FSAWWA Paper and Presentation Floridan Aquifer 12022015

FSAWWA 2015 Paper GJ Schers, et al. Date November 30, 2015
“Floridan Aquifer” Lessons Learned Page 1 of 32
Salinity Increases in the Upper Floridan Aquifer Wellfields in South Florida:
What have we learned and how do we plan new systems?
Authors:  GJ Schers1
PMP, Ed Rectenwald1
PG, PMP, Jim Anderson2
PG, Andy Fenske3
,
Amanda Barnes PE4
, Howard Brogdon5
, and Tom Uram6
PG

1
MWH Global Inc, 2
JLA Geosciences, Inc., 3
City of Cape Coral, 4
Town of Jupiter, 5
Collier County and
6
Palm Beach County

1. Introduction
The use of brackish ground water as a source for potable water supply has gained interest throughout the
country. Population growth in areas of fresh water scarcity, coupled with an affordable brackish water
reverse osmosis (BWRO) treatment technology, have led to implementation of many systems in Texas,
Florida and California. Production well and treatment technology have improved tremendously over the
past decades and long term operational experiences have provided the utilities with valuable information
on design and operational criteria and pitfalls. Three aspects need to be carefully considered during the
implementation of a BWRO system: (1) wellfield design and related source water productivity and quality,
(2) required pre‐treatment for RO and (3) disposal of the RO concentrate.
The wellfield design and related source water productivity and quality depend on aquifer conditions and
heterogeneity, which vary by region, but design criteria for production wells are commonly understood.
Criteria like well spacing, capacity, redundancy, depth and flow and withdrawal control of production
wells are nowadays carefully considered to provide a sustainable wellfield in terms of both production
capacity and water quality. Some wells have experienced water quality degradation over time and, if not
anticipated during design, treatment modifications can become expensive. Also treatment technologies
have improved over time and current low‐energy RO thin film composite membrane technology has
become the treatment of choice.
The type of pre‐treatment is dependent upon the local ground water chemistry where sand, iron,
hydrogen sulfide, organics, and silicates can be present. Each substance requires dedicated attention in
regards to pre‐treatment to avoid membrane fouling and/or scaling. In Florida the presence of sand in the
aquifer, without removal, can cause physical damage to the membranes and hydrogen sulfide and
dissolved iron, when oxidized, can cause membrane fouling. In parts of Texas, the major issue for BWRO
pre‐treatment includes radionuclides, arsenic, and heavy metals. In Southern California, elevated levels
of iron and manganese may require upstream media or greensand filtration.
Disposal of RO concentrate varies per region. Common methods of disposal, including surface water
discharge and deep well injection, are not readily available for landlocked areas. Areas with deep aquifers
or in close vicinity to the ocean, like coastal areas in Florida, can use more common methods of disposal.
Disposal methods in Texas are variations of surface disposal and while Southern California has access to
ocean disposal, there is a trend towards using regional concentrate transmission such to improve the
inland salt balance. Alternatives for concentrate treatment include evaporation ponds, membrane
distillation and thermal treatment, although these methods are typically only applied when zero‐liquid
discharge is required. While these technologies are effective, they are also expensive and the pros and
cons need to be evaluated prior to implementation.

This paper will focus on BWRO systems in Florida and source water quality. The Upper Floridan Aquifer
(UFA) is widely used here as a water source for potable and industrial water supply. The current (2014)
permitted capacity of BWRO systems for municipal use is 551 MGD, which represents close to 25% of the
total permitted capacity. In South Florida the aquifer contains brackish ground water and many systems
have used this source in the last 40 years. The Cities of Venice and Cape Coral along the west coast were
among the first to implement these systems successfully in the 1970’s and 1980’s. Many other water
utilities in that region followed their footsteps including Lee County, Collier County, Bonita Springs, and
the cities of Fort Myers and North Port. In 1990, the Town of Jupiter was the first east coast utility to
implement BWRO.  Martin County followed shortly thereafter with the construction of its North plant in
Jensen Beach.  In the 2000’s other utilities including the City of North Miami Beach, the Town of Davie,
and Palm Beach County implemented UFA wellfield and BWRO treatment systems.
Although there are many commonalities between east and west coast UFA systems, there are also distinct
differences. Aquifer salinity, expressed as total dissolved solids (TDS), typically ranges from 2,000‐5,000
mg/L on the west coast, and is often more saline (3,500‐8,000 mg/L TDS) on the east coast. The production
zone of the aquifer (or typical well depth), is deeper in east Florida because the aquifer dips steeply to the
Southeast.  In general, the UFA is more productive on the Southeast coast. Typical well production rates
on the west coast are 350‐700 gpm as compared to 800‐2,000 gpm towards the Southeast. One
commonality for the UFA is that the wellfield salinity generally increases over time, requiring improved
wellfield management by including redundant production wells and treatment modifications, which have
increased the costs of producing potable water.
The salinity increases may impact the BWRO treatment system, which typically is limited by the raw water
salinity it can treat. The limits are caused by upper design criteria of individual components of the
treatment system, like the horsepower of RO feed pump motors or the pressure rating of membranes,
membrane vessels or pipework. In existing systems, the operation is restricted by the limits of the
materials and equipment and unless these are replaced, it may not be able to treat higher salinity raw
water. Fortunately, there have also been improvements in membrane technology which provide for better
salt rejections at lower feed water pressure and developments in scale inhibitor which allow for higher
system recoveries. In several cases these improvements have been implemented and have offset the
salinity increases allowing continued successful use of the BWRO systems. In terms of planning for a new
system, the designer needs to allow for some form of water degradation. This flexible design approach
has been documented by this author in several publications and focuses on selecting conservative design
criteria for RO feed pumps, chemical pre‐treatment feed systems, RO skid design, and RO bypass pipeline
and valving.
This paper will describe the general hydrogeology of the Floridan Aquifer in South Florida, will provide
details on wellfield and source water quality of certain BWRO systems and will present impacts of source
water salinity on the treatment.

2. Florida Aquifers
Three major aquifer systems underlie Florida: Surficial Aquifer System (SAS), Intermediate Aquifer System
(IAS), and Floridan Aquifer System (FAS). The IAS is only present in the Southwestern half of the state and
has variable permeability. The aquifer systems are composed of multiple, discrete aquifers separated by
low permeability “confining” units that occur throughout this Tertiary/Quaternary age sequence.
Brackish ground water in Florida is mainly found in the lower FAS, but is also present in the IAS and SAS
along coastal areas that have been impacted by lateral saline water intrusion. The brackish to highly saline
ground water found at depth in the lower FAS is connate water that was trapped in the marine limestones
as they were deposited. Very highly saline water with TDS concentrations exceeding 100,000 mg/L is
found below the Cretaceous‐aged anhydrite sequence underlying the FAS and is caused by the long term
dissolution of rock units.
2.1 Southwest Florida Aquifers
In Southwest Florida, freshwater resources occur within the SAS and IAS.  The more abundant sources of
water occur within the FAS, with water quality that ranges from brackish to saline.   The FAS is defined as
a vertically continuous sequence of permeable carbonate rocks of tertiary age that are hydraulically
connected in varying degrees, and whose permeability is generally several orders of magnitude greater
than that of the formations above and below (Miller, 1986).  The system is subdivided into the Upper
Floridan aquifer (UFA), middle confining unit (MCU) and the Lower Floridan aquifer (LFA).  The FAS in the
west coast study area is composed predominately of limestone with lower occurrences of dolomitic
limestone and dolomite (Miller, 1986).
The UFA is composed of a series of variable permeable carbonate formations including, in descending
depth, the Lower Hawthorn, Suwannee and Ocala. The MCU is composed of a series of low porosity
limestones and dolomites that consists of the Avon Park formation. The LAS consists of the highly
transmissive Boulder Zone found within the lower Avon Park and Oldsmar Formation.  Potential sources
of drinking water are found in the UFA above the regulatory Underground Source of Drinking Water
(USDW), which is defined as having TDS levels of 10,000 mg/l or less and is expected to occur at
approximately 1,100 to 1,300 feet below land surface.  Portions of the LFA are used for disposal of RO
concentrate and/or treated wastewater. The source water of BWRO systems is provided from the UFA
with water quality generally ranging between 1,500 and 4,000 mg/L TDS up to about 15,000 mg/L in
deeper and more coastal areas.  Water quality in the LFA is likely saline, with a TDS concentration of
approximately 37,000 mg/L, based on sparse existing data.  A summary of hydraulic, water quality and
potential use of these aquifers is shown in Figure 1.
Lateral saltwater intrusion occurs when seawater migrates inland from a natural reduction of freshwater
heads or pumping of wells. Increases in pumping lowers the hydraulic potential by stressing the aquifer
allowing the seawater to move inland at a faster rate. Fractures which are also evident in carbonate
aquifers of Florida may also increase movement of saltwater laterally into coastal wellfields. Vertical
saltwater intrusion occurs when saline water moves upward through fractures from underlying more
brackish aquifers. Production wells are occasionally drilled into fractures that are oriented vertically or at
high angles. These fractures may act as conduits for saline waters to move upward rapidly degrading the
water quality of some wells soon after they go into production (see Figure 2).

Figure 1: Southwest Florida Aquifer Hydrogeology
Figure 2: Sources and Migration Pathways of brackish ground water in Coastal Southwest Florida
[Source USGS Circular 1262, 2003]

Production Zone:
1500-3000 mg/L TDS

2.2 Southeast Florida Aquifers
In Southeast Florida, freshwater resources occur within the SAS and Biscayne Aquifer System (BAS). Water
resources that occur within the FAS, with water quality that ranges from brackish to saline. The FAS is
defined as a vertically continuous sequence of permeable carbonate rocks of tertiary age that are
hydraulically connected in varying degrees, and whose permeability is generally several orders of
magnitude greater than that of the formations above and below (Miller, 1986). The system is subdivided
into the Upper Floridan aquifer (UFA), middle confining unit (MCU) and the Lower Floridan aquifer (LFA).
The FAS in the east coast study area is composed predominately of limestone with lower occurrences of
dolomitic limestone and dolomite (Miller, 1986).
The UFA is composed of a series of carbonate formations with variable permeability including, in
descending depth, the Arcadia Formation of the Basal Hawthorn Unit, Suwannee, Ocala and Avon Park.
The MCU is composed of a series of low porosity limestones and dolomites that consists of the Avon Park
Formation. The LFA consists of the highly transmissive Boulder Zone found within the lower Avon Park
and Oldsmar Formation. Potential sources of drinking water are found in the UFA above the regulatory
Underground Source of Drinking Water (USDW), which is defined as having TDS levels of 10,000 mg/l or
less and is expected to occur at approximately 1,000 to 1,400 feet below land surface. Portions of the LFA
are used for disposal of RO concentrate and/or treated wastewater. The source water of BWRO systems
is provided from the UFA with TDS generally ranging between 3,000 mg/L to 6,000 mg/L up to about
15,000 mg/L in deeper and more coastal areas. The UFA within some parts of Palm Beach County and
northern Broward Counties exhibits a reversal in salinity, with higher TDS concentration in the upper
sections of the UFA and lower TDS concentrations in the lower sections (Reese and Memberg, 2000).
Water quality in the LFA is likely saline, with a TDS concentration of approximately 37,000 mg/L. A
summary of hydraulic, water quality and potential use of these aquifers is shown in Figure 3. The pathways
of lateral and vertical saltwater intrusion are similar than in Southwest Florida Aquifers.

Figure 3: East Florida Aquifer Hydrogeology

3. Wellfield and Water Quality
Water quality trends can occur in two fashions; slow trends over time within the wellfield, and fast
changes in individual wells. Certain mechanisms can be responsible for these trends or quick changes,
however, many times the exact answer is not known without intense and potentially expensive
investigations. There are however ways to minimize the effects of water quality changes.
Several wellfields tapping the UFA have shown some type of abrupt water quality declines, including the
North Collier Regional WTP UFA wellfield (CDM, 2005), North Lee County wellfield (SFWMD Permit
Information Files), the City of Cape Coral North RO wellfield (MWH, 2007,) and the City of Fort Myers
wellfield. Four utilities, the City of Cape Coral, Collier County, the Town of Jupiter, and Palm Beach County,
gave permission to use their water quality data in this report. Also current water quality data are provided
in this report from other utilities, including Bonita Springs Utility, City of Venice, City of North Miami
Beach, Town of Davie and Broward County, to complement the data from the four case studies and to
enable a presentation over a wide range of source water quality. However historical trends are not
provided. The next sections will present the data on the four featured case studies.
3.1 Southwest Florida Case Studies
City of Cape Coral
The City of Cape Coral is a pre‐platted community that relies on domestic self‐supply in areas not served
by the utility system. Limited fresh ground water sources from the IAS are available to supply domestic
users. The City is in the process of expanding the utility service again to meet the demands of a growing
population, after 6 years of decline between 2006 and 2012. The City operates two BWRO systems. The
Southwest BWRO system is the older system, which was originally put in operation in 1976 at a capacity
of 3 MGD. Expansions occurred in 1985 to 15 MGD and in 2008 to 18 MGD. In 2008, as part of plant
expansion, also the number of production wells was increased from 24 to 32, each with an approximate
depth of 700 ft. The North BWRO system is the newer system with a capacity of 12 MGD, put in operation
in 2010. This system includes 22 production wells to a similar depth than the Southwest wells.

A well location map and a photo of a North BWRO production well is included above. The City kept records
of well pumpage and water quality since inception. While pumpage of each well was recorded
continuously, water sampling for water quality was carried out monthly at each production well.  Samples
were analyzed for hardness, alkalinity, chlorides, conductivity, TDS, pH, hydrogen sulfide, color, fluoride
and turbidity.  Trends for each of these water quality parameters was developed for each well and for all
wells combined.  Figure 4 shows the increasing raw water chlorides in all wells combined from each
wellfield. The Southwest wellfield combined chlorides increased from 600 mg/L in 1988 to 900 mg/L in
2014, while the North wellfield chlorides increased from 800 mg/L in 2010 to 1,100 mg/L in 2014. Similar
trends were established for sodium, TDS, hardness and conductivity.  On the other hand, limited to no
variations were observed for other parameters, such as the source water alkalinity, pH, hydrogen sulfide,
radionuclides, fluoride and turbidity.
Water quality trends have occurred in two fashions; slow trends over time within the wellfield, and fast
changes observed in individual wells. The referenced figure includes two graphics depicting the chloride
increases in individual wells. In the Southwest wellfield, 21% of the wells have seen a chloride increase of
5% or higher during each 12 months of operation. The ‘bad’ wells are 105, 112, 114, 214 and 231 and are
spread randomly throughout the wellfield. In the North wellfield, 50% of the wells have seen a chloride
increase of 5% or higher during each 12 months of operation. The ‘bad’ wells are 301, 302, 303, 305, 306,
307, 318, 320, 322, 323 and 324 and are grouped in certain areas in North Cape Coral.
Collier County
The County has kept records of the North Collier County well pumpage and water quality since the
beginning. The North Collier brackish wellfield was originally constructed in 1998 with 10 production wells
in the lower Hawthorn aquifer and now currently has a total of 25 production wells. Six of the production
wells are constructed into the mid Hawthorn aquifer with casing and total depths approximately 400 feet
and 515 feet, respectively.  With the other 19 production wells constructed in the lower Hawthorn aquifer
with casing and total depths of the wells approximately 750 and 950 feet below land surface (bls),
respectively.
Wells RO‐001 through RO‐004 at the western end of the wellfield which are producing from the lower
Hawthorn aquifer experienced rapid increases in salinity shortly after they were placed into operation.
The chloride concentration of water samples obtained from wells RO‐001 through RO‐004 during 2000
and 2001 (after they were initially constructed) ranged from approximately 2,000 to 3,000 mg/L.  Chloride
concentrations in these wells increased to between 6,000 to 10,000 mg/L within two year of operation.
The membrane processes used at the NCRWTP are unable to adequately treat the higher salinity waters
so wells RO‐001 through RO‐004 have largely been unused since 2002.  A total of 19 additional production
wells have been added to date to increase the raw water supply capacity to the RO WTP.  Individual well
yields in the wellfield generally range from 500 to 700 gpm with chlorides concentrations ranging from
850 mg/L to 3,000 mg/L (see Figure 5) and have shown no signs of degradation. In the North wellfield,
21% of the wells have seen a chloride increase of 5% or higher during each 12 months of operation. The
‘bad’ wells are 001, 002, 003, 004 and 009.
The County also has kept records of the South Collier County well pumpage and water quality since the
beginning of operation.   The South Collier brackish wellfield was originally constructed in 2001 to 2002
with 11 production wells in the mid Hawthorn aquifer and 4 production wells in the lower Hawthorn
aquifer for a total of 15 production wells.  In 2006 through 2007, the County constructed 25 additional
production wells in the mid Hawthorn aquifer and 2 production wells in the lower Hawthorn aquifer for a

grand total of 42 production wells.  All of the production wells constructed in the mid Hawthorn aquifer
have casing and total depths approximately 300 feet and 420 feet, respectively.  And the production wells
constructed in the lower Hawthorn aquifer have casing and total depths of the wells approximately 630
and 1,000 feet below ground surface, respectively.
All production wells in the South County Wellfield show somewhat stable chlorides throughout the period
of record which typically average from approximately 2,000 to 3,000 mg/L.  However, RO‐7, 10, 13, 14,
17, 39 and 41 all have average chloride concentrations between 3,000 to 4,600 mg/L within one year of
operation and have seen rapid inclines of chlorides over time.   Individual well yields in the wellfield
generally range from 500 to 700 gpm with chlorides concentrations ranging from 2,000 mg/L to 3,000
mg/L and have shown no signs of degradation. In the South wellfield, 13% of the wells have seen a chloride
increase of 5% or higher during each 12 months of operation. The ‘bad’ wells are 007, 010, 013, 014 and
039.
3.2 East Florida Aquifers
Town of Jupiter
Information on the Town of Jupiter UFA wellfield was collected from historical pumping and water quality
data provided by the Town. The Towns UFA wellfield was originally constructed in 1995 with 4 production
wells in the UFA. The wellfield was periodically expanded westward as the Towns water demands
increased and as water quality changed in older production wells.  The Towns UFA wellfield expansion
occurred in several phases with the most recent in 2003 with the newer wells being constructed away
from the Towns Water Treatment Plant along the C17 canal with well spacing of approximately 2,000 feet.
The average UFA well casing and borehole depths are approximately 1,215 and 1,560 feet bls,
respectively. Individual well yields range between 500 gpm and 1,600 gpm.
The Towns older UFA production wells RO‐2 through RO‐6 have experienced the most significant increases
in TDS with at the northern end of the wellfield experienced increases in salinity shortly after they were
placed into operation. The chloride concentration of water samples obtained from wells RO‐2 through
RO‐7 during 1995 and 1997 (after they were initially constructed) ranged from approximately 1,350 to
2,700 mg/L. Chloride concentrations have increased between 2,110 mg/L (RO‐2) and 556 mg/L (RO‐13)
with the largest increases (>1,000 mg/L) in wells RO‐2, RO‐3, RO‐5, RO‐6, RO‐7. Overall, chloride
concentrations have increased between 2% and 5% per year. This increase in salinity is directly related to
the well usage.
In 2004, JLA Geosciences suggested the need for uniform and equitable pumpage of the RO wells following
rapid increases in chloride and specific conductance in water produced from wells RO‐2 and RO‐3. At that
time as much as 46% of the water supplying the plant was being produced from RO‐2 and 58% from RO‐
3, with an average chloride of approximately 3,000 mg/L. With the installation of wells RO‐11, RO‐12 and
RO‐13 (2004), pumpage from RO‐2 and RO‐3 declined to level off the produced water quality. The leveling
off of chloride on the RO‐2 is likely the result of reduced stress on the well from the even distribution of
well pumpage and the increased number of wells available for use with the installation of RO‐11, RO‐12
and RO‐13.

Palm Beach County
Information on the Palm Beach County Water Utilities Department (PBCWUD) Water Treatment Plan No.
11 (WTP‐11) UFA wellfield was collected from historical pumping and water quality data provided by
PBCWUD. The WTP‐11 was originally placed into service in 2008 with 7 UFA production wells producing
approximately 10 MGD raw water. The wellfield extends northward with well spacing of approximately
800 feet. Average well casing and borehole depths are approximately 1,150 feet below land surface (bls)
and 1,450 feet bls, respectively. Due to declines in well performance and rapid water quality degradation
the WTP‐11 UFA wellfield was expanded in 2012 (Well PW‐8) and in 2014 (Wells PW‐9 and PW‐10). The
newly constructed wells were completed with boreholes at shallower depths of approximately 1,350 feet
bls, to target sections of the UFA with better water quality. Additionally, individual well withdraw rates
were reduced from an average of 2 MGD per well to 1MGD per well to reduce the rate of water quality
degradation.
The existing Upper Floridan Aquifer wells in the Lake Region WTP11 wellfield have lost capacity since they
were constructed in 2005 (TP‐1 and TP‐2), 2007 (PW‐3 – PW‐7) and 2012 (PW‐8) due to a combination of
over pumping and water quality degradation. Wells in the northern portion of the wellfield, TP‐1, TP‐2,
PW‐4 through PW‐7, have experienced upconing of higher saline water with a current range of 5,000 to
10,000 mg/L TDS in the source water.

Figure 4: Summary of City of Cape Coral Floridan Aquifer production wells
Summary of
Production Wells
Southwest Wells North Wells

Start of Operation 1976 (3 MGD) 2010 (12 MGD)
Capacity 15 MGD (exp. in ’85)
18 MGD (exp. in ‘08)
12 MGD (original)
Number
Average Capacity
34
500 gpm
24
500 gpm
Specific capacity 10‐100 gpm/ft 10‐100 gpm/ft
Depth
Diameter
700 ft
12 inch FRP
700 ft
12 inch FRP
Original TDS
Current TDS
1,400 mg/L (1988)
2,200 mg/L (2014)
2% increase/year
2,000 mg/L (2010)
2,500 mg/L (2014)
5% increase/year
Other source water
quality parameters
Chloride 900 mg/L,
Hardness 575 mg/L as
CaCO3, H2S 3 mg/L
Chloride 1100 mg/L,
Hardness 625 mg/L as
CaCO3, H2S 3 mg/L
0%
5%
10%
15%
20%
25%
30%
35%
40%
101
103
105
107
109
111
211
213
215
217
219
221
223
225
227
229
231
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
Chlorides increase (%/Year of Operation)
Southwest Wellfield ‐ Well ID
Chlorides Concentration (mg/L)
Chlorides (avg first 6 m)
Chlorides Increase During Ops
Chlorides Increase (%/Yr Ops)
0%
5%
10%
15%
20%
25%
30%
35%
40%
301
303
305
307
309
311
313
317
319
321
323
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
North Welllfield ‐ Well ID
SW Wells: 21% bad
(>5% incr/yr)
N Wells: 50% bad
(>5% incr/yr)
0
4
8
12
16
20
24
28
0
500
1,000
1,500
Total Pumpage (mgd)
Concentration Chloride (mg/L)
Chlorides South
Chlorides North
Total Pumpage North + South

Figure 5: Summary of Collier County Floridan Aquifer production wells
Summary of
Production Wells
South Wells North Wells
Capacity 12 MGD (exp. in ’07) 8 MGD (exp. In ‘03)
Number
Average Capacity
42
300 gpm
25
300 gpm
Depth
Diameter
300‐400 ft (mid Hawtorn)
600‐1000 ft (low Hawtorn)
12 inch FRP
400‐500 ft (mid Hawtorn)
700‐900 ft (low Hawtorn)
12 inch FRP
Original TDS
Current TDS
4,500 mg/L (2002)
5,500 mg/L (2013)
2.5% increase/year
5,500 mg/L (2000)
4,780 mg/L (2013)
No increase
Other source water
quality parameters
Chloride 2,750 mg/L,
Hardness 1,500 mg/L as
CaCO3, H2S 3 mg/L
Chloride 2,000 mg/L,
Hardness 1,100 mg/L as
CaCO3, H2S 3 mg/L

0
2,000
4,000
6,000
8,000
Concentration Chloride (mg/L)
Chlorides South
Chlorides North
12 per. Mov. Avg. (Chlorides South)
12 per. Mov. Avg. (Chlorides North)
0%
5%
10%
15%
20%
25%
30%
35%
40%
001
003
005
007
009
011
013
015
017
019
021
023
025
027
029
031
033
035
037
039
041
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
South Wellfield ‐ Well ID
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
001
003
005
007
009
011
013
015
017
019
101
114
116
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
North Welllfield ‐ Well ID
S Wells: 13% bad
(>5% incr/yr)
N Wells: 21% bad
(>5% incr/yr)

Figure 6: Summary of Jupiter Floridan Aquifer production wells

Figure 7: Summary of Palm Beach County Floridan Aquifer production wells

3.3 Solutions to Minimize Saline Water Migration
As presented in the previous sections, water degradation due to migration of poor water quality is quite
common, in particular in the larger wellfields at both the east and west coast. Upward migration of poor
quality water can have detrimental effects not only for the individual well, but for the entire wellfield. As
presented by the authors in other publications, there are some solutions that can be imposed on brackish
water wells that are experiencing impacts from poor quality water. At times, multiple solutions need to
be considered simultaneously to achieve the desired effect. Some of these solutions were discussed in
the sections on the four case studies.
Back Plugging with Cement
It is possible that wells may be usable in the future if they are back plugged. Since wells can have multiple
distinct flow zones in the borehole, they can be back plugged to minimize the connection to poorer quality
water. Grout can be forced into small fractures, thus plugging off even small conduits outside of the
borehole wall. Back plugging reduces the borehole stresses from the previously exposed vertical conduits,
decreasing the possibility of upward migration. During construction of the southwest wells, the City of
Cape Coral used this method effectively to ‘save’ one of wells without affecting the wellfield.
Hydraulic Control and Water Quality Blending
Since a well may be connected or in close proximity to a vertical conduit, it is quite possible that back
plugging may not be completely successful and the well will continue to show signs of degradation since
any vertical conduit will always be within the capture zone (drawdown cone) of this well. Further
operational analysis may show that the well can be used at lower flow rates thus reducing drawdown and
stresses on the aquifer and the water produced can be diluted into the raw water stream to the res
treatment system. The wellfields exhibited in the case studies use this method, although in several cases
wells were retrofitted with variable frequency drives and flow meter control since their construction. A
recent example is the Palm Beach County Region 11 wells retrofit.
Well Abandonment
A facility could also plug and abandon a well and look for new location where production could be as good
or better without the degrading water quality. If the poor water quality is originating from the upper half
of the production interval just below the casing then this may be the only option available. This solution
is also not a guarantee and could be more costly if the new location identified the same water quality
issues as the well that was plugged and abandoned. Well abandonment due to severe water quality
impacts within an active wellfield will have a much lower chance of success. If the conduit connection to
the poor quality water is not severed and abandonment activities are not successful, then the poor quality
water can be pulled or captured by the next closest operating well if the poor quality water is allowed to
enter the raw water aquifer. The option of well abandonment should be considered as the last option
available for many reasons. Besides the capital investment in the construction of the well and pipeline,
abandonment removes all potential for hydraulic control of the migration of poor water quality, and may
artificially migrate through the wellfield by pumping stresses alone. The exhibited case studies have wells
which are very infrequently used or have even by abandoned because of severe water quality.

Redundant Production Wells
Some facilities are moving forward to better manage changing water quality occurrences by adding
additional wells to their system for redundancy.  The poor water quality may be occurring due to stressing
a particular area for too long and not allowing the aquifer to recharge naturally.  If property is available
and location is favorable within the proximity of the main raw water lines, a facility may want to include
redundant production wells, with sufficient spacing to existing wells.  This will allow the facility to cycle
the use of the wells with better management to keep from stressing the aquifer in one specific area for a
long period of time.   The facility could take wells offline in areas where the aquifer is being stressed more
than usual and operate the redundant production wells. In particular, the exhibited wellfield in Southwest
Florida have used this method extensively to control water degradation. Both the City of Cape Coral and
Collier County have a number of standby wells in each wellfield.
Pro‐active Wellfield Management System
On‐line monitoring of certain well parameters to allow the implementation of a pro‐active wellfield
management system is another method to create a sustainable wellfield operation in terms of production
capacity and water quality. Several utilities have implemented this method successfully in the last 10
years. Multiple parameters are collected on‐line, in real time, to monitor the operations of a well,
including the well drawdown, production flow and water quality. This information can be used in a pro‐
active program to control the wellfield. All exhibited case studies use on‐line monitoring extensively and
have some form of pro‐active wellfield management system. For instance the City of Cape Coral keeps
careful track of drawdown, flow, total flow and conductivity and use that for development of a series of
trends for each production well.

4. Reverse Osmosis Treatment

4.1 General Description of RO Treatment
One of the most critical factor for a successful operation of a BWRO system is the quality of the RO feed
water, which is determined by the source water quality and the pre‐treatment effectiveness. For the
treatment system design, a good understanding of source water quality and chemistry is needed including
future water quality trends, variability between wells and wellfields, and seasonal variations.
The typical process used in Florida to treat brackish ground water uses chemical pretreatment, cartridge
filtration, reverse osmosis (RO), degasification, disinfection, and corrosion control (see Figure 8). Sand
separation, upstream of the chemical pre‐treatment, is optional and depends on the expected sand
production from wells. Pretreatment chemicals are used to manage scaling in the RO membranes and
reduce the pH to optimize hydrogen sulfide stripping in the degasifiers. Post treatment chemicals are used
to perform primary disinfection and to adjust the pH, hardness and alkalinity for corrosion control.
Pre‐treatment
Sand separators are used to separate sand and other solid matter larger than a certain diameter (generally
≥0.1 mm) from the source water that could either plug the downstream cartridge filters, or damage or
foul the downstream RO membrane systems. Sand separators are typically used as a pretreatment step,

treating the full ground water wellfield flow, in addition to the pretreatment steps of chemical treatment.
There are different types of sand separators and its selection depends on the sand/silt characterization
and plant operation. Typically, RO manufacturers require the feed water turbidity and silt density index
(SDI) to be below specific maximums as a requirement for the RO membrane warranty; in this regard, the
sand separators may help the pretreatment system comply with these warranty requirements.
The primary function of cartridge filters is to remove particulate and colloidal matter larger than a certain
diameter from the source water that could either damage or foul downstream RO membranes. Cartridge
filters serve two important roles: 1) to remove relatively large particulates in order to protect the RO/NF
membrane integrity, and 2) as an inexpensive backup in the event of a failure in one of the other upstream
pre‐treatment systems.

Figure 8: Typical Schematic of BWRO Treatment Process
Iron is naturally present in shallow limestone aquifers in South Florida and, if exposed to air and allowed
to oxidize, the ferrous bicarbonate forms an insoluble ferric hydroxide that is difficult to remove from the
membrane surface. The approach here is to keep the iron in the reduced form (Fe2+
) by minimizing air
intrusion and applying an acid to the feed water. Hydrogen sulfide, at low concentrations though, is
present in the shallow aquifers in South Florida. The deeper, brackish aquifers contain elevated levels of
hydrogen sulfide and, if exposed to air and allowed to oxidize, elemental sulfur (S0
) will be formed, which
will block the cartridge filters and RO membranes and is difficult to remove. In this case also, minimizing
air intrusion is very important.
Chemical pre‐treatment with acid and scale inhibitor is practiced to minimize membrane scaling, with a
general trend in the industry to limit or even eliminate acid and to rely mostly on a scale inhibitor.
Acidification is often achieved with sulfuric acid (and less commonly hydrochloric acid) to prevent

precipitation of carbonate scale on the membranes. An additional impact of the sulfuric acid addition is
the conversion of carbonate ion (alkalinity) to carbonic acid in the source water (see Figure 9), which
passes as carbon dioxide gas through the membranes. Sulfuric acid is preferred over hydrochloric acid due
to cost and safety reasons, but the addition of sulfuric acid may increase the scaling potential for sulfate
salts and lower the recovery. All polyamide membranes are intolerant to chlorine and may result in
breakdown of the membrane material with prolonged use.

Figure 9: (L) Carbon Dioxide and (R) Hydrogen Sulfide Dissociation in Water as Function of pH
As the RO permeate passes through the membranes, the remaining concentrate becomes increasingly
concentrated with dissolved solids. At a certain point, the solubility of various salts can be exceeded,
causing precipitation onto the membranes, called “scaling.” Scaling can reduce the flow or flux of
permeate and can also damage the membrane itself. As mentioned, scale inhibitor is commonly used in
conjunction with acidification to inhibit the formation of phosphate and sulfate scaling on membranes,
and reduce the acid dosage required to inhibit formation of carbonate scales. Threshold scale inhibitors
suppress precipitation by interrupting the kinetics of normal crystallization, thus delaying precipitation
beyond the residence time in the membrane system. Scale inhibitors allow the membrane system to
increase recovery beyond limiting salt saturation limits. The sparingly soluble salts of concern in most
waters include calcium carbonate (or LSI), calcium sulfate, strontium sulfate, barium sulfate and silica
dioxide. It is important to select the appropriate scale inhibitor for the design application – some scale
inhibitors may act as coagulants, facilitating the accumulation of organic carbon on the membrane
surfaces and increasing fouling potential. There are well‐documented industry guidelines on the limits of
the saturation indexes of these sparingly soluble salts with or without the use of scale inhibitors.

0.00
0.20
0.40
0.60
0.80
1.00
4 5 6 7 8 9 10 11 12 13 14
Molar Fraction
pH
Carbonic Acid (H2CO3)
Bicarbonate Ion (HCO3‐)
Carbonate Ion (CO32‐)
0.00
0.20
0.40
0.60
0.80
1.00
4 5 6 7 8 9 10 11 12 13 14
Molar Fraction
pH
Hydrogen Sulfide (H2S)
Bisulfide Ion (HS‐)
Sulfide Ion (S2‐)

Main treatment
High pressure pumps are used to increase the
feed water pressure to overcome osmotic
pressure and hydraulic losses in the connecting
pipework and RO trains. Two methods exists for
the high pressure pump arrangement: (1)
decentralized system with a dedicated feed
pump per RO train or (2) centralized system with
one common pump station and a common
header and flow control valves to feed each of
the RO trains. Both methods have their specific
advantages and disadvantages with a decision
mainly driven by the owner.
RO trains in South Florida typically consist of two single‐pass stages with the 1st
stage concentrate used as
the feed for the 2nd
stage. Permeate flows of both stages join for the total permeate while the 2nd
stage
concentrate flow is the total train concentrate. Each train consist of multiple, parallel pressure vessels
which can either hold six or seven standard 40‐inch long and 8‐inch diameter RO elements. The train array,
including the number of pressure vessels in each stage and related flow and flux distribution, is dependent
upon the feed water quality and the overall train design concept.
The RO process produces a high‐pressure concentrated waste stream. When this concentrate stream is
depressurized, the energy that is lost can be recovered using energy recovery devices (ERDs), which can
reduce overall energy requirements by 10 to 50 percent. Energy recovery is not economically justified for
all RO membrane systems; those with tight membranes, low recovery and high concentrate flow and
pressure (e.g. high TDS brackish ground water) are more likely to find energy recovery beneficial with low
pay‐back periods and improved flow balancing between the membrane train stages. Those systems with
lose membranes, high recovery and low concentrate flow and pressure (e.g. low TDS brackish ground
water) will find 1st
stage permeate throttling more cost‐beneficial for flow balancing between the
membrane train stages. ERDs will minimize the feed pressure required, which in turn minimizes the
operating power costs.
There are different devices available with direct‐
transfer pressure exchangers for high efficiency (90‐
95%) –see picture to the right–, turbo‐chargers
which combine recovery device and pump in one for
medium efficiency (50‐70%) and more‐traditional
turbines with medium‐high efficiency (80‐85%). The
devices are typically installed on a membrane train
to transfer pressure/energy in the concentrate to
the 2nd
stage feed water, reducing the size of the RO
feed and/or inter‐stage pumps.

Bypassing a portion of the feed water around the membrane process, treating it with cartridge filters only,
and blending it with the membrane permeate may allow the system to meet treated water quality goals
while treating less of the incoming flow stream. Blending of the RO bypass water with permeate may be
beneficial when the permeate water quality requires re‐mineralization. The bypass will reduce the amount
of post‐treatment chemicals and the amount of feed water that needs to be treated, both reducing the
capital and O&M costs for the plant.
Post treatment
Degasifiers are typically used as post‐treatment to remove hydrogen sulfide (H2S) and carbon dioxide
(CO2) from the RO permeate by counter current mass transfer of air and water. The removal of H2S and
CO2 is optimized by a reduction of the pH to levels around 5.8‐6.0 (see Figure 11). The addition of chlorine
to the degasified water will oxidize any remaining dissolved sulfide in the water into colloidal sulfur,
increasing the finished water turbidity. Elemental sulfur is a sticky substance that is difficult and
cumbersome to remove from the downstream clearwell and can create variations in finished water
turbidity by sloughing off of sulfur sediments. Degasifiers serve several important roles: 1) reduction of
effluent turbidity by removing sulfide from the water stream before chlorination; 2) odor control for the
treated effluent; and 3) corrosion control through
the removal of excess CO2.
Odors from degasifiers can result in complaints
from neighbors in the vicinity of the installation
which may present community relations
challenges for the owner. Odor control through
dilution and dispersion, or odor removal systems
(like wet chemical scrubbers or biological filters)
may need to be added to degasifier systems to
meet local air quality and odor limit requirements
at the site of the installation.
Depending on the downstream requirements chemical addition to the treated water may be required for
primary disinfection, pH adjustment and corrosion control. The need for these chemicals depends on
specific raw water quality and treated water quality goals, and should be evaluated on a case by case
basis. The concept of removing excess carbon dioxide in the degasifier and then having to dose it again
for corrosion control in the clearwell may be considered inefficient. Some utilities have been studying
alternative technologies for hydrogen sulfide removal, such as oxidation.
4.2 Specific Considerations to address Salinity Increases
As presented before, some degradation of raw water quality can be expected in Floridan Aquifer water
supply and treatment systems. A conservative design of a RO treatment system will accommodate some
degradation while maintaining the required capacity and finished water quality. Also the design will be
specific to the raw water quality anticipated for that system and in South Florida the salinity can vary by
region, with TDS levels of around 2,000 mg/L in certain parts going up to levels around 8,000 mg/L in other
parts. As can be expected, this variance has a significant influence on the system design and equipment
specifications. As part of this work, raw water quality data was obtained from different systems, as
summarized in Table 1 to create several case‐studies, with the following observations:

 In general, TDS are higher along the east coast with some exceptions
 Some parameters relevant to chemistry equilibrium of sparingly soluble salts, like barium, silica
and strontium appear relatively higher on the west coast
 Hardness is higher along the east coast, with a higher relative contribution from magnesium
whereas alkalinity is relatively constant throughout the region despite varying TDS levels
 Sulfate levels, important for saturation indexes of sparingly soluble salts, in general follow the TDS
trend
 Hardness and sulfate levels are extremely high in the Sarasota County wellfields which may impact
the RO recovery rate or led to alternative technologies, such as electro dialysis reversal (EDR)
 Potassium appears to be higher on the east coast
Though not included in the table, the Floridan Aquifer water also contains hydrogen sulfide, with
concentrations varying from 2 to 5 mg/L, and radionuclides with gross alpha concentrations varying
between 5 and 40 pCi/L.
The raw water quality data sets, presented in the table, were used to model the RO treatment process for
each particular case study. Proprietary membrane software was used to develop the system design and
predict the treatment performance. Subsequently, also proprietary scale inhibitor software was used to
determine the required chemical pre‐treatment (type and dose) to control membrane scaling. The
following design assumptions and goals were used as guidelines for the design efforts:
Pre‐Treatment
 Sand separators and cartridge filters to bring the Silt Density Index below 3
 Sulfuric acid dosing to suppress the feed water pH to 6.0. A few scenarios were run with reduced
acid dose in the RO feed water and relying on a scale inhibitor, while maintaining a Langelier
Saturation Index (LSI) of 1.8 or less
RO Train Design
 Dedicated feed pump per train
 2‐stage array, single pass
 Dependent upon design need, with or without ERDs. In our particular case studies, a direct
transfer pressure exchanger was selected
 Average, conservative system flux is 12.5 gfd
 2‐1 vessel array, with 7 elements per vessel
 Capacity of RO train and associated bypass is 3 MGD
 TFC HR RO membranes, 40‐inch long and 8‐inch diameter with 5 year element age and 25% fouling
allowance
 1st
and 2nd
stage back pressure 20 psi, interstage pressure loss 5 psi
 Use of software design warnings to guide the design effort
Post Treatment
 Blend permeate with RO bypass
 Sulfuric acid dosing to suppress the feed water pH to 5.8‐6.0.
 Degasifier to remove carbon dioxide and hydrogen sulfide

 Liquid lime (Ca(OH)2) and carbon dioxide (or gas CO2) dosing in clearwell to meet the finished
water quality goals, including a pH of 8.0, hardness of 80 mg/L as CaCO3 and total alkalinity of 60
mg/L as CaCO3. This is somewhat arbitrary and has to be evaluated on a case by case basis and
depends largely on the corrosion control strategy.
A summary of the results of the membrane modeling efforts is included in Table 2, with increasing TDS
levels in the wellfield presented from left to right. The table does not include the modeling results of the
City of Venice due to different water chemistry composition here and its negative impact on possible RO
recovery rates, which would skew the trends presented further in this report.
General observations from the modelled case studies with TDS levels varying from 1500 mg/L to 9500
mg/L as summarized in the table are:
 RO recovery rate reduces from 85% to 75%
 RO bypass reduces from 20% to 2%, with the permeate flow making up the difference
 Train array increases from 48‐24 vessels to 60‐30 vessels to produce the additional required
permeate flow at higher raw water TDS
 Feed pressure increases from 188 to 392 psi, without ERD, and from 188‐282 with ERD
 Post treatment chemicals to adjust alkalinity and calcium are necessary across the full range of
raw water quality however for instance CO2 dosages increase from 14 to 44 mg/L
 Electricity and chemical costs for RO treatment only increase from $0.32 to $0.72 per 1000 gallons
treated water
The table can facilitate in quick assessments in the following conditions: (1) by a utility planning a new
BWRO system to verify typical design criteria and operational parameters based on initial well water
quality and (2) by a utility operating an existing BWRO to estimate impacts of degrading raw water quality
on the design configuration and operations.
In the sections below, specific aspects of the BWRO treatment system will be described in regards to
different TDS levels in the wellfield.

Table 1: Water Quality Data Sets from Case Studies and Others
Parameter
(current ‐ 2015, or
otherwise noted)
Units
Cape Coral,
South RO 2000
Cape Coral,
North RO 2010
Cape Coral,
North RO
Venice RO
North Miami
Beach RO
Town of Davie
RO
Collier County
South
Jupiter RO
Broward
County
System 1
Palm Beach
County
System 11
Total Dissolved Solids mg/L 1,516 2,000 2,623 3,000 3,200 4,950 5,350 7,880 7,470 6,100
Barium mg/L 0.03 0.04 0.04 0.03 0.01 0.01 0.03 0.02 0.01 0.04
Fluoride mg/L 1.4 1.4 1.4 1.7 0.9 1.1 1.4 1.8 0.8
Nickel mg/L U U U U U U U 0.01U 0.01U 0.01U
Nitrate mg/L as N 0.01U 0.01U 0.01U U U U 0.50 0.02U 0.01U 0.50U
Sodium mg/L 343 420 600 265 780 1,450 1,370 2,310 2,100 1,590
Chloride mg/L 589 890 1,210 528 1,400 2,500 2,530 4,110 3,850 2,660
Iron mg/L 0.01U 0.01U 0.01U U U 0.01U 0.02U 0.02U 0.05 0.02U
Manganese mg/L 0.01U 0.01U 0.01U U U U 0.01U 0.01U 0.01U 0.012U
Sulfate mg/L 269 280 330 1,315 460 510 720 595 935 530
pH mg/L 7.7 7.7 7.7 7.6 7.8 7.7 7.5 7.6 7.8 7
Ammonium‐N mg/L 0.32 0.35 0.39 0.49 0.35 0.50 n/a 0.74
mg/L as CaCO3 141 142 145 105 115 132 152 120
mg/L 172 173 177 128 140 0 161 n/a 146
Calcium mg/L 90 108 125 415 105 150 270 197 210
Hydrogen Sulfide mg/L 3.0 3.0 3.0 3.0 3.5 3.2 4.0
Magnesium mg/L 86 92 105 178 110 205 280 290
Potassium mg/L 19 22 25 9 35 55 68 131
Silica mg/L 15 16 18 25 15 19 10
Strontium mg/L 17 19 21 14 3 15 15 12
Temperature °C 25 25 25 25 25 25 25 23 25 22
Bicarbonate Alkalinity

Table 2: Membrane Modeling Results
Modeling Scenarios
Cape Coral,
Southwest RO
(1990)
Cape Coral,
North RO
(2010)
Cape Coral,
North RO
North Miami
Beach
Cape Coral,
North RO
(projected)
Town of Davie
Collier County
South RO
Palm Beach
County System
11
Jupiter RO
Broward
County WTP1
(projected)
Raw Water TDS (mg/L) 1516 2000 2623 3250 3850 4690 5350 6060 7600 9356
Permeate TDS 43 51 76 90 112 169 153 197 244 282
Finished Water TDS Contrib. Bypass (mg/L) 405 400 375 360 337 281 296 251 202 163
Bypass Limit as % of Finished Water 20% 20% 14% 11% 9% 6% 6% 4% 3% 2%
Bypass Flow (gpm) 438 402 313 242 191 131 120 90 58 38
Permeate Flow (gpm) 1,753 1,754 1,878 1,945 1,988 2,054 2,056 2,084 2,115 2,135
Finished Water Flow (gpm) 2,191 2,156 2,191 2,187 2,179 2,185 2,176 2,175 2,173 2,172
Array Recovery 85% 80% 80% 80% 80% 80% 80% 75% 75% 70%
Stage 1 Pressure Vessels 48 50 52 54 56 58 58 58 58 60
Stage 2 Pressure Vessels 24 25 26 27 28 29 29 29 29 30
Average Flux (gfd) 12.5 12.0 12.4 12.3 12.2 12.1 12.2 12.3 12.5 12.2
Feed Water pH 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
Feed Water Pressure w/ Fouling Allowance 188 195 215 210 220 234 243 251 270 282
Interbank ERD Pressure Gain (psi) 0 0 0 43.7 58.9 82.8 99.1 102 137 153
Design Warnings None None None None None None None None None None
Saturation Indices (If Scaling)
Langlier Index 0.57 0.29 0.36 0.41 0.43 ‐ 0.65 ‐ ‐ ‐
CaSO4 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐
CaF2 2.5 1.4 1.3 1.4 2.4 ‐ 1.2 ‐ ‐ ‐
BaSO4 14.3 11.9 11.35 10.82 10.42 2.5 9.41 1.8 2.36 1.6
SrSO4 6.1 4.2 4.2 4.0 3.9 1.8 2.8 1.9 1.6 1.1
SiO2 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐
Degasified Water Quality (range)
Ca. Hardness (mg/L as CaCO3) 59.3 52.8 44.7 36.8 32.2 22.4 35.3 15.8 14.4 10.1
Mg. Hardness (mg/L as CaCO3) 92.8 74.0 61.8 53.1 49.3 44.5 44.1 43.4 32.6 22.9
Total Hardness (mg/L as CaCO3) 152 127 106 90 81 67 79 59 47 33
TDS (mg/L) 434 421 428 414 430 434 415 443 435 433
pH 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0
Alkalinity (mg/L as CaCO3) ‐ Treated Water 44 35 28 24 21 15 15 13 11 10

Table 2: Membrane Modeling Results (Continued)
Modeling Scenarios (Table Continued)
Cape Coral,
Southwest RO
(1990)
Cape Coral,
North RO
(2010)
Cape Coral,
North RO
North Miami
Beach
Cape Coral,
North RO
(projected)
Town of Davie
Collier County
South RO
Palm Beach
County System
11
Jupiter RO
Broward
County WTP1
(projected)
Finished Water Quality Goals
Total Hardness (mg/L as CaCO3) ‐ Goal 80 80 80 80 80 80 80 80 80 80
Alkalinity (mg/L as CaCO3) ‐ Goal 60 60 60 60 60 60 60 60 60 60
Post‐Treatment Chemicals
Additional Hardness Dosed (mg/L as CaCO3) 0 0 0 0 0 13 1 21 33 47
Calflo (Ca(OH)2) (mg/L) 0 0 0 0 0 10 0 15 24 35
Carbon Dioxide (mg/L) 0 0 0 0 0 12 1 18 29 41
Additional Alkalinity Dosed (mg/L as CaCO3) 16 25 32 36 39 45 45 47 49 50
Additional Bicarbonate Dosed (mg/L) 19 31 39 44 47 55 54 58 60 61
Calflo (Ca(OH)2) (mg/L) 12 19 23 26 29 33 33 35 36 37
Carbon Dioxide (mg/L) 14 22 28 31 34 40 39 42 43 44
Electricity Use 0 0 0 0 0 0 0 0 0 0
Feed Flow Per Train (gpm) 2062 2192 2347 2431 2485 2568 2569 2779 2821 3049
Feed Pressure (psi) 188.2 195.3 215 209.6 220.2 234 243.4 251 270 282
Feed Pump Suction Pressure (psi) 30 30 30 30 30 30 30 30 30 30
Feed Pump Efficiency 78% 78% 78% 78% 78% 78% 78% 78% 78% 78%
Interbank Flow (gpm) 675 806 811 778 741 703 683 900 872 1,094
Interbank ERD Pressure Gain (psi) 0 0 0 44 59 83 99 102 137 153
Energy Cost ($/kWh) $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12
Annual Energy Cost ($/year) $191,461 $213,992 $256,477 $257,906 $279,132 $309,360 $323,841 $362,753 $399,806 $453,862
Energy Cost ($/1000 gallons) $0.17 $0.19 $0.22 $0.23 $0.25 $0.27 $0.29 $0.33 $0.36 $0.41
Chemical Use $0 $0 $0 $0 $0 $0 $0 $0 $0 $0
Sulfuric Acid Dose (mg/L) 100 101 104 108 107 92 93 93 97 102
Sulfuric Acid Unit Cost ($/gallon) $2.19 $2.19 $2.19 $2.19 $2.19 $2.19 $2.19 $2.19 $2.19 $2.19
Sulfuric Acid Cost ($/1000 gallons) $0.11 $0.12 $0.13 $0.15 $0.15 $0.13 $0.14 $0.15 $0.16 $0.18
Anti‐scalant Dose (mg/L) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Anti‐scalant Unit Cost ($/lb) $1.25 $1.25 $1.25 $1.25 $1.25 $1.25 $1.25 $1.25 $1.25 $1.25
Anti‐scalant Cost ($/year) $5,653 $6,008 $6,434 $6,665 $6,811 $7,038 $7,043 $7,618 $7,732 $8,359
Calflo Dose (mg/L) 11.7 18.8 23.5 26.5 28.5 33.5 33.0 35.1 36.2 37.0
Calflo Unit Cost ($/lb) $0.24 $0.24 $0.24 $0.24 $0.24 $0.24 $0.24 $0.24 $0.24 $0.24
Calflo Cost ($/year) $26,665 $42,863 $53,579 $59,267 $62,116 $74,984 $71,914 $76,457 $78,887 $80,458
Carbon Dioxde Dose (mg/L) 17.4 27.9 34.9 39.3 42.4 49.8 49.1 52.2 53.9 54.9
Carbon Dioxide Unit Cost ($/lb) $0.11 $0.11 $0.11 $0.11 $0.11 $0.11 $0.11 $0.11 $0.11 $0.11
Carbon Dioxide Cost ($/year) $18,775 $30,181 $37,726 $41,732 $43,738 $52,798 $50,637 $53,835 $55,546 $56,652
Chemical Cost ($/1000 gallons) $0.16 $0.19 $0.22 $0.24 $0.26 $0.25 $0.26 $0.27 $0.29 $0.31
Total Energy + Chemical Cost ($/1000 gallons) $0.32 $0.38 $0.44 $0.47 $0.51 $0.53 $0.55 $0.60 $0.65 $0.72
The chemical costs covers only the chemicals explicitly mentioned above. The electricity costs only covers RO feed pump, and does not cover the well pumps,
transfer pumps and high service pumps; neither does is include other electrical consumers, such as the degasifier blowers.

Pre‐Treatment – Acid
In the last ten to fifteen years significant improvements have been made in terms of scale inhibitors.
Different types of scale inhibitors have been developed with each a specific objective in mind, like
inhibition of calcium carbonate scaling, inhibition of certain sparingly soluble salts scaling and/or
reduction of ferrous fouling. Currently, many utilities operating BWRO treatment systems have reduced
or even eliminated the use of sulfuric acid in the RO feed stream for cost and/or safety reasons. As the
optimal pH of the degasifier influent is around 5.8 to 6.0, utilities still need to dose sulfuric acid to the
degasifier influent or have converted to carbonic acid (or carbon dioxide gas), dosed to the blend stream
of RO permeate and RO bypass, to reduce the pH. In considering this the utility needs to consider the total
system chemistry, including the use of post treatment chemicals as liquid lime and carbon dioxide to meet
the finished water hardness and alkalinity goals. This has been done for three case‐studies: (1) Cape
Coral’s North RO, (2) Town of Davie and (3) Town of Jupiter RO. The results are presented in Figure 10.
Based on modeling, sulfuric acid is still required in the RO feed to maintain a LSI of 1.8 or less and acid is
also needed in the degasifier inlet to maintain optimal pH conditions of 5.8‐6.0, although the overall acid
consumption reduces. The figure shows that acid reduction is partly offset with an increase in the scale
inhibitor, liquid lime and carbon dioxide dose, although overall chemical costs are lower for all case studies
with limited sulfuric acid addition.

Figure 10: Chemical Costs, with Acid and Limited Acid, for some Case Studies

$0.13
$0.05
$0.13
$0.05
$0.16
$0.05
$0.01
$0.02
$0.01
$0.02
$0.01
$0.03
$0.03
$0.05
$0.05
$0.05
$0.05
$0.05
$0.05
$0.06
$0.07
$0.07
$0.07
$0.08
$0.00
$0.05
$0.10
$0.15
$0.20
$0.25
$0.30
$0.35
2623 2623
(limited acid)
4690 4690
(limited acid)
7600 7600
(limited acid)
Chemical Costs ($ per 1000 gallons treated)
Raw Water Total Dissolved Solids (mg/L)
Sulfuric Acid Cost ($/1000 gallons) Anti‐scalant Cost ($/1000 gallons)
Carbon Dioxide Cost ($/1000 gallons) Calflo Cost ($/1000 gallons)

RO Bypass
As mentioned before, bypassing a portion of the raw water around the membrane process and blending
it with the RO permeate helps meeting the finished water quality goals through re‐mineralization, while
treating less of the incoming flow stream. The ability to bypass and the amount of the bypass flow is
primarily dependent on the raw water TDS and finished water quality goals, but can also be influenced by
the membrane salt rejection performance. As is expected, the bypass flow will need to be reduced when
the raw water TDS increases or is higher. This concept is presented in Figure 11 illustrating the reduction
in the bypass flow from just below 20% to around 6% of the raw water flow when the TDS in the raw water
increases from 2,000 to 4,700 mg/L. Consequently, and to maintain the treatment plant capacity (at
100%), the permeate flow will need to be increased from 80 to 94%. This requires modifications to the RO
trains to accommodate more pressure vessels and RO elements for higher production while maintaining
the same flux rate. The RO Bypass flow at raw water TDS levels of above 5,000 mg/L is low and practicing
RO bypass becomes less attractive.

Figure 11: Bypass Water and Permeate Flows as Function of Raw Water TDS

RO Train
Using the design assumptions and goals presented before, a RO train design was developed for each case
study as summarized in Table 2. The concept of increasing the number of pressure vessels and RO
elements to maintain the same finished water flow is evident. For a 3 MGD system, the RO array needs to
be increased from 48‐24 to 58‐29 pressure vessels in the first and second stage respectively, when the
TDS in the raw water increases from 1,500 to 7,600 mg/L. At the same time the RO recovery rate decreases
from 85% to 75% and the feed pressure increases from 188 to 392 psi without ERD (and 188 to 282 psi
0%
20%
40%
60%
80%
100%
120%
1,500 2,500 3,500 4,500 5,500 6,500 7,500 8,500 9,500
Flow (% of Design Flow)
Bypass Flow WTP (%) Permeate Water Flow WTP (%)
Rated Finished Water Capacity WTP (%)

with ERD). The RO feed pumps are the single largest electrical consumers at any BWRO treatment system
and ERDs to obtain the residual pressure from the second stage concentrate, which would be lost when
concentrate is discharged, and to convert that into feed pressure energy to the second stage feed has
become very popular. For each case study, the payback period was calculated and the results are provided
in Figure 12. As illustrated the payback period of ERDs is less than 10 years and will become interesting
when the raw water TDS exceeds 3,000 mg/L. Below 2,500 mg/L TDS, the payback period of an ERDs is
above 15 years and is therefore less interesting. The combination of number of pressure vessels and the
inclusion of an ERD in the BWRO treatment system are provided in Figure 13.

Figure 12: Payback Period of an ERD as Function of Raw Water TDS

0
5
10
15
20
25
30
35
40
45
1,500 2,500 3,500 4,500 5,500 6,500 7,500 8,500 9,500
Interstage ERD Payback Period (Years)


Figure 13: RO Array Design as Function of Raw Water TDS

Post Treatment
The RO permeate is combined with the RO bypass and treated in the degasifier vessels to remove the
hydrogen sulfide and excess carbon dioxide. The chemistry of the blend stream will change as a function
of the membrane performance but also as a result of the RO bypass flow percentage. Therefore, also the
chemistry of the degasified water will change as a function of the raw water TDS content. This concept is
illustrated in Figure 14. The alkalinity of the degasified water will decrease from just above 40 to around
15 mg/L CaCO3 when the raw water TDS increases from 1500 to 5000 mg/L, while total hardness drops
from 120 to 70 mg/L CaCO3. (The little blip on the hardness curve is due to the relatively higher hardness
in the Collier County raw water at 5350 mg/L TDS.) The alkalinity is a measure of the buffering ability of
the water and a certain minimum threshold or goal is recommended for corrosion control and stable
chlorine residual. The exact alkalinity goal will need to be defined by each owner and is dependent upon
many factors like distribution system, finished water quality and corrosion control strategy. In this
particular report, alkalinity and hardness goal of 60 and 80 mg/L CaCO3 respectively are assumed
requiring the addition of post–treatment chemicals to add alkalinity and hardness to the treated water.
Different chemicals can be used for this purpose but over the last couple of years the combination of
carbon dioxide and liquid lime has become popular. As can be found in Table 2, for a raw water TDS of
5,000 mg/L about 30 mg/L liquid lime and 40 mg/L carbon dioxide is needed to recondition the degasified
water to the set points for corrosion control.
48 50 52 54 56 58 58 58 60
24
25
26
27
28
29 29 29
30
0
20
40
60
80
100
120
140
160
180
200
0
10
20
30
40
50
60
70
80
90
100
1,516 2,000 2,623 3,250 3,850 4,690 6,060 7,600 9,356
Interstage ERD Pressure Gain (psi)
RO Train Array
Stage 1 Pressure Vessels Stage 2 Pressure Vessels Interbank Booster Pump (psi) ‐ Max


Figure 14: Finished Water Quality, prior to Post‐Treatment Chemicals as Function of Raw Water TDS

Electricity and Chemical Costs
For each case study, electricity and chemical costs were calculated as shown in Figure 15. The costs
increase from $0.33 to $0.72 per 1000 gallons of water treated over the range of raw water TDS levels
from our case studies. The increase in electricity is more significant than the increase in chemical costs,
despite the use of ERDs for TDS levels of 3000 mg/L and above.
Four different chemicals make up the BWRO system chemical costs as shown in this figure, e.g. sulfuric
acid, scale inhibitor, liquid lime and carbon dioxide. Further details are depicted in Figure 16, which shows
that the costs of the scale inhibitor is relative constant across the range of TDS levels while the cost of
sulfuric acid increases slightly. However the largest relative increase to the chemical costs is due to the
increased dosages of liquid lime and carbon dioxide to maintain stable finished water.
0
20
40
60
80
100
120
140
1,500 2,500 3,500 4,500 5,500 6,500 7,500 8,500 9,500
Total Hardness and Alkalinity in RO Permeate (mg/L as
CaCO3)
Total Hardness (mg/L as CaCO3) ‐ Treated Water
Alkalinity (mg/L as CaCO3) ‐ Treated Water
Total Hardness (mg/L as CaCO3) ‐ Goal
Alkalinity (mg/L as CaCO3) ‐ Goal
Increase Alkalinity
Increase Hardness
Needed


Figure 15: Chemical and Electricity Costs as Function of Raw Water TDS

Figure 16: Chemical Costs as Function of Raw Water TDS
$0.17 $0.19 $0.22 $0.23 $0.25 $0.27 $0.29 $0.33 $0.36
$0.41
$0.16
$0.19
$0.22 $0.24
$0.26 $0.25
$0.26
$0.27
$0.29
$0.31
$0.00
$0.10
$0.20
$0.30
$0.40
$0.50
$0.60
$0.70
$0.80
1,516 2,000 2,623 3,250 3,850 4,690 5,350 6,060 7,600 9,356
Operating Cost ($ per 1000 gallons treated)
Total Dissolved Solids (mg/L)
Energy Cost ($/1000 gallons) Chemical Cost ($/1000 gallons)
$0.11 $0.12 $0.13 $0.15 $0.15
$0.13 $0.14 $0.15 $0.16
$0.18
$0.01 $0.01
$0.01
$0.01 $0.01
$0.01 $0.01
$0.01 $0.01
$0.02
$0.04 $0.04
$0.05
$0.05
$0.06
$0.07 $0.07
$0.07
$0.07
$0.07
$0.03 $0.03
$0.03
$0.04
$0.04 $0.05 $0.05
$0.05
$0.05
$0.05
$0.00
$0.05
$0.10
$0.15
$0.20
$0.25
$0.30
$0.35
1,516 2,000 2,623 3,250 3,850 4,690 5,350 6,060 7,600 9,356
Chemical Costs ($ per 1000 gallons treated)
Sulfuric Acid Cost ($/1000 gallons) Anti‐scalant Cost ($/1000 gallons)
Calflo Cost ($/1000 gallons) Carbon Dioxide Cost ($/1000 gallons)

5. Conclusions
Important lessons have been learned over 40 years of operation of this brackish source. The UFA is
complex and heterogeneous aquifer where well specifics may differ moving from the west to east coast.
However there are many commonalties in the wellfield design and operation as well. Many wellfields have
experienced degrading water quality due to migration of pockets and areas of poor water quality due to
human‐induced changes in the aquifer. This paper has presented several case studies of BWRO systems
with degrading raw water quality impacting wellfield and treatment operations. The paper can provide
guidance to utilities who are either operating or planning a BWRO system in terms of best practices of
wellfield and treatment plant design.

Literature References
GJ Schers, and Andy Fenske, Reducing Adverse Impacts of Declining Water Quality on RO WTP by
Implementing Operational Changes to the Wellfield; paper presented at FWRC 2007
Stefan Schuster, GJ Schers, and Michael Weatherby, Brackish Ground Water Supply in the US: 40 Years of
Experience with RO Design and Operation; paper presented at Texas Water 2014
Ron Cass, GJ Schers et al (2006); Optimizing existing facilities: finding another three MGD at the existing
Cape Coral RO WTP; paper presented at FWRC 2006
FDEP Division of Water Resource Management, Desalination in Florida: Technology, Implementation, and
Environmental Issues 2010
Karla Kinser, GJ Schers and Andy Fenske (2007 and 2008); Chemical optimization for a new brackish
ground water RO WTP, paper presented at the FSAWWA, FWRC and AMTA conferences in 2007 and 2008,
and article was published in the FWRJ 2008
MWH (2011), Best Practice Design Guides for Sand Separators, RO and Degasifiers
Ed Rectenwald, Mike Weatherby, Significant water quality trends observed in the lower Hawthorn Aquifer
of Southwest Florida, occurrences and solutions, paper presented at FSAWWA 2007
GJ Schers et al; Designing a RO plant for changing raw water quality, paper presented at the FWRC 2007
GJ Schers et al; Reducing adverse impacts of declining water quality on RO WTP by implementing
operational changes to the wellfield; paper presented at the FSAWWA and FWRC conferences 2007
USGS, National Brackish Groundwater Assessment 2013
U.S. Department of the Interior Bureau of Reclamation, Desalination and Water Purification Research and
Development Program Report No. 155 Treatment of Concentrate 2009
U.S. Geological Survey. 2003. Desalination of Ground Water: Earth Science Perspectives. Fact Sheet 075‐
03, October 2003.

To Presented at:
FSAWWA 2015
Wed 3A: Dec. 2, 2015
Presented by: GJ Schers PMP

2
• Introduction in Florida Aquifer
• Featured Wellfields and Salinity
Trends
• Floridan Aquifer Water Quality
• Treatment Evaluations
• Conclusions
*
Cape Coral
Collier County *
*Jupiter
*
Palm Beach
County
*
Venice
*Bonita Springs
*
Broward (TW)
Davie
North Miami
Beach
*
*

Floridan Aquifer Wellfield and Treatment
3

4
• Relatively deep; brackish source
• Used since 1970’s
– Cape Coral, Venice
• Represents 25% of permitted capacity
• Benefits:
– Is considered an Alternative Water Supply (AWS)
– Requires localized/regionalized only permitting
– (can be) Small scale, easy expandable
– Therefore, Floridan Aquifer is good supplemental source

5
• Important Aspects for Implementation of BWRO systems:
1. Wellfield productivity and water quality
2. Pre-Reverse Osmosis (RO) treatment
3. RO
4. Post-RO treatment
5. Concentrate disposal Red: addressed in paper
• Objective paper: develop best practices for BWRO based
on existing operational systems

6
• Collect operational data on performance of 4 case studies:
• West coast: Cape Coral, Collier County (Venice, Bonita)
• East coast: Jupiter and Palm Beach County (NMB, Davie,
Broward)
• Analyze and compare wellfield data
• Develop ‘wide’ set of source water quality
• Evaluate impacts on water treatment
• Develop best practices on salinity impacts

7

9
Item West Coast East Coast
In operation since 1970’s 1990’s
Productivity expressed in
typical well capacity (gpm)
350-700 800-2,000
Depth wells (ft fls) 500-1,000 1,000-1,600
Aquifers Upper Floridan
Mid, Lower Hawthorn
Upper Floridan
Water Quality in TDS (mg/L) 1,500-4,000 3,000-7,500
Salinity reversal in area
Concentrate Disposal (ft bls) Boulder Zone
(>2,000)
Boulder Zone
(>2,000)
Several publications addressed experiences with water quality trends
• Slow trend over time in wellfield
• Fast change in individual wells

10
Summary of Production
Wells
Southwest Wells North Wells
Capacity 15 MGD (exp. in ’85)
12 MGD (original)
Number
Average Capacity
34
600 gpm
24
600 gpm
Depth
Diameter
700 ft
12 inch FRP
700 ft
12 inch FRP
Original TDS
Current TDS
1,400 mg/L (1988)
2,200 mg/L (2014)
2% increase/year
2,000 mg/L (2010)
2,500 mg/L (2014)
5% increase/year
Other source water quality
parameters
Chloride 900 mg/L
Hardness 575 mg/L as CaCO3
H2S 3 mg/L
Chloride 1100 mg/L,
Hardness 625 mg/L as CaCO3
H2S 3 mg/L

11
0
4
8
12
16
20
24
28
0
200
400
600
800
1,000
1,200
1,400
TotalPumpage(mgd)
ConcentrationChloride(mg/L)
Chlorides South
Chlorides North
Total Pumpage North + South

12
-5%
0%
5%
10%
15%
20%
25%
30%
35%
101
103
105
107
109
111
211
213
215
217
219
221
223
225
227
229
231
-1,000
0
1,000
2,000
3,000
4,000
5,000
6,000
TDSincrease(%/100MG)
Well ID
TDSConcentration(mg/L)
TDS increase
Avg first 6 m
Increase (%/100 MG)

13
Summary of Production
Wells
Town of Jupiter RO Production wells
Start of Operation 1995 (6 MGD)
Capacity
Number
Average Capacity
12
1,400 gpm
Specific capacity 50 gpm/ft
Depth
Diameter
1,400 ft
17.4 inch PVC/FRP
1,600 ft
16, 12 inch PVC/FRP
Original TDS
Current TDS
3,000 mg/L (1995)
Avg. 6,500 mg/L (max 9,700 mg/L)
3%‐12% increase/year
Other source water
quality parameters
Chlorides 4,000 mg/L
Hardness 1,650 mg/L as CaCO3
H2S 3 mg/L

14
0
2
4
6
8
10
12
0
2,000
4,000
6,000
8,000
10,000
12,000
TotalPumpage(mgd)
AverageConcentrationTDS(mg/L)
TDS AVERAGE
Total Pumpage

15
0%
5%
10%
15%
20%
25%2
3
5
6
7
8
9
10
11
12
13
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
TDSIncrease(%/100MG)
Well ID
TDSConcentration(mg/L)
TDS avg (first 6m) TDS increase TDS Increase (%/100 MG)

• Similar patterns were developed for other case studies
16
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
ConcentrationChloride(mg/L)
Chlorides South
Chlorides North
12 per. Mov. Avg. (Chlorides South)
12 per. Mov. Avg. (Chlorides North)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
TotalPumpage(mgd)
AverageConcentrationTDS(mg/L)
TDS Average
Pumping
Average

• Back plugging with cement
• Hydraulic control and water quality blending
• Redundant production wells
• Pro-active wellfield management system
• Well abandonment
17

18

19
Parameter
(current - 2015, or
otherwise noted)
Units
Cape
Coral,
South RO
Cape
Coral,
North RO
North
Miami
Beach RO
Town of
Davie RO
Collier
County
South
Jupiter
RO
TDS mg/L 1,516 2,623 3,200 4,950 5,350 7,880
Barium mg/L 0.03 0.04 0.01 0.01 0.03 0.02
Fluoride mg/L 1.4 1.4 0.9 1.1 1.4
Sodium mg/L 343 600 780 1,450 1,370 2,310
Chloride mg/L 589 1,210 1,400 2,500 2,530 4,110
Sulfate mg/L 269 330 460 510 720 595
Bicarbonate Alkalinity mg/L 172 177 140 0 161 182
Calcium mg/L 90 125 105 150 270 197
Hydrogen Sulfide mg/L 3.0 3.0 3.5 3.2
Magnesium mg/L 86 105 110 205 280
Potassium mg/L 19 25 35 55 68
Strontium mg/L 17 21 3 15 15

20

22
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
4 5 6 7 8 9 10 11 12 13 14
MolarFraction
pH
Carbonic Acid (H2CO3)
Bicarbonate Ion (HCO3-)
Carbonate Ion (CO32-)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
4 5 6 7 8 9 10 11 12 13 14
MolarFraction
pH
Hydrogen Sulfide (H2S)
Bisulfide Ion (HS-)
Sulfide Ion (S2-)

• Use range of source water quality
• Apply generic design assumptions BWRO
• Utilize membrane, scale inhibitor and chemistry software
models to develop conceptual designs BWRO
• Table the results
23
Snapshot of Output Table

• LSI in RO feed < 1.8 (scale inhibitor)
• pH degasifier inlet < 6.0
– Acid in RO feed or
– Limited acid in RO feed and additional acid in permeate
• Treated water Hardness > 80 mg/L, Alkalinity > 60 mg/L CaCO3
• Meet the treated water goals (for corrosion control) by:
– RO Bypass and addition of carbon dioxide and liquid lime
24

25
$0.13
$0.05
$0.13
$0.05
$0.16
$0.05
$0.01
$0.02
$0.01
$0.02
$0.01
$0.03
$0.03
$0.05
$0.05
$0.05
$0.05
$0.05
$0.05
$0.06
$0.07
$0.07
$0.07
$0.08
$0.00
$0.05
$0.10
$0.15
$0.20
$0.25
$0.30
$0.35
2623 2623
(limited acid)
4690 4690
(limited acid)
7600 7600
(limited acid)
ChemicalCosts($per1000gallonstreated)
Sulfuric Acid Cost ($/1000 gallons) Anti-scalant Cost ($/1000 gallons)
Carbon Dioxide Cost ($/1000 gallons) Calflo Cost ($/1000 gallons)

• Bypass limited by treated water TDS < 440 mg/L
• Upper limit 20%
• Total capacity system remains at 100%
• Reduction in RO Bypass compensated by increase permeate
26

27
0%
20%
40%
60%
80%
100%
120%
1,500 3,500 5,500 7,500 9,500
Flow(%ofDesignFlow)
Bypass Flow WTP (%)
Permeate Water Flow WTP (%)
Rated Finished Water Capacity WTP (%)
48 50 52 54 56 58 58 58 60
24 25 26 27 28 29 29 29 30
0
20
40
60
80
100
120
140
160
180
200
0
10
20
30
40
50
60
70
80
90
100
1,516 2,000 2,623 3,250 3,850 4,690 6,060 7,600 9,356
InterstageERDPressureGain(psi)
ROTrainArray
Stage 1 Pressure Vessels Stage 2 Pressure Vessels
Interbank Booster Pump (psi) - Max

• Use of direct pressure exchanger from
concentrate to second stage feed
• Electricity $0.12/kWh
28
0
5
10
15
20
25
30
35
40
45
1,500 3,500 5,500 7,500 9,500
InterstageERDPaybackPeriod
(Years)

29
• Hardness and
Alkalinity goal of 80
and 60 mg/L CaCO3
• Bypass as before
0
20
40
60
80
100
120
140
1,500 2,500 3,500 4,500 5,500 6,500 7,500 8,500 9,500
TotalHardnessandAlkalinityinROPermeate
(mg/LasCaCO3)
Total Hardness (mg/L as CaCO3) - Treated Water
Alkalinity (mg/L as CaCO3) - Treated Water
Total Hardness (mg/L as CaCO3) - Goal
Alkalinity (mg/L as CaCO3) - Goal
Increase
Alkalinity Needed
Increase Hardness
Needed

30
$0.17 $0.19
$0.22 $0.23 $0.25 $0.27 $0.29
$0.33 $0.36
$0.41
$0.16
$0.19
$0.22
$0.24
$0.26
$0.25
$0.26
$0.27
$0.29
$0.31
$0.00
$0.10
$0.20
$0.30
$0.40
$0.50
$0.60
$0.70
$0.80
1,516 2,000 2,623 3,250 3,850 4,690 5,350 6,060 7,600 9,356
OperatingCost($per1000gallonstreated)
Energy Cost ($/1000 gallons) Chemical Cost ($/1000 gallons)

31

• Wellfield:
– Aquifer is complex and heterogeneous
– Many wellfields have experienced water quality degradation
• In wellfield
• Individual wells
– Best practice of wellfield design and operation available
• Treatment:
– Membrane and scale inhibitor technology improved
– Design should accommodate some form of degradation
– Impacts/trends on treatment assessed
32

33

FSAWWA Paper and Presentation Floridan Aquifer 12022015

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