Case Study: Treating Manganese

in Groundwater

Merrimack Village District

Wells 7 & 8

Michael Unger, P.E. Senior Project Engineer

NHWWA/NHDES Manganese Seminar

June 1, 2016

Well 7

• Installed 1996

• Approved for 500 gpm

or 720,000 gpd

2

Well 8

• Installed 1999

• Approved for 750 gpm

or 1,080,000 gpd

3

Wells 7 & 8

• Combined pumping rate of 1,250 gpm

• Represents 30% of MVD supply capacity

• Good water quality when wells put on line

• BUT Iron (Fe) & Manganese (Mn) have

increased over time with use of wells

4

5

0

0.5

1

1.5

2

2.5

3

3.5

Jan-92 Jan-96 Jan-00 Jan-04 Jan-08 Jan-12 Jan-16

mg

/L

Sample Date

Well #7 - Iron

3 times the SMCL

Secondary MCL

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

Jan-92 Jan-96 Jan-00 Jan-04 Jan-08 Jan-12 Jan-16

mg

/L

Sample Date

Well #7 - Manganese

6 Times the SMCL

6

Secondary MCL

00.2

0.40.60.8

11.21.4

1.61.8

2

Jan-92 Jan-96 Jan-00 Jan-04 Jan-08 Jan-12 Jan-16

mg

/L

Sample Date

Well #8 - Iron

6 Times the SMCL

7

Secondary MCL

Well Offline

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Jan-92 Jan-96 Jan-00 Jan-04 Jan-08 Jan-12

mg

/L

Sample Date

Well #8 - Manganese

5 Times the SMCL

8

Secondary MCL

Well Offline

Need for Project --

Wells #7 and #8 Water Quality

• Customer complaints attributable to Fe/Mn

• Fe/Mn increase distribution system

maintenance required

• Sequestration not effective

• Treatment is only reliable way to reduce

Fe/Mn at full capacity

9

Need for Project – Supply Capacity

• Have not been able to use Well 8 since 2008

• Use Well 7 only when necessary due to

demand

– Results in customer complaints

• Puts more stress on other wells

• Demand is increasing

• Need full capacity of Wells 7 & 8 without

sacrificing water quality

10

Supply Needed

11

*Based on 2005 through 2012 production data.

** 320 gpm capacity needed, based on a 24 hour pumping day

*** 472 gpm capacity needed, based on a 24 hour pumping day

Current

Shortfall*

Year 2030

Shortfall

MGD MGD

Annual Average

Day Demand

0 0

Summer Average

Day Demand

0 0.46**

Maximum Day

Demand

0 to 0.18 0.68***

Water Supply Improvement

Options Evaluated

• Increase Capacity of Well #2

• Treat Well #6

• Treat Wells #7 & #8 and Blend

• New Groundwater Source

• Pennichuck Water Works (PWW)

• Manchester Water Works (MWW)

• Surface Water Treatment Plant

• Some combination

12

Pilot Testing

13

1. Compare Greensand Plus and Pyrolusite

2. Recommend operating parameters:

• Chlorine Dose

• pH range

• Surface Loading Rates filter sizing

3. Evaluate backwash:

• Solids settling feasibility to recycle supernatant

• Backwash characteristics (physical and chemical)

• Production rates

Pilot Testing - Conclusions

14

• Both Greensand Plus and Pyrolusite effective at Fe/Mn

removal

• Chlorine Dose 2.0 to 2.4 mg/L

• pH range 6.8 to 7.0

• Surface Loading Rates 5 to 7 gpm/sq.ft. for 24 hour run

times

• Solids settled quickly

Project Overview

• Iron & Manganese Treatment Facility

– Capacity = 1,250 gpm (1.8 MGD)

• Full capacity of Wells 7 and 8

• Improvements to Wells 7 and 8

• Provisions for Well 6 or new well treatment in

future

15

16

17

WELL 7

WELL 8

FILTRATION

BUILDING

18

19

20

21

22

23

24

25

26

27

28

29

31

32

33

34

Performance

35

Raw Finished

Iron 1.5 – 1.89 mg/L 0.03 mg/L

Manganese 0.155 mg/L 0.006 mg/L

Pre-Treated Finished

Chlorine Residual 1.5 – 2.25 mg/L 0.8 – 1.0 mg/L

(no post-feed)

pH 6.8 – 7.0 6.8 – 7.0

(no post-caustic)

Filter Run Times = 48 hours +/- (5 psid)

36

Acknowledgments

• Merrimack Village District

• Blueleaf, Inc.

• NHDES – State Revolving Loan Fund

• PRB Construction

37

Questions?

38