ARCHIVED REPORTS XR0011091 - Laserfiche WebLink

Home Browse Search

Y GaologicaI7-KhaiesInc Page 5 Groundwater Monitoring Report Project No. 750.2 May 14,2002 '-' As required under AB2886, the laboratory data was submitted electronically to GeoTracker on April 15, 2002, with confirmation number 5899060130. w 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analyses show the following: • Well MW-1 has consistently contained low concentrations of gasoline range petroleum hydrocarbons (TPH-G, BTEX). The concentrations of TPH-G recorded for this event are less than half of those recorded during the November 2001 event. • Figure 5 illustrates groundwater elevation and TPH-G concentrations in MW-1 versus time. The graph suggests a reasonably direct relationship between groundwater elevation changes and contaminant concentrations. Figure 6 illustrates groundwater elevation and MTBE concentrations in MW-1 versus `+ time. After an initial high of 220 µg/L the concentrations of MTBE have fallen to 80 µg/L. • For the fourth consecutive event, the discretely screened deep well MW-101 did not contain.contaminant concentrations above the laboratory reporting limits. This suggests that the previously recorded contamination was a drilling artifact, ✓ • The remaining wells were found to be free of contaminants, which is consistent with other events. • Vertical groundwater gradient was calculated for the event of January 2, 2002, and was determined to be downward and greater than the horizontal gradient of the water table, suggesting that the contaminants in the water table may be transported to deeper depths in the subsurface. V • Vertical groundwater gradient was calculated for the event of March 2, 2002, and determined to be upward and greater than the horizontal gradient of the water table, suggesting that the contaminants in the water table are hampered from downward migration by the I.C. which has been in operation since February 5, 2002. • Oxidation-Reduction Potential measurements (Table 4) are positive for all the wells +r suggesting that the volume of contaminants leaching into groundwater is minimal and that biodegradation of the contaminants is at a rate sufficient to keep the BTEX/TPH-G plume in a small area around the source without depleting the oxygen to a level which would slow the reaction process. La Recommendations: • Continue Quarterly groundwater monitoring at the site. The next event will occur by �,. June 2002. • Operate the vapor extraction system for a period of six months to remove the high concentration of contaminants in the vadose and provide protection of the groundwater. t..