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e �Aqu;fer Cleanup `r d conlinuetl from page 34 coarser-grained strata compared to the other petroleum-related substances. Also, if downgradient plume control is finer-grained layers because the coarser- Microorganisms use the electrons in required, extraction trenches may be grained aquifer sediments usually con- these compounds to fuel their metabolism needed to intercept and remove a suffi. tain lower levels of naturally occurring for growth, maintenance and reproduc- cient quantity of contaminated groundwa- organic material that adsorb organic tion. When the electrons are removed ter to appreciably influence the plume. contaminants readily. from the organic contaminants, their For each of these cases, the aquifer These variabilities require careful chemical natures change. recovery rate will be longer than for design evaluations of the locations and In a number of cases, the changes are treatment of coarser-grained aquifers. means of stimulating in situ biodegra- subtle, and the altered contaminant may This likelihood must be explained to the dation of the contamination. be directly incorporated into microbial responsible party,the regulatory agencies The nature of the aquifer's contami- biomass or become incorporated into and the concerned public before proceed- nation will influence the means to initi- humic materials (naturally occurring, ing with in situ bioremediation of finer- ate in situ bioremediation. Some complex organic molecules). Both of these grained aquifers. contaminants require oxic conditions, chemical fates usually result in toxicity Complex stratigraphy also can com- others require anoxic conditions, and reductions. plicate the installation, operation and finally some appear to require alter- In other cases, microbial-induced effectiveness of an in situ bioremediation nating oxiclanoxic conditions before changes in the contaminant can continue system. An aquifer consisting of multiple appreciable rates of in situ biodegrada- until most of the carbon atoms in the strata of varying geologic natures tends to tion are initiated. organic contaminants are converted to exhibit varying physical and chemical Oxic Conditions. Most of the organic carbon dioxide(mineralized). characteristics. Groundwater flow and contaminants we are concerned with are The electrons removed from the con- contaminant transport in coarser-grained reduced organic compounds. In other taminants by the microorganisms must strata tends to be higher than in the words,these compounds are electron-rich. be deposited on an electron-acceptor for finer-grained strata. Examples of electron-rich contaminants the microbes to garner the biologically Furthermore, sorbed contaminant include the constituents of gasoline, die- useful energy efficiently. The most ener- concentrations tend to be lower in the sel fuel, creosote, waste oils and many geticaily favorable electron-acceptor is l ;REDUCE EF�LUEIi]T- D1SCk1ARIGE — j /';1GflOn: Control Se¢liWoter Usage I ' FEtff<ttF-is-�-}o�casi�re};p{�le�j-td--s}mp[�e"tII' of � / control;device designed s cificallyto re ate I moinito(yyour individuol s 1 I oter requir erts. ope focile� sav d r `663 'iilion r Ions per.do of I expensive, ce ve ffluent by'instdlling sA EUNiT atrok�- j I j E I That's right. EPA's RCRA regs for your PC for only $99. That's 40 CFR 240-299. 1 Complete and current through this month. ! Find what you need in the table of I I - contents. Instantly view any section. Or instantly _ �� `' .�► access any reference while a history list keeps track of where you've been in the database. You can even print a hard copy. - = �• And there is more �bject4�.e�luaprave�n�riro,imera 1dDg SARA regs. TSCA regs_ WATER regs. AIR In{heearh for'toal warty's Mme mill'have Jroqvcan. regs.Transportation ans Safety regs, too. All fora value o e'Wt lin '. only $99 each] 5tra eg nerve Process Emuent11 To order, call 1-880-326-9625 R ansi er .a leve c s ie in ca o u o n t i l n r' nn.._ w `ter itrecim is#excessi e I to . '. 7REGILYAIYON /MSC.ANNEVG ® I AAn Sof matfc Inc.. (I i Circle 29 on card. n;e36 r. ENVIR0NMENTAL PROTECTION