April 3, 2006

Subject: Slope Review

Reference: SubSurface Designs, Inc., March 1, 2005, Slope Review Letter, Canoga Country Hills Estates, West Hills, California.

Dear Board of Directors:

On March 30, 2006, a representative from our office performed a site review of the graded and natural slopes around the Canoga Country Hills Homeowners Association community. In addition, the accompanying drainage devices were reviewed. The review consisted of walking the community’s slopes and observing existing conditions that might contribute to the future instability of the slopes. The review was not made for the purpose of mapping in detail each individual slope, therefore, it is not possible to comment on the present or future stability of every slope. Previous reviews of the slopes and common areas were performed by this firm with our findings, conclusions and recommendations presented in letters dated June 12, 1995; October 17, 1996; September 23, 1997; November 19, 1998; October 8, 1999; September 28, 2000; November 12, 2001; March 5, 2003; July 8, 2004; and, March 1, 2005.

This letter provides a general discussion of site conditions and recommendations for improving those site conditions as necessary. In addition, attached to this letter is a Plot Plan that illustrates specific locations within the Association that require attention.

GENERAL DISCUSSION

It appears that some of the items discussed in the previous letter(s) have been addressed and other items have not been addressed by the Association in the past year. This office is particularly concerned with a PVC drain that outlets directly onto a slope, wood and large amounts of trash debris accumulated in concrete swales, and a batting cage that is eroding directly into a concrete swale. These concerns are discussed and located on the attached Site Plan, Plate A. In addition, numerous cracks in the terrace drains have not been repaired as previously recommended.

It appears that the majority of the terrace drains are cleared of debris on a regular basis. However, a moderate to heavy amount of debris has accumulated in the terrace drains and drainage systems throughout the association during the recent rains of March, 2006.

Evidence of rodent activity was also observed. Additionally, sparse and/or dry vegetation was also noted on many properties. Whereas sparse vegetation can contribute to slope instability, dry vegetation is a key factor in the spread of fire.

Where sparse vegetation exists, a landscape architect and/or landscape contractor should be contacted to provided input. Where dry vegetation exists, it should, as a minimum, be trimmed as per the City of Los Angeles Fire Department regulations.

RECOMMENDATIONS

General

A PVC drain pipe, located in the rear-yard area of 23918 Ingomar Street, outlets directly onto the descending slope. To prevent any possible future slope instability, it is recommended that the drain pipe be extended to outlet in the nearby concrete swale.

A moderate amount of construction wood and timber is stock-piled in a concrete swale located behind the residence at 24041 Ingomar Street. The stock-piled wood and timber should be removed to prevent potential blockage of collected rain and surface water. Blocked water in the drainage devices may lead to overflow, which in turn, may compromise the stability of slopes.

An abandoned batting cage is located up-slope of a concrete swale in the rear-yard area of 23929 Strathern Street. The earth material of the dilapidated structure is eroding directly into the concrete swale, thus generating a heavy amount of debris. It is recommended that the batting cage be upgraded or demolished and all associated earth material be wasted off-site in order to prevent future build-up of heavy amounts of debris in the concrete swale. At the same address, large articles of trash debris have accumulated in the concrete swale. The trash should be removed to prevent potential blockage of collected rain and surface water. Blocked water in the drainage devices may lead to overflow, which in turn, may compromise the stability of slopes.

Slope Planting

Inadequate ground cover was encountered on several slopes. Soil erosion can and is likely to occur if the slopes are not planted or if planted with unsuitable ground cover. In other areas, slopes need to be cleared of dry brush and planted.

To reduce the potential for future erosion and soil slippage, it is recommended that slope areas be planted with an erosion retardant ground cover adhering to the following criteria:

• is effective in preventing surface erosion;
• is drought resistant;
• has a relatively low surface mass weight;
• has a fairly deep and extensive root system;
• requires a minimum of maintenance by owner;
• has a low irrigation demand; and,
• is fire retardant.

It requires approximately two (2) to three (3) years before an adequate erosion-resistant, fire retardant ground cover can become established on a slope. It is recommended that you consult with a landscape architect to determine specific botanicals that will serve as an effective erosion-resistant, fire retardant ground cover for your area.

Drainage Devices

Several terrace drains, down drains and swales have accumulated moderate amounts of debris (vegetation, soil, etc.). Vegetation should be cut back to the edge of swales. All slope drainage devices should be cleaned and maintained on a seasonal basis, or as debris accumulates, which ever is the shorter time frame. All slope drainage devices should be in good working order prior to the commencement of the rainy season (between November 1, and April 15, per the Los Angeles Building Code, Sec. 7002.).

The presence of efflorescence suggests improper or interrupted drainage. It is recommended that drains and slotted drain covers should have water run through them on a regular basis in order to verify that they are functioning properly.

In addition, some of the terrace drains have cracks of various size and location. The cracks should be repaired, patched or replaced immediately in order to facilitate proper drainage and to avoid water infiltrating into the underlying soil that may result in future distress and/or soil slippage.

Erosion

Some areas reported above were observed to have erosion occurring that was causing undermining of drains. These areas need to be repaired so that the integrity of the drainage system is not compromised.

Rodent Control

Dirt mounds and holes were noticed on the several of lots. These mounds and holes indicate burrowing animals. An ongoing program which eliminates or controls burrowing animals should be implemented as soon as possible. The uncontrolled burrowing by rodents has proved to be one of the major causes for surficial slope stability problems.

CONCLUSIONS

The conditions of the site appear to continue to be general maintenance issues. Although general, the above listed items, or combination of some or all of them, can cause areas of slope instability. This office recommends the following steps to be taken to maintain the stability of the slopes:

1. Repair and maintain areas of erosion.
2. Repair and/or patch all cracked terrace drains, down drains and swales, and sidewalks.
3. Control or eliminate burrowing animals.
4. Debris should be cleaned from all drainage systems and outlets.
5. . Dry brush should be removed. Deep-rooted plants should be planted on areas indicated on site plan. Additionally, all areas where inadequate ground cover exists on slopes should be planted. Replace these areas, and voided areas with trees or suitable vegetation.
6. Reduction of landscape watering should be instituted to avoid saturating the soil. Wet and saturated soils can result in settlement of structures and possibly slope instability. If you have any questions, please do not hesitate to contact this office.

Respectfully submitted:

SUBSURFACE DESIGNS, INC.

Gregory J. George- Staff Geologist
Jon Mahn -Project Engineer