1995-10-02_REVISION - M1977493 (7)

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COMPARISON OF MAYFLOWER SEEP AND WELLS GWM -1 AND GWM -2 Water quality data for seep water from the Mayflower Pond were compared with data for ground water at wells GWM -1 and GWM -2. The object of the comparison was to determine if there was evidence that the seep water was impacting ground water in the vicinity of the monitor wells. Table 1 summarizes data for Mayflower seep water and ground water at wells GWM -1 and GWM -2. Data are taken from from quarterly sampling at the wells between June, 1987 and May, 1993, and from the fourth quarter of 1993 to the fourth quarter of 1994. Data from the Mayflower seep are from sampling in September, 1993, June, 1994, and December, 1994. Tables 2, 3, and 4 contain a complete listing of data used for this evaluation. The following discussion, based on the water quality data summarized in Table 1, indicates that the Mayflower seep water is not impacting ground water in the vicinity of the monitor wells. Although major ion composition may be similar for seep water and ground water, conservative constituents do not behave similarly. The dissimilar behavior indicates a lack of connection between seep water and ground water. Major Ions and Geochemical Character The proportions of major ions can be used to differentiate between sources of water. Typically, calcium, magnesium, potassium and sodium are the major cations in water and bicarbonate, chloride and bicarbonate are the major anions. To evaluate the major ion make -up and geochemical character of the water, hardness, total dissolved solids (TDS), sulfate, alkalinity and pH were evaluated. • For typical waters, hardness consists mainly of calcium with a small contribution from magnesium. Therefore, hardness values indicate that ground water and seep water contain calcium. As indicated in Table 5, there is 1.5 to 3.5 times as much hardness in the seep water as in GWM -1 water and 4.5 to 22 times as much hardness in the seep water as in GWM -2 water. TDS is a summation of all constituents, but is dominated by major cation and anion contributions. Alkalinity is often under - represented in TDS. Alkalinity data are only available for the Mayflower seep and range from 25 to 42 mg /1 as calcium carbonate (CaCO However, alkalinity is related to pH so estimates of relative alkalinity can be made based on pH data. Typically, alkalinity increases as pH increases. For ground water at the two wells, pH values were near neutral to neutral. The seep water pH values were also near neutral but were slightly lower than ground water values. Therefore, ground water alkalinity is expected to be higher than seep water alkalinity. Anion composition also is indicated by comparing the numerical values of sulfate and TDS. Sulfate concentrations represent half or more of the numerical value of TDS for ground water and seep water. Therefore, sulfate is the dominant cation for these waters, although bicarbonate wellcomp.doc 1/31/96 1