SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Groundwater Assessment Plan camients (cont'd) Page # Camment 58 Tris last paragraph proposes using bentonite and fresh water as the drillinq fluid during continuous coring. Since there is no concern, in this instance, for borehole stabilization, or minimization of the inflow of formation water into the borehole, why is bentonite being added to the fresh water? 59 The last paragraph proposes to abandon each exploration borehole by pressure grouting fran the bottan up with neat cement. The abandonment procedure for the deep barings, haaever, calls for placement of the grout using a tremie pipe. Please explain these differing rationales for well abandonment. 61 The first paragraph proposes to use No. 50 foundry sand as the sealant material above the gravel pack. Please explain the use of this material in lieu of bentonite pellets, and provide a reference, if possible, comparing the two methodologies. 63 The first paragraph proposes to use Monterey No. 3 sand as the filter pack material. The selection of filter pack material must be based on a grain size analysis of the formation materials and the slot size of the well screen. Given that the existing wells screens at the site have not been truly "designed", and there is no real precedent to operate from, the appropriate filter pack materials for the monitoring wells will not be known until the grain size analyses are carried wit at each well. 63 Paragraph 2 states that the watertight well seal will support the weight of the suspended daanhole pump assembly. If the pump assembly is inside the inner casing, it is unclear how the welded seal will directly support the pump assembly. A more detailed figure is needed here that shags the pump assembly. 64 The bentonite to water ratio should have been indicated in paragraph 2. 66 The first paraqrph indicates that two cuttings will be collected from each shallaa monitor well for analysis of VOCs (essentially, grab samples Fran a 55 gallon drum) . Rather than place all of the cuttings in a common drum, those samples that possess OVA readings in excess of a certain threshold level (simply hold OVA or HNU probe over cuttings) would be placed in one drum, while samples below this level would be placed in another drum. The two samples for analysis of VOCs would be then be taken from the drum containing the cuttings with the higher OVA readings.