compliance with the new arsenic mcl - new hampshire …
TRANSCRIPT
Compliance with the New Arsenic MCL
Epping, NH
Introduction
• Speaker: Devon Smith, PE
• Employer: Underwood Engineers
• Position: Senior Project Engineer
2
Purpose
• Regulations
• Existing System
• Treatment Process
• Water Treatment Plant
• Questions
Epping
• A case study on the Epping water treatment plant and the arsenic removal process.
Agenda
3
Arsenic (As)What is it?
• Naturally occurring metalloid• Colorless, tasteless & odorless in
drinking water
Health Effects?• Cancer• Diabetes • Neurological disorders • Birth defects
4
Regulations
“The U.S. Environmental Protection Agency (EPA) typically sets MCLs for drinking water contaminants at a level at which a lifetime of exposure would result in one excess cancer in one million people exposed…The 10 ppb MCL for arsenic is associated with a far greater risk – 3,000 in a million (roughly 1 in 300)..”
• Current Maximum Contaminant Level (MCL) • 10 parts per billion (ppb) or micrograms per liter
• January 2006
• Federal Regulation
• Future Maximum Contaminant Level (MCL)• 5 parts per billion (ppb) or micrograms per liter
• Expected July 2021
• State Regulation
5
Existing Water Supply System – Epping NH
Pleasant Street Tank250,000 Gal.
Gauthier Tank300,000 Gal
Epping Crossing Well Field Pilot Plant, 100 gpm
Existing System
• Storage = 550K Gal.
• Capacity = 183 gpm
Well Fields
• Epping Crossing
• As = 19 ppb
• Hoar Pond
• As = 9 ppb
• Cannot meet future As regulation
Hoar Pond Wells83 gpm
6
Epping Crossing Well Field
Pilot PlantCapacity = 100 gpm Well E1
PPV = 225 gpm
Well D2PPV = 210 gpm
NHDES Env-DW 404.01
• Capacity > MDF
• Capacity > ADF with largest well off
• Future Capacity = 210 gpm
• Permit Well F1
Well F1Expected Capacity = 80 gpm
7
Existing Pilot Plant • Capacity
• 100 gpm
• Filters
• No. = 3
• Diameter = 3.5 ft
• Media
• Clack MTM
• Chemical Feed
• 40% Ferric Chloride
• 12.5% Sodium Hypochlorite
8
Epping Crossing Well Field – Water Quality
> 10 ppb (soon to be 5)
> 0.3 mg/L (SMCL)
> 0.05 mg/L (SMCL)
Standard
EPA Health Advisory for Mn• 0.3 mg/L for infants
NHAGQS for Mn• 0.84 mg/L
9
Arsenic Removal by Iron Removal Oxidation
• Convert inorganic soluble As (III) to insoluble As (V)
Adsorption & Co-Precipitation• As becomes entrapped within
growing Fe by inclusion, occlusion or adsorption.
Filtration• Greensand media acts as a catalyst
in oxidation reduction reaction for Fe and Mn.
Key Parameters• As to Fe ratio
• pH = 6.2 -8.5
10
Treatment Process Selection
Additional Fe and lowering the pH is
necessary for optimal As removal
11
Blue Leaf Piloting • 4 Pilot Parameters (Fe /pH)
• HH
• HL
• LH
• LL
• Results
• As = 0.7 – 3.6 ppb
• Mn = 0.006 - 0.015 mg/L
• Fe = 0.03 – 0.59 mg/L
• Backwash Run Times• 20 HRs – 48 HRs
• Backwash Triggers• Turbidity breakthrough
• Pressure differential
12
13
Manganese Greensand Process• Filters
• No = 3• Diameter = 8 ft
• Greensand Plus Media • Loading Rate = 2-12 gpm/sf • Anthracite Cap
• Delays filter blinding
• Regeneration
• Backwash• Combined water and air scour• Flow = 10-12 gpm/sf• Volume = 10,000 gal. – 16,000 gal.
14
= Influent
= BW Waste
= Effluent
= BW Influent= Filter to Waste
15
Backwash Equalization Tanks• Limited sewer capacity • 26,400 Gal. useable storage
• Backwash performance requirement• Backwash recycle was not provided
Freeboard
Min. PumpSubmergence
16
• Wetlands and Buffers
• Conservation Easement
• Well Protection Zone
Site Plan Wetland Boundary
Wetland Buffer
Conservation Easement
Well Protection Zone
Wetland Buffer
PilotPlant
Water TreatmentPlant
17
Floor Plan
Capacity • 435 gpm (0.63 MGD)
Building Dimensions• 67’-4” x 37’-8• 2,536 sf
Building Materials• Wood Frame• Fiber Cement Siding• FRP Paneling • Asphalt Shingles
18
Hydraulics
Static Head
• Min = 162.5 ft
• Max = 378.6 ft
EL =126.0 ft Static GWT
EL = -90.1 ft180 Day Drawdown
EL = 288.5 ftSystem HGL
HGL Diagram (Simplified) Well D2
Filter
Storage Tank
Submersible Well Pump Curve
19
Project Status
• Contractor: PRB Construction
• Construction Cost: $3,046,000
• Percent Complete: 10% (7/2/20)
• NTP: 6/1/2020
• Sub. Completion: 5/26/21
• Final Completion: 7/25/2021
20
References
1. NHDES. December 2018. Review of the Drinking Water Maximum Contaminant Level (MCL) and Ambient Groundwater Quality Standard (AGQS) for Arsenic. Concord, New Hampshire.
2. U.S. EPA. April 2006. Design Manual Removal of Arsenic from Drinking Water Supplies by Iron Removal Process. Columbus, Ohio
22