WORK PLANS - Laserfiche WebLink

Home Browse Search

Work Plan—Byron Road,Tracv,California June 16,2003 06-6102-00-2931-030 Page 8 TPHg and TPHd were detected in only one sample analyzed at a concentration of 720 and 520 gg/L, respectively. Concentrations of TPHd (140 µg/L) were also detected from a grab groundwater sample that was non-filtered. In September 1998, Geomatrix installed two monitoring wells (TW-1 and TW-2) to confirm detections of TPHd and TPHg in groundwater. The wells were installed at the approximate locations as the two borings that contained detections in grab groundwater samples collected from the July 1998 investigation. Monitoring well borings were advanced to a depth of 14 feet bgs and were screened from 4 to 14 feet bgs. Depth to groundwater during the sampling event was measured at seven feet bgs. Groundwater samples were collected from both wells, although one well (TW-2) was observed to have petroleum sheen at the time of sampling (a groundwater sample was collected at the request of the SJCPHS). Groundwater samples were analyzed for TPHg, TPHd, BTEX, and PAHs. A second round of groundwater sampling, with the same list of analytes, was conducted on October 16, 1998. Because of observed petroleum sheen in one well, no groundwater samples were collected on October 16, 1998. Petroleum hydrocarbons were not detected in one of the two wells sampled (TW-1) in September 1998. Based on the initial sampling of the well observed to have petroleum sheen, TPHg, TPHd, ethylbenzene, and xvienes were detected at 1,200, 520, 1.7, and 4.1 gg/L, respectively. Concentrations of acenaphthene, fluorene, and phenanthrene were also detected at 0.9, 2.2,and 1.4 gg/L,respectively. In July 1999, Geomatrix installed an additional well (TW-3) to assess groundwater quality north of the southern property boundary at the request of RWCQB. In a letter dated November 8, 1999, the RWQCB approved the destruction of well TW-2 due to the residence being built on top of the TW-2 location. The remaining two wells were sampled and monitored for four quarters. Groundwater samples were submitted for analyses of TPHg, TPHd with and without silica gel cleanup, BTEX, and PAHs. TPHg, BTEX, or PAHs have not been detected in the groundwater samples from either of the remaining wells. However, TPHd has been detected in both remaining wells prior to silica gel cleanup over the last four quarters of sampling. In August 2002, Geomatrix prepared a Health Risk Screening Evaluation (HRE). Exposure pathways considered included: inhalation of volatile organic chemicals from soil and groundwater, inhalation of airborne dust from soil; ingestion of soil and groundwater; and dermal contact with soil and groundwater. Geomatrix identified ingestion of groundwater as being the pathway associated with the highest risk. Based on the results of the HRE, Geomatrix concluded residual petroleum hydrocarbon constituents in soil or groundwater do not pose an unacceptable health risk to humans or other environmental receptors. In a letter dated February 28. 2003, the RWQCB had reviewed the HRE, but did not make a final determination concerning "no further action" until the Department of Toxics Substances Control (DTSC) has completed the review of the HRE and additional groundwater monitoring of the site wells was performed. The RWQCB requested a work plan be prepared proposing an additional quarter of groundwater sampling. In a letter dated May 5, 2003, the RWQCB approved the work plan submitted by SAIC to conduct an additional quarterly monitoring and sampling of the two remaining wells. The monitoring and sampling is scheduled for June 2003. K:CVX-OVP\RO W_SITES\westsidechannel\draftworkplan.doc