SITE INFORMATION AND CORRESPONDENCE

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Ms. Daisy Wei . - 2 - • 3 April 2012 - The soil data obtained in the former bagging plant area suggest that the soil buffering capacity has been consumed, resulting in acidic soils which may be resulting in aluminum toxicity, as the Root Zone Work Plan suggests. In our 15 March conversation, Ms. Wei proposed mixing agricultural lime with the trench backfill in order to raise the pH to about pH 6. In a 26 March telephone conversation with Ms. Wei, we agreed that the amount of agricultural lime shall not exceed 75 pounds per trench, as configured in the Root Zone Work Plan. Additional soil analyses that would assist Koppel in interpreting the soil condition include cation exchange capacity, and percent base saturation. The cation exchange capacity provides an estimate of the number of cationic exchange sites available on the soil surfaces, and the percent base saturation provides an analysis of what cations occupy what percentages of these exchange sites. Koppel should also obtain soil samples from a healthy area of the phyto- remediation planting (near normal pH) to analyze for soil pH buffering capacity, cation exchange capacity and percent base saturation. This data enables a site-specific standard of comparison, and it may indicate if other soil areas will be expected to also turn acidic in the near future. Cleanup Goals in Soil In our 15 March conversation, Ms. Wei referenced a cleanup goal for nitrogen in soil as 200 mg/kg for the sum of nitrate as nitrogen plus total Kjeldahl nitrogen. While this is the cleanup goal expressed in Central Valley Water Board staff's 16 May 1997 letter and reiterated in its 20 January 2000 Memorandum, Central Valley Water Board staff recognize that total Kjeldahl nitrogen is not a good indicator of a pending nitrogen impact to groundwater. Instead, the 200 mg/kg goal for nitrogen sources in soil should be the sum of nitrate as nitrogen and ammonium. Ammonium Treatment in Soil Koppel may wish to consider spot treatments of ammonium in soil. Some treatments that have been successful at other locations include incorporating woody mulch into the soil. The woody material provides a carbon source for microbial degradation, and the microbes obtain their nitrogen requirements from the soil ammonium. Application of humic acids may be another means of promoting microbial degradation of ammonium. Monitoring Wells Several of Koppel's monitoring wells are on Port of Stockton property and occasionally have been difficult to locate due to overburden. Of these wells, Koppel may wish to consider destroying monitoring wells MW-8S, MW-7S and MW-7D. These wells are no longer needed to define the extent of the pollution or measure upgradient concentrations. Monitoring wells MW-9S and MW-12S now provide that function. If Koppel wishes to destroy MW-8S, MW-7S and MW-7D, it must provide a work plan to Central Valley Water Board staff for concurrence. Meanwhile, Koppel plans to install flexible stakes to identify the locations of these wells for future monitoring events. Central Valley Water Board staff concur with this interim measure.. Aquifer Test The Root Zone Work Plan proposes an aquifer test at monitoring well KP-3. In our 15 March 2012 discussion, Ms. Wei proposed that the aquifer test is to determine if the aquifer could not provide a sustained yield of 200 gallons a day. This threshold is identified in the Basin Plan as one of the criteria that could lead to the Central Valley Water Board removing a groundwater basin from the beneficial use designation of being suitable for municipal or domestic uses. The process to present a proposal to the Central Valley Water Board to consider delisting a