Laserfiche WebLink
<br /> <br />long term. How does the pump-back system impact the steady state assumption? Was the <br />pump-back system operating at the time the water level measurements were made and if so, at <br />what flow rate? <br />Page 20-21 .. Section 3.1.4.1.. This paragraph states "well DW-1 used for dewatering during <br />active mining in the west pit was operated at an average flow rate of approximately 150 GPM", <br />and [he paragraph continues to indicate "there is no reason to expect that the rate of recharge to <br />the West pit will decline in [he future". Continuing in the next paragraph, "During active mining <br />in the west pit, a steady source of groundwater inflow occurred into [he southeast comer of the <br />pit. The rate of flow was approximately 60 GPM..." Apparently during mining the recharge to <br />the pit, exclusive of precipitation in the pit area, was azound 210 GPM. Is this correct? <br />On page 23, [he last sentence in the second paragraph indicates "The estimated rate of <br />groundwater flow using [he historical dewatering pumping rate is reasonably within the range of <br />100 to 150 GPM." This assumption appears to discount the historic pumping rate of the <br />dewatering well, apparently due to changes in gradient, and ignore the historic flows into the <br />southeast corner of the pit from the Rito Seco alluvium. Flows into the south east portion of [he <br />pit from [he alluvium are still occurring as evidenced by the water quality data. There is <br />inadequate information currently available to define pit inflows with any degree of precision. <br />From the data presented, it would appear that pit inflows could exceed 150 GPM if all sources <br />are considered, and a range of 100-200 GPM maybe more appropriate. <br />Page 23, third paragraph..The Darcy calculation suggests an outflow from the pit through the <br />alluvial window of 80 GPM. This accounts for only part of the flow the water balance suggests <br />should be entering the pit. If we ignore additional sources and assume BMG's flow rate of 150 <br />GPM from the water balance, only 53% of the water is accounted for in flow through the <br />"alluvial window". It is further unclear here if the dewatering and pump back system was <br />operating when the physical measurements of gradient were developed. If the dewatering-pump <br />back system were operating at this time, considerably more water should have been moving <br />through the alluvial "window" at [he south pit face , or exiting the pit somewhere else. <br />Page 32, Paragraph 3.2.2 .. The last sentences of this section indicate " Concentrations of <br />manganese in SF-2 and SF-3 are elevated, but the single set of analysis does not faurly represent <br />the chemical characteristics of groundwater in the Santa Fe Formation. Additional samples will <br />be required to confirm the initial interpretation of [he water quality data due [o the low-yielding <br />nature of the Santa Fe Formation and the concomitant difficulties in fully developing [he <br />monitoring wells." <br />• Why is manganese analysis incorrect? <br />• What additional sampling of the Santa Fe wells is anticipated? <br />• The incomplete development of these wells is a problem. The permeability derived from <br />the slug tests is highly dependent on full development of the well. If the well is <br />incompletely developed, testing (and particularly slug testing) could yield incorrect <br />values that are orders of magnitude in error. <br />