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Chris, That's because the volume of water moving will increase as the porosity increases. However this will also increase the dilution potential as the contaminant enters the groundwater from the soil above. But if you're just running a groundwater Level 3 rather than the soil Level 3 you won't get the dilution effects as you're using groundwater rather than soil concentrations. My advice would be to try and reproduce the concentrations you've recorded in the groundwater using know soil concentrations (if you have them) in the Soil Level 1 and Level 2 calculations, this will allow you to more accurately estimate the porosity to reflect the dilution as the contaminant enters the groundwater and use the same porosity for the groundwater flow. Alternatively you can consider the rainfall, saturated thickness catchment hydraulic gradient and permeability to determine the flow and thus the effective porosity. All these parameters are interlinked and dependent on each other, so that you can't have a mudstone with a high porosity, high permeability and high hydraulic gradient, something has to give. Dan Riding -----Original Message----- From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of People, Christopher Sent: 15 July 2008 14:01 To: [log in to unmask] Subject: Re: Effective Porosity? Thanks everone, all the messages have been very useful. Essentially this is for ground water risk assessment (EA Remedial Targets). In regards to Dan's comment below regarding porosity - I've played with Level 3 with a range of porosity literature values for Mudstone. The literature gave a total porosty range between 2 and 25%. This resulted in a remedial target that varied from ~1ug/l to 240mg/l so this would indicate that the RTM is fairly sensitive to porosity ???? Don't know if anyone has any comments on this... Anyway, will see what the lab results flag up. Thanks again. Chris -----Original Message----- From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of McMahon, Paul Sent: 15 July 2008 13:50 To: [log in to unmask] Subject: Re: Effective Porosity? The link below might help too ..... Total Porosity (see Section 3) and Effective Porosity (see Section 4); Meaurement procedure (see Section 4.2). http://web.ead.anl.gov/resrad/datacoll/porosity.htm Stepping back a little though, how accurately do you need to assess the effective porosity, given the natural variability of soils and also by reference to Dan's comments below about the assumed value for porosity being relatively insensitive when using calculations to predict contaminant migration. Regards, Paul ________________________________ From: Contaminated Land Management Discussion List on behalf of Dan Riding Sent: Tue 15/07/2008 12:49 To: [log in to unmask] Subject: Re: Effective Porosity? Chris, Please be aware that these laboratory tests will only provide you with total porosity (total voids). Effective porosity is dependent on whether the voids in the soil/rock are interconnected and therefore can only accurately be determined through large scale field tests and calibration of models. However as the calculation for contaminant migration are not very sensitive to porosity, published values for typical soils and rock are usually adequate. Dan Riding -----Original Message----- From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of McMahon, Paul Sent: 15 July 2008 10:37 To: [log in to unmask] Subject: Re: Effective Porosity? Hi Chris, Any reputable geotechnical laboratory could make this determination for you. They will need to determine bulk density, moisture content and specific gravity for the various soil fractions present in your soil to determine the void ratio and hence porosity. You are also likely to require a particle size analysis and/or sedimentation test to assess the overall variability of the soil, since it may not have a unique porosity, but moreover it will vary. Unfortunately I do not have current laboratory testing rates but these are NOT expensive tests. It would be inappropriate of me to recommend a specific laboratory for you to approach, but there are many. Good Luck. Regards, Paul Dr. Paul H. McMahon Senior Geotechnical Lecturer Built Environment & Civil Engineering University of Bolton Deane Road Bolton BL3 5AB Direct Line: 01204 903849 http://www.bolton.ac.uk/staff/phm2 <https://webmail.bolton.ac.uk/exchweb/bin/redir.asp?URL=http://www.bolto n.ac.uk/staff/phm2> ________________________________ From: Contaminated Land Management Discussion List on behalf of Chris People Sent: Tue 15/07/2008 10:06 To: [log in to unmask] Subject: Effective Porosity? Morning Everyone. Does anyone have any experience of assessing Effective Porosity? I presume you may need a U100 to be tested - but cant find any further information on it. Is there a standard lab test that can provide this? If so do you have any idea of a approximate cost? Thanks! Chris