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(,eokgecaI r"echlacs lfu Page b ' atm Quarter 2002 Groundwater Monitoi ing Report Pioject No 507 2 • March 7, 2003 ' 4 The plume is defined to the northwest and southwest by wells MW-10 and MW-7 respectively ' 5 The BTEX/TPH-G groundwater contamination plume is defined by MW-109 in the vertical plane, which is screened 40 feet below MW-9 This suggests that the vertical gradient is not moving the contaminants to any degree 6 The groundwater gradients flow to the northeast or east with relatively flat slopes, which appears not to significantly influence contaminant migration ' 7 The site exhibits a predominantly downward component of vertical groundwater flow, which is approximately the same slope as the horizontal gradient These components of groundwater flow appear not to cause preferential contaminant migration ' 8 The groundwater contaminant concentrations are on the rise, which correlates with a decrease of groundwater levels The center of the plume has not migrated beyond the source area giving evidence that the plume is not migrating laterally or vertically by ' advective flow Recommendations ' + Maintain the modified quarterly monitoring schedule • Monitor the site wells for indicators of remediation by natural attenuation e Use the geologic cross sections showing Isoconcentration contours of petroleum Ncontaminants in the soil and groundwater as the basis for performing contaminant mass estimate calculations ' O A work plan for "In Situ Remediation Feasibility Study" dated September 20, 2002 and an addendum to this plan was submitted on December 20, 2002 Once the County � approves the plan, we will submit a cost pre-approval package to the Fund 4.0 LIMITATIONS ' This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered It should be recognized that definition ' and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that standards existing at the present time may change as knowledge increases and the state of the practice ' continues to improve Further, that differing subsurface soil characteristics can be experienced within a small distance and therefore cannot be known in an absolute sense All ' conclusions and recommendations are based on the available data and information. The tasks proposed and completed during this project were reviewed and approved by the ' local regulatory agency for compliance with the law No warranty, expressed or implied, is made