ARCHIVED REPORTS_2013_7 - Laserfiche WebLink

Home Browse Search

The results of the five-year COC monitoring event indicate that with the exception of one chlorinated herbicide (dicamba), no organic COCs were detected in the groundwater and surface water samples. Since similar concentrations of dicamba were measured in the upstream and downstream samples, it is believed that the source of the herbicide is from agricultural activities up-stream of the landfill. Several inorganic COCs were detected in both up-gradient and down- gradient wells and surface water stations. The similarity in the concentrations in both up- gradient and down-gradient wells and surface water stations suggest that the inorganic COCs are naturally occurring and not related to the landfill. As a result, no changes to the current monitoring program are recommended at this time. Groundwater quality conditions beneath the Austin Unit during the first quarter 2013 monitoring period are generally similar to historical results. Non-statistical exceedances for VOCs were identified at Detection Monitoring Program(DMP)wells AMW-6, AMW-13 and AMW-14. Trend analyses indicate that statistically significant increasing temporal trends were calculated for tetrachloroethene and trichloroethene in well AMW-13. These results are similar to previous results and it has been recommended that wells AMW-6, AMW-13, and AMW-14 be re- designated as corrective action program(CAP) wells since they have historically contained VOCs. For the routine inorganic monitoring parameters, CLs were exceeded for constituent concentrations in DMP wells MW-2A, MW-13, -14,MW-15, and MW-23R. With the exception of nitrate-N concentrations measured in well MW-14 and sulfate concentrations measured in well MW-15, there were no statistically significant increasing trends calculated for the CL exceedances during the current monitoring period. In the CAP wells, trend analyses are performed instead of comparison to CLs. During the current monitoring period, statistically significant increasing trends were noted for three VOCs in CAP well AMWA, while decreasing VOC trends were noted for several VOCs in CAP wells AMWA, AMW-4,AMW-10, and AMW-11. The increasing trend exhibited for cis-l,2-dichloroethene at well AMW-1 and generally decreasing (organic and inorganic)trends noted in all of the CAP wells, suggests that corrective action measures have been successful in reducing facility related groundwater impacts downgradient of the Austin Unit. Surface water samples collected from the upstream and downstream surface water monitoring stations during the first quarter 2013 monitoring period are generally consistent with each other and no VOCs were detected. These results suggest that landfill operations are not impacting surface water. The results of the five-year COC monitoring event indicates that with the exception of one semi- volatile organic compound(di-n-butyl phthalate), no organic COCs were detected in the groundwater and surface water samples. It should be noted that phthalates are used as plasticizers in PVC, which is a common monitoring well material. Therefore,the presence of di- n-butyl phthalate in well AMW-4 at an estimated trace concentration is believed to be a field contaminant. Several inorganic CDCs were detected in both up-gradient and down-gradient wells and surface water stations. The similarity in the concentrations in both up-gradient and down-gradient wells and surface water stations suggest that the inorganic COCs are naturally occurring and not related to the landfill. As a result, no changes to the current monitoring program are recommended at this time. C A2013-0021\FomardLtr_1Q 13 -2-