Alkaline materials including hydroxides and carbonates are commonly added during enhanced reductive dechlorination (ERD) to maintain ph greater than 6.  Our recent tech tip described a simplified approach for estimating the amount of base required to raise the aquifer pH to an appropriate level and maintain it at that level for the duration of active treatment.  Here we provide you with the ESTCP design tool developed to aid in estimating the right amount of base required to  maintain a neutral pH during ERD.

Design tool users must enter the following information.

1. Treatment zone dimensions and design period for this phase of remediation.
2. Site characteristics including average K, porosity, hydraulic gradient, contaminant concentrations in aquifer material and groundwater, and amount of electron acceptors produced or consumed (i.e. O₂, NO₃, Fe, SO₄, CH₄).
3. Background pH, total inorganic carbon, mineral acidity, and pH buffering capacity (pHBC). A database of pHBC measurements is provided to aid users in selecting design values when laboratory measurements are not available.
4. Mass of organic substrate and base to be injected.
5. When vegetable oil is used as a substrate, the fraction of injected oil that is consumed during the design period.
6. Target pH

The design tool calculation procedures include the following assumptions.

1. The pH is between 5 and 8.
2. The carbonate system is the primary aqueous pH buffer.
3. Any H₂ or acetate produced by substrate fermentation that is not consumed through reduction of chlorinated solvents and background electron acceptors (O₂, NO₃, iron oxides, and SO₄) is consumed by methanogenesis.