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Gary A. Reents 4 14 April 1989 <br /> Plume Delineation <br /> The presentation of water quality data collected to date is in <br /> conformance with the requirements of the Cleanup and Abatement Order. <br /> Graphs of TDS versus time for each well are presented. Three <br /> isoconcentration contour maps were developed (Oct. 1988 , Jan. and March <br /> 1989) . Background levels were based on the results from well 4 with TDS <br /> = 200 mg/l , chloride = 10 mg/l and EC = 255 micromhos/cm. . <br /> Data gaps in the TDS contour maps were identified along the southern <br /> boundary of the property and in the north between wells 9 and 12 . <br /> Therefore, four (4) shallow monitoring wells are proposed, three (3) <br /> along the southern boundary and one (1) between wells 9 and 12 . The <br /> southern wells are proposed due to the fluctuations in the ground water <br /> gradient that seem to indicate a seasonal southerly flow of ground <br /> water. <br /> A significant increase in TDS in well 2 (from 2100 to 4160 mg/1) was <br /> noted. The consultant suggests that the cause of this increase may be <br /> due to the leaching of salts from a backfilled exploration trench near <br /> well 2 . An explanation is given that purge waters from nearby <br /> monitoring wells were discharged onto this backfilled area, and that <br /> this practice (since October 1988) led to the increase in TDS in well <br /> 2 . However, there is no proposal to evaluate this source of ground <br /> water contamination. Therefore, Southwest Hide Company should <br /> investigate this potential source of contamination. <br /> The vertical extent of contamination is unknown. Only one (1) <br /> monitoring well has been installed below 30 feet. This well <br /> (No. 7A) is screened from 59 to 69 feet below the ground surface and <br /> has TDS levels of 1000 to 1100 mg/1, chlorides of 330 to 360 mg/1, and <br /> E.C. levels of 1500 to 1700 micromhos/cm. . The consultant estimates <br /> that the depth of contamination may be as deep as 140 feet, but provides <br /> no rational for this estimate. <br /> The on-site production well (120) was sampled in November 1987 and had <br /> a chloride content of 695 ma/l and a TDS of 1990 mg/l . It is stated <br /> that the salt plume from Southwest Hide has caused this contamination <br /> in their production well , however, no information is given on the depth <br /> of this well . It is likely that the production well is greater than 140 <br /> feet in depth, and due to the sandy nature of the substrata and the lack <br /> of a low permeable layer, it is possible that contaminants are being <br /> drawn downward by the pumping of the production well . <br /> Southwest Hide Company should consider the affect of the pumping of <br /> their production well on contaminant migration patterns. The production <br /> well should be sounded to determine its depth. The 140 foot estimate <br /> of the vertical depth limit of ground water contamination should also <br /> be explained. <br /> It is proposed that one deep well (7C) approximately 140 feet deep be <br />