Alum Treatment at Pinto Lake Completed


April 10, 2017 – The Pinto Lake alum application project was completed ahead of schedule!  As planned, the exact dose of over 118,000 gallons of alum and buffer were applied in a precise, uniform…and most importantly…safe manner.

The Project

Pinto Lake is a 120 acre recreational lake in Watsonville, CA.  The lake develops massive algal blooms every later summer and fall and algal toxin levels typically exceed the State health criteria.  As a result, the lake is classified as “impaired” and is closed for contact recreation during the bloom periods.  Of particular interest, the death of 31 endangered southern sea otters have been traced to algal toxins which have accumulated in shellfish eaten by the otters.  Pinto Lake is the likely source of the toxins in the shellfish and the cause of the otter deaths.  Excessive amounts of the nutrient phosphorus is the main cause of the toxic algal blooms.  Internal phosphorus loading (leaching from the lakebed sediments) and watershed runoff both contribute phosphorus to Pinto, but a study in 2011 showed that the majority (85%) was coming from the lakebed.

Samples from the bottom of the lake confirmed that phosphorus was very high in the sediments and available to be released into the overlying water column.  HAB Aquatic Solutions will be conducting a buffered alum application over a ten day period in early April.  The application produces a “floc” that settles to the bottom of the lake.  The floc has sites where phosphorus in the sediments become chemically bound as it leaches from the bottom.  The floc effectively intercepts and binds the phosphorus, which makes it unavailable for the algae to use for growth.  The goals of the project are to dramatically reduce the internal loading of phosphorus from the sediments, lower the amount of phosphorus available to algae in the water, reduce the amount of algae and associated toxins and remove the recreational restrictions at the lake.

Read the day-by-day documentation of HAB Aquatics Solutions below. You can also visit their website here.


HAB spent day one of the project preparing equipment for the application.  This included assembly of the barge’s application boom, programming the barge’s computerized dosing system, launching the barge into the lake, setting up on-shore storage tanks and confirming the delivery plan for the alum and buffer.  The lake will remain open for approved uses during the application, but part of the parking lot is closed for use by the delivery trucks.


Day 2 of the Pinto Lake project was very productive for HAB.  The final two storage tanks were placed in the staging area.  A fence was installed around the staging area to keep the park users at a safe distance from the alum storage and barge filling locations.  Final calibrations of the barge computer system were conducted and a jar test of the lake alum dose was performed to confirm the safety of the dose.  Tanks were filled from the delivery trucks and by mid afternoon were ready to begin applying alum to the lake.  About 6,000 gallons of alum and buffer were applied over a 9 acre area of the lake during the late afternoon.  We were excited to get the application underway and look forward to a full day of application tomorrow!


Today marked the first full day of application and the lake was busy with many visitors and observers. Over 19,000 gallons of alum and buffer were applied to a 39 acre portion of the lake and the project is off to a very smooth start. A group of over 50 students from the University of Liverpool in England visited the lake to observe and learn about the Pinto Lake restoration project. Dr. Holz had the opportunity to provide an onsite lecture on the role of phosphorus in lakes, internal loading of phosphorus and benefits of alum in reducing phosphorus concentrations and improving water quality. Great group of students with great questions!


This morning we provided a tour of the alum application operation and an overview of the project goals to numerous community and agency visitors. It is great to see so much interest in getting Pinto Lake’s water quality back to acceptable conditions available for the community to use. We also received a tour of the Watsonville water resources plant to observe and learn more about their own specific use of alum (in addition to use in lakes, alum is commonly used in the drinking/waste water treatment industry). Meanwhile, the lake application continued all day during cooler and rainy weather. Over 20,000 gallons of alum and buffer were simultaneously applied to a 32 acre portion of the lake.


HAB worked through more cool and rainy weather today to apply over 24,000 gallons of alum and buffer to nearly 39 acres of the lake.  HAB’s application equipment is well-suited for the precision required for the Pinto Lake restoration project.  Any gaps in coverage would allow for phosphorus from untreated lakebed sediments to leach into the overlying water column and stimulate future algal blooms.  An onboard computer system ensures that application is complete and uniform by integrating the location of the barge with GPS, the barge speed, water depth and alum flow rates.  The exact dose is programed into the software and inline flow sensors measure the flow of alum through the distribution lines in real time.  Automated valves, which are controlled by the computer, open and close as needed to adjust for barge speed, location and depth to make certain the prescribed dose is applied.  Tadd Barrow (HAB’s application specialist) follows a grid and each application path is recored and displayed on the guidance monitor to prevent gaps in the application.  At the end of the project, HAB produces a coverage map showing every application path and confirms the complete coverage of the lake.

We also really appreciated the visits and interest from even more agency staff today. It takes a lot of hard work, commitment and collaboration to make a project like this happen!


HAB applied over 20,000 gallons of alum and buffer to a 32 acre section of lake and we have now completed 75% of the total application. We also spent time this afternoon conducting our daily chemical and environmental testing of the lake water. Alum is widely used in lakes and the drinking/wastewater treatment industry due to it’s known safety. In fact, an important consideration in selecting an alum application as the preferred restoration technique for Pinto Lake was it’s long record of safe use. Pinto is considered a sensitive lake as it home to the threatened Western Pond Turtle, provides nesting habitat for Bald Eagles, Great Blue Herons, Snowy Egrets, Mallards, Coots and Canada Geese, and supports an outstanding Largemouth Bass fishery. Water from Pinto Lake also flows through critical feeding habitat for the endangered southern sea otter before reaching Monterey Bay. The use of alum is well-suited for lakes such as Pinto and HAB carefully monitors and documents the safe lake conditions during all of their application projects.


HAB’s productivity has been high the last few days and we are slightly ahead of the remaining alum truck deliveries.  We applied 18,0000 gallons of alum and buffer to a 29 acre section of the lake before ending our workday at little early this afternoon.  This allowed us time to accept an invitation from a Pinto Lake resident to visit their home and gain a different perspective of the lake from the surrounding hills.  We also took the opportunity to enjoy a few competitive games of horseshoes and the beautiful weather and gorgeous view! It was much appreciated and demonstrates the deep support and interest in the Pinto Lake restoration project.  We have noticed this support all week and it really defines the importance of Pinto Lake to the Watsonville community.  It has been a fun experience to be a part of that!  We are on schedule to complete the application around noon tomorrow.

DAY 8 – APRIL 10

Today the Pinto Lake alum application project was completed ahead of schedule!  As planned, the exact dose of over 118,000 gallons of alum and buffer were applied in a precise, uniform…and most importantly…safe manner.  There is no greater measure of success than safety and Pinto marks HAB’s 55th project without a safety incident.  A special thanks to HAB’s Alum Transfer Specialist (Bernie Ruppert) for ensuring the our company Safety Plan is enforced and followed on all of our projects.  This level of detail and dedication is critical to successful applications.

This is the last of our daily postings, but check back periodically (or receive automatic notifications by entering your email address in the footer below) for additional project updates in the future.  Thanks for your interest and following our progress.  Don’t forget to check out HAB on Facebook, Twitter and Instagram too.  Finally, a big thanks to the community of Watsonville and the City of Watsonville staff for all of their support.  This support is also critical to successful projects.  We have definitely enjoyed our time here.  We are packing up and heading to Minneapolis for HAB’s next two projects…

This entry was posted on Wednesday, April 12th, 2017 at 8:48 am and is filed under City Manager, City of Watsonville, Homepage News, Public Works . You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.