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' Pomho Property — Subsurface investigation Report Page: 10 1 � �l The groundwater samples with low concentrations of contamination, obtained from boring BIO, BI 1, and B12 at depths 16 to 23 feet and boring B9 at 33 feet, were discretely collected from within the well sorted sand present at the base of ' the borings (lower sand). All three monitoring wells also terminate�inr � the lower sand. -1 - :'' (� l�� eni/1 ' The lateral and vertical extent of soil and groundwater contamination has been defined in this phase of the environmental investigation. Soil contamination appears to be restricted to the immediate vicinity of the former underground storage tank and the distribution controlled by the thin shallow, confined to semi- confined, sandy unit (upper sand). High concentrations of groundwate r contamination are restricted to the thin shallow, confined to semi-confined, sand ' unit (upper sand). Migration of the groundwater contamination has been retarded by the presence of a low permeability restrictive unit that underlies the upper sand. Low concentrations of contamination have penetrated the restrictive ' horizon. A direct down gradient monitoring well has not been installed, however the low concentrations of groundwater contamination detected in the lower sand unit preclude the need for additional sampling points. The lateral extent of ' contaminate migration has been defined by the monitoring wells. Appropriate remedial measures for this site should include source removal of all possible contaminated soil from the area of the former underground storage tank. i Also, continued monitoring of the permanent monitoring wells to confirm the groundwater flow direction and, since MTBE has not been identified at this site, ' verify the attenuation of the residual hydrocarbons. The potential risk posed by the residual soil and groundwater contamination should be evaluated and recommendations for additional work or site closure provided at that time. j The above represents our best professional opinion as to environmental conditions at this site. These opinions were derived using data at hand, and standards of care ' common to the environmental consulting community in Northern California. There is the possibility that even with proper application of the above methodologies, there may exist on the subject property conditions that could not be identified within the scope of this assessment or which were not reasonably identifiable from the available information. The methodologies included in this report are not intended to produce all inclusive or comprehensive results, but ' rather to provide the client with information regarding apparent suspicions of existing and potential adverse environmental conditions relating to the subject property. Additional work at this site may generate data that could lead to a ' change of opinion regarding conditions or appropriate remediation procedures or both. 1 1