2909 17-Mile Drive © 2000 by Leo Poppoff

Pebble Beach, CA 93953

\(831\) 375-3302

July 20, 2000

Basin Watch

by

Leo Poppoff

QUESTIONS ABOUT BMPS HERE AND ELSEWHERE

On the eve of our stepped up campaign to restore the Tahoe watershed,
nagging questions persist. Do current erosion control projects (called
BMPs, or Best Management Practices, in the trade) stem the flow of
nutrients to the lake? What kinds of projects work best, and just how
well do those work? If they're effective at stopping erosion, is that
enough? And then, there's the bottom line question -- are current BMPs
worth the money?

Those of you who've scanned my columns over the years know that we've
discussed this issue of BMP effectiveness before. And you're probably
tired of hearing about it. Well, it seems that we're not alone in asking
these questions.

Two consultants in Southern California are leading a crusade to
reevaluate the practice of blindly using BMPs to protect receiving
waters from pollutant flows. These consultants have evaluated BMPs and
make a startling conclusion. They believe that many millions of dollars
of public and private funds are being wasted.

Scott Taylor, a hydrologist, is one of the crusaders. He is Vice
President of Water Resources at Robert Bein, William Frost Associates.
Taylor also lectures in hydrology at UC-Irvine and CSU-Long Beach. In a
recent newsletter, he writes that structural BMPs should only be used if
they are cost effective. That means, according to Taylor, that the BMPs
accomplish project goals for the least cost while providing a benefit
that exceeds the cost.

In his newsletter, he points out that most BMPs control erosion by
somehow trapping sediments. Some BMPs are fairly efficient at
controlling coarser sediments and stopping detritus and trash. Yet,
dissolved chemicals aren't removed very well, if at all. And, usually,
it's the dissolved chemicals, nutrients and toxic substances, that
effect the waters that need protection.

Taylor also notes that research and evaluation of BMPs is grossly
inadequate. Work done to date is sparse, and doesn't necessarily apply
to other watersheds. Soils, climates, vegetation, and impervious
coverage conditions are unique to specific locations. Nonetheless,
evaluations that have been done aren't encouraging.

For example, Taylor cites a 1997 study by Maxted and Shaver of eight
watersheds. Two of the watersheds had been retrofitted with retention
basins to control storm water. The installations were mature and each
watershed had more than 20% impervious coverage.

Results of the study showed that using the BMPs did not benefit the
receiving waters. The researchers point out that watershed systems are
so complex, they can't really be understood with a single data set. But,
the results seem to be similar to what we're seeing here in the Tahoe
Basin.

Roadways are large generators of storm water flow and cleaning that
water is important. Various pollutants from autos are deposited on
roadways. Deicing chemicals and sand are spread on them. And they act as
a conduit for overland flows containing nutrients and toxic substances.

The most commonly used devices to control runoff from streets and
highways are drop inlets. Runoff flows into the inlets, which are
installed along the roadside, and silt is trapped in baskets, bags, or
trays. We depend on them here in the Tahoe Basin.

Still, according to Taylor, these drop inlets are largely ineffective at
reducing sediment and pollutant loads, even when they are adequately
maintained. And a recent news item in our local papers reported a fine
levied on Caltrans because drop inlets were not maintained and the
overflow ran directly into the lake.

Here's the kind of efficiency that Taylor quotes for drop inlets. For
solids, 10% reduction; for nutrients, 5% reduction; for pesticides, 5%:
for metals, 5%; and for bacteria, 5%. It's not very impressive.

Taylor's figures for other BMPs are much better but not very
encouraging. For extended detention basins, he quotes a 75% reduction in
solids, but only 25% reduction of nutrients. For vegetated swales,
Taylor quotes a 70% reduction in solids and a 30% reduction in
nutrients.

Infiltration, according to Taylor, is a popular solution because it
treats the discharge on the site. Then, other more ineffective and
expensive BMPs aren't needed. Infiltration is most effective in
relatively permeable soils. Yet, there are questions about their effect
on groundwater.

Phosphorus bonds quickly to soils and can be removed with infiltration.
Even so, dissolved phosphorus is found in ground water in the Tahoe
Basin. Nitrogen is very mobile in water and will hardly be affected.
Also infiltration devices can be clogged and not do the job. They need
maintenance. Taylor recommends ground water monitoring in areas where
infiltration devices are installed.

There's more to this important story. Next time we'll look at a study on
the effectiveness of wetlands for cleaning water \-- here in the Tahoe
Basin.