6.6. SR 03-15-2010 - Laserfiche WebLink

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Page ~ a~ 6 Letter to I~r. Galin [its ~ 1l~r, NCi att Ledvin~ R~: Revised SUA i~ydragealogic evaluation ~te~art ~~k River Lanc~~ll, ~r~c, A maximum spacing of QUO feet between downgradient compliance boundary monitoring wells has be used fay the existing landfirl~ ~t is suggested that this maximum spacing be maintained for the landfill expansion. This implies that several additional upper autwash monitoring wells would be included in the monitoring network, The outwash unit cansistutes the uppermost saturated grou~~dwater ~.ow pathway ~.t the Site. hydraulic head rn.onitoring at the ~~~ indicates there is a downward hydraulic potential between the outwasl1 and lower autwash units, ~a~~nwax~d :~o~ ~o~entia~ ~s not unusual for erx~eable units underlain b low ern~eabilit r de osxts and It ~s x~.4t ind.i.cative of actual :~.ow direction. The weight o:~ the evidence su ~ usts tl~.at flaw in bath out~wash units is h.ori~o.x~tal and that these units a~•e not i.n direct h draulic co~~aectian. rl~his evidence includes ~~~ST ~cr our l~l~eti~1 r, however the otential does not ;however, downward migration of groundwater is not predicted due to the continuous till deposit at the bite. Different h ldraulic ~ radi.ents between units u~~ifornait of tl~:e radients~flaw hold. in each u~~it -- i~` their were a si rni~icant connaction it would, be reflected in the .,radients. Accordingly, v~~~ proposes routinely rnonitaring groundwater quality in the outwash unit, ~~ t~~e-p~~-r~~~.~-- CJ.~fJGC"i~~ sti _#~~ r.~ ~Z~~ ti(~xY rn cr h ~'~'~.~~ ~ ~ ' , ' ~""~.~'~: ~~~d~.oc~r-~-i-~~g~~;-~-~t should also be noted that ~M~ will continue to monitor groundwater quality in residential walls west of tl~c SDA an an annual basis, The ~QO foot spacing interval on the downgradient side of the existing facility was largely based on the presence of the unlined, pre~subtitle D portion of the landfill, Tl~e spacing of the proposed monitoring points for the SD,A is nearly 4Q~ feet but tapes into account the till highs that act as boundaries to groundwater flow along the west and sartthern property lines. S. gage ~~, ~~'erl Z~~stallatia~ ~`c~edule; The report states that the current network of monitoring wells is sufficient to monitor the expansion of the~ll area through `ell ~0, The sauthe~ly limit of~ll of `ell ~~ would car~espond to plarz station 24,100 based an available engineering plans far site development. f'r'om the ~`anceptual .~ydrogealogic I~lodel, .figure ~ ~, a southwesterly component to groundwater f low from portions of the proposed~ll area is apparent, There are no monitoring wells existing ar planned within a reasonably close distanoe that would intercept these groundwater flaw lines, The suitability of the existing network of wells to monitor the development of the site through `ell ~0 is questionable. The expected life of the facility is more t1~an ~9 yearn The total remaining life of the existing permitted landfill area and the expansion area is more than Z8 years, The existing and proposed monitoring wells are located at the distance roughly X00 feet from the ultimate f ll boundaries. The functionality of an early warning monitoring system during the operational l fe of the site with wells located in the proposed positions is questionable The a~verall schedule far the placement of mar~itaring wells in relation to the site development needs to be further evaluated.