ARCHIVED REPORTS XR0012691 - Laserfiche WebLink

Home Browse Search

BC&D Property Phase 11-Ground Water Assessment Proposal Page: 3 drilling,soil samples will be collected to characterize the strata and correlate this work with the previous investigation. One monitoring well(MW 6)will be installed into the second aquifer. In construction of this well,the upper aquifer will be cased before drilling through the aquitard into the second aquifer. A large diameter hole will be drilled to a depth of about 15 or 16 feet using a 10-inch auger. The depth may vary slightly depending on the depth of the interface between the sand(first aquifer)and the clay(aquitard)layer. After this hole has been bored,the auger will be removed an 8-inch PVC casing(schedule 80)will be installed into the hole. The casing will be driven into the aquitard a distance of 1 foot forming a water-tight seal. This will isolate the upper water layer from the drill hole and prevent an interchange of ground water between the two aquifers. Drilling will continue down thrm;igh the second aquifer with a 7.25-inch hollow stem auger. Continuous split spoon sampling will be performed through the second aquifer into ' its lower bounding clay layer. Into this hole a 2-inch monitoring well will be installed. It will be perforated(0.04 inch slots)from the bottom of the hole up to one foot above the aquifers upper surface. The filter pack will be constructed of aquarium sand that will extend 2 feet above the the perforations. An annular seal of bentonite grout(Quick Gel&Benseal)will be installed above the sand pack and extent to within 3 feet of the surface. A surface seal will be formed of concrete and a water tight well cover. The well casing will be secured by installing a locking cap. Design of this well is illustrated in Figure 6. After installation of these monitoring wells all seven monitoring wells in the first aquifer will `- be developed and sampled as described in sections 4.8 and 4.4. On the mL:itoring well#o the second aquifer(MW-6)a time-endurance ground water sampling test will be run. This is accomplished by pumping the well continuously for several hours during which ground water samples are periodically collected throughout the test. The purpose of this is to draw water from as large a radius as possible by creating a cone of depression with an ever enlarging zone of influence. All groundwater samples will be analyzed for gasoline,benzene,toluene.,nd xylene,(BTX by EPA method 602)at a California certified laboratory. Monitoring well tops will be surveyed for their elevation above mean seal level(MSL). This data will be used to calculate water gradient. Ground water depth measurements will be — collected after well installation,after development and sampling,and two to four weeks after installation. It is also recommended that gradient be monitored quarterly for one year to track the flow of ground water. Once this phase of investigation has been completed,a report will be written which integrates data from both phases of study and makes recommendations for further action.