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• pH values varying from b to 8 h icrobial active can change the H of groundwater. A difference azy g activity g P in pH between the contaminated and uncontaminated groundwater is another indicator of biological activity. ' Conductivity Aqueous conductivity is a measure of the ability of a solution to conduct electricity. The conductivity of groundwater is directly related to the concentration of ions in solution, conductivity increases as ionic concentration increases. Conductivity is used to ensure that groundwater samples collected at a site are representative of groundwater in which the dissolved phase contaminants may be present. If the conductivities of samples taken from different sampling points differ significantly, they may represent different hydrogeologrc zones, or the groundwater may be affected by dissolved contaminants Temperature Groundwater temperature directly affects the solubility of oxygen and other geochemical ' parameters The solubility of dissolved oxygen is temperature dependent, being more soluble in cold water than in warm water. For instance, at 25°C DO solubility in pure water is 8 4 mg/L. At 5°C, DO solubility is 12.8 mg/L Groundwater temperature also affects the metabolic activity of '• bacteria_ Rates of hydrocarbon biodegradation may double for every 10°C increase in temperature over the temperature range between 5 and 25°C. Groundwater temperatures are typically about 10°C. Groundwater temperatures less than about 5°C (rarely found) tend to inhibit biodegradation, tand slow rates of biodegradation are generally observed in such groundwater. Alkaiuuty The total alkalinity of a groundwater system is indicative of a water's capacity to neutralize acrd. Alkalinity is defined as the net concentration of strong base in excess of strong acid with a pure CO2 water system as the point of reference(Domenico and Schwartz 1990). Alkalinity results from the presence of hydroxides, carbonates, and bicarbonates of elements such as calcium, magnesium, sodium, potassium, or ammonia. These species result from the dissolution of rock (especially carbonate rocks), the transfer of CO, from the atmosphere, and respiration of microorganisms. An increase in alkalinity across a contaminant plume is potentially an indicator of bioactivity. Alkalinity is important in the maintenance of groundwater pH because it buffers the groundwater system against acids generated through both aerobic and anaerobic biodegradation processes Nitrate(NO,) After dissolved oxygen has been depleted in the microbiological treatment zone, nitrate may be used as an electron acceptor for anaerobic biodegradation. In this process of denitrification, nitrate is reduced to nitnte (NOD. Therefore, changes in nitrate concentrations across a contaminant plume can be used as an indicator for bioactivity. 6