Laserfiche WebLink
1 <br /> ' 30 April 1999 <br /> AGE-NC Project No 98-0450 <br /> Page 4 of 5 <br /> ' 4.0. DISCUSSION AND CONCLUSIONS <br /> Based upon data collected during the February 1999 quarterly monitoring event, AGE concludes <br /> ' • The ground water was flown toward the south at gradient g g nt of approximately 0 0035 <br /> ' • With the exception of MW-5, the wells are properly screened to adequately sample shallow <br /> ground water Ground water was approximately 4 25 feet over the top of the screened <br /> interval of MW-5 <br /> • MTBE was detected at concentrations greater than the State of California Action Limit in <br /> ground water samples collected from monitoring wells BMW-2, BMW-4 and MW-5 The <br /> ' MTBE was encountered in ground water samples at concentrations ranging as high as <br /> 850µg/1 (BMW-4) <br /> • The concentrations of benzene in ground water samples from five wells (BMW-1, BMW-2, <br /> ' BMW-3, BMW-4 and BMW-5) exceed the state maximum contaminant level (MCL) of 1 <br /> ,ugll, the concentration of xylenes in BMW-4 (21,000 ugll) exceeds the MCL of 1,750 ppb <br /> • Between August 1998 and February 1999, concentrations of most analytes substantially <br /> decreased in the three wells sampled during both events (MW-5, BMW-1 and BMW-3) <br /> However, the sample from well BMW-4, installed in the former UST excavation, contained <br /> significantly higher concentrations of all analytes, thereby indicating a higher overall mass <br /> of dissolved contamination at the site than was previously indicated <br /> ' • The greatest concentrations of dissolved hydrocarbons and MTBE continues to be in the area <br /> of well BMW-4, the former UST area <br /> • This quarter, the plume of impacted ground water is defined at the southern edge of the site <br /> ' by analytical results of samples collected from well MW-5 and to levels of less than 1,000 <br /> ugll of TPH-g, less than 10 µg11 of benzene, and less than detectable concentrations of <br /> ' MTBE on the southeast by well BMW-5 and on the west by wells BMW-1 and BMW-3 <br /> 5.0. RECOMMENDATIONS <br /> Based upon data collected from the site, AGE recommends <br />' • Continued <br /> quarterly monitoring and sampling <br />' • Installation of ground water monitoring wells west of the former UST Iocation and south- <br /> southwest of the subject site near the Kragen Auto Supply site, to complete definition of the <br /> Advanced CeoEnvironmental,Inc <br />