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KLEINFELDER EXPECT MORE" 5 MONITORING WELL DISINFECTION The RWQCB has requested this workplan to include a plan for disinfection of groundwater monitoring wells that contain detectable concentrations of total coliform and to confirm if the disinfection has been effective. The following is a plan per the RWQCB's request. The RWQCB has not developed a guidance document for this process specifically for monitoring wells. Therefore in developing this plan, Kleinfelder has reviewed several documents related to disinfection of drinking water wells from the American Water Works Association (AWWA) and the California Groundwater Association (CGA). The RWQCB has indicated that wells exhibiting positive results for total coliform should be disinfected. Prior to disinfection activities, each of the new wells and the existing affected wells will be developed as summarized in Section 3.1. For those wells with detected coliform additional efforts will be made to remove sediment from the base of each well. If the suction pump methodology is not sufficient for removing sediment from the bottom of a well using, a pneumatic well development tool will be used in an effort to remove potentially contaminated sediment within the well casing. Greater than 48 hours after development and sampling of the affected wells, liquid chlorine bleach will be added to the wells at a volume and concentration calculated to provide a chlorine solution of 50 parts per million of the calculated water in the respective casing volumes of the affected wells. The intent of adding the chlorine will be to meet the chlorine demand of each individual well and to provide free residual chlorine in the well, which will then become an effective disinfectant to the coliform bacteria detected. The methodology of disinfecting the wells will be as follows: • Loose debris, sediment, organic residue, etc will be removed from existing exterior casings and near surface internal portions of the casing. These surfaces will be wiped with a 50 ppm chlorine solution. Installation of new wells will include new, individually wrapped casings and will be handled with new polypropylene gloves during installation. Existing well caps/pressure caps will be soaked in a chlorine solution of 50 ppm. New wells will be provided with new pressure caps • The disinfectant including 50 ppm chlorine solution will be poured slowly into the respective wells by wetting the inside portions of the casing circumference. • The wells will be surged using a surge block to distribute the disinfectant throughout the water column and well sand pack. The wells will be surged for approximately 10 minutes. The diameter of the surge block will be close to the interior well diameter of the well casing such that surging will lift the water column and create a flushing action in the sand pack located above groundwater (as applicable to the individual well). 48093.E01/ST07R052/CJC/Iv Page 9 of 15 ©2007 Kleinfelder, Inc January 26, 2007