ARCHIVED REPORTS_XR0011907 - Laserfiche WebLink

Home Browse Search

east-west and the flow direction was interpreted to be northward This quarter, the contours wrap • around a low spot in the area near GT-I, causing the flow to converge in a general southeastward or eastward direction However, part of this change may be due to repair of the well casing to GT-1 during the quarter Therefore, this well will be re-surveyed in the second quarter to correct any errors in the casing elevation 3,3 Analytical Results Diesel was detected in four of the five monitoring wells (Table 2) The concentrations rose slightly in GT-1 and GT-5, but are still within the lower part of their historical ranges The concentration was unchanged in GT-6, and although diesel was reported in GT-9, the concentration is only about 10 parts per billion above the detection limit 4.0 CONCLUSIONS Hydrocarbon concentrations have been stable for the past nine months Particularly noteworthy is that purging the wells has no statistically significant effect on diesel concentrations, which were very similar this quarter to last quarter, even though the wells were not purged this quarter This is particularly true of GT-6, where the concentration has changed (declined) by only 40 parts per billion since June 2002 and rose only 10 ppb this quarter Concentrations in GT-3 (the nearest well to the former UST excavation) have been below the detection limit for the past four years, and the concentration in the Gillies domestic well (G-1) has exceeded the detection limit only once in the past 4 5 years The concentration in GT-1 has been below 100 ppb for three consecutive quarters, and below 300 ppb for four years Hence, morntonng data continue to demonstrate that contaminant concentrations are very minor at this site, especially within the Modesto aquitard, and have remained Iow ever since the static water level dropped below the base of the Modesto Aqulfer in late 1999 • 3