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Joe Aldridge Former Beacon# 12474 Page 2 of 3 Included in the report was a recommendation that two additional, intermediate- depth monitoring wells be installed, specifically, one well 100 feet southeast of MW-15, offsite in the street right of way and one well onsite southwest of MW- 16. Upon review of the site map, it is apparent that all of the investigative borings and well installations have been located along the site perimeter. Iso- concentration maps included in this report for TPHg and benzene have definitive lines in the center of the site, but with no data to support these interpretations. 1,2-DCA data was not included on these figures, only TPH-g and benzene data are plotted. There are substantial distances between known data points where petroleum contaminants are present in the northern portion of the site and the proposed point at the same depth of concern in the down-gradient, southeast portion of the site. The northerly MW-11, which had the most recently detected 1,2-DCA, (screened 50'-70') is 120 feet north of the closest down-gradient monitoring well with 1,2-DCA present at the same depth (MW-7). The SCM portion of the report is incomplete, as it does not include adequate figures, cross-sections, complete soil data tables, or iso-concentration maps for all the significant constituents of concern at all depths of concern. 1,2-DCA is a major concern at this site in both soil and ground water. The two cross-sections showed only TPHg and benzene soil data and the distribution figures plotted only the TPHg and benzene data. None of these figures included the 1,2-DCA data. Also missing in the SCM update was a historical CPT soil data table. The SCM should include cross-sections, site map/iso-concentration figures for both soil and ground water and present the 1,2-DCA data, as well as TPHg and benzene data. An adequate SCM for this site should also include professional estimates and interpretations of contaminant mass, potential or recognized contaminant migration pathways, and plume stability or migration potential. These issues must be addressed to evaluate the threat of the contaminant plume to human health, the environment and the groundwater resource, and to effectively assist you in moving your site toward closure. I Please submit a revised SCM addressing these issues to EHD no later than 23 August 2005. EHD considers installation of an intermediate depth monitoring well southwest of MW-16 to be adequate and necessary, but questions the proposed location of the well southeast of MW-15. EHD considers the distance between the closest upgradient intermediate-depth well and this proposed offsite intermediate-depth well 100 feet southeast of MW-15 to be excessive (over 240 feet). Additionally, the contamination noted in CPT-3/13-10 at the intermediate level of concern (approximately 90'-100' bgs) has not been adequately characterized. Repeatable ground water monitoring and sampling in this southwest corner at this depth of interest is needed.