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Former Exxon Service Stat,jn #73942 - 2 - — 21 August 2014
<br /> 4444 Pershing Ave., Stockton
<br /> San Joaquin County
<br /> above background, not to exceed the water quality objectives. Please submit a work plan to
<br /> determine background levels for; sodium, sulfate, nitrate, ammonia, iron, manganese, cadmium,
<br /> chromium, hexavalent chromium, bromate, lead and total dissolved solids.
<br /> The monitoring plan proposed by Cardno includes analysis for petroleum hydrocarbons, methane,
<br /> totals dissolved solids, total organic carbon, ions: chloride, nitrate, sulfate, sulfide and metals:
<br /> iron, chromium, phosphorus, barium, cadmium, calcium, copper, lead, magnesium, manganese,
<br /> mercury, molybdenum and nickel on a quarterly frequency. The monitoring program may be
<br /> reduced to include analysis for petroleum hydrocarbons, sodium, sulfate, nitrate, ammonia, iron,
<br /> manganese, cadmium, chromium, hexavalent chromium, bromate, lead and total dissolved solids.
<br /> Sampling and reporting on a quarterly frequency should be sufficient and should continue until
<br /> you have demonstrated that concentrations of injectant and any by-products have stabilized and
<br /> are shown to be reducing to achieve background in a reasonable time.
<br /> The wells selected as compliance zone wells are greater than 270 feet from the injection area.
<br /> Given this distance and an estimated groundwater flow of 10 to 100 feet per year (Cardno
<br /> estimates hydraulic conductivity of 10 feet per day in the Notice of Intent, is unlikely) it could take
<br /> 2 to 20 years for groundwater to reach these wells. Therefore, a lengthy commitment to monitor
<br /> the injection project will need to be made given the current design of the project. I suggest you
<br /> reconsider the assignment of wells identified as transition and compliance wells for the injection
<br /> project. Use of the treatment zone could remain as proposed and with the installation of an
<br /> additional transition zone well northwest of V3, then RW4 and MW10 could be used as the
<br /> compliance zone wells.
<br /> The Contingency Plan proposed by Cardno proposes to increase the frequency of monitoring if an
<br /> order of magnitude increase in TDS and /or sulfate is observed in transition zone wells. Cardno
<br /> proposes to stop injecting if TDS or sulfate concentration increase by an order of magnitude in
<br /> compliance zone wells. Although stopping injection may be appropriate, these proposed
<br /> activities may not be sufficient to address impacts that occur as a result of driving pollutants
<br /> down-gradient through the addition of up to 36,000 gallons of water with 5% injection solution.
<br /> Additional active remedial steps need to be proposed if increases greater than 20% above
<br /> background or above water quality objectives are observed in compliance wells. A Plan to
<br /> actively reduce deleterious by-products needs to be developed such that activities can be
<br /> implemented in a short turn-around time and effectively reduce and control migration of
<br /> compounds that degrade the beneficial uses of the groundwater in this area.
<br /> Please submit a Work Plan for developing background for: sodium, sulfate, nitrate, ammonia, iron,
<br /> manganese, cadmium, chromium, hexavalent chromium, bromate and total dissolved solids by
<br /> 30 September 2014. In addition, prepare a more aggressive approach to correcting any potential
<br /> adverse impacts caused by the injection of PersulfOx and include this as an Addendum to the
<br /> Notice of Intent by 30 September 2014.
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