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M Daniel Villanueva From: Daniel Villanueva < dvillanueva@advgeoenv.com > Sent: Tuesday, January 24, 2012 2:58 PM To: ' Lori Duncan [EHJ' Cc: bmillman@advgeoenv.com; wlittle@advgeoenv.com; Robert E. Marty (rm arty@advg eo env.co m) Subject: 602 California Street, Stockton, CA - Stallworth Auto Sales - Baseline Sampling Ms. Duncan, Advanced GeoEnvironmental (AGE) staff has reviewed the San Joaquin County Environmental Health Department (SJCEHD) directive letter dated 15 December 2011 for the site located at 602 California Street, Stockton, California . In the directive letter SJCEHD staff made several comments on the AGE-prepared Ground Water Remediation Feasibility Study Work Plan, dated 31 October 2011. Among the comments SJCEHD states that'.. "baseline alkalinity measurements must be taken to determine the amount of acid that would be necessary to reduce the pH level to the appropriate level to maintain solubility of the iron ." Additionally, SJCEHD states that... "baseline iron content in the groundwater should also be taken into consideration to determine the dosing requirement" . AGE agrees with SJCEHD that baseline alkalinity and dissolved iron content is an important consideration in design of the above pilot test and provides the following recommendations prior to re-submitting a revised Ground Water Feasibility Study Work Plan for the site: • Ground water samples should be collected from wells MW1A, MW-2, MW-6, MW-7, MW-8 and MW-10 and analyzed for dissolved iron and alkalinity; wells sampled should provide an adequate representation of the dissolved plume conditions in the "core" area of the plume where conditions are likely highly anaerobic and on the fringe of the "core" area of the plume where conditions are expected to more aerobic; • The recommended method for analyzing for dissolved iron and alkalinity from above selected monitoring wells is low-flow purging (defined as less than 1 L/minute and low-flow sampling as defined at less than 300 mL/minute) . The wells will be purged with a low-flow peristaltic pump with disposable tubing, or a low-flow down hole pump with the capability to reduce flow rates. Purged ground water will be monitored through a flow-through cell, not exposed to the atmosphere, for pH, conductivity and temperature. The volume of purged ground water will be limited, not reducing the water level within the wells, during purging. The purge of ground water will continue until ground water parameters have stabilized. Dissolved oxygen (DO) and oxidation reduction potential (ORP) parameters will be monitored from down-hole probes within the upper two feet of the water table; measurements will be collected prior to purging, during each purge volume and after the final purged volume of water. The ground water samples for dissolved iron and alkalinity analysis will be collected within zero-head space or air-less containers (septa sealed 500-mL amber container) . The samples for analysis will collected through the purge tubing and discharged to the inside base of the containers until filled. This will be required to reduce the exposure of the ground water to atmosphere conditions. Inline sample filtration with a 0.45 micron-filter will be also be conducted during the purging and monitoring. • Results from the baseline sampling would be provided as findings in the Revised Ground Water Feasibility Study Work Plan and would be used to further develop the work plans injection procedures. AGE would also like to request an extension to the submission due date of the Revised Feasibility Study Work Plan provided in the above referenced letter. AGE is requesting the extension so that the proposed wells can be sampled and data gained from the sampling can be evaluated in the revised work plan. 1