API Publ 4758-2006 pdf download.Strategies for Addressing Salt Impacts of Produced Water Releases to Plants, Soil, and Groundwater.
Approach: 1) Improve drainage, if necessary. 2) Calculate how much gypsum to add using Calculation Method 1 or Method 2 (below) or use this Rule of Thumb: Add 13 pounds of gypsum per 100 sq. feet of impacted soil 3) Add chemical amendments to affected soil. • Solid Amendment: Incorporate from surface to depth of 1 to 2 ft using plow. Make sure amendment is in powdered or granular form. • Liquid Amendment: Apply over soil surface with or without mechanical incorporation. 4) Adding mulch and fertilizer may enhance rapid restoration (see page 6). 5) Use perimeter berms to contain rainfall or use sprinkler irrigation in affected area to increase infiltration and leach salts (sodium) from affected soils. Rules of Thumb: • ADD CHEMICAL AMENDMENTS BEFORE IRRIGATION OR A PERIOD OF HEAVY RAIN. • Pulse flooding (watering with a few inches of water every few days) can reduce water requirements by half. • A final top dressing of gypsum or mulch can protect the soil surface from dispersing after a rainfall or water event. • See page 5 for amount of supplemental irrigation that is needed. • Install erosion controls, if necessary.
Using the Planning Model Results of this modeling are combined with other site-specific information to determine the potential effects on groundwater. To use the Planning Model, perform the following steps: Step 1 : Estimate Mass of Chloride using volume and chloride concentration of a produced water release, OR Estimate Mass of Chloride using the area of produced water release (area of affected soil) and the chloride concentration of the soil (page 1 0) Step 2: Estimate Chloride Loading Rate to Groundwater using the Annual Precipitation, (page 1 1 ) Step 3A: Estimate Increase in Chloride Concentration in Groundwater at the Release Point using the width of the release area, (page 1 2) Step 3B: Refine the estimate from Step 3A using site-specific information (either the site location, or more detailed hydrogeologic info), (page 1 3) Step 4: (Optional) Estimate the Increase in Chloride Concentration in Groundwater at a Downgradient Point using the distance from the release area (and other parameters), (page 1 4) Key assumptions and limitations of the Planning Model include: 1 ) salts are mixed evenly throughout the soil; 2) the percentage of the rainfall that infiltrates through the soil to groundwater is proportional to the amount of rainfall; 3) the recharge rate is the 80 th percentile of recharge rates from data compiled from API Publication 4643; 4) almost all the salts in affected soils can be flushed out with 1 2 inches of recharge (from API 4663); 5) no capillary effects, evaporation, or other transport processes except advection, mixing, and dispersion in the saturated zone are present; 6) no density effects are assumed in transport of chloride in groundwater; 7) salt is mixed throughout the water-bearing unit; 8) a 2x safety factor is assumed; and BACKGROUND To estimate the increase in chloride concentration in groundwater, the chloride loading rate is divided by an estimate of the groundwater flow that mixes with the chloride. The groundwater flow is assumed to be the groundwater Darcy velocity (hydraulic conductivity times hydraulic gradient) multiplied by the estimated mixing zone thickness for the water-bearing unit underlying the release area. For this method, a typical value for groundwater discharge of 1 000 cubic feet per year per foot of water-bearing unit width was derived from: i) a statistical study of 400 hazardous waste sites prepared by API (API Report No. 4476) when a mid-range Darcy groundwater velocity of 33 ft/yr was indicated; and ii) an estimated value for the mixing zone thickness of 30 feet.
Aquatic Life Protection The U.S. EPA (1 988; 2006) developed ambient aquatic life criteria for chloride for acute exposures (860 mg/L) and chronic exposure (230 mg/L). Several states developed aquatic life criteria for non-priority pollutants including TDS that range from 250 mg/L to 2500 mg/L (Iowa, 2003).