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Human Services Agency - 2 - 2 August 2021 145 South Sutter Street Stockton, San Joaquin County the Contingency Plan to be overly complicated and impractical, and requested further revision of the Contingency Plan, which Weston proposed in the Revised Addendum. Central Valley Water Board staff concurs with the proposed BOS-200 remedial action, as long as the following comments are incorporated: 1. In the Work Plan, Weston proposed a single baseline sampling event. However, in order to establish effective Action Levels, staff requests a second baseline sampling event performed at least 30 days after the first, with analysis to include Suite B as summarized in Table 4 and Table 5 below. 2. In the Work Plan, Weston proposes nitrate and sulfate to be part of analytical Suite A. However, as Suite A includes hydrocarbons, and Suite B includes remedial parameters, staff requests that nitrate and sulfate be included as part of Suite B. 3. In the Work Plan, Weston proposes to perform remedial monitoring at different frequencies for treatment and compliance zone wells. Weston also proposes initial remedial sampling 3, 6, and 12 months after injection. Staff requests that both treatment and compliance zone wells be sampled on the same frequency. In order to better monitor the potential production of deleterious byproducts, please perform sampling monthly for the first 3 months and quarterly after that for the first year. After the first year, please reduce the monitoring frequency to semi-annual, as proposed. 4. In the Work Plan, Weston proposes to perform initial compliance zone sampling with Suite B analysis 12 months after injection. Staff requests that Suite B analysis frequency match that of Suite A since Suite B analytes are used to evaluate the potential production of deleterious byproducts. 5. In the Revised Addendum, in the event that concentrations of selected remedial parameters in compliance zone wells exceed Action Levels by 20%, Weston proposes to collect confirmation samples 30 days after the initial exceedance and then perform batch extraction if exceedances persist. Weston proposes to sample the wells again after batch extraction and perform additional rounds of batch extraction as needed if exceedances remain. However, in the event that exceedances remain after batch extraction, staff requests that you please collect confirmation samples 30 days later, before performing another round of batch extraction. 6. By 5 November 2021, please submit the results of the amendment analysis and two rounds of baseline sampling as discussed in Tables 3 and 5 below.