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Cosumnes power plant (01-afc-19) data response, set 1A

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Attachment LU-57


Call To:

Bill Campbell

Phone No.: (916) 361-8384 Date: July 17, 2001

Call From: Katy Carrasco Time: 02:51 pm

Subject: Applicability of Sacramento County General Plan and Zoning to Natural Gas Pipeline Siting in Elk Grove

I spoke with Bill Campbell, senior planner for the City of Elk Grove through Pacific Municipal Consultants. Mr. Campbell stated that the City of Elk Grove general plan and zoning is several months (minimally 18 to 24 months) away from being completed and that the County general plan and zoning are applicable to the City. I asked him if there were otherwise polices that the City had regarding the siting of natural gas pipeline and he said that there were not, other than County encroachment or private easement requirements. He stated that it was likely to be easier to site a pipeline in the far western and eastern portions of the City since those areas had not been developed as of yet. He stated that for specific siting assistance, it would be best to work through the County since the data and experience that the City has on existing utility lines is limited.

INSERT Figures 6.1-1a to 6.1-1g

INSERT Figures 8.4-2a to 2e

INSERT Figures 8.4-3a to 3e

Technical Area: Noise

CEC Author: Jim Buntin

CPP Authors: Mark Bastasch and Farshad Farhang


The applicant presumes that compliance with the 45 dBA criterion of the LORS will be sufficient to avoid a significant noise effect, mitigated by the offer to provide additional sound insulation for affected residences. The applicant’s data indicates compliance with the 45 dBA criterion would result in an increase of about 11 dBA to 17 dBA, based upon the L90 values measured at Site M1 during the quietest hours of the day and night. This will be excessive in terms of producing a significant change in background noise levels, as the Energy Commission staff has concluded that a potential for a significant noise impact exists where the noise of the project plus the background exceeds the background by 5 dBA L90 or more at the nearest location where the sound is likely to be perceived.

However, staff will carefully consider the question of establishing a reasonable and practical noise standard for very quiet environments. With this in mind, it will be useful to know the practical effects of setting a noise standard which allows an increase in background noise levels greater than 5 dBA, while limiting the noise level to the maximum practical extent. For example, the Model Community Noise Control Ordinance prepared by the State Office of Noise Control suggests a nighttime exterior noise level standard of 40 dBA for rural suburban land uses.

  1. Please provide an acoustical analysis to address compliance with a noise standard of 40 dBA L90 at the nearest residences. Include a listing of any additional required noise control measures.

Response: This question will be responded to on February 4, 2002.

  1. Please provide a map or a listing showing the sensitive receptors that are predicted to be exposed to construction noise levels which exceed the typical daytime ambient L90 values by 5 dBA.

Response: Figure NO-63 presents generalized noise contours during the Site Clearing and Excavation Phase (Tables 8.5-6 and 8.5-7 of the AFC). Figure NO-63 includes the atmospheric and ground absorption effects. Average daylight (7 am to 7 pm) L90 was 33 dBA. Sound levels will vary depending on the type, number and location of equipment.

  1. Please provide a map or a listing showing the sensitive receptors that are predicted to be exposed to plant operation noise levels which exceed the typical quietest ambient L90 values by 5 dBA.

Response: This question will be responded to on February 4, 2002.

  1. Using the responses to the two previous questions, please address the question of whether the noise level data collected at site M1 reasonably represent the noise exposure at the residences affected.

Response: This question will be responded to on February 4, 2002.

The AFC indicates that pile driving is not currently anticipated. The AFC further states that pile driving, if required, would be at sufficient distance so that noise and vibration would not adversely affect the nearest residential receptors. Energy Commission staff is concerned that, if pile driving is later deemed necessary, adequate analysis be provided to ensure that there will be no significant noise or vibration effects.


  1. Please provide a description of potential locations for pile driving, and their proximity to residences, should pile driving be required.

Response: Potential locations for pile driving cannot be determined with precision until geotechnical studies and civil/structural engineering are complete. However, it can be reasonably assumed that there will not be the need for pile driving under the major equipment foundations.

The AFC indicates that horizontal drilling will be required for the gas line. The Sacramento County Code provides an exemption to the noise standards of Chapter 6.68 for construction during specific hours of the day. The Code further exempts an “unavoidable condition” occurring during a construction project “under conditions which will not jeopardize inspection acceptance or create undue financial hardships.” Since horizontal drilling would be a 24-hour activity, it may be necessary to impose conditions upon this activity to minimize noise effects on residential receptors. To assess the potential for concern, it will be necessary to describe the locations where horizontal drilling will be required, and the amount of time required for such activity at each site.


  1. Please provide a description of potential locations where horizontal drilling may be required, and their proximity to residences.

Response: At this time, there are four potential horizontal directional drilling locations (reference AFC Figure 6.1-4):

  • Cosumnes River Crossing (MP 12.39 to MP 12.87)

  • UPRR Crossing (MP 13.28 to MP 13.61)

  • Highway 99 Crossing (MP 14.11 to MP 14.35)

  • Laguna Creek Crossing (MP 20.47)

These four locations are in agricultural and rural areas. The boring equipment location (or rig set up location) will be selected to avoid impacts to residences. At this time, it appears closest residence, at the Cosumnes River Crossing, will be about 300 yards from the actual boring operation.

  1. Please describe typical time requirements for horizontal drilling at any one site.

Response: It is expected that each boring operation will take less than three weeks (mobilization to demobilization). However, the actual boring could be less than one week.
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