Salt Contamination of Private Wells: Its Not as Simple as It May - - PowerPoint PPT Presentation

Salt Contamination of Private Wells: It’s Not as Simple as It May Seem

Presented to: Unity College Presented by: Keith R. Taylor, C.G. November 2016

November 2016 2

Background

• Road salt contamination of groundwater and

surface water well-documented

– 490,000 tons of rock salt were purchased in 2008-09 in Maine. – Roughly 750 pounds for every Maine resident, or 21 tons per road mile.

• Sodium and chloride are not “toxic”

– Can ruin piping, furnace, etc. due to corrosion – Tastes bad at high concentrations – Secondary drinking water standard for chloride = 250 mg/l, No standard for sodium

St.Germain Collins

November 2016 3

Case Study (Naples)

St.Germain Collins

November 2016 4

Case Study (Naples)

St.Germain Collins

Well Crooked River Slope Slope

November 2016 5

Case Study (Naples)

• Geology, Well Construction

– Sand and gravel, 13’ deep at well, overburden dry at well – 100’ well cased only to the bedrock

• Water Quality History
• Assessment Methods

– Expanded sampling that included some additional parameters (K, Ca, Mg, Mn, Fe, SO4, etc.) – Geophysical Surveys targeted salt storage, well area – Geoprobe borings for geology, water quality

St.Germain Collins

Sep-02 Jan-03 Sodium 115 405 Chloride 190 902

November 2016 6

Case Study (Naples)

November 2016 7

Case Study (Naples)

• Conceptual Model

– Salt originated from road application (steep intersection), not storage site – Ground water moved easily between bedrock and overburden – Well had little casing and likely drew water from shallow bedrock

St.Germain Collins

Old Well New Well

• Solution is a new well
• Results

– Bedrock at 37’, casing to 50’, water at 215’. – Sodium = 14 ppm, Chloride = 10 ppm

November 2016 8

Case Study (Brunswick)

St.Germain Collins

November 2016 9

Case Study (Brunswick)

St.Germain Collins

Well

November 2016 10

Case Study (Brunswick)

• Geology, Well Construction

– <10’ till, bedrock exposed in area – Well 220’ deep, 20’ casing

• Water Quality History
• Assessment Methods

– Expanded sampling that included some additional parameters – Borehole geophysics

St.Germain Collins

7/14/04 11/8/04 12/9/04 4/11/05 Sodium 68 74 NA 55 Chloride 288 290 NA 250 Nitrate <1.0 4.3 3.8 4.3

November 2016 11

Case Study (Brunswick)

Fluid Conductivity

November 2016 12

Case Study (Brunswick)

• Conceptual Model

– Increased conductivity, abrupt temperature change, increased flow at fracture at depth of 81’ – Orientation of 81’ fracture puts it at the surface in the drainage ditch where bedrock was exposed – Most or all of the salt is migrating from ditch to well via the 81’ fracture

• Solution

– Replacement well not feasible due to small parcel and leachfield (100’ setback required) – Instead, installed a “jaswell” seal to a depth of 110’ to isolate fracture

St.Germain Collins

November 2016 13

Case Study (Brunswick)

• Results

– Seal prevented most of the salt from entering the well – Sodium = 38 ppm, Chloride = 120 ppm (Nitrate still 5 ppm) – Still higher than background but appears to have worked

St.Germain Collins

November 2016 14

Case Study (Windham)

St.Germain Collins

November 2016 15

Case Study (Windham)

St.Germain Collins

Well

November 2016 16

Case Study (Windham)

• Geology, Well Construction

– <8’ till, bedrock exposed on site, mostly unsaturated – 142’ well, 10’ of casing

• Water Quality History

– Unusually high salt levels for road application source

St.Germain Collins

Nov-93 Apr-01 Apr-01 Aug-02 Sep-03 Nov-03 Feb-04 Sodium NA NA NA NA 620 493 325 Chloride 73 860 320 NA 1600 940 951 Calcium NA NA NA NA NA NA 90 Magnesium NA NA NA NA NA NA 14 Potassium NA NA NA NA NA NA 7.2 Alkalinity NA NA NA NA NA NA 36 Sulfate NA NA NA NA NA NA 19.5

November 2016 17

Case Study (Windham)

• Assessment Methods

– Expanded Sampling – Geoprobe borings

• Continous soil sampling to

bedrock

• Ground water analysis for salt
• Because only one location had

water, analyzed soil for salt

– Geophysical Survey

• Borehole geophysics only partially

successful because of existing Jaswell seal in place

St.Germain Collins

November 2016 18

Case Study (Windham)

• Conceptual Model

– Very shallow overburden, mostly unsaturated, full of salt – “Bowl” shape to bedrock surface; contains overburden ground water – Salty runoff from road (no curbs or ditches) is captured in bedrock “bowl” and moves down rather than laterally

• Solutions that Failed

– Previous well driller tried Jaswell seal but it failed – We moved Jaswell down to 125’ but salt returned – Salt entering from bottom of well 

• New well needed but…

– Very little land – No obvious location because of bedrock “bowl”

St.Germain Collins

November 2016 19

Case Study (Windham)

• Solution that worked

– Constructed well with 200’ casing – 60 gpm at 450’; sodium = 10 ppm, chloride = 2 ppm

St.Germain Collins

Old Well Highland Lake New Well

November 2016 20

Case Study (Scarborough)

St.Germain Collins

November 2016 21

Case Study (Scarborough)

St.Germain Collins

Wells 12 ASR 10 ASR

November 2016 22

Case Study (Scarborough)

• Geology, Well Construction

– Shallow Till – Two wells – 10 Ash Swamp Road = 30’ from road – 12 Ash Swamp Road = 150’ from road

• Water Quality History

St.Germain Collins

7/21/05 12/28/05 4/12/06 7/11/06 10/24/06 1/4/07 Choride 188 74 101 232 57 66 Sodium 122 44 51 94 51 46 7/21/05 12/28/05 4/12/06 7/11/06 10/24/06 1/4/07 Choride

• 77

116 126 36 58 Sodium

• 51

59 79 40 44 10 Ash Swamp Road 12 Ash Swamp Road

November 2016 23

Case Study (Scarborough)

• Assessment Methods

– Expanded Sampling and Geochemical Analysis

• A good example of where expanded suite of parameters very

useful

• Used simple ionic ratios to compare to Maine DOT 1990

study of road salt, seawater intrusion, and relict salt water sources

• Seawater intrusion unlikely since closest brackish water

(Scarborough Marsh) is about 2 miles away

• Results

– No bromide, normally indicator of seawater (new or old) – But salt concentrations are low, maybe bromide too low to detect? – Focused on ionic ratios

St.Germain Collins

November 2016 24 St.Germain Collins

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Road Salt Trapped Seawater 10 Ash Swamp Rd 12 Ash Swamp Rd Ionic Ratio

Na/Cl SO4/Cl K/Cl Ca/Cl

Case Study (Scarborough)

November 2016 25

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

Na/Cl SO4/Cl

Trapped Seawater Road Salt 10 Ash Swamp Rd 12 Ash Swamp Rd

Case Study (Scarborough)

November 2016 26

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.00 0.02 0.04 0.06 0.08 0.10 0.12

K/Cl SO4/Cl

Trapped Seawater Road Salt 10 Ash Swamp Rd 12 Ash Swamp Rd

Case Study (Scarborough)

November 2016 27

Case Study (Scarborough)

• Conceptual Model

– Salt concentrations very similar in wells despite difference in distance from road – Road layout, topography not suggestive of high road salt area or runoff toward wells – Ionic ratios with SO4 strongly suggest relict seawater

• No solution pursued since road salt not the source
• Good example of misleading clues

– Shallow overburden – No bromide detected – Initially suggests road salt

November 2016 28

Conclusions

• Careful Assessment of Salt Source Needed

– Surface Topography – Overburden Type and Thickness – Bedrock Type and Depth – Well Construction – Ground Water Depth and Flow – Bedrock Structure and Topography – Geochemistry

• Easy to be mislead by one or two “obvious”

conditions

St.Germain Collins

November 2016 29 St.Germain Collins