Final Mitigated Negative Declaration and Response to Comments

the edges of the rubber sheets for underwater securement as well as for removal after
the application period is complete. Once the preparation stage is complete, the rubber
barrier material will be transferred to a barge or boat and delivered to the field site.
Placement of the rubber material at the field site
The rubber barriers and associated weights (rebar rods and/or chain link) for the rubber
sheets will be lowered to the lake bottom from the side of the barge using a winch or
backhoe. The materials will be lined up along the edge of the delineated field site.
Float bags may be used to secure the rubber bottom barrier material underwater to
reduce the weight of each rubber barrier roll. The rubber barriers will be rolled out
underwater by divers. It is estimated that approximately 6 divers per day for 20 days (3
hours each in water, 4 in the water at any one time) is required for this task. Shorter
dives to schedule work to avoid high visitor use periods or for other reasons would
increase the number of days required to complete work. After the rubber barriers are
rolled out, the edges and seams of the rubber treatment site will be covered with rebar
and other weights (no sand bags will be used) and staked down where necessary; it is
estimated that this task will take 10 days (total of 6 divers, 3 hours each in water, 4
people in water at any one time).
Design and testing of alternative treatment methods
Benthic barrier treatment has been shown to be a very effective method to kill AC in
Lake Tahoe, but there are some situations where flow through the substrate underneath
the barriers allows clams to survive in a highly stressed state. In these limited
situations, alternative methods to supplement benthic barrier treatment will be required
to control AC. One alternative tested will be insertion of supplemental material such as
straw (organic matter) under the barriers to determine whether the supplements
adequately decrease dissolved oxygen under the mats to increase the effectiveness of
the benthic barriers where there is some subsurface flow. Suction removal of AC has
been tested in Lake Tahoe but the method was determined to be more costly than the
benthic barrier treatment method. We may engineer and test new suction removal
technology to attempt to bring the cost down and this method may be used to
supplement benthic barrier treatment in Emerald Bay. Additionally, a literature review
and pilot testing of additional methods such as freezing clams in place in the substrate
may be employed depending on treatment cost. All treatment methods will be vetted
through the permitting agencies and included in all permit applications.
Removal and decontamination of rubber material
After greater than 6 months but less than 20 24 months, the rubber bottom barriers and
all associated materials will be removed from the lake bottom. The initial step in this
process is to remove all weights from the field treatment site. It is estimated this task
will take 20 days (total of 6 divers, 3 hours each in water, 4 in water at any one time).
Shorter dives to schedule work to avoid high visitor use periods or for other reasons
would increase the number of days required to complete work. The next step is the
removal of each rubber barrier sheet. A diver will attach the edges of each sheet to a
rolling system that will be operated from the barge. The rolling system will draw the
sheet up as it rolls it up from the bottom of the lake and will require no diver labor other
Asian Clam Control Project IS/MND
Emerald Bay State Park
California Department of Parks and Recreation
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