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� CAMBRIA <br /> • Alkalinity The total alkalinity of groundwater indicates the groundwater's ability to <br /> neutralize acid High alkalinity (high pH) conditions occur when groundwater contains <br /> elevated hydroxides, carbonates, and bicarbonates of elements such as calcium, magnesium, <br /> sodium, potassium, or ammonia Because these species are created by the respiration of <br /> microorganisms, high alkalinity is an indicator of biological activity However, these species <br /> may also result from the dissolution of rock (especially carbonate rocks) and the transfer of <br /> carbon dioxide from the atmosphere Alkalinity also buffers groundwater pH against acid <br /> generation by both aerobic and anaerobic biodegradation processes Ylgher alkalmity in the <br /> source area compared to the areas outside the plume suggests that biodegradation is <br /> occurring �,}4n a,� kq, J1.t <br /> • Nitrate: After DO has been depleted in the microbiological treatment zone, nitrate may be <br /> used as an electron acceptor for anaerobic biodegradation In this process, called <br /> denitrification, nitrate is reduced to nitrite Reduced nitrate concentrations in the source area <br /> compared to the areas outside the plume suggests that anaerobic biodegradation is occurring <br /> • Sulfate After DO and nitrate have been depleted in the microbiological treatment zone, <br /> sulfate may be used as an electron acceptor for anaerobic biodegradation If sulfate <br /> concentrations vary indirectly with hydrocarbon concentrations, anaerobic biodegradation of <br /> fuel hydrocarbons is probably occurring <br /> • Ferrous Iron In some cases, ferric iron is used as an electron acceptor during anaerobic <br /> biodegradation of petroleum hydrocarbons In this process, ferric iron is reduced to ferrous <br /> iron, which may be soluble in water Therefore, if the ferrous iron concentrations vary <br /> directly with hydrocarbon concentration, anaerobic biodegradation may be occurring <br /> To summarize these parameter relationships, biodegradation is suggested by an indirect <br /> relationship between hydrocarbon concentrations and DO, ORP, nitrate and sulfate <br /> concentrations, and a direct relationship between hydrocarbon concentrations and alkalinity and <br /> ferrous iron concentrations <br /> 1399 5 <br />