Recommendation for Monitoring Approach to Determine Land-based Inputs of Oil to the Sea

The range of uncertainty in the estimated loadings to the sea of petroleum hydrocarbons from land-based sources is four orders of magnitude. This means that it could be the largest source of petroleum hydrocarbon by a wide margin. While it is questionable whether petroleum hydrocarbons from land-based sources poses an ecological threat in the sea, the PAH fraction does, so it is recommended that both be included in a monitoring program.

It is recommended that all major rivers that have significant urban development in their watersheds be monitored for petroleum hydrocarbon and PAH at the first EPA water quality monitoring station upstream of the end of the reverse tidal flow zone. Samples should be taken monthly (or at minimum seasonally) at the bottom, mid-depth and surface of the river. It is desirable to keep the samples separate, but if cost does not permit that, they can be composited in proportion to the relative velocity of the river at the depth that each sample is taken. The river discharge must be measured at the time the samples are taken. These samples should be analyzed for the petroleum hydrocarbon and the PAH suite of compounds identified in Table 3-3, which are the compounds measured by Environment Canada. Further, these analyses should be performed on both the filtrate and residue of the filtered samples.

In addition, urban runoff and municipal wastewater effluents should be monitored in several urban coastal cities. At least one full year of sampling should be done at each site. For urban runoff a flow weighted composite sample for each storm is adequate to determine an Event Mean Concentration for the site. It is recommended that at least the following types of land use be monitored: 1) typical residential, 2) typical shopping center, and 3) urban highway with high density, slow moving rush hour traffic. Runoff samples should be filtered and the filtrate and residue analyzed for TPH and the suite of PAH compounds identified in Table 3-3.

Since not all PAH compounds are petroleum derivatives, it would be important to first determine the fraction of TPH that is PAH. Once that fraction is determined, it could be used to partition the PAH measurements in river, waste effluent and urban runoff samples into petroleum derived PAH and those derived by other sources.