Evaluation and Reporting on Contaminant Hydrogeological

12-12-01

Conditions at the Tajiguas Landfill

Page 11 of 24

counts recorded at the landfill's surface water discharge point (specifically,

sample point p-I 7) during the wet season (i.e., late winter and spring

months). Potential sources for this bacterial contamination include: native

fauna, runoff from green waste, runoff from the active landfill surface, and

avian feces deposited over a wide area of the watershed.

Bacteria contribution from native fauna does not appear to be a dominant

source based on the observation that sites upstream from the landfill exhibit

low levels of Enterococcus and fecal coliform/E. Coil relative to other sites in

the watershed. Just below these sites, at the green waste disposal area,

relatively high indicator levels are observed at TJ-03, however runoff from

this area is nearly always contained in the out-of-channel sedimentation basin

and rarely enters lower Pila Creek, eliminating green waste as a likely

dominant contributor. Surface water runoff at the active landfill face during

rainfall events is managed so that it is not likely to contribute significantly to

bacteria loads. Waste is exposed only during operational hours, which

minimizes runoff contact with the waste. However, the widespread presence

of feces from the large seagull population that is attracted to the landfill is

exposed to runoff during rainfall events and could be a contributing factor.

During the wet season, the degree of bacteria transport to the ocean water at

the mouth of Pila Creek is consistent with conditions at other creek locations

in the region such as Arroyo Buno, Jalama, Refugio, and Rincon. During the

summer months, it does not appear that landfill operations affect

bacteriological water quality at the point where Pila Creek discharges to the

ocean.”

Subsurface investigation is required to define the potential migratory pathways

for groundwater contaminated by the landfill waste mass, between the beach and

landfill, and to define the vertical and lateral extent of the existing landfill waste mass

relative to all adjacent hydrogeologic regimes. Geophysical (such as areal

temperature survey) an/or geological investigations should be performed to verify

groundwater flow path regimes from recharge in the upper watershed, through the

interceptor trench, and final discharge to the beach. An example of the type of point

source which sould undergo subsurface investigation is identified on page 2-23 of

the draft EIR, which states,

“At some time during either the final closure period or postclosure

maintenance period, at existing facilities such as the scale house and

maintenance shop are no longer required or are replaced by new facilities,

they will be removed. Specific permits that may be required for the

removal/demolition of facilities would be obtained at the time of closure of

each facility.