In the development of a shallow subsurface investigation design strategy, a fundamental objective is the quantification of pollutants both vertically and horizontally within the subsurface. The dilemma produced in the design phase is one of a tradeoff between study costs and sufficient data collection to meet the study objectives. A novel application of two devices normally used in geotechnical engineering was tested at Naval Air Station Moffett Field for their ability to provide low cost, and timely hydrogeologic and chemical data.
The first device, a cone penetrometer, is capable of determining variations in soil media physical properties, both in saturated and unsaturated media, by measuring friction and pore water pressure. It provides a continuous log of unconsolidated materials through depth thus allowing for delineation of aquifer and aquitard zones. The second device, a hydropunch, is similar in nature to a well point and is capable of collecting in-situ pore water samples from depths up to 250 feet. A volume of 500 ml may be retrieved through a porous stainless steel tip and removed by closing upper and lower check valves.
Over 130 such CPT/Hydropunch measurements were used to characterize the mixed rivertine and estuarine sediments at the Mountain View, California Naval Air Station. The base which is on the National Priorities List contains numerous sites where pollutants have been identified. The study described in this paper focuses on the methods and results obtained from comprehensive use of the CPT/Hydropunch™ screening methodology in variably saturated media, to a depth of 60 feet.