SITE INFORMATION AND CORRESPONDENCE

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ti.. l Ms. Wendy Cohen/Attn: Ms. Polly Lowry Regional Water Quality Control Board October 12, 1995 RE: Ground Water investigation And Containment Of Chloroform Plume Triple E Produce, Tracy, San Joaquin County Page 2 Recharge was included in an attempt to simulate the effects of the ongoing ground water aeration which Triple E employs as part of its bioremediation activities. The simulated capture zone would be larger than shown if recharge was not included in the model, or if recharge was less. The capture zone predicted by the modeling is mentioned in the text of the Revised Work Plan on page 8, paragraph 5, and in Section 3.4, The Effect Of Pumping On Downgradient Monitoring Well MW-7. 2. Alternative to MW-4A Monitoring well MW-4A has experienced several years of constant pumping as part of the biological remediation program used by 'Triple E. This pumping has demonstrated an attainable yield on (lie order of 5 gpm. if this rate can not be sustained, it is very likely that additions of biological amendments to the well has resulted in clogging of the well screens. For this reason, improvements in well yield can occur from redevelopment. Redevelopment is significantly less costly than a new well and can be performed several times for a fraction of tine cost. If redevelopment does not produce adequate flow, a combination of pumping from MW-4A and MW-2 will be used. Triple E currently pumps from MW-2 for its bioremediation activities and all electrical and piping has been installed. Combined pumping from both wells should succeed in attaining the 5 gpm design goal. 3. Details of Construction and Development of XW-1 in the addendum to the Revised Work Plan submitted 15 August 1995 (See Soil Sampling, page 4, paragraph 5.3.5), the proposed chloroform level to determine the handling and disposal of soil cuttings from below the water table was inadvertently written as 45 mg/kg. The level should be 4.5 mg/kg. Tine rationale for using 4.5 mg/kg of chloroform is based on the Designated Level Methodology, page 39, Equation 181 and that the site conditions at the Triple E facility are considered to be typical of conditions encountered throughout the Central Valley. Triple E, therefore, used the general environmental attentuation and leachability factors for the purpose of determining the handling and disposal of below-water table soil cuttings from the installation of XW-l. In view of the fact that the Proposition 65 water quality criterion level for chloroform is 4.5 µg/L, that the general attenutation factor is 100, and that the leachability factor is 10 (Designated Level Methodology, 1989, page 37), 'Triple E believes that a level less than 4.5 mg/kg of chloroform in the soil cuttings will provide protection for the underlying ground water from the disposal of the cuttings on the soil surface at "appropriate locations on site". N&I n CONDOR