ARCHIVED REPORTS_MONITORING WELL INSTALLATION AND BIOSPARGE EVALUATION REPORT

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Former Columbo/Toscana Bakery - 2 - 29 April 2009 1444 S. Lincoln St., Stockton inconclusive data results for the 2008 TS pilot test. As a result of the inconclusive 2008 pilot study, PSC requests collection of additional site soil and groundwater data during installation of the new monitoring wells, for the purpose of further assessment of the viability of the remedy prior to submitting . a workplan for a biosparging pilot study. Per PSC, the proposed new wells installation and sampling will take up to 5 weeks to complete, including drilling and additional saturated soil sampling and analyses consisting of intrinsic permeability of the aquifer zone, dissolved iron, total aerobic heterotrophs and total aerobic hydrocarbon degraders (bacteria population), ammonia as nitrogen, total organic carbon, phosphorous as ortho-phosphate, and sulfate. Additional groundwater sampling would include alkalinity as CaCO3 for CO2, and ferric and ferrous iron. TheEvaluation includes a section titled Preliminary Plan for Biosparge Pilot Test, which does not ' provide the level of detail necessary for a pilot study workplan, but does include discussion of baseline groundwater sampling prior to the pilot study, including ammonia as nitrogen, nitrate-nitrite, orthophosphate, bacteria population, biological oxygen demand (BOD),-and chemical oxygen demand (COD). During the pilot study, PSC would conduct an evaluation of the effects of impermeable layers ' on airflow, and determine injection bubble radius and oxygen consumption rates. Inclusion of the full scale system design will be included in a Remedial Action Plan at some unspecified future date. The Workplan states Sara.Lee has an agreement with the neighboring former Texaco.(TX) and other nearby sites to co=monitor wells on the same quarter y sc e u e an to are ata ort a sties; wit the eventual goal to reduce the number of new wells needed for monitoring the inferred commingled plume. The Site wells will use the new designation "CT_" (Columbo/Toscana) followed by "MW- (well number) - (screened zone depth bgs)". The three proposed wells are shown on air photograph Figure 10 as: • CT—MW-8-80 and CT—MW-8-120 are located approximately 20'to 40' southwest of the former USTs (near A-zone well TX—MW-14). • CT MW-9-120 is located approximately 200' east of the former USTs (near B-zone well TX—MW-21-80). The proposed wells were designed to address the following data gaps at the Site: . ' hydraulic conductivity for all aquifer zones, horizontal and vertical groundwater gradients, • lateral and vertical extent of contamination, • determination of extent of onsite impacts versus offsite sources impacts to the site. 1 A schedule with proposed dates of the tasks necessary for the implementation of the Workplan was not, provided in the Workplan. 1 The VIS Report provides the results of the shallow soil gas survey conducted to evaluate potential threats from vapor intrusion to workers at the Site, a construction company warehouse in a commercially zoned block, with no known plans for redevelopment as residential housing, schools, or day care centers. Eight shallow soil gas probes (SG-Test [tank pit] and SG-1 through SG-7) were �., installed and sampled in and around the building for petroleum hydrocarbons constituents as vapor. Although maximum results were reported at SG-4 as TPHg, 18,000 minrams per cubic meter (ug/m); benzene, 68 ug/m3; toluene, 1,800 ug/m3; ethylbenzene, 62 ug/m ; and xylenes, 222 ug/m3; 1 the VIS Report states the SG-4 data are suspected as unrepresentative of Site conditions (higher that actual) due to sampler error when insufficient purging resulted in a lower than usual sample volume collected in the Summa canister, reportedly by over tightening of line connections that caused restriction in the vapor line to the Summa canister during leak testing prior to sample collection. r