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URS CLOSURE REQUEST Data presented in this report together with that provided in Additional 1,2-DCA Investigation and Site Conceptual Model and Second Quarter 2004 Groundwater Monitoring Report (URS, 2005) complete existing agency requirements for data substantiating that the site meets closure criteria Closure has previously been requested in July 2002 (URS, 2002) based on the presentation of data indicating the site meets the criteria for designation as a "low risk groundwater site"These cntena are as follows • The leak has been stopped and sources removed or remediated, + The site has been adequately characterized, + The dissolved contaminant plume is not migrating, and chemical concentrations are not increasing with time, + No water wells, deeper aquifers, surface water, or other sensitive receptors are likely to be impacted, and, + The site represents no significant risk to human health or safety The agencies subsequently requested additional data including four quarters of groundwater monitoring results, assessing 1,2-DCA in groundwater With this report the collection, presentation, and assessment of that data has been completed The results show a limited extent of 1,2-DCA in groundwater at low concentrations that are declining with time Site closure is therefore requested CONCLUSIONS AND RECOMMENDATIONS Conclusions The following conclusions may be made from the data for the third and fourth quarters of 2004, four quarters of data from the two new monitoring wells installed in March 2004, as well as the overall historical data for the site + Groundwater elevations have declined by approximately 12 feet to -32 feet MSL since reaching a High of approximately-18 feet MSL in May 2000 + The groundwater gradient in December 2004 was 0 02 feet/foot to the northwest, which is consistent with the average groundwater gradient at the site • TPH has not been reported in any of the samples since June 2004, and has been reported only ' sporadically since approximately December 2001 • 1,2-DCA was reported for four wells sampled during the third quarter of 2004 at concentra- tions ranging from 19 to 27 µg/L 1,2-DCA was reported for three wells sampled during the fourth quarter of 2004 at concentrations ranging from 2 5 to 25 pg/L PCE was reported only in the samples collected from DMW-9 during the third and fourth quarters, at concentrations of 7 1 and 3 4 gglL,respectively ' + The trend of concentrations of 1,2-DCA is either downward or level for all four wells in which that constituent has been reported consistently The trend analysis includes four quarters of monitoring in DMW-8 and DMW-9, which were installed during the first quarter of 2004 for the purpose of assessing 1,2-DCA • The lack of detections of 1,2-DCA in DMW-8 compared to the shallower well DMW-9 suggests a lack of vertical migration for that constituent r G VOB1AFP\Quarterly1Q404WQ04AFP_rev0i doc