Wednesday, November 30, 2011
I read materials about whether or not our airport should be in Walla Walla County's Critical Aquifer Recharge Area. These materials include a letter from a Seattle attorney (Gordon Derr) and a letter (including 1994 and 2006 geologic maps) from a Seattle consultant (Aspect).
Having worked for the Washington Division of Geology and Earth Resources, I know the five geologists who made these geologic maps.
Indeed, the lead geologist met with some members of the geology department at Whitman College to discuss the local geology, including loess, Missoula flood deposits and floodplain alluvium.
The Aspect letter states that Golder Associates performed geologic mapping, including information on the 1994 map, and concluded that much of the airport property is highly vulnerable to potential sources of contamination because of underlying permeable alluvium (stream deposits).
However, based on the newer and more detailed 2006 map, which shows somewhat less permeable sands and silts beneath much of the airport, Aspect ranked this area to have moderate vulnerability.
The city of Walla Walla and Mill Creek are topographically downhill and hydrologically down-gradient of the airport. Contaminants could travel to the floodplain of Mill Creek and the underlying shallow gravel aquifer.
Although the fine-grained silts of Missoula flood deposits slow the vertical movement of groundwater, beds of coarser sand interbedded with the silts allow water to move in a horizontal direction.
Hence, any pollution that enters the ground may move laterally for long distances. The Port recognizes that much of the airport is underlain by sediments of moderate permeability. Should potential contamination of our shallow aquifer be tolerated because the risk is only moderate?
Neither letter mentions the use of existing information obtained from nearby wells. Many of the drillers' logs of wells within a few miles of the airport show near-surface gravel, some of which is permeable because it is not cemented (Newcomb's 1965 Water Supply Bulletin). Therefore, the assessment by Aspect is incomplete.
Because our shallow aquifer is so valuable, I recommend a more thorough hydrogeologic assessment be made before the Port delineates our airport as being outside of the Critical Aquifer Recharge Area.
This would include examining drillers' logs, probably digging trenches and possibly drilling a new well through the sediments beneath the airport. Our health and our economy are partly dependent on this aquifer. We should not take a chance on contaminating it.