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C L E A R W"A" T ER rc ROLP [ \ ( E-mental Services rsummarized on Table 2, and shown graphically on Figure 4 Copies of the laboratory report and chain- of-custody form are attached rDistribution of Residual Contaminants in Groundwater Dissolved-phase contamination in groundwater samples continued to be detected only in very low r levels this monitoring event All wells except MW-1, MW-2, and MW-6 were completely non-detect for all contaminants Maximum contaminant levels found in these three wells were TPHg 550 µg/L (MW-1), Benzene 2 6 tig/L, and MTBE 78 pg/L (MW-2) The samples collected from both sparge wells, screened deeper than the other monitoring wells, were P P g P g r also free of detectable contaminant concentrations This is noteworthy in that the results effectively delineate the vertical extent of residual dissolved-phase contamination on-site Additionally, the domestic well continues to remain free of gasoline contaminants The Fuel Oxygenate MTBE was the only oxygenate detected in groundwater samples MTBE was detected in MW-1 (6 3 lig/I ) and MW-2 (78 pg/I) No other Fuel Oxygenates (TBA, ETBE, DIPE, TAME) rnor Lead Scavengers (1,2-DCA, EDB) were detected in any groundwater sample-, collected Recent and cumulative groundwater sample aralytical data are summarized on Table 3, and is shown on graphically on Figure 5 Copies of the laboratory report and chain-of-custody form are attached �Q Discussion I� Confirmation soil sampling was conducted to compare pre-remediation hydrocarbon contammarion levels, both in soil and groundwater, to those levels following the successful operation of the SVE/AS system Soil borings were advanced in locations along a cross section through the area estimated to be the extent of pre-remediation groundwater contamination A comparison of pre- to post-remediation levels of soil contamination at various depths across the site is sheKn on Table 4 Based on the results of the confirmation soil samples, it appear-, that the last of The residual soil contamination exists at the bottom of .he former south underground storage tank (Figure 4) The 10 foot depth level in CB1 corresponds io this location. At this location, pre-remediation levels of gasoline in soil were X10,000 mg/kg (Table 4) The results from the -,amples rn CB1 indicate a post-remediation level of 230 mg/kg at this 10 foot depth level At the -;,iine depth at the base of the former north underground storage tank pit, pre-remediation levels ref gasoline in soil were also X10,000 mg/kg Results from the sample at 10 feet bgs to CB2 indicate a post-remediation level of gasoline in soil of <1 mg/kg rIn Clearwater's Problera Assesswent Report Feasivilttif Smdy, and Rentediai Action Plan, dated • February 21, 1996, the total ma-,s of gasoline in the vados- zon. pi for to remediation waS estimated to be 5,050 lbs , or 842 gallon-, of gaEoline U�[ng the sanic formula as Stated .i theft report, the post- remediation remaining coracim.rant mass c in M,i estimate'. ZB107C Conf Borings/GWVR 1Q00 S March 27, 2000