during the freshet period because at that time it is not needed by the TSF and therefore spills to Wasp Lake. However, it would be possible to capture that water with the expansion of the headwater channel retention pond or simply in the TSF. The potential water available from this means is indicated by the difference between the values in Tables 1b and 1c, which respectively present the water from Prosperity Lake that is diverted to the TSF and that is spilled to Wasp Lake. For example, under extremely dry conditions in Year 11 (5th percentile results), only 267,000 m 3 of water are diverted to the TSF, while an additional 1.6 million m 3 of water are spilled to Wasp Lake. This spilled water could potentially be captured and utilized when needed in the TSF; and Pumping from deep groundwater aquifers. Tables 2a to 2c present corresponding TSF pond deficit, Prosperity Lake transfer, and Prosperity Lake spill volumes for the high runoff (wet climate) scenario, and Tables 3a to 3c present similar results for the low runoff (dry climate) scenario. Under the wet scenario there is an extremely low probability of a water deficit occurring in the TSF, and an abundance of water available in Prosperity Lake to meet this need even during the very driest conditions. Not surprisingly, in contrast under the dry scenario there is a very high probability of a substantial water deficit occurring in the TSF, and a similarly high probability that there will be an insufficient supply of water available in Prosperity Lake to meet this need. In such a situation, water would have to be obtained from other sources and/or addressed with operational adjustments such as a reduction of tailings production. Figure 1 presents the full practical range of possible TSF reservoir volumes, from the 5% confidence limit of the dry climate scenario to the 95% confidence limit of the wet climate scenario. This figure indicates that under the most probable runoff scenario there is an approximate 50% probability that the targeted minimum pond volume of 3 million m 3 could be maintained without the need of additional water sources, as discussed above. Furthermore, under the wet runoff scenario a large surplus of water accumulates over the life of the mine, there is a 5% chance that this surplus exceed approximately 51 million m 3 by the end of the operational mine life. In contrast, under the driest conditions of the dry runoff scenario there the TSF pond volume would dry up completely unless flows were supplemented by additional means, as discussed above. Figure 2 presents a comparison of concurrent water levels in Prosperity Lake and the TSF pond, for the full range of climatic scenarios. In all cases, including very low probability extremely wet and dry conditions, the Prosperity Lake water level always remains at least 1 m above that of the TSF pond level, thereby maintaining a hydraulic gradient that forces seepage flows towards the TSF. The difference between the levels progressively narrows throughout the mine life, as one would expect since the lake level remains relatively constant while the pond level progressively increases with the ongoing production of tailings. The Prosperity Lake water level fluctuates very little over the mine life, as indicated by the values in Table 4, with the maximum lake level fluctuation occurring during initial filling of the lake just 3 of 7 VA August 2, 2009

6 prior to the commencement of mining operations. Once the lake is established, the annual fluctuations generally stabilize at around 0.3 m, independent of the climate scenario. Such a change generally corresponds to a change in lake area of approximately 81,000 m 2. In response to EA comments, SRK has identified the possibility that an additional 70 million tonnes (35 million m 3 ) of potentially acid-generating (PAG) waste rock could exist. It should be noted that storage requirements for this additional waste can be accommodated in the TSF, but that this condition was not considered directly in the water balance model. The specific gravity of the rock is 2.65 and its placed density is 2.04 tonnes/m 3. This additional storage would consume approximately 8 million m 3 of water over a 16 year period which corresponds to the period when PAG waste rock is removed during active mining. Therefore, should all this additional storage of PAG waste rock be required, the TSF pond volume would be reduced by an average of approximately 0.5 million m 3 per year during this 16-year period. Such storage would increase the potential need to access additional contingency water sources to maintain the targeted 3 million m 3 of water in the TSF pond, and could require a slight raise in the final embankment height to accommodate the additional rock and a corresponding raise in the level of Prosperity Lake to maintain the desired hydraulic gradient. Flow Diversion to Beece Creek River morphology is the result of a spatially and temporally dynamic relationship between sediment supply, water discharge, and external controls. These processes produce a wide range of channel forms that influence channel stability, aquatic and riparian habitat, recreational water uses, aesthetic values, flood water levels, and water quality. The following discussion presents a desktop assessment of the potential affects of the proposed hydrologic changes on fluvial processes in Beece Creek. Catchment and Channel Characteristic The headwaters of Beece Creek form in the Chilcotin Ranges, surrounded by Anvil Mountain, Taseko Mountain and Mount Vic. It flows out of this mountainous region into the Taseko Valley. Near the Wasp Creek confluence, Beece Creek meanders across the valley flat, which has been eroded some 30 m to 50 m into the surrounding terrain surface. Based on aerial imagery (Google Earth, 2009), the channel is largely single thread with large bar deposits, although some channel braiding and remnant channels are evident. Beece Creek then flows onto a large alluvial fan where it meets the Taseko River. Affects of Increased Discharge on Fluvial Process Potential responses due to changes in sediment and water supply include changes in channel width, depth, slope, surface grain size distribution and/or characteristic channel morphology. Increasing discharge effectively increases the stream s ability to transport material. Without a concurrent increase in sediment supply, three responses are possible: 1. Sediment transport increases and the channel degrades and/or widens 2. Larger bed material can now be moved, fines are removed, and the bed surface coarsens and the channel becomes armoured, and 3. Sediment transport increases and the channel gradient reduces by eroding the banks, introducing more sediment into the system, and becoming more sinuous. In reality, any response would be a combination of the three, and any effects would be most prominent where streamflow has been affected most. These changes could, in turn, affect aquatic habitats and water quality. 4 of 7 VA August 2, 2009

7 Formative Discharge A common theme in fluvial geomorphology literature is that channel morphology is the result of some formative discharge. Very large flows may alter a channel s shape, but they occur infrequently, while small flows occur regularly but are not capable of significantly affecting the channel (Wolman and Miller, 1960). Thus, the formative discharge is considered to be the flow that just fills the channel; hence, it is often referred to as bankfull flow. Typically, the bankfull flow has a return period of approximately 1 to 2 years. Eaton (2007) recommends using the mean annual peak daily flow. There are several other factors that influence channel morphology, but formative discharge is often used as a preliminary screen for potential impacts. The mean annual peak daily flow for Beece Creek was determined from regional data presented in the Prosperity hydrometeorology report (KPL, 2007), and a discharge of 16.6 m 3 /s was estimated for the catchment just downstream of the confluence point of the outflows from Wasp Lake. Peak daily flows are expected in June, due to rainfall combined with snowmelt, or in October/November due to heavy rainfall. The greatest overflow volumes from Wasp Lake are expected in June when mean monthly overflow for the low, most probable and high runoff scenarios are 0.6 m 3 /s, 1.2 m 3 /s, and 1.6 m 3 /s, respectively. Overflow is expected to be quite steady through the month as runoff will be attenuated by the HCRP, Prosperity Lake, and Wasp Lake. Nonetheless, outflows from Wasp Lake will not be constant, and based on the natural variability of flows in upper Fish Creek, it is conservatively estimated that daily outflows from Wasp Lake could exceed the monthly average outflows by upwards of 50%. Correspondingly, application of this 50% factor results in estimated peak daily June outflows from Wasp Lake of 0.9 m 3 /s, 1.8 m 3 /s, and 2.4 m 3 /s for the low, probable, and high runoff scenarios, respectively. These flows, should they occur coincidentally with the formative discharge, represent relative increases of 5%, 11%, and 15%, respectively. Given the moderate potential increases in the formative discharge, it seems unlikely that the increased flows due to overflow from the Wasp Creek watershed would significantly affect channel morphology in Beece Creek. The maximum predicted annual volume of overflows from Wasp Lake is approximately 7,000,000 m 3, as indicated on Figure 3. If released steadily over two months, this volume is equivalent to a discharge of 1.3 m 3 /s. A flow duration curve for Beece Creek at the Wasp Lake overflow confluence is shown on Figure 4. This Figure indicates that 1.3 m 3 /s could be released during more than 95% of the year without the combined flows exceeding the formative discharge of 16.6 m 3 /s. Diverted Flows to the HCRP and Prosperity Lake Figure 5 presents the outflow pattern from the HCRP that is proposed for enhancing spawning conditions in the channel between the HCRP and Prosperity Lake. Also shown are the hydrographs corresponding to the modelled inflows to the HCRP for extreme wet, extreme dry, and median flow conditions. Corresponding monthly values for the wet, dry and most probable climate scenarios are provided in Table 5. This figure and table generally indicate that with controlled releases from the HCRP there are sufficient inflow volumes available in both the wet and most probable climate scenarios to generally meet the proposed release targets, except during dry conditions for the most probable scenario, but that the targets can rarely be reached in any conditions for the dry climate scenario. If the dry climate scenario should prove to most accurately represent actual conditions, which is believed to be extremely unlikely, then alternate sources of water such as those discussed previously will be required to meet the flow targets. It should be noted, however, that under the extreme dry condition flows in natural streams would also be well below optimal levels, and that under such conditions it may be appropriate to modify the target levels accordingly. 5 of 7 VA August 2, 2009

8 Conceptual Diversion System from Prosperity Lake to the TSF Pond The system to divert excess flows from Prosperity Lake to the TSF Pond during operations, should this be required, would consist of the following: On-shore pump (electric or diesel powered); Power supply (power line or environmental fuel tank, depending on pump selection); Under-water intake structure with screens to prevent interaction with fish; Outlet pipe around east abutment of Prosperity Lake dam and feeding down to the active TSF pond; and Flow-monitoring gauge on the pipeline. Should some or all of the excess water from Prosperity Lake be required to be diverted to the TSF Pond, it will be transferred using this pumping system. A majority of the excess flows annually will enter Prosperity Lake during the freshet period (April, May and June), and therefore the pumping system would only be expected to operate during part of this 3-month window when excess flows are available for diversion to the TSF Pond. We trust that the provided information is sufficient to meet your needs. If you have any questions or concerns please contact the undersigned. Yours truly, KNIGHT PIESOLD LTD. Original document stamped with professional designation, signed and dated. Prepared by: Erin Rainy, EIT Staff Engineer Reviewed by: Jaime Cathcart, Ph.D., P.Eng. Specialist Hydrotechnical Engineer Greg Smyth Senior Scientist References 1. Eaton, B., The University of British Columbia Regime Model, Draft User s Manual. University of British Columbia, Vancouver, BC. 2. Google Earth, Viewed online 30 July KPL (Knight Piésold Ltd), Prosperity Gold-Copper Project Hydrometeorology Report. VA /01-2, Knight Piésold Ltd., Vancouver, BC 4. Wolman, M.G. and Miller, J.P., Magnitude and frequency of forces in geomorphic processes. Journal of Geology 68, of 7 VA August 2, 2009

9 Attachments: Table 1a Rev 0 Annual Water Deficit in Tailings Storage Facility Most Probable Runoff Scenario Table 1b Rev 0 Annual Excess Water from Prosperity Lake Diverted to TSF Most Probable Runoff Scenario Table 1c Rev 0 Annual Excess Water from Prosperity Lake Diverted to Wasp Lake Most Probable Runoff Scenario Table 2a Rev 0 Annual Water Deficit in Tailings Storage Facility High Runoff Scenario Table 2b Rev 0 Annual Excess Water from Prosperity Lake Diverted to TSF High Runoff Scenario Table 2c Rev 0 Annual Excess Water from Prosperity Lake Diverted to Wasp Lake High Runoff Scenario Table 3a Rev 0 Annual Water Deficit in Tailings Storage Facility Low Runoff Scenario Table 3b Rev 0 Annual Excess Water from Prosperity Lake Diverted to TSF Low Runoff Scenario Table 3c Rev 0 Annual Excess Water from Prosperity Lake Diverted to Wasp Lake Low Runoff Scenario Table 4 Rev 0 Prosperity Lake Annual Lake Level and Surface Area Variations Table 5 Rev 0 HCRP Inflows and Spawning Channel Outflows Figure 1 Rev 0 Water Volumes in the TSF Pond Figure 2 Rev 0 Water Levels for Prosperity Lake and the TSF Figure 3 Rev 0 Annual Discharge to Beece Creek from Wasp Lake Figure 4 Rev 0 Flow Duration Curve - Beece Creek at Wasp Lake Outflow Confluence Figure 5 Rev 0 Monthly Inflow and Spawning Channel Outflow for the HCRP Copy To: Tom Watson, Triton Environmental Ltd GLS/er 7 of 7 VA August 2, 2009

10 TABLE 1A ANNUAL WATER DEFICIT IN TAILINGS STORAGE FACILITY MOST PROBABLE RUNOFF SCENARIO Print Aug/04/09 13:19:54 Year Volume required (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile ,324,700 1,411,100 1,761, , ,380 2,716, ,264,800 3,474,500 3,961,500 6,032, ,233,700 4,281,500 4,660,500 6,652, ,442,600 3,598,300 4,030,600 6,027, ,300 3,064,900 3,555,700 5,544, ,360 3,208,100 3,736,800 5,759, ,320,600 2,913,500 5,202, ,835,400 2,468,100 4,932, ,380,900 3,009,300 5,590, ,660 3,262,100 3,920,200 6,614, ,080 3,712,800 4,324,100 6,953, ,906,500 3,642,600 6,386, ,036,900 1,816,700 4,908, ,769, , , ,091,800 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Fig 1 Tab 1a2a3a - TSF_Results.xls]Table 1a avg 1. MOST PROBABLE MEAN ANNUAL UNIT RUNOFF = 128 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m 3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

11 TABLE 1B ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO TSF MOST PROBABLE RUNOFF SCENARIO Print Aug/04/09 14:17:10 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile ,070 1,420, , , , , , , , ,509,750 2,082,670 2,168,300 2,315, ,834,600 2,089,100 2,125,700 2,196, ,243,600 1,522,300 1,587,400 1,832, , ,400 1,245,700 1,336,100 1,500, , ,200 1,191,700 1,278,600 1,583, , , , ,900 1,224, , , , ,000 1,165, , , , ,000 1,309, , ,600 1,072,000 1,211,000 1,487, , ,300 1,207,000 1,325,000 1,529, , , , ,000 1,445, , , , , , , , , , , ,600 27,000 50,000 64,000 93, ,700 20,000 28,000 36,000 16, ,000 54,000 45,000 62, ,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1b2b3b - PL_overflows_to_TSF.xls]Table 1B - avg 1. MOST PROBABLE MEAN ANNUAL UNIT RUNOFF = 128 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m 3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

12 TABLE 1C ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO WASP LAKE MOST PROBABLE RUNOFF SCENARIO Print Aug/04/09 14:23:49 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile , ,883,900 3,187,500 3,496,100 4,508, ,512,900 3,408,300 3,653,400 3,728,600 4,116, ,700 2,320,000 3,416,100 3,520,300 3,968, ,300 1,541,100 2,865,000 3,206,000 3,830, ,021,900 2,354,700 2,781,000 3,057,000 3,931, ,289,200 2,554,000 2,729,000 2,996,000 3,613, ,388,400 2,618,000 2,781,000 2,812,000 3,633, ,953,100 2,839,000 3,168,000 3,222,000 3,777, ,079,500 2,951,000 3,297,000 3,225,000 3,529, ,779,000 2,830,000 3,142,000 3,131,000 3,504, ,629,000 2,644,000 2,973,000 3,045,000 3,632, ,581,000 2,641,000 2,934,000 2,994,000 3,669, ,011,000 2,677,000 3,147,000 3,173,000 3,615, ,493,000 3,156,000 3,309,000 3,458,000 3,522, ,876,000 3,314,000 3,356,000 3,416,000 3,434, ,188,000 3,444,000 3,514,000 3,536,000 3,534, ,286,000 3,455,000 3,447,000 3,541,000 3,569, ,101,000 3,440,000 3,488,000 3,462,000 3,606,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1c2c3cPL_overflows_to_WL.xls]Table 1c - avg 1. MOST PROBABLE MEAN ANNUAL UNIT RUNOFF = 128 mm. 2. ALL EXCESS OVERFLOW WATER FROM PROSPERITY LAKE NOT REQUIRED BY THE TSF FOR ANY GIVEN MONTH IS DIVERTED TO WASP LAKE. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

13 TABLE 2A WATER DEFICIT IN TAILINGS STORAGE FACILITY HIGH RUNOFF SCENARIO Print Aug/04/09 13:24:06 Year Volume required (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile , ,350 1,332, ,390, ,990 2,965, ,608, ,259, ,368, ,572, ,295, ,563, ,482, ,757, ,952, , M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Fig 1 Tab 1a2a3a - TSF_Results.xls]Table 2a high 1. HIGH MEAN ANNUAL UNIT RUNOFF = 168 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m 3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

14 TABLE 2B ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO TSF HIGH RUNOFF SCENARIO Print Aug/04/09 14:19:29 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile ,700 1,769,700 2,041,300 3,922, , , , , ,210 8,900 11,800 15, , , , , , , ,900 1,125, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,800 17,500 21,700 24, ,000 4,200 3,900 13, , , ,600 7,600 6,200 9,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1b2b3b - PL_overflows_to_TSF.xls]Table 2B - high 1. HIGH MEAN ANNUAL UNIT RUNOFF = 168 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m 3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

15 TABLE 2C ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO WASP LAKE HIGH RUNOFF SCENARIO Print Aug/04/09 14:25:24 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile , ,310 1,348, ,480 4,347,900 4,942,390 5,148,190 6,364, ,856,120 4,460,700 4,863,900 5,011,500 5,521, ,880,200 4,447,400 4,799,000 4,863,000 5,273, ,530,900 4,449,000 4,768,000 4,813,000 5,022, ,108,300 4,443,000 4,744,000 4,798,000 5,292, ,273,000 4,423,000 4,709,000 4,819,000 4,939, ,429,000 4,422,000 4,701,000 4,707,000 5,054, ,671,000 4,434,000 4,691,000 4,745,000 5,127, ,847,000 4,520,000 4,662,000 4,682,000 4,898, ,504,000 4,477,000 4,644,000 4,713,000 4,817, ,650,000 4,446,000 4,736,000 4,752,000 4,865, ,466,000 4,487,000 4,713,000 4,840,000 5,042, ,488,000 4,439,000 4,600,000 4,631,000 4,911, ,011,000 4,434,000 4,625,000 4,715,000 4,851, ,095,000 4,438,000 4,600,000 4,646,000 4,765, ,313,000 4,511,000 4,652,000 4,658,000 4,920, ,312,000 4,432,000 4,640,000 4,629,000 4,786, ,478,000 4,500,000 4,513,000 4,664,000 4,747,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1c2c3cPL_overflows_to_WL.xls]Table 2c - high 1. HIGH MEAN ANNUAL UNIT RUNOFF = 168 mm. 2. ALL EXCESS OVERFLOW WATER FROM PROSPERITY LAKE NOT REQUIRED BY THE TSF FOR ANY GIVEN MONTH IS DIVERTED TO WASP LAKE. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

16 TABLE 3A ANNUAL WATER DEFICIT IN TAILINGS STORAGE FACILITY LOW RUNOFF SCENARIO Print Aug/04/09 13:25:56 Year Volume required (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile ,690 1,574,300 1,827,500 1,906,300 2,142, ,988,800 3,000,000 5,752,500 7,000, ,351,000 3,000,000 3,000,000 9,279,700 10,767, ,191,500 3,000,000 3,000,000 10,865,000 13,435, ,742,200 2,990,300 3,000,000 10,636,000 13,463, ,922,900 2,992,200 3,000,000 9,957,800 13,240, ,281,200 3,000,000 3,000,000 9,887,500 13,165, ,309,000 2,985,100 2,999,700 8,973,700 12,285, ,881,300 3,000,000 3,000,000 8,519,700 11,193, ,493,100 2,985,300 3,000,000 9,287,500 11,477, ,486,400 3,000,000 3,000,000 10,163,000 12,510, ,961,400 3,000,000 3,000,000 10,609,000 13,298, ,170,600 3,000,000 3,000,000 10,064,000 12,922, ,270,100 3,000,000 3,000,000 8,268,900 11,118, ,731,000 3,000,000 6,811,600 7,884, ,821,900 2,969,600 5,666,400 6,933, ,573,000 2,987,600 5,137,600 6,699, ,944,000 3,000,000 6,622,600 7,856, ,683 2,991,800 3,000,000 8,465,000 9,858,700 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Fig 1 Tab 1a2a3a - TSF_Results.xls]Table 3a low 1. LOW MEAN ANNUAL UNIT RUNOFF = 88 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

17 TABLE 3B ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO TSF LOW RUNOFF SCENARIO Print Aug/04/09 14:21:51 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile , ,630 1,178, ,930 2,024,000 2,419,350 2,463,270 2,624, ,749,870 2,105,600 2,252,600 2,281,700 2,357, ,769,600 2,123,000 2,184,800 2,171,000 2,193, ,826,800 2,025,100 2,027,900 2,035,400 1,981, ,819,400 2,017,300 2,039,500 2,050,000 2,112, ,863,300 1,926,000 1,867,000 1,862,000 1,905, ,901,100 1,829,000 1,880,000 1,885,000 1,933, ,818,000 1,931,000 1,965,000 1,979,000 1,997, ,848,000 1,980,000 2,076,000 2,092,000 2,151, ,886,000 2,039,000 2,086,000 2,104,000 2,135, ,802,000 1,962,000 1,955,000 1,944,000 1,949, ,828,000 1,682,000 1,696,000 1,681,000 1,705, ,358,000 1,318,000 1,311,000 1,321,000 1,339, , ,000 1,044,000 1,047,000 1,114, ,000 1,032,000 1,198,000 1,253,000 1,316, ,000 1,430,000 1,534,000 1,580,000 1,672,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1b2b3b - PL_overflows_to_TSF.xls]Table 3B - low 1. LOW MEAN ANNUAL UNIT RUNOFF = 88 mm. 2. ALL EXCESS WATER AVAILABLE FROM PROSPERITY LAKE IS BEING DIVERTED TO TSF WHEN POND VOLUME FALLS BELOW MINIMUM OF 3 M m 3. VOLUME REQUIRED REPRESENTS ADDITIONAL WATER NEEDED TO MAINTAIN POND MINIMUM. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

18 TABLE 3C ANNUAL EXCESS WATER FROM PROSPERITY LAKE DIVERTED TO WASP LAKE LOW RUNOFF SCENARIO Print Aug/04/09 14:27:03 Year Volume available (m 3 ) 5% Percentile Median 75% Percentile 80% Percentile 95% Percentile ,069, ,860 1,621,200 1,960,700 2,515, , , , , ,110 90, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,500 1,043,400 1,170,400 1,345, ,580 1,248,800 1,603,600 1,645,300 1,783, ,600 1,200,500 1,572,000 1,534,600 1,830, , ,600 1,068,500 1,192,000 1,496,000 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Tab 1c2c3cPL_overflows_to_WL.xls]Table 3c - low 1. LOW MEAN ANNUAL UNIT RUNOFF = 88 mm. 2. ALL EXCESS OVERFLOW WATER FROM PROSPERITY LAKE NOT REQUIRED BY THE TSF FOR ANY GIVEN MONTH IS DIVERTED TO WASP LAKE. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

19 TABLE 4 PROSPERITY LAKE ANNUAL LAKE LEVEL AND SURFACE AREA FLUCTUATIONS Maximum change in lake level (m) Change in surface area (m 2 ) Maximum change in lake level (m) Change in surface area (m 2 ) Maximum change in lake level (m) Change in surface area (m 2 ) , , ,037, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,294 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Fig 2 Tab 4 - PL vs TSF_Results.xls]Tab 4 - PL wl vs sa Year Dry Climate Scenario (5th percentile) Mean of Most Probable Climate Scenario 1. DRY CLIMATE SCENARIO = 88 mm MEAN ANNUAL UNIT RUNOFF. 2. MOST PROBABLE CLIMATE SCENARIO = 128 mm MEAN ANNUAL UNIT RUNOFF. 3. WET CLIMATE SCENARIO = 168 mm MEAN ANNUAL UNIT RUNOFF. 4. MAXIMUM WATER LEVEL CHANGE IS THE DIFFERENCE BETWEEN THE MINIMUM MONTHLY WATER LEVEL AND THE MAXIMUM WATER LEVEL ON AN ANNUAL BASIS. Print Aug/04/09 13:30:20 Wet Climate Scenario (95th percentile) 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

20 TABLE 5 HCRP INFLOWS AND SPAWNING CHANNEL OUTFLOWS Print Aug/04/09 14:15:06 Month Volume (m 3 ) Dry Climate Scenario Most Probable Climate Scenario Wet Climate Scenario 5% Percentile Median 95% Percentile 5% Percentile Median 95% Percentile 5% Percentile Median 95% Percentile Outflow to spawning channel Jan Feb Mar Apr 48, , ,730 70, , ,900 91, , ,610 32,000 May 725,290 1,519,200 2,747,100 1,052,300 2,200,600 4,035,800 1,361,900 2,848,000 5,223,300 1,339,200 Jun 218, , , , ,480 1,113, , ,740 1,441, ,200 Jul ,680 Aug ,840 Sep ,480 Oct Nov Dec TOTAL 991,892 2,153,770 4,038,560 1,437,530 3,125,850 5,889,200 1,860,480 4,045,470 7,622,010 3,142,400 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\[Fig 5 Tab 5 - HCRP_inflows.xls]Tab 5 - HCRP table 1. DRY CLIMATE SCENARIO = 88 mm MEAN ANNUAL UNIT RUNOFF. 2. MOST PROBABLE CLIMATE SCENARIO = 128 mm MEAN ANNUAL UNIT RUNOFF. 3. WET CLIMATE SCENARIO = 168 mm MEAN ANNUAL UNIT RUNOFF. 0 01AUG'09 ISSUED WITH LETTER VA ER JGC DATE DESCRIPTION PREP'D CHK'D APP'D JGC

21 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\Fig 1 Tab 1a2a3a - TSF_ResultsFig 1 - TSF vol fig Print 8/4/2009 1:27 PM 60 95th percentile for the Wet Climate Scenario 50 Median for the Most Probable Climate Scenario TSF Pond Volume (Mm 3 /year) th percentile for the Dry Climate Scenario Minimum TSF Pond Volume Time (years) 1. THE CURVES CORRESPOND TO THE 5th PERCENTILE OF THE DRY CLIMATE SCENARIO, THE MEDIAN OF THE MOST PROBABLE CLIMATE SCENARIO, AND THE 95TH PERCENTILE OF THE WET CLIMATE SCENARIO. 2. DRY CLIMATE SCENARIO = 88 MM MEAN ANNUAL UNIT RUNOFF. 3. WET CLIMATE SCENARIO = 168 MM MEAN ANNUAL UNIT RUNOFF. 4. MOST PROBABLE CLIMATE SCENARIO = 128 MM MEAN ANNUAL UNIT RUNOFF. 5. THE TSF POND VOLUMES INCLUDE SURPLUS WATER FROM PROSPERITY LAKE. WATER BALANCE WATER VOLUMES IN THE TSF POND 0 01AUG'09 ISSUED WITH LETTER ER JGC JGC DATE DESCRIPTION PREP'D CHK'D APP'D P/A NO. VA /9 FIGURE 1 REF NO. VA

22 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\Fig 2 Tab 4 - PL vs TSF_ResultsFig 2 - PL water level Print 8/4/2009 1:32 PM Water Level (m) Prosperity Lake (95th percentile of Wet Climate Scenario) Prosperity Lake (Median of Most Probable Climate Scenario) Prosperity Lake (5th percentile of Dry Climate Scenario) TSF (95th percentile of Wet Climate Scenario) TSF (Median of Most Probable Climate Scenario) TSF (5th percentile of Dry Climate Scenario) Time (years) 1. THE CURVES CORRESPOND TO THE 5th PERCENTILE OF THE DRY CLIMATE SCENARIO, THE MEDIAN OF THE MOST PROBABLE CLIMATE SCENARIO, AND THE 95TH PERCENTILE OF THE WET CLIMATE SCENARIO. 2. DRY CLIMATE SCENARIO = 88 mm MEAN ANNUAL UNIT RUNOFF. 3. WET CLIMATE SCENARIO = 168 mm MEAN ANNUAL UNIT RUNOFF. 4. MOST PROBABLE CLIMATE SCENARIO = 128 mm MEAN ANNUAL UNIT RUNOFF. 0 01AUG'09 ISSUED WITH LETTER ER JGC JGC DATE DESCRIPTION PREP'D CHK'D APP'D WATER BALANCE WATER LEVEL FOR PROSPERITY LAKE AND TSF P/A NO. VA /9 FIGURE 2 REF NO. VA

23 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\Fig 3 - Outflow to BeeceFig 3 - Beece outflow Print 8/4/2009 1:34 PM th percentile of Wet Climate Scenario Mean of Most Probable Climate Scenario 5th percentile of Dry Climate Scenario 6.0 Annual Overflow Volume (Mm 3 /year) Time (years) 1. THE CURVES CORRESPOND TO THE 5th PERCENTILE OF THE DRY CLIMATE SCENARIO, THE MEDIAN OF THE MOST PROBABLE CLIMATE SCENARIO, AND THE 95TH PERCENTILE OF THE WET CLIMATE SCENARIO. 2. DRY CLIMATE SCENARIO = 88 mm MEAN ANNUAL UNIT RUNOFF. WATER BALANCE 3. WET CLIMATE SCENARIO = 168 mm MEAN ANNUAL UNIT RUNOFF. ANNUAL DISCHARGE TO BEECE CREEK 4. MOST PROBABLE CLIMATE SCENARIO = 128 mm MEAN ANNUAL UNIT RUNOFF. FROM WASP LAKE 0 01AUG'09 ISSUED WITH LETTER ER JGC JGC DATE DESCRIPTION PREP'D CHK'D APP'D P/A NO. VA /9 FIGURE 3 REF NO. VA

24 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\Fig 4 - FDC Figure 4 - FDC Print 8/4/2009 1:37 PM Discharge (m 3 /s) % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent of Time Exceeded NOTE: 1. DATA MEASURED AT H8C WERE SCALED UP TO MATCH THE BEST ESTIMATE OF MEAN ANNUAL DISCHARGE FOR BEECE CREEK AT THE CONFLUENCE WITH DISCHARGES FROM WASP LAKE. 0 31JUL'09 ISSUED WITH LETTER TJP JGC JGC DATE DESCRIPTION PREP'D CHK'D APP'D FLOW DURATION CURVE BEECE CREEK AT WASP LAKE OUTFLOW CONFLUENCE P/A NO. VA /9 FIGURE 4 REF NO. VA

25 M:\1\01\00266\09\A\Correspondence\VA (Additional Info for EA - July 31_09)\Fig 5 Tab 5 - HCRP_inflowsFig 5 - HCRP inflows Print 8/4/2009 1:39 PM 6.0 High inflows (95th percentile of Wet Scenario) 5.0 Median inflows for Most Probable Scenario Low inflows (5th percentile of Dry Scenario) 4.0 Target outflow to spawning channel Volume (Mm 3 /month) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 1. THE INFLOW HYDROGRAPHS CORRESPOND TO THE 5th PERCENTILE OF THE DRY RUNOFF SCENARIO, THE MEDIAN OF THE MOST PROBABLE RUNOFF SCENARIO, AND THE 95% PERCENTILE OF THE WET RUNOFF SCENARIO. 2. OUTFLOW VOLUMES FROM THE HCRP FOR SPAWNING ARE DISTRIBUTED AS FOLLOWS: 32,000 m 3 FROM APRIL 16-31; 1,987,200 m 3 FROM MAY 1 - JUNE 15; 794,880 m 3 FROM JUNE 16 - JULY 31; 267,840 m 3 FROM AUGUST 1 - AUGUST 31; AND 60,480 m 3 FROM SEPTEMBER AUG'09 ISSUED WITH LETTER ER JGC JGC DATE DESCRIPTION PREP'D CHK'D APP'D WATER BALANCE MONTHLY INFLOW AND SPAWNING CHANNEL OUTFLOW FOR THE HCRP P/A NO. VA /9 FIGURE 5 REF NO. VA