SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Bert E. Van Voris • - 6 - • 17 September 2004 Supervising Engineer wastestreams subjected to only preliminary treatment(i.e., screening). The quality of combined discharge to the reservoir is projected to contain 900 to 1,100 mg/L IDS, which will include bicarbonate (492 mg/L), sodium(284 mg/L), and chloride (204 mg/L). The BOD of the combined discharge to the reservoir(prior to aeration) will range from 800 to 900 mg/L. Stone water contributions to the reservoir are expected to contain low concentrations of BOD and IDS. The reservoir will be aerated to "achieve reduction of organic levels via aerobic biological activity to the extent possible."' The BOD of blended wastewater will be reduced to a target range of 40 to 50 mg/L, a quality"suitable for onsite storage and land application."z The target BOD range is reportedly comparable to effluent quality established by other regional water quality control boards in waste discharge requirements for winery wastewater reuse. Recycled water containing 40 to 50 mg/L BOD "can require management of odor generation in the water prior to irrigation.s3 Proposed odor control measures include discharging wastewater directly from the reservoir; designing irrigation pipelines to allow complete drainage; and, if necessary, implementing additional treatment for BOD removal (e.g., peroxide addition or filtration). Musco is currently evaluating the relative percentage of soluble BOD in wastewater stored in the reservoir. If necessary, filtration will be implemented to reduce insoluble BOD and thus overall BOD levels to within the target range. The RWD indicates that the potential for impounded wastewater to be released to groundwater is low due to the low permeability of the native clay soil under the reservoir. The permeability of these soils,based on soil borings advanced as part of reservoir design(TW-2), is estimated to be 10' to 10-7 cm/sec. The RWD acknowledges that quarterly monitoring data of groundwater passing through MW-16, a shallow monitoring well 250 feet downgradient from the dam, shows an increase in TDS and sodium subsequent to wastewater impoundment. However,based on estimated low permeability of soils underlying the reservoir, the RWD concludes that this increase was not due to wastewater impoundment. Agricultural uses of the Jepsen Ranch include forage and vegetable cropping. Historically,the Jepsen Ranch's irrigation supply was water from the Delta-Mendota Canal. In the mid-1990s, the property's water entitlements were transferred and an onsite agricultural supply well became the source of the Ranch's irrigation supply. The Ranch has not been irrigated for the last three to five years and is currently fallow. No information is provided regarding the Ranch's onsite agricultural supply well. On 6 July 2004, Kleinfelder installed a new groundwater monitoring well ("Kagehiro-1") on the Ranch's western edge that extends to 100 feet below ground surface (bgs) and is perforated from 65 to 85 feet bgs. Depth to water was 67 feet bgs following well development. According to Musco personnel, the Valley View Thoroughbred Farm has been used to graze and board horses.since the mid-1990s. The irrigation supply for the Valley View Thoroughbred Farm is from an onsite well (0). No information is provided regarding the construction details of this well. Additional data on ambient groundwater quality in the proposed use areas is from one sample collected from the "Hansen Road Well,"which serves as domestic supply for a residence about two miles northwest of the Jepsen Ranch. The well is"believed to have a total depth of 248 feet bgs and the depth to water is unknown."4 The RWR characterizes groundwater quality in the proposed use areas based primarily on one sample each from the Kagehiro Well, Hansen Road Well, and Valley View Thoroughbred Farm Well. Analytical results from this sampling event showed the following ranges: TDS (1,170 to 2,800 mg/L), sodium (310 to 720 mg/L), chloride (270 to 1,200 mg/L), bicarbonate alkalinity (100 to 230 mg/L), hardness (270 to 550 mg/L), and nitrate-nitrogen (0.2 to 14 mg/L). The Hansen Well and Kagehiro Well samples