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alley Organics, Inc. —Ak- - 2 - Ak, 15 November 2007 Underlying groundwater quality appears to be degraded in the vicinity of well MW-4. Based on the data presented, depth to groundwater ranges between 4.5 and 23 feet bgs. The shallowest groundwater depths are in the vicinity of the Sanchez Property, where the proposed composting facility will be located. Groundwater appears to flow from the southwest to the northeast, based on the data presented. The groundwater gradient is unknown. Groundwater quality between wells MW-1, MW-2, MW-3, and MW-5 varies slightly from well to well when comparing EC and TDS. This holds true for other constituents of concern as well. However, groundwater quality in well MW-4 appears to contain elevated concentrations of all constituents analyzed when compared to wells MW-1 through MW-3, and MW-5. As an example, EC, TIDS, chloride, and calcium detected in well MW-4 are 5.9, 8, 12.3, and 21 times higher than the average concentrations of these constituents found in the other wells. The highest quality groundwater is found in well MW-5, southwest or upgradient of the Sanchez Property. The poorest groundwater is found in well MW-4, east-northeast or down gradient of the Sanchez Property. Based on the data presented, Valley Organics has not provided sufficient evidence of underlying groundwater quality of the Sanchez Property. Upgradient and down gradient wells provide some indication of groundwater quality, but water quality between the two wells varies significantly. Specific groundwater information is required to evaluate what the underlying groundwater quality is beneath the Sanchez Property. Staff recommends Valley Organics conduct a limited investigation to collect_grab groundwater samples for analyses. Valley Organics proposes to compact the native soil onsite to help create a low permeable barrier to protect underlying groundwater. According to the Letter Response, laboratory testing of dry density and failing head permeability were conducted and concluded that if onsite soils were compacted between 88 and 90 percent relative compaction, permeability would increase to between 1.1x10-5 and 8.9x10-5 cm/sec. In essence, Valley Organics is proposing to develop a low permeability working surface prior to composting operations taking place. Although this is not a Title 27 regulated facility, staff recommends Valley Organics submit a Construction Quality Assurance (CQA) Plan in accordance with Title 27, Section 20323 and 20324(a) through (i) and to use the referenced sections as guidance when constructing the compost area. Valley Organics proposes to utilize BMPs to control process water and storm water flowing across the compost area and compact the native soil to achieve a minimum of 10-5 cm/sec permeability. BMPs to control process water and storm water flowing across the site are appropriate measures as is compacting the native soil to lower permeability rates. However, additional characterization of the underlying groundwater quality must be conducted. Based on the data presented in the 26 October 2007 Letter Response, additional data is required to evaluate the underlying water quality beneath the Sanchez Property. Staff recommends Valley Organics conduct a limited groundwater investigation that includes collecting grab groundwater samples 'beneath the Sanchez Property. The grab groundwater samples shall be analyzed for the constituents listed in Table 1 below.