Document: NUREG-0800
Document ID: 57051ec2-9a01-488e-8294-573ed557f3eb
Document Type: srp
Title: GROUNDWATER
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070262.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.12
CFR Part: 
CFR Title: 

Content:
h-south groundwater ridge at the plant area, and groundwater flow is to the north, east, and west. The groundwater gradient in the plant area is about 6 to 7 feet 1.8 to 2.1 m (6 to 7 ft) per 100 feet 30.5 m (100 ft). 32 33 Permeability is controlled by the extent and distribution of fractures in the bedrock and by the size and distribution of pores in the overlying soil. The applicant has made laboratory and field permeability tests and has determined values ranging from zero to about 5000 feet 1500 m (5000 ft) per year. Measured depths from the existing ground 34 surface to the groundwater table on the ridges range from about 40 to 80 feet 12 to 24 m (40 to 80 ft). However, the proposed plant grade will be at about existing groundwater 35 level. The groundwater table is generally at or near the surface in valleys and draws near the site. In order to meet the requirements of General Design Criterion 2; 10 CFR Part 100; and 10 CFR Part 100, Appendix A, with respect to groundwater levels and its effects on the plant, especially during postulated seismic events, the applicant proposes to permanently lower the groundwater levels in the vicinity of safety-related structures. This is to be accomplished by using a system of seismic Category I underdrains and exterior wall drains. The underdrains will consist of a series of interconnected flow channels spaced on 20-foot 6-m (20-ft) centers located under the foundation slabs. The exterior wall drains 36 will consist of zoned filter materials around the walls, which will drain to a horizontal perforated pipe located at mat level. Both the underdrains and the perforated pipe will discharge to a sump located inside the auxiliary building from which the water will be pumped to the plant storm drains system for gravity flow to an auxiliary holding pond 2.4.12-9 DRAFT Rev. 3 - April 1996 onsite. The underdrain system of connected flow channels will be located at the top of rock or at the top of first level of fill concrete below