PERMFILE114605 - Laserfiche WebLink

Home Browse Search

highest permeability values and a hydraulic gradient of 0.01 results in a maximum recharge rate of about 5 x 111-4 gals per day per foot of channel. This rate of recharge is clearly insufficient to provide enough • water to support subirrigation in the adjacent alluvial deposits. If subirrigation is occurring in this area it is snore likely to be supported by recharge from the Upper Williams Fork Sandstone units wlticlt occur 10- 20 leet below the valley surface. On the basis of [he information available it is TCC's contention that activities at the Foidel Creek mine will not materially damage [Ite waters supplying the alluvium in sections 21, 22 and 28 and will not prevent or preclude farming in this area. "1'Ite alluvial valley Floor areas along Fish Creek upstream from the Fish Creek Tipple area may have subirrigation functions which could potentially be impacted by recharge of Fish Creek waters if the salinity of these waters during the recharge period exceeds the threshold levels for plant tolerance. Data Irom the 1002/26 monitoring site during the period of record (1979-1985) indicates that TDS levels are typically in the range of 400 to 700 mg/I during the latter portions of the growing season (August-October) and in the range 200 to 500 mg/I during the spring runoff (Figure 6-k). An anomalously high TDS value was recorded in August-1980 when the recorded Flow was only 0.1 cfs and also in March of 1980 when a discharge measurement could not be taken due to frozen conditions. The 10 year, 7 day low Flow based on USGS data for the upstream 1001 site is calculated to be 0.64 cfs. It should be noted that the specific conductance levels measured in micromhos/cm at the time of sampling indicate approximately a I:I ratio with TDS values measured in mg/I. As salinity threshold levels are determined in terms of the specific conductance, TDS levels in Fish Creek would have to increase to approximately 1,000 mg/I before detrimental effects to plant growth may be seen. Table 65, Fish Creek Salt Load Analysis for TDS, shows that during low Flow periods discharge of mine inFlow waters is likely to result in slight increases in salinity. It can be seen that projected salinity levels • remain well below the threshold value for all measure Flows during the last six years. The only exceedaitce occurs during the anomalously low Flow event in August 1980 when projected mine discharges would actually have resulted in an improvement of TDS levels. Recharge to alluvial deposits in the Fislt Creek drainage primarily occurs during the Itiglt runoff period following spring snowmelt. due to the generally better water quality (Figure 6K) and the high runoff volumes (Figure SB), the projected mine discharges have negligible impact on salinity levels during this period. Consequently, no material damage to waters that would supply the alluvial materials which support subirrigation is anticipated as a result of discharges to Fish Creek from the mining operation. Following additional analyses conducted in the confluence area of Foidel, Middle, and Trout Creeks during the summer of 1986, a determination was made as to the probable hydrologic consequences of mine related discharges to these areas. This analysis is presented in Exhibit 42, PHC for Mine Related Discharges at Confluence Area Foidel, Middle, and Trout Creeks. EASTERN MINING DISTRICT Another analvsis of the effects on Trout Creek downstream from the conFluences with Middle Creek and Fish Creek is presented below. Drainages of [he area include [he following creeks: • Trout Creek -the major north-south drainage wide two tributaries entering from the west • Middle Creek -the first tributary entering Trout Creek from the west • Foidel Creek - a tributary to Middle Creek (just before entering Trout Creek) • Fish Creek -the second tributary entering Trout Creek from the west (downgndienQ MR 97- I ~4 2.06-?? 12/0997