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Mr. Harlin Knoll October 19, 1999 Page 5 of 6 f ' in the sample collected from boring SB3 (1,400 ppb). No groundwater samples were collected from any of the hand augered borings. Analytical results of groundwater' samples are summarized in Table 4. Laboratory reports and chain of custody documentation are included in Jkttachment B. M 5.0 CONCLUSIONS AND RECOMMENDATIONS k 5.1 Conclusions Groundwater beneath the site was generally encountered at 3.depth of approximately 6-7 feet bgs. Residual petroleum hydrocarbons are present in shallow saturatedsoil and groundwater beneath the site. Soil contamination appears to be limited to depths between approximately 6 and 13 feet bgs and is generally' found in the area immediately adjacent to the former USTs to the south and west. Residual contamination in! the soil appears to attenuate rapidly, as no contamination w detected in any soil samples collected from 15� feet bgs or below. An estimated 1,300 cubic yards of soil b tween the depths of approximately 6 and 13 feet, bgs has been impacted beneath the site. Figure 3 shows the estimated extent of soil contamination at the site. The lateral extent of shallow groundwater contamination be ricath the site is largely defined to the north andil the south, but has not been fully defined to the west or the east. Groundwater apparently flows toward the: southwest based on the estimated configuration of the dissolved contaminant plume. This presumption is; supported by the known groundwater gradient at a nearby site, according to Mr. Harlin Knoll of PHS/EHD. it The estimated extent of dissolved TPHG and benzene contamination in groundwater beneath the site is l presented on Figures 4 and 5,respectively. i 5.2 Recommendations ,f Based upon field and analytical data collected during thi investigation, Ground Zero recommends the installation of 4-5 groundwater monitoring wells to further refine the lateral extent of soil and groundwater contamination beneath the site. Recommended locations o proposed monito Figure 6. ring wells are presented on Based upon site conditions, active interim soil and/or ground water remediation may prove problematic. Soil excavation would require the removal of approximately 1,100 cubic yards of uncontaminated overburden and approximately 1,300 cubic yards of contaminated soil. In addition, virtually all of the contaminated soil lies within the saturated zone and its removal would require careful handling as a result. The removed contaminated soil would likely require spreading to aerate/ vaporate the water prior to disposal. Interim groundwater remediation could consist of pumping and disposal of groundwater from the excavation. This interim measure would not likely be effective if impacted soil is not also removed. Another alternative, if I` approved by PHS/EHD and the UST Cleanup Fund, would be to mix Oxygen Releasing Compound (ORC) with fill material prior to backfilling the excavation. Adding the ORC compound could be an effective method of promoting the bacterial growth necessary for ective bioremediation of residual petroleum hydrocarbon contaminants in both soil and shallow ground r in the vicinity of the former USTs. Any interim remedial measure for soil and/or groundwater co itamination will likely be dictated by economic IM feasibility related to potential development of the property. 6.0 CERTIFICATION Signature of this report certifies that Ground Zero's professional services have been performed, our findings manserZsummary.doc