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December 1985 to August 1991 of 33% overall; however, an <br /> increase of PCE from June 1991 to August 1991 of 153% was <br /> recorded. TCE concentrations, in LM-32 , from December 1985 <br /> to August 1991 decreased in concentration by 47%, but <br /> increased from June 1991 to August 1991 of 171%. <br /> At least some of the variations from the May to the August <br /> 1991 quarterly rounds would appear to be seasonal. Further <br /> quarterly monitoring will confirm or refute this premise. <br /> 21. Within well cluster LM-68, LM-69, and LM-70, the well <br /> screened within the lower horizon (LM-70) demonstrated an <br /> increase in concentration of TCE. This is the nearest <br /> downgradient well to Area 3 , completed in the lower <br /> hydrostratigraphic zone. While it is likely that the <br /> contaminants in this horizon are migrating downward from the <br /> upper and middle units near Area 3 , it is also probable that <br /> they are migrating from on-site, already within the lower <br /> hydrostratigraphic unit. In any case, these contaminants <br /> are going unchecked as they leave DDRW-Tracy. <br /> 22 . The statement is made in Section A. 2. 1 that "purge water <br /> from wells located within the farmers ' property was <br /> discharged to the ground, at the farmers ' request, to assist <br /> within ongoing irrigation of the fields. " This activity is <br /> questionable based on the analytical data that shows at <br /> least some of the wells had contaminants above EPA Action <br /> Levels. <br /> • A more appropriate approach would have been to contain <br /> the water pending analysis. If the analytical data <br /> indicated that the constituents were below the levels <br /> set by 40 CFR Ch. 1, 268.41, Table CCWE, disposal on <br /> the property would have been appropriate. <br /> 23 . According to Articles 5 and 10 of Subchapter 15, Chapter 3 , <br /> Title 23 of the California Code of Regulations, Section <br /> 2550.7 (e) (12) (B) , "wells shall be purged immediately after <br /> sampling to the extent necessary to remove the parcel of <br /> water that was in the well-bore at the time of sampling. " <br /> • Indicate whether both pre-sampling and post-sampling <br /> purging was done. <br /> • If this regulation was followed, please include its <br /> description in the next quarterly monitoring report. <br /> 7 of 7 <br />