Although six UFA locations exist worldwide, the six UFA instruments at UFA Ventures are the only commercially available instruments for service work. So the standard being developed by ASTM will be an opportunity for UFA Ventures to be the front-runner in an emerging market. The draft standard's title is Test Method for Determining Unsaturated and Saturated Hydraulic Conductivity in Porous Media by Open-Flow Centrifugation. After the draft standard emerged from its task group (Vadose Zone Monitoring), it met challenges at its subcommittee (Subcommittee on Ground Water) and committee (Soil and Rock Committee) levels. The draft standard is now before the entire ASTM. Reaching consensus is a process of responding to negative comments that surface during successive ballots. The draft becomes an ASTM standard when voting by the entire ASTM turns up no negative comments or recommended revisions.

Using the UFA Method^SM, an operator can determine the hydraulic conductivity of soil, rock, sediment, concrete, sludge, ceramic, and other porous material. Hydraulic conductivity, the single most important transport property, is the rate at which fluids move through geologic materials. These data are important in determining and describing flow and transport of contaminants through saturated and unsaturated subsurface soils and rocks. The ability of the UFA Method^SM to supply hydraulic conductivities for all materials more rapidly and at less cost than other methods has implications for improving characterization, restoration strategies, landfill designs, monitoring, and risk and performance assessments.

The UFA Method^SM consists of an ultracentrifuge and a constant, ultralow flow pump. The centrifugal force acts like gravity on the samples but is adjustable to higher forces than actual gravity. This increased force means that in hours and for any porous media, the UFA Method^SM can measure hydraulic conductivities over a full range of field moisture contents, from saturated down to 10-11 cm/s.

The ultralow-flow pump provides fluid to the sample surface through a rotating seal assembly. The operator controls the flow rates to the sample and the centrifuge's acceleration to directly achieve the full range of field moisture conditions.

Effluent from the sample is collected in a volumetrically calibrated chamber at the bottom of the sample assembly. When the amount of fluid coming out of the sample into the effluent chamber equals the amount of fluid being introduced into the sample by the pump, hydraulic steady state has been reached. At this point, the operator weighs the sample to determine its water content. The above procedure is repeated for the next set of parameters. After the last set of parameters for a particular sample is run and the final hydraulic steady state is reached, the operator dries the sample in an oven to obtain the dry weight and volume. At each step of this desaturation process, the operator records the volumetric water content and hydraulic conductivity. By plotting each volumetric water content with its associated hydraulic conductivity, a characteristic curve is obtained for each sample that describes the relationship between the two measurements for a particular sample—be it soil, rock, concrete, or other porous media.

In addition to hydraulic conductivity, UFA Ventures can provide to its clients direct measurements of all other transport properties of porous media as a function of water content. These data include moisture potential and retention, electrical conductivity, retardation factor, distribution coefficient, gas permeability, and pore water extraction. Data about the material's transport properties can be compared with the chemical, physical, and mineralogical properties to determine relationships between physical and hydrologic characteristics. Knowledge of these relationships is essential in predicting migration of contaminants through the subsurface and for testing various remediation strategies.

For more information about the services UFA Ventures provides and its UFA Method^SM, see http://ufa.owt.com on the Internet. James Conca can be reached at UFA Ventures at 2000 Logston Blvd., Richland, WA 99352. His telephone number is (509) 375-3268.