SITE INFORMATION AND CORRESPONDENCE

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1 ChevronTexaco - 3 - 26 March 2004 Mountain House Sites #1 and#2 I have the following comments relating to those activities where the construction excavations will likely intercept petroleum hydrocarbon impacted soil arid/or groundwater and possibly poor quality shallow groundwater. Streambed alteration: • The bottom elevation of the reconstructed stream channel appears to be 10 feet below the current streambed, and potentially 5 feet below the water table. As noted on Figure 4 in the addendum, petroleum hydrocarbons in soil and groundwater were identified in close proximity to the proposed construction Iocation. Excavation below the water table could result in Mountain House Creek becoming an effluent (gaining) stream. The presence of petroleum hydrocarbons within the poor quality shallow groundwater that could discharge into Mountain House Creek, could raise questions relating to conditions contained in the 20 June 2003 Water Quality Certification issued to Trimark Communities, the San Joaquin Basin Plan, and/or the Clean Water Act. Bridge construction: • Review of the cross section in Figure 4 indicates that excavation for the spread footings will extend to approximately 25 feet below grade, up to ten feet or more below the water table, or approximately 20 feet below the bottom of the existing streambed. As seen on the figure, petroleum impacted soil and groundwater is present in the subsurface (12 to 35 feet below grade) where the spread footings are proposed. Additionally, it appears that other areas along the creek, Byron Road and UPRR right-of-way not yet investigated may be impacted as well. • Review of the data indicates that to accommodate installation of the footings and the streambed excavation, it appears a construction dewatering system would be needed to temporarily lower the shallow groundwater table. Shallow groundwater extracted during construction dewatering that is not impacted with petroleum hydrocarbons, and where the extracted water quality is as good or better than the underlying groundwater quality, may be suitable for discharge to land subject to Resolution R5-2003-0008, the waiver for a Report of Waste Discharge (RWD). • Discharges to land of either unimpacted shallow groundwater, or treated groundwater from a dewatering process cannot enter or be discharged into a waterway considered or connected to a Water of the State without an appropriate NPDES (National Pollution Discharge Elimination System) permit. • However, similar to conditions present with the recently completed Westside Channel Outfall System project in Tracy, groundwater at the Mountain House Creek project is known to be impacted with petroleum hydrocarbons, and if extracted and treated during construction dewatering, would be subject to permitting in accordance with "General Order for Land Disposal of Groundwater or Surface Water frorn Cleanup of Petroleum Pollution, Order No. R5- 2003-0044" and require a Report of Waste Discharge (RWD). Additionally, it is likely that at this site as well as elsewhere in the area, the shallow groundwater is of poor quality and has elevated total dissolved solids.