There are a few things you need to understand about sewage treatment to make sense of this timeline. First, if you dump treated sewage in the ocean, you don't just use a big open pipe. Instead, you poke holes in your pipe, so the stuff trickles out and diffuses. You may remember the scene in "Finding Nemo" where the crabs were crawling on the sewer pipe -- the sewage was trickling out through a diffuser. Second, federal law requires that, for ocean dumping, sewage should be treated at the secondary level. That is cleaner than primary-treated sewage, but not suitable for watering crops. Third, any sewage treatment plant that empties into a river must treat its sewage at the tertiary level.
Now consider the effects of these regulations on bacterial contamination at Huntington Beach. First, OCSD started treating sewage, presumably at the primary level, in 1954. Shortly thereafter, they started measuring bacterial concentrations in the water at Huntington Beach. In 1965, they installed a new diffuser on the outfall, but it seems to have been a bad design, and resulted in very bad beach contamination. This incident suggests that, the original 2.1 km outfall pipe was a source of contamination at the beach. The fact that water quality improved when the outfall pipe was lengthened (to 7.5 km in 1972) suggests that less contamination reaches the beach from the longer pipe.
An incident in 1969 indicates another source of beach contamination. When the sewage plant upriver from Huntington Beach accidentally spilled raw sewage into the Santa Ana River, the worst-ever beach contamination at Huntington Beach occured. Clearly, bacterial contamination can move from the mouth of the Santa Ana River to Huntington Beach. The outlet from Talbot Marsh is right next to the mouth of the Santa Ana River, and therefore also a possible source of contamination.
In 1972, the Federal Clean Water act defined the required level of sewage treatment for outfalls in different areas. The Federal government also provided money for various sewage treatment upgrades, but the upgrades take a while. Orange County Sanitation District used some federal money to lengthen their outfall pipe from 2.1 km to 7.5 km. However, they received a waiver allowing them to treat only half of their sewage at the secondary level; half of OCSDs effluent is treated only at the primary level.
In 1999, the State of California defined what it means for a beach to be clean enough for swimming. They enacted a law (State Law AB411) that required beaches to be closed if they were too dirty. Huntington Beach promptly closed for 2 months, resulting in a great loss of income. Local environmentalists immediately blamed the sewage outfall, calling it the "smoking gun". They wanted to use this issue to force OCSD to upgrade their treatment to the full secondary level, at a cost of a few hundred million dollars.
OCSD promptly checked and patched all their pipes, and started treating some of the runoff from nearby storm drains and a mobile home park. These actions improved beach water quality. OCSD claimed that their outfall was too far offshore (7.5 km) to affect the beach, and that the cold effluent was trapped by a layer of warm surface water. Just to make sure, they commissioned a $5 million study to determine whether it was possible for effluent from the outfall to reach the beach. They made this a peer-reviewed study to make clear that they weren't trying to buy off the scientists, and I organized the review panel.
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