Item 6: Ordinance on Delta Sand and Gravel

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(e.g., the minimum distance should be 250 feet from residences on Admiral Street without additional mitigation). Since these setbacks would not be met, additional mitigation in the form of a berm 6 – 9 feet tall is also recommended by DSA, the shorter berm being satisfactory if the excavation is limited to less than 30 minutes each hour, use of the noisier heavy equipment is limited, and excavation is prohibited before 7:00AM. The DSA memorandum also states the applicant’s intent to construct a 10 foot tall berm prior to excavating the trench, which will likely be constructed in 300 – 500 foot segments as needed. After construction the berm would be removed. The record indicates that the impact of “impulse” noise, such as the banging of dump trucks to shake loose all the material being dumped, was not quantified. The DSA report explains this away for the excavation because the dumping of material would normally occur at the processing plant or other far-away sites. However, construction of the aquaclude involves filling the trench with less permeable materials. It is probable that dump trucks will be used, and that there will be impulse noises associated with this activity. The adequacy of the berm to minimize impulse noise is not addressed by the applicant. The applicant proposes to limit construction activities to the hours of 7 o’clock AM to 10 o’clock PM. For comparison, building construction in the city is usually limited in the city to the hours of 7 o’clock AM to 7 o’clock PM to limit disturbances (EC 6.750 (d)). In summary, there would be digging activities 50-100 feet nearer some existing residences if the variance were granted for the aquaclude. A berm 10 feet tall might be required by the county. Construction of the berm would itself cause temporary noise impacts to these properties. More discussion about noise impacts not associated with the aquaclude is contained in a different section of this report. Staff Recommendation: Noise: Amend findings related to noise as recommended below, not in a separate set of findings exclusively related to the aquaclude variance. Dust. The excavation activity and construction of noise-mitigating berms would be located between 50 to100 feet closer to some residences after the variance. The conditions of approval applicable to mining activity, such as watering haul roads to keep dust down, would not automatically apply to the aquaclude area of construction. The record does not indicate whether LRAPA standards would differ in the area of the aquaclude. There is evidence in the record that dust particles settle out from the air over greater distances. The greater the separation, the less dust remains in the air. Therefore it is logical that the variance allowing the installation of the aquaclude and earthen berms nearer to existing residences would have a detrimental effect, though one that is not quantified in the record.