U.S. Department of the InteriorU.S. Geological Survey

UPDATE: A Potential Approach For Assessing the Freshwater/Saltwater Interface (USDW, 10,000 TDS) in the Floridan Aquifer System

Lester J. Williams and Rick M. Spechler

2/28/2012

Problem:

No statewide maps available showing the 10,000 mg/L or 35,000 mg/L interface(s)

Makes it difficult to assess the regional freshwater flow system and how it interacts with the saline portions of the aquifer

Several different methods have been used over the years leading to a disparity between interpretations of it’s position

Consistent representation of the interface(s) in local and regional models is important

USDW Initiative In Sept 2010 the USGS and FGS presented a

proposal to the WMDs to construct a statewide USDW map in but funding was not available to proceed at that time

The need for such a map is obvious and would be highly beneficial for ongoing water-resource studies

Much of the data needed for this assessment has been already been compiled through the USGS Saline Aquifer Mapping project (L.J. Williams)

FGS and USGS have continued to discuss how a state-wide mapping project can be accomplished

Project Objectives and Funding Sources

Objective: Produce a state-wide map depicting the position of

USDW (10,000 mg/L TDS) in the Floridan aquifer system and cross sections showing the nature of the interface (sharp, diffuse, alternating). Outlet: FGS or USGS map series (within 2-years?)

Mapping of other levels (3,000; 5,000 etc.)

Funding:USGS cooperative funding matched by other

agenciesFGS is targeting several federal grants

Presentation Outline

Status of current mapping efforts (what has been done thus far)

The next stepDiscuss major tasks that need to be

accomplishedOther discussions…

Definitions

FRESHWATER shall mean any surface or ground waters of the State whose total dissolved solids content is less than 1,000 milligrams per liter.

UNDERGROUND SOURCE OF DRINKING WATER (USDW) shall mean an aquifer or its portion: (a) Which supplies any public water system, or (b) Which contains a sufficient quantity of

ground water to supply a public water system and: 1. Currently supplies drinking water for human

consumption or 2. Contains fewer than 10,000 milligrams per liter

total dissolved solids and is not an exempted aquifer.DEP Rules CHAPTER 62C‑25

Sources of Data

Florida DEP Oil and Gas Program FilesPreviously published reportsOngoing USGS Regional Studies in the

Floridan Aquifer SystemWell Log analysisWater quality data compilation

Florida DEP Oil and Gas Program

When drilling an oil test well:(b) Water Quality Analysis. If necessary to

determine the depth to the base of the deepest USDW, the Department shall require resistivity and porosity logs be run before setting surface casing and a representative water sample taken immediately after drilling out of the surface casing.

DEP Rules CHAPTER 62C‑27

Base of Potable Water (250 mg/L)FGS MS-42

Klein, 1971, Revised 1975

Upper Floridan aquifer Conc. Maps OFR 81-1103 PP 1403I

Sprinkle, 1981 Sprinkle, 1989

Ron Reese’s Reports in South Florida

From: Water-Resources Investigations Report 98-4253Hydrogeology and the Distribution of Salinity in the Floridan Aquifer System,Southwestern FloridaPrepared in cooperation with the South Florida Water Management District (Reese, 2000)

Ron has also mapped the saline water zone(35,000 TDS)

Brackish Water Zone Map ~ 10,000 TDS

All Wells Ron Analyzed for BWZ and SWZ

Map compiled from:Water- Resources Investigations Report 94-4010 (Reese, R.S., 1994)Water-Resources Investigations Report 98-4253 (Reese, R.S., 2000)Water-Resources Investigations Report 03-4242 (Reese, R.S., 2004)Water-Resources Investigations Report 99-4061 (Reese, R.S., and Memberg, S.J., 2000)

South Florida Salinity Maps

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Emily Richardson SFWMD, Written Commun., 2010

Upper Floridan Avon Park Permeable Zone Lower Floridan

St. Johns “CL5K” map

5,000 mg/L chloride

Uses water quality data from wells

Brian McGurk, SJRWMD

Saline Water Aquifer Mapping Project (Ongoing)

USGS Groundwater Resources Program (GWRP) Study

Began Oct. 2009Compiling of well-log data (database)Conducting well-log analysisArea being studied is coincident with the

Floridan Aquifer SystemWork is being conducted parallel to the

Floridan Aquifer System modeling effort

Scope of the USGS Saline Aquifer Mapping Project

Floridan Aquifer System Base of freshwater

system Deep saline zones

Coastal Plain System Fresh/Saltwater

interface in each major aquifer

Lateral continuity of fresh and saline aquifers

Status of USGS Log Database

In FY2010 we compiled well log data from:479 wells in FL13 wells offshore111 wells in GA

Log analysis

Status as of Sept. 2010

Status of USGS Log Database

In FY2011 we added: Class I injection wells

and deep test well data

Expanded coverage into southern Alabama and added additional logs in the Panhandle

Deep test holes in coastal Georgia

Status as of Sept. 2011

Types of logs

pre-1958 (old electric logs)Electrical Surveys “E-Logs”

1960’s-70’s Induction-Electric Logs

Post Mid 1970’s Dual Induction Logs (DILL and DISFL)

Borehole Compensated Sonic LogsDensity (Gamma-Gamma) LogsNeutron Logs

Log Database (Neuralog)

database

images

Resistivity-Porosity Method

Uses resistivity values obtained from induction or e-logs

Uses porosity from sonic, density, or neutron log

Freshwater

Salt Water

Transition

Approach for assessing the freshwater/saltwater interface

Geophysical Logs

• Locate the interface(s) in a consistent manner using available geophysical logs from:– Oil and gas tests wells– Class I and IV injection

wells and test holes– Deep monitoring well

clusters

• Resistivity-Porosity Method

Water-Quality Data

• Confirm interfaces where possible with deep water quality data

• Water samples collected while drilling samples

• Packer tests• Use water quality to

help refine the formation factors being used in the methods

Status in Sept. 2010

Red circles: we have completed an initial analysis

Green circles: these are in progress

Purple: nextRed squares:

Ron Reese completed sites

Saline Water Aquifer Mapping Project, USGS, GWRP

Status as of Sept. 2011

This map shows the sites that have been used to evaluate salinity variations in the lower part of the Floridan Aquifer System

Includes both water quality and log-analysis sites

Additional sites continue to be added to dataset

Saline Water Aquifer Mapping Project, USGS, GWRP

~300 sites in master database

Basic Spreadsheet Calculation

Deep-reading resistivity, DT, RHOB, or estimated porosity entered into spreadsheet

Thermal gradient calculated from BHTs

“Salinity zone” depths picked off of graph

Salinity Zones Master Database

Depths of “salinity zones” recorded in master table

Z1 to Z4 Z1 = 3,000 TDS Z2 = 5,000 TDS Z3 = 10,000 TDS Z4 = 32,000 TDS

Separate columns are used to calculate altitudes

nde = not deep enoughBBFAS = estimated depth below bottom of FAS

Rough Altitude of 10,000 TDS

Produced from initial dataset developed Sept. 2011

Used this to get a rough idea of where the interface was positioned

In central highlands and north-central areas the depth of the 10,000 may be near the base of the FAS

Much variation in salinity seen with respect to the middle confining units within the main body of the FAS

This produces complications moving from the central highlands out to the coastal areas

Southwest Florida Much additional

water quality data needs to be incorporated in Hillsborough and Pinellas Counties

Only a few points have been used along with some older references to map the interface position

Salinity inversion observed in areas due to presence of MCUII and highly permeable zones

Northeast Florida

This area needs a lot of work. See previous map by McGurk and others.

We have started to incorporate water quality data

Panhandle

A lot more data (mostly water quality) exists for the cities along the Gulf Coast but we have not incorporated that yet.

The next step

Hardening of the interface Water quality data needs to be integrated into the analysis to refine

the position estimated using the well logs Iterative process needs to be taken looking at water quality data,

going back to the well logs, adjusting a and m parameters, etc., then recalculating salinty profile

Salinity Inversions and complicating factors Some of the middle confining units control salinity variations within

the main body of the FAS Additional study may be warranted to show these relations Some cross sections would be helpful in certain areas to show this

in the report

Salinity variations over time The WMD’s, DEP, etc. have compiled a large amount of water

quality data that could be used to depict changes over time

Major Tasks

Log analysis of additional sites (to be done on an as-needed basis)Northeast FloridaGulf Coast

Several iterations will be needed to refine position of interface based on all available data – this is a time consuming process but necessary

Cross-checking between wells, using deep monitoring well clusters, refining our knowledge of the nature of the interfaces

Report

Contacts:

Rick M. Spechler, P.G.

Hydrologist

U. S. Geological Survey

12703 Research Parkway

Orlando, Fl 32826

Phone: (407) 803-5523

email: spechler@usgs.gov

Lester J. Williams

Hydrologist

U.S. Geological Survey

3039 Amwiler Rd, Suite 130

Atlanta, GA 30360

Phone: 404.906.5761

email: lesterw@usgs.gov

Andy Smith, P.G.

Rodney S. DeHan DVM, Ph.D.

Florida Geological Survey

Gunter Building, Florida State

University Campus

Phone: 850-487-9455 Ext. 150

FAX: 850-412-0495

Tallahassee, FL. 32304

E-Mail:

andy.smith@dep.state.fl.us

rodney.dehan@dep.state.fl.us