Ocean Alkalinity Enhancement (OAE) is a promising marine carbon dioxide removal (mCDR) approach, with the potential for gigaton-scale CO₂ removal. As coastal regions are increasingly being considered for deployment, the effects of coastal outfall interaction on carbon uptake must be constrained. Using a 3-D hydrodynamic-biogeochemical model, we assess the spatial and rate-dependent effects on the co-location of alkalinity outfalls in southeastern Australia. We find that short separation distances and high addition rates induce strong plume interaction, leading to reduced CO₂ removal (>5 %) and localised increases in pH. In contrast, low rates or wider spacing improve co-located CO₂ removal. This behaviour arises from the nonlinear, diminishing sensitivity of pCO₂ to increasing alkalinity. While this effect is transient, we show that it can persist for months, with any export of unequilibrated waters preserving unrealised CO₂ removal for extended periods. This export leads to increased cumulative radiative forcing relative to the more complete removal achieved from outfalls with reduced plume interaction. Additionally, co-location may have implications for uptake attribution, and therefore monitoring, reporting, and verification. Our results provide practical guidance for scaling OAE, demonstrating that careful planning of outfall spacing, informed by local hydrodynamics and observations, is essential to maximise carbon removal while minimising efficiency losses.