Surface Stabilizer Site Layout at New River West

Formation Environmental
2019-02-01
Imperial Irrigation District

1 INTRODUCTION

The Surface Stabilizer Pilot Study was developed for the Imperial Irrigation District (IID) as a part of the Salton Sea Air Quality Mitigation Program (SS AQM Program) (IID 2018, In Review). Surface stabilizers are commonly used as dust suppressants on unpaved roads, construction sites, and other disturbed lands. It is anticipated that surface stabilizers could provide interim dust control in isolated areas prone to dust emissions, or in areas that require minimal dust control infrastructure and/or have planned alternative land uses (e.g., geothermal development). More importantly, surface stabilizers could provide quick, effective control and prevent the spread of emissive areas while more permanent dust control measures (DCMs) are evaluated for longer-term use. The purpose of this pilot study is to quantify the effectiveness of a variety of surface stabilizers in controlling wind-blown dust on representative playa surfaces with different surface characteristics and soil properties.

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The New River West site was selected for the pilot study. Application of the selected surface stabilizers is anticipated in fall 2019, followed by one year of performance monitoring. The following sections describe the selection of surface stabilizers for use in this pilot study (Section 2), benchtop studies and laboratory testing (Section 3), site selection (Section 4), site characterization (Section 5), site layout (Section 6), implementation and performance monitoring (Section 7), and the estimated timeline for implementation (Section 8). References are included in Section 9.

2 SURFACE STABILIZERS

Surface stabilizers are commonly used as dust suppressants on unpaved roads, construction sites, and other disturbed lands. They are usually applied topically and can include water, salts and brines, organic non-petroleum products, synthetic polymers, organic petroleum products, or mulch and fiber mixtures. Surface stabilizers abate dust either by binding the soil particles together or by changing the physical properties of the soil surface. The mechanisms by which surface stabilizers abate dust vary with product type.  Some form crusts or protective surfaces on the soil, some act as binding agents causing particles to agglomerate together, and some attract moisture to the soil particles. The effectiveness of surface stabilizers varies with the product type, environmental conditions, soil type, weather, and application rate.

Many surface stabilizer products are available on the market. Over 15 products were reviewed to identify the most feasible products for this pilot study. Selection criteria included the following:

1) material safety, 2) ease of application, and 3) cost efficiency. Based on these criteria, five products were selected: Soiltac®, DirtGlue®, Dust Control Plus, Soil Stabilization Plus, and Terra-Ferr. Each product is cost-efficient and can be applied with a spray truck or similar method that enables uniform application over large areas. The mechanisms of dust abatement, material safety, and proposed vendors for each product are summarized in Table 1.

TABLE 1. SUMMARY OF SURFACE STABILIZER PRODUCTS SELECTED FOR THE PILOT STUDY

Soiltac®

DirtGlue®

Dust Control Plus

Soil Stabilization Plus

Terra-Ferr

Surface Stabilizer Product Overview

Soiltac® is a high molecular weight, synthetic vinyl copolymer dispersion stabilizer that becomes transparent after curing. The copolymer molecules coalesce to form cross-linked bonds between soil particles, generating a three- dimensional crust. The crust created is water-resistant and if applied at heavier application rates can assume qualities of concrete.

DirtGlue® is an aqueous acrylate polymer emulsion. The polymer penetrates the surface, binding to soil particles to create a three- dimension matrix layer.

Dust Control Plus binds the soil by penetrating the soil and bonding soil particles. By doing this, it alters the micro-structure of treated surfaces. It is also known as Envirotac II and RhinoSnot and is one of the earlier dust control products made of acrylic polymer. It dries odorless and transparent.

Soil Stabilization Plus works in the same manner as Dust Control Plus as it is the same product with a higher percentage of solids (55% as opposed to 35%). The active ingredients are polyethylene glycol phenoxy ether and polyethylene glycol phenyl ether.

Terra-Ferr is an aqueous blend of lignin liquor, whey, and magnesium chloride. The lignin liquor is a tarry, water- soluble anionic polyelectrolyte polymer. It is a byproduct of wood pulp (near- pure cellulose) production via sulfite pulping. Lignin is an organic polymer that provides structural support, especially in cell walls of wood and bark, but also in all other vascular plants. The substance seeps into the top layer of soil and binds the soil particles together. It usually appears reddish-brown to brown.

Material Safety

 

 

 

 

The material is chemically inert and deemed safe for the environment.

 

Although the aqueous mixture is not flammable, the dried material will burn in a fire.

 

The product is not listed as carcinogenic under California’s Proposition 65.

The material is chemically inert and deemed safe for the environment.

DirtGlue® has a Hazard Rating of 1 (slightly hazardous) in the Health category.

The product is not listed as carcinogenic under California’s Proposition 65.

The material is chemically inert and deemed safe for the environment.

This product has also been used by the U.S. Military, for example, at the Forward Operating Base, Camp Rhino. The product has approval to be used in California (California Prop 65).

Soil Stabilization Plus has a Hazard Rating of 1 (slightly hazardous) in the Health category.

The material is chemically inert, and deemed safe for the environment.

The material is chemically inert and deemed safe for the environment.

Proposed Vendor

 

 

 

 

Soilworks, LLC

Global Environmental Solutions LLC

EP&A Envirotac, Inc.

EP&A Envirotac, Inc.

AACE Sales, Inc.

3 BENCHTOP STUDIES AND LABORATORY TESTING

Before scaling up to the field-scale pilot study implementation, a benchtop (laboratory-scale) test will be performed to evaluate each proposed surface stabilizer’s baseline effectiveness. Another benchtop test will focus on variations of a more novel and potentially cost-effective surface stabilizer: bio-grout. Bio- grouting is a general term for soil stabilization using cementation of soil particles with calcite (CaCO3).Bio-grouting in essence mimics nature’s biologically mediated processes using water supersaturated with CaCO3 to create CaCO3-bearing rocks, commonly referred to as limestone, or caliche, in soil. Recent investigation into bio-grout includes an application to prevent wind-driven erosion originating from silty fine sand in Arizona.

Bio-grout is classified based on whether microbes are involved in creating the chemical conditions conducive for calcite precipitation. The first type of bio-grout, Microbially Induced Calcite Precipitation (MICP), uses microbes that generate urease to promote urea hydrolysis and denitrification. The second type of bio-grout, Enzyme Induced Calcite Precipitation (EICP), requires direct application of urease for urea hydrolysis. Both methods increase the pH and partial pressure of carbon dioxide (CO2) in the soil pore space, creating a chemical environment conducive to calcite precipitation.

The following sections outline benchtop study designs for the proposed surface stabilizers and for bio- grout.

3.1 SURFACE STABILIZER BENCHTOP STUDY DESIGN

The benchtop study for the proposed surface stabilizers will involve filling 18 (three replicates of each soil stabilizer and three controls) 16-inch diameter hog pans with homogenized Salton Sea playa soils. The total volume needed to fill the hog pans is 12,672 cubic inches (55 gallons; 11 five-gallon buckets). The homogenized soils will be collected from the top 3 inches of playa surface within a 30.25 square- foot (5.5 ft x 5.5 ft) area at the New River West site. Before collection, the top three inches of soil will be disturbed. The disturbance is intended to simulate the harrowing planned for the field-scale pilot study. A sample of the collected soil will be submitted to the Stanworth Consultants (Stanworth) laboratory in Blythe, CA, for soil texture analysis.

Each hog pan will be treated separately with the different surface stabilizer products (the five listed in Table 1 and a control). Because the volume of the treatments recommended by the manufacturers will saturate the soil column in the hog pan and additionally leave standing product at the surface, the application rates will be proportionally adjusted so that the product requiring the highest volume at application, DirtGlue®, will just saturate the hog pan soil column. The application rates of the remaining surface stabilizer products will be normalized to the DirtGlue® application rate; therefore, they will not saturate the entire 3.5 inches of the hog pan soil column. Table 2 lists the required volumes for product application in the hog pans. A porosity value of 0.3, assuming a sandy soil, was used to calculate the application volumes. Based on the soil texture analysis results from Stanworth, the volumes in Table 2 may increase slightly because heavier soils have higher porosity values. After the treatments cure, their soil stabilizing capabilities will be evaluated with a Portable In-situ Wind Erosion Laboratory (PI-SWERL) (Figure 1) and penetrometer tests, further described in Section 5.

TABLE 2. SURFACE STABILIZER APPLICATION RATES NORMALIZED TO DIRTGLUE® AND ADJUSTED FOR HOG PANS

 

Surface Stabilizer

Manufacturer Recommended Application Rates (gal/acre)

Values Normalized to DirtGlue®

 

Adjusted Application Volume for Hog Pans (gal)

Soiltac®

1,100

0.28

0.25

DirtGlue®

3,940

1.00

0.91

Dust Control Plus

985

0.25

0.23

Soil Stabilization Plus

2,200

0.56

0.51

Terra-Ferr

1,100

0.28

0.25

3.2 BIO-GROUT BENCHTOP STUDY DESIGN

The bio-grout will be tested on a smaller scale than the conventional surface stabilizers. Cupcake tins will be filled to test the concept’s feasibility. There will be five treatments that include a control and testing both the MICP and the EICP methods of induced calcite precipitation. Each method will include two tests using different water sources: water from the Salton Sea, and canal water. The canal water will be amended to attain the same level of calcite supersaturation as the Salton Sea water. In addition, the ratio of carbonate ions to calcium will be maintained at 0.3 in both water sources. Soil will be amended to ensure sufficient calcium for ion exchange. Each treatment will have three replicates, totaling 15 cupcake tins. The MICP tests will require inoculation of the soil samples with a recommended dose of soil bacteria. The bacteria theoretically will produce their own urea, which then goes through hydrolysis, releasing bicarbonate for use in calcite precipitation. The EICP tests will all be treated with a quantity of urease that will ensure that it is not a limiting factor in calcite precipitation. The chemistry of the soil used in the study will be determined at Stanworth Labs.

Treatments are as follows. Note: all soil will be the same, and water sources will be amended to maintain calcite supersaturation and a ratio of 0.3 for carbonate to calcium.

  • Treatment 1: soil (control)
    • Treatment 2: soil + SS water + MCIP bacteria
    • Treatment 3: soil + canal water + MCIP bacteria
    • Treatment 4: soil + SS water + urease
    • Treatment 5: soil + canal water + urease

FIGURE 1. PI-SWERL TO EVALUATE SURFACE STABILIZER EFFECTIVENESS

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4 SITE SELECTION

As described in Section 1, the purpose of this pilot study is to quantify the effectiveness of a variety of surface stabilizers in controlling wind-blown dust on a variety of representative playa surfaces. A pilot study site was selected primarily based on known areas of potential emissions identified as a part of the SS AQM Program (IID 2018, In Review). For this pilot study, additional site selection criteria included: 1) accessibility, 2) adequate extent for the required plot configuration as constrained by site boundaries, the shore, prohibitively soft surfaces, and existing vegetation, 3) relatively homogeneous site conditions (i.e., no significant, inherent variability), and 4) avoidance of conflict with other, ongoing, or proposed studies. Based on these criteria, the New River West site was selected for this pilot study.

5 SITE CHARACTERIZATION

A background investigation will be performed to characterize site conditions prior to pilot study implementation. Soil core samples (which provide texture via FieldSpec4 spectroradiometer data, chemistry, and core logs) and EMI (electromagnetic induction) datasets are already available for the site. In addition to these existing datasets, additional site characterization data will be collected to provide the basis for comparison of site conditions, surface stabilizer products, and dust control performance. The following activities will be completed during the background site characterization:

1) Collect Soil Samples. Soil properties may affect the integrity or dissociation of stabilizers and their resulting dust control effectiveness. Therefore, soil sampling data will be valuable in understanding how and to what degree soil properties influence the necessary application rate and duration of dust control performance. Soil samples will be collected from each test plot to determine bulk density and soil moisture conditions. Soil samples will be collected in a composite sampling scheme from two different sample depths (0-3 and 3-12 inches). In addition, penetration resistance of the surface soil will be determined using averaged penetrometer test results. Table 3 provides a list of soil properties that will be characterized.

2) Perform Surface Survey. Playa surface crusts are the main source of emissions of particulate matter less than 10 microns in diameter (PM10) and are therefore the focus of dust control activities. A surface survey will be conducted to map the distribution of surface playa characteristics and to quantify their physical properties. These properties directly affect dust emissions and will inform the pilot study configuration. The playa surface survey will result in a map depicting similar surface units (analogous to a soil map unit) that are grouped and characterized by crust type, crust thickness, crust hardness, free surface sand percentages, soil texture, and crust relief. Unmanned Aerial Vehicle (UAV) imagery will be collected prior to the survey event and used to guide the mapping effort. A description of surface characteristics to be surveyed is provided in Table 3.

3) Collect PI-SWERL Samples. Emissions potential will be assessed for each plot using a PI-SWERL (Figure 1). After placement on the ground surface, the PI-SWERL exerts a known friction velocity upon the tested surface and measures the resulting PM10 and saltation flux, thus providing an estimate of emissions potential under a range of simulated wind conditions. An example of PI-SWERL output data is shown in Figure 2. Sampling results will inform emissions potential before surface stabilizer application and provide important baseline data regarding each product’s dust control performance.

TABLE 3. SUMMARY OF BACKGROUND SITE CHARACTERIZATION ACTIVITIES

Site Characterization Activity

Conditions

 

Soil sampling

  • § Texture (by feel)
  • § Bulk density
  • § Penetration resistance
  • § Soil moisture

Surface survey

  • § Crust type
  • § Crust thickness
  • § Crust hardness
  • § Soil texture
  •  § Evidence of erosion
  • § Free surface sand
  • § Macro/micro relief
  • § Presence of vegetation

PI-SWERL sampling

  • § Emissions potential before product application

 

FIGURE 2. EXAMPLE OF PI-SWERL DATA – PM10 EMISSIONS INCREASE (LEFT) AS THE ROTATIONS PER MINUTE (RPMS)OF THE INNER FAN INCREASE (RIGHT)

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6 SITE LAYOUT

To evaluate a wide range of potential conditions, the pilot study will be configured as a randomized complete block design (RCBD). In the RCBD, the field is divided into rows, and each row is further divided into several plots equal to the number of stabilizers to be tested and a control plot with no treatment. This type of study design reduces the error caused by irrelevant sources of known variation in dust emissions, while simultaneously isolating the primary “factors” providing dust control (i.e., the surface stabilizers).

The pilot study at New River West will cover approximately 8 acres. Each test plot will be 50 by 140 feet (0.16 acres). The site layout, plan view of the study, and plot detail are shown in Figure 3, Figure 4, and Figure 5, respectively. The entirety of the study sites will be disturbed with a harrow or similar implement to ensure that the surface stabilizers are being tested on emissive surfaces. After disturbance, the study areas will be divided into 4 test rows. Within each test row, 6 test plots will be created. These test plots will be treated with the five surface stabilizer products and the sixth plot will be left untreated as a control plot. Bio-grout will not be included in the site layout as it will only be laboratory tested for the purposes of this study. The control plot will be used as a baseline for comparing the effectiveness of the products. Between each plot, there will be a 25-foot open space where tillage furrows will be established. The purpose of the tillage furrows is to reduce potential cross- contamination and/or dust emissions from adjacent plots. Each plot will additionally have a 5-foot overspray perimeter, included in the aforementioned plot area dimensions, where the applied surface stabilizer will act as a buffer to its own respective monitoring area. An access path will be constructed for each plot perpendicular to the dominant wind directions.

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7 IMPLEMENTATION AND PERFORMANCE MONITORING PLAN

This section describes implementation of the Surface Stabilizer Pilot Study and the performance monitoring plan.

7.1 IMPLEMENTATION

Vendor-recommended application methods and rates will be used. During purchase of the stabilizers, the vendors will be consulted for the recommended application rates. The application rates will be based on the request that the surface treatment should last 12 months and may vary based on soil type. Preliminary application methods and rates are summarized in Table 4.

TABLE 4. SUMMARY OF PRELIMINARY PRODUCT APPLICATION METHODS AND RATES

Surface Stabilizer

Application Summary

Soiltac®

Approximately 176 gallons of Soiltac® will be mixed with 528 gallons of water (this mixture yields a 3:1 water-to-product ratio) and applied over four assigned plots, one in each row for a total 28,000 square feet, or 0.64 acres. The total gallons applied will be approximately 704. The application rate may vary based on soil type but is approximately:

  • ·         275 gallons of raw product per acre
  • ·         1,100 gallons of dilute product per acre

DirtGlue®

Approximately 280 gallons of DirtGlue® will be mixed with 2,240 gallons of water (this mixture yields an 8:1 water-to-product ratio) and applied over four assigned plots, one in each row for a total 28,000 square feet, or 0.64 acres. The total gallons applied will be approximately 2,520. The application rate may vary based on soil type but is approximately:

  • 435 gallons of raw product per acre
  • 3,940 gallons of dilute product per acre

Dust Control Plus

Approximately 70 gallons of Dust Control Plus will be mixed with 560 gallons of water (this mixture yields an 8:1 water-to-product ratio) and applied over four assigned plots, one in each row for a total 28,000 square feet, or 0.64 acres. Total gallons applied will be approximately 630. The application rate may vary based on soil type but is approximately:

  • ·         110 gallons of raw product per acre
  • ·         985 gallons of dilute product per acre

Soil Stabilization Plus

Approximately 128 gallons of Soil Stabilization Plus will be mixed with 1,280 gallons of water (this mixture yields a 10:1 water-to-product ratio) and applied over four assigned plots, one in each row for a total 28,000 square feet, or 0.64 acres. Total gallons applied will be approximately 1,408. The application rate may vary based on soil type but is approximately:

  • 200 gallons of raw product per acre
  • 2,200 gallons of dilute product per acre

Surface Stabilizer

Application Summary

Terra-Ferr

Approximately 710 gallons of Terra-Ferr will be applied over four assigned plots, one in each row for a total 28,000 square feet, or 0.64 acres. The application rate is approximately 1,100 gallons of product per acre.

7.2 PERFORMANCE MONITORING PLAN

Monitoring will be conducted to evaluate dust control effectiveness and changes in playa surface conditions as described below.

7.2.1 DUST CONTROL EFFECTIVENESS

Emissions potential will be assessed for each plot using a PI-SWERL (Figure 1). PI-SWERL sampling will occur after the surface stabilizer product has cured (typically 24 hours) and then at quarterly intervals. PI-SWERL sampling locations will be accessed by the access paths constructed for each plot (Figure 3). PI-SWERL samples will be completed using a three-step test. The test will consist of a 60-second cleaning cycle followed by three periods of increased simulated friction velocities, 0.39, 0.55, and 0.69 m/s, which respectively occur at 2,000, 3,000, and 4,000 RPMs (Figure 2). Sampling results will be analyzed to determine if and when the effectiveness of the products has declined and to assess the relative performance of each product.

7.2.2 PLAYA SURFACE CONDITIONS

During PI-SWERL sampling, a qualitative analysis will be conducted for the following: crust type, crust thickness, crust hardness, free surface sand, evidence of erosion and deposition, surface soil moisture, and macro- and micro-topography, among other parameters. Table 5 provides a summary of parameters to be qualitatively assessed during PI-SWERL sampling. Figure 6 is an example of photo documentation during surface characterization assessment.

TABLE 5. PLAYA SURFACE CHARACTERISTICS ASSESSED DURING PI-SWERL SAMPLING

Parameter

Description

Crust Type

Categories include: smooth, botryoidal, weak botryoidal, barnacle bed, no crust, and open water. The dominant crust type of the observation area will be characterized, and if other types are present in smaller amounts, they will be noted as inclusions.

Crust Thickness

Crust thickness is measured from the top of salt crust to the top of soil. In some places, the salt crust will be divided into two distinctly different layers: top crust and sub crust. Top crust is usually a harder, salt-cemented crust that forms a shell over the surface. Sub crust usually has weak structure (i.e., soft or crumbly) and extends from the bottom of the top crust to the underlying, often looser soil. In some cases, a top crust will exist without a sub crust and will be directly overlaying the soil. Total crust thickness is considered the sum of top crust and sub crust.

Crust Hardness

Crust hardness indicates the degree of erosion resistance. Crust hardness is characterized by the amount of force necessary to crush the salt crust by hand according to USDA-NRCS guidelines (Schoeneberger et at. 2011). On average, smooth and week botryoidal crust types are the softest.

Penetration Resistance

Penetration resistance is measured with a penetrometer in pounds per square inch (psi). A penetrometer is inserted through the total crust depth to assess crust resistance. Local penetration resistance can vary substantially and is measured at several points to calculate an average penetration resistance for a crust type.

Surface Type

Surface type provides a combined description of the moisture state and relief exhibited by the surface (e.g., dry/saturated high/low salt crust).

Boundary Type

Boundary type describes the boundary conditions (e.g., abrupt vs. gradual transition) between unique surfaces within ~100 feet of the sampling location. This informs how applicable PI-SWERL sampling results may be to adjacent areas.

Soil Moisture

Soil moisture will be qualitatively assessed for the first one to two inches of soil directly below the crust. Soil moisture will be classified based on USDA- NRCS classification parameters (Schoeneberger et al. 2011). Soils usually range from slightly moist to saturated where crust exists and dry to saturated where no crust exists.

Soil Texture

Soil texture (e.g., fine, moderately fine, coarse) will be qualitatively classified for the top one to two inches of soil.

Loose Surface Sand

Loose surface sand is visually determined by estimating the percentage of free, sand-sized particles in a 3-foot by 3-foot frame of playa surface. The amount of loose sand can vary seasonally with crust development because forming crusts can encapsulate surface sand as they harden. Loose sand particles on the surface are often very fine and settle into very small depressions in crust surfaces.

Salt Efflorescence

Salt efflorescence describes the presence or absence of efflorescent salt. Efflorescent salt is formed when salts held in solution migrate to the surface and evaporate, leaving a bright white salt crust devoid of any soil particles. Efflorescent salt crusts are typically found after rainfall or on recently exposed playa surfaces.

Crust Relief Crust

Crust relief is measured to provide a more refined understanding of surface roughness. Roughness affects wind resistance and surface wind velocities and is therefore useful in wind-erosion modeling. Crust relief is determined by measuring the distance from the bottom of a crust depression to the top of a typical crust ridge. Botryoidal crusts usually have the greatest relief.

Surface Erosion and Deposition

Surface erosion is generally characterized as a percentage of total crust area that appears to have been eroded by wind.

Percentage Vegetation, Overflow, and Other Features

General descriptors of vegetative cover, dune area, berm area, overflow area, and representative playa area will be documented. These estimates will provide a distribution of small inclusions relative to the dominant mapped surface condition. These features also have implications for the formation of crusts and erodibility; percent overflow area and vegetative cover are probably the most influential of these features.


FIGURE 6. EXAMPLE OF PLAYA SURFACE CHARACTERIZATION DOCUMENTATION

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8 ESTIMATED TIMELINE OF IMPLEMENTATION

The Surface Stabilizer Pilot Study schedule is shown in Table 6. As shown in the table, product application is anticipated to occur in the fall of 2019. The pilot study site will be monitored for approximately one year, and data analysis will be completed shortly thereafter.

TABLE 6. SURFACE STABILIZER PILOT STUDY SCHEDULE

Estimated Timeframe

Activity

Fall 2018

Work planning, including site selection, site characterization, design, and development of monitoring protocols.

Fall 2019

Application of surface stabilizer products and implementation of tillage furrows between plots.

Fall 2019 – Fall 2020

Performance monitoring of the study site.

Winter 2020

Complete data analysis and reporting for all data collected during the pilot study.

9 REFERENCES

Imperial Irrigation District. 2018, In Review. Draft Proactive Dust Control Plan for the 2017/2018 Dust Season. Prepared by the Salton Sea Air Quality Team.

Schoeneberger, P.J., Wysocki, D.A., and Benham, E.C. (editors). 2011. Field book for describing and sampling soils, Version 3.0. Natural Resources Conservation Service, National Soil Survey Center, Lincoln, NE.

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