Subsurface borings for soil investigation and for monitoring well construction are drilled with a CME-45 or equivalent drilling rig. Drilling locations are selected and/or reviewed by a registered Geologist. Where underground petroleum lines or utilities are a possibility the drilling rig is used to initially penetrate any surface concrete or asphalt and a hand auger is used to penetrate to a depth of five feet below land surface. Subsequent soil samples are obtained with a split-spoon sampler at five-foot intervals in each soil test boring, in accordance with ASTM protocols, to the total depth of the borehole.
Soil samples from all borings are visually classified in accordance with the Unified Soil Classification System and are inspected for visual and odorous evidence of contamination. Each sample is placed in clean plastic bags or glass jars, half-filling the containers. The samples are stored for at least five minutes to permit any volatile organic vapors in the samples to volatilize into the headspace. The headspace of each sample is then tested for volatile organic vapors using a Photo Ionization Detector (PID). Based upon the headspace measurements, the sample exhibiting the most contamination from each boring is retained for chemical analysis. When the headspace measurement indicates that no contamination is present in the boring, the deepest unsaturated sample or the sample immediately above the water table is retained for chemical analysis. Samples below the water table are not considered for analysis since this material reflects groundwater and not soils contamination.
Great care is exercised to prevent cross contamination from occurring. Prior to beginning and between each boring, the drill rig, augers and down hole equipment are thoroughly decontaminated by steam cleaning to prevent accidentally spreading contamination. Additionally, the split-spoon sampler is cleaned using EPA approved protocol before each
sample is taken.
Each boring not used for monitoring well construction is filled to the surface with bentonite chips to seal the borehole and protect against future vertical migration of liquids from the surface or potentially contaminated zones within the borehole.