WORK PLANS - Laserfiche WebLink

Home Browse Search

Geosyntec consultants Soil behavior type (SBT) will be interpreted using relationships between these parameters. The SBT log from each location will be evaluated and used to select up to two groundwater sampling depth interval(s). 2.2.3 Membrane Interface Probe(MIP) In order to further delineate the distribution of toluene previously detected in deeper soil near the northwest corner of the former Site building, a grid of six MIP borings will be advanced. The MIP is a direct push tool .used in situ to provide real-time, discrete depth information on the subsurface distribution of volatile organic compounds (VOCs), including toluene. The.MIP sensor consists of a semi-permeable membrane located a few inches above a direct push drill rod. An inert carrier gas, typically nitrogen, circulates through tubing within the drill rod and sweeps behind the membrane in the sensor at a flow rate of approximately 20 to 60 milliliters per minute (mL/min). VOCs diffuse across the membrane due to a concentration gradient between the subsurface and the clean carrier gas. A heating block located slightly below the membrane helps accelerate diffusion.- As the MIP sensor is advanced downward, volatile constituents are swept upwards within the drill rods via the carrier gas tubing to detectors at the surface. Detector responses are correlated to probe depth, yielding a log of detector response and temperature (used to identify the approximate elevation of groundwater) versus depth (approximately 0.1 to 0.2 feet vertical resolution).- Three detectors may be used in conjunction with a MJP: a photoionization detector (PID), an electron capture detector (ECD), and,a flame ionization detector (FID). In general, a PID responds to most VOCs and is particularly sensitive to aromatic hydrocarbons like benzene and toluene; an ECD responds to chlorinated VOCs such as TCE; and a FID responds to a j broader range of hydrocarbons. The MIP software can process up to four detector signals at.one time and provides plots of the detector readings versus depth. Vironex of Concord, California will provide the MIP module, which will be used in conjunction with the CPT. The MIP module fits behind the standard cone and is pushed into the ground where it acts as an interface between the contaminants in the subsurface and gas phase detectors at the surface. As shown on Figure 4, the six MIP borings will be advanced in a grid arrangement.. Each MIP boring will be advanced to a target total depth of approximately 40 ft bgs with the final depth of each boring determined in the field based on the observed MIP response. Final Work Plan>doc 7 27 June 2012 i