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GROUND WATER MONITORING WORK PL7�N DREDGE MATERIAL DISPOSAL SITE 1,ROBERTS ISLAND,PORT OF STOCKTON tensions are indicative of increasingly drier conditions. Stronger water potential corresponds to lower water migration and impeded diffusion of acidity resulting in accumulations of un-neutralized acidity on soil surfaces. Low pH associated with stronger water potentials, therefore, may not be indicative of threats to ground water,but rather of a localized disequilibrium soil condition. Water potential will be measured in the field using a tensiometer. ■ Water pH(EPA Method 150.1 and 9045)-measures the acidity due to hydrogen ions that are free in solution within a mixture of sediment and water. It does not represent "reserve" acidity, the capacity of the sediment to become acidic or basic, or the capacity to neutralize generated acid. ■ Exchangeable Acidity-measures the amount of reserve acidity present in the sample, and is predominantly aluminum cations adsorbed to negatively charged soil surfaces. Compared with water pH, exchangeable acidity is more representative of the sustainable chemical equilibrium in the sample, and is,therefore, a better indicator of likely leaching potential. The exchangeable acidity will be measured using the Shoemaker, McLean, and Pratt(SMP) single buffer method, as described in the American Society of Agronomy (ASA) No. 9 12-3.4. ■ Total Organic Carbon (Method SW 9060))-measures the total amount of organic carbon(TOC), which is directly proportional to organic matter content. TOC is the primary source of organic and inorganic attenuation capacity. ■ Cation Exchange Capacity (Method SW 9080)-measures the capacity of the soil to exchange cations (such as metals) with interstitial waters and is largely a function of organic matter content and the clay mineralogy within the foundation soils. Cation exchange capacity(CEC) is important to neutralization potential and is a direct measure of chemical attenuation capacity. ■ Total dissolved solids (EPA Method 160.1)-is the total concentration of dissolved materials (TDS), including all anions, cations, and uncharged solutes (inorganic and organic) and is used a general indicator of water quality. ■ Alkalinity (Method SM2320B)-is the acid neutralizing capacity from free bicarbonate, hydroxide, and carbonate, and aids characterization of TDS, EC,pH. ■ Electrical Conductivity(field measurement) -is a direct measure of the electrolyte's capacity to conduct electrical current(EC) and is directly proportional to their concentration. Acid generating or neutralizing processes can elevate EC. ■ Ca,Mg, K,Na(EPA Method 6020) -These are the major cations in most ground waters and are conventionally used to discriminate between major ground water types and are useful in graphical representation of ground water characteristics. As January 2005 Page 14 Environmental Risk Services,Corp.