Abstract

Stormwater runoff from oilfield facilities can transport suspended solids, organic matter, salts, hydrocarbons, and trace metals to receiving waters, yet baseline data are limited in the region. This study provides the first integrated assessment of stormwater quality at three Iraqi oilfield facilities: Central Waste Management Area (CWMA), Central Process Facility (CPF), and Tank Loading Station (TLS) in Shewashok Oilfield. The samples were collected during storm events in January and May 2018, then analysed for physicochemical properties, oxygen-demand indicators, major ions, nutrients, hydrocarbons, and dissolved metals, and compared with Iraqi standards. Water quality was further evaluated using the Water Quality Index (WQI), Heavy Metal Pollution Index (HMPI), and Pollution Load Index (PLI).

CWMA showed the highest and most persistent contamination, with repeated exceedances in COD (410–951 mg/L), chloride (6780 mg/L), sulphate (945–1120 mg/L), boron (2170–6460 µg/L), and fluoride (up to 2540 mg/L). CPF showed moderate impairment, including elevated BOD (93 mg/L), COD (103–191 mg/L), sulphate (460 mg/L), and high TSS (up to 3200 mg/L). In contrast, TLS remained largely compliant, with low COD (<6–32 mg/L), low TSS (14–35 mg/L), and only a minor aluminium exceedance.

WQI values (11.83–70.20) ranked sites as CWMA > CPF >> TLS, with deterioration from January to May at CWMA and CPF, while TLS remained stable. HMPI (0.015–1.083) and PLI (0.009–0.041) were low, indicating limited metal pollution. These findings establish a regional baseline and highlight the usefulness of combining threshold and index-based approaches for stormwater management in Csa-climate environments.