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IJAR-24-80 16 51 From WOODWARD CLYDE ¢ T-735 P 30/34 Jab-462 applicable only in cases where there is a net flow through the well-screen interval in the aquifer being sampled. Recent hold trials of the sampler using this protocol conducted by United States Dapanrnont Of Energy (USDOE) contractors and Unitad States Environmental Protection Agency (USEPA) porsonnel have shown that a not flour . through the gall is essential to tho no-purga scenario SEMP Mg?7G1at=1 lign The design of any sampling program should first have the following questions answered. 0 What is the specific purpo" of the crimpling event? 0 What parameters or constituents are the target of the sampling? U What is the nature of the sampling environment (i o , stratigraphy, hydraulic conduebvity of the water producing zone or the measured flow-rate through the well)? 0 What are the potential sources for error during the sampling event? These questions are central to every sampling protocol issue Detective monitoring programs on the other hand have as their main objectives, the characterization of the site and placement of sampling points so as to permit detection of indicator parameters Fundamental to these purposes are the following objectives Q Avoidance of gross sampling errors, 0 Minimization of costs in dollars, time, and human resources; 0 Complete data collection of both hydrogeologic parameters and chemical concentrations sufficient to permit decision malting at a known level of confidence Some ftsentthd Hitltdumma Co Alccurnee 11Dmft Acgtnls ihom Flow rates through ground-water monitoring wells of less than 3 gallon per day, or hydraulic conductivities M of 10-5 and lower may not produce the desired sampling results in a no-purge scenario, better results ® from such wells may be obtained through purging. Under such circumstances, low-flow (low-stress) purging and sampling is probably a better choice, although considerably more expensive, to insure a higher level of sampling accuracy. Filtration of ground-water samples for metal analyses will not provide accurate information concerning the mobility of metal contaminants (14) This is because some mobile species are removed by the action of filtration, required as a process protocol for the specific species analytical procedure. Acetal contaminants may move through fractured or porous media not only as dissolved species,but also as precipitated phases, polymeric species or adsorbed to inorganic or organic particles of colloidal dimensions Analytical methods used to determine "dissolved" metal concentrations have lustoncally used 0 45 nucron filters to separate dissolved and particulate phases (15) If the purpose of such determinations is an evaluation of "mobile" species in solution, significant underestimation of mobility may result, due to potential colloidal associations Facilitated transport of some radionuclides in association with mobile colloidal particles has been suggested (lb) These colloids were either homogeneous hydrous precipitates, or were formed from the adsorption of the radionuclide onto colloidal size mineral particles Sheapherd showed that significant quantities of radionuclides adsorbed onto colloid size mineral particles(20). Further work by Sheapherd concluded that transport of radionuclides by colloidal clay particles must be conbidered in any contaminant transport model of metal species associated with radionuclides(21) Iii addition, colloidal transport should be considered for certain hydrophobic mineral species B24ormInIm S the Purpwe aT Samm pllterg 4 of 8 3114/914 22 PM