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CAMBROA Sample Frequency Reduction Cambria recommends reducing the sampling frequency of the domestic wells associated with this site and also recommends performing laboratory analysis for MTBE only on water samples from these wells and from the deep monitoring wells (MW-12, MW-13, and MW-14) The reasoning behind the recommendation is that we feel it has been well demonstrated through the sampling history at this site that there has not been impact to any of the domestic wells related to the release at the Shell site The domestic wells are located more than 800 feet to the south/southeast of the Shell site Groundwater flow direction at the Shell site has been well documented to flow predominantly to the northeast with some variation to the southwest This suggests that it is unlikely that the plume at the Shell site would migrate toward the domestic wells The monitoring well network at the Shell site suggests the release at the site has remained predominantly onsite Monitoring wells between the Shell site and the domestic wells have been clean, which suggests that the plume is not migrating toward the domestic wells Furthermore, we have been performing intermittent GWE activities at the site for nearly two years and will soon have a permanent GWE system in place at the Shell site These intermittent GWE activities have provided limited migration control at the site and the permanent GWE system will soon provide full time migration control further reducing the possibility that the plume at the Shell site could impact the domestic wells Analyzing these wells only for MTBE is proposed because MTBE is the compound in gasoline that migrates the fastest and farthest and is the most likely compound to first be detected in any of these wells Should MTBE be detected in any of these wells we will likely recommend that the normal suite of analyses be resumed in that well, We propose that the domestic wells be sampled annually and analyzed only for MTBE by EPA Method 8260 In addition we propose that the bailer sample be discontinued at the Sanella well Since the Boardman well had a recent anomalous detection of MTBE, we will continue quarterly monitoring of this well and collect groundwater samples from both the sample port and with the bailer If these additional monitoring events at the Boardman well support the idea that the recent MTBE detection is an anomaly, then we will later propose annual sampling for this well and then only from the sample port We propose that wells MW-12, MW-13, and MW-14 be sampled quarterly and only for MTBE by EPA Method 8260 0783 3