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Project 113-26, Page 5 <br /> Table 2 <br /> Water Sample Analysis Results* <br /> Cheaper) #37 <br /> 15 East Grant Lme Road,Tracy, California <br /> Samples Collected February 26, 1993 <br /> Sample #_ Tr-H-g Benzene Toluene .- Ethylbenzene Xylenes <br /> W-1 ND < 50 ND <0 5 ND <0 5 ND <0.5 1.5 <br /> W-2 3100 1200 62 80 230 <br /> W-3 ND < 50 1.1 ND <0.5 ND <0.5 0.90 <br /> W-4 160,000 5900 10,000 5200 22,000 <br /> W-5 300,000 11,000 36,000 7400 37,000 <br /> W-6 _ 20,000 150 490 700 2200 . <br /> Concentrations are n parts per bdhon, or Icg/L ND= Not Detected <br /> The sample # refers to the number of the borehole that supplied the sample. <br /> Concentration profiles for TPH-g contamination are presented in the Appendix. The <br /> alternate maps show that the current data (monitoring well samples from 2/16/93 <br /> and borehole water samples from 2/26/93) can be represented either by a localized <br /> plume centered around the old tank location, or by an offsite plume crossing the <br /> property from southeast to north <br /> III. Discussion and Conclusions <br /> Groundwater flow direction at 15 East Grant Line Road is toward the southeast <br /> Over the past several years groundwater gradients have been to the north, both at <br /> Cheaper! #37 and at a variety of other sites along Grant Lane Road. This shift in <br /> groundwater flow may reflect the recent heavy rains of the winter of 1992-1993 and <br /> the end of the six-year drought. The water table rose by over 1.6 feet between <br /> September, 1992, and February, 1993, and heavier recharge to the north and west <br /> could temporarily tip the relatively flat gradient found at this site. El Pescadero Park <br /> and North School, a 7 6-acre area northwest of the study property, may have tipped <br />' the water table here by its higher infiltration rate, while the area to the southeast <br /> loses most of its precipitation through runoff. If this is true, the water table will <br /> slowly flatten and return to a northward gradient. Further monitoring of <br /> groundwater levels wall clarify this situation <br /> The sand layers are much more conducive to groundwater movement than the <br /> clays and clayey sands. Hydraulic conductivittes for medium-grained sands run <br /> about 10-3 to 10-4 meters/second (3,500 to 350 feet/month) but range from 10-5 to 10.9 <br /> meters/second (35 to 0.035 feet/month) for silts and clays. <br /> 23 <br /> Parker Environmental Services 4185 Rialto Court Pittsburg CA 94565-6116 <br />' Phone (510) 439-1024 Fax (510) 439-2566 <br />