FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

it IS difficult if not impossible to explain why a;low level of toluene was found in S13-1. However, certain observations may be made regarding the location and depth of the simple and regarding possible toluene sources other than the former tank site. These observations may in turn support an interpretation of the,reason for the ?ow level toluene presence. As noted in the August 19, 1991 report, soil sample SB-1 was collected iron, a depth of 4.5 to 4.8 feet below ;he ground surface and contained 0.03 mg/Kg of toluene. SB-1 is located approximately thir'y `feet northwest of the former tank site and MW-1. Soil sample SB-3 was collected from a depth of 4.5 to 4.6 feet below the ground surfaceapproximately 14 Feet from the tank site anc, contained no toluene. As moth of these samples were collected from the capillary fringe zone (damp zone above the water table) and absent any othe► information, one might infer that hydrocarbons in the soil in this zone were left as a residual ` when contaminated groundwater moved through the zone. However, the fact that the soil sample closest to the. former tank location (SB-3) was clean casts doubt on this ry unlikely to find such a residual in the sample furthest from interpretation. .,it would be ve the former tank site but not in the sample closest to the former tank site. This is adequate rationale for not linking the low level of toluene in S13-1 to the form. er tank site and for seeking an alternative explanation for the toluene presence. There are at least two possible toluene sources on the site. First, the toluene rmght have been introduced into the soil by way of the underground pipes near the sample location. As shown on Figure 1, there is both a storm sewer and a sanitary sewer within a few feet of the'sample locations. Toluene is derived from tar oil (The Merck index, 1983) and the tar like sanitary sewer joint compound could have contained toluene which could have leached into the adjacent soil. Second, toluene might have been derived from the asphalt tar used to pave the parking lot at the site. The close proximity of a large asphalt narking lot might be enough to introduce a low level of toluene into the soil sample. Regardless of the exact reason for the toluene presence in the sample SB-1, the more r or not this presence is a threat to the environment or human important issue is whether p ` health. Repeated groundwater sampling from all wells on the site, especially wells MW-1 and MW-4, has demonstrated that there is no toluene (or any other hydrocarbon) impact on groundwater at the site. Furthermore, repeated air duality monitoring during field work with an HNu instrument showed no detectable volatile hydrocarbons in any of the monitoring wells or in the two soil borings. Consequently, WESTON strongly asserts that the 0.03 mg/K- of toluene found in SB-1 has K E .C,4tP�.+ - *1 nr Ef no significant impact on the environmental condition of he o.. �= grUuild�`atcr• 5.0 RECOMMENDA'T'IONS Based on the data collected from the site and presented to the EHD in the PAR and the two < addcndurrns to the PAR,VJESTON.a;ain recommends that no additional investigative work be conducted on the site and that the EHD and RWQCB grant underground tank site closure to the Souza Grantline Plaza site. l