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ORC TECHNICAL BULLETIN # IV.6 0 Oxygen Release Compound,ORC® Iron Fouling Calculations and Observations "How much iron can be in the aquifer and not plug the well?". The assumption is that we are talking about soluble iron (many routine analyses are for total iron) Also, ignoring the complexities of chelating reactions which actually reduce the problem, let us assume 20 ppm of soluble iron is in an aquifer Under these conditions, the example below examines the potential for precipitation in the well There are 1 5 cubic feet a day moving through a six inch well that is 20 feet deep in an aquifer with a flow of 0 5 feet per day, and a porosity of 0 3 At 20 ppm there are 840 mg/day of iron moving through the zone as described Assuming the entire 840 mg of ferrous ion becomes oxidized to ferric ion and then precipitates as ferric hydroxide, 1.6 grams would be produced each day In the 180 day average life of the ORC falter socks to this system, the total amount of ferric hydroxide that can come out of solution in a well with 20 ppm of soluble iron, is 288 grams This is a very small amount - which in turn will precipitate, for the most part, on the ORC filter socks that are eventually removed Oxygen release will not be inhibited from the filter sock surface If all of the iron precipitates on the surface of the socks, it would be less than 1 mm thick and deposited irregularly on the surface - sporadically crystallized at nucleating centers From practical experience a dispersed, spotty patina of iron hydroxide, has been observed, on ORC samples after about 9 months in a well with a background of 10 to 40 ppm of soluble iron Therefore, a high level of soluble iron, on the order of 20 ppm, will not produce a significant amount of precipitated iron The worst cases generally related for an observed concentration of soluble iron, is 100 ppm Therefore, if the above scenario is multiplied five-fold, it still appears to be manageable Ultimately, one has to defer to the actual field results The degree to which precipitated iron can foul the system is the operative issue If well screens and packing foul, various acids such as HCl, hydroxyacetic and sulfamic are acceptable and commonly used Also, tripolyphosphates can be used to inhibit iron precipitation and is a practice used in conventional water well development The simplest solution to any perceived problem is to monitor the process If excessive iron is being deposited, this will become apparent by the nature of the filter sock when it is withdrawn EGE N ES 1 -------------------------------------------------------------------------------------- ioremediation Products 27130A Paseo Espada, Ste 1407, San Juan Capistrano, CA 92675 Phone 714-443-3136 Fax 714-443-3140