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DORMER AMERICAN FOREST PRODUCTS Appendix D Closure Summary Report July 2009 URS Project 17322736 Page D-4 6. Selection of Tier 1 ESLs and Comparison to Site Data (see Section 2.2): • Summarize how Tier I ESLs were selected with respect to the information provided above and additional assumptions as applicable. Tier 1 ESLs were selected based on the depth to groundwater, which is significantly greater than 3 meters, and on the lack of beneficial use of the groundwater,based on shallow groundwater in an urban setting and demonstrated lack of any downgradient water supply wells either within the extent of the plume or to a radius of 2,000 feet. • Compare site data to the selected summary Tier I ESLs (presented in Volume 1) and discuss general results. All maximum concentrations for constituents of concern fell significantly below the Tier 1 ESLs for both residential and industrial uses. • If desired or recommended, compare site data to detailed ESLs for individual environmental concerns(presented in Volume 2, Appendix 1) and discuss specific, potential environmental concerns present at site. Not applicable. 7. Conclusions (see Section 2.10): • Describe the extent of soil and groundwater impacts above Tier 1 ESLs, using snaps and cross sections as necessary. As demonstrated.by Table D-1,no site groundwater impacts exceed Tier 1 ESLs. _.. • Discuss if a condition of potential risk to human health and the environment exists at the site. Based on the results of previous risk assessments, which are summarized in Section 4 of the 2001 Closure Request Report(URS, 2001), the risk to human health from TPH residues remaining in the soil is low, based primarily on the assumption that residual soil impacts are located at depths greater than 20 feet. Fate and transport modeling has indicated that at groundwater depths greater than 35 feet bgs, predicted groundwater impacts would be below the MCL for the indicator parameter used. Risk of exposure to groundwater impacts is also limited by distance to active water supply wells, and the fact that water supply wells in the vicinity are screened in deeper, semi-confined aquifer, as opposed to the shallow unconfined aquifer, which is impacted at the site. The Tier 1 screening assessment conducted for this report indicates no risk with respect to indoor air for a residential scenario, due to residual groundwater concentrations. • Discuss if a more site-specific risk assessment is warranted at the site. Based on the results of the Tier 1 risk assessment, no further more site-specific risk assessment is warranted. • Present a summary of recommended future actions proposed to address environmental concerns at the site. No additional environmental work is recommended. 1:.\�"pr.cess;'�"'�o--Am�riaiForestCl�surc-Si,mcnar}-R�wtt-Rct-7idui