ARCHIVED REPORTS XR0000218 - Laserfiche WebLink

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manner are not in accordance with SJCEHD requirements As a result, the SJCEHD inspector requested that the well be destroyed and replaced with a new monitoring well In addition, SJCEHD records indicate that the well was placed within a 30-centimeter (12-inch)-diameter boring instead of ' a 25-centimeter (10-inch)-diameter boring as was previously indicated on the well description provided by Caltrans tThe monitoring well was destroyed using a truck-mounted hollow-stem auger BK-81 drill rig The well was destroyed with the approval of the SJCEHD by overdrilling the casing and boring with 30- centimeter (12-inch) augers to 25 5 meters (85 0 feet) below ground surface (bgs) The overdnlling was performed for the purpose of removing the monitoring well casing, sandpack, sanitary seal, and ' cement grout The monitoring well was backfilled with neat Portland cement grout mixed at a ratio of 19-liters (5 gallons) of water per 38 kilogram (94-pound) sack of cement and approximately 3% bentonite The grout was introduced into the boring with a tremie pipe extending to the bottom of the drilled hole The cuttings from the overdrilling of the well were contained in Department of Transportation (DOT)-approved 209-liter (55-gallon) drums and subsequently stored onsite pending laboratory analysis Following the destruction of the monitoring well, a new monitoring well (MW-14A) was installed 1 approximately 0 9 meter (3 feet) northeast of the destroyed well by advancing a soil boring to a maximum exploration depth of 18 2 meters (60 feet) bgs using a truck-mounted hollow-stern auger BK-81 drill rig The approximate location of the well is depicted on Figure 2 Soil samples were collected at approximate 1 5-meter (5-foot)-intervals The 25 4-centimeter (10-inch)-diameter soil ' boring was constructed as a 10 16-centimeter (4-inch)-diameter groundwater monitoring well using a 1016-centimeter (4-inch)-diameter schedule 40 PVC casing The well was screened from approximately 12 to 18 2 meters(40 to 60 feet)bgs with 0 508-millimeter(0 020-inch)-slotted screen PVC casing A filter pack consisting of Colorado No #3 silica sand was placed around the well screen from the total depth of the boring to approximately 0 3 meter (1 foot) above the top of the screen The well was surged after the placement of the sand to assure proper settlement of the filter pack An approximate 0 6-meter(2-foot) thick seal consisting of hydrated bentonite chips was placed above the filter pack Above the seal, a cement grout was placed to within 0 15-meter (0 5 foot) of surface grade The well cap was secured with a locking cap and completed within a 30 48-centimeter (12-inch) traffic-rated well box secured with concrete cement The top of casing elevation of the well was surveyed by a licensed surveyor Well construction details are presented on the bonnglwell log in Appendix B ' Soil cuttings, decontamination fluids, and purge water generated during the drilling and sampling activities were stored onsite in labeled DOT-approved 209-liter(55-gallon) drums The drums will be subsequently picked up by ABCO Environmental and transported to a disposal facility Project No 58475-06-02 -5- December 26,2001