Waughop Lake is the
centerpiece of the popular Fort Steilacoom Park in the city of Lakewood,Washington.
The park is on state-owned land that is leased to the City of Lakewood (City).
Waughop.
Lake has a long history
of cyanobacteria (i.e., blue-green algae) blooms that severely limit use of the
lake. The City has made the protection and restoration of Waughop Lake a high
priority.
In 2014, the City
received a grant from the Washington State Department of Ecology (Ecology) to develop
a lake management plan (LMP) for Waughop Lake. The overall goal of the LMP is
to develop strategies to improve and protect the lake uses impaired by excess
nutrients. The City retained Brown and Caldwell (BC) and the University of
Washington Tacoma (UWT) to help develop the LMP.
BC and UWT prepared a
Quality Assurance Project Plan (QAPP) to guide data collection in support of the
Waughop LMP. The QAPP included monitoring the quality of the lake water, lake
bottom sediment, stormwater, and groundwater to identify and quantify sources
of phosphorus loading and support the evaluation of management measures.
The City provided
opportunities for public stakeholder input during LMP development (Blogmaster: 8
bulleted items follow)
The monitoring program
was conducted from October 2014 – October 2015. The monitoring found that
phosphorus is the limiting nutrient for cyanobacteria blooms and the internal
cycling of phosphorus from the lake bottom sediment to the water column is the
largest source. Based on the monitoring results and stakeholder input, the City
confirmed that the primary objective for the Waughop LMP should be to minimize
the frequency of cyanobacteria blooms.
The project team
evaluated a wide range of potential lake management measures and identified several
that appear suitable for Waughop Lake. Table ES-1 below ummarizes the estimated
costs and potential benefits of these measures. (Blogmaster: Table ES-1
follows)
As noted in Table ES-1,
dredging of lake bottom sediment would provide the greatest long-term benefit
but would also have a high initial cost and extensive permitting requirements.
Sediment cores would need to be collected throughout the lake and analyzed to
develop a more accurate estimate of the volume to be dredged, determine
sediment dewatering and disposal requirements, and refine the construction cost
estimate. Dredging could take 6 to 8 months and have temporary impacts on park
visitors and wildlife. Securing the funds needed for dredging may be difficult,
especially if costs are closer to the high end of the range shown in Table
ES-1. It could take several years or more to complete additional sediment
characterization, secure funding, obtain permits, perform dredging, and
properly dispose of the sediments.
Sediment phosphorus
inactivation using whole-lake alum treatment would quickly reduce phosphorus
concentrations in the lake, reduce the release of phosphorus from the sediment,
and reduce cyanobacteria blooms. Compared to dredging, alum treatment has a much
lower initial cost, less intensive data collection and permitting requirements,
and less disruption for park visitors and wildlife (see Table ES-1). However,
the benefits of alum treatment decline over time, so treatments would need to
be periodically repeated. In addition, alum treatment could increase macrophyte
growth by allowing sunlight to reach deeper into the lake.
Aeration of the lake
bottom would help decrease the anoxic conditions that enable phosphorus release
from sediments, while vertical mixing would disrupt cyanobacteria growth and
favor benign algal species.
A pump and treat system
could be installed to remove phosphorus from lake water using a coagulation
facility or a constructed wetland treatment system. The estimated cost for this
measure assumes 3 to 10 acres of upland area would be made available for the
treatment system at no cost.
Because of treatment
capacity limitations, pump and treat systems are expected to be less effective than
the other measures listed in Table ES-1, so they are not recommended at this
time.
The City does not
currently have any funds to implement this LMP. Implementation of this LMP will
depend on the City’s ability to secure funding from other sources such as state
budget allocations and grants (see Section 6).
Therefore, the City
proposes a phased approach for implementing this LMP, as described below.
Phase 1 would consist of
a whole-lake alum treatment to remove phosphorus from the water column and
inactivate phosphorus in the sediment, thereby reducing the potential for
cyanobacteria blooms.
The City (or partners)
would monitor the lake to estimate the effectiveness and longevity of the alum treatment.
During this phase, the City would collect the additional sediment data needed
to refine the construction cost estimates and support permit applications for
dredging. The City would also identify and pursue potential funding sources for
long-term implementation.
Phase 2 would involve
dredging to remove phosphorus-rich sediment from the lake bottom, provided that
the City can secure the necessary funds and permits. The lake monitoring study
found that bottom sediment is by far the largest source of phosphorus for
cyanobacteria blooms. Dredging is expected to be the most effective long-term
measure for reducing cyanobacteria blooms because it would remove sediments
that have been contaminated by farming and other human activities over the past
100 years or so. Funding for dredging would be pursued along with collection of
information regarding public support for improved lake use.
If the City cannot
secure the funds needed for dredging and the Phase 1 monitoring indicates that alum
treatment is likely to last at least several years, Phase 2 may consist of a
follow-up whole-lake alum treatment. Conversely, if the City cannot secure
sufficient funds for dredging and Phase 1 monitoring suggests that alum
treatment benefits are short-lived, Phase 2 could include a pilot study to
evaluate whether a bottom aeration and vertical mixing system would
significantly reduce phosphorus release from bottom sediments and disrupt
cyanobacteria in the water column. If the pilot results are promising and the
necessary capital and operating funds can be obtained, Phase 2 could include
installation of a full-scale bottom aeration and mixing system.
Source:
Executive Summary Waughop Lake Management Plan – February, 2017
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