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Public Works 2 27 July 2016 1810 HazeIton Avenue Stockton, San Joaquin County An MRP is needed to establish which Site wells will be used to monitor background (naturally occurring constituents), identify treatment, transition, and compliance zone wells, and detail the frequency of sampling and constituents to be analyzed at each well. Background wells should be located outside the area of petroleum impacts, and have historically not had any detections of pollutants, such as Site well MW-7. The need for establishing background levels of metals in groundwater is due to the potential production of harmful byproducts caused by the use of strong oxidizers, such as ozone, in the subsurface. Treatment zone wells should be located within the area of proposed active ozone injection, and transition zone wells should be located just down-gradient of the active injection area. Compliance zone wells should be located down-gradient from the transition zone wells, outside of the area of active injection but not greater than 50 feet from the injection area. An example zone setup diagram is included as Attachment D of the General Order. Please identify treatment, transition, and compliance zone wells in the MRP to be submitted as part of the NOI Addendum due 30 October 2016. The network of existing and proposed wells does not allow for the establishment of proper transition and compliance zone monitoring. Additional monitoring wells need to be proposed to align this project with the General Order in order to operate under this permit. By 30 September 2016, please submit a Work Plan which proposes additional downgradient monitoring wells for transition and compliance zone monitoring related to proposed ozone injection. Analysis of samples from background wells must include at a minimum: arsenic, total chromium, hexavalent chromium, bromide, and total dissolved solids (TDS). Background sample concentrations are used to establish Action Levels. An Action Level is set at 20% above the naturally occurring background concentrations. If background levels already exceed the Water Quality Objective (WQO), the Action Level is set at the background concentration and is not allowed to increase in compliance zone wells above what is naturally occurring. The WQ0s for arsenic, total chromium, hexavalent chromium, bromide, and TDS are 10 ug/L, 50 ug/L, 10 ug/L, 2,300 ug/L, and 450,000 ug/L, respectively. Analysis of background samples should be performed by methods that provide Practical Quantitation Limits (laboratory reporting limits) that are lower than the WQ0s to comply with the requirements of the General Order, and provide usable data. Please identify background wells and provide background data (including above listed analytes) as part of the NOI Addendum 30 October 2016. A Contingency Plan is needed to detail actions that will be taken in the event that chemicals of concern in compliance zone wells exceed Action Levels. A Contingency Plan must include more than just discontinuing injection, but must also state active steps that will be implemented to reduce concentrations of constituents exceeding Action Levels. Please submit a Contingency Plan which includes calculated Action Levels as part of the NO1 Addendum due 30 October 2016. The lateral and vertical extent of the petroleum hydrocarbon pollution in groundwater has not been defined to the Water Quality Objects at this Site. MW-4 recently contained concentrations of MTBE of 11 ug/L, which is above the WOO of 5 ug/L. Additionally, the distance of approximately 230 feet between MW-3 and MW-4 is not adequate for delineation