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16777 Howland Road, Lathrop, IW -2 Destruction Proposal <br />Page 2 <br />do not indicate the above conditions have been met at the time of installation. Therefore the <br />conductor casing must be removed. <br />Section 4.2: Aquifers penetrated that contain poor quality water shall be sealed to prevent <br />contamination. Arcadis stated the groundwater below the Corcoran to be of poor quality, but the <br />requested variant does not prevent migration between different aquifers or strata, nor does it meet <br />this requirement. <br />The Central Valley Regional Quality Control Board Water Quality Control Board (the Basin Plan) <br />for the Sacramento River Basin and San Joaquin River Basin, does not distinguish between <br />groundwater aquifer from below and above the Corcoran Clay layer for beneficial use. All <br />groundwater as defined under the Basin Plan is designated for beneficial use. <br />Arcadis stated detonation as a destruction method is a concern since it may result in "fracturing" <br />of the Corcoran Clay layer, and potential for migration of poor quality groundwater from below the <br />said layer to the good quality groundwater in the aquifer(s) above the Corcoran Clay. EHD was <br />unable to find any published literature supporting this concern, as most fracturing is related to the <br />bedrock rather than in a sedimentary layer. Where fracturing is performed in clay, most literature <br />cited hydraulic fracturing rather than by explosives. Based on conversations with several <br />contractors, the amount of grains in the explosive charges can be controlled to minimize the zone <br />of effect if "fracturing" of the clay is a concern. <br />Arcadis stated two rounds of sand removal by development/bailing between October and <br />December (year not specified) were unsuccessful, but no details were provided. The EHD was <br />not consulted before this sand removal attempts nor was the EHD on site during the attempts. <br />These two attempts are insufficient to warrant nor approve the requested variant to leave the sand <br />behind, as the SJC Well Standards requires removal of all obstructions as already referenced <br />above. <br />If you have any questions please contact Jeffrey Wong, Lead Senior Environmental Health Specialist, at <br />jwong@sjgov.org or (209) 468-0335. <br />A6C--2�1 <br />Steven Shih, REHS <br />Program Coordinator <br />