SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

0—L., CALIFORNIA REGION NATER QUALITY CONTROL BOARD ..� CaVEPA CENTRAL VALLEY RE!tTrON 3443 Roµtier Rpad,Suite A Sacramento,CA 95827-3098 __: °`m Phone(916)255-3000 FAX(916)255-3015 37 SSP 13 Pete Wilson,Governor -� �R.� (0� 28 August 1997 Mr. Tom Welch Westrec Marinas P.O.Box 6688 Huntington Beach CA 92615-6688 REVIEW OF SECOND QUARTER, 1997, GROUNDWATER MONITORING REPORT FOR TOWER PARK MARINA, 14900 EST HIGHWAY 12, LODI(SAN JOAQUIN COUNTY) Staff has reviewed the Second Quarter, 1997 Groundwater Monitoring Report (Report) for the Tower Park facility, which was prepared and submitted by SECOR International in accordance with Monitoring and Reporting Program (MRP) Order 95-802. This letter summarizes our conclusions about the Report and addresses considerations regarding the proposed Risk-Based Corrective Action assessment. 1. Review of the second quarter report found that free product was again present in Monitoring Well 3, with thickness as measured by interface probe, of 0.02 feet on 9 June 1997. This is an increase over the thickness observed during the last two sampling rounds. Although data on concentration of dissolved constituents are of questionable value when taken from a well with free product, staff notes that benzene was detected in MW-3 at 1.0 gg/L on 9 June 1997. This is equal to the California Primary Maximum Concentration Level (MCL) land exceeds the 1-in-a-million incremental cancer risk level of 0.35 µg2 as established by the California Environmental protection Agency. It also is the first time since September 1995 that benzene has been detected in this well. Concentration of dissolved ethylbenzene and toluene also increased in this well over the last sampling round (although both of these compounds are significantly lower than one year ago). The dissolved diesel component has decreased again compared to the last round, in a fluctuating pattern of increase and decrease that has recurred since sampling began. BTEX components were not detected in the other four monitoring wells on the site, but dissolved hydrocarbons resembling diesel (reported as TPH-d) were present in all four of the other wells on the site. Staff believes that these results show a probability that a source of dissolved product still exists at the site, whether a new release of product on the water table or in the soil. The upward-and- downward fluctuations in concentration may be a response to changes in water table elevation and changing contact with a product source in the soil. Indirect evidence for this suggestion is given in the Second Quarter 1997 report on page 2, which describes a significant rise in both water table at the site and water level in Potato Slough in response to heavy rains in late 1996. Potato Slough is described as nearly having flooded the levee. These events were followed in March 1997 by detections of unweathered diesel in Monitoring Wells 2,4, and 5 as well as MW-3 at the site. This is to be compared to preceding and subsequent June 1997 detections being reported as weathered product. It also raises the question of whether product "stored" in the soil profile could somehow be protected from weathering so that it would appear as fresh-looking material. Staff continues to regard the detections in MW-5, a cross-gradient well, as a concern. We believe the contaminant plume has not been shown to be stable and that the occurrences in MW-5 remain unexplained. AM., Recycled Paper Our mission is to preserve and enhance the quality of California's water resources,and ensure their proper allocation and efficient use for the benefit of present and future generations.