Evaluation of Water Quality Impacts from Dust Suppressants (TPD1111004)

Table: Suppressants Selected for Study

Soil Selection Criteria

• No visible contamination
• Native land, no farming/industrial history
• Normal soil range of metals
  • 6010 test for metals
  • 7471 test for Mercury

Soils Selected

• Clark County AQMD and Maricopa County AQD recommended sample locations
  • Based on soil maps of each county
  • Maps classify soils by texture and dust-emitting potential
• One Gallon Samples – 5 per county
• Bulk Samples (five cubic yards) – 1 per county

Map: Sampling Locations in Clark County

Map: Sampling Locations in Maricopa County 

Soil Samples

• One gallon samples taken by hand
  • Evaluate sensitivity of select water quality parameters to soil chemistry differences
• Bulk samples taken by excavators
  • Pre-tests for metals contamination
  • Shipped to SDSU-SERL in super sacks

Photo: One Gallon Samples

Photo: Job Site/Heavy Equipment

Soil Processing

• Sizeable rocks and debris removed
• Performed sand, silt, and clay analysis
• Thorough mixing at laboratory
• Chain of custody procedures followed

Graph and Table: Particle Size Distributions for Bulk Soils 

Test Protocol

• Control Plots Treated with Reverse Osmosis Water Only
• Surface Leaching (Runoff to Surface Waters)
  • Simulated rainfall (0.7, 1.3, and 2.4 inches/hour)
  • Simulated heating
  • Tested for general chemicals of concern
  • Tested for aquatic toxicity (fish, algae, and invertebrates)
• Column Migration (Potential to Reach Groundwater – Subsurface Leaching)
  • Migration rate
  • Tested for general chemicals of concern

Sample Preparation

• One of two reapplication/soil disturbance scenarios
  • A. Soil surface raked daily and product applied each day
  • B. Soil surface raked daily and product applied on days 1, 3, and 5
  • For synthetic products, B scenario was higher initial application and no reapplication
• Duration for both scenarios is consecutive 5-day period following initial application
  • Each of 5 days, soil raked in alternating directions
  • Reapplication rates same as original application

Rainfall Events

• 0.7 inches per hour for 150 minutes
• 1.3 inches per hour for 80 minutes
• 2.4 inches per hour for 43 minutes

Photo: Runoff Collection from Test Tray 

Photo: Runoff Collection/Soil Test Tray

Schematic: Soil Bed Layout

Photo: Tilting Bed SDSU-SERL

Photo: Rain Heads SDSU-SERL

Photo: Plan View of Tilting Soil Bed

Schematic: Vertical Leaching Experiment

Photo: Preparing Migration Test Cylinders

Photo: Typical AZ (Left) and NV (Right) Soil Columns

Table: Products Tested

Table: Experimental Parameters

Analytical for Runoff and Leachate

• Ph
• Electrical Conductivity
• TSS
• TDS
• DO
• TOC
• Nitrate and Nitrite
• Total Phosphorous
• Aquatic Toxicity (Runoff only)

Qualitative Analysis of Test Results

• Surface Leaching Tests
  • All six products met study DQOs for pH, TDS, TOC, DO, and Nitrate
  • Most significant effect – High TSS in runoff from soils treated with Durasoil and EnviroKleen
  • AZ soil runoff typically had higher conductivity, TDS, TOC, nitrate, nitrite, and phosphate
  • NV soil runoff had higher pH and TSS
  • DO similar for both soils
• Vertical Migration Tests
  • Water migration through a 12­inch column of soil
  • Average results by product for eight of nine parameters meet DQOs
  • TSS results varied but typically not a concern for groundwater quality
• Pilot Tests
  • Evaluated soil/water/product mixtures
  • TDS for Enviro Roadmoisture 2.5 and Durasoil samples significantly higher than control samples – Not observed in runoff tests

Aquatic Toxicity Tests

• Runoff samples for toxicity collected as part of SDSU’s surface leaching tests
• Toxicity tests conducted by EPA Region 9 Lab
  • Fish (flathead minnow) – acute tests
  • Algae – chronic tests
  • Invertebrate (Daphnia Magna) – acute tests
• Control samples based on RO water only

Aquatic Toxicity Testing

• Fish Tests
  • No toxicity to fish observed in any runoff sample
• Algae tests
  • No toxicity to algae observed in any runoff sample
  • Test may underestimate impact due to fine filtration of samples to remove sediments required by test protocol
• Invertebrate Tests – Daphnia magna
  • For 4 surfactants, majority of samples showed no toxic effect relative to control samples
  • Adverse physical effect on daphnids for Envirokleen and Durasoil samples compared to control (Daphnids trapped on surface not able to re-enter water column).
  • Additional tests with smaller invertebrate (Ceriodaphnia Dubia) conducted on product samples of Envirokleen and Durasoil did not show physical entrapment effect.