the present invention provides a method of aqueous solution remediation by selectively mobilizing metal oxides in colloidal form having a net - positive surface charge in the aqueous solution which comprises the metal oxide colloids and other polyvalent anionic solids by ( a ) adding a cationic surfactant to the aqueous solution , thereby shielding said metal oxide colloids from at least a portion of the negatively charged sites associated with said polyvalent anionic solids ( i . e ., phyllosilicate clays ) present in the aqueous solution , resulting in a suspension of the metal oxides in the aqueous solution ; ( b ) flocculating the resulting suspension , resulting in a sediment precipitate of metal oxides and a supernatant liquid ; and ( c ) separating the resulting precipitate from the supernatant liquid , resulting in the removal of the precipitate and the remediation of the aqueous solution . the described process relies on the novel ability to selectively mobilize iron , aluminum , manganese , and other metal oxides at levels that will increase the capture of oxide - bound contaminants without significantly reducing the permeability of the aquifer that often accompanies large - scale colloid dispersion . in the current invention , significant quantities of groundwater colloids are mobilized by the introduction of dilute solutions , preferably ≈ 0 . 001m , of cationic surfactants , preferably a quaternary alkylammonium surfactant such as hexadecyltrimethylammonium bromide ( hdtma ), without adversely affecting aquifer permeability . the resulting oxide suspensions generated using cationic surfactants are stable and will not significantly settle after several days . the hdtma mobilizes the metal oxides without significantly reducing the hydraulic permeability of the aquifer by reducing and shielding the negative charge present on other clay minerals . initial sorption of the hdtma is at the cation exchange sites , but at higher surface loadings , surfactant partitioning into this hydrophobic layer of sorbed hdtma exceeds the cation exchange capacity of the clay and imparts a net - positive charge to the clay surface . the ability to induce charge reversal typically increases with increasing charge density of the clay sorbent . thus , high charge clays , such as smectites , tend to readily sorb excess quantities of the surfactant and develop a positive surface charge . once the suspension has been extracted from the subsurface via the capture well , flocculation of the extracted suspension preferably is induced by adjusting the ph to neutrality . the adjustment of the ph to neutrality reduces the positive surface charge and also increases net sorption by the iron oxide suspension of any soluble metal species that were with the mobilized suspension . after settling , a clear solution results containing the original surfactant and can be recycled for use as the treatment solution . in the preferred embodiment of the process of the invention , the dilute cationic surfactant is delivered to the geologic zone of interest using an injection well and a capture well that is located some distance downgradient . pumping of the capture well is preferably initiated at a similar rate to that of the treatment solution injection . the pumps drive the fluid through the injection well system , across the contaminated aquifer so that the metal oxide colloids contained therein are selectively mobilized . the fluid bearing the mobilized colloids then flows into the extraction well system , where the fluid is pumped to the surface and the mobilized colloids are separated from the fluid by sedimentation induced by ph adjustment . the precipitated contaminants can be treated or disposed of in one of a variety of ways known in the art to minimize their health and environmental dangers . the supernatant solution containing the cationic surfactant can be recycled back into the groundwater through the injection well to enhance further colloid mobilization . the invention also provides an apparatus for in - situ groundwater remediation comprising : ( a ) means for injecting a cationic surfactant to the groundwater ; ( b ) means for capturing groundwater containing the cationic surfactant ; ( c ) means for flocculating the captured groundwater to settle colloids , resulting in a precipitate of metal oxides and a supernatant liquid ; and ( d ) means for returning the now remediated supernatant liquid to the groundwater . referring to fig1 the preferred embodiment of the apparatus of the invention is a field scale system is comprised of an injection solution reservoir 1 , a post - capture treatment tank 2 , a sedimentation tank 3 , at least one injection well 6 , and at least one capture well 7 . arrow 8 indicates the direction of groundwater flow and dotted - line 9 indicates the water table . injection solution resevoir 1 , associated with the injection well 6 , is for mixing , storing , and monitoring the concentration of the surfactant injection solution . the injection solution is delivered to the injection well 6 screened within the contaminated aquifer via a controlled metering system 4 ( i . e . pumps and flow controls ). at the same time , groundwater is collected down - gradient 8 from the injection well 6 to capture pump 5 at capture well 7 and stored initially in the post - capture treatment tank 2 . a sampling valve ( not shown ) is preferably provided in the feed line to post - capture treatment tank 2 so that groundwater samples may be collected for chemical analysis prior to any post - collection treatment . within post - capture treatment tank 2 , the ph of the collected groundwater suspension is continuously adjusted to neutrality ( ph ≈ 7 - 8 ) by the addition of dilute alkaline solutions , preferably alkaline or alkaline - earth hydroxides such as , for example , naoh , ca ( oh ) 2 or koh . any additional reactants required to ensure precipitation of solution phase contaminants would also be added in post - capture treatment tank 2 depending on the exact nature of the contaminated groundwater . the neutral suspension then is delivered to the sedimentation tank 3 which functions as a settling and storage chamber . after the suspension has settled , the clear solution containing the surfactant is recirculated to injection solution reservoir 1 for reinjection into the contaminated aquifer through injection well 6 . prior to transfer of the reclaimed solution to the injection solution reservoir 1 , chemical analysis of the clear solution can be performed to confirm the effectiveness of the post - capture treatment process . additional reaction chambers may be added depending on the exact nature of the reclamation project . the steps of this process are preferably continued / repeated as necessary to remediate the groundwater . the captured groundwater is monitored to determine the level of remaining contamination . the determination as to what level of contamination constitutes remediated groundwater are made with consideration of the balance of the acceptability of some contamination in the remediated groundwater versus the additional cost of removal of the remaining contaminants . the level of contamination acceptable in the remediated groundwater may be set by federal , state or local ordinance or regulations , or the specific needs of that area . additionally , once reclamation has been completed , the aquifer can be leached with a dilute (≈ 0 . 01m ) salt solution that will stabilize the remaining kaolinite , and other polyvalent anionic solids ( i . e ., phyllosilicate clays ), and facilitate the removal of the remaining surfactant . calcium salts , such as cacl 2 and caso 4 , are preferred as the salt solution because they are highly effective at flocculating aluminosilicate clays ( e . g ., smectite , kaolinite , etc .) and generally are more competitive than other groundwater species such as na + , k + , and mg + 2 for the cation exchange sites occupied by hdtma . the use of sodium containing solutions is discouraged because it is expected that the residual clays would be highly dispersive after the reclamation method has removed a significant fraction of the iron oxides that act as stabilizing agents within these formations . the surfactant may be removed by circulating the salt solution through the aquifer between the injection well 6 and capture well 7 to stabilize the remaining clay minerals within the formation against dispersion and remove residual surfactant adsorbed to clay surfaces through cation exchange . using calcium salts , for example , the surfactant adsorbed to the clay surfaces would be removed through cation exchange with ca + 2 . while hdtma is the preferred injection solution , other cationic surfactants , such as trimethylphenylammonium ( tmpa ), tetramethylammonium ( tma ), tetraethylammonium ( tea ), tetradecyltrimethylammonium ( tdtma ), benzyltrimethylammonium ( btma ), benzyltriethylammonium ( btea ), and benzyldimethyltetradecylamonium ( bdtda ), and their salts , may be employed . all of the halide salt forms ( cl , br , i , etc .) of the cationic surfactants should be effective as the injection solution . however , salts composed of polyvalent anions , if available , would be less effective because of the flocculating ability of the polyvalent anion for the dispersed positively - charged iron oxides . in the selection of the appropriate cationic surfactant , a primary concern is formation clogging due to particle capture in pore constrictions which limit the remediation efforts . in choosing a surfactant , some additional factors to consider are : ( 1 ) the extent of adsorption of the surfactant to the aquifer matrix ; ( 2 ) the fate of the residual surfactant ; ( 3 ) the degradability of the surfactant ; ( 4 ) the health risks associated with the surfactant ; ( 5 ) the cost and availability of the surfactant ; and ( 6 ) regulatory concerns associated with a particular surfactant formulation . evaluation of these concerns by one of ordinary skill in the art will determine which surfactant offers the greatest potential for use in the field and may be done without undue experimentation . quaternary alkylammonium surfactants provide the best balance of these concerns . while the process of the present invention can be used in a variety of environments , the method is particularly well - suited for use in aquifers containing highly weathered sediments , typical of the upper coastal plain of the southeastern united states , a geographic region extending from mississippi to new jersey . in these aquifers , organic carbon content is very low and the sediments are coarse - textured and oxide - coated . the mineralogy of clay typically found in such areas consists primarily of kaolinite , geothite , and mica ( illite ). similar sediments are found in central and south america , australia , china , and other regions in asia and the far east . the invention is further illustrated by the following examples which are not intended to be limiting . column experiments were performed in 10 cm and 30 cm long plexiglass tubes with an interior diameter of 5 cm . field moist sample from the barnwell aquifer was packed in columns to a uniform bulk density of ≈ 1 . 5 g cm - 3 . a given repacked column was used for only one leaching treatment before the matrix was replaced with fresh material . acid washed coarse (& gt ; 500 μm ) sand layers ( 1 cm in depth ) were placed above and below the sample to reduce the potential for colloid generation by turbulent flow and distribute flow . the columns were oriented vertically and slowly saturated from the outlet with deionized water (& lt ; 0 . 25 ml min - 1 ). after saturation , the columns were turned horizontally and flow was initiated at a constant rate of 1 ml min - 1 ( darcy velocity of ≈ 0 . 72 m d - 1 ) with deionized water for & lt ; 0 . 20 pore volumes prior to the initiation of the fluid treatment . the ec , ph and turbidity ( ntu ) of the effluent were monitored continuously , and leachate fractions were collected for analysis of solution cations by atomic absorption spectrometry . the pressure head was measured at the inlet of the column as an indicator of hydraulic conductivity ( k ) and column plugging . an o - 1 psl pressure transducer was attached to the column inlet and the output voltage was calibrated using a water column that was open to the atmosphere at the inlet of the column . treatments consisted of leaching the column for a prescribed number of pore volumes , in most cases 10 , with a treatment solution followed by leaching with diw ( deionized water ) to simulate dilution within the aquifer from low ionic strength native groundwater . all trends with respect to effluent chemistry and colloid generation were confirmed with at least two treatment replications using fresh matrix material . no significant effluent turbidity (& lt ; 1 ntu ) was observed for columns leached exclusively with diw , indicating that colloid generation was controlled by solution chemistry and not an artifact of the disruptive influence of sampling and column packing . the operability of this invention has been demonstrated in tests conducted with sediments from the tobacco road and barnwell / mcbean formation located on the upper coastal plain in aiken , s . c . the hdtma treatment solution was injected into the tobacco road and barnwell / mcbean sediments , which consist mainly of deep red , fine to coarse sands and clayey sands with interbeds of clay , sandy clay , and gravel . elevated levels of effluent turbidity were observed during the injection of the cationic surfactant , in excess of 1 , 000 nephelometric turbidity units ( ntu ), without an observed increase in hydraulic head associated with column plugging . in contrast , columns leached with a na - polyphosphate solution , a nonselective dispersing agent , at equivalent injection rates displayed a steady increase in hydraulic head throughout the course of leaching that was indicative of column plugging due to large - scale , nonselective dispersion of both oxides and aluminosilicate clays present within the column . the cationic surfactant appears to have both increased net - positive surface charge on mobile iron oxide colloids and blocked cation exchange sites that could potentially result in the capture of these particles during transport , but did not increase the mobility of phyllosilicates at low surface coverages . aluminum exchange and hydrolysis reactions promoted by the cationic surfactant lowered the solution ph and increased positive surface charge on variable charge minerals such as iron oxides . additionally , adsorption of the surfactant at cation exchange sites effectively inhibited their ability to induce flocculation without increasing the colloidal mobility of these clay minerals ( phyllosilicates such as mica , kaolinite , and hiv ), thereby reducing the attraction for each other . in essence , hdtma increased the positive charge character and the zero point of net charge ( zpnc ) for the formation so that submicron fe oxides became readily mobile . fig2 shows the thermogravimetric analysis ( tga ) patterns for the bulk clay and colloids mobilized . when heated , geothite ( fe oxyhydroxide ) and kaolinite ( 1 : 1 layer phyllosilicate clay ), the two predominate clay minerals in the aquifer sediments , display characteristic weight losses at ≈ 250 °- 350 ° c . and 450 °- 500 ° c ., respectively , with the area of the derivative peaks being indicative of the relative quantity of these two minerals . based on the tga patterns , the treated material ( fig2 b ) is enriched in iron oxides compared to the bulk clay suspension from the sediments ( fig2 a ). tga patterns for column suspensions generated by injection of the na - polyphosphate solution , the nonselective dispersing agent , were essentially identical to that of the bulk clay ( i . e ., fig2 a ). this in - situ remediation method can be applied to any number of contaminated sites , including , for example , aquifers proximate to radioactive waste or chemical waste burial sites . it is very cost effective and more efficient than other in situ methods currently available . the specific cationic surfactant can be selected for remediation of a specific mineral type . one skilled in the art can develop predictive models based on the chemical structure of the surfactant ( i . e ., alkyl chain lengths and aromatic alkyl substitutions ) without undue experimentation . although the present invention has been described with respect to particular embodiments , it will be apparent to those skilled in the art that modifications to the method of the present invention can be made which are within the scope and spirit of the present invention and its equivalents .