What water monitoring can tell us about pollution sources

SOURCE: MOBUOY Q2 2026 · REPORT DATED 2 SEPTEMBER 2026 · NI

What the report found

The Mobuoy Road site is an uncontrolled-waste site near the River Faughan. NIEA monitors groundwater beneath the site and surface water in and around the river. Its Q2 2026 report covers April to June 2026; DAERA added the report to its monitoring page in September.

In the river, benzo(a)pyrene and fluoranthene exceeded their respective environmental quality standards at SW6, upstream of Mobuoy. Benzo(a)pyrene also exceeded its standard at SW8, downstream. PAH concentrations at the downstream point were comparable with those upstream. The report interpreted that pattern as indicating an upstream source for those river detections.

Groundwater within the waste site remained contaminated, including detections of benzene, toluene and several PAHs above applicable screening criteria. For this quarter, NIEA reported no adverse River Faughan water-quality impact attributable to Mobuoy. That finding describes the monitored period and does not mean the groundwater is clean or that future monitoring is unnecessary.

The practical lesson: compare, then interpret

A detected substance, or even a result above a screening standard, does not by itself identify the source. Upstream or background samples, downstream results, groundwater direction, drainage pathways, historical data and the conceptual site model all matter. The question is whether the whole pattern supports a credible source–pathway–receptor linkage.

The comparison points must be chosen for the site and the question being investigated. A sample taken “upstream” in one watercourse may not describe another pathway, such as a drain or a groundwater plume. Professional interpretation should also consider when samples were collected and whether conditions changed between monitoring rounds.

What this does—and does not—mean for heating-oil spills

The principle of source attribution applies to domestic heating-oil investigations, especially when a drain, well, stream or neighbouring property is affected. It helps prevent a single laboratory result from being treated as proof that a particular leak caused the impact.

Mobuoy is a large, complex waste site, not a domestic kerosene spill. Its contaminants, monitoring frequency and screening criteria should not be copied into a household investigation. A heating-oil assessment needs its own site history, fuel information, pathways, receptors and proportionate sampling plan.

Primary source and further guidance

NIEA / DAERA, Mobuoy Remediation Project: Quarterly Monitoring Report Q2 2026 (PDF). See also our Knowledge Hub for the wider assessment and monitoring framework.

Editorial note: This Insight interprets a published monitoring example for general information. It does not assess an individual spill or replace site-specific professional advice.