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r ADDITIONAL ASSESSMENT WORKPLAN COLBERG BOAT WORKS APRIL 2001 The results of the investigation were documented in Apex's report titled Results of Subsurface Investigation dated August 21, 1997. Colberg has been monitored quarterly for petroleum hydrocarbon constituents in the groundwater since July 1997. In September 1998, Apex submitted aremediation plan entitled Workplan for.Pilot Test and Feasibility Analysis for removal of hydrocarbons from groundwater. An Addendum to Workplan for Pilot Testing and Feasibility Analysis was resubmitted in January 1999. Prior to acceptance of the remediation plan, the County requested a mass balance calculation to determine whether remediation was necessary. In April 1999, Apex submitted a report entitled Mass Balance for Remaining TPH.G. Upon review of the report, the County determined that the extent of contamination had not been tdelineated east of MW-3. Based on the response of the County,Apex submitted a Workplan for Additional Subsurface d Site Characterization dated June 9 1999. On r Investigation an � September 29, 1999, Apex I. 6� g personnel implemented the Workplan and installed five geoprobes at the site to establish the extent of petroleum impacted groundwater east of monitoring well MW-3. The data obtained from the investigation was incorporated into a report entitled Estimated Mass of Petroleum Hydrocarbon Constituents Remaining in Groundwater, and submitted to the County on February 8, 2000. GHH assumed consulting responsibility for the site in May 2000. The County responded to the February 2000 Apex report in February 2001 by requesting additional soil and groundwater investigation east of MW-3 and soil boring SB-21 as shown on Figure 2. The County letter is included in Appendix A. Objective L. The objective of this Workplan is to present a scope of work which will evaluate the extent of impacted groundwater where it is currently undefined on the eastern portion of the site. This Workplan addresses the areas of concern with a screening investigation consisting of six geoprobes to approximately 15-feet below ground:surface (bgs). Soil and groundwater samples collected during the geoprobe investigation will be analyzed to determine the amount of hydrocarbons and oxygenates present at the site. Samples will be analyzed for the presence of total petroleum hydrocarbons as gasoline (TPH G); benzene,toluene ethylbenzene, and xylenes (BTEX); 1;2-dichloroethane 1,2 (DCA); ethyl dibromide (EDB); and oxygenated fuel additives including methyl-tertiary-butyl-ether(MTBE), DIPE, ETBE, TAME and TBA using EPA Methods 8015 Modified, 8020, and.8260B, respectively. Upon review and analyses of the screening investigation results, one to two additional groundwater monitoring wells may be installed to define the extent of impacted groundwater to the east of MW-3 and provide repeatable sampling data points. 2 I'�