<p>Arsenic (As) contamination in stormwater represents a growing environmental and public health concern, particularly in regions affected by industrial activity and legacy pollution. This study evaluates the adsorption performance of biochar derived from Colorado soft pine for the removal of arsenic from synthetic stormwater, with a focus on performance enhancement through physical activation. Biochar samples were activated at 850°C for 3 h under a CO₂ atmosphere, and batch adsorption experiments were conducted across an initial As concentration range of 0.5–10 mg/L. Standard calibration procedures and spectrophotometric measurements were employed to quantify arsenic uptake and estimate adsorption capacities. The physically activated biochar exhibited an enhanced adsorption capacity (0.0315 mg/g) compared with untreated biochar (0.02375 mg/g), representing a 32% increment. The significance of this performance improvement is mechanically supported by BET analysis, which demonstrates that activation more than doubled the specific surface area from 351.09 to 752.46 m²/g, providing substantially more active sites for adsorption. These results indicate that physically activated biochar derived from soft pine biomass is a promising, low-cost, and sustainable adsorbent for mitigating arsenic contamination in stormwater systems and may support broader implementation of biochar-based treatment strategies in urban and coastal water management applications.</p>