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Mr. Mv]m' Baday ~, °JM~rac~ m,d c~ Jaruiary 18, 1999 Pale t7 Comment 33 - On Fuse 1 of Tab 16, SCC states that incmases in TDS of 41 % and 255% am fussibfe in tlp otedxmlat aryl tlx axrl ayu~en. 71~ Cdrnado Dppmcnau of Health Basic Standmrls for Grcroul Waar has a mrcroruon a!loreuf~e TDS cwtm:traticve of 1.25 times t/x backgrotorlletrL It appear that t{x estirrrael incmases in TDS wall exa~l dx CDOH starrlmd SCC' furt]xr states in Tab 17 that t1KSe incmases -utrll not hate a sigrufrraru on srnja~ wiser and grourzkeater. Wish the lack of darengradiatt nx-titwveg7edls, Evrr~-call SCE' ieriJy those oaadicsions? Please protade a popose<l plant for rmtitorvtg dx oter&mlat and mxl aytvfers doungrac6ett fron tlx dtstuda~l amiss, or provide an explmwtin: for tle apparau lack of doungradtau rrxsutar~tg at tlx ocr+fxmfert arul ctal aquifers in tEp vicmiry of r1x .South Expmrsiar Ama The baseline TDS values from samples collected at monitoring well WW4 for the Wadge Coal aquifer ranged from a minunum of 34I me/L to a maximttm of 1 886 L, with a mean value of 769 mg/L. Projected increases range from 75% to 639% above baseline values..... 2,518 mg,%L (639%) above the minimum baseline value; 2,733 mg/L (255%) above the mean baseline value; and 3,292 mpg/L (75%) above the maximum baseline value. See Table 17-40, Summary of Projected Impacts to the Wadge Qverburden and Wadge Coal Aquifers. It is imponant to note that the projected increases to TDS are "Taom-care" projections based on data from historic spoil discharge as collected from Seneca II Pond 004 outflows. Based on the calculations it appeazs that actual increase to the baseline 7DS concentrations will probably not exceed the maximum allowable TDS concentration of 1.25 times the background level. As stated on page 104 of Tab 17, the projected TDS increases are thought to be of minimal impact because: 1. The extent of the TDS impatts will probably be localized within a close proximity downgradient of the spoil aquifer with potential for significant mixing, dilution and attenuation which will occur m a downgradient dvection and increase with distance from the pits; 2. Low hydraulic conduttivity values resulting in relative}y slow groundwater velocities; 3. The existing natural brackish water quality in the overburden aquifer which is currently marginal to unsuitable for stock and imgation, and does not produce the volume necessary for imgation; 4. Only the maximum projetted TDS level in the Wadge Coal aquifer could exceed 5,000 mg/L (litestock stmtdmdJ; and 5. The Wadge Coal aquifer will not yield a large enough volume of water for seasonal imgation. If, during the post-mining monitoring period, TDS values should begin to exceed the maximum allowable TDS concentration of 1.25 times the background level, SCC will confer with DMG to develop a remedial action plan. Wadge overburden and coal aquifer monitoring is addressed in Comment 23