SITE INFORMATION AND CORRESPONDENCE_1992

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Work Plan Addendum -6- 21 September 1992 DORW, Sharpe 4. Annular seals for the monitor wells are to be constructed using a cement slurry composed of up to 20 gallons of water per sack (94 pounds) of cement. This volume of water is unacceptable because the integrity of the well seal will be compromised if 20 gallons of water per sack of cement is used. Twenty gallons of water is almost four times the recommend volume of water (5.2 gallons) per sack of cement (94 pounds) for Class A cement with a yield of 1.18 cubic feet per sack. For each percent of bentonite added, 5.3 percent water should be added for the slurry mixture. 5. The Work Plan Addendum states that four additional monitor wells will be installed in the investigation of the non-fuel USTs. Three monitor wells will be installed in the areas of USTs No. 48 (waste oil ) and No. 71 (waste oil/ contaminated fuel ) . The fourth well will be installed as a replacement to MW- 472A which will be destroyed when the excavation for UST No. 27 is conducted (page 2-26) . PCBs were detected in the sample from MW-472A at 90.9 Ag/l , which exceeds the Primary MCL of 0.5 Ag/l . Sharpe may need to consider the installation of deeper monitor wells in the area of UST No. 27 due to the high concentrations of PCBs found in MW-472A and thus, the potential for the presence of dense non-aqueous phase liquids (ONAPLs) . 6. The Work Plan Addendum states that if the amount of the soil contamination exceeds approximately 500 cubic yards (in the investigation of the non-fuel USTs) , that additional soil borings and monitor wells may need to be installed to define the extent of soil and ground water contamination (page 2-30) . The Addendum appears to indicate that if these borings and wells are needed, they will be installed in the same phase of investigation. If additional borings and wells are needed, Sharpe should inform the Project Managers of the status of the investigation for their concurrence. If a sufficient number of borings and wells are needed, a work plan, preferably informal , should be prepared to document the rationale for the placement of these additional borings and wells. 7. In the investigation of the pesticide mix area, soil samples were collected and analyzed for organochlorine (OC) pesticides, chlorinated herbicides and bromacil (pages 3-1 and 3-3) . Soil samples apparently were not analyzed for organophosphorus (OP) or carbamate pesticides. The OP pesticides tend to be comprised of primarily of insecticides, the carbamate pesticides tend to include herbicides and insecticides whereas, the OC pesticides include herbicides, fungicides and insecticides. Insecticides tend to be more persistent in the environment, as demonstrated by the high concentrations of chlordane and DDD, DDE and DDT found in the soil samples in the pesticide mix area. In addition, the breakdown products or metabolites of the OP pesticides are toxic. The existing studies indicate that soil samples were analyzed for selected pesticides, rather than conducting a screening for all potential types of pesticides. Because this area was used for pesticide mixing, the initial studies should have included screening for all of the different types of pesticides. Due to the lack of a complete screening of pesticides, confirmation sampling in the pesticide mix area should include analyses for OP and carbamate pesticides, in addition to the OC pesticides. We have previously written in our 17 April 1992 letter regarding the need for a wider screening of pesticides.