ARCHIVED REPORTS_XR0002900 - Laserfiche WebLink

Home Browse Search

Working to Restore Nature June 1993 Quarterly Groundwater Sampling & Analysis August 16, 1993 Quik Stop Market No. 132, Stockton, California F7132.93 November 1990). New double-walled fiberglass USTs were installed at the site and the remaining excavation was backfilled with clean fill. The canopy, pumps, and concrete surface were replaced and the station put back in operation in March 1991. Well MW-1 was destroyed on October 3, 1990, due to concerns that it may have connected two water bearing units. On April 2, 1991, RESNA replaced the destroyed groundwater monitoring well with two monitoring wells designated MW-1R and MW-5. MW-1R was designed to monitor the lower aquifer and MW-5 to monitor the upper aquifer discovered during the installation of MW-1. Analyses of all subsurface and analytical data indicated the presence of two aquifers beneath the eastern portion of site. It was found that the lower aquifer had no detectable TPHG or BTEX and the upper aquifer contained TPHG and some BTEX components (Excel tech/RESNA, July 1991). At the time of the initial groundwater sampling for MW-1R and MW-5, the San Joaquin County Public Health Services (SJCPHS) required that groundwater samples be collected from all monitoring wells and analyzed for fecal coliform. On April S, 1991, sampling for this analysis was-performed and fecal coliform was only detected in the sample collected from MW-2. It was the decision of SJCPHS that the groundwater samples from this well should continue to be analyzed for fecal coliform. In subsequent sampling, no fecal coliform has been detected in this well. It is known that a main sewer line is located beneath West Hammer Lane, approximately 30 to 40 away from MW-2. Since this is the only well in which fecal coliform has been detected and it is the well closest to this sewer line, it appears that this sewer line may be the source of the fecal coliform. Another source may be contamination inadvertently introduced during sampling or laboratory analysis. Such conditions are beyond the control of Quik Stop Markets. The purpose of these monitoring wells is to aid in the determination of the presence and/or extent of petroleum hydrocarbons in the groundwater. It was the recommendation of RESNA that Quik Stop t Markets be permitted to discontinue fecal coliform testing of the groundwater collected from monitoring well MW-2. In a letter to Quik Stop Markets dated December 5, 1991, the SJCPHS reduced the required fecal coliform sampling frequency in monitoring well MW-2 to semi-annual (every other quarter) (SJCPHS, December 5, 1991). Since the initial occurrence of fecal coliform in April 1991 fecal coliform has not been detected in this well. Information obtained as of August 1991 indicated that the gasoline plume extends beyond the station boundary to the east. In an effort to determine the extent of this possible contamination RESNA and Quik Stop Markets requested permission to enter the property to the east. These requests were not successful. This site is occupied by a Taco Bell restaurant. In August 1991, RESNA recommended and initiated quarterly pumping of monitoring well MW-5. This pumping was agreed upon with the SJCPHS in August 1991 as a temporary interim remedial activity pending receipt of permission to enter adjacent downgradient properties. When well sampling purge water and equipment rinse water is transported from the site by Exceltrans (a licensed hauler), monitoring well MW-5 is pumped using a vacuum truck with A-2