DCL-10-083, Diablo Canyon Groundwater Gradient Analysis

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Diablo Canyon Groundwater Gradient Analysis
ML11166A168
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 03/31/2010
From:
Entrix
To:
Office of Nuclear Reactor Regulation
References
DCL-10-083
Download: ML11166A168 (16)


Text

DIABLO CANYON POWER PLANT SAN Luis OBISPO, CALIFORNIA Groundwater Gradient Analysis MARCH, 2010 PREPARED BY SENTFIIX ENTRIX 201 North Calle Cesar Chavez, Suite 203 Santa Barbara, CA 93103 805.962.7679 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 Table of Contents Executive Summary SE CTI ON 1.1 SECTION 2.1 2.2 2.3 SECTION.°..°............................°.°.°°°.°.°..

°°.... ...E.....°.........°.°....

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ES-I I Introduction

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1-1 Overview of DCPP Groundwater Resources

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1-1 1.1.1 Industry Groundwater Protection Initiative

[NEI 07-07] .............................

1-1 1.1.2 P rev iou s S tu dies ...........................................................................................

1-2 2 Description of Available Water Resources Data .................................

2-1 A vailable G roundw ater D ata ....................................................................................

2-1 2.1.1 Groundwater Monitoring near Powerblock

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2-1 2.1.2 M onitoring W ell at Parking Lot #7 ..............................................................

2-3 2.1.3 W ater W ell 02 (W W 2) ................................................................................

2-5 Groundwater Gradient Near Powerblock

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2-6 Comparison of Water Levels at Powerblock and Well #2 ........................................

2-8 3 Conclusions and Recommendations

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3-1 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luls OBISPO, CA MARCH 2010 This Page Intentionally Left Blank ii ENTRIX, INC.ii ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 Executive Summary At the request of Diablo Canyon Power Plant (DCPP) Radiological Environmental Management Program (REMP) staff, ENTRIX has conducted an analysis of available groundwater information for the vicinity of the DCPP powerblock.

This work is based in part on the Nuclear Energy Institute (NEI) "Industry Groundwater Protection Initiative", document NEI 07-07, which is a nationwide effort aimed at improving detection of inadvertent release of licensed material to soil and/or groundwater.

Many aspects of adherence to the NEI 07-07 groundwater protection action items have already been addressed by REMP staff and are documented in other reports and this report is structured as an update to those reports.The focus of this analysis in regards to the NEI 07-07 guidelines is to evaluate available groundwater data in the powerblock vicinity and determine predominant flow characteristics and gradients.

This work also provides a review of any potential water quality threats to the recently rehabilitated and increasingly utilized DCPP "Water Well 02" (WW2), located approximately 3,600 ft east-northeast of the powerblock.

Water level data collected in August, 2009 from on-site wells, including powerblock well OW 1, a monitoring well in Parking Lot 7 and water wells in Diablo Canyon (WW02 and WW05), constitute a dataset which is used to prepare the contour map of the local groundwater gradient.

Analysis of the contour map indicates that groundwater in the powerblock area flows generally to the southwest, towards the Pacific Ocean. Although the existing data preclude determination of the exact groundwater gradient, the available data indicate that groundwater from beneath the powerblock will migrate to the Pacific Ocean and discharge in the vicinity of Diablo Cove or the Intake Cove.Based upon comparison of groundwater water levels at the well OW I and the ranges of water levels at WW2 during both pumping and non-pumping conditions, it is evident that even at the lowest water levels documented during extensive groundwater pumping at WW2, water levels at the powerblock are always at a lower elevation than at WW2. This relationship precludes migration of groundwater from the powerblock vicinity towards WW2.If improved accuracy of the groundwater gradient direction is needed, this could be accomplished by (a)continuing the existing groundwater water level monitoring program as conducted by REMP staff and expanding the program to include all accessible monitoring wells in the powerblock vicinity, including the monitoring well in Parking Lot 7 and (b) installing a small number of shallow monitoring wells in strategic locations north and northeast of the powerblock.

ENTRIX, INC. ES-i ENTRIX, INC.ES-1 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luls OBISPO, CA MARCH 2010 S E C T I ON I Introduction 1.1 OVERVIEW OF DCPP GROUNDWATER RESOURCES The groundwater resources underlying the DCPP property have been evaluated as part of several previous technical programs, including original site design and permitting, the Independent Spent Fuel Storage Installation (ISFSI) program and as part of evaluations for other facility-related purposes.

Basic information about the site groundwater resources is known to varying levels of accuracy for different areas. In the powerblock area, DCPP has maintained a groundwater monitoring effort for many years by regularly measuring water levels and water quality from a series of data collection facilities (as illustrated in Figure 1).Of these facilities, there are several groundwater monitoring devices located immediately beneath the DCPP powerblock.

Older wells that were located at varying distances away from the powerblock have been mostly abandoned and are no longer available as monitoring devices.Another group of wells, located up the canyon approximately 3,600 ft east-northeast of the powerblock, provide additional water resources data. One of these wells (Water Well #2 or "WW2") is used as an auxiliary water supply for the steam generation system. There are also two monitoring wells near WW2, which are known as WW4 and WW5.1.1.1 Industry Groundwater Protection Initiative

[NEI 07-071 In response to a series of events at several nuclear power plants in the midwest and eastern United States, the Nuclear Energy Institute

("NEI") developed the Groundwater Protection Initiative Guidance Document.

This document identifies actions that nuclear facility operators can implement to ensure timely and effective groundwater protection.

Of the several targeted actions in this initiative, this report is focused on evaluating the following components outlined in NEI 07-07: " Objective 1.1 a: Perform hydrogeologic and geologic studies to determine predominant groundwater flow characteristics and gradients." Objective 1.1 d: Establish the frequency for periodic review of site hydrogeologic studies. As a minimum, review should be performed whenever any of the following occurs: o Substantial on-site construction; o Substantial disturbance of site property;o Substantial changes in on-site or nearby off-site use of water; or, o Substantial changes in on-site or nearby off-site pumping rates of groundwater.

For Objective 1.1 a, ENTRIX has conducted a review of existing groundwater water level data available for the Diablo Canyon site, including current and past datasets collected during various phases of the plant ENTRIX, INC. 1-1 ENTRIX, INC.1-1 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 construction and operations.

These data were collected and analyzed in an effort to determine the groundwater gradient in the vicinity of the powerblock.

For Objective 1.1 d, ENTRIX conducted an evaluation of the refurbished WW2 water level data, during both pumping and non-pumping conditions.

These data are compared with known water levels in the powerblock area to provide an assessment of any possible hydraulic connection between these two regions of the site.Figure 1. Site Map 1.1.2 Previous Studies Groundwater resources have been evaluated in the course of several previous technical efforts, primarily during the initial site permitting evaluations and during the Independent Spent Fuel Storage Installation (ISFSI) Final Safety Analysis Report (FSAR) project effort. The ISFSI chapter on groundwater (chapter 2.5)provides a general summary of groundwater conditions in the powerblock vicinity as well as at the ISFSI area. This summary provides two (2) data points from the Parking Lot 7 piezometers.

These piezometers, one of which was discovered as part of the current investigation, were measured to have groundwater levels that ranged from 40 to 77 ft below ground surface in 1996 to 1997. Evidence of a perched water table was also noted in this area, although details of how this was measured and the possible geographic extents of the perched groundwater were not provided.More recently, in 2007, a technical analysis of groundwater water and groundwater water quality was prepared by S.M. Stoller Corporation

("Stoller").

This report focused on the evaluation of the locations and 1-2 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luls OBISPO, CA MARCH 2010 magnitude of licensed material releases, mainly tritium, and provided a general evaluation of groundwater conditions in the powerblock vicinity.

Although the Stoller report was able to identify a variety of issues and technical conclusions related to releases of licensed material, the limited amount of groundwater water level data prevented definitive determination of the groundwater gradient in the DCPP powerblock vicinity.ENTRIX, INC.1-3 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 S E C T 1 ON 2 Description of Available Water Resources Data 2.1 AVAILABLE GROUNDWATER DATA As discussed in previous sections, there have been several episodes of monitoring well installation and data collection at the power plant beginning in the 1970's during pre-construction phases, and including the more recent ISFSI planning efforts. Most of the monitoring wells installed during those phases have been abandoned.

In an effort to determine if past water level data collected from these older wells would be helpful to assess groundwater gradients, a thorough files search was conducted by PG&E staff and others.Unfortunately, relevant data were not located by this effort.2.1.1 Groundwater Monitoring near Powerblock At the DCPP powerblock, four (4) groundwater monitoring devices were installed as part of original plant construction.

Basic well information is provided in Table I. The basic construction characteristics of the wells are illustrated in Figures 2 and 3. Two of these wells are constructed as "observation wells" (OWl and OW2), and are essentially groundwater monitoring wells. Because these wells tie into French drain systems that underlie each of the reactor vessels, the observed water levels are representative of the averaged groundwater water level across those interconnected areas. The design of these wells generally allows for them to be independently representative of the groundwater water levels underlying each of the reactors.Separate from the observation wells are two (2) drywells (DY 1 and DY2) which connect to French drain systems underlying the fuel handling building just northeast of the reactors (illustrated in Figure 3). One of these drywells (DY 1) is not accessible and neither current nor historical water level data are available.

REMP staff has collected water level and water quality data from these wells since February 2006. These data represent the available groundwater data in the power block vicinity.

As an initial evaluation step, the water level data for each well are illustrated on.Figure

4. Well OWl exhibits a clear relationship to winter rainy periods and summer dry periods. However, based upon the lack of a similar water level response in wells OW2 and DY2, it is evident that OW2 and DYI are not responsive to local aquifer water level changes.Either as a result of original construction methods or subsequent well clogging or other effects, wells OW2 and DY 1 do not provide meaningful groundwater water level data. Therefore, for the purposes of this evaluation, well OWl will be used for groundwater water level information for the powerblock area.ENTRIX, INC. 2-1 ENTRIX, INC.2-1 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT MARCH 2010 Figure 2. Schematic illustration of Observation wells located adjacent to each reactor (courtesy of REMP staff).FUEL HANDLING BLDG U-2 SFP HOT MACHINE SHOP U-i SFP SIVFLAVAIION DISCHARGE ONTO BLACKTOP 42TELEVA110N?

-DRYWF H. 1] 5'(DRYWELL 02)L z DRYWFLI 115'(DRYWELL 01, NO ACCESS!C II SO'QE i VATfON ABOUT 10'ELEVATION.t ltVATION DISCHARGE ONTO BLACKTOP OVELEVAIION N ABOUT 7VELEVATION III ABOUT SLt EIVADtON A II1 Ni HI)AI'24 DIAMETER WELL CASINGS 1

  • 4'4" 4ELEVArION Figure 3. Schematic illustration of Dry wells located adjacent to powerblock (courtesy of REMP staff).2-2 ENTRIX, INC.2-2 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 Table 1. Data for Monitoring and Water Wells on DCPP property.Well Wpll Infnrmn;tinn Well Information (V 0 r V).2 (V S(.0:7 V)V)CU (V_j ('U CM 05 Observation Well 01 (OW1) 1968 85 42 45.8 Feb '06 to present Quarterly Observation Well 02 (OW2) 1968 85 42 N/A Feb '06 to present Quarterly DryWell 01 (DYl) 1968 115 73 N/A Feb '06 to present N/A DryWell 02 (DY2) 1968 115 73 N/A not accessible Quarterly Parking Lot 7 (8S3) 1996 100 78 67 2009 only Quarterly Well #2 (WW2) 1985 333 350 208.3 1985- present Continuous Well #4 (MW4) 2007 452 506 N/A 2007 -present Occasional Well #5 (MW5) 2007 304 409 214.7 2007 -present Continuous 2.1.2 Monitoring Well at Parking Lot #7 During field reconnaissance efforts seeking to locate existing monitoring wells from previous groundwater investigations, a well in Parking Lot #7 was discovered to be well preserved and usable for groundwater monitoring purposes.

This well is identified in the DCPP ISFSI report (Figure A-2) as "WLA-96-3", or alternately as "DCSF 96-3". Using the local REMP naming conventions, this well is identified as "8S3". As stated in section 2.1 above, efforts were made to discover original well construction and data collection history, although data were not found. Based upon a depth-sounding test in October, 2009, the well is 78 feet deep. Based upon contour maps, the wellhead elevation is -100 ft MSL. The recent addition of water level monitoring from this well has been important to allow determination of the groundwater gradient in the powerblock vicinity.Over the past several months, water level measurements and water quality samples have been collected at regular intervals.

Water level data are illustrated on Figure 4. Because the well is located within the parking area, it is constructed with a sub-grade well vault typical of monitoring wells. As a result of a poor well plate seal, stormwater runoff following rain events has been observed to seep into the well vault, fill the vault area, and subsequently overflow into the well casing causing the water level to rise and be unrepresentative of true groundwater water level. Water level measurements collected in October and November, 2009 were affected by this issue and are not representative of natural groundwater water levels. Following a period of equilibration, the water level in the well recovers and the well appears to document natural groundwater water ENTRIX, INC. 2-3 ENTRIX, INC.2-3 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT MARCH 2010 levels. On going monitoring at 8S3 will be conducted with attention to collecting water level data at times that are at least one week following rain events.As suggested in the Recommendations section of this report, collection of additional water level data from this monitoring well will provide important data to develop a more reliable assessment of groundwater gradients in the powerblock area.80 ...................................................................

76 70 Owl* 0W2 Dyl (0=.2 0 S uJ.5 S 4-0 S 83 (0 C6FK-3)65 ,t 9 -9 60 so~t s0 45 A U~~ ~ 00, 4. ..asIs336 gdt a P X 00 NONNIN UU UM g 53 W OO a 40 -35 30- --.. .-... .Figure 4. Groundwater Water levels in vicinity of DCPP Powerbiock for period fromi 2006 to present.2-4 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 2.1.3 Water Well 02 (WW2)This is the primary water supply well that provides supplemental water augmenting the seawater reverse osmosis system for the DCPP steam generation system. This well is located in Diablo Canyon, above the main Switchyard.

Recent well rehabilitation has allowed a greater amount of groundwater to be produced from this well. A continuous water level recording device in the well provides reliable data on both pumping and non-pumping water levels.Figure 5 provides an illustration of the water level measurements at Well 2 and compares these data with water levels from powerblock monitoring well OWl. Comments on the potential groundwater flow directions between these two locations are provided in section 2.3.Diablo Canyon Power Plant Groundwater Level Monitoring 250 200-J 150.5 E u.IS w O 0 o1_A? &Figure 5. Groundwater Water level comparison chart for WW2 and OWl.ENTRIX, INC. 2-5 ENTRIX, INC.2-5 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT MARCH 2010 2.2 GROUNDWATER GRADIENT NEAR POWERBLOCK In an effort to develop a preliminary estimate of the groundwater gradient given the limited groundwater data available at the powerblock, a water level contour map was prepared utilizing water level data from the following wells:* OW-1* DCSF96-3 ("8S3" in Parking Lot #7) monitoring well* Water Well #2* Water Well #5 As identified in the Stoller report, all of these wells tap fractured bedrock of the Miocene Obispo Formation.

Although local formation differences may exist and may have localized effects on groundwater conditions, the average direction of saturated zone groundwater flow is represented by the water levels in the monitoring wells.Water level data collected in August, 2009 from the above listed on-site wells constitute a dataset which is used to prepare the contour map of the local groundwater gradient (Figure 6). Analysis of the contour map indicates that groundwater in the powerblock area flows generally to the southwest, towards the Pacific Ocean. Although the existing data preclude determination of the exact groundwater gradient, the available data indicate that groundwater from beneath the powerblock will migrate to the Pacific Ocean and discharge in the vicinity of Diablo Cove or the Intake Cove. Greater certainty of the groundwater flow direction could be attained by a combination of additional water level data from existing monitoring wells and from the installation of strategically-located monitoring wells.2-6 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luis OBISPO, CA MARCH 2010 Figure 6. Preliminary groundwater gradient contour map based upon groundwater water levl data collected August, 2009. Because of the limited number of monitoring wells and associated water l~eve data,, the direction of the groundwater gradient couli vary such that groundwater from beneath the powerbiock could discharge into the Pacific Ocean between Diablo Cove and the Intake Cove.ENTRIX, INC.2-7 GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT MARCH 2010 2.3 COMPARISON OF WATER LEVELS AT POWERBLOCK AND WELL #2 In accordance with NEI 07-07 Objective

1. 1(d), a review of site hydrologic conditions is needed as a result of the modifications and improvements to Well #2 that were conducted in 2008 and 2009. A key aspect of this review is to evaluate the relationship of groundwater water levels in the vicinity of the powerblock with those at Well #2. To accomplish this comparison, water level monitoring data from both wells were reviewed by converting both datasets to a common mean sea level (MSL) datum.Well 2 is located in Diablo Canyon, approximately 3,600 ft east-northeast of the powerblock.

Although, the wellhead elevation of Well 2 (333 ft MSL) is considerably higher than that of the powerblock monitoring wells (85 ft MSL), it is necessary to compare both the non-pumping

("static")

water level and the pumping water level of Well 2 with the powerblock wells to most conservatively assess if groundwater flow could occur from the powerblock toward Well 2. For this comparison, well OW-I is used as representative of water levels in the powerblock vicinity.Water levels at OWl have been regularly measured by REMP staff since 2006. In this time period, the water levels have ranged from 46 to 67 ft MSL. At Well 2, water levels have been measured since 1985, although with some extended periods of quite infrequent measurements.

The range of measured water levels in Well 2 is between 77 ft MSL (pumping water level) and 225 ft MSL (static water level) as illustrated in Figure 5.The most conservative manner of evaluation is to compare the periods of maximum drawdown induced by pumping at Well 2 with the measured water levels at OWl. A graphical illustration of this relationship is provided as Figure 5 which illustrates the conditions during late 2008 to 2009, and includes a period of groundwater demand at Well 2 that represents the most intensive pumping ever conducted at Well 2. An additional factor that ensures the comparison is conservative is that regional drought conditions have existed in this area for the past several years, which correspond with lower groundwater levels that would be typically present.The observation that the lowest measured water level at Well #2 is 10 ft higher than the highest measured water level at OW-I indicates that, based upon these data Well 2 cannot physically draw water from the powerblock area, even during intensive pumping during drought conditions.

This relationship should continue to be evaluated during various hydrologic periods (e.g., higher rainfall periods) to ensure that short-term water level changes do not affect this condition.

Additionally, Figure 5 also demonstrates that the intensive pumping at Well #2 did not generate any additional drawdown at OW-1. This observation represents an additional line of evidence that there is not a hydraulic connection between the groundwater near the powerblock and the groundwater near Well 2.2-8 ENTRIX, INC.

GROUNDWATER GRADIENT ANALYSIS DIABLO CANYON POWER PLANT, SAN Luls OBISPO, CA MARCH 2010 S E C T I 0 N 3 Conclusions and Recommendations This report is prepared in an effort to comply with portions of Objective 1.1 of the Industry Groundwater Protection Initiative Guidance Document [NEI 07-07]. Data collection and analysis were conducted to evaluate predominant groundwater flow gradients in the powerblock area, and also to evaluate potential effects on on-site groundwater use represented by the recent rehabilitation of Well 2.A groundwater gradient contour map was prepared for the powerblock area which illustrates the groundwater flow direction.

The recent addition of water level monitoring at well 8S3 has been important for the ability to determine the groundwater gradient in the powerblock vicinity.

These data indicate that groundwater from beneath the powerblock will migrate southwesterly to the Pacific Ocean and discharge in the vicinity of Diablo Cove or the Intake Cove. If greater certainty in the groundwater flow direction is needed, this could be accomplished by (a) continued water level measurements at wells OWl, 8S3, Well 2 and Well 5, and (b)the installation of two or more strategically-located monitoring wells near the powerblock.

The new monitoring wells would best be located southeast and northeast of the powerblock at locations that could be determined in coordination with considerations for ease of access, safety and hydrologic significance.

Although any data collected from these additional efforts would help to clarify the specific groundwater gradient flow direction, it is unlikely that the new data would indicate a flow direction that is appreciably different from the southwesterly direction illustrated on Figure 6.An additional evaluation conducted as part of this effort was to detemine if there is any potential hydraulic connection between the groundwater in the powerblock vicinty with that of Well 2. Based upon the water level data available for this evaluation, a relatively certain determination is made that groundwater flow from the powerblock towards Well 2 is highly unlikely.ENTRIX, INC.3-1