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• <br />• <br />L J <br />Hydra(ogic Data fntapre[ation and lmpac[ Assessmem for [Ite Permit and Adjaca[[ Areat <br />• Barren Member well 8-32 exhibited virtually <br />no response to seasonal influences which <br />indicates no apparent connection to surface <br />recharges. <br />• "F'-seam wells SOM-2, and SOM-16 show <br />no seasonal or annual Buctuation and have <br />little or no surface water connection. <br />from the well. The sample results indicate the <br />lower refuse pile is not impacting the groundwater <br />zone near Sylvester Creek. Due to the low perme- <br />ability of the colluvial soil and the lack of a <br />groundwater table near the surface in the colluvi- <br />um (except along the margin of Sylvester Creek), <br />no significant future impacts to the groundwater <br />regime are anticipated. <br />• Barren Member wells SOM-13 and SOM-80 <br />have shown seasonal variations in previous <br />years. During 1987, SOM-SO showed very <br />little or no response to seasonal Buctuation <br />while SOM-13 was similar to previous years. <br />Since 1988, neither well has shown a response <br />to seasonal (]actuation. <br />• The shallow subsidence monitoring wells, <br />SW-1 through SW-6, were generally the same <br />as in previous years. <br />Lower Refuse Pile <br />During 1990, mine development waste from the <br />underground mining operations was placed in the <br />lower refuse pile. The lower refuse pile was per- <br />mitted for permanent disposal of some 1.7 million <br />cubic yards of mint development waste, coal <br />processing waste, and sediment pond cleanout <br />material. In 1990 approximately 98,612 tons <br />(110,000 cu. yd.) were placed in the lower refuse <br />pile in the phase 111 and IV areas. Approximately <br />50,000 tons was from development of the "B"seam <br />slopes. <br />Table 7 shows the 1990 sampling results from <br />monitoring well GP-1 as well as baseline data <br />Conductivity and TDS from samples of monitoring <br />well GP-1 were closely monitored because conduc- <br />tivity was slightly higher than the baseline samples <br />in some instances during 1986. However, this does <br />not appear to be a continuing problem. During <br />1990, both conductivity and TDS values were <br />essentially within the ranges of baseline values. <br />Concentrations of iron in the 1990 monitoring <br />samples were higher than in those identified during <br />baseline monitoring. This increase may be associat- <br />ed with the "B" development waste. Concentra- <br />tions of iron in the 1991 samples will be observed <br />to see if the elevated levels continue. <br />Refuse pile monitoring wells GP-3 through GP-5, <br />remained dry throughout water year 1990. Also, <br />there was no Bow from the toe underdrain during <br />water year 1990. However, pond MB~i collected <br />surface runoff from the refuse pile as well as any <br />flows from the underdrain and can be considered <br />representative of refuse pile conditions. A sample <br />taken from MB-6 on 13 April 1990 indicated pH, <br />conductivity, dissolved oxygen, turbidity, iron, and <br />manganese were 8.3, 0.78 mmhos/cm, 6.8 percent, <br />385,10.4 mg/l, and 0.12 mgA, respectively. Another <br />sample taken on 3 Junc 1990 indicated pH, con- <br />ductivity, dissolved oxygen, turbidity, iron, and <br />fable 7 Comparison of Gl'-L Baseline and 1990 Sampling Results, M[. Gunnison No. (Mine <br />Sampling <br />Date <br />Turbidity pH <br />(units) Conduct. <br />(µmhos/cm) TDS <br />(mg/L) Temp. <br />(°C) Fe <br />(mg/L) Mn <br />(mg/L) <br />08/08/85 048 7.5 990 56(i.0 10.1 <0.02 0.21 <br />08/08/85 048 7.5 990 526.0 10.0 <0.02 0.21 <br />(Dap) <br />10/]0/85 U54 -- 693 870.0 7.5 <0.02 0.05 <br />04/13/90 011 7.5 800 580 8.3 2.58 0.04 <br />06(03/90 009 7.1 991 6l6 9.2 8.8 0.30 <br />08/07/90 008 6.9 916 648 9.2 14.5 0.55 <br />12 <br />