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The water quality data from Wadge Overburden wells prior to 1979, or from wells which are not directly down
<br />gradient from mining activities, indicates that ground water in this aquifer is characteristically a sodium bicarbonate
<br />type with relatively low concentrations of calcium magnesium and sulfate ions, as depicted graphically by Figure 4-
<br />a, Ground Water Quality Data. TDS concentrations are typically in the range of 400 — 3000 mg/l. Concentrations
<br />of trace elements are typically very low. For example, iron concentrations are usually less than 0.4 mg/1, and
<br />manganese concentrations are usually less than 0.2 mg/l.
<br />Ground water data from the Wadge Overburden prior to 1983 represent "baseline" conditions for the Foidel Creek
<br />Mine. Examination of water quality data from certain wells directly down -gradient from the adjacent surface
<br />mined areas indicate that recharge of the Wadge Overburden through backfilled areas has caused changes in the
<br />natural quality of waters in the Wadge Overburden. Backfill water quality is typically much higher in TDS, and is
<br />dominantly a calcium, magnesium, sulfate type. The 009-79-4 Well data (Table 8, Ground Water Data) shows an
<br />increase in most major solute concentrations, particularly sulfate, after 1982 when mining operations became active
<br />upgradient of the mine area. Water quality data from Well TW -1, directly down -dip from old reclaimed backfilled
<br />areas, also indicates significantly high than average concentrations of TDS and sulfate. Water quality changes in
<br />wells further downdip from the historic surface operations have not been detected in the baseline.
<br />The influence of recharge of higher TDS water from up -gradient spoils adjacent to the Eckman Park operation is
<br />also indicated from examination of electrical conductivity data collected from inflows into the Foidel Creek Mine.
<br />An examination of electrical conductivity (EC) values from the 1985 inflow survey (Map 35, 1985 Water Inflow
<br />Survey) shows a regular trend of decreasing values form the up -dip spoils. The data indicates that significant
<br />increases above baseline EC levels exist up to 2,500 feet from the spoils. Ground water inflows further down -dip
<br />from the old spoil areas have EC values which are characteristic of the natural Wadge Overburden water quality.
<br />The recognition of the effects of previous mining activity on overburden water quality is significant because it
<br />strongly suggests that the quality of ground water inflows into the vast majority of the underground mine workings
<br />will be of much better° quality than is presently observed. This is discussed in some detail in the Probable
<br />Hydrologic Consequences section of this permit application.
<br />"r` an,Qr level fluctuations in Jdadbe O,verburden wells reflect some seasonal influencE, parcicuiarly foilowing spring
<br />snowmelt when the majority of bedrock recharge is believed to occur. Seasonal variation in water quality during
<br />the baseline period is not evident from the data, although some variation in the values for individual parameter
<br />occurs.
<br />A 15 foot -thick clay barrier was placed between the old spoils and the old surface mine highwall near the poi -tai
<br />entries of the Foidel Creek Mine prior to the initiation of mining to try to minimize recharge to the undisturbed
<br />overburden from the spoils. The effectiveness of the barrier is apparently limited since bypass appears to be
<br />indicated by the inflow: of ground ',Yater v,,ith TDS levels of up to 4,000 mg,'l, which is typical of spoils water.
<br />Much of the recharge from the spoils to the undisturbed Wadge Overburden may, however, have occurred prior to
<br />placement of the barrier. The undisturbed Wadge Overburden permeability is very low, in the range of 0.01 to 0.1
<br />ft/day. The clay barrier would be expected to have permeability on the order of 0.001 ft/day. Given that the
<br />permeability of the barrier is at least an order of magnitude lower than the natural permeability of the undisturbed
<br />overburden, it probably offers some resistance to flow. The limited extent of the barrier, and the potentially
<br />si.-nifican; head at the i;iterfaee, probably results in a marginal difference from the hydrologic situation F✓11ie11
<br />aJ ;kjid e`= st ;f rh(i 'e 7; ere no barrier.
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<br />'UCJ,5 %tE ill; St:!`.a' c ;ItI!!e C lt_t'�iUCAI. 6 i1�, I'Ca`o)l tib CC15C1181-cIe f)e all tG OC is ill Iv! -4 is final �1P?F7 poll
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<br />T1Pe liar 1i&_ " f_,f;CI' ie`. tl M 'he d'ov111-(Jip portions OE the spalls is auO;re 11y ground surface. as indicated by . � erq;k
<br />-" ._�li'f ___< aii._E al_�r kFi 6 lie '.�Ia.�• Sir!�a.
<br />_',Alf :h !r? il�__ r i. !_t_ ?_Jt11
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<br />su_ ace :Csu,its
<br />ro-, 7 s°eenarge To the spoils
<br />at higher elevatio-ns and
<br />?.€ie nertlleabllity of the yit 31.1-ei '^
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<br />'1 r_ r_I E�oo11I a'fc le aged
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<br />11e I �r �11e old 11i-i1tT'alls.
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