ARCHIVED REPORTS XR0009035 - Laserfiche WebLink

Home Browse Search

• 0 the past or that lighter hydrocarbons(gasoline)were not released 4) The source of the diesel contamination is uncertain The dispenser and its assocaitated piping could be the source However, the high diesel concentration in groundwater from the abandoned domestic well and its limited extent in both the soil and groundwater suggest that diesel may have been disposed of in this well at some tune in the past and leaked through the broken casing into the surrounding soil The absence of any detectable contaminants in TT-3 and the eastward groundwater gradient make it unlikely that the contamination came from an off-site source to the north 5) Methyl tertiary butyl ether (MTBE) is not present in the soul or groundwater at this site We recommend that MTBE be deleted from the analytical protocol in future sampling events 6) In our opinion, San Joaquin County PHS/EHD erred when it directed that excavation be terminated at 25 feet on December 11 If excavation had continued, the lower limit of residual soul contamination would have been reached within a few feet Now that the dispenser excavation has been backfilled, removal of the residual soil contamination would require re-excavation of the clean backfill Prior to taking this step, the cost-effectiveness of removing the remaining 275 cubic yards of soil_ should be weighed against the potential risk for finiher groundwater contamination 7) Although the domestic well could be used for groundwater gradient mapping as well as for sampling or removing contaminated groundwater, we recommend destroying it now before the new fueling facility and canopy are constructed Once the canopy is in place, it will impede drill ng access to the well and make its destruction difficult 8) At the present time, residually contaminated soil is limited to a zone a few feet thick beneath the dispenser island If the soul that is presently stockpiled south of the tank excavation were used to backfill that excavation, a much larger area of residual contamination would result Hence, we do not recommend using the contammated stockpile as backfill for the excavation This soul should either be hauled to a Class II disposal fatIty or moved to a convenient on-site location where it could be bioremediated 9) The site should be placed on a schedule of periodic groundwater monitoring to firmly establish the prevailing groundwater gradient and to determine whether contaminant concentrations are stable We recommend a quarterly monitoring schedule for a period of one year; the next event should take place in May Groundwater samples should be collected from all four wells and analyzed for TPH-g, TPH-d, and BTEX 10) Contamination at this site appears to pose a low risk to public health The evidence indicates that carcinogenic, volatile hydrocarbons are not present, contaminants have not migrated a significant distance from the the former fueling facility, groundwater does not appear to flow toward a highly populated area, and surrounding land use is primarily commercial We recommend that a domestic well survey be done to insure that public drinking water supplies are not threatened, but further assessment is not warranted at this time i